Source: http://patents.com/us-10189699.html
Timestamp: 2019-02-23 04:54:42
Document Index: 451040763

Matched Legal Cases: ['art 110', 'art 110', 'art 110', 'art 110', 'arts 110', 'art 110', 'art 102']

US Patent # 1,018,9699. MEMS device and MEMS vacuum microphone - Patents.com
United States Patent 10,189,699
Walther , et al. January 29, 2019
Family ID: 1000003785741
15/819,767
US 20180099867 A1 Apr 12, 2018
15066741 Mar 10, 2016 9828237
Current CPC Class: B81B 3/0086 (20130101); H04R 19/005 (20130101); H04R 19/04 (20130101); H04R 2201/003 (20130101); B81B 2203/0127 (20130101); H04R 31/006 (20130101); B81B 2201/0257 (20130101)
Current International Class: B81B 3/00 (20060101); H04R 19/00 (20060101); H04R 19/04 (20060101); H04R 31/00 (20060101)
2015/0078592 March 2015 Uchida
This application is a continuation of U.S. patent application Ser. No. 15/066,741, entitled "MEMS Device and MEMS Vacuum Microphone," filed on Mar. 10, 2016, which application is hereby incorporated herein by reference in its entirety.
1. A method of reading out a MEMS device, the MEMS device comprising first membrane element, a second membrane element spaced apart from the first membrane element, a low pressure region between the first and second membrane elements, the low pressure region having a pressure less than an ambient pressure, and a counter electrode structure comprising a first conducting layer, which is at least partially arranged in the low pressure region or extends in the low pressure region, wherein the first conducting layer comprises a segmentation providing an electrical isolation between a first portion of the first conducting layer and a second portion of the first conducting layer, the method comprising: providing a signal generated by a deflection of the first membrane element and a deflection of the second membrane element.
2. The method according to claim 1, further comprising: biasing the first portion of the first conducting layer of the counter electrode structure with a first voltage, and reading-out the signal.
3. The method according to claim 1, wherein the counter electrode structure comprises the first conducting layer and, further, a second conducting layer, wherein the second conducting layer comprises a further segmentation providing an electrical isolation between a first portion of the second conducting layer and a second portion of the second conducting layer, the method further comprising: biasing the first portion of the first conducting layer with a first voltage, biasing the first portion of the second conducting layer with a second voltage, and reading-out the signal.
4. The method according to claim 3, wherein the first portion of the first conducting layer and the first portion of the second conducting layer are not electrically connected, and wherein the first voltage and the second voltage are different.
5. The method according to claim 3, wherein the second portion of the first conducting layer is electrically connected to the first and second membrane element, and wherein the second portion of the second conducting layer is electrically connected to the first and second membrane element.
6. The method according to claim 1, further comprising: biasing the first membrane element and the second membrane element with a reference potential, and reading-out the signal.
7. The method according to claim 1, further comprising: biasing the first membrane element with a first voltage, biasing the second membrane element with a second reference potential, and reading-out the signal.
8. A method of reading out a MEMS device, the MEMS device comprising a first membrane element, a second membrane element spaced apart from the first membrane element, a low pressure region between the first and second membrane elements, the low pressure region having a pressure less than an ambient pressure, and a counter electrode structure comprising a first conducting layer which is at least partially arranged in the low pressure region or extends in the low pressure region, wherein the first membrane element comprises a segmentation providing an electrical isolation between a first portion of the first membrane element and a second portion of the first membrane element, and wherein the second membrane element comprises a further segmentation comprising an electrical isolation between a first portion of the second membrane element and a second portion of the second membrane element, the method comprising: providing a signal generated by a deflection of the first membrane element and a deflection of the second membrane element.
9. The method according to claim 8, further comprising: biasing the first conducting layer of the counter electrode structure with a reference voltage, and reading-out the signal.
10. The method according to claim 8, wherein the second portion of the first membrane element and the second portion of the second membrane element are electrically connected to the first conducting layer of the counter electrode structure.
11. The method according to claim 8, wherein the MEMS device further comprises a second conducting layer, the method further comprising: biasing the first conducting layer with a first voltage, biasing the second conducting layer with a second voltage, and reading-out the signal.
12. The method according to claim 11, wherein the first portion of the first membrane element and the first portion of the second membrane element are not electrically connected, and wherein the first voltage and second voltage are different.
13. The method according to claim 11, wherein the second portion of the first membrane element and the second portion of the second membrane element are electrically connected to the first and second conducting layer of the counter electrode structure.
.times..times. ##EQU00001## wherein C.sub.o is the useful capacitance and C.sub.p is the parasitic capacitance of the microphone. Thus, given a useful capacitance C.sub.o, a reduced parasitic capacitance C.sub.p results in reduced factor k and, thus, in an increased SNR of the transducer output signal.
As it is also shown in FIG. 1a, the first membrane element 102 comprises a displaceable (movable) portion iota and a fixed portion 102b, and wherein the second membrane element 104 comprises a displaceable or movable portion 104a and a fixed portion 104b. The fixed portion 102b of the first membrane element 102 is, for example, mechanically connected to the first spacer element 113, wherein the fixed portion 104b of the second membrane element 104 is mechanically connected (attached) to the second spacer 114. Moreover, the counter electrode structure 108 is, for example, fixed (sandwiched) between the first and second spacer elements 113, 114. Thus, the first portion 110a of the conductive layer 110 is arranged between the displaceable portion iota of the first membrane element 102 and the displaceable portion 104a of the second membrane element 104.
Thus, the first portion 110a of the conductive layer 110 is a middle or center portion of the conductive layer, wherein the second portion 110b of the conductive layer 110 is a fringe or edge portion of the conductive layer 110. Thus, the middle or central portion 110a may be regarded as the "electrically active" portion of the conductive layer 110 and contributes to the useful capacitance Co and, thus, to the useful signal component of the sensor output signal.
Thus, variable active capacitances CA and CB, which form in combination the useful capacitance Co, are respectively formed. The variable active capacitance CA is formed between the displaceable portion iota of the first membrane element 102 and the counter electrode structure 108 (i.e. the first portion 110a of the conductive layer 110), wherein the variable active capacitances CB is formed between the displaceable portion 104a of the second membrane element 104 and the counter electrode structure 108 (i.e. the first portion 110a of the conductive layer 110).
FIG. 2d shows a configuration where isolation layer 116 covers (at least in the area adjacent to the segmentation 112) the conductive layer 110, i.e. the first and second portions 110a, 110b, wherein the gap 112 between the first and second portions 1101a, 110b of the conductive layer 110 is free of any isolating material (i.e. does not comprise any isolating material) of the isolation layer 116.
As shown in FIG. 4a, the counter electrode structure 108 comprises the (first) conductive layer 110 and a further (a second) conductive layer 210, wherein the second conductive layer 210 is electrically isolated from the first conductive layer 110. A further segmentation 212 provides an electrical isolation between a first portion 210a of the second conductive layer 210 and a second portion 21ob of the second conductive layer 210. Furthermore, an insulating layer 202 may be arranged between the first and second conductive layers 110, 210 of the counter electrode structure 108 for providing an insulation and separation of the further portions 110a, 210a of the first and second conductive layers 110, 210.
As it is also shown in FIG. 4a, the first membrane element 102 comprises a displaceable (movable) portion 102a and a fixed portion 102b, and wherein the second membrane element 104 comprises a displaceable or movable portion 104a and a fixed portion 104b. The fixed portion 102b of the first membrane element 102 is, for example, mechanically connected to the first spacer element 113, wherein the fixed portion 104b of the second membrane element 104 is mechanically connected (attached) to the second spacer 114. Moreover, the counter electrode structure 108 is, for example, fixed (sandwiched) between the first and second spacer elements 113, 114. Thus, the first portion 110a of the first conductive layer 110 is arranged between the displaceable portion iota of the first membrane element 102 and the displaceable portion 104a of the second membrane element 104.
Thus, the first portion 110a of the first conductive layer 110 is a center or middle portion of the conductive layer, wherein the second portion 110b of the first conductive layer 110 is a fringe portion of the conductive layer 110. Thus, the center portion 110a may be regarded as the "electrically active" portion of the first conductive layer 110 and contributes to the useful capacitance Co and, thus, to the useful signal component of the sensor output signal. Furthermore, the first portion 210a of the second conductive layer 110 is a center or middle portion of the second conductive layer 210, wherein the second portion 210b of the second conductive layer 210 is a fringe portion of the second conductive layer 210. Thus, the middle portion 210a may be regarded as the "electrically active" portion of the conductive layer 210 and contributes to the useful capacitance Co and, thus, to the useful signal component of the sensor output signal.
Thus, variable active capacitances CA and CB, which form in combination the useful capacitance Co, are respectively formed. The variable active capacitance CA is formed between the displaceable portion 102a of the first membrane element 102 and the counter electrode structure 108 (i.e. the first portion 110a of the first conductive layer 110), wherein the variable active capacitances CB is formed between the displaceable portion 104a of the second membrane element 104 and the counter electrode structure 108 (i.e. the first portion 210a of the second conductive layer 210).
As optionally shown in FIG. 4a, the second portion 110b of the first conductive layer no may be electrically coupled by means of a first connection element 118 to the first membrane element 102, wherein the second portion 210b of the second conductive layer 210 may be electrically coupled by means of a second connection element 120 to the second membrane element 104. The first and second membrane elements 102, 104 may be mechanically coupled. Further, the first and second membrane elements 102, 104 may also be electrically coupled or may be electrically decoupled (insulated).
In case of the MEMS device 100 of FIGS. 4a-b, the first and second membrane elements 102, 104 and the counter electrode structure 108 may have a rectangular shape, wherein also the segmentations 112, 212 in the form of the circumferential narrow gap/recess, i.e. the segmentation grooves 112, 212, may also comprise a rectangular shape. However, it should become clear that the first and second membrane elements 102, 104 and the counter electrode structure 108 may have a circular shape, wherein also the segmentation may be formed circularly. However, it should become clear that independent from the shape of the first and second membrane elements and/or the counter electrode structure 108, the circumferential narrow gap in the first conductive layer 110 and the second conductive layer 210 may have any appropriate (circular, rectangular, (nearly-closed) polygonal) circumferential shape. The (at least one) conductive layer 110 of the counter electrode structure 108 may be made of, or may comprise, an electrically conductive material, for example, poly-silicon or any metallization. By the provision of the segmentation of the counter electrode structure 108, the parasitic capacitances may be reduced greatly, since the separated and insulated second (inactive) portion 110b of the first conductive layer 110 and the second (inactive) portion 210b of the second conductive layer 210, which may be electrically connected to the first and second membrane elements, respectively, do not (or at least in a very reduced way) contribute to the creation of parasitic capacitances. Hence, the capacitance of the MEMS device 100 as a whole may comprise the active capacitance CA created between the displaceable portion iota of the first membrane element 102 and the counter electrode structure 108, i.e. the first portion 110a of the first conductive layer 110, as well as the further active capacitance CB between the displaceable portion 104a of the second membrane element 104 and the counter electrode structure 108, i.e. the first portion 210a of the second conductive layer 210.
In the following, the distance d.sub.1 describes the distance between (the adjacent edges of) the first narrow gap 112 and the first spacer element 113 (with respect to a vertical projection), the distance d.sub.2 describes the distance between (the adjacent edges of) the second narrow gap 212 and the second spacer element 114 (with respect to a vertical projection), wherein the distance d.sub.3 describes the distance between (the adjacent edges of) the first and second narrow gaps 112 and 212 (with respect to a vertical projection and assuming an essentially constant distance between the first and second narrow gaps). The distances are also shown in FIG. 5c below.
The following evaluations will further show that the specifically selected values for the distances d.sub.1, d.sub.2 and d.sub.3 will be made with respect to a tradeoff between the necessary robustness of the resulting counter electrode structure 108 and the resulting parasitic capacitances originating from the counter electrode structure 108. To be more specific, the greater and equal the chosen distances d.sub.1 and d.sub.2 are, the smaller are the resulting parasitic capacitances which originate from the first and second conductive layers 110, 210. However, in the same relation, if the distances d.sub.1 and d.sub.2 are increased, then the resulting useful capacitances CA, CB decrease due to the accordingly reduced (active) area of the displaceable portion 102a of the first membrane element 102 and of the displaceable portion 104a of the second membrane element 104. Moreover, the greater the distance d.sub.3 is between the first and second narrow gaps 112, 212, the greater is the resulting mechanical robustness of the counter electrode structure 108, however having asymmetric electrical properties of the first and second conductive layers 110, 210.
As shown in FIG. 5a, the segmentation is a gap 112, 212 through the first and second conductive layers 110, 210 and the insulating layer 202. Thus, the distance d.sub.3 between (the adjacent edges of) the first and second narrow gaps 112 and 212 is zero. As shown in FIG. 5a, the gap 112 is essentially not filled as only the thin (optional) insulating layer 116 covering the first main surface of the first conductive layer 110 and the surface of the gap 112. Moreover, a further (optional) insulating layer 216, which may comprise a nitride material, may be arranged on the main surface area of the second conductive layer 210. The thickness of the first and second optional insulating layers 116, 216 may be chosen for achieving a sufficient mechanical strength or robustness of the resulting counter electrode structure 108.
FIG. 5b shows a configuration wherein the first and second circumferential narrow gaps 112, 212 are laterally offset (by the distance d.sub.3) to each other. The first main surface area of the first conductive layer 110 and the circumferential narrow gap 112 may be covered with the optional insulating layer 116. Moreover, the second circumferential narrow gap 212 may extend to the second conductive layer 210 and at least partially into/through the isolating layer 202. In this configuration of FIG. 5b, the insulating layer 202 is partially interrupted. This structure of the second circumferential gap 212 with the partially interrupted insulating layer 202 can be achieved by etching the insulating layer 202 during the release etch of the cavity 106 in the substrate under the MEMs device, i.e. the vacuum MEMS microphone.
FIG. 5c schematically shows the resulting and remaining (most dominant) parasitic capacitances CP.sub.1-3 caused by the segmented first and second conductive layers 110, 210. Due to the segmentation of the first and second conductive layers 110, 210 and the electrical connection between the second portion 110b of the first conductive layer 110 to the first membrane element 102, and of the second portion 210b of the second conductive layer to the second membrane element 104, the resulting parasitic capacitances can be greatly reduced since the isolated (separated) portions 110b, 210b of the first and second conductive layers 110, 210 only marginally contribute to the creation of parasitic capacitances. The resulting reduced capacitances are CP.sub.1 between the first and second portions 110a, 110b of the first conductive layer, CP.sub.2 between the first and second portions 210a, 210b of the second conductive layer 210, and CP.sub.3 between the second conductive portion 110b of the first conductive layer 110 and the first portion 210a of the second conductive layer.
The distance d.sub.1 describes the distance between (the adjacent edges of) the first narrow gap 112 and the first spacer element 113 (with respect to a vertical projection), the distance d.sub.2 describes the distance between (the adjacent edges of) the second narrow gap 212 and the second spacer element 114 (with respect to a vertical projection), wherein the distance d.sub.3 describes the distance between (the adjacent edges of) the first and second narrow gaps 112 and 212 (with respect to a vertical projection and assuming an essentially constant distance between the first and second narrow gaps).
The parasitic capacitance CP.sub.3 is based on the shift (distance d.sub.3) between the first and second narrow gaps 112, 212. As an increased distance d.sub.3 provides for an increased mechanical robustness of the resulting counter electrode structure 108, the distance d.sub.3 should be chosen as small as possible to limit the parasitic capacitance CP.sub.3 between the second portion 110b of the first conductive layer and the first portion 210a of the second conductive layer as indicated in FIG. 5c.
In the following, an exemplary relationship between the distances d.sub.1, d.sub.2 and d.sub.3 and the resulting parasitic capacitances CP.sub.1, CP.sub.2 and CP.sub.3 is described. For example, the parasitic capacitance Cp.sub.1 is essentially proportional to the width and length of the narrow gap 112, the thickness of layer 110 and the dielectric coefficient of the material at the level of gap 112. The same applies for the parasitic capacitance Cp.sub.2. The parasitic capacitances Cp.sub.1 and Cp.sub.2 may be typically >0.1 pF. For example, the parasitic capacitance Cp.sub.3 is proportional to the distance d.sub.3, the length of segmentation line (so it depends on the size of the central part 110a in this way) and the dielectric coefficient of the material of the insulating layer 202. For example, for a 1 mm square counter electrode structure 108 and a distance d.sub.3 of 4 .mu.m, the parasitic capacitance Cp.sub.3 is in the order of 1 pF (versus a 5 to 10-times higher parasitic capacitance without segmentation).
As the resulting signal-to-noise ratio of the output signal of the MEMS device 100 depends on the following relation 1/(1+co/cp), it becomes clear that an increased useful capacitance Co and a reduced parasitic overall capacitance CP, which is based on a combination of CP.sub.1, CP.sub.2 and CP.sub.3, results in an increased signal-to-noise ratio SNR.
The thickness of the insulating layer 202, which may comprise an oxide material, between the first and second conductive layers 110 and 210 (i.e. between the two static electrodes 110, 210) is in the range of 0.3 .mu.m, and typically between 0.1 to 1 .mu.m, between 0.2 to 5 .mu.m, or between 0.25 to 0.35 .mu.m. The oxide material may be, for example, silicon dioxide SiO.sub.2.
The narrow gaps 112, 212 are (preferably) located outside the anchored area (i.e. the anchoring area of the first and second spacer elements 113, 114), wherein the distance (d.sub.1 or d.sub.2) between (adjacent edges of) the outer narrow gap and the associated anchoring area (i.e. the first spacer element with respect to the first conductive layer 110, and the second spacer element 114 with respect to the second conductive layer 210) can be in the typical range of 10 .mu.m, typically between 1 und 20 .mu.m, between 5 und 15 .mu.m, or between 8 und 12 .mu.m, but can also vary from 1 .mu.m to half of the radius of the respective membrane element 102, 104, for example.
In the following some typical dimensions of the narrow gaps 112, 212 are discussed with respect to the resulting influence on the remaining parasitic capacitances. The lateral dimensions of the narrow gaps 112, 212 are typically in the range between 0.1 and 10 .mu.m, between 1.0 and 8 .mu.m, or between 3 and 5 .mu.m. The lateral dimension of the narrow gaps describes the distance between the first and second portions 110a-110b, 210a-210b of the first and second conductive layers 110, 210. The lateral dimensions of the first and second narrow gaps are chosen sufficiently large enough in order to minimize the remaining parasitic capacitances CP.sub.1 or CP.sub.2. The first and second narrow gaps 112, 212 in the first and second conductive layers 110, 210 may be, with respect to a vertical projection to the counter electrode structure 108, laterally offset to each other, i.e. may be arranged in a non-overlapping configuration.
Such a non-overlapping configuration of the two narrow gaps 112, 212 enables to avoid any mechanical weak point of the resulting counter electrode structure 108. However, the lateral shift (distance d.sub.3) should be as minimal as possible in order to reduce the remaining parasitic capacitance CP.sub.3. Thus, a typical dimension for the distance d.sub.3 is in the range of a few micrometers. The two narrow gaps 112, 212 can be located, with respect to a vertical projection, inside the anchoring area, which is formed by the first and second spacer elements 113, 114. However, to reduce the resulting parasitic capacitances CP.sub.1, CP.sub.2 at least of one of the two narrow gaps 112, 212 should be located outside the anchoring area 115, 117.
In order to provide a balance between the remaining parasitic capacitance CP.sub.3 between the first and second conductive layers 110, 210, the distance d.sub.3 between the first and second narrow gap 112, 212 can be "inverted" as indicated below in FIG. 6b, for example.
To avoid any crossing of the first and second narrow gaps 112, 212 (with respect to a vertical projection), the inversion of shift (of the distance d.sub.3) can be done at the level of a hole in the respective electrode (the first or second conductive layer 110, 210) or at the border of the electrode (the first or second conductive layer 110, 210), for example where the respective electrode is anchored. In case of holes in the electrodes (first and/or second conductive layers 110, 210, for example for release purposes), the respective narrow gap 112, 212 (segmentation) should avoid these holes with a distance of typically or at least 0.5 .mu.m. The shape of segmentation line can be adapted to avoid the holes, e.g. by means of a sinusoidal form of the segmentation line (narrow gap).
As shown in FIG. 6c with respect to an enlarged partial view of the counter electrode structure 108, openings or holes 108a may be provided in at least one of the first and second conductive layers 110, 210. The holes 108a in the first and/or second conductive layers 110, 210 may be provided due to stress relief reasons, for example. In order to avoid an undesired decrease of the mechanical robustness of the resulting counter electrode structure 108, the first and second circumferential narrow gaps 112, 212 may have a course, e.g. a sinus-like course, to avoid connecting or intersecting the hole(s) 108a in the first and/or second conductive layers 110, 210 of the counter electrode structure 108. As shown in FIG. 6c, the first and second (vertically offset) circumferential narrow gaps 112, 212 are arranged as sinus-like segmentation lines. It should be noted that any further appropriate shape, e.g. zig-zag etc., of the respective segmentation lines can be chosen and adapted in that to avoid that the first and/or second circumferential narrow gap 112, 212 contacts or intersects at least of the plurality of the holes in the counter electrode structure 108. Thus, the distance d.sub.3 between the first and second narrow gap 112, 212 should be greater than the diameter of the holes 108a and smaller than the length L (which is the diameter of the holes 108a plus the distance between the holes 108a).
As shown in FIG. 7a, the first portion 110a of the first conductive layer 110 is connected with a potential V.sub.1 so that the first portion 110a is polarized with the voltage V.sub.1. The movable structure 102, 104, i.e. the first and second membrane elements 102, 104, are read out by a differential amplifier 306, wherein the first and second membrane elements 102, 104 are each connected to a different input connection of the differential amplifier 306, which provides the output signal SOUT. Thus, FIG. 7a provides a differential read out configuration for a vacuum MEMS microphone having one conductive layer.
With respect to a differential read out configuration of a vacuum MEMS microphone 100 having a single conductive layer 110 as the counter electrode structure 108, it should be noted that the (single) conductive layer 110, i.e. the counter electrode, is split in an outer part 110b and an inner part 110a, wherein the outer part 110b comprises two electrically isolated portions 110b-1, 110b-2. Thus, the electrically isolated outer parts 110b-1, 110b-2 of the single conductive layer are respectively electrically connected to one of the movable membrane elements 102, 104 to avoid a shorting of the two membrane elements 102, 104. By biasing the inner part 110a of the counter electrode no, the two membrane elements 102, 104 can be differentially read out.
In FIG. 7b the first and second membrane elements 102, 104 may be connected (e.g. grounded) by a membrane connection 302 to an electric reference potential VREF (e.g. ground potential). The first portion 110a of the first conductive layer may be electrically connected to a first connection 304 to a first power supply circuit 307 and also to a first input of an amplifier 306. The first power supply circuit 307 comprises a voltage source 308 (providing a first potential V.sub.1) and a resistor 310 having a very high resistance (several Giga-Ohms or higher). The amplifier 306 may be a differential amplifier. The first portion 210a of the second conductive layer 210 may be connected to a second connection 312 to a second power supply circuit 313 and a second input of the amplifier 306. The second power supply circuit 313 comprises a second voltage source 314 (providing a second potential V.sub.2) and a second resistor 316 that typically has about the same resistance as the first resistor 310. The first and second power supply circuits 307, 313 electrically bias the first portions 110a, 210a of the first and second conductive layers 110, 210, respectively, against the electric reference potential VREF (e.g. ground potential).
Thus, the movable part 102, 104 (i.e. the first and second membrane elements 102, 104) are polarized with a voltage V.sub.1, wherein a differential sensing/read out is conducted on the static electrode 108, i.e. the first portions 110a, 210a of the first and second conductive layers 110, 210.
FIG. 7d shows a schematic circuit diagram of a further illustrative read out configuration for the MEMS device 100. To be more specific, as shown in FIG. 7d, the first portion 110a of the first conductive layer is connected to a first potential V.sub.1, i.e. is polarized with a first voltage V.sub.1, wherein the first portion 210a of the second conductive layer 210 is connected to a second potential V.sub.2, so that the first portion 210a of the second conductive layer is polarized with the second voltage V.sub.2.
To summarize, the two electrodes (the first portions 110a, 210a of the first and second conductive layers 110, 210) of the static membrane (the counter electrode structure 108) are polarized with different voltages V.sub.1, V.sub.2, for example to opposite voltages with V.sub.2=-V.sub.1. Thus, the movable structure can be read out based on a single-ended amplifier configuration (single-ended read out).
With the exception of the specific segmentation of the counter electrode structure 108 of the MEMS device 1010 and 200 (as shown in FIGS. 1-7) and of the membrane elements 402, 404 of the MEMS device 400 (as shown in FIGS. 8a-b), the characteristics, dimensions and materials of the elements of the MEMS device 400 (of FIG. 8a-b) are comparable to the elements of MEMS device 100 or 200 (of FIGS. 1-7). To be more specific, in the figures and the specification identical elements and elements having the same functionality and/or the same technical or physical effect are usually provided with the same reference numbers and/or with the same name, so that the description of these elements and of the functionality thereof as illustrated in the different embodiments are mutually exchangeable or may be applied to one another in the different embodiments.
For the MEMS device 400 in FIG. 8b, the first and second membrane elements 402, 404 can be polarized, i.e. provided with a reference potential V, and can be electrically connected, wherein the first and second conductive layers 410, 411 (not electrically connected) can be differentially read out. Alternatively, for MEMS device 400 in FIG. 8b, the first and second conductive layers 410, 411 (not electrically connected) can be polarized differently, i.e. provided with different reference potentials V.sub.1, V.sub.2, wherein the first and second membrane elements 402, 404 (which can be electrically connected) can be single ended read out.
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