Comb tooth structure for MEMS accelerometer

Abstract

The present disclosure describes an accelerometer that includes stator comb teeth that are interleaved with rotor comb teeth such that a capacitor is formed. The tops of all rotor comb teeth are recessed from the top surface of the device layer in the z-direction by a first recess depth D1. The tops of some of the stator combs are recessed from the top surface of the device layer in the z-direction by a second recess depth D2 greater than D1.

Description

Technical Field

[0001] The present disclosure relates to MEMS accelerometers, and in particular to accelerometers in which a proof mass moves both in and out of the plane of the device. Background Art

[0002] A MEMS accelerometer may be equipped with a capacitor for measuring the movement of a proof mass.

[0003] Figure 1a A MEMS device is schematically shown having a single proof mass 11 in its rest position in the xy plane (defined by the device layers in which the proof mass is made) and a fixed structure 12 next to the proof mass. The fixed structure may be referred to as a stator. The proof mass comprises a set of comb-tooth electrodes (e.g., 111) on the proof mass, which are interleaved with corresponding comb-tooth electrodes (112) on the fixed structure 12. If the proof mass 11 and the fixed structure 12 are made of conductive or semiconductor material, they may together form a measuring capacitor and / or an actuating capacitor.

[0004] Figure 1a The comb arrangement shown allows any displacement of the proof mass 11 in the y direction relative to the fixed structure 12 to be detected as a change in capacitance. Alternatively, a voltage applied between the electrodes via a feedback loop may prevent displacement of the proof mass 11, and the magnitude of this voltage may be proportional to the acceleration experienced by the MEMS device.

[0005] It is also possible to implement two alternating and electrically separated sets of fixed comb teeth adjacent to the proof mass. A separate output signal can then be measured from each set. This has been done in Figure 1b It is shown in Figure 1b In the figure, fixed comb teeth 121 form one group, and fixed comb teeth 122 form another group (the fixed structure to which these comb teeth are attached is omitted in the figure). Comb teeth 121 form a first capacitor with the detection mass comb teeth 113, and comb teeth 122 form a second capacitor with the detection mass comb teeth 113.

[0006] Figure 1b The arrangement shown in facilitates differential capacitance measurements, which can greatly improve the accuracy of capacitance measurements. Figure 1a In the case of the capacitor shown in , the measured signal will show a nonlinear dependence on the displacement of the proof mass in the y direction. In contrast, if Figure 1bIf the first capacitor (113+121) in is designated as C1 and the second capacitor (113+122) is designated as C2, then when the proof mass 11 is displaced upward, C1 will increase, while C2 will decrease. When the proof mass is displaced downward, C1 decreases, while C2 increases. However, the differential signal C1–C2 will show an ideal, almost linear dependence on the displacement of the proof mass in the y direction. Figure 1b The differential arrangement shown in FIG. 1 also generally produces a ratio Figure 1a In some cases, it may also be less sensitive to mechanical stress because the comb-tooth electrodes on the fixed structure can be placed closer to each other.

[0007] In some applications, double differential measurements can be used to further improve accuracy. Figure 1c A MEMS device is shown having two proof masses 11 and 12 and four capacitors connected to these proof masses: 111+121 (with capacitance C1), 111+122 (with capacitance C2), 111+123 (with capacitance C3) and 111+124 (with capacitance C4). The double differential signal (C1-C2)+(C3-C4) will not only exhibit a linear dependence on the displacement in the y-direction, but will also automatically cancel (at least partially) the signal components caused by vibration disturbances that are not intended to be measured. Such disturbances may, for example, include a rotational motion that moves one mass in the positive y-direction and the other in the negative y-direction.

[0008] The level of thermal noise in the output signal depends on the size of the proof mass. When the proof mass is larger, the thermal noise is lower. Some accelerometers use a separate proof mass to measure acceleration in each direction. In other words, one proof mass responds to acceleration in the x-direction, another responds to acceleration in the y-direction, and another responds to acceleration in the z-direction. The motion of each proof mass is then measured separately. A common problem with this arrangement is that each proof mass must be very small due to area limitations, but a small proof mass results in high noise in the output signal for each measurement.

[0009] Some accelerometers contain a proof mass designed to respond to acceleration in the xy plane and also to acceleration in the z direction perpendicular to the xy plane. When a proof mass can detect motion in multiple directions, the proof mass can be made larger and thus reduce the noise in the output signal of each measurement. If multiple proof masses are used, they can be coupled with a coupling device that synchronizes their motion responses.

[0010] However, in such a measurement setup, proof mass motions in different directions must be distinguished from one another. One way of doing this is to build a separate measurement capacitor for each direction (e.g., x, y, and z). However, size and complexity can be significantly reduced if the same measurement capacitor can be used to measure motion in multiple directions (e.g., y and z). Such a capacitor must be carefully designed to ensure that the signal resulting from displacement in one direction (e.g., y) can be reliably distinguished from the signal resulting from displacement (possibly simultaneously) in the other direction it is designed to measure (in this case, z). Summary of the invention

[0011] An object of the present disclosure is to provide a measuring device that measures the displacement of a proof mass in two perpendicular directions with high accuracy.

[0012] The objects of the present disclosure are achieved by a device characterized by what is stated in the independent claim. Preferred embodiments are disclosed in the dependent claims. The measuring device is based on a specific pattern of recessed comb teeth. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the following, the present disclosure will be described in more detail by means of preferred embodiments with reference to the accompanying drawings, in which:

[0014] Figure 1a , Figure 1b and Figure 1c A MEMS device known in the prior art is shown.

[0015] Figure 2a , Figure 2b , Figure 2c and Figure 2d A MEMS device according to a first embodiment is shown.

[0016] Figure 3a to Figure 3b The comb tooth heights in both the first embodiment and the second embodiment are shown.

[0017] Figure 4 A MEMS device according to a second embodiment is shown. DETAILED DESCRIPTION

[0018] The present disclosure describes a micro-electromechanical accelerometer that includes one or more proof masses in a device layer. The device layer defines an xy plane and a z direction perpendicular to the xy plane. The one or more proof masses include a first set of rotor comb teeth extending along the x direction and a second set of rotor comb teeth also extending along the x direction.

[0019] The accelerometer includes four sets of stator comb teeth in the device layer. The comb teeth extend in the x-direction. Each of the four sets of stator comb teeth is electrically insulated from the other three of the four sets of stator comb teeth. One or more detection masses are movable relative to the four sets of stator comb teeth in at least the y-direction and the z-direction.

[0020] The four groups of stator comb teeth include a first group of stator comb teeth and a second group of stator comb teeth, and the first group of stator comb teeth and the second group of stator comb teeth are interlaced with the first group of rotor comb teeth, so that on the side of each rotor comb tooth in the first group of rotor comb teeth:

[0021] - having on one side stator teeth from a first set of stator teeth and

[0022] - On the opposite side there are stator comb teeth from a second set of stator comb teeth.

[0023] Thereby, the first group of stator comb teeth and the first group of rotor comb teeth form a first capacitor, and the second group of stator comb teeth and the first group of rotor comb teeth form a second capacitor.

[0024] The four groups of stator comb teeth also include a third group of stator comb teeth and a fourth group of stator comb teeth, and the third group of stator comb teeth and the fourth group of stator comb teeth are interlaced with the second group of rotor comb teeth, so that on the side of each rotor comb tooth in the second group of rotor comb teeth:

[0025] - on one side there are stator teeth from the third group of stator teeth located to the side thereof and

[0026] - On the opposite side there are stator teeth from the fourth group of stator teeth flanking it.

[0027] Thereby, the third group of stator comb teeth and the second group of rotor comb teeth form a third capacitor, and the fourth group of stator comb teeth and the second group of rotor comb teeth form a fourth capacitor.

[0028] The device layer has top and bottom surfaces parallel to the xy plane and facing opposite z directions. The bottoms of all rotor comb teeth in the first and second groups of rotor comb teeth and the bottoms of all stator comb teeth in the four groups of stator comb teeth are flush with each other.

[0029] The tops of all stator comb teeth in the first group of stator comb teeth and the tops of all stator comb teeth in the fourth group of stator comb teeth are flush with the top surface of the device layer. The tops of all rotor comb teeth in the first group of rotor comb teeth and the second group of rotor comb teeth are recessed from the top surface of the device layer by a first recessed depth D1 in the z direction. The tops of all stator comb teeth in the second group of stator comb teeth and the tops of all stator comb teeth in the third group of stator comb teeth are recessed from the top surface of the device layer by a second recessed depth D2 in the z direction. D2 is greater than D1.

[0030] The proof mass may also be referred to as a rotor. The proof mass described in the present disclosure may be capable of linear and / or rotational motion relative to a fixed structure. Such motion may occur in an xy plane (which may also be referred to as a device plane) or out of the xy plane. In-plane and out-of-plane motion may occur simultaneously. The term "rotor comb" refers to an elongated structure that forms part of a proof mass and that may be used to measure motion of the proof mass (together with adjacent stator comb teeth).

[0031] The fixed structure adjacent to the rotor may be referred to as a stator. The term "stator comb teeth" refers to an elongated structure that forms part of the fixed structure and is used to measure the motion of the detection mass (together with the adjacent rotor comb teeth). Both the rotor and the stator may be formed in a device layer. The device layer may be, for example, a silicon wafer or a silicon layer deposited on a carrier layer. The rotor comb teeth may be interlaced with the stator comb teeth to form a capacitor, as described in more detail below. The capacitor described in any embodiment of the present disclosure may be used as a measuring capacitor or an actuating capacitor.

[0032] In any embodiments presented in the present disclosure, each of the first and second sets of rotor teeth and each of the four sets of stator teeth may include a large number of teeth, such as more than 20, more than 50, or more than 100 teeth.

[0033] In any embodiments of the present disclosure, one or more proof masses may be configured to displace in response to accelerations in the x-, y-, and z-directions. In the case of accelerations in the x- and y-directions, such displacements may be in-plane motions, and in the case of accelerations in the z-direction, they may be out-of-plane motions. The present disclosure will primarily focus on describing how these displacements may be measured.

[0034] However, detection mass displacement does not necessarily have to occur. The accelerometer can also be implemented with a signal feedback loop that performs a force feedback function. The capacitor is then configured to act as an actuator that keeps one or more detection masses stationary even when the accelerometer experiences acceleration. The voltage required at each actuator capacitor to keep the detection mass stationary can be recorded, and this value is proportional to the magnitude of the acceleration. All of the benefits of differential measurement and double differential measurement described in the present disclosure are also realized in a force feedback implementation. This is because there is a direct correspondence between (a) the capacitive measurement signal generated by a given amount of detection mass displacement in a given capacitor (if the detection mass is allowed to move) and (b) the capacitive actuation signal that must be applied to the same capacitor to prevent the same detection mass from moving (in a force feedback implementation).

[0035] First embodiment

[0036] Figure 2a An accelerometer is shown, wherein the one or more proof masses include a first proof mass 21 and a second proof mass 22, and the first proof mass 21 and the second proof mass 22 are configured to rotate in opposite rotational directions out of the plane of the device in response to an acceleration in the z-direction. A first set of rotor comb teeth are located on the first proof mass, and a second set of rotor comb teeth are located on the second proof mass. The rotational axes of the first proof mass and the second proof mass extend in the y-direction.

[0037] The first proof mass 21 is suspended from a first anchor point 291 and the second proof mass 22 is suspended from a second anchor point 292. The anchor points are rigid parts of the fixed structure of the MEMS accelerometer. The suspension structure 29 is a flexible spring that allows the proof masses 21 and 22 to move when the accelerometer experiences acceleration. The rotation axes of the two proof masses are located on the suspension structure 29 shown. The geometry of the suspension structure 29 can alternatively be more complex. The suspension structures 29 allow the respective proof masses to rotate about a rotation axis extending in the y direction and they also allow for example Figure 2b As shown, it rotates in the xy plane.

[0038] The proof masses 21 and 22 are connected to each other by means of a coupling spring 28. The anchor point and the suspension structure are Figure 2a The ? are shown inside the opening of the proof mass, but they may alternatively be located outside the proof mass.

[0039] The suspension structure 29 and the proof masses 21 and 22 can be designed so that when the accelerometer experiences acceleration in the y-direction, the two proof masses rotate in opposite directions within the plane of the device, as Figure 2b They can also be designed so that when the accelerometer experiences acceleration in the z direction, the two proof masses rotate in opposite directions out of the plane of the device, as shown in Figure 2c The coupling spring can be designed so that it can flexibly adapt to Figure 2b and Figure 2c The anti-phase motion shown, and rigidly resisting the in-phase motion of the two proof masses rotating in the same direction.

[0040] although Figure 2b to Figure 2c Rotational motion is shown, but the capacitors described in the present disclosure may alternatively be used to detect linear motion. In other words, one or more proof masses may be suspended using a suspension device that allows one or more proof masses to move linearly in the y-direction and / or the z-direction. Thus, in the present disclosure, the term "rotor" may refer to an object that rotates or to an object that moves linearly.

[0041] Alternatively, the suspension structure 29 and proof masses 21 and 22 may be designed so that when the accelerometer experiences acceleration in the x-direction, both proof masses translate linearly in the same x-direction. Such in-phase motion is not shown.

[0042] Figure 2a A first set of rotor comb teeth 211 on the first proof mass 21 and a second set of rotor comb teeth 212 on the second proof mass 22 are shown. The first set of rotor comb teeth and the second set of rotor comb teeth are shown inside the openings in the proof masses 21 and 22, at the outer ends of the proof masses (left edge of 21 / right edge of 22). However, these groups may alternatively be located outside the proof masses, and they may alternatively be placed at the inner ends (right edge of 21, left edge of 22).

[0043] Figure 2a Also shown are a first group of stator comb teeth 231, a second group of stator comb teeth 232, a third group of stator comb teeth 233, and a fourth group of stator comb teeth 234. The first group 231 of stator comb teeth is connected to a first fixed structure 241, the second group of stator comb teeth 232 is connected to a second fixed structure 242, the third group of stator comb teeth 233 is connected to a third fixed structure 243, and the fourth group of stator comb teeth 234 is connected to a fourth fixed structure 244. These fixed structures 241 to 244 are electrically insulated from each other, so the four groups of stator comb teeth 231 to 234 are also electrically insulated from each other. This facilitates four separate capacitance measurements between the rotor comb teeth and the stator comb teeth. Figure 2a The arrangement shown is only one option. The four groups of stator comb teeth 231 to 234 can also be electrically insulated from each other by other means. The stator comb teeth 231 to 234 are stationary, so when the device experiences acceleration, the stator comb teeth 231 to 234 do not move relative to the surrounding device package. The details defined in this paragraph also apply to the second embodiment presented below.

[0044] exist Figure 2a It can be seen in FIG. 2 that, at the detection mass 21, each rotor comb tooth 211 in the first group of rotor comb teeth has a stator comb tooth 231 from the first group of stator comb teeth located on its side on one side, and a stator comb tooth 232 from the second group of stator comb teeth located on its side on the opposite side. Conversely, at the detection mass 22, each rotor comb tooth 212 in the second group of rotor comb teeth has a stator comb tooth 233 from the third group of stator comb teeth located on its side on one side, and a stator comb tooth 234 from the fourth group of stator combs located on its side on the opposite side. This is also true in the second embodiment presented below.

[0045] Optionally, each rotor comb tooth 211 in the first group of rotor comb teeth may have a stator comb tooth 231 from the first group of stator comb teeth located on its side facing the positive y direction and a stator comb tooth 232 from the second group of stator comb teeth located on its side facing the negative y direction, and each rotor comb tooth 212 in the second group of rotor comb teeth may have a stator comb tooth 233 from the third group of stator comb teeth located on its side facing the positive y direction and a stator comb tooth 234 from the fourth group of stator comb teeth located on its side facing the negative y direction. In other words, in the positive y direction ( Figure 2a The comb teeth adjacent to the rotor comb teeth 211 in the negative y direction (upper side) are stator comb teeth 231 from the first group, while Figure 2a The comb teeth adjacent to the same rotor comb tooth 211 on the lower side (in the figure) are stator comb teeth 232 from the second group. Also, the comb teeth adjacent to the rotor comb tooth 212 in the positive y direction are stator comb teeth 233 from the first group, while in the negative y direction ( Figure 2a The comb teeth adjacent to the same rotor comb tooth 212 on the lower side in FIG. 1 are stator comb teeth 234 from the second group. The details defined in this paragraph also apply to the second embodiment presented below.

[0046] Alternatively, each rotor comb tooth 211 in the first group of rotor comb teeth may have a stator comb tooth 231 from the first group of stator comb teeth located on its side facing the positive y direction and a stator comb tooth 232 from the second group of stator comb teeth located on its side facing the negative y direction, and each rotor comb tooth 212 in the second group of rotor comb teeth may have a stator comb tooth 234 from the fourth group of stator comb teeth located on its side facing the positive y direction and a stator comb tooth 233 from the third group of stator comb teeth located on its side facing the negative y direction. The details defined in this paragraph may also be implemented in the second embodiment.

[0047] Since the four fixed structures 241 to 244 are electrically insulated from each other, the four groups of stator comb teeth 231 to 234 are also insulated from each other (even if they are located in the same device layer, such as Figure 3a to Figure 3b . The insulation (or physical isolation, which also gives electrical isolation) between adjacent stator comb tooth groups can be made in many different ways. The following options can be used for all embodiments presented in this disclosure.

[0048] The accelerometer may, for example, include an additional device layer, which may be formed of a silicon layer, which is parallel to the device layer previously described in the present disclosure and rigidly fixed to the device layer. Figure 2d It is shown in Figure 2d In FIG. 2 , 201 is a device layer, and 202 is an additional device layer. The comb teeth 231 and 232 have different y coordinates, such as Figure 2c 247 indicates an interface between the stator comb teeth 232 and the second fixed structure 242 .

[0049] With the help of fixed extension structures 248 and 249 prepared in the additional device layer 202, the first fixed structure 241 extends beyond the second fixed structure 242 in the x-direction. The second fixed structure 242 can have a gap in the additional device layer 202 at the y-coordinate where the extension structure 248 is located. The bypass formed by 248 and 249 allows the stator comb teeth 231 to be electrically separated from the stator comb teeth 232. The additional device layer 202 can also be used to form additional moving mass elements on the detection masses 21 and 22. Figure 2d This option is not shown in the Figure 2d Only the fixed stator structure is shown.

[0050] Even using only a single device layer, it is possible to create a conductive fixed bypass structure (similar to Figure 2d The vertical bypass structures (which may also be referred to as bridge structures) may be made of polysilicon, for example. Another alternative is to not use fixing structures 241 to 244 at all, but instead to build each stator comb tooth as a separate structure anchored to the underlying anchoring substrate. All comb teeth belonging to the same group of stator comb teeth 231, 232, 233 or 234 may then be connected to each other by electrical wiring in the anchoring substrate.

[0051] exist Figure 2a In the embodiment, the electrical isolation (insulation) between adjacent stator comb tooth groups forms four separate capacitors: a first capacitor (comb tooth group 211+231) between the detection mass block 21 and the fixed structure 241, a second capacitor (comb tooth group 211+232) between the detection mass block 21 and the fixed structure 242, a third capacitor (comb tooth group 212+233) between the detection mass block 22 and the fixed structure 243, and a fourth capacitor (comb tooth group 212+234) between the detection mass block 22 and the fixed structure 244.

[0052] For illustration purposes, Figure 2a The number of comb teeth in the rotor comb teeth is very small. As mentioned above, the number of comb teeth will be much larger in practice. The number of rotor comb teeth in the first set of rotor comb teeth can be equal to the number of stator comb teeth in the first set of stator comb teeth, and equal to the number of stator comb teeth in the second set of stator comb teeth. Similarly, the number of rotor comb teeth in the second set of rotor comb teeth can be equal to the number of stator comb teeth in the third set of stator comb teeth, and equal to the number of stator comb teeth in the fourth set of stator comb teeth. The number of rotor comb teeth in the second set of rotor comb teeth can also be equal to the number of rotor comb teeth in the first set of rotor comb teeth. For any number of rotor comb teeth and stator comb teeth, it can be achieved Figure 2aThe details defined in this and the previous paragraph also apply to the second embodiment.

[0053] Optionally, the accelerometer may include additional comb structures that form additional capacitors that can be used to measure or actuate motion in the x-direction. Figure 2a Additional fixing structures 27 are shown inside the openings in the proof masses 21 and 22 and additional stator comb teeth 26 extending in the y-direction from these fixing structures 27. Additional rotor comb teeth 25 also extend in the y-direction inside the openings. This option also applies to the second embodiment, but it is completely optional and the accelerometer can alternatively be realized as a device in which the proof masses move only in the z-direction and the y-direction and not in the x-direction.

[0054] The first proof mass 21 and the second proof mass 22 may be substantially mirror-symmetrical with respect to an axis of symmetry 281 extending in the y direction. The position and size of the first set of rotor comb teeth 211 may be substantially mirror-symmetrical with respect to the axis of symmetry 281 and the position and size of the second set of rotor comb teeth 212. The position and size of the first set of stator comb teeth 231 may be substantially mirror-symmetrical with respect to the axis of symmetry 281 and the position and size of the third set of rotor comb teeth 233. The position and size of the second set of stator comb teeth 232 may be substantially mirror-symmetrical with respect to the axis of symmetry 281 and the position and size of the fourth set of rotor comb teeth 234. Alternatively, 231 may be symmetrical with 234, and 232 may be symmetrical with 233.

[0055] The size and geometry of all the rotor comb teeth in the first and second groups may be substantially the same, but the size and geometry of the stator comb teeth in the first, second, third and fourth groups may not be the same.

[0056] The following discussion Figure 3a to Figure 3b The paragraphs of also apply to the second embodiment. In the present disclosure, the words "bottom" and "top" refer to two opposite sides of an object with different z coordinates. Words such as "up" and "down" refer to two opposite z directions. The z-axis is perpendicular to the device layer (xy plane). The device layer can be bonded to, attached to, or deposited on an adjacent support layer with its top side facing the support layer or with its bottom side facing the support layer. A cover layer can be attached to the other side (bottom or top).

[0057] Figure 3a and Figure 3b In the schematic side view (yz section) Figure 2a The same comb set shown in . Figure 3a and Figure 3bAlso shown are the top surface 298 of the device layer and the bottom surface 299 of the device layer. It can be seen that the bottoms of stator comb teeth 231 and 232 and rotor comb teeth 211 are flush with each other, and the bottoms of stator comb teeth 233 and 234 and rotor comb teeth 212 are also flush with each other.

[0058] The bottom of all groups of comb teeth is at Figure 3a and Figure 3b The 294a and 295b are also flush with the bottom surface 299 of the device layer. Alternatively, they can all be recessed upward from the bottom surface 299 in the positive z-direction by the same amount (this option is not shown).

[0059] However, some of the comb teeth are recessed from the top side. First, as Figure 3a to Figure 3b As shown, the first set 211 of rotor comb teeth and the second set 212 of rotor comb teeth are recessed from the top surface 298 of the device layer by a first recess depth D1. In other words, the sets 211 and 212 are recessed by the same amount. Secondly, the second set 232 of stator comb teeth and the third set 233 of stator comb teeth are recessed from the top surface 298 by a second recess depth D2. In other words, the sets 232 and 233 are recessed by the same amount. In any embodiment presented in the present disclosure, D2 can be, but does not necessarily have to be, twice as large as D1.

[0060] In any of the embodiments presented in the present disclosure, the distance D2-D1 (i.e. Figure 3a The difference between the z coordinate of the top of the smaller stator comb tooth 232 and the z coordinate of the top of the rotor comb tooth 211) and D1 (i.e., Figure 3a The difference between the z-coordinates of the tops of the middle rotor teeth 211 and the tops of the larger stator teeth 231) may each be at least 1.5 times the gap between each adjacent stator tooth-rotor tooth pair in the y-direction.

[0061] In any of the embodiments presented in the present disclosure, the distances D2-D1 and D1 may be greater than 3 microns. Figure 3a 232 of them, Figure 3b The height of the stator teeth (233) in the z direction can be greater than 5 microns. It can be in the range of 10 microns to 25 microns or in the range of 10 microns to 30 microns or 20 microns to 30 microns. Figure 3a 231 of them, Figure 3b The height of the rotor teeth 234) can be, for example, in the range of 35 μm to 80 μm, 40 μm to 80 μm, or 40 μm to 60 μm, and can be equal to the thickness of the device layer. The height of the rotor comb teeth 211 can be, for example, in the range of 25 μm to 40 μm or in the range of 25 μm to 35 μm.

[0062] This comb geometry facilitates reliable measurement of proof mass displacement in both the y-direction and the z-direction in a dual differential arrangement comprising first (211+231), second (211+232), third (212+233), and fourth (212+234) capacitors. In any embodiment, all one or more proof masses may be at the same potential. Alternatively, if there are two or more proof masses, they may be at different potentials.

[0063] exist Figure 3a As can be seen in Figure 1, displacement of the proof mass in the positive z direction (which necessarily involves displacement of the rotor comb teeth 211 and 212 in the same direction) increases the capacitance C1 of the first capacitor and the capacitance C4 of the fourth capacitor. The overlap area of ​​211-231 and 212-234 remains unchanged, but the additional area exposed towards the stator comb teeth from the bottom of each rotor comb tooth is increased. The same displacement reduces the capacitance C2 of the second capacitor and the capacitance C3 of the third capacitor because the overlap area of ​​211-232 and 212-233 is reduced.

[0064] On the other hand, displacement in the negative z-direction decreases C1 and C4, and increases C2 and C3. Displacement in the positive y-direction will increase C1 and C3 (due to the decrease in the distance between the rotor and stator teeth in the y-direction), but decrease C2 and C4 (due to the increase in the distance between the rotor and stator teeth). Conversely, displacement in the negative y-direction decreases C1 and C3, but increases C2 and C4.

[0065] A first differential signal S1 = C1 - C2 may be measured from the first capacitor and the second capacitor. A second differential signal S2 = C3 - C4 may be measured from the third capacitor and the fourth capacitor. The first differential signal and the second differential signal may be analog signals.

[0066] The double differential signal can be calculated by adding or subtracting the S1 and S2 signals from each other. This calculation can be performed after the signals S1 and S2 are digitized. It can be shown that the first output signal DD1=S1-S2 will be proportional to the displacement of the detection mass in the z direction, but will be insensitive to displacement in the y direction (i.e., DD1 remains substantially constant when one or more detection masses move in the y direction). The second output signal DD2=S1+S2 will be proportional to the displacement of the detection mass in the y direction, but will be insensitive to displacement in the z direction. Therefore, displacements in two perpendicular directions can be reliably measured by this device.

[0067] Second embodiment

[0068] Figure 4An embodiment is shown in which one or more proof masses consist of a first proof mass 21. The first proof mass 21 is configured to rotate out of the device plane in response to an acceleration in the z-direction. The rotation axis 481 of the first proof mass 21 extends in the y-direction.

[0069] Reference numerals 291, 29, 25 and 27 show Figure 4 Zhongyu Figure 2a Reference numerals 211-212, 231-234 and 241-244 also denote the same elements as in the first embodiment, but their placement is different from the first embodiment when only one proof mass is used.

[0070] exist Figure 4 In the embodiment of the present invention, the first group of rotor comb teeth (211) and the second group of rotor comb teeth (212) are located in the opening of the first detection mass 21. The first group of stator comb teeth (231), the second group of stator comb teeth (232), the third group of stator comb teeth (233) and the fourth group of stator comb teeth (234) are located in the same opening. Alternatively, the first group of rotor comb teeth and / or the second group of rotor comb teeth can be located outside the detection mass 21 in the xy plane, and the stator group 231+232 and / or 233+234 can be located outside the detection mass 21 accordingly.

[0071] For the sake of clarity, Figure 4 Only a single rotor comb tooth in each group (211 and 212) is shown. When additional comb teeth are added, the alternating sequence of rotor comb teeth and stator comb teeth will correspond to Figure 2a in the order shown.

[0072] As in the first embodiment, the four fixed structures 241-244 are electrically insulated from each other, and the four groups of stator comb teeth 231-234 are also insulated from each other. Thus, four separate capacitors are formed, exactly at Figure 2a The same as in: a first capacitor (comb teeth group 211+231) between the detection mass block 21 and the fixed structure 241, a second capacitor (comb teeth group 211+232) between the detection mass block 21 and the fixed structure 242, a third capacitor (comb teeth group 212+233) between the detection mass block 21 and the fixed structure 243, and a fourth capacitor (comb teeth group 212+234) between the detection mass block 21 and the fixed structure 244.

[0073] Figure 3a to Figure 3b The vertical recess scheme shown in also applies to Figure 4This allows two double differential signals to be calculated, exactly as in the first embodiment. One of them indicates the acceleration in the y direction and the other in the z direction, as described above in the first embodiment. An optional measurement can be made between the comb teeth 25 and 26 to detect the acceleration in the x direction. Figures 3a to 3b All features and options described also apply to this second embodiment.

Claims

1. A micro-electromechanical accelerometer comprising one or more proof masses in a device layer, wherein: The device layer defines an xy plane and a z direction perpendicular to the xy plane, and the one or more proof masses include a first set of rotor comb teeth extending along the x direction and a second set of rotor comb teeth also extending along the x direction, and the accelerometer further comprises four groups of stator comb teeth extending along the x-direction in the device layer, and each of the four groups of stator comb teeth is electrically insulated from the other three of the four groups of stator comb teeth, and the one or more detection masses are movable relative to the four groups of stator comb teeth at least in the y-direction and the z-direction, and The four groups of stator comb teeth include a first group of stator comb teeth and a second group of stator comb teeth, and the first group of stator comb teeth and the second group of stator comb teeth are interlaced with the first group of rotor comb teeth, so that each rotor comb tooth in the first group of rotor comb teeth: - on one side there are stator teeth from the first set of stator teeth flanking it and - on the opposite side there are stator teeth from the second set of stator teeth flanking it, Thus, the first group of stator comb teeth and the first group of rotor comb teeth form a first capacitor, and the second group of stator comb teeth and the first group of rotor comb teeth form a second capacitor, and The four groups of stator comb teeth further include a third group of stator comb teeth and a fourth group of stator comb teeth, and the third group of stator comb teeth and the fourth group of stator comb teeth are interlaced with the second group of rotor comb teeth, so that each rotor comb tooth wing in the second group of rotor comb teeth: - on one side there are stator teeth from the third group of stator teeth flanking it and - on the opposite side there are stator teeth from said fourth group of stator teeth flanking it, Thereby, the third group of stator comb teeth and the second group of rotor comb teeth form a third capacitor, and the fourth group of stator comb teeth and the second group of rotor comb teeth form a fourth capacitor, and The device layer has a top surface and a bottom surface parallel to the xy plane and opposite to each other in the z direction, the bottoms of all the rotor combs in the first group of rotor comb teeth and the second group of rotor comb teeth and the bottoms of all the stator comb teeth in the four groups of stator comb teeth are flush with each other, It is characterized in that the tops of all stator comb teeth in the first group of stator comb teeth and the tops of all stator comb teeth in the fourth group of stator comb teeth are flush with the top surface of the device layer, and the tops of all rotor comb teeth in the first group of rotor comb teeth and the second group of rotor comb teeth are recessed from the top surface of the device layer by a first recessed depth D1 in the z direction, and the tops of all stator comb teeth in the second group of stator comb teeth and the tops of all stator comb teeth in the third group of stator comb teeth are recessed from the top surface of the device layer by a second recessed depth D2 in the z direction, and D2 is greater than D1.

2. The micro-electromechanical accelerometer according to claim 1, wherein: Each rotor comb tooth of the first set of rotor comb teeth has a stator comb tooth from the first set of stator comb teeth flanked on a side facing the positive y-direction and a stator comb tooth from the second set of stator comb teeth flanked on a side facing the negative y-direction, and Each rotor comb tooth in the second group of rotor comb teeth has a stator comb tooth from the third group of stator comb teeth located on its side facing the positive y direction, and has a stator comb tooth from the fourth group of stator comb teeth located on its side facing the negative y direction.

3. A micro-electromechanical accelerometer according to any preceding claim, wherein: The one or more detection masses include a first detection mass and a second detection mass, and the first detection mass and the second detection mass are configured to rotate in opposite rotational directions outside the device plane in response to the acceleration in the z-direction, and the first set of rotor comb teeth are located on the first detection mass, and the second set of rotor comb teeth are located on the second detection mass, and the rotation axes of the first detection mass and the second detection mass extend along the y-direction.

4. The micro-electromechanical accelerometer according to claim 3, wherein: The first detection mass block and the second detection mass block are basically mirror-symmetrical with respect to the symmetry axis extending along the y direction, and the position and size of the first group of rotor comb teeth are basically mirror-symmetrical with the position and size of the second group of rotor comb teeth with respect to the symmetry axis, and the position and size of the first group of stator comb teeth are basically mirror-symmetrical with the position and size of the third group of rotor comb teeth with respect to the symmetry axis, and the position and size of the second group of stator comb teeth are equivalent to the position and size of the fourth group of rotor comb teeth that are basically mirror-symmetrical with the symmetry axis.

5. The micro-electromechanical accelerometer according to any one of claims 3 to 4, wherein: The first proof mass and the second proof mass are configured to rotate in opposite directions in the device plane when the accelerometer experiences acceleration in the y-direction.

6. The micro-electromechanical accelerometer according to any one of claims 3 to 5, wherein: The first proof mass and the second proof mass are configured to translate linearly in the same x-direction when the accelerometer experiences acceleration in the x-direction.

7. The micro-electromechanical accelerometer according to any one of claims 1 to 2, wherein: The one or more proof masses are suspended by a suspension arrangement that allows linear movement of the one or more proof masses in the y-direction.

8. The micro-electromechanical accelerometer according to any one of claims 1 to 2, wherein: The one or more proof masses are suspended by a suspension arrangement that allows linear movement of the one or more proof masses in the z-direction.

9. The micro-electromechanical accelerometer according to any one of claims 1 to 2, wherein: The one or more proof masses include a first proof mass, and the first proof mass is configured to rotate out of the device plane in response to an acceleration in the z-direction, and a rotation axis of the first proof mass extends along the y-direction.

10. A micro-electromechanical accelerometer according to any preceding claim, wherein: D2 is twice as large as D1.

11. A micro-electromechanical accelerometer according to any preceding claim, wherein: The device layer is made of silicon.

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