CONTACT LENS, METHOD FOR DETECTING A STRUCTURE-BORNE SOUND WITH THE AID OF A CONTACT LENS, METHOD FOR PRODUCING A CONTACT LENS

Abstract

A contact lens. The contact lens comprises an acceleration sensor for detecting a structure-borne sound produced by a wearer of the contact lens.

Claims

1. A contact lens, comprising: an acceleration sensor configured to detect a structure-borne sound produced by a wearer of the contact lens.

2. The contact lens as recited in claim 1, wherein the acceleration sensor is situated in an interior of the contact lens in such a way that the acceleration sensor is completely enclosed by one or multiple layers of the contact lens.

3. The contact lens as recited in claim 1, wherein the acceleration sensor has a total thickness of less than 300 pm.

4. The contact lens as recited in claim 1, wherein the acceleration sensor is situated in a cavity formed using a MEMS chip and/or an ASIC chip, the cavity being hermetically sealed with the aid of a bonding frame.

5. The contact lens as recited in claim 4, wherein the MEMS chip and/or the ASIC chip has at least one via, the at least one via being a through silicon via, the acceleration sensor is in the form of a chip scale package.

6. The contact lens as recited in claim 1, wherein the acceleration sensor has a 3 dB bandwidth of at least 2 kHz for detecting the structure-borne sound.

7. The contact lens are cited in claim 1, wherein the acceleration sensor has a 3 dB bandwidth of at least 2.5 kHz for detecting the structure-borne sound.

8. The contact lens as recited in claim 1, wherein the acceleration sensor is configured to output a structure-borne sound signal as a function of the structure-borne sound (200) detected by the acceleration sensor, a low-pass filter and/or a band-pass filter being provided for outputting and/or further processing of the structure-borne sound signal, the band-pass filter having a 3 dB frequency limit between and including 2 kHz and 2.5 kHz and/or the band-pass filter having a lower 3 dB frequency limit of less than or equal to 60 Hz and an upper 3 dB frequency limit of at least 2 kHz.

9. The contact lens as recited in claim 1, wherein the acceleration sensor is further configured to detect low-frequency accelerations, the low frequency accelerations being below 60 Hz, the acceleration sensor being configured to output an acceleration signal as a function of the detected low-frequency accelerations, a low-pass filter having a 3 dB frequency limit of less than or equal to 60 Hz, being provided for outputting and/or further processing of the acceleration signal.

10. The contact lens as recited in claim 1, wherein the acceleration sensor is further configured to detect low-frequency accelerations, the low frequency accelerations being below 20 Hz, the acceleration sensor being configured to output an acceleration signal as a function of the detected low-frequency accelerations, a low-pass filter having a 3 dB frequency limit of less than or equal to 20 Hz, being provided for outputting and/or further processing of the acceleration signal.

11. The contact lens as recited in claim 4, wherein: (i) the contact lens includes an energy supply device configured to supply the acceleration sensor, and/or (ii) the contact lens includes a communications circuit having a signal transmission interface and/or a signal reception interface, the communications circuit being part of the ASIC chip or being a component developed separately from the ASIC chip.

12. A method for detecting a structure-borne sound using a contact lens, the contact lens including an acceleration sensor configured to detect a structure-borne sound produced by a wearer of the contact lens, the method comprising: detecting, by the acceleration sensor, the structure-borne sound produced by the wearer of the contact lens.

13. A method for producing a contact lens, the method comprising: integrating an acceleration sensor into a contact lens.

14. The method as recited in claim 13, wherein the acceleration sensor is produced with the aid of a bonding step, a MEMS chip and an ASIC chip being connected to each other in the bonding step, the bonding step being in performed before the acceleration sensor is integrated into the contact lens.

15. The method as recited in claim 14, wherein the MEMS chip and the ASIC chip are connected to each other using eutectic bonding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIGS. 1a and 1b show schematic illustrations of a human head.

[0032] FIG. 2 shows a schematic illustration of a contact lens according to a specific embodiment of the present invention.

[0033] FIG. 3 shows schematically a transfer function of an acceleration sensor of a contact lens according to an exemplary embodiment of the present invention.

[0034] FIG. 4 shows a schematic illustration of an acceleration sensor for a contact lens according to a specific embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0035] In the various figures, identical parts are always provided with the same reference symbols and are therefore normally labeled or mentioned only once.

[0036] FIG. 1a schematically shows a human head, in which acoustic sound waves are produced while speaking. As shown schematically in FIG. 1b, a structure-borne sound 200 (or structure-borne sound waves 200) arise in the head 201 when speaking, which reaches, inter alia, also the region around the human eye.

[0037] FIG. 2 is a schematic illustration of a contact lens 4 according to one specific embodiment of the present invention in a top view. Multiple electronic components are arranged around the central lens area 5 in the outer area of contact lens 4, that is, outside of the visual range, in particular an acceleration sensor 1 for structure-borne sound detection, a communication circuit 2 (for example a communications chip) for transmitting/receiving data, which may be connected, in particular wirelessly, to devices outside of contact lens 4, as well as an energy supply device 3, for example a miniature battery, which may possibly also be rechargeable. Between all of the electronic components 1, 2, 3, electrical connections are preferably developed, which are not shown in FIG. 2 for the sake of clarity. Energy supply device 3 supplies acceleration sensor 1 and communications circuit 2 with voltage and current. Signals between acceleration sensor 1 and communications circuit 2 may be transmitted via a bidirectional data protocol (for example I.sup.2C, I.sup.3C, SPI). A signal processing of the raw data of acceleration sensor 1 may be performed in acceleration sensor 1 itself and/or in communications circuit 2. For this purpose, acceleration sensor 1 and/or communications circuit 2 may contain a microcontroller for signal processing. Via one or multiple wireless interfaces (for example Bluetooth), communications circuit 2 communicates with external devices such as smart phones, wearables and/or IoT (Internet of Things) devices, for example. As an alternative to the represented embodiment, it is also possible that communications circuit 2 is integrated in acceleration sensor 1. This presents special challenges for miniaturization, however, for due to the ring-shaped geometry (viewed from the top) and the outwardly increasing flatness (in the cross section) of the contact lens geometry, it is problematic to integrate chips into the contact lens whose edge length in the radial direction exceeds 1 mm, whose edge length in the tangential direction exceeds 2 mm and whose overall height exceeds a few 100 μm.

[0038] Acceleration sensor 1 has at least the function of a structure-borne sound sensor, that is, it is not merely an inertial sensor, which exclusively aims for low-frequency signals (slow movements of the eyes or head). In order for this to function reliably with all frequencies that can be produced by the human voice, acceleration sensor 1 preferably has a bandwidth f.sub.3dB of at least 2 kHz, preferably 2.5 kHz, and for frequencies below this frequency limit it has a maximally flat transfer function so as to be able to reproduce a sound of the voice that is as natural and unaltered as possible.

[0039] FIG. 3 schematically shows a corresponding transfer function 300 (that is, the level of the electrical output signal S as a function of the voice frequency f) of an acceleration sensor 1 of a contact lens 4 according to an exemplary embodiment of the present invention. The 3 dB frequency limit is in this case 2.5 kHz. Such a flat transfer function of acceleration sensor 1 may be ensured for example via a mechanical transfer function of the micromechanical sensor element that is flat within the bandwidth combined with a simple low-pass filter in the evaluation ASIC. For such a form of implementation, acceleration sensor 1 may have for example a sufficiently high resonant frequency (f.sub.res>>f.sub.3dB) and/or may be damped relatively highly (Lehr's damping factor ˜0.7) in that the sensor cavity of acceleration sensor 1 is filled with a gas of suitable viscosity.

[0040] Alternatively, such a flat total transfer function of acceleration sensor 1 may also be achieved via a resonant frequency of the sensor, which is for example only a factor 2 to 3 above the frequency limit f.sub.3dB, combined with a markedly sub-critical damping (for example D˜0.1). In this case, however, the ASIC must compensate again for the frequency sensitivity of the mechanical transfer function via suitable electronic filters. This configuration is particularly favorable with regard to the achievable noise level, since otherwise either the electronic noise in the case of an excessively high resonant frequency or the Brownian noise in the case of excessively high damping (due to the statistical movement of the seismic mass of the sensor as a result of molecular collisions) may become too great. Both noise terms, electronic and Brownian noise, must be added quadratically for calculating the total noise power density. As soon as one of the terms becomes to great, the total noise is therefore too high.

[0041] The acceleration sensor 1 may be designed as a one-axis, two-axis or three-axis acceleration sensor, that is, it may be sensitive in one, two or three spatial directions. When using multi-axis sensors, the signals measured in the different axes may be added quadratically in order to generate an effective signal analogous to a microphone output signal. This signal processing may be performed for example either in the microcontroller of acceleration sensor 1 or of communications circuit 2 (or of communications chip 2).

[0042] For implementing configurations according to specific embodiments of the present invention in a contact lens 4, the miniaturization of the components 1, 2, 3 to be integrated in contact lens 4 is of great importance. In conventional acceleration sensors 1, the MEMS chip and the ASIC chip are frequently packaged in molded housings. An LGA2×2 molded housing, that is, a housing having lateral dimensions of 2×2 mm.sup.2 and overall heights between 0.6 and 1.0 mm is frequently used for this purpose. Such standard sensors, however, are clearly too large for integration in an intelligent contact lens 4.

[0043] According to one specific embodiment of the present invention, it is therefore particularly advantageously possible to omit an outer packaging of the MEMS chip and the ASIC chip. FIG. 4 shows a schematic illustration of an acceleration sensor 1 for a contact lens 4 according to a specific embodiment of the present invention.

[0044] Acceleration sensor 1 is formed by a wafer stack, comprising a MEMS wafer 10 and a CMOS or ASIC wafer 100. The MEMS wafer 10 is preferably produced using surface-micromechanical methods. A first insulating layer 22, preferably as an oxide layer, and a first functional layer 24, preferably as a polycrystalline silicon layer, are deposited and patterned on silicon substrate 20. A first fixed evaluation electrode 25 is optionally situated in first functional layer 24. Functional layer 24 is moreover used for the electrical redistribution within the MEMS chip. A second insulating layer 26, again preferably as an oxide layer, and above it at least one second, thicker functional layer 30, preferably of polycrystalline silicon, are situated above first functional layer 24. Functional layer 30 is patterned using a trench process (for example Deep Reactive Ion Etching, DRIE) in order to produce suspensions 34, a movable sensor mass 32, at least one spring 36 and, if indicated, fixed counter electrodes for an acceleration sensor 1 that is laterally movable, that is, parallel to plane of the chip.

[0045] CMOS wafer 100 comprises a silicon substrate 60, doping areas 62 for producing transistor circuits and the CMOS back end stack 64 made up of insulator layers and metal layers, which can be connected to one another by way of metallic vias. The MEMS and CMOS wafers 10, 100 are connected to each other mechanically and electrically using a metallic bonding method. Bonding layer 40 preferably may be produced using an eutectic bonding method, for example with aluminum on one wafer and germanium on the other wafer. On the one hand, a circumferential bonding frame 42 may be situated in bonding layer 40, which encloses cavity 110 formed by the mutually facing sides of the MEMS and ASIC wafers 10, 100. On the other hand, electrical contacts 44 between the MEMS and ASIC wafers 10, 100 may also be produced via the metallic bonding layer. Optionally, a further fixed evaluation electrode 66 for detecting movements perpendicular to the chip plane is situated in the uppermost metallization layer of the ASIC. The arrows in FIG. 4 indicate that the sensor may be movable laterally and/or vertically, that is, it can detect accelerations in the corresponding directions. In particular, there may be a single movable sensor mass, which is deflectable in multiple directions (xy, xz oder xyz) on the basis of suitable spring geometries. Such a configuration is particularly advantageous for the application since Brownian noise is reduced due to the in this case particularly great common sensor mass (Brownian noise scales with 1/root(mass)).

[0046] In the exemplary embodiment of FIG. 4, furthermore, through silicon vias (TSVs) 80 and on the back side of the ASIC a redistribution layer (RDL) 94, and external pads 90 for contacting the sensor are situated in CMOS wafer 100 for the input/output signals of the ASIC. Redistribution layer 94 is electrically separated from ASIC substrate 60 by one or multiple passivation layers 92.

[0047] For the integration into contact lens 4, it is advantageous that the overall height of acceleration sensor 1 is very small. In a particularly advantageous manner, the wafer stack made up of MEMS wafer 10 and ASIC wafer 100 is highly thinned by grinding and CMP processes in order to produce overall heights in the order of magnitude of 150 to 400 μm. For this purpose, both wafers 10, 100 are preferably highly back-thinned. ASIC wafer 100 is preferably ground back to a lesser thickness than MEMS wafer 10 in order to render the TSV process particularly simple and cost-effective.

[0048] According to alternative specific embodiments of the present invention, other designs of an acceleration sensor than the one illustrated in FIG. 4 are possible as well, for example different wafer stacks, different external contacting, different MEMS process, etc.

[0049] According to the present invention, acceleration sensor 1 preferably may be used as a structure-borne sound sensor in the frequency range of approximately 60-2500 Hz and thus as a microphone substitute. Furthermore, it is also possible, however, to measure low-frequency signals of the acceleration sensor 1 and thus to implement, in addition to its basic function of voice detection/voice transmission, further functions (for example the detection of eye blinking, orientation of the eyes, inclination of the head), and thus to make possible further applications for the intelligent contact lens via an acceleration sensor 1.