JP6550141B2 - MEMS device - Google Patents

Description

  The present invention relates to a MEMS device, and more particularly to a high dynamic range MEMS device, to a Micro Electro Mechanical Systems (MEMS) device having a thin film type vibrator and a vibration or acoustic signal detection device using the same.

  In recent years, the effectiveness of detecting characteristic vibration waveforms or acoustic signals in many fields, such as failure prediction of mechanical devices, detection of natural disaster precursors, resource exploration, etc., has been examined, and high sensitivity for this application Sensing system is required. As a sensor used for such a system, a MEMS type sensor which can mass-produce a high-precision sensor inexpensively by applying semiconductor manufacturing technology has been developed.

  There are various operation principles and structures of the MEMS type sensor, but the MEMS type sensor provided with a thin film type vibrator (membrane) is enhanced in sensitivity by increasing the thickness of the vibrator and high frequency of the detection vibration frequency Is relatively easy.

  When the sensor sensitivity is enhanced by thinning the vibrator, the amplitude of the vibrator becomes excessive when a strong signal is input unexpectedly, and the possibility of breakage is increased. In order to prevent this, a method of utilizing elastic deformation of a flexible substrate holding a sensor chip (Patent Document 1), a method of providing a mechanical stopper (Patent Documents 2 and 3), a method by electrical means (Patent Document 4) , 5) is disclosed.

Japanese Patent Application Laid-Open No. 5-164775 JP 2008-30182 A Patent No. 4373994 gazette JP, 2014-153136, A JP, 2014-153363, A

  When the sensitivity of the sensor is increased and the above-described destruction prevention measures are implemented, there arises a problem that the signal can not be accurately detected even if the sensor does not break when a strong signal is input. In the configuration described in Patent Document 1, the signal waveform of the sensor is distorted because the substrate is elastically deformed by the strong signal input. In the configurations described in Patent Documents 2 and 3, when the diaphragm is mechanically pressed, signal detection becomes impossible. Further, in the configuration described in Patent Document 4, accurate signal detection also becomes difficult because signals of opposite phases are electrically added in order to suppress movement of the diaphragm. In the configuration described in Patent Document 5, changing the stiffness of the spring by applying a spring softening voltage is used as a protection means, but in this method, the stiffness changing means by voltage application is applied to a part of the integrated spring. There is a problem that the range of sensitivity change is small because of only giving, and the design of each operation mode with different sensitivity can not be optimized.

  An object of the present invention is to provide a MEMS type sensor that enables accurate signal measurement with high sensitivity and without being destroyed at the time of strong signal input.

  The above and other objects and novel features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

  The outline of typical ones of the inventions disclosed in the present application will be briefly described as follows.

  The MEMS type sensor according to the present invention has a configuration in which a plurality of MEMS elements having different sensor sensitivities are integrated. For example, in the case of using a membrane type MEMS element, the sensitivity can be enhanced by means such as reducing the thickness of the membrane or widening the distance between the fixing portions for holding the membrane. Conversely, it is possible to increase the resistance to breakage (reduce the sensitivity) by increasing the thickness of the membrane, adding a reinforcing beam structure to the membrane, or narrowing the distance between the fixed parts holding the membrane. is there. In general, in the MEMS manufacturing process to which the silicon integrated circuit manufacturing process is applied, the fabrication of the MEMS elements as described above is possible in a single wafer process. Therefore, it is easy to fabricate a plurality of MEMS elements on a single silicon wafer as described above. Note that the present invention does not exclude a method of integrating a plurality of types of MEMS elements manufactured by different wafer processes in the mounting stage.

  In the MEMS type sensor in which a plurality of MEMS elements are integrated as described above, means for increasing sensitivity and resistance to breakage will be described. Here, the case where two types of MEMS elements are integrated with high sensitivity and low sensitivity will be described. It goes without saying that combining three or more types of MEMS elements is also possible in the same manner.

  The two types of MEMS elements independently detect signals. When the signal input is small, high sensitivity characteristics are realized by mainly using the output signal of the high sensitivity element. At the same time, the low sensitivity element is also performing signal detection operation, and a trigger signal is generated promptly when the low sensitivity element detects a signal input slightly smaller than the high sensitivity element causing a risk of destruction. Let The trigger signal is connected to the high sensitivity element, and a constant DC voltage is applied to the electrode of the high sensitivity element in response to the trigger signal to apply a constant force to the high sensitivity element membrane, and the external force is high. It acts to protect the membrane against vibrational input.

  When the signal input drops again to such an extent that the high sensitivity element does not break down, the trigger signal is quickly released. As for the signal output from the MEMS sensor, the output signal of the low sensitivity element is adopted in the time zone in which the trigger signal is generated, and the output signal of the high sensitivity element is adopted in the other time zones. Signal synthesis is performed by using an electronic circuit. The electronic circuit processing described above can be realized in both analog circuits and digital circuits.

  The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

  According to the MEMS sensor according to the present invention, high sensitivity and high accuracy signal detection becomes possible by the high sensitivity MEMS element in minute signal input, and a powerful (or excessive, hereinafter the same) signal input is realized. The low sensitivity MEMS element enables signal detection in In the case of further strong signal input, a protective means for the highly sensitive MEMS element is provided. This enables signal detection with a wide dynamic range that can not be realized with conventional single MEMS elements, from minute signals to strong signals.

It is a principal part sectional view and a circuit diagram symbol of a MEMS sensor concerning Example 1 of the present invention. It is a time-series graph which shows the operation state of the MEMS sensor concerning Example 1 of the present invention. It is a flow chart explaining operation of a MEMS sensor concerning Example 1 of the present invention. It is a circuit diagram of a MEMS sensor concerning Example 1 of the present invention. It is a circuit diagram of a MEMS sensor concerning Example 2 of the present invention. It is explanatory drawing of the switch circuit which concerns on Example 3 of this invention. It is principal part sectional drawing of the transistor used for the switch circuit which concerns on Example 3 of this invention. It is a circuit diagram of a MEMS sensor concerning Example 4 of the present invention. It is a graph which shows the frequency characteristic of the high sensitivity element concerning the Example 5 of this invention, and a low sensitivity element. It is principal part sectional drawing explaining the mechanical protection of the high sensitivity element which concerns on Example 6 of this invention. It is principal part sectional drawing of a MEMS sensor containing the Helmholtz-type acoustic filter which concerns on Example 7 of this invention.

  In the following embodiments, when it is necessary for the sake of convenience, it will be described by dividing into a plurality of sections or embodiments, but they are not unrelated to each other unless specifically stated otherwise, one is the other And some or all of the variations, details, and supplementary explanations.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), it is particularly pronounced and clearly limited to a specific number in principle. It is not limited to the specific number except for the number, and may be more or less than the specific number.

  Furthermore, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily essential unless explicitly stated or considered to be obviously essential in principle. Needless to say.

  Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components etc., unless specifically stated otherwise and in principle not considered otherwise in principle, etc., It includes those that are similar or similar to the shape etc. The same applies to the above numerical values and ranges.

  Further, in all the drawings for describing the embodiments, the same reference numeral is attached to the same member in principle, and the repetitive description thereof will be omitted. In order to make the drawings easy to understand, hatching may be attached even to a plan view.

  A MEMS sensor according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an essential part of the MEMS sensor in the first embodiment. To form a capacitive MEMS device using a standard silicon CMOS integrated circuit fabrication process, as shown in FIG. 1 (a), forming a groove 102 on a silicon substrate 101, lower electrode to the bottom of the groove A membrane is formed on the upper side of the groove, and the formation of 103. Here, the membrane is composed of two types of film thickness, and comprises a membrane 106 corresponding to the high sensitivity element 104 and a membrane 107 corresponding to the low sensitivity element 105. An upper electrode 108 is formed on a portion of the upper surface of each of the membrane 106 and the membrane 107 so as to be opposed to the lower electrode 103. Here, for example, a tungsten film is used for the lower electrode 103, a polycrystalline silicon film is used for the membranes 106 and 107, and an aluminum film is used for the upper electrode 108, for example. Note that the lead wires from the lower electrode 103 and the upper electrode 107 or the contact portions leading thereto are omitted in this cross-sectional view.

  The high sensitivity element 104 and the low sensitivity element 105 do not necessarily have to be manufactured in a single integrated circuit manufacturing wafer process. As shown in FIG. 1B, chips of corresponding elements may be cut out from a plurality of wafers on which MEMS elements manufactured by different processes are mounted, and these may be mounted on a mounting substrate 109.

  If the above-mentioned MEMS element is described by the symbol (symbol) of a circuit diagram, it will be like FIG.1 (c) and (d). The high sensitivity element 104 has a lower electrode terminal 110 and an upper electrode terminal 111, and the low sensitivity element 105 has a lower electrode terminal 112 and an upper electrode terminal 113. In the usual case, the lower electrode terminals 110 and 112 are often grounded, so the ground symbol is used in FIG. 1 (c). It is also possible to use the high sensitivity element 104 and the low sensitivity element 105 in a floating state regardless of the description of this figure.

  The operation of the MEMS sensor according to the first embodiment of the present invention will be described with reference to FIG. 2 and FIG. In FIG. 2, the input signal waveform 120 is shown in the graph of the time 121 of the horizontal axis (this horizontal axis is the time axis) and the amplitude 122 of the vertical axis. In the figure, the dashed dotted line indicates the trigger level 123 which is set to a value slightly smaller than the amplitude at which the high sensitivity element 104 may break down. Here, the trigger level of the positive potential is defined as 123a, and the trigger level of the negative potential is defined as 123b. In the figure, the signal input exceeding the trigger level 123 occurs over two time zones. At this time, the electronic circuit connected to the low sensitivity element 105 quickly generates a trigger signal. In response to this, the high sensitivity element 104 generates a high sensitivity element protection voltage 124 as shown in FIG. The above operation is shown in the flowchart of FIG. In the normal state, it is measured by the high sensitivity element 104, and the absolute value of the output voltage is equal to or higher than the trigger level 123 or lower than the trigger level 123 constantly or at a constant cycle in the low sensitivity element 105. It is judged whether or not it is. When this determination is YES, that is, when the absolute value of the output voltage is less than the trigger level 123, the signal of the low sensitivity element 105 is output, and when NO, that is, the absolute value of the output voltage is more than the trigger level 123 If so, the signal of the high sensitivity element 104 is processed to be output.

  Next, the operation of the electronic circuit will be described with reference to FIG. Although FIG. 4 is divided into (a), (b) and (c), the terminals with the same name are connected to each other, and constitute one circuit as a whole. The upper electrode terminal 113 of the low sensitivity element 105 is connected to the input terminal 131 of the low sensitivity element capacitance-voltage converter 130 shown in FIG. 4A, and the signal of the low sensitivity element 105 is an analog signal output of the low sensitivity element. It is converted and output as 132. This signal is simultaneously connected to the positive voltage comparator 133 and the negative voltage comparator 134. A positive reference voltage 135 and a negative reference voltage 136 are applied to these comparators, respectively. These reference voltages can be adjusted, for example, to have an arbitrary reference voltage value after element fabrication depending on the breakdown resistance of the high sensitivity element 104. Therefore, even if some characteristic variations occur in the manufacturing process, it can be corrected by this function. The outputs of comparators 133 and 134 generate trigger signal 138 via OR circuit 137. The function of the OR circuit 137 is that it is necessary to generate a trigger signal 138 for the protection function for the sensitive element 104, whether the signal amplitude exceeds the reference voltages 135 to 136 in either positive or negative direction.

  The trigger signal 138 is led to two sets of switch circuits 139 and 140 as shown in FIG. 4 (b). Switch circuits 139 and 140 generate constant voltages equal to one another when trigger signal input 138 is generated. The outputs of the two switch circuits 139 and 140 are led to the differential input terminal of the high sensitivity device capacitance-voltage converter 141. When the trigger input 138 is generated, the high sensitivity element analog signal output voltage value 142 becomes zero because the same voltage is applied to the differential input. On the other hand, when the trigger signal 138 is not generated, the output of the switch circuit 139 is fixed to the ground potential, and the output terminal of the switch circuit 140 is in the open state. The output terminal 142 is connected to the output terminal 111 of the high sensitivity element 104. Since the output terminal of switch circuit 140 is in the open state and the differential input terminal of capacitor-voltage converter 141 for the high sensitivity element is also in the high impedance state, the output of high sensitivity element 104 is for loss without loss Guided to a capacitance-to-voltage converter 141, an accurate sensitive element analog signal output 142 is obtained.

  Next, as shown in FIG. 4C, the low sensitivity element analog signal output 132 and the high sensitivity element analog signal output 142 are independently converted to digital signals by the low sensitivity element AD converter 143 and the high sensitivity element AD converter 144, respectively. It is converted. These digital outputs are led to the digital signal processor 145, and in response to the trigger input 138, the signals of a plurality of elements having different sensitivities are synthesized to correspond to the flow chart shown in FIG.

  The total delay time of the capacitance-voltage converter 130, the positive voltage comparator 133, the negative voltage comparator 134, the OR circuit 137, and the switch circuit 140 is the inverse of the maximum frequency component of the signal handled by the MEMS sensor. Design to less than half of. This is necessary to prevent the high sensitivity element 104 from being destroyed by a high speed signal input that does not meet the response time of the circuit.

  This embodiment shows another configuration of the electronic circuit shown in the first embodiment. Descriptions of common parts are omitted.

  The output terminal 113 of the low sensitivity element 105 is connected to the low sensitivity element AD converter 143 from the low sensitivity element capacitance-voltage converter 130 shown in FIG. 5A and converted into a digital signal. Further, the low sensitivity element digital signal processor 147 corrects the frequency response characteristic of the low sensitivity element and performs noise removal processing to obtain the low sensitivity element digital output 148, and further to the digital signal processor 145 shown in FIG. It is led. In this processor, a logic control signal 149 corresponding to the trigger signal 138 shown in the first embodiment is obtained by digital processing.

  The circuit configuration shown in FIG. 5B has many points in common with FIG. 4B, and the trigger signal 138 may be replaced with the logic control signal 149. The circuit configuration of the high sensitivity device capacitance-voltage converter 141 and the subsequent circuits is the same as that for the low sensitivity device in FIG. 5A, and passes through the high sensitivity device AD converter 144 and the high sensitivity device digital signal processor 150. Thus, a high sensitivity element digital output 151 is obtained. This output 151 is led to the digital signal processor 145 of FIG. 5C to obtain the combined output 146 in the same manner as in the first embodiment. The request for the delay time of this circuit is also the same as in the first embodiment.

  The present example illustrates one mode of the switch circuit 140 shown in the first example and the second example. When the trigger signal 138 is not generated, the output terminal of the switch circuit needs to be in the open state. This requirement can be easily realized by using the p-channel MOSFET 152 in the output stage of the switch circuit. The power supply voltage VDD is applied to the source electrode (S) of the p-channel MOSFET 152, and the trigger signal 138 or a signal obtained by appropriately converting the signal level is applied to the gate electrode. First, since the p-channel MOSFET 152 is turned on in the state where the trigger signal 138 is generated, a voltage substantially equivalent to the power supply voltage VDD is supplied to the drain electrode (D) via the upper electrode terminal 111 and a high sensitivity element Is applied to the upper electrode 108 of the In the normal case, since the lower electrode 103 is at the ground potential, attraction of the membrane 106 to the lower electrode 103 is generated by voltage application to suppress vibration of the membrane, thereby preventing breakage. It is needless to say that an appropriate voltage is applied so that this attraction does not cause stiction (sticking of the membrane to the lower electrode).

  Next, the p-channel MOSFET 152 is turned off when the trigger signal 138 is not generated. At this time, the upper electrode terminal 111 viewed from the upper electrode 108 is in an open state in terms of direct current. However, since this MOSFET also serves as a capacitive load for the high sensitivity element 104, the sensitivity is reduced unless the capacitive load is reduced. One means for solving this is illustrated in FIG. In a normal MOSFET, as shown in FIG. 7A, the capacitance between the gate electrode 160 and the drain diffusion layer 161 is relatively large. In particular, in a conventional MOSFET, the diffusion layer 161 has a so-called diffusion layer overlap 162 structure in which the diffusion layer 161 extends to the lower part of the gate electrode. Therefore, the gate-drain capacitance is increased. In order to solve this, as shown in FIG. 7B, the load capacity as viewed from the high sensitivity element 104 is significantly reduced by the diffusion layer non-overlap 163 structure. Such a transistor can be easily manufactured by using an offset sidewall 164 in contact with the gate electrode 160.

  This embodiment is another embodiment of acquisition of the trigger signal 138 shown in Embodiment 1 and is illustrated with reference to FIG. The circuit diagram of FIG. 8 shares many points in common with the circuit diagram of FIG. 4A, and a differentiating circuit 170 is inserted between the output of the low sensitivity element capacitor-to-voltage converter 130 and the positive voltage comparator 133. There is. In the circuit of the first embodiment, when a signal with a very sharp rise and a large amplitude is input, there is also a possibility that the risk of breakage of the high sensitivity element may increase despite the design conditions shown in the first embodiment. Therefore, the risk can be mitigated by detecting the sharp rise of the signal by the differentiation circuit as shown in this embodiment and generating the trigger signal 138. When the trigger output 138 is generated, it is also effective to form a 4-input OR circuit by combining not only the OR circuit shown in FIG. 8 but also the OR circuit shown in FIG.

  Furthermore, in the case of digital processing of the second embodiment, the logic control signal 149 can be more accurately acquired by differentiating the digital signal.

  The frequency characteristics of the high sensitivity and low sensitivity elements which are desirable from the viewpoint of the performance function of the MEMS sensor shown in the first and second embodiments will be described with reference to FIG. In general, a membrane type MEMS device has a device-specific self-resonant frequency, and the response characteristic (sensitivity) sharply drops at frequencies higher than this. In the MEMS sensor of the present invention, the output of the low sensitivity element is configured to obtain a trigger output for preventing breakage of the high sensitivity element. Therefore, it is required that the frequency band of the low sensitivity element be wider. FIG. 9 exemplifies the sensitivity characteristic 180 of the high sensitivity element and the sensitivity characteristic 181 of the low sensitivity element. This graph shows the relative value of the output signal level of each element to a fixed acoustic vibration input level. Here, both sensitivities differ by about 20 dB, that is, by about 10 times. The frequency to be the self resonance point 182 of the high sensitivity element is lower than the frequency to be the self resonance point 183 of the low sensitivity element.

  In the second embodiment, digital signal processors 147 and 150 perform correction of frequency characteristics, that is, removal of peak characteristics. The dotted line in FIG. 9 indicates the frequency characteristic 184 corrected by the digital processing. Needless to say, the same processing can be performed by the digital signal processor 145 also in the first embodiment.

  According to the configurations shown in the first to fifth embodiments, it is possible to effectively destroy the high sensitivity element 104 in a state in which the electronic circuits connected to the high sensitivity element 104 and the low sensitivity element 105 are energized and operated normally. Can be prevented. However, in a state where the MEMS sensor is not functioning, for example, vibration during transportation or installation may destroy the high sensitivity element. In the present embodiment, means for preventing this destruction will be described with reference to FIG.

  First, an easily conceivable method is to always generate a trigger signal 138 in a non-functioning state of the MEMS sensor, that is, when measurement is not performed, and to continue applying a voltage to the upper electrode 108 of the high sensitivity element 104. is there. This may be provided with a circuit that automatically generates a trigger signal 138 when the measurement of the MEMS sensor is stopped. In addition, at the time of transportation or the like, power may be constantly supplied by a backup battery.

  As another method shown in the present embodiment as another method, as shown in FIG. 10A, the pressing plate 190 is installed on the upper electrode 108 of the high sensitivity element and driven by the piezoelectric actuator 191 to hold the pressing plate 190. By contacting the upper electrode 108, the membrane is protected from breakage. At this time, driving of the piezo actuator 191 is performed through the control circuit 192 operated by power supply from the backup battery 193. As shown in FIGS. 10 (b) and 10 (c), in the specific operation, the piezo actuator 191 expands to bring the pressure plate 190 into contact with the upper electrode 108 at the time of stop. In this case, a piezo actuator of a type that expands when a positive voltage is applied may be used. In operation, i.e., in measurement, no voltage is applied to the piezo actuator 191, and the pressure plate 190 does not inhibit the movement of the upper electrode 108 and the membrane 106.

  However, in the above method, it is necessary to keep supplying power at the time of shutdown. In the method illustrated in FIGS. 10 (d) and 10 (e), a piezo actuator of a type that contracts when a positive voltage is applied is used. Then, the positional relationship between the pressure plate 190 and the upper electrode 108 is adjusted so that the pressure plate 190 contacts the upper electrode 108 in a state where power is not supplied to the piezoelectric actuator. In such a state, the power supply is supplied to the piezoelectric actuator during operation to contract, and the pressure plate 190 does not inhibit the movement of the upper electrode 108 and the membrane 106.

  According to still another method, as illustrated in FIGS. 10 (f) and 10 (g), a piezo actuator 191 of a type that expands when a positive voltage is applied is used to press the plate 108 (and a member for holding the same). ) And the substrate 101. Further, the positional relationship between the pressure plate 190 and the upper electrode 108 is adjusted so that the pressure plate 190 contacts the upper electrode 108 in a state where power is not supplied to the piezoelectric actuator 191. In such a state, the power supply is supplied to the piezo actuator during operation to be extended, and the pressure plate 190 does not inhibit the movement of the upper electrode 108 and the membrane 106.

  In any of the above methods, it is possible to take measures to prevent the breakage of the high sensitivity element at the time of stopping without impairing the function as the MEMS sensor described in the first to fifth embodiments.

  According to the configurations shown in the first to fifth embodiments, even when a high frequency and large amplitude signal is input to the MEMS sensor, accurate measurement can be performed while preventing destruction of the high sensitivity element. In some applications, it may be desirable that the acoustic signal in a particular frequency range is very strong and it is desirable to attenuate it in advance and measure it with a MEMS sensor. In the present embodiment, a configuration corresponding to such a case will be described with reference to FIG. Helmholtz resonators are used to attenuate acoustic signals in a specific frequency range. The configuration shown in FIG. 11 is intended to attenuate signals of two types of frequency ranges, and includes two types of Helmholtz resonators 200 and 201 having different resonance frequencies. A cylindrical acoustic conduit is provided in the sensor cavity 202 surrounding the high sensitivity element 104 and the low sensitivity element 105, and an acoustic signal for measurement is input from an acoustic signal inlet 203 on the upper side. Then, when passing through the acoustic conduit, the Helmholtz resonators 200 and 201 provided on the inner wall attenuate the acoustic signal of the specific frequency range and prevent the acoustic signal of excessive amplitude from being input to the MEMS sensor. Can. Since the attenuation characteristics can be measured in advance, it is possible to correct the frequency characteristics as shown in the second and fifth embodiments without any problem.

101 silicon substrate 102 groove 103 lower electrode 104 high sensitivity element 105 low sensitivity element 106 membrane 107 corresponding to high sensitivity element membrane 108 corresponding to low sensitivity element upper electrode 109 mounting substrate 110 high Lower electrode terminal 111 of the sensitivity element Upper electrode terminal 112 of the high sensitivity element Lower electrode terminal 113 of the low sensitivity element Upper electrode terminal 120 of the low sensitivity element Input signal waveform 121 Time 122 An amplitude 123 Trigger level 124 High sensitivity element protection voltage 130 ... Low sensitivity element capacitance-voltage converter 131 ... Low sensitivity element capacitance-voltage converter input terminal 132 ... Low sensitivity element analog signal output 133 ... positive voltage comparator 134 ... for negative voltage Comparator 135 ... positive reference voltage 136 ... negative reference voltage 137 ... OR circuit 138 ... trigger signal 139 ... switch circuit 14 ... Switch circuit 141 ... Capacitance-voltage converter 142 for high sensitivity element ... High sensitivity element analog signal output 143 ... AD converter for low sensitivity element 144 ... AD converter for high sensitivity element 145 ... Digital signal processor 146 ... Combined output 147 ... Digital signal processor for low sensitivity element 148 ... Low sensitivity element digital output 149 ... Logic control signal 150 ... Digital signal processor for high sensitivity element 151 ... High sensitivity element digital output 152 ... p channel MOSFET
160: gate electrode 161: drain diffusion layer 162: diffusion layer overlap 163: diffusion layer non overlap 164: offset side wall 170: differentiation circuit 180: sensitivity characteristic of high sensitivity element 181: sensitivity characteristic of low sensitivity element 182: high sensitivity Element self-resonance point 183 ... Self-resonance point 184 of low sensitivity element ... Frequency characteristic 190 corrected by digital processing ... Suppression plate 191 ... Piezo actuator 192 ... Control circuit 193 ... Backup battery 200 ... Helmholtz resonator 201 ... Helmholtz resonator 202 ... sensor cavity 203 ... acoustic signal inlet

Claims (15)

Having first and second MEMS elements having a vibration system;
The first MEMS element has lower operation sensitivity relatively than the second MEMS element, and leads to element destruction by the input of an external vibration having a relatively high amplitude or high speed And
It has detection means for detecting in advance the large amplitude or high speed input of the strength at which the second MEMS element breaks down using the output signal of the first MEMS element,
Electrical output in a direction to inhibit movement of the vibration system of the second MEMS element with respect to the second MEMS element based on the amplitude equal to or greater than the predetermined strength detected by the detection means MEMS device characterized by giving. The output signal of the first MEMS element is employed in a time zone in which the amplitude exceeds the predetermined intensity or the speed exceeds the predetermined intensity, and in the time zone other than the time zone, the second MEMS element An output signal is employed, and a desired signal output is obtained by combining an output signal of the first MEMS element and an output signal of the second MEMS element in time series. MEMS devices.   The MEMS device according to claim 2, wherein frequency characteristics of the first and second MEMS elements are different.   The MEMS device according to claim 3, wherein a resonance frequency of the MEMS element is higher in the first MEMS element than in the second MEMS element.   4. The MEMS device according to claim 3, further comprising means for correcting a frequency characteristic unique to an output signal of the first and second MEMS elements. The output signal of the first MEMS element is employed in a time zone in which the amplitude exceeds the predetermined intensity or the speed exceeds the predetermined intensity, and in the time zone other than the time zone, the second MEMS element An output signal is used, and in signal synthesis for combining an output signal of the first MEMS element and an output signal of the second MEMS element in time series, the first MEMS element and the second MEMS element switching of the output signal, and said second signal amplitude to the threshold concerning speed according to the activation of the function of inhibiting the movement of the MEMS device, according to claim, characterized in that it is electrically adjustable structure The MEMS device according to 1.   The MEMS device according to claim 1, wherein a comparator using an operational amplifier circuit is used to detect a large amplitude input whose strength causes the first MEMS element to break down.   2. The MEMS device according to claim 1, wherein a differential circuit using an operational amplifier circuit is used to detect a high-speed input with a rapid rise until the first MEMS element breaks down. The electrical output in the direction to inhibit the movement of the first MEMS element applies a DC voltage to the one electrode of the pair of electrodes of the first MEMS element by a switch circuit with low output impedance,
The first stage of the amplifier for detecting the output signal of the first MEMS element is configured as a differential input, and to apply equal DC voltage to both terminals of the differential input,
In the state where the protection signal for the first MEMS element is not generated, the DC voltage application switch circuit increases the impedance seen from the output end, and the DC voltage application switch circuit sees the electrostatic seen from the output end The MEMS device of claim 1, wherein the MEMS device is configured to reduce capacitance.   By electrically connecting the drain electrode of the MOS transistor to one electrode of the pair of electrodes of the first MEMS element, the MOS transistor is brought into a conduction state, thereby suppressing the movement of the first MEMS element 10. The high dynamic range MEMS device of claim 9, wherein the high dynamic range MEMS device is configured to:   11. The MEMS device according to claim 10, wherein the MOS transistor uses a non-overlap transistor so that the drain capacitance in the cutoff state becomes small.   Digitally convert input signals for both more sensitive MEMS devices and less sensitive MEMS devices, process the signals with a digital signal processor and / or logic circuit, and detect large amplitude to high speed input The MEMS device according to claim 1, wherein the suppression of the more sensitive element is performed by generating a predetermined DC voltage from the detected digital signal.   The MEMS device according to claim 1, wherein a mechanical stopper operates when blocking movement of the first MEMS element in a non-operating state of the MEMS element.   14. The mechanical stopper according to claim 13, wherein the mechanical stopper is electrically driven, and in a state in which the power supply of the apparatus is shut off, the movement of the more sensitive element is inhibited. MEMS devices. 2. The MEMS device according to claim 1, wherein a Helmholtz-type filter having one or more resonance frequencies is installed in an acoustic vibration flow path leading to the first or second MEMS element.

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