THIN, FLEXIBLE ELECTRONIC DEVICES AND ASSOCIATED SYSTEMS AND METHODS
20250385656 ยท 2025-12-18
Assignee
Inventors
Cpc classification
H03H9/02574
ELECTRICITY
H03H9/02614
ELECTRICITY
International classification
Abstract
Devices (e.g., resonators) comprising a single-crystalline material, and related systems and methods, are generally described.
Claims
1. A surface acoustic wave resonator, comprising: a substrate; and a single-crystalline piezoelectric material positioned at least partially over the substrate; wherein: the single-crystalline piezoelectric material has a thickness of less than or equal to 300 nm and/or the resonator has a minimum detectable strain less than or equal to 0.1% at an energy consumption less than or equal to 810.sup.8 Joules per measurement; and the resonator is configured such that the single-crystalline piezoelectric material resonates to generate a mechanical wave during operation of the resonator.
2. The surface acoustic wave resonator of claim 1, wherein the resonator has a minimum detectable strain less than or equal to 0.1% at an energy consumption less than or equal to 810.sup.8 Joules per measurement.
3. (canceled)
4. The surface acoustic wave resonator of claim 1, wherein the resonator has a minimum detectable strain less than or equal to 0.05% at an energy consumption less than or equal to 810.sup.8 Joules per measurement.
5. The surface acoustic wave resonator of claim 1, wherein the single-crystalline piezoelectric material comprises a semiconductor material.
6. The surface acoustic wave resonator of claim 1, wherein the substrate comprises a cavity.
7. The surface acoustic wave resonator of claim 6, wherein the single-crystalline piezoelectric material is positioned at least partially over the cavity of the substrate.
8. The surface acoustic wave resonator of claim 1, wherein the single-crystalline piezoelectric material is or is part of a freestanding layer.
9. The surface acoustic wave resonator of claim 8, wherein the freestanding layer has a thickness of at least 10 nm.
10. The surface acoustic wave resonator of claim 8, wherein the freestanding layer has a thickness of less than or equal to 100 mm.
11. A device, comprising: a substrate comprising a cavity; and a single-crystalline material positioned at least partially over the cavity of the substrate, wherein: the single-crystalline material is or is part of a freestanding layer; and the single-crystalline material has a thickness of less than or equal to 300 nm.
12. The device of claim 11, wherein the single-crystalline material comprises a single-crystalline piezoelectric material.
13. The device of claim 12, wherein the single-crystalline piezoelectric material comprises a semiconductor material.
14. The surface acoustic wave resonator of claim 1, further comprising a plurality of interdigitated electrodes.
15. The surface acoustic wave resonator of claim 14, wherein the plurality of interdigitated electrodes is in electrical communication with the single-crystalline piezoelectric material.
16. (canceled)
17. The surface acoustic wave resonator of claim 14, wherein the plurality of interdigitated electrodes are patterned.
18. The surface acoustic wave resonator of claim 14, further comprising an antenna.
19-26. (canceled)
27. A method of forming a device, comprising: transferring a single-crystalline material from a growth substrate to a receiving substrate such that at least a portion of the single-crystalline material is positioned over a cavity of the receiving substrate, wherein, after the transferring, the single-crystalline material is or is part of a freestanding layer, and the single-crystalline material has a thickness of less than or equal to 300 nm.
28-29. (canceled)
30. A method of operating the surface acoustic wave resonator of claim 1, comprising: applying an electrical potential to the surface acoustic wave resonator such that the single-crystalline piezoelectric material resonates to generate a mechanical wave; and determining a change in a resonant frequency of the single-crystalline piezoelectric material in response to an environmental change.
31-33. (canceled)
34. The surface acoustic wave resonator of claim 1, wherein the single-crystalline piezoelectric material has a thickness of less than or equal to 300 nm.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:
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DETAILED DESCRIPTION
[0083] Devices (e.g., resonators) comprising a single-crystalline material, and related systems and methods, are generally described.
[0084] The inventors have recognized that there is an unmet need and opportunity for innovation in the field of resonators for use in wireless devices (e.g., e-skin-based health monitoring platforms). Conventional wireless e-skin-based health monitoring devices consist of rigid integrated circuit chips, such as near-field communication/radio frequency identification chips (NFC/RFID chips), microprocessors, or analog-to-digital converters (ADCs), that can compromise the overall flexibility of the device. Moreover, due to the power-constraint of the wireless e-skin systems, the high power consumption of these chips, which contain thousands of transistors, often leads to reduced sensitivity (due to the power-sensitivity tradeoff in analog-to-digital converters), significant heat generation, and reduced communication distance. LC resonator-based sensors have also been developed for chip-less and wireless e-skin devices, but the application of these sensors has been limited to strain and/or pressure detection with relatively low sensitivity due to the limitations of capacitive sensor designs.
[0085] Described herein is a device comprising a single-crystalline material that is or is part of a freestanding layer. The device may be, in some embodiments, a resonator, such as a surface acoustic wave resonator. The device is, in accordance with certain embodiments, configured such that the single-crystalline material serves as a piezoelectric resonator that generates a mechanical wave (e.g., a surface acoustic wave) during operation of the device. In some embodiments, the device may comprise a plurality of interdigitated electrodes in electrical communication with the single-crystalline material. The device may comprise an antenna in electrical communication with the plurality of interdigitated electrodes, in accordance with certain embodiments. The plurality of interdigitated electrodes is, in accordance with some embodiments, configured to deliver electrical energy from the antenna to the single-crystalline material, which converts the input electrical signal into a mechanical wave (e.g., a surface acoustic wave). The frequency of the mechanical wave may, in some embodiments, be sensitive to an environmental change resulting from one or more stimuli, such as mechanical strain, light exposure, and/or mass changes. In certain embodiments, the mechanical wave, after exposure to one or more environmental changes, is converted back into an electrical signal and retransmitted back through the antenna. In accordance with some embodiments, changes in the resonant frequency of the mechanical wave resulting from the one or more environmental changes yields information about the stimulus/stimuli (e.g., mechanical, optical, and/or biochemical stimuli). According to some embodiments, configuring the device in this way advantageously provides a multi-modality chip-less wireless sensor that is flexible and functions to detect one or more environmental changes (e.g., a mechanical strain, light, and/or chemical concentrations) with high sensitivity and without high-power consumption.
[0086] The single-crystalline material is grown (e.g., epitaxially grown), in certain embodiments, over a two-dimensional (2D) material positioned over a growth substrate that is lattice-matched with the single-crystalline material. In some such embodiments, a potential field from the growth substrate reaches beyond the 2D material such that the growth substrate seeds the growth of the single-crystalline film, even in cases where the 2D material is continuous. That is to say, the growth substrate can, in some embodiments, seed the growth of the single-crystalline material even when the 2D material is not patterned or otherwise arranged to have through thickness defects that allow for direct contact between the growth substrate and the single-crystalline film. In some embodiments, the potential field from the growth substrate penetrates through the 2D material to facilitate growth of the single-crystalline material with substantially no defects. In certain embodiments, the single-crystalline material may then be transferred from the growth substrate to a preconfigured receiving substrate, thereby bypassing the need to back-etch the receiving substrate to reach the single-crystalline material. According to certain embodiments, the epitaxial growth of the single-crystalline material advantageously yields a freestanding layer with an ultrathin thickness (e.g., less than or equal to 300 nm) that is stretchable and configured to conform to a portion of skin of a user for long-term wearability and biocompatibility.
[0087] In some embodiments, the device comprises a substrate. The substrate may, in certain embodiments, comprise a cavity.
[0088] In certain embodiments, cavity 104 may extend through the bulk of substrate 102, for example, from first surface 112a of substrate 102 to second surface 114a of substrate 102 that is opposite first surface 112a. In other embodiments, although not shown in the figures, the cavity may extend only partially through the bulk of the substrate.
[0089] The cavity may be any of a variety of suitable shapes and/or sizes. According to certain embodiments, for example, the cavity may be square shaped, circular shaped, and/or dumbbell shaped. Other shapes are also possible.
[0090] According to certain embodiments, the substrate may comprise one or more auxetic holes (e.g., a plurality of auxetic holes).
[0091] In some embodiments, and as shown in
[0092] According to certain embodiments, and as shown in
[0093] The plurality of auxetic holes may be patterned, according to certain embodiments. In some embodiments, for example, a first portion of the plurality of auxetic holes may be substantially aligned in a first orientation, and a second portion of the plurality of auxetic holes may be substantially aligned in a second orientation. Referring to
[0094] According to certain embodiments, the first portion of the plurality of auxetic holes substantially aligned in the first orientation may be substantially evenly spaced. Referring to
[0095] The substrate may comprise any of a variety of suitable materials. In some embodiments, for example, the substrate comprises a polyimide and/or polydimethylsiloxane (PDMS). Other materials are also possible. The substrate cavity and/or the one or more auxetic holes may be occupied by any of a variety of suitable non-solid materials (e.g., one or more gases, one or more liquids), in accordance with certain embodiments.
[0096] The substrate may have any of a variety of suitable thicknesses. Referring to
[0097] According to certain embodiments, the device comprises a single-crystalline material. Referring, for example, to
[0098] In some embodiments, the single-crystalline material is or is part of a freestanding layer. Referring to
[0099] A layer is a form factor having a thickness dimension and two lateral dimensions, with each lateral dimension perpendicular to the thickness and to the other lateral dimension, and in which each lateral dimension has a length that is at least three (3) times the thickness dimension. A layer also has two major surfaces, which are surfaces that are defined by the two lateral dimensions. In
[0100] As used herein, a layer is said to be freestanding if, for at least a portion of the layer (referred to as the freestanding portion of the freestanding layer), the major surfaces of the layer are not in contact with another solid material. The freestanding layer will generally be bound, in accordance with certain embodiments, along some or all of its edges to a solid substrate, with the freestanding portion of the layer being free of contact on both sides with solid material. According to certain embodiments, the single-crystalline material that is or is part of the freestanding layer may be configured such that the single-crystalline material is positioned and/or aligned over the cavity of the substrate (and, in some embodiments, portioned and/or aligned over one or more auxetic holes of the substrate). Configuring the device in this way advantageously allows the single-crystalline material to resonate (e.g., through the cavity of the substrate and/or the one or more auxetic holes of the substrate).
[0101] As explained in further detail below, the freestanding layer may comprise, in addition to the single-crystalline material, a plurality of interdigitated electrodes (e.g., over the single-crystalline material) and/or an overlayer (e.g., a protective material, a stimuli detecting material), in accordance with certain embodiments.
[0102] In some embodiments, the single-crystalline material is a piezoelectric material (e.g., a single-crystalline piezoelectric material). As used herein, the term piezoelectric material is given its ordinary meaning in the art and generally refers to a material that has the ability to generate electrical charge from applied mechanical stress. In some embodiments, the piezoelectric material comprises a semiconductor material. In certain embodiments, the piezoelectric material comprises an insulator material.
[0103] According to some embodiments, the single-crystalline material comprises a semiconductor material (e.g., a single-crystalline semiconductor material).
[0104] In certain embodiments, the single-crystalline material comprises a III-nitride material. The term III-nitride material is used herein to refer to any Group III element-nitride compound. Non-limiting examples of III-nitride materials include gallium nitride (GaN), boron nitride (BN), aluminum nitride (AlN), indium nitride (InN), and thallium nitride (TlN), as well as any alloys including Group III elements and Group V elements (e.g., Al.sub.xGa.sub.(1-x)N, Al.sub.xIn.sub.yGa.sub.(1-x-y)N, In.sub.xGa.sub.(1-x)N, Al.sub.xIn.sub.(1-x)N, GaAs.sub.aP.sub.bN.sub.(1-a-b), Al.sub.xIn.sub.yGa.sub.(1-x-y)As.sub.aP.sub.bN.sub.(1-a-b), and the like). III-nitride materials may be doped n-type or p-type, or may be intrinsic.
[0105] The phrase gallium nitride material refers to gallium nitride (GaN) and any of its alloys, such as aluminum gallium nitride (Al.sub.xGa.sub.(1-x)N), indium gallium nitride (In.sub.yGa.sub.(1-y)N), aluminum indium gallium nitride (Al.sub.xIn.sub.yGa.sub.(1-x-y)N), gallium arsenide phosphoride nitride (GaAs.sub.aP.sub.bN.sub.(1-a-b)), aluminum indium gallium arsenide phosphoride nitride (Al.sub.xIn.sub.yGa.sub.(1-x-y)As.sub.aP.sub.bN.sub.(1-a-b)), and the like. In certain embodiments, the gallium nitride material comprises GaN.
[0106] The phrase aluminum nitride material refers to aluminum nitride (AlN) and any of its alloys, such as aluminum gallium nitride (Al.sub.xGa.sub.(1-x)N), aluminum indium nitride (Al.sub.xIn.sub.(1-x)N), aluminum indium gallium nitride (Al.sub.xIn.sub.yGa.sub.(1-x-y)N), aluminum indium gallium arsenide phosphoride nitride (Al.sub.xIn.sub.yGa.sub.(1-x-y)As.sub.aP.sub.bN.sub.(1-a-b)), and the like. In certain embodiments, the aluminum nitride material comprises AlN.
[0107] According to certain embodiments, the single-crystalline material comprises a III-phosphide material. The term III-phosphide material is used herein to refer to any Group III element-phosphide compound. Non-limiting examples of III-phosphide materials include gallium phosphide (GaP), boron phosphide (BP), aluminum phosphide (AlP), indium phosphide (InP), and thallium phosphide (TlP), as well as any alloys including Group III elements and Group V elements (e.g., Al.sub.xGa.sub.(1-x)P, Al.sub.xIn.sub.yGa.sub.(1-x-y)P, In.sub.xGa.sub.(1-x)P, Al.sub.xIn.sub.(1-x)P, GaAs.sub.aP.sub.bN.sub.(1-a-b), Al.sub.xIn.sub.yGa.sub.(1-x-y)As.sub.aP.sub.bN.sub.(1-a-b), and the like). III-phosphide materials may be doped n-type or p-type, or may be intrinsic.
[0108] In some embodiments, the single-crystalline material comprises a III-arsenide material. The term III-arsenide material is used herein to refer to any Group III element-arsenide compound. Non-limiting examples of III-arsenide materials include gallium arsenide (GaAs), boron arsenide (BAs), aluminum arsenide (AlAs), indium arsenide (InAs), and thallium arsenide (TlAs), as well as any alloys including Group III elements and Group V elements (e.g., Al.sub.xGa.sub.(1-x)As, Al.sub.xIn.sub.yGa.sub.(1-x-y)As, In.sub.xGa.sub.(1-x)As, Al.sub.xIn.sub.(1-x)P, GaAs.sub.aAs.sub.bN.sub.(1-a-b), Al.sub.xIn.sub.yGa.sub.(1-x-y)As.sub.aP.sub.bN.sub.(1-a-b), and the like). III-arsenide materials may be doped n-type or p-type, or may be intrinsic.
[0109] In certain embodiments, the single-crystalline material comprises an oxide. Non-limiting examples of oxides include barium titanate (BaTiO.sub.3 or BTO), barium strontium titanate (Ba.sub.xSr.sub.1-xTiO.sub.3 or BST), strontium titanate (SrTiO.sub.3 or STO), strontium ruthenium oxide (SrRuO.sub.3 or SRO), lanthanum aluminate (LaAlO.sub.3 or LAO), lead magnesium niobate-lead titanate (Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3PbTiO.sub.3 or PMN-PT), yttrium iron garnet (Y.sub.3Fe.sub.5O.sub.12 or YIG), lithium niobate (LiNbO.sub.3), lithium titanate (Li.sub.2TiO.sub.3), zinc oxide (ZnO), and the like.
[0110] The single-crystalline material may have any of a variety of suitable thicknesses. Referring to
[0111] The freestanding layer may have any of a variety of suitable thicknesses. Referring to
[0112] The single-crystalline material may have any of a variety of suitable lengths and/or widths. Referring to
[0113] The freestanding layer may have any of a variety of suitable lengths and/or widths. In some embodiments, the freestanding layer has a length and/or width of greater than or equal to 1 m, greater than or equal to 10 m, greater than or equal to 100 m, greater than or equal to 300 m, greater than or equal to 500 m, greater than or equal to 1 mm, greater than or equal to 10 mm, or greater. In certain embodiments, the freestanding layer has a length and/or width of less than or equal to 100 mm, less than or equal to 10 mm, less than or equal to 1 mm, less than or equal to 500 m, less than or equal to 300 m, less than or equal to 100 m, less than or equal to 10 m, or less. Combinations of the above recited ranges are possible (e.g., the freestanding layer has a length and/or width of greater than or equal to 1 m and less than or equal to 100 mm, or greater than or equal to 300 m and less than or equal to 1 mm). Other ranges are also possible. In certain embodiments, the freestanding portion of the freestanding layer has a length and/or width of greater than or equal to 1 m, greater than or equal to 10 m, greater than or equal to 100 m, greater than or equal to 300 m, greater than or equal to 500 m, greater than or equal to 1 mm, greater than or equal to 10 mm, or greater. In certain embodiments, the freestanding portion of the freestanding layer has a length and/or width of less than or equal to 100 mm, less than or equal to 10 mm, less than or equal to 1 mm, less than or equal to 500 m, less than or equal to 300 m, less than or equal to 100 m, less than or equal to 10 m, or less. Combinations of the above recited ranges are possible (e.g., the freestanding portion of the freestanding layer has a length and/or width of greater than or equal to 1 m and less than or equal to 100 mm, or greater than or equal to 300 m and less than or equal to 1 mm). Other ranges are also possible.
[0114] The single-crystalline material may have any of a variety of suitable facial surface areas. The term facial surface area is used to describe the surface area of a major surface of the layer (which, generally, is the same for each major surface of the layer). In some embodiments, the single-crystalline material has a major surface having a facial surface area of greater than or equal to 1 m.sup.2, greater than or equal to 10 m.sup.2, greater than or equal to 100 m.sup.2, greater than or equal to 1 mm.sup.2, greater than or equal to 10 mm.sup.2, greater than or equal to 100 mm.sup.2, greater than or equal to 1,000 mm.sup.2, or greater. In certain embodiments, the single-crystalline material has a major surface having a facial surface area of less than or equal to 10,000 mm.sup.2, less than or equal to 1,000 mm.sup.2, less than or equal to 100 mm.sup.2, less than or equal to 10 mm.sup.2, less than or equal to 1 mm.sup.2, less than or equal to 100 m.sup.2, less than or equal to 10 m.sup.2, or less. Combinations of the above recited ranges are possible (e.g., the single-crystalline material has a major surface having a facial surface area of greater than or equal to 1 m.sup.2 and less than or equal to 10,000 mm.sup.2, or greater than or equal to 1 mm.sup.2 and less than or equal to 10 mm.sup.2). Other ranges are also possible. In some embodiments, the freestanding portion of the single-crystalline material (when it is freestanding) has a major surface having a facial surface area of greater than or equal to 1 m.sup.2, greater than or equal to 10 m.sup.2, greater than or equal to 100 m.sup.2, greater than or equal to 1 mm.sup.2, greater than or equal to 10 mm.sup.2, greater than or equal to 100 mm.sup.2, greater than or equal to 1,000 mm.sup.2, or greater. In certain embodiments, the freestanding portion of the single-crystalline material (when it is freestanding) has a major surface having a facial surface area of less than or equal to 10,000 mm.sup.2, less than or equal to 1,000 mm.sup.2, less than or equal to 100 mm.sup.2, less than or equal to 10 mm.sup.2, less than or equal to 1 mm.sup.2, less than or equal to 100 m.sup.2, less than or equal to 10 m.sup.2, or less. Combinations of the above recited ranges are possible (e.g., the freestanding portion of the single-crystalline material has a major surface having a facial surface area of greater than or equal to 1 m.sup.2 and less than or equal to 10,000 mm.sup.2, or greater than or equal to 1 mm.sup.2 and less than or equal to 10 mm.sup.2). Other ranges are also possible.
[0115] The freestanding layer may have any of a variety of suitable facial surface areas. In some embodiments, the freestanding layer has a major surface having a facial surface area of greater than or equal to 1 m.sup.2, greater than or equal to 10 m.sup.2, greater than or equal to 100 m.sup.2, greater than or equal to 1 mm.sup.2, greater than or equal to 10 mm.sup.2, greater than or equal to 100 mm.sup.2, greater than or equal to 1,000 mm.sup.2, or greater. In certain embodiments, the freestanding layer has a major surface having a facial surface area of less than or equal to 10,000 mm.sup.2, less than or equal to 1,000 mm.sup.2, less than or equal to 100 mm.sup.2, less than or equal to 10 mm.sup.2, less than or equal to 1 mm.sup.2, less than or equal to 100 m.sup.2, less than or equal to 10 m.sup.2, or less. Combinations of the above recited ranges are possible (e.g., the freestanding layer has a major surface having a facial surface area of greater than or equal to 1 m.sup.2 and less than or equal to 10,000 mm.sup.2, or greater than or equal to 1 mm.sup.2 and less than or equal to 10 mm.sup.2). Other ranges are also possible. In some embodiments, the freestanding portion of the freestanding layer has a major surface having a facial surface area of greater than or equal to 1 m.sup.2, greater than or equal to 10 m.sup.2, greater than or equal to 100 m.sup.2, greater than or equal to 1 mm.sup.2, greater than or equal to 10 mm.sup.2, greater than or equal to 100 mm.sup.2, greater than or equal to 1,000 mm.sup.2, or greater. In certain embodiments, the freestanding portion of the freestanding layer has a major surface having a facial surface area of less than or equal to 10,000 mm.sup.2, less than or equal to 1,000 mm.sup.2, less than or equal to 100 mm.sup.2, less than or equal to 10 mm.sup.2, less than or equal to 1 mm.sup.2, less than or equal to 100 m.sup.2, less than or equal to 10 m.sup.2, or less. Combinations of the above recited ranges are possible (e.g., the freestanding portion of the freestanding layer has a major surface having a facial surface area greater than or equal to 1 m.sup.2 and less than or equal to 10,000 mm.sup.2, or greater than or equal to 1 mm.sup.2 and less than or equal to 10 mm.sup.2). Other ranges are also possible.
[0116] The single-crystalline material may have any of a variety of suitable electromechanical coupling coefficients (k.sup.2). In some embodiments, for example, the single-crystalline material has a k.sup.2 of greater than or equal to 0.001%, greater than or equal to 0.01%, greater than or equal to 0.1%, greater than or equal to 1%, greater than or equal to 10%, greater than or equal to 20%, greater than or equal to 40%, greater than or equal to 60%, or greater than or equal to 80%. In certain embodiments, the single-crystalline material has a k.sup.2 of less than or equal to 100%, less than or equal to 80%, less than or equal to 60%, less than or equal to 40%, less than or equal to 20%, less than or equal to 10%, less than or equal to 1%, less than or equal to 0.1%, or less than or equal to 0.01%. Combinations of the above recited ranges are possible (e.g., the single-crystalline material has a k.sup.2 of greater than or equal to 0.001% and less than or equal to 100%, or greater than or equal to 1% and less than or equal to 10%). Other ranges are also possible.
[0117] According to certain embodiments, the value of k.sup.2 is determined by measuring the reflection coefficient (S.sub.11) of the interdigitated transducer, from which the conductance, G=Re(Y), and the susceptance, B=Im(Y), at a resonant peak are calculated, followed by calculating the electromechanical coupling coefficient (k.sup.2) using the equation, k.sup.2=/4N (G/B).sub.when f=f.sub.
[0118] The single-crystalline material may have any of a variety of suitable resonant frequencies. In some embodiments, for example, the single-crystalline material has a resonant frequency greater than or equal to 1 kHz, greater than or equal to 10 kHz, greater than or equal to 100 kHz, greater than or equal to 1 MHz, greater than or equal to 10 MHz, greater than or equal to 100 MHz, greater than or equal to 1 GHz, or greater than or equal to 10 GHz. In certain embodiments, the single-crystalline material has a resonant frequency less than or equal to 100 GHz, less than or equal to 10 GHz, less than or equal to 1 GHz, less than or equal to 100 MHz, less than or equal to 10 MHz, less than or equal to 1 MHz, less than or equal to 100 kHz, or less than or equal to 10 kHz. Combinations of the above recited ranges are also possible (e.g., the single-crystalline material has a resonant frequency greater than or equal to 1 kHz and less than or equal to 100 GHz, or greater than or equal to 10 MHz and less than or equal to 100 MHz). Other ranges are also possible.
[0119] In certain embodiments, the resonant frequency of the single-crystalline material is measured by exposing the device to electromagnetic (EM) waves (e.g., initiated by an external source, such as a wireless reader) and scanning the return loss reflection coefficient (S.sub.11) over a range of frequencies using the external source.
[0120] According to certain embodiments, although not shown in the figures, one or more intermediate layers may be positioned between the substrate and the single-crystalline material. In some such embodiments, the one or more intermediate layers may be configured as described above with respect to the substrate.
[0121] According to certain embodiments, the device comprises a plurality of interdigitated electrodes. Referring to
[0122] The plurality of interdigitated electrodes 110 and electrode array 111 may, in some embodiments, be in electrical communication with single-crystalline material 106. Referring, for example, to
[0123] In certain embodiments, the plurality of interdigitated electrodes are patterned. In some embodiments, for example, the distance between adjacent interdigitated electrodes may be substantially equal, according to certain embodiments. In some embodiments, the distance between adjacent interdigitated electrodes may be any of a variety of suitable distances (e.g., at least 1 nm, at least 10 nm, at least 50 nm, at least 100 nm, at least 200 nm, at least 300 nm, at least 400 nm, at least 500 nm, at least 1 m, at least 2 m, at least 5 m, at least 10 m, at least 20 m, etc.). In other embodiments, at least a portion of the plurality interdigitated electrodes may be randomly dispersed, as the disclosure is not meant to be limiting in this regard.
[0124] The plurality of interdigitated electrodes may comprise any of a variety of suitable materials. In some embodiments, for example, the plurality of interdigitated electrodes comprise an electrically conductive material, such as one or more metals, one or more conductive ceramics, and/or one or more conductive polymers. In certain embodiments, the plurality of interdigitated electrodes comprise nickel nitride (NiN.sub.x), gold (Au), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), titanium (Ti), titanium nitride (TiN), chromium (Cr), aluminum (Al), silver (Ag), copper (Cu), molybdenum (Mo), iron (Fe), magnesium (Mg), zinc (Zn), and/or tungsten (W). Other materials are also possible.
[0125] The device may comprise any of a variety of suitable numbers of interdigitated electrodes. In some embodiments, for example, the device comprises at least 1, at least 10, at least 100, at least 1,000, at least 10,000, or at least 100,000 interdigitated electrodes. In certain embodiments, the device comprises less than or equal to 1,000,000, less than or equal to 100,000, less than or equal to 10,000, less than or equal to 1,000, less than or equal to 100, or less than or equal to 10 interdigitated electrodes. Combinations of the above recited ranges are possible (e.g., the device comprises at least 1 and less than or equal to 1,000,000 interdigitated electrodes, the device comprises at least 100 and less than or equal to 10,000 interdigitated electrodes). Other combinations are also possible.
[0126] Each interdigitated electrode of the plurality of interdigitated electrodes may have any of a variety of suitable lengths. Referring, for example, to
[0127] Each interdigitated electrode of the plurality of interdigitated electrodes may have any of a variety of suitable facial surface areas. In some embodiments, each interdigitated electrode has major surface having a facial surface area of greater than or equal to 1 nm.sup.2, greater than or equal to 10 nm.sup.2, greater than or equal to 100 nm.sup.2, greater than or equal to 1 m.sup.2, greater than or equal to 10 m.sup.2, greater than or equal to 100 m.sup.2, greater than or equal to 1 mm.sup.2, greater than or equal to 10 mm.sup.2, greater than or equal to 100 mm.sup.2, or greater. In certain embodiments, each interdigitated electrode has a major surface having a facial surface area of less than or equal to 500 mm.sup.2, less than or equal to 100 mm.sup.2, less than or equal to 10 mm.sup.2, less than or equal to 1 mm.sup.2, less than or equal to 100 m.sup.2, less than or equal to 10 m.sup.2, less than or equal to 1 m.sup.2, less than or equal to 100 nm.sup.2, less than or equal to 10 nm.sup.2, or less. Combinations of the above recited ranges are possible (e.g., each interdigitated electrode has a major surface having a facial surface area of greater than or equal to 1 nm.sup.2 and less than or equal to 500 mm.sup.2, or greater than or equal to 10 m.sup.2 and less than or equal to 100 m.sup.2). Other ranges are also possible.
[0128] According to some embodiments, the device comprises an antenna. Referring to
[0129] The antenna may comprise any of a variety of suitable materials. In some embodiments, for example, the antenna comprises an electrically conductive material, such as one or more metals, one or more conductive ceramics, and/or one or more conductive polymers. In certain embodiments, the antenna comprises Ti, TiN, Au, Pt, Pd, Ni, NiN.sub.x, Cr, Al, Ag, Cu, Mo, Fe, Mg, Zn, and/or W. Other materials are also possible.
[0130] The antenna may have any of a variety of suitable shapes. In certain embodiments, for example, the antenna may be a square or rectangular patch antenna. In other embodiments, the antenna may be a circular loop antenna. Other shapes are also possible.
[0131] The antenna may have any of a variety of suitable lengths and/or widths. Referring, for example, to
[0132] The antenna may have any of a variety of suitable facial surface areas. In some embodiments, the antenna has major surface having a facial surface area of greater than or equal to 1 nm.sup.2, greater than or equal to 10 nm.sup.2, greater than or equal to 100 nm.sup.2, greater than or equal to 1 m.sup.2, greater than or equal to 10 m.sup.2, greater than or equal to 100 m.sup.2, greater than or equal to 1 mm.sup.2, greater than or equal to 10 mm.sup.2, greater than or equal to 100 mm.sup.2, greater than or equal to 1,000 mm.sup.2, or greater. In certain embodiments, the antenna has a major surface having a facial surface area of less than or equal to 5,000 mm.sup.2, less than or equal to 1,000 mm.sup.2, less than or equal to 100 mm.sup.2, less than or equal to 10 mm.sup.2, less than or equal to 1 mm.sup.2, less than or equal to 100 m.sup.2, less than or equal to 10 m.sup.2, less than or equal to 1 m.sup.2, less than or equal to 100 nm.sup.2, less than or equal to 10 nm.sup.2, or less. Combinations of the above recited ranges are possible (e.g., the antenna has a major surface having a facial surface area of greater than or equal to 1 nm.sup.2 and less than or equal to 5,000 mm.sup.2, or greater than or equal to 10 m.sup.2 and less than or equal to 100 m.sup.2). Other ranges are also possible.
[0133] The antenna may, in certain embodiments, be in electrical communication with the plurality of interdigitated electrodes. Referring to
[0134] The interconnecting material may comprise any of a variety of suitable materials. In some embodiments, for example, the interconnecting material comprises an electrically conductive material, such as one or more metals, one or more conductive ceramics, and/or one or more conductive polymers. In certain embodiments, the interconnecting material comprises Ti, TiN, Au, Pt, Pd, Ni, NiN.sub.x, Cr, Al, Ag, Cu, Mo, Fe, Mg, Zn, and/or W. Other materials are also possible.
[0135] In some embodiments, at least a portion of the device may comprise one or more overlayers. Referring, for example, to
[0136] The device may comprise any of a variety of suitable overlayers. In some embodiments, for example, the overlayer comprises a protective material. The protective material may be configured to protect one or more components of the device from physical and/or chemical damage that can damage and/or disconnect one or more electrical components of the device (e.g., the plurality of interdigitated electrodes, the antenna, the interconnecting material), in accordance with certain embodiments. In some embodiments, for example, the protective material may be configured to protect one or more components of the device from sweat, blood, saliva, tears, urine, and/or water.
[0137] In some embodiments, the protective material may be over at least a portion of the substrate, the single-crystalline material, the plurality of interdigitated electrodes, the antenna, and/or the interconnecting material. Suitable protective materials include, for example, a polyimide, a parylene, an epoxy, bisbenzocyclobutene (BCB), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polystyrene (PS), polydimethylsiloxane (PDMS), styrene-ethylene-butylene-styrene block copolymer (SEBS), and the like. In certain embodiments, the protective material may comprise one or more auxetic holes that facilitate the exposure of the single-crystalline material to one or more stimuli (e.g., UV light, ions).
[0138] In certain embodiments, the overlayer comprises a stimuli detecting material. The stimuli detecting material may comprise an ion-selective membrane that is configured to trap (e.g., absorb) one or more ions, in accordance with certain embodiments. In some embodiments, for example, the ion-selective membrane is configured to trap sodium ions (Na.sup.+), potassium ions (K.sup.+), calcium ions (Ca.sup.2+), and/or the like. The stimuli detecting material (e.g., the ion-selective membrane) may be over at least a portion of the single-crystalline material and/or the plurality of interdigitated electrodes, according to some embodiments. The stimuli detecting material (e.g., the ion-selective membrane) may, in certain embodiments, comprise an ionophore, an ion-exchanger, a polymer, and/or a plasticizer. In some embodiments, for example, suitable stimuli detecting materials include, 4-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester; tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB); poly(vinyl chloride) (PVC); bis(2-ethylhexyl) sebacate (DOS); valinomycin; and/or sodium tetraphenylborate (NaTPB).
[0139] In certain embodiments, the ion-selective membrane may be configured to trap (e.g., absorb) Na.sup.+ ions to the exclusion of all other possible ions. In some such embodiments, the stimuli-detecting material may comprise 4-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester, TFPB, PVC, and/or DOS.
[0140] In some embodiments, the ion-selective membrane may be configured to trap (e.g., absorb) K.sup.+ ions to the exclusion of all other possible ions. In some such embodiments, the stimuli-detecting material may comprise valinomycin, NaTPB, PVC, and/or DOS.
[0141] In some embodiments, a method of forming a device is described.
[0142] In certain embodiments, the method comprises providing a two-dimensional (2D) material (e.g., graphene) positioned over a growth substrate and forming the single-crystalline material over the 2D material positioned over the growth substrate. See, for example, steps 250 and 252 in
[0143] The fabrication of single-crystalline materials on 2D materials (including fabrication via remote epitaxy methods) is further described in International Patent Application No. PCT/US2016/050701, filed Sep. 8, 2016, published as International Patent Application No. WO 2017/044577 on Mar. 16, 2017, and entitled SYSTEMS AND METHODS FOR GRAPHENE BASED LAYER TRANSFER, which is incorporated herein by reference in its entirety for all purposes.
[0144] The growth substrate may comprise any of a variety of suitable materials. In some embodiments, for example, the growth substrate comprises silicon, sapphire (e.g., aluminum oxide), STO, zinc oxide, magnesium aluminate, gadolinium gallium garnet, yttrium iron garnet, gadolinium scandate, lanthanum aluminate, barium titanate, lithium niobate, lithium tantalate, lead magnesium niobate-lead titanate, silicon carbide (SiC), a Ill-nitride material (e.g., GaN), and the like.
[0145] In some embodiments, the 2D material consists of a single monolayer of 2D material (e.g., a single monolayer of graphene). In other embodiments, multiple layers of 2D materials (e.g., multiple layers of graphene) can be used.
[0146] While the 2D material may be or comprise graphene (e.g., monolayer graphene or multilayer graphene), other types of 2D materials could also be used, as the disclosure is not meant to be limiting in this regard. In some embodiments, the 2D material comprises one or more transition metal dichalcogenide (TMD) monolayers, which are atomically thin materials of the type MX.sub.2, with M being a transition metal atom (e.g., Mo, W, etc.) and X being a chalcogen atom (e.g., S, Se, or Te). In a TMD lattice, one layer of M atoms is usually sandwiched between two layers of X atoms. In another embodiment, the 2D material comprises boron nitride (e.g., hexagonal boron nitride). In yet another example, the 2D material can include a single-atom layer of metal, such as palladium and rhodium. Out of these 2D materials, graphene can have several desirable properties. For example, graphene is a crystalline film and is a suitable substrate for growing epitaxial over-layers. Second, graphene's weak interaction with other materials can substantially relax the lattice mismatching rule for epitaxial growth, potentially permitting the growth of most semiconducting films with low defect densities. Third, epilayers grown on a graphene substrate can be easily and precisely released from the substrate owing to graphene's weak van der Waals interactions, thereby allowing rapid mechanical release of epilayers without post-release reconditioning of the released surface. Fourth, graphene's mechanical robustness can increase or maximize its reusability for multiple growth/release cycles.
[0147] In certain embodiments, the method comprises transferring the single-crystalline material from the growth substrate to a receiving substrate. The single-crystalline material may be transferred from the growth substrate to the receiving substrate, in some embodiments, by removing (e.g., exfoliating) the single-crystalline material from the 2D material positioned over the growth substrate. In certain embodiments, the 2D material can be used as a release layer. The single-crystalline material may, in some embodiments, be removed from the 2D material positioned over the growth substrate using a transfer substrate (e.g., a stressor and/or handler). Referring to step 254 in
[0148] The transfer substrate may be a metal stressor, in some embodiments. In some such embodiments, the transfer substrate may be used to peel the single-crystalline material from the 2D material positioned over the growth substrate under an internal stress of greater than or equal to 100 MPa and less than or equal to 1 GPa.
[0149] In certain embodiments, after removal of single-crystalline material 106 using transfer substrate 524, 2D material 520 and growth substrate 522 may be recycled and reused to grow (e.g., epitaxially grow) a subsequent single-crystalline material, thereby reducing overall fabrication and processing costs.
[0150] In certain embodiments, the single-crystalline material may be transferred to the receiving substrate such that at least a portion of the single-crystalline material is positioned over a cavity of the receiving substrate. Referring to step 258 in
[0151] The receiving substrate may comprise any of a variety of suitable materials, including those described above with respect to the substrate of the device (i.e., a polyimide and/or PDMS).
[0152] According to some embodiments, after the transferring, the single-crystalline material is or is part of a freestanding layer and has a thickness of less than or equal to 300 nm, as described above. In some embodiments, for example, the single-crystalline material that is or is part of the freestanding layer may be positioned and/or aligned over one or more through-holes extending from the first surface of the receiving substrate to the second surface of the receiving substrate that is opposite the first surface.
[0153] At least a portion of the single-crystalline material may be associated with (e.g., bound to) the receiving substrate via an epoxy, according to certain embodiments. In certain embodiments, for example, the single-crystalline material may be bound to the receiving substrate along some or all of its edges, with at least a portion of the surface of the single-crystalline material over the receiving substrate being free of contact with the receiving substrate or any other solid material.
[0154] In certain embodiments, the method comprises forming one or more interdigitated electrodes. In some embodiments, for example, one or more electrically conductive materials (e.g., NiN.sub.x and/or Au) may be deposited on a portion of the device (e.g., on the single-crystalline material). In some embodiments, depositing the interdigitated electrode materials may comprise sputtering and/or physical vapor deposition (e.g., electron-beam evaporation). According to certain embodiments, a photoresist may be used in conjunction with the deposition of the electrically conductive interdigitated electrode materials to form a patterned plurality of interdigitated electrodes.
[0155] In some embodiments, the method comprises forming an antenna. In certain embodiments, for example, one or more electrically conductive materials (e.g., Ti and/or Au) may be deposited on a portion of the device (e.g., on the substrate). In some embodiments, depositing the electrically conductive antenna materials may comprise physical vapor deposition (e.g., electron-beam evaporation). According to certain embodiments, a photoresist may be used in conjunction with the deposition of the electrically conductive antenna materials to form the antenna.
[0156] In certain embodiments, the method comprises forming an interconnecting material. In certain embodiments, for example, one or more electrically conductive materials (e.g., Ti and/or Au) may be deposited on a portion of the device (e.g., on the substrate). In some embodiments, depositing the electrically conductive interconnecting materials may comprise physical vapor deposition (e.g., electron-beam evaporation). According to certain embodiments, a photoresist may be used in conjunction with the deposition of the electrically conductive interconnecting materials to form the interconnecting material.
[0157] In some embodiments, the method comprises forming an overlayer (e.g., a protective material, a stimuli detecting material). In certain embodiments, for example, one or more protective materials (e.g., a polyimide) and/or stimuli detecting materials (e.g., an ion-selective membrane) may be deposited on a portion of the device. In some embodiments, for example, the protective material may be deposited on at least a portion of the substrate, the single-crystalline material, the interdigitated electrodes, the antenna, and/or the interconnecting material. In certain embodiments, the stimuli detecting material may be deposited on at least a portion of the single-crystalline material and/or the interdigitated electrodes. In certain embodiments, depositing the overlayer may comprise spin coating.
[0158] In certain embodiments, the method comprises forming one or more auxetic holes through the substrate and/or the overlayer (e.g., the protective material, the stimuli detecting material). According to some embodiments, for example, one or more auxetic holes may be formed through the substrate and/or the overlayer using a photoresist and an etching process.
[0159] According to some embodiments, the device may be positioned over a portion of skin of a user.
[0160] The device may be positioned over a portion of skin of a user for any of a variety of suitable durations. In some embodiments, for example, the device is configured to be positioned over the portion of skin of the user for at least 30 minutes, at least 1 hour, at least 6 hours, at least 1 day, at least 2 day, at least 3 days, at least 4 days, at least 5 days, at least 6 days, at least 1 week, at least 2 weeks, at least 3 weeks, or at least 1 month. In certain embodiments, the device is configured to be positioned over the portion of skin of the user for less than or equal to 6 months, less than or equal to 1 month, less than or equal to 3 weeks, less than or equal to 2 weeks, less than or equal to 1 week, less than or equal to 6 days, less than or equal to 5 days, less than or equal to 4 days, less than or equal to 3 days, or less than or equal to 2 days. Combinations of the above recited ranges are possible (e.g., the device can be configured to be positioned over the portion of skin of the user for at least 30 minutes and less than or equal to 6 months, or for at least one week and less than or equal to two weeks). Other ranges are also possible.
[0161] In some embodiments, the device may be applied over the portion of skin of the user, removed from the portion of skin of the user, and reapplied to the portion of skin of the user (or, in some embodiments, reapplied to a different portion of skin of the user).
[0162] According to certain embodiments, a method of operating a device (e.g., a resonator) is described. In some embodiments, for example, the device is a resonator (e.g., a surface acoustic wave resonator) comprising a single-crystalline material having a thickness of less than or equal to 300 nm that is or is part of a freestanding layer, as described herein.
[0163] In some embodiments, the method comprises applying an electrical potential to the device (e.g., surface acoustic wave resonator). According to certain embodiments, and as would generally be understood by a person of ordinary skill in the art, the application of an electrical potential to the device results in the single-crystalline material serving as a resonator (e.g., a piezoelectric resonator) that generates a mechanical wave (e.g., a surface acoustic wave). In some embodiments, for example, the plurality of interdigitated electrodes delivers electrical energy from the antenna to the single-crystalline material, which converts the input electrical signal into a mechanical wave (e.g., a surface acoustic wave). The electrical potential may be applied to the device via any of a variety of suitable means, including, but not limited to, an external source (e.g., a wireless reader) that initiates EM waves, in accordance with certain embodiments.
[0164] In certain embodiments, the method comprises determining a change in a resonant frequency of the single-crystalline material in response to an environmental change. In some embodiments, for example, the resonant frequency of the mechanical wave generated by the single-crystalline material may be sensitive to a number of stimuli, such as, for example, mechanical strain, light exposure, and/or mass changes. In certain embodiments, the one or more stimuli resulting from an environmental change surrounding the device may alter the resonant frequency of the mechanical wave. In some embodiments, the mechanical wave is converted back into an electrical signal that is retransmitted back to the antenna. The electrical signal may, in some embodiments, be measured by the external source (e.g., wireless reader), therefore yielding information about the environmental change resulting from the mechanical, optical, and biochemical stimuli.
[0165] In certain embodiments, the device (e.g., resonator) is configured to detect a strain (e.g., a tensile strain). According to some embodiments, for example, the device may be configured such that resonant frequency shifts in the mechanical wave (e.g., surface acoustic wave) produced by the single-crystalline material resulting from a mechanical strain may be detected as an electrical signal by the antenna. In some embodiments, the device is configured to measure strain resulting from an arterial pulse wave and/or strain resulting from one or more bending cycles of the device.
[0166] The minimum detectable strain (e.g., tensile strain) of the device may be any of a variety of suitable values. In some embodiments, for example, the device has a minimum detectable tensile strain of less than or equal to 0.1%, less than or equal to 0.09%, less than or equal to 0.08%, less than or equal to 0.07%, less than or equal to 0.06%, less than or equal to 0.05%, less than or equal to 0.04%, less than or equal to 0.03%, less than or equal to 0.02%, less than or equal to 0.01%, less than or equal to 0.001%, or less, at an energy consumption less than or equal to 810.sup.8 Joules per measurement. In certain embodiments, the device has a minimum detectable tensile strain of greater than or equal to 0.0001%, greater than or equal to 0.001%, greater than or equal to 0.01%, greater than or equal to 0.02%, greater than or equal to 0.03%, greater than or equal to 0.04%, greater than or equal to 0.05%, greater than or equal to 0.06%, greater than or equal to 0.07%, greater than or equal to 0.08%, or greater than or equal to 0.09% at an energy consumption less than or equal to 810.sup.8 Joules per measurement. Combinations of the above recited ranges are also possible (e.g., the device has a minimum detectable tensile strain of greater than or equal to 0.0001% and less than or equal to 0.1% at an energy consumption less than or equal to 810.sup.8 Joules per measurement, or greater than or equal to 0.04% and less than or equal to 0.06% at an energy consumption less than or equal to 810.sup.8 Joules per measurement). Other ranges are also possible.
[0167] The maximum detectable strain (e.g., tensile strain) of the device may be any of a variety of suitable values. In some embodiments, for example, the device has a maximum detectable tensile strain of less than or equal to 1000%, less than or equal to 100%, less than or equal to 50%, less than or equal to 25%, less than or equal to 20%, less than or equal to 19%, less than or equal to 18%, less than or equal to 17%, or less than or equal to 16%, less than or equal to 15%, less than or equal to 10%, or less, at an energy consumption less than or equal to 810.sup.8 Joules per measurement. In certain embodiments, the device has a maximum detectable tensile strain of greater than or equal to 1%, greater than or equal to 10%, greater than or equal to 15%, greater than or equal to 16%, greater than or equal to 17%, greater than or equal to 18%, greater than or equal to 19%, greater than or equal to 20%, greater than or equal to 25%, greater than or equal to 50%, greater than or equal to 100%, or greater, at an energy consumption less than or equal to 810.sup.8 Joules per measurement. Combinations of the above recited ranges are also possible (e.g., the device has a maximum detectable tensile strain of greater than or equal to 1% and less than or equal to 1000% at an energy consumption less than or equal to 810.sup.8 Joules per measurement, or greater than or equal to 16% and less than or equal to 17% at an energy consumption less than or equal to 810.sup.8 Joules per measurement). Other ranges are also possible.
[0168] According to certain embodiments, the minimum detectable strain and/or the maximum detectable strain of the device may be determined by providing a flexible test substrate with known modulus and known thickness, disposing the device on the test substrate, applying a known bending radius, and calculating the strain (e.g., tensile strain).
[0169] The device may be configured to withstand any of a variety of suitable bending cycles without a fracture. In certain embodiments, for example, the device is configured to withstand greater than or equal to 500 bending cycles, greater than or equal to 1,000 bending cycles, greater than or equal to 5,000 bending cycles, greater than or equal to 10,000 bending cycles, greater than or equal to 50,000 bending cycles, or greater than or equal to 100,000 bending cycles without a fracture. In some embodiments, the device is configured to withstand less than or equal to 1,000,000 bending cycles, less than or equal to 100,000 bending cycles, less than or equal to 50,000 bending cycles, less than or equal to 10,000 bending cycles, less than or equal to 5,000 bending cycles, or less than or equal to 1,000 bending cycles without a fracture. Combinations of the above recited ranges are possible (e.g., the device is configured to withstand greater than or equal to 500 bending cycles and less than or equal to 1,000,000 bending cycles without a fracture, or greater than or equal to 1,000 bending cycles and less than or equal to 5,000 bending cycles without a fracture). Other ranges are also possible.
[0170] According to certain embodiments, the bending cycles of the device may be determined by providing a flexible test substrate with known modulus and known thickness, disposing the device on the test substrate, applying a known bending radius, calculating the strain (e.g., tensile strain), and repeating the bending cycles. Each bending cycle can comprise starting with the device in a no strain state, bending the device to a known bending radius and/or the maximum detectible strain of the device, and returning the device to a no strain state.
[0171] In certain embodiments, the device (e.g., resonator) is configured to detect light. In some embodiments, for example, the device is configured to detect UV light. According to some embodiments, the device may be configured such that resonant frequency shifts in the mechanical wave (e.g., surface acoustic wave) produced by the single-crystalline material resulting from exposure to UV light may be detected as an electrical signal by the antenna.
[0172] The detectable UV light intensity of the device may be any of a variety of suitable values. In some embodiments, for example, the device has a detectable UV light intensity of greater than or equal to 0.0001 mW/cm.sup.2, greater than or equal to 0.001 mW/cm.sup.2, greater than or equal to 0.01 mW/cm.sup.2, greater than or equal to 0.1 mW/cm.sup.2, greater than or equal to 1 mW/cm.sup.2, greater than or equal to 10 mW/cm.sup.2, greater than or equal to 100 mW/cm.sup.2, or greater than or equal to 1,000 mW/cm.sup.2. In certain embodiments, the device has a detectable UV light intensity of less than or equal to 10,000 mW/cm.sup.2, less than or equal to 1,000 mW/cm.sup.2, less than or equal to 100 mW/cm.sup.2, less than or equal to 10 mW/cm.sup.2, less than or equal to 1 mW/cm.sup.2, less than or equal to 0.01 mW/cm.sup.2, or less than or equal to 0.001 mW/cm.sup.2. Combinations of the above recited ranges are also possible (e.g., the device has a detectable UV light intensity of greater than or equal to 0.0001 mW/cm.sup.2 and less than or equal to 10,000 mW/cm.sup.2, or greater than or equal to 0.01 mW/cm.sup.2 and less than or equal to 1 mW/cm.sup.2). Other ranges are also possible.
[0173] In certain embodiments, the UV responsivity is measured by exposing the device to UV light of varying intensities using, for example, a UV conformal photocurrent microscopy (UVCPM) system, and recording the output signals of the device using a vector network analyzer (VNA).
[0174] According to some embodiments, the device (e.g., resonator) is configured to detect chemical concentrations. In certain embodiments, for example, the device is configured to measure ion concentrations (e.g., Na.sup.+, K.sup.+ and/or Ca.sup.2+ concentrations). As explained above, in accordance with certain embodiments, a stimuli detecting material, such as an ion-selective membrane that is configured to trap ions and undergo changes in mass, may be positioned over at least a portion of the device (e.g., the single-crystalline material, the plurality of interdigitated electrodes). In some such embodiments, the device may be configured such that resonant frequency shifts in the mechanical wave (e.g., surface acoustic wave) produced by the single-crystalline material resulting from changes in the concentration of ions trapped in the ion-selective membrane may be detected as an electrical signal by the antenna.
[0175] The detectable ion concentration of the device may be any of a variety of suitable values. In certain embodiments, for example, the device is configured to detect an ion concentration greater than or equal to 0.5 mM, greater than or equal to 1 mM, greater than or equal to 2 mM, greater than or equal to 5 mM, greater than or equal to 10 mM, greater than or equal to 20 mM, or greater than or equal to 50 mM. In some embodiments, the device is configured to detect an ion concentration less than or equal to 100 mM, less than or equal to 50 mM, less than or equal to 20 mM, less than or equal to 10 mM, less than or equal to 5 mM, less than or equal to 2 mM, or less than or equal to 1 mM. Combinations of the above recited ranges are also possible (e.g., the device is configured to detect an ion concentration greater than or equal to 0.5 mM and less than or equal to 100 mM, or greater than or equal to 2 mM and less than or equal to 5 mM). Other ranges are also possible.
[0176] In certain embodiments, the ion concentration detected by the device is measured by exposing the device to ion-containing solutions (e.g., solutions of NaCl) comprising varying concentrations of ions using a peristaltic pump at a consistent flow rate, and recording the output signals of the device using a VNA.
EXAMPLE
[0177] The following example describes a chip-less wireless e-skin-based health monitoring sensor device based on a surface acoustic wave resonator. The device achieves marked improvements in strain sensitivity, versatility, power efficiency, and long-term wearability compared to conventional e-skin sensors. The improvements are permitted by integrating ultrathin, single-crystalline, freestanding membranes of gallium nitride (GaN) as a material for sensing and wireless communication (
[0178] Remote homoepitaxy of GaN on graphene-coated GaN substrates allowed buffer-free growth of ultrathin GaN epitaxial layers, which were easily released from weak graphene-GaN interfaces by a 2D material-based layer transfer (2DLT) process. The freestanding GaN nanomembranes (200 nm) produced SAWs with electromechanical coefficients higher than those of SAWs produced by thicker, non-freestanding counterparts. Stretchable and highly sensitive SAW-based e-skin sensor devices that are configured to wirelessly detect strain, chemical concentrations, and UV light without having any wireless chips were fabricated. In addition, the GaN nanomembrane was integrated on ultrathin PDMS patches (20 m) containing dense arrays of perforations that allow removal of sweat and skin byproducts, thereby providing for long term health monitoring for more than 1 week.
[0179]
[0180] In the chip-less wireless e-skin device described herein, an ultrathin GaN SAW sensor replaces the bulky chip and circuit components used in conventional chip-based wireless e-skin systems. The SAW sensor is made of a rectangular slab of a GaN nanomembrane (size: 408 m640 m, thickness: 200 nm) integrated onto a silicone patch. Patterns of inter-digitated metal electrodes (NiN.sub.x/Au20/20 nm) deliver electrical energy from the antenna (Ti/Au2/100 nm) into the GaN nanomembrane, which serves as a piezoelectric resonator that converts the input electrical signal into a mechanical wave. This is a unique advantage of GaN-based e-skin devices over the more conventional Si-based e-skins systems, which lack piezoelectric properties. The SAW is sensitive to mechanical strain, UV exposure (via optical absorption by GaN), and mass changes (via absorption and desorption of ions in coatings on top). The SAW is converted back into an electrical signal and transmitted through the antenna, and changes in resonant frequency yields information about the mechanical, optical, and biochemical stimuli detected by the SAW sensor. Because the functional GaN and metal layers are all ultrathin, the silicone elastomer can also be much thinner (20 m) than those used in chip-based e-skin systems, therefore improving the softness, skin-conformability, and long-term wearability of the chip-less wireless SAW-based e-skin device. In addition, the SAW devices consume significantly less power compared to the wireless chip systems, which need to support power for thousands of transistors and other circuit components. The low power consumption of the SAW-based e-skin device also has the potential to increase communication distances compared to other battery-less e-skin systems based on wireless chips.
[0181] Traditional wireless SAW sensors have relied on thick, non-freestanding GaN films that are tethered to a wafer, which are difficult to integrate into flexible e-skin systems. The single-crystalline GaN film, produced via remote epitaxy and 2DLT, achieves thickness and flexibility that allows for conformal adhesion on human skin. The required GaN thicknesses for conformal skin adhesion was estimated by simulating the correlation between built-in strain energy per area and GaN thickness (
[0182] The capability of the single-crystalline GaN membranes to laminate conformally on skin was verified experimentally by attaching the membranes on skin replica samples made of Ecoflex silicone. The left SEM image in
[0183] To understand the optoelectronic performances of the GaN nanomembranes, GaN-metal Schottky junction diodes were fabricated using 200 nm-thick membranes of both single-crystalline GaN, obtained via remote epitaxy and 2DLT, and poly-crystalline GaN, which is widely available via sputtering techniques, and their sensitivities to UV light were compared. UV radiation is the primary driver of skin cancers and thus represents an important tracking target for e-skin health monitoring devices. It is also a unique application area for SAW-based e-skin devices, because existing chip-less wireless e-skin systems based on LC resonators lack semiconductor components to detect light, and the indirect band gap of GaN allows significantly higher photosensitivity compared to Si-based photodetectors.
[0184] The excellent piezoelectricity and perfect single-crystallinity of the ultrathin GaN film enhances the degree to which the device provides wireless communication without using NFC/RFID chips. The chip-less wireless e-skin device was created by developing the formation of highly sensitive SAWs on ultrathin single-crystalline GaN freestanding membranes; and developing the freestanding SAW device as a biosensing platform. Upon successful lamination on the human body, the e-skin device generates a SAW that responds sensitively to physiological activities, the changes of which are detected wirelessly through the antenna. It has been previously reported that SAW generated by ultrathin GaN films grown on a sapphire or SiC substrate is negligible due to the strong binding of the film to substrate. The free standing, highly crystalline GaN films that have been declamped from the substrate, however, generate SAWs with a greatly enhanced electromechanical coupling value.
[0185] The simulation of SAW generation in GaN (
[0186]
[0187] The wireless strain-sensing capability of the e-skin device was demonstrated by first calibrating the resonant peak shifts in the SAW devices in response to strain induced by bending the patch (
[0188] Owing to the high strain sensitivity of the SAW e-skin device, continuous chip-less wireless measurement of arterial pulse waves on the wrist was demonstrated. As shown in
[0189] The SAW sensor's communication range, in the produced prototype, was limited to 14 mm. Reliable bending response was obtained upon displacement of antenna to 14 mm in z-direction, 7.5 mm in x-direction, and 30 degrees in -direction (
[0190] The biomedical sensing capability of the SAW-based e-skin device was expanded to wirelessly monitor ion concentrations in sweat, which can serve as indicators for conditions such as hyponatremia, kidney failure, and hypertension. The extremely small dissolution rate of GaN in most solutions makes it perform stably as a sweat sensor. The surface of the GaN SAW device was coated with ion-selective membranes (ISMs), which can trap ions inside and undergo changes in viscosity and mass. The resonant peak shifts in ISM-coated SAW device can therefore be used to wirelessly detect variation in ionic concentrations in surrounding fluids (see
[0191]
[0192]
[0193] Excellent optoelectronic characteristics and piezoelectricity of GaN also allow wireless detection of UV light using the e-skin device. Light absorption by the GaN SAW device leads to variation in its electrical conductivity, which in turn alters the patterns of acoustic wave generation. The SAW sensor was first exposed to UV light by forming holes through the polyimide protection layer coating the device (
[0194] In summary, chip-free e-skin platforms utilizing GaN SAW devices for sensing and wireless communications were fabricated. The GaN SAW devices were built using single-crystalline, ultrathin, freestanding, and piezoelectric GaN films prepared by remote epitaxy. Remote homoepitaxy of GaN allowed buffer layer-free growth of ultrathin GaN epitaxial layers, which were readily released from substrates. The freestanding and highly crystalline nature of the films enable the SAW devices with a very high electromechanical coupling coefficient (k.sup.2). The GaN SAW devices enable wireless e-skin systems with high sensitivity and low power consumption, without the use of bulky wireless integrated circuit chips. The e-skin device can be used for wireless monitoring of strain, UV light, and ions for biosensing applications via combination with a wide variety of biomolecular binder types, therefore opening new directions for implementing highly sensitive and power-saving versatile wireless e-skin devices.
[0195] The following describes the materials and methods used to fabricate and characterize the chip-less wireless e-skin-based health monitoring sensor device based on a SAW resonator, described above.
[0196] Production of GaN nanomembranes via remote homoepitaxy: A Veeco Gen200 plasma-assisted molecular beam epitaxy system was used to grow GaN thin films on 2D materials coated GaN substrates. The GaN substrates were commercial 5 m GaN grown on sapphire. Prior to growth, the GaN substrate were cleaned by acetone, IPA and HCl before loading into the reaction chamber. 1-3 layers of 2D materials were deposited on GaN substrates after being outgassed at 700 C. for 15 minutes. Then, 200 nm to 1.8 m GaN epilayers were grown at substrate temperature from 680 C. to 730 C. Gallium rich conditions were used to ensure enhanced surface diffusion. Gallium residues were etched by FeCl.sub.3 after growth. To exfoliate the GaN epilayer, a Ni stressor (2.5 m) with Cr adhesion layer (30 nm) was deposited to the GaN surface which induces a mechanical strain at the GaN/2D material interface. Thermal release tape (TRT) was applied to the metal stressor/GaN multilayers, followed by lifting of the TRT from the substrate edge, resulting in mechanical exfoliation of the GaN nanomembranes with the metal stressors. The whole process is illustrated in
[0197] Fabrication of electronic modules in perforated e-skin devices: Singe-crystalline GaN nanomembranes (200 nm) were fabricated by remote homoepitaxy processes as piezoelectric, wide bandgap semiconductor layers of strain sensors and UV sensors. For fabrication of single-crystalline GaN e-skin devices, a polyimide precursor, poly(pyromellitic dianhydride-co-4,4-oxydianiline) in n-methyl-2-pyrrolidone (purchased from Sigma Aldrich), was spin coated and cured on Al/Ti (500 nm/20 nm)-coated, heavily-doped Si substrate (<0.01 cm) at 300 C. for 1 hour. An epoxy resin (
[0198] Perforated e-skin fabrication: For integration of the electronic modules to the auxetic dumbbell hole patterned polydimethylsiloxane (PDMS) adhesives (SYLGARD 184, Dow Corning), detachment of the electronic modules from the Al/Ti/Si wafer by electrochemical lift-off process (dissolution of Al layer) was the first step. Before the lift-off process, the electronic modules were attached to TRT. Between modules and TRT, a 2-m-thick poly(methyl methacrylate) (PMMA) layer was inserted. After electrical wiring at the backside of the Si substrate, the samples were dipped into sodium chloride solution (0.9% NaCl) together with Pt wire as a counter electrode. As 1.8 V was applied to the Si wafer, the Al was dissolved in NaCl solution and electronic modules were transferred to the TRT accordingly. To form auxetic dumbbell hole patterns on the electronic modules and the PDMS adhesives, Si mold-based soft lithography processes were utilized (
[0199] Preparation of skin replica: Dragon Skin silicone (1:1 ratio of part A to part B by weight; Dragon Skin 30; Smooth-On, Inc.) was poured on the forearm, allowed to cure for 1 hour at room temperature, removed from skin, and placed in a Petri dish with the skin-textured side facing upward. Pouring Ecoflex (1:1 ratio of part A to part B by weight; Ecoflex 30; Smooth-On, Inc.) into the Petri dish, letting it cure at room temperature for 12 hours, and peeling it away yielded the skin replica samples made of Ecoflex.
[0200] GaN film characterization: The structural properties of GaN thin films were characterized by using a Bruker D8 high-resolution X-ray diffraction. Surface morphologies of GaN thin films were measured by using a Zeiss Merlin scanning electron microscope and by using a Park NX10 atomic force microscope (AFM). For dislocation density determination, GaN thin films were etched in phosphoric acid at 160 C. for 0.5 hours. For TEM, the cross-sectional specimens were extracted from the GaN thin film by a lift-out technique in a dual-beam FIB/SEM (Helios G4, Thermo Fisher Scientific, U.S.). Prior to the ion-milling in a FIB/SEM, layers of carbon were deposited on the sample surface to protect the sample. The inner structures of single-crystalline GaN were observed using an aberration-corrected TEM (ARM-200F, JEOL, Japan) on the cross-sectional specimens at an acceleration voltage of 200 kV. The microscope was equipped with an aberration corrector in the objective lens (image corrector) and a Gatan OneView camera.
[0201] Evaluation of UV sensing performance: UV conformal photocurrent microscopy (UVCPM) system was established to assess UV sensing performance of single-crystalline GaN and polycrystalline GaN. The output currents from sensors were recorded with varying biases and illumination intensity by an Agilent B1500A semiconductor device parameter analyzer.
[0202] Measurement of SAW e-skin device: A handheld low-cost open hardware vector network analyzer (VNA), NanoVNA H4, or a tabletop laboratory VNA, Agilent N5230A VNA (as a comparison to NanoVNA), were used for measurements of SAW devices (
[0203] Evaluation of wireless UV sensor performance: The GaN SAW e-skin device had hole patterns etched through the top polyimide layer to expose the GaN surface to UV light. The UCVPM system was used, and the output signals upon irradiation of UV light with varying intensities (24.65 W/cm.sup.2, 65.64 W/cm.sup.2, 256.2 W/cm.sup.2, 403.4 W/cm.sup.2, 671.0 W/cm.sup.2, and 898.5 W/cm.sup.2) were recorded by VNA.
[0204] Fabrication and evaluation of ion sensing performance: The GaN SAW e-skin device had hole patterns etched through the top polyimide layer. On top of either the GaN SAW e-skin device or quartz crystal microbalance (QCM), ion-selective membrane solutions in tetrahydrofuran (
[0205] COMSOL Multiphysics simulation: Finite element analysis of the GaN SAW e-skin device was evaluated using COMSOL Multiphysics software. The geometry of the device, drawn two-dimensionally, is shown in
where N and f.sub.r are the number of IDT finger pairs and resonant frequency, respectively.
[0206] While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and/or methods, if such features, systems, articles, materials, and/or methods are not mutually inconsistent, is included within the scope of the present invention.
[0207] The indefinite articles a and an, as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean at least one.
[0208] The phrase and/or, as used herein in the specification and in the claims, should be understood to mean either or both of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the and/or clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to A and/or B, when used in conjunction with open-ended language such as comprising can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
[0209] As used herein in the specification and in the claims, or should be understood to have the same meaning as and/or as defined above. For example, when separating items in a list, or or and/or shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as only one of or exactly one of, or, when used in the claims, consisting of, will refer to the inclusion of exactly one element of a number or list of elements. In general, the term or as used herein shall only be interpreted as indicating exclusive alternatives (i.e. one or the other but not both) when preceded by terms of exclusivity, such as either, one of, only one of, or exactly one of. Consisting essentially of, when used in the claims, shall have its ordinary meaning as used in the field of patent law.
[0210] As used herein in the specification and in the claims, the phrase at least one, in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase at least one refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, at least one of A and B (or, equivalently, at least one of A or B, or, equivalently at least one of A and/or B) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
[0211] In the claims, as well as in the specification above, all transitional phrases such as comprising, including, carrying, having, containing, involving, holding, and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases consisting of and consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.