MEMS devices and methods for their manufacture

Abstract

Device with a microelectromechanical system (MEMS) comprising the following: a first record (101), a second plate (105) which is arranged above the first plate (101), a first movable plate (102) arranged between the first plate (101) and the second plate (105), and a second movable plate (103) arranged between the first movable plate (102) and the second plate (105), the MEMS device comprising a first input / output node coupled to the first plate (101), a second input / output node coupled to the second plate (105), a third input / output node coupled to the first movable plate (102), and a fourth input / output node coupled to the second movable plate (103), wherein the first input / output node is different from the second input / output node, and wherein the third input / output node is different from the fourth input / output node, wherein the first movable plate (102) is rigidly coupled to the second movable plate (103), wherein the first movable plate (102) is designedto be shielded from capacitive coupling with the second movable plate (103).

Description

[0001] The present invention claims priority to U.S. Provisional Application No. 61 / 847,874, filed July 18, 2013, which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present invention relates generally to microelectromechanical system devices and, more particularly, to MEMS devices, interface circuits, and methods of fabricating the same. BACKGROUND OF THE INVENTION

[0003] Microelectromechanical systems (MEMS) based on sensors, such as microphones, collect information from the environment by measuring physical phenomena. The electronics then process the signal information derived from the sensors, despite the presence of noise and interference. Advantageously, MEMS devices can be manufactured in batches using manufacturing techniques similar to those used for integrated circuits. The functionality, reliability, and sophistication can therefore be integrated onto a small silicon chip at relatively low cost.

[0004] MEMS devices can be implemented as oscillators, resonators, accelerometers, gyroscopes, pressure sensors, microphones, micromirrors, and others. MEMS devices typically use capacitive sensing techniques to measure the physical phenomenon being measured. In all of these applications, the capacitive sensor's change in capacitance is converted into a usable voltage using interface circuits. However, interface circuits can become challenging due to sensor miniaturization, the presence of noise, and reduced sensing capacitance.

[0005] US 2013 / 0 044 899 A1 discloses an electret condenser microphone comprising a diaphragm disposed between an upper backplate and a lower backplate. The upper backplate comprises a first electret fluoropolymer layer, and the lower backplate comprises a second electret fluoropolymer layer. The diaphragm and the two backplates are coupled to a total of two input nodes.

[0006] US 2011 / 0 033 079 A1 discloses a flat loudspeaker comprising two stacked vibrating membranes, an insulation layer, and a plurality of electrodes. Each membrane is arranged opposite an electrode, separated from each other by the insulation layer. The membranes are, in particular, electret membranes. The two membranes are connected to a signal source, and the two electrodes are connected to ground.

[0007] US 2009 / 0 060 233 A1 discloses an electroacoustic device comprising a first electrode, a second electrode, and an electret arrangement arranged between the two electrodes. The electret arrangement comprises a first electret and a second electret, each electret being associated with a conductive layer. An insulating layer is arranged between the two conductive layers. The first electrode with the second conductive layer and the second electrode with the first conductive layer are coupled to a signal source.

[0008] Some of the key characteristics of a MEMS device include sensitivity, bandwidth, linearity, dynamic range, minimum detectable signal, stability, size, and cost. The sensitivity of a MEMS device is the change in output margin for a derived change in capacitance at the capacitive sensor of an input physical phenomenon (for example, time-varying pressure). Bandwidth is the range of frequencies over which the sensor can be used.

[0009] Another important metric of a capacitive microphone, however, is linearity. Sensor linearity is a measurement of how close the output calibration curve is to a straight line compared to the input calibration curve at a given frequency. The gradient between the input pressure and the output voltage provides the transducer's sensitivity at that frequency. At high input amplitudes, the transducer's output deviates from an ideal straight line. The lower and higher ends of the linear range are determined by both the sensor interface circuitry and the sensor. The lower end is limited by system noise, such as thermal noise, 1 / f noise, and mechanical noise.The higher end of the linear range is determined by structural non-linearities, such as the stiffening of a spring, or by circuit non-linearities, such as clipping.

[0010] The dynamic range of a capacitive transducer is defined as the ratio of the maximum and minimum input signals to the linear range. Any deviation of the output from the ideal linear curve causes distortion in the microphone output. If the system is excited at a single frequency, the distortion can be calculated as the minimum input amplitude that causes the output to deviate from linearity by a fixed percentage.

[0011] One of the challenges therefore concerns the production of MEMS devices and circuits with better functionality and reliability without increasing costs. SUMMARY OF THE INVENTION

[0012] There is a need to provide an improved concept for a microelectromechanical system (MEMS) device and a sensor circuit.

[0013] Such a demand can be met by the subject matter of the claims.

[0014] Some embodiments relate to a microelectromechanical system (MEMS) device comprising a first plate, a second plate disposed above the first plate, a first movable plate disposed between the first plate and the second plate, and a second movable plate disposed between the first movable plate and the second plate.

[0015] The first movable plate is rigidly coupled to the second movable plate.

[0016] The first movable plate is further configured to be shielded from capacitive coupling with the second movable plate.

[0017] Optionally, the device further comprises a bottom cavity disposed below the first plate, a second cavity disposed between the first plate and the first movable plate, and a second cavity disposed between the second plate and the second movable plate.

[0018] Optionally, the first movable plate is designed to be coupled to a potential node with a different potential than the second movable plate.

[0019] Furthermore, the first movable plate is optionally designed to be coupled to a voltage source through a first filter, wherein the second movable plate is designed to be coupled to the voltage source through a second filter.

[0020] Optionally, the first filter and the second filter have different RC filters.

[0021] Furthermore, the first plate is a first stationary plate and the second plate is a second stationary plate.

[0022] Optionally, the first stationary plate is configured to be coupled to a voltage source through a first filter, and the second stationary plate is configured to be coupled to the voltage source through a second filter.

[0023] Optionally, the device further comprises a third movable plate and a fourth movable plate and a third stationary plate and a fourth stationary plate, wherein the third movable plate is capacitively coupled to the third stationary plate, wherein the fourth movable plate is capacitively coupled to the fourth movable plate.

[0024] The first movable plate is further optionally configured to be coupled to a first voltage source through a first filter, the second movable plate is configured to be coupled to the first voltage source through a second filter, the third movable plate is configured to be coupled to a second voltage source through a third filter, and the fourth movable plate is configured to be coupled to the second voltage source through a fourth filter.

[0025] Optionally, the first and second filters have different RC filters, and the third filter and fourth filter have different RC filters.

[0026] Some embodiments relate to a sensor circuit comprising a first filter circuit coupled between a voltage source and a first input bias node configured to be coupled to a first plate of a first type of capacitive sensor, and a second filter circuit coupled between the voltage source and a second input bias node configured to be coupled to a second plate of the first type of capacitive sensor, wherein the capacitive sensor comprises the first plate of the first type capacitively coupled to a first plate of a second type, and wherein the second plate of the first type is capacitively coupled to a second plate of the second type.

[0027] Optionally, the first filter circuit comprises a first resistor coupled between the voltage source and the first input bias node, and a first capacitor coupled between a steady-state potential and the first input bias node, and the second filter circuit comprises a second resistor coupled between the voltage source and the second input bias node, and a second capacitor coupled between the steady-state potential and the second input bias node.

[0028] Furthermore, the first resistor optionally comprises a diode or a metal / insulator / semiconductor transistor, wherein the first capacitor comprises a metal / insulator / semiconductor capacitor.

[0029] Optionally, the first plate of the first type is rigidly coupled to the second plate of the first type.

[0030] Furthermore, the capacitive sensor has a microphone with a microelectromechanical system (MEMS).

[0031] Optionally, the first plate of the first type is a first movable plate, the second plate of the first type is a second movable plate, the first plate of the second type is a first stationary plate, and the second plate of the second type is a second stationary plate.

[0032] Furthermore, the circuit optionally further comprises a first amplifier having an input node coupled to a first output bias node for coupling to the first stationary plate of the capacitive sensor, and a second amplifier having an input node coupled to a second output bias node configured to be coupled to the second stationary plate of the capacitive sensor.

[0033] Optionally, the circuit further comprises a first feedback capacitor coupled between the first input bias node and an output node of the first amplifier, and a second feedback capacitor coupled between the second input bias node and an output node of the second amplifier.

[0034] Optionally, the circuit further comprises a first feedback capacitor coupled between the second input bias node and an output node of the first amplifier, and a second feedback capacitor coupled between the first input bias node and an output node of the second amplifier.

[0035] Further optionally, the first plate of the first type is a first stationary plate, the second plate of the first type is a second stationary plate, the first plate of the second type is a first movable plate, the second plate of the second type is a second movable plate.

[0036] Optionally, the circuit further comprises a first amplifier having an input node coupled to a first output bias node configured to be coupled to the first movable plate of the capacitive sensor, and a second amplifier having an input node coupled to a second output bias node configured to be coupled to the second movable plate of the capacitive sensor.

[0037] Optionally, the circuit further comprises a first feedback capacitor coupled between the input node of the first amplifier and an output node of the first amplifier, and a second feedback capacitor coupled between the input node of the second amplifier and an output node of the second amplifier.

[0038] Optionally, the circuit further comprises a first feedback capacitor coupled between the input node of the second amplifier and an output node of the first amplifier, and a second feedback capacitor coupled between the input node of the first amplifier and an output node of the second amplifier.

[0039] Some embodiments relate to a method of forming a microelectromechanical system (MEMS) device, the method comprising the steps of forming a first plate in or above a substrate, forming a second plate above the first plate, forming a first movable plate between the first plate and the second plate, and forming a second movable plate between the first movable plate and the second plate.

[0040] Optionally, the first movable plate and the second movable plate are formed as part of one and the same movable mass, and the first movable plate is configured to be shielded from capacitive coupling with the second movable plate.

[0041] Optionally, the method further comprises forming a bottom cavity in the substrate below the first plate, forming a first cavity between the first plate and the second movable plate, and forming a second cavity between the second plate and the second movable plate.

[0042] This and other problems are generally solved or obviated, and technical advantages are generally achieved, by illustrative embodiments of the present invention.

[0043] According to one embodiment of the present invention, a microelectromechanical system (MEMS) device includes a first plate, a second plate disposed above the first plate, and a first movable plate disposed between the first plate and the second plate. The MEMS device further includes a second movable plate disposed between the first movable plate and the second plate.

[0044] According to one embodiment of the present invention, a sensor circuit comprises a first filter circuit coupled between a voltage source and a first input bias node configured to be coupled to a first plate of a first type of capacitive sensor. The sensor circuit further comprises a second filter circuit coupled between the voltage source and a second input bias node configured to be coupled to a second plate of the first type of capacitive sensor. The capacitive sensor comprises the first plate of the first type capacitively coupled to a first plate of a second type, and the second plate of the first type capacitively coupled to a second plate of the second type.

[0045] According to one embodiment of the present invention, a method for forming a microelectromechanical system (MEMS) device comprises forming a first plate in or above a substrate and forming a second plate above the first plate. A first movable plate is formed between the first plate and the second plate. A second movable plate is formed between the first movable plate and the second plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] For a full understanding of the present invention and its advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings in which: a conventional MEMS sensor circuit in Fig. 1 is illustrated, Fig. 2 illustrates a MEMS device and a front-end circuit according to an embodiment of the present invention, Fig. 3 illustrates a positive feedback MEMS device according to an embodiment of the present invention, Fig. 4 illustrates a block diagram of a negative feedback MEMS device according to an alternative embodiment of the present invention, Fig. 5, which the Fig. 5A and Fig. 5B illustrates an alternative implementation of a MEMS device in which bias voltage is applied to the stationary plates while the movable plates form the sensing plates, Fig. 6, which the Fig. 6A and Fig. 6B illustrates a MEMS circuit having capacitive positive feedback according to another alternative embodiment of the invention, Fig. 7, which the Fig. 7A and Fig. 7B illustrates a MEMS circuit having capacitive negative feedback according to another alternative embodiment of the invention, Fig. 8, which the Fig. 8A and Fig. 8B illustrates a MEMS circuit having more than two movable membranes that are independently coupled, according to an alternative embodiment of the present invention, Fig. 9 illustrates a cross-sectional view of a MEMS device according to an embodiment of the present invention, Fig. 10, which the Fig. 10A and Fig. 10B illustrates a plan view of the first movable plate and the second movable plate according to an embodiment of the present invention, Fig. 11 illustrates a cross-sectional view of an alternative MEMS device according to an embodiment of the present invention, and Fig. 12, which the Fig. 12A-12E, a MEMS device during different stages of manufacture according to an embodiment of the present invention.

[0047] Corresponding reference numerals and symbols in the various figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0048] The making and using of various embodiments are discussed below. However, it is understood that the present invention provides many applicable inventive concepts that can be practiced in a wide variety of specific contexts. The specific embodiments discussed illustrate only specific ways of making and using the invention and do not limit the scope of the invention.

[0049] A conventional MEMS sensor circuit in Fig. 1. The MEMS device 100 shown in Fig. 1 is a dual-backplate device comprising two stationary backplates: a first stationary plate 101 and a second stationary plate 105. A movable plate 102 is disposed between the first and second stationary plates 101 and 105. The output from the MEMS device 100 is input to the first and second amplification stages 60 and 70. A filter may be inserted between the voltage source and the MEMS sensor.

[0050] A dual backplate MEMS device therefore has two capacitors that change in opposite directions due to an incident pressure.

[0051] To handle MEMS manufacturing tolerances and support different output sensitivity specifications, the sensor circuit must provide the ability to adjust gains other than unity. One way to adjust the gain is to provide additional gain stages or to use amplifiers other than source followers. However, such techniques increase amplifier noise and can also result in higher power consumption. Inverting amplifiers would also reduce the linearity of the system.

[0052] Another way to adjust the gain is to adjust the bias of the voltage source or the potential at the membrane. However, this method can only reduce the signal delivered by the MEMS device (under optimal bias conditions), resulting in a less than optimal signal-to-noise ratio (SNR) of the system. Additionally, the bias affects both signal paths in the same way (the same gain factor). Therefore, adjusting the bias does not provide a solution for applying different gains to each of the two signal paths, for example, to optimize a differential signal or create two different channels.

[0053] Embodiments of the invention improve gain without compromising the linearity (or vice versa) of the MEMS device by using at least a dual membrane concept. In various embodiments of the present invention, the MEMS device achieves a balance between performance, efficiency, and cost.

[0054] Fig. 2 illustrates a MEMS device and a front-end circuit according to an embodiment of the present invention.

[0055] Embodiments of the present invention implement a dual backplate, dual membrane MEMS device to significantly improve linearity and gain. Referring to Fig. 2, a MEMS device 200 includes a first stationary plate 101, a second stationary plate 105, a first movable plate 102, and a second movable plate 103. In one embodiment, a linear readout circuit is used. As illustrated, the first movable plate 102 and the second movable plate 103 are coupled to a low-impedance voltage source, while the first stationary plate 101 and the second stationary plate 105 are sensed with high impedance. The MEMS device 200 operates in constant load mode, and the output voltage at the first and second outputs is proportional to the membrane movement, i.e., movement of the first movable plate 102 and the second movable plate 103, respectively.

[0056] Various embodiments of the present invention describe and employ passive feedback techniques, for example, around the source follower and the high-voltage bias filter. To implement such a technique, the MEMS device 200 comprises two separate electrically isolated parts: the first movable plate 102 and the second movable plate 103. While the first movable plate 102 and the second movable plate 103 are electrically isolated from each other (not directly or capacitively coupled), they are mechanically connected such that when the first movable plate 102 moves toward the first stationary plate 101, the second movable plate 103 moves away from the second stationary plate 105. In other words, the first movable plate 102 is rigidly coupled to the second movable plate 103. In various embodiments, the MEMS device 200 therefore comprises four functionally relevant terminals.

[0057] The first stationary plate 101 and the second stationary plate 105 detect the movement of the first movable plate 102 and the second movable plate 103, respectively, as a corresponding load change, which is input to the first and second amplification stages 60 and 70, which have a gain factor of one.

[0058] The high-voltage bias branch filter comprises two parts, a first filter circuit 11 and a second filter circuit 111. In one or more embodiments, the first filter circuit 11 and the second filter circuit 111 may comprise different low-pass filters. In one embodiment, the first filter circuit 11 may comprise a first resistor 10 with a first capacitive filter 20, and the second filter circuit 111 may comprise a second resistor 110 and a second capacitive filter 120. In particular, due to the two separate paths, the response at the first stationary plate 101 and the second stationary plate 105 can be adjusted independently. The gains of both paths can be set to similar levels. Advantageously, this embodiment requires minimal power consumption.

[0059] In various embodiments, the first resistor 10 and the second resistor 110 may be formed from linear diodes, non-linear diodes, and / or metal / insulator / semiconductor transistors (operating in reverse). Similarly, the first capacitive filter 20 and the second capacitive filter 120 may comprise metal / insulator / semiconductor capacitors.

[0060] In various embodiments, the values ​​of the first resistor 10, the first capacitive filter 20, the second resistor 110, and the second capacitive filter 120 may be programmable. For example, they may be programmed during initial factory testing after manufacturing. In one or more embodiments, the feedback loop may be implemented as part of an ASIC chip, while the MEMS device 200 may be implemented in a MEMS wafer. In other embodiments, some of the components of the feedback loop may be implemented within the MEMS wafer.

[0061] The detection circuit 35 can be implemented with a source-follower circuit having a first gain stage 60 and a second gain stage 70 due to their higher noise performance compared to the higher-impedance detection circuits. Both the first gain stage 60 and the second gain stage 70 can have zero gain, i.e., a gain equal to one. A disadvantage of the source-follower circuit is that it cannot provide programmable gain, but advantageously (ideally) the gain is unity, which can be tightly controlled.

[0062] Fig. Figure 3 illustrates a differential positive feedback microphone according to an embodiment of the present invention.

[0063] Fig. Figure 3 illustrates gain enhancement through a positive feedback loop according to an alternative embodiment of the present invention. In this embodiment, positive feedback is applied from the output of the gain stage to the movable plate, for example, a first feedback loop between the output of the first gain stage 60 and the first movable plate 102, and a second feedback loop between the output of the second gain stage 70 and the second movable plate 103. In particular, due to the two separate feedback loops, the corresponding response at the first stationary plate 101 and the second stationary plate 105 can be adjusted independently. Furthermore, by applying positive feedback from the output to the filter bias node, the available output signal is actually boosted, even though the first and second gain stages 60 around 70 have a unity gain.

[0064] In various embodiments, the gain enhancement is achieved using positive feedback without active circuitry and without significant noise and performance degradation. In this embodiment, the gain at the first gain stage 60 (A60) is approximately as follows (assuming that the capacitance of the capacitive filter is much larger than the variable capacitance between the plates of the MEMS device 200): A60 = 1 + C130 / C120, where C130 is the capacitance of the first capacitor 130 and C120 is the capacitance of the first capacitive filter 120. Similarly, the gain at the second gain stage 70 (A70) is approximately as follows: A70 = 1 + C140 / C20, where C140 is the capacitance of the second capacitor 140 and C20 is the capacitance of the second capacitive filter 20.In some embodiments, the capacitance of the first capacitor 130 and the capacitance of the second capacitor 140 may be approximately equal. Similarly, the capacitance of the first capacitive filter 120 may be equal to the capacitance of the second capacitive filter 20.

[0065] Fig. 4 illustrates a block diagram of a negative feedback MEMS sensor according to an alternative embodiment of the present invention.

[0066] With reference to Fig. 4, in this embodiment, the output of the gain stages is coupled to the opposite movable plate node of the MEMS device 200. Unlike the previous embodiment, in which the gain was increased using positive feedback, this embodiment implements attenuation using negative feedback. As shown in Fig. 4, the second capacitor 140 is coupled to the first movable plate 102, while the first capacitor 130 is coupled to the second movable plate 103.

[0067] In this embodiment, the gain at the first gain stage 60 (A60) is approximately as follows (assuming that the capacitance of the capacitive filter is much larger than the variable capacitance between the plates of the MEMS device 200): A60 = 1 - C130 / C20, and the gain at the second gain stage 70 (A70) is approximately as follows: A70 = 1 - C140 / C120. This embodiment therefore results in negative gain.

[0068] In various embodiments, the structure of the MEMS device 200 is changed from a single movable membrane to at least two movable membranes that are electrically isolated from each other but independently biased, so that the movable membranes can be used with passive feedback structures and the differential topology allows gain and attenuation adjustment with capacitive feedback.

[0069] The Fig. 5 to 7 illustrate an alternative implementation of the Fig. Circuits described in 2 to 4.

[0070] Fig. Figure 5A illustrates an alternative implementation of a MEMS device 200 in which bias is applied to the stationary plates while the movable plates are sensed and coupled to gain stages for further processing. In this embodiment, the bias is applied to the first stationary plate 101 through a first filter comprising a first resistor 100 and a first capacitive filter 120, and to the second stationary plate 105 through a second filter comprising a second resistor 10 and a second capacitive filter 20. As with the embodiment described previously with reference to Fig. 2, the bias signal at the first node coupled to the first stationary plate 101 and the second stationary plate 105 is independently varied using the filters.

[0071] Fig. Figure 5B illustrates an alternative embodiment using a single voltage source.

[0072] Fig. 6, which the Fig. 6A and Fig. 6B illustrates a MEMS circuit having capacitive positive feedback according to another alternative embodiment of the invention.

[0073] As in the embodiment using the Fig. 3, are described with reference to Fig. 6A, a first capacitor 130 and a second capacitor 140 are used to form two independent positive feedback loops to independently support varying the bias signal at the node coupled to the first stationary plate 101 and the second stationary plate 105. This embodiment implements positive gain at the outputs of the first gain stage 60 and the second gain stage 70. Similarly, in Fig. 6B, the first capacitor 130 is coupled to the first movable plate 102, while the second capacitor 140 is coupled to the second movable plate 103 to provide positive gain.

[0074] Fig. 7, which the Fig. 7A and Fig. 7B illustrates a MEMS circuit having capacitive negative feedback according to another alternative embodiment of the invention.

[0075] As in Fig. 7A, this embodiment uses feedback similar to that shown in Fig. 4. The first capacitor 130 is coupled to the second stationary plate 105, and the second capacitor 140 is coupled to the first stationary plate 101, thereby creating independent negative feedback loops. Similarly, in Fig. 7B, the first capacitor 130 is coupled to the second movable plate 103, while the second capacitor 140 is coupled to the first movable plate 102 to provide negative feedback.

[0076] Fig. 8, which the Fig. 8A and Fig. 8B illustrates a MEMS circuit having more than two movable membranes that are independently coupled, according to an alternative embodiment of the present invention. Fig. Figure 8B illustrates an enlarged view of the MEMS device used in Fig. 8A is illustrated.

[0077] With reference to Fig. 8A and Fig. 8B, the movable mass comprises a first movable plate 102 and a second movable plate 103, as described in the above embodiments. Furthermore, the movable mass comprises a third movable plate 104 and a fourth movable plate 106, as shown in Fig. 8. The third movable plate 104 is capacitively coupled to a third stationary plate 108, while the fourth movable plate 106 is capacitively coupled to a fourth stationary plate 109. Each of the movable plates may be coupled using separate and independent filter circuits. In one case, for example, the third movable plate 104 may be coupled to a second voltage source through a filter having a third resistor 215 and a third capacitor 225, while the fourth movable plate 106 may be coupled to the second voltage source through another filter having a fourth resistor 310 and a fourth capacitor 320. The output of the third stationary plate 108 and the fourth stationary plate 109 may be coupled to respective gain stages 60' and 70'.

[0078] Furthermore, as an illustration in Fig. 8B shows the first and second movable plates 102 and 103 and the first and second stationary plates 101 and 105 in an embodiment with different dimensions.

[0079] Embodiments of the present invention therefore describe a differential capacitive microphone with improved gain, the use of which allows for the subtraction of common-mode noise. Such differential capacitive microphones can exhibit better performance than other microphones, for example, with higher sensitivity due to the additional capacitor, higher controllable bias, and better linearity.

[0080] In various embodiments, the MEMS circuits used in the Fig. 2 to 8 may at any time consist of a MEMS device comprising a microphone, oscillators, resonators, mechanical, pressure sensors, motion sensors, etc.

[0081] Fig. 9 illustrates a cross-sectional view of a MEMS device according to an embodiment of the present invention.

[0082] In various embodiments, Fig. 9 a MEMS device incorporating the embodiments of the MEMS circuit shown in the Fig. 2 to 8. With reference to Fig. 9, the MEMS device 200 includes a substrate 210 having a backside cavity 230. The backside cavity 230 extends continuously from the backside of the substrate 210 to the frontside of the substrate 210.

[0083] A first stationary plate 101 and a second stationary plate 105 are arranged above the back cavity 230. The stationary plates may also be called back plates.

[0084] In one or more embodiments, the MEMS device includes a membrane layer having a first movable plate 102 and a second movable plate 103 spaced apart from the first movable plate 102, all disposed above the substrate 210. The membrane layer may be supported above the substrate 210 by the support structure 220, which may also include separate support structures for the membrane layer and the stationary plates. In one or more embodiments, the first and second movable plates 102 and 103 are circular.

[0085] Additionally, a first cavity 250 is disposed between the first stationary plate 101 and the first movable plate 102, while a second cavity 240 is disposed between the second stationary plate 105 and the second movable plate 103. The first and second movable plates are therefore anchored along the peripheral area but otherwise freely suspended. The presence of the first cavity 240 and the second cavity 250 allows the first and second movable plates 102 and 103 to move freely.

[0086] In various embodiments, the first movable plate 102 is electrically isolated from the second electrical plate 103. In one or more embodiments, the first movable plate 102 is not capacitively coupled to the second movable plate 103, i.e., the capacitive coupling is minimized or substantially zero. The intermediate layer 260 may thus be made of an insulating material, for example, a low-k dielectric, to prevent capacitive coupling.

[0087] In various embodiments, the first movable plate 102, the second movable plate 103, and the intermediate layer 260 are mechanically coupled or connected as an integral unit such that they oscillate with each other. Therefore, the first movable plate 102 moves toward the first stationary plate 101, and the second movable plate 103 simultaneously moves away from the second stationary plate 105.

[0088] The first and second stationary plates 101 and 105 may also have a plurality of protrusions on the side facing the membrane layer to prevent the membrane layer from sticking to the membrane layer. The first and second plates 101 and 105 may also have a plurality of holes 170. The plurality of holes 170 may be used during the manufacture of the internal cavities by providing a hole for the passage of the etching liquid. Additionally, the plurality of holes 170 may provide an air passage during vibration of the membrane layer and therefore minimize damping effects. Due to the plurality of holes 170, the first and second stationary plates 101 and 105 are (less) insensitive to incident acoustic pressure.In contrast, the first and second movable plates 102 and 103 are effectively attached to the substrate 210 by springs and therefore vibrate with the incident sound pressure. The MEMS device 200 can be enclosed in a sealed chamber.

[0089] A first contact 45 may be formed on the surface of the support structure 220 to electrically couple the first stationary plate 101. Additionally, second contacts 55, third contacts 65, and fourth contacts 75 may be used to electrically couple the first movable plate 102, the second movable plate 103, and the second stationary plate 105, respectively. Thus, the first movable plate 102 and the second movable plate 103 may be coupled to different potential nodes, even though they move together as a mechanical mass unit.

[0090] In various embodiments, the locations of the second contacts 55 are selected to be as far away from the third contacts 65 as possible to prevent capacitive coupling. In various embodiments, the intermediate layer 260 is designed not to impair the mechanical behavior of the membrane system, for example, because it is designed to be a non-conductive, low-voltage layer. In another alternative embodiment, the intermediate layer 260 is used to improve the robustness of the membrane system compared to a single-layer membrane. The two conductive layers, i.e., the first movable plate 102 and the second movable plate 103, may not be the same material or the same size in various embodiments.

[0091] Fig. 10, which the Fig. 10A and Fig. 10B illustrates a plan view of the first movable plate and the second movable plate according to an embodiment of the present invention.

[0092] In various embodiments, the first movable plate 102 and second movable plate 103 can be fabricated to minimize capacitive coupling. In one embodiment, the overlap between the conductive portions of the first movable plate 102 and the conductive portions of the first movable plate 102 and the second movable plate 103 is minimized.

[0093] Fig. For example, Figure 10A illustrates a first movable plate 102 having alternating conductive regions and insulating regions. For example, the shaded box A11 has a conductive region, while the unshaded box A21 has an insulating region.

[0094] In contrast, Fig. 10B the corresponding area of ​​the second movable plate 103, which is located directly below the first movable plate 102. As Fig. 10A, the unshaded box A11 in Fig. 10B has an insulating region, while the shaded box A21 has a conductive region. The pattern in the second movable plate 103 is therefore reversed from the pattern in the first movable plate 102.

[0095] Fig. 11 illustrates an alternative MEMS device according to an embodiment of the present invention.

[0096] In this embodiment, the capacitive coupling between the first movable plate 102 and the second movable plate 103 is minimized by introducing an air gap or multiple small cavities. The first movable plate 102 is still rigidly mechanically coupled to the second movable plate 103 using connections 270, which are support posts.

[0097] Fig. 12, which the Fig. 12A-12E illustrates a MEMS device during different stages of fabrication according to an embodiment of the present invention.

[0098] Fig. 12A illustrates a semiconductor substrate after forming the first stationary plate of the MEMS structure according to an embodiment of the present invention.

[0099] Fig. 12A illustrates a support structure 220 formed above a substrate 210. The substrate 210 may be a semiconductor substrate in various embodiments. The substrate 210 may be a bulk semiconductor substrate or, in some embodiments, a semiconductor-on-insulator substrate. Some examples of the substrate 210 include a bulk monocrystalline silicon substrate (or a layer grown thereon or otherwise formed therein), a layer of {110} silicon on a {100} silicon wafer, a layer of a silicon-on-insulator (SOI) wafer, or a layer of a germanium-on-insulator (GeOI) wafer. In various embodiments, the substrate 210 may include blanket epitaxial layers.In various embodiments, substrate 210 may be a silicon wafer, a germanium wafer, or a mixed semiconductor substrate comprising indium antimonide, indium arsenide, indium phosphide, gallium nitride, gallium arsenide, gallium antimonide, or combinations thereof. In one embodiment, substrate 210 may comprise a heteroepitaxial layer, such as gallium nitride grown on a silicon wafer.

[0100] The support structure 220 includes an insulating layer in various embodiments. In one embodiment, the support layer 220 may include a nitride layer. In another embodiment, the support structure 220 may include an oxide layer. In various embodiments, the support structure 220 may be formed by thermal oxidation, nitriding using vapor deposition processes such as chemical vapor deposition, plasma vapor deposition, and / or spin-on deposition. In various embodiments, the support structure 220 may include multiple layers applied at different stages of processing.

[0101] In one or more embodiments, the second stationary plate 105 is fabricated above the substrate 210. The second stationary plate 105 may include a polysilicon layer in one embodiment. For example, one or more polysilicon layers may be deposited and patterned to form the second stationary plate 105.

[0102] Fig. 12B illustrates a semiconductor substrate after forming the movable membrane layers of the MEMS structure according to an embodiment of the present invention.

[0103] The first and second movable plates 102 and 103 can then be manufactured. In one embodiment, the first and second movable plates 102 and 103 are patterned sequentially. For example, the second movable plate 103 can be deposited and patterned, followed by the deposition and patterning of the first movable plate 102. Alternatively, the first and second movable plates 102 and 103 can be deposited sequentially and patterned sequentially after the deposition of both layers.

[0104] The first and second movable plates 102 and 103 may comprise polysilicon. In an alternative embodiment, the first and second movable plates 102 and 103 comprise an amorphous silicon layer. In alternative embodiments, the first and second movable plates 102 and 103 comprise a conductive layer. The first and second movable plates 102 and 103, together with the intermediate layer, may have a thickness in various embodiments of about 100 nm to about 2000 nm. In one or more embodiments, the total thickness of the movable portion of the MEMS device may have a thickness of about 200 nm to about 1000 nm.

[0105] A layer of the intermediate layer 260 may be applied and optionally patterned after the application of the second movable plate 103, before the application of the first movable plate 102. Another layer of the support structure 220 may also be applied and planarized.

[0106] Fig. 12C illustrates a semiconductor substrate after forming the top stationary plate of the MEMS structure according to an embodiment of the present invention.

[0107] As in Fig. As illustrated in Figure 12C, the first stationary plate 101 is disposed above the movable membrane layers. The first plate 101 may be deposited and patterned. In one embodiment, one or more layers of polysilicone may be deposited and patterned. In one embodiment, another layer of the support structure 220 may be deposited and planarized after the first stationary plate 101 is deposited.

[0108] Fig. Figure 12D illustrates a semiconductor substrate after processing the front side of the MEMS structure according to an embodiment of the present invention.

[0109] Contacts may be formed to contact the substrate 210, the first stationary plate 101, the second stationary plate 105, the first movable plate 102, and the second movable plate 103. The contacts may be formed after masking and patterning the support structure 220.

[0110] The front side may be protected during subsequent backside processing by forming a protective layer 280. In various embodiments, the protective layer 280 may comprise silicon nitride or silicon oxide.

[0111] Fig. Figure 12E illustrates the MEMS device after forming a cavity according to an embodiment of the present invention.

[0112] The back processing is based on Fig. 12E to form a backside cavity 230. The substrate 210 is inverted or flipped to expose the backside. A protective resist is then applied and patterned to the exposed backside (not shown), and a portion of the substrate 210 in the MEMS device area is exposed. The exposed substrate 210 is etched until the portions of the support structure 220 are exposed.

[0113] In various embodiments, the substrate 210 may be etched using a Bosch process, or by applying a hard mask layer and etching the substrate 210 using a vertical reactive ion etching process. In one embodiment, only solder mask is used. If the solder mask budget is insufficient, the hard mask and vertical reactive ion etching can be used to achieve a smooth sidewall. However, this integration system requires the removal of remaining hard mask remnants. Therefore, in some embodiments, a Bosch process may be used without an additional hard mask.

[0114] In the Bosch process, an isotropic plasma etching step and a step for applying a passivation layer are alternated. The etching / deposition steps are repeated many times during the Bosch process. The plasma etching is designed to etch vertically, for example, using sulfur hexafluoride [SF6] in the plasma. The passivation layer is applied, for example, using octafluorocyclobutane as a source gas. Each individual step can be activated for a few seconds or less. The passivation layer protects the substrate 210 and prevents further etching. However, during the plasma etching phase, the directed ions bombarding the substrate remove the passivation layer at the bottom of the etched trench (but not along the sides), and etching continues. The Bosch process is stopped when the support structure 220 is exposed. The Bosch process creates sidewalls that are curved.

[0115] For example, with reference to Fig. 8, portions of the exposed support structure 220 are removed from a first cavity 240 and a second cavity 250, for example, using a wet etch chemistry. The wet etch may be selective in one or more embodiments. The release etch may be performed from the front and / or back of the substrate 210 in various embodiments. Subsequent processing may continue during conventional MEMS processing.

[0116] Although this invention has been described with reference to illustrative embodiments, this description should not be construed in a limiting manner. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will become apparent to those skilled in the art upon reference to the description. As an illustration, the embodiments shown in the Fig. 2 to 12 may be combined with each other to form alternative embodiments. It is therefore intended that the appended claims encompass any such modifications or embodiments.

[0117] Although the present invention and its advantages have been described in detail, it is clear that various changes, substitutions, and alterations may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. For example, it will be apparent to those skilled in the art that many of the features, functions, operations, and materials described herein may be varied while remaining within the scope of the present invention.

[0118] Furthermore, it is not intended that the scope of the present invention be limited to the particular embodiments of the process, machine, manufacture, structure of matter, means, methods, and steps described in the specification. As will be readily apparent to those skilled in the art from the disclosure of the present invention, processes, machines, manufacture, structure of matter, means, methods, or steps now existing or later developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be used in accordance with the present invention. The appended claims are therefore intended to include within their scope such processes, machines, manufacture, structure of matter, means, methods, or steps.

Claims

[1] A microelectromechanical system (MEMS) device comprising: a first plate (101), a second plate (105) arranged above the first plate (101), a first movable plate (102) arranged between the first plate (101) and the second plate (105), and a second movable plate (103) arranged between the first movable plate (102) and the second plate (105), wherein the MEMS device comprises a first input / output node coupled to the first plate (101), a second input / output node coupled to the second plate (105), a third input / output node coupled to the first movable plate (102), and a fourth input / output node coupled to the second movable plate (103), wherein the first input / output node is a different input / output node than the second input / output node, and wherein the third input / output node is a different input / output node than the fourth input / output node, wherein the first movable plate (102) is rigidly coupled to the second movable plate (103), wherein the first movable Plate (102) is designed,to be shielded from capacitive coupling with the second movable plate (103). [2] The device of claim 1, further comprising: a floor cavity (230) arranged under the first plate (101), a first cavity (250) disposed between the first plate (101) and the first movable plate (102), and a second cavity (240) disposed between the second plate (105) and the second movable plate (103). [3] Device according to one of the preceding claims, wherein the first movable plate (102) is adapted to be coupled to a different potential node than the second movable plate (103). [4] Apparatus according to any one of the preceding claims, wherein the first movable plate (102) is adapted to be coupled to a voltage source through a first filter, and wherein the second movable plate (103) is adapted to be coupled to the voltage source through a second filter. [5] The apparatus of claim 4, wherein the first filter and the second filter comprise different RC filters. [6] Apparatus according to any one of the preceding claims, wherein the first plate (101) is a first stationary plate, and wherein the second plate (105) is a second stationary plate. [7] The apparatus of claim 6, wherein the first stationary plate is adapted to be coupled to a voltage source through a first filter, and wherein the second stationary plate is adapted to be coupled to the voltage source through a second filter. [8] Apparatus according to claim 6 or 7, further comprising: a third movable plate and a fourth movable plate, and a third stationary plate and a fourth stationary plate, wherein the third movable plate is capacitively coupled to the third stationary plate, wherein the fourth movable plate is capacitively coupled to the fourth stationary plate. [9] The device of claim 8, wherein the first movable plate (102) is adapted to be coupled to a first voltage source through a first filter, wherein the second movable plate (103) is adapted to be coupled to the first voltage source through a second filter, wherein the third movable plate is adapted to be coupled to a second voltage source through a third filter, and wherein the fourth movable plate is adapted to be coupled to the second voltage source through a fourth filter. [10] The apparatus of claim 9, wherein the first filter and the second filter comprise different RC filters, and wherein the third filter and the fourth filter comprise different RC filters. [11] A method of forming a microelectromechanical system (MEMS) device, the method comprising: Forming a first plate in a substrate or above a substrate, Forming a second plate above the first plate, Forming a first movable plate between the first plate and the second plate and Forming a second movable plate between the first movable plate and the second plate, wherein coupling a first input / output node to the first plate (101), coupling a second input / output node to the second plate (105), coupling a third input / output node to the first movable plate (102) and Coupling a fourth input / output node to the second movable plate (103), wherein the first input / output node is a different input / output node than the second input / output node, and wherein the third input / output node is a different input / output node than the fourth input / output node, wherein the first movable plate (102) is rigidly coupled to the second movable plate (103), wherein the first movable plate (102) is configured to be shielded from capacitive coupling to the second movable plate (103).

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