DELAMINATION PROCESSES AND FABRICATION OF THIN FILM DEVICES THEREBY

Abstract

Interfacial delamination processes for physically separating a film structure from a substrate, and processes of fabricating a thin-film electronic device. The processes entail providing the substrate with an electrically-conductive separation layer on a surface of the substrate and optionally providing a pin hole free barrier layer on the electrically-conductive separation layer, forming a film structure on the electrically-conductive separation layer or, if present, the barrier layer, to yield a multilayer structure, and separating the film structure from the substrate by subjecting the multilayer structure to interfacial debonding that comprises contacting at least an interface between the film structure and the electrically-conductive separation layer or, if present, the barrier layer, with water or an electrolyte solution.

Claims

1. An interfacial delamination process for physically separating a film structure from a substrate, the process comprising: providing the substrate with an electrically-conductive separation layer on a surface of the substrate; forming a film structure on the electrically-conductive separation layer to yield a multilayer structure; and separating the film structure from the electrically-conductive separation layer by subjecting the multilayer structure to microbubble assisted interfacial debonding that comprises contacting at least an interface between the film structure and the electrically-conductive separation layer with water or an electrolyte solution and applying a voltage between the electrically-conductive separation layer and an anode that is also in contact with the water or electrolyte solution to generate microbubbles at the interface that delaminate and buoy the film structure from the electrically-conductive separation layer.

2. The process according to claim 1, wherein the film structure is a thin film device chosen from the group consisting of optoelectronic, integrated circuit, and biosensor devices.

3-4. (canceled)

5. The process according to claim 1, the process further comprising bonding the film structure to a second substrate.

6. (canceled)

7. The process according to claim 1, wherein the microbubbles are hydrogen gas bubbles.

8. The process according to claim 7, wherein the interface between the film structure and the electrically-conductive separation layer is contacted with the electrolyte solution.

9. The process according to claim 8, wherein the electrolyte solution has a molar concentration of up to about 2M of sodium chloride or sodium hydroxide.

10-12. (canceled)

13. The process according to claim 1, wherein the electrically-conductive separation layer remains adhered to the surface of the substrate after the separating step.

14. The process according to claim 13, wherein after the separating step the process further comprises forming a second film structure on the electrically-conductive separation layer of the substrate to yield a second multilayer structure.

15. The process according to claim 1, wherein the film structure floats to a surface of the water or electrolyte solution after the separating step.

16. The process according to claim 1, wherein the film structure comprises a dielectric polymeric film on and bonded to the electrically-conductive separation layer of the substrate, and the separating step debonds the dielectric polymeric film from the electrically-conductive separation layer.

17. The process according to claim 1, further comprising encapsulating the film structure with a polymeric material and then exposing the interface through the polymeric material prior to the separating step.

18. A process of fabricating a thin-film device, the process comprising: providing a substrate with an electrically-conductive separation layer on a surface of the substrate; applying and bonding a dielectric polymeric film to the electrically-conductive separation layer of the substrate; forming the thin film device on the dielectric polymeric film to yield a multilayer structure; and separating the multilayer structure from the electrically-conductive separation layer by subjecting the multilayer structure to microbubble assisted interfacial debonding that comprises contacting at least an interface between the dielectric polymeric film and the electrically-conductive separation layer with water or an electrolyte solution and applying a voltage between the electrically-conductive separation layer and an anode that is also in contact with the water or electrolyte solution to generate microbubbles at the interface that delaminate and buoy the multilayer structure from the electrically-conductive separation layer.

19. The process according to claim 18, wherein the thin film device is chosen from the group consisting of optoelectronic, integrated circuit, and biosensor devices.

20. (canceled)

21. The process according to claim 18, the process further comprising bonding the multilayer structure to a second substrate.

22. (canceled)

23. The process according to claim 18, wherein the microbubbles are hydrogen gas bubbles.

24. The process according to claim 23, wherein the interface between the multilayer structure and the electrically-conductive separation layer is contacted with the electrolyte solution.

25. (canceled)

26. The process according to claim 18, wherein the electrically-conductive separation layer remains adhered to the surface of the substrate after the separating step.

27. The process according to claim 26, wherein after the separating step the process further comprises forming a second dielectric polymeric film on the electrically-conductive separation layer of the substrate and a second thin-film electronic device on the second dielectric polymeric film to yield a second multilayer structure.

28. The process according to claim 18, wherein the multilayer structure floats to a surface of the water or electrolyte solution after the separating step.

29. The process according to claim 18, further comprising encapsulating the multilayer structure with a polymeric material and then exposing the interface through the polymeric material prior to the separating step.

30. An interfacial delamination process for physically separating a film structure from a substrate, the process comprising: providing the substrate with an electrically-conductive separation layer on a surface of the substrate and a pin hole free barrier layer on the electrically-conductive separation layer; forming a film structure on the barrier layer to yield a multilayer structure; and separating the film structure from the barrier layer by subjecting the multilayer structure to interfacial debonding that comprises contacting at least an interface between the film structure and the barrier layer with water or an electrolyte solution.

31. The process according to claim 30, wherein the interface between the film structure and the barrier layer is contacted with the electrolyte solution, the process further comprising applying a voltage between the electrically-conductive separation layer and an anode that is also in contact with the electrolyte solution to generate microbubbles at the interface that delaminate and buoy the film structure from the electrically-conductive separation layer.

32. The process according to claim 31, wherein the microbubbles are hydrogen gas bubbles.

33. The process according to claim 31, wherein the electrolyte solution is chosen from the group consisting of a sodium chloride electrolyte solution and a sodium hydroxide electrolyte solution.

34. The process according to claim 31, wherein the barrier layer is formed of aluminum oxide, hafnium oxide, silicon nitride, or silicon dioxide.

35. The process according to claim 30, wherein the interface between the film structure and the barrier layer is contacted with water.

36. (canceled)

37. The process according to claim 30, wherein the electrically-conductive separation layer remains adhered to the surface of the substrate after the separating step.

38. The process according to claim 37, wherein after the separating step the process further comprises forming a second film structure on the electrically-conductive separation layer of the substrate to yield a second multilayer structure.

39. The process according to claim 30, wherein the film structure is a thin film battery.

40-41. (canceled)

42. The process according to claim 30, the process further comprising bonding the film structure to a second substrate.

43. (canceled)

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0016] FIG. 1 schematically illustrates an interfacial delamination process in which a film structure is debonded from an electrically-conductive separation layer in accordance with a nonlimiting embodiment of this invention.

[0017] FIG. 2 is a detail of FIG. 1 schematically representing microscale bubbles generated at an interface between the film structure and the electrically-conductive separation layer to debond the film structure and produce a mild buoyancy force capable of completely separating the film structure from a donor/host substrate in accordance with a nonlimiting aspect of this invention.

[0018] FIGS. 3, 4, and 5 contain three images representing the delamination of a thin film device from a rigid, flat donor/host/fabrication substrate in accordance with nonlimiting aspects of this invention.

[0019] FIGS. 6 and 7 are two graphs evidencing the effect of electrolyte concentration and applied voltage on time to delaminate a polyimide film from a donor Si wafer coated with a metal film, such as an Au film.

[0020] FIGS. 8, 9, and 10 are graphs plotting the measured current-voltage (I-V) curves of, respectively, a representative resistor, diode, and transistor embedded in thin film devices and evidencing that no significant degradation occurred in the electronic performances of the devices after delamination.

[0021] FIGS. 11 and 12 contain graphs relating to the performances of a thin film electrophysiological sensing electrode that was delaminated and applied to elastic substrates (lefthand graphs) and commercial electrodes (righthand graphs). FIG. 11 contains ECG data relating to the performances of the thin film electrophysiological sensing electrode (lefthand graph) and a commercial ECG electrode (righthand graph), and FIG. 12 contains EMG data relating to the performances of the thin film electrophysiological sensing electrode (lefthand graph) and a commercial EMG electrode (righthand graph).

[0022] FIG. 13 schematically illustrates an interfacial delamination process wherein microscale bubbles are generated at an interface between a thin film battery and a multilayer stack to debond the thin film battery and produce a mild buoyancy force capable of completely separating the thin film battery from a donor/host substrate in accordance with a nonlimiting aspect of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The following describes interfacial delamination processes that enable the fabrication of thin film devices on a wide variety of surfaces and substrates of interest. The delamination processes are generated by electrochemical reactions at the interface between a pre-fabricated thin film device and a donor/host substrate on which the device was fabricated. The processes can be controlled to facilitate intact separation of relatively large thin film devices from donor/host substrates without the need to use mechanical peeling tools or equipment. The devices may then be transferred to flexible, stretchable, and/or transparent substrates, and yield flexible, stretchable, and/or transparent thin film devices.

[0024] The delamination processes further enable the physical separation of prefabricated thin film devices from a host/donor substrate (e.g., a semiconductor wafer or glass substrate) to enable wafer-scale, defect-free delamination of multiple-stacked thin film devices, and enable the host/donor substrate to be reused multiple times as a host/donor substrate for subsequent device fabrication to yield significant cost-savings to device fabrication. During investigations leading to the invention, high performance thin film devices, including resistors, diodes, and transistors that incorporate monocrystalline doped Si membranes, were intactly delaminated from fabrication host/donor substrate s of over 4 inches (about 10 cm) in size and then printed on a variety of diverse substrates. This aspect enables a wide range of applications in the construction of many electronic devices, such as optoelectronics (including plasmonic devices), integrated circuits, and biosensors, on a variety of desirable substrates and surfaces. Other devices of particular interest include thin film batteries, though it should be understood that the processes are more generally applicable to a wide range of thin film devices, such as optoelectronics (including plasmonic devices), integrated circuits, and biosensors, and their transfer to a variety of different substrates and surfaces.

[0025] FIG. 1 shows a schematic illustration of an interfacial delamination process that utilizes a microbubble-assisted interfacial debonding mechanism. In the nonlimiting example shown, a thin polyimide film (PI, e.g., about 1 to about 2 μm thick) has been spin-coated on an electrically-conductive (e.g., metal or doped silicon) separation layer (e.g., about 50 nm thick gold (Au) layer) on a substrate (silicon (Si) wafer) as a flexible support and dielectric layer for a thin film device that has been fabricated on the PI film, for example, using standard semiconductor micro/nano-fabrication processes. The entire multilayer structure has been completely encapsulated with polymethyl methacrylate (PMMA, e.g., about 1 μm thick) to avoid any potential degradation of the device during the subsequent electrochemical reaction process. The multilayer structure is represented in FIG. 1 as having been entirely immersed in an electrolyte solution, in this nonlimiting case either a sodium chloride (NaCl) or sodium hydroxide (NaOH) electrolyte solution. Prior to immersion, an edge of the substrate has been trimmed to expose the multilayer structure in order to provide direct contact between the electrolyte solution and the interface between the PI film and the electrically-conductive separation layer. FIG. 1 depicts a platinum (Pt) plate as also immersed in the electrolyte solution, and a voltage has been applied to the Pt plate (anode) and separation layer (cathode) to produce the following electrochemical reactions:

[00001]$\begin{array}{cc}4H_{2}O+4e^{-}=2H_2\left(\mathrm{microbubbles}\right)+4{\mathrm{OH}}^{-}& \left(\mathrm{cathode}\right)\\ 2H_{2}O-4e^{-}=O_2+4H^{+}& \left(\mathrm{anode}\right)\end{array}$

[0026] A more detailed side view schematically illustrated in FIG. 2 depicts microscale bubbles (H.sub.2) generated at the separation layer (cathode), which produce a mild buoyancy force that is believed to overcome interfacial adhesion between the PI film and the separation layer and facilitate their complete interfacial separation at wafer-scale without the thin film device carried by the PI film suffering from any damage, cracks, etc.

[0027] As a nonlimiting example, a pre-prepared specimen was fabricated to contain a thin film device on a 2 μm-thick PI film applied to an Au-coated 4-inch silicon (Au/Si) wafer and encapsulated by 1 μm-thick PMMA. The specimen was immersed in an aqueous NaCl electrolyte solution along with a Pt anode, and a positive potential (about 6V) was applied to the Au layer. FIGS. 3, 4, and 5 show a series of optical images of the specimen during the delamination process. As a result, the thin film device delaminated from the Au/Si wafer and floated to the surface of the electrolyte solution, where it was possible to remove the device and transfer it to another substrate or surface. The donor Au/Si wafer remained intact and reusable for another fabrication process. The investigation evidenced the ability to eliminate the need of any mechanical peeling tools or equipment, such as 90-degree mechanical peeling tools that are commonly used in conventional interfacial debonding methods.

[0028] The debonding mechanism represented in FIGS. 1 and 2 can be controlled by controlling the applied voltage and selecting the molar concentration with the electrolyte solution to promote the ability to successfully achieve defect-free delaminations. FIGS. 6 and 7 show delamination time as a function of NaCl concentration using a testbed specimen (2×2 cm.sup.2) of 2 μm thick-PI film on a donor Au/Si wafer. The results indicated that the delamination process was accelerated with increasing concentrations of the NaCl solution until the electrochemical reaction became supersaturated (in turn, the delamination time is saturated) when the NaCl molar concentration becomes greater than 2M. FIGS. 6 and 7 also evidence that the average delamination rate increased as the applied voltage was increased from 5V to 10V while maintaining a constant concentration of the NaCl electrolyte solution. It was noted that, based on delamination times, applied voltage appeared to be relatively less influential than the electrolyte concentration. Depending on the construction and materials used to fabricate a particular electronic device, voltages of up to about 10 volts, preferably in a range of about 5 to about 10 volts, could foreseeably be used.

[0029] As an alternative to the delamination process described above and depicted in FIGS. 1 and 2, it is foreseeable that delamination of a thin film device from a fabrication (donor or host) substrate, for example, as represented in FIGS. 1 and 2, could be achieved with the interfacial debonding technique described in U.S. Pat. No. 9,337,169 to Lee et al., whose contents are incorporated herein by reference. In this case, the thin film device represented in FIGS. 1 and 3 is delaminated from the substrate by delaminating the support layer from the barrier layer in the presence of water at room temperature using a fluid-assisted interfacial debonding technique that generates electrochemical reactions at the interface between the support layer of device and the separation and barrier layers of the substrate on which the device was fabricated. As with the process depicted in FIGS. 1 and 2, the electrically-conductive separation layer remains adhered to the substrate.

[0030] Further investigations resulted in various other specimen devices being successfully delaminated, floated on the surface of water, and transferred on diverse non-conventional substrates, including fabric, a leaf, and an artificial hand. The devices were ultra-thin and sufficiently flexible to deform over a human hair. FIGS. 8, 9, and 10 show the measured current-voltage (I-V) curves of a representative resistor, diode, and transistor embedded in some of specimen devices. These results confirmed that no significant degradations occurred in the electronic performances of the circuit components after the delamination process.

[0031] As further examples, FIGS. 11 and 12 contain graphs relating to electrophysiological sensing electrodes that were delaminated and applied to elastic substrates. These devices contained thin layers of PI film (about 1.5 μm) and Au (about 100 nm) patterned to form filamentary serpentine meshes that served as measurement, ground and reference electrodes and connecting leads. The devices were initially fabricated on a donor Au/Si wafer, and then delaminated by using the delamination process described herein. The electrodes were coupled to the skin of a human volunteer to measure electrocardiogram (ECG) and electromyogram (EMG) signals from the chest and forearm areas of the volunteer, respectively. The resulting ECG data (FIG. 11) and EMG data (FIG. 12) obtained from the devices (lefthand graphs in FIGS. 11 and 12) were qualitatively comparable to those recorded with commercial ECG and EMG electrodes (righthand graphs in FIGS. 11 and 12).

[0032] FIG. 13 shows a schematic representation of another interfacial delamination process that involves a microbubble-assisted interfacial debonding mechanism in accordance with another nonlimiting aspect of the invention. In the example shown, a barrier layer 14 has been formed on an electrically-conductive (e.g., metal or doped silicon) separation layer 12 deposited on a substrate 10 (e.g., a semiconductor wafer or glass substrate), and a thin film battery 16 has been fabricated in any manner suitable for the intended construction and application for the battery 16. The separation layer 12 is preferably formed of a ductile metal, for example, a single metal or metal alloy, including nickel, copper, aluminum, gold, or another metal or metal alloy having a percentage elongation at break of at least about 8%. The barrier layer 14 is a pinhole-free layer, as nonlimiting examples, a layer of aluminum oxide, hafnium oxide, silicon nitride, or silicon dioxide that has been deposited on top of the separation layer 12 by atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), or an equivalent process capable of depositing a pinhole-free layer on the separation layer 12. The battery 16 is schematically represented as comprising multiple layers, one of which preferably serves as a flexible dielectric support layer 18 that initially overlies and contacts the barrier layer 14. A nonlimiting example of a suitable support layer 18 is polyethylene terephthalate (PET). The entire battery structure may be completely encapsulated with a removable polymer (not shown), a nonlimiting example being polymethyl methacrylate (PMMA, e.g., about 1 μm thick), to avoid any potential degradation of the battery during the subsequent delamination process.

[0033] The battery 16 and its support structure (substrate 10, separation layer 12, and barrier layer 14) are represented in FIG. 13 as having been entirely immersed in an electrolyte solution, in this case a sodium hydroxide (NaOH) electrolyte solution, though the use of sodium chloride (NaCl) and other electrolyte solutions is foreseeable. Prior to immersion, an edge of the substrate 10 may be trimmed to expose at least the support layer 18 of the battery 16 and the separation and barrier layers 12 and 14 on the substrate 10 in order to provide direct contact between the electrolyte solution and the interface between the support layer 18 and the barrier layer 14. An anode 20 is also represented as being immersed in the electrolyte solution, after which a voltage is applied to the anode 20 and separation layer (cathode) 12 to produce the following electrochemical reactions:

[00002]$\begin{array}{cc}4H_{2}O+4e^{-}=2H_2\left(\mathrm{microbubbles}\right)+4{\mathrm{OH}}^{-}& \left(\mathrm{cathode}\right)\\ 2H_{2}O-4e^{-}=O_2+4H^{+}& \left(\mathrm{anode}\right)\end{array}$

[0034] FIG. 13 depicts microscale hydrogen gas (H.sub.2) bubbles generated at the separation layer (cathode) 12, which produce a mild buoyancy force that is believed to overcome interfacial adhesion between the support layer 18 and barrier layer 14 and facilitate their complete interfacial separation at wafer-scale without the battery 16 carried by the support layer 18 suffering from any damage, cracks, etc. As such, the delamination process serves to delaminate the thin film battery 16 from its fabrication (donor or host) substrate 10 in a defect-free manner, and allows the substrate 10 to be reused in subsequent manufacturing cycles. Following delamination, the thin-film battery 16 may be bonded to nearly any kind of receiver substrate, including but not limited to a flexible polymeric substrate, enabling the target surface of the receiver substrate to serve as a desired power source.

[0035] The physical delamination of the battery 16 from the substrate 10 and its separation and barrier layers 12 and 14 can be performed at room temperature, and is fundamentally driven by the physical and chemical separation of atoms and molecules at the barrier-support layer interface in a manipulated environment, wherein the nucleation location and propagation direction of the debonding process can be controllably triggered and mediated. The debonding mechanism can be controlled in part by controlling the applied voltage and selecting the molar concentration with the electrolyte solution to promote the ability to successfully achieve defect-free delaminations. As noted above in reference to FIGS. 6 and 7, investigations performed with other thin film devices indicate that the delamination time of the battery 16 is a function of the electrolyte concentration, wherein delamination is accelerated with increasing concentration until the electrochemical reaction becomes supersaturated (in turn, the delamination time is saturated), and the delamination rate also increases as the applied voltage increases, though to a less pronounced extent.

[0036] Conventional fabrication processes for high performance thin film batteries and other thin film devices often require high-temperature processes or deposition techniques. Particularly at high temperatures, for example about 550° C. and higher, such processes and deposition techniques could deform or change the crystallinity of the separation layer 12, leading to an increased interfacial adhesion between the separation layer 12 and the thin film battery 16. As a result, the battery 16 might not cleanly delaminate from the separation layer 12. As a solution, the pin-hole free barrier layer 14 is preferably included in the layer stack on the substrate 10, and in particular is deposited on top of the separation layer 12 by atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), or an equivalent. As used herein, “pin-hole free” refers to the barrier layer 14 having through-thickness porosity having a maximum cross-sectional dimension of not greater than 10 nm. To avoid recrystallization or physical deformation of the separation layer 12, the barrier layer 14 is preferably at least about 3 nm thick, for example, about 5 to about 10 nm thick. This aspect is especially desirable when the required product quality (device performance) is high, in which case high temperature processes are required for the thin film devices.

[0037] As an alternative to the delamination process described above and depicted in FIG. 13, it is foreseeable that delamination of a thin film battery (or other device) from a fabrication (donor or host) substrate, for example, as represented in FIG. 13, could be achieved with the interfacial debonding technique described in U.S. Pat. No. 9,337,169 to Lee et al., whose contents are incorporated herein by reference. In this case, the thin film battery 16 represented in FIG. 13 is delaminated from the substrate 10 by delaminating the support layer 18 from the barrier layer 14 in the presence of water at room temperature using a fluid-assisted interfacial debonding technique that generates electrochemical reactions at the interface between the support layer 18 of the battery 16 (or other device) and the separation and barrier layers 12 and 14 of the substrate 10 on which the battery 16 was fabricated. As with the process depicted in FIG. 13, the electrically-conductive separation layer 12 remains adhered to the substrate 10.

[0038] The delamination processes described above provide simple, low-cost, versatile and scalable transfer printing methods by using water or an electrolyte solution at room temperature, and therefore at lower temperatures that occur during existing debonding techniques, such as those that exploit laser-assisted liftoff, thermal mechanical peeling, controlled spalling, electrochemical delamination, and ultrasonication-induced microbubbles.

[0039] While the invention has been described in terms of particular embodiments and investigations, it should be apparent that alternatives could be adopted by one skilled in the art. For example, devices produced by the processes could differ in appearance and construction from the embodiments described herein and shown in the drawings, process parameters could be modified, and appropriate materials could be substituted for those noted. As such, it should be understood that the above detailed description is intended to describe the particular embodiments represented in the drawings and certain but not necessarily all features and aspects thereof, and to identify certain but not necessarily all alternatives to the represented embodiments and their described features and aspects. As a nonlimiting example, the invention encompasses additional or alternative embodiments in which one or more features or aspects of a particular embodiment could be eliminated, or two or more features or aspects of different embodiments could be combined. Accordingly, it should be understood that the invention is not necessarily limited to any embodiment described herein or illustrated in the drawings, and the phraseology and terminology employed above are for the purpose of describing the illustrated embodiments and investigations and do not necessarily serve as limitations to the scope of the invention. Therefore, the scope of the invention is to be limited only by the following claims.