Micro-electro-mechanical system microphone with dual backplates

Improving noise rejection of a micro-electro-mechanical system (MEMS) microphone by utilizing a membrane sandwiched between oppositely biased backplates is presented herein. The MEMS microphone can comprise a diaphragm that converts an acoustic pressure into an electrical signal; a first backplate capacitively coupled to a first side of the diaphragm—the first backplate biased at a first direct current (DC) voltage; a second backplate capacitively coupled to a second side of the diaphragm—the second backplate biased at a second DC voltage; and an electronic amplifier that buffers the electrical signal to generate a buffered output signal representing the acoustic pressure.

TECHNICAL FIELD

The subject disclosure generally relates to embodiments for a micro-electro-mechanical system (MEMS) microphone with dual backplates.

BACKGROUND

Conventionally, a MEMS microphone is susceptible to electromagnetic interference (EMI). In this regard, conventional microphone technologies have had some drawbacks, some of which may be noted with reference to the various embodiments described herein below.

DETAILED DESCRIPTION

Conventional microphone technologies have had some drawbacks with respect to susceptibility to EMI. Various embodiments disclosed herein can improve noise rejection of a MEMS microphone by utilizing a membrane sandwiched between oppositely biased backplates.

For example, a MEMS microphone can comprise a flexible diaphragm, e.g., comprising a semiconductor material, conductor, etc. that converts an acoustic pressure, e.g., sound pressure, sound waves, etc. into an electrical signal. Further, the MEMS microphone can comprise a first, e.g., perforated, backplate and a second, e.g., perforated, backplate—the first backplate capacitively coupled to a first side of the flexible diaphragm and biased at a first, e.g., positive, direct current (DC) voltage, and the second backplate capacitively coupled to a second side of the flexible diaphragm and biased at a second, e.g., negative, opposite, etc. DC voltage. Furthermore, the MEMS microphone can comprise an electronic amplifier that buffers the electrical signal from the flexible diaphragm to generate a buffered output signal, e.g., voltage output, current output, etc. representing the acoustic pressure.

In this regard, the first DC voltage and/or the second DC voltage facilitate measuring sound pressure induced deflections of the flexible diaphragm as a time varying voltage and/or current—the sound pressure induced deflections generating a change in capacitance between the flexible diaphragm and the first/second backplate as the flexible diaphragm moves towards/away from the first/second backplate.

Further, in embodiment(s), the first/second backplate comprises a conductor/semiconductor that can at least partially shield, e.g., the flexible diaphragm, from unwanted noise, electromagnetic radiation, etc.—the first DC voltage and the second DC voltage effectively acting, e.g., via small signal analysis, as respective ground potentials shunting externally generated electromagnetic radiation, EMI, noise, etc. to an alternating current (AC) ground.

In an embodiment, the MEMS microphone can comprise a first DC voltage source, e.g., positive charge pump, which biases the first backplate at the first DC voltage, e.g., a positive DC voltage. Further, the MEMS microphone can comprise a second DC voltage source, e.g., negative charge pump, that biases the second backplate at the second DC voltage, e.g., a negative DC voltage, e.g., equal in magnitude, but opposite in polarity, to the positive DC voltage. In this regard, electric fields generated by the first DC voltage/positive DC voltage and the second DC voltage/negative DC voltage can center the flexible diaphragm between the first backplate and the second backplate, e.g., to prevent, limit, etc. the flexible diaphragm from generating an asymmetrical buffered output signal in response to not being centered between the first backplate and the second backplate.

In another embodiment, the first DC voltage and the second DC voltage can control a sensitivity of the MEMS microphone with respect to decibels (dBs) of sound pressure level (SPL) that have been applied to the flexible diaphragm. For example, the dynamic range of the MEMS microphone can be increased, e.g., to detect a large SPL, e.g., greater than 140 dB, by increasing respective gaps between the flexible diaphragm and the first and second backplates, e.g., to prevent the flexible diaphragm from impacting, contacting, etc. the first/second backplates during application of the large SPL. In this regard, the first DC voltage and the second DC voltage can be increased to maintain a constant sensitivity of the MEMS microphone in response to the respective gaps being increased.

In yet another embodiment, a MEMS microphone can comprise a pair of oppositely biased, e.g., perforated, backplates, e.g., comprising a conductor, a semiconductor, etc. Further, the MEMS microphone can comprise an acoustic membrane, e.g., comprising a conductor, a semiconductor, etc. that is sandwiched, via respective air gaps, between the pair of oppositely biased backplates. Furthermore, the MEMS microphone can comprise an electronic amplifier that buffers the electrical signal to generate an output signal representing the acoustic vibration.

In an embodiment, a first backplate of the pair of oppositely biased backplates is biased with a first DC voltage, and a second backplate of the pair of oppositely biased backplates is biased with a second DC voltage, e.g., the first DC voltage being equal in magnitude, but opposite in polarity, to the second DC voltage.

In one embodiment, the MEMS microphone further comprises a first DC voltage source that generates the first DC voltage, and a second DC voltage source that generates the second DC voltage. In another embodiment, the first DC voltage and/or the second DC voltage controls a sensitivity of the MEMS microphone with respect to dBs of SPL that have been applied to the acoustic membrane.

In yet another embodiment, a first backplate of the pair of oppositely biased backplates and/or a second backplate of the pair of oppositely biased backplates shields the acoustic membrane from at least a portion of electromagnetic radiation.

In an embodiment, a method can comprise enclosing a diaphragm between backplates—the diaphragm converting an acoustic pressure into an electrical signal. Further, the method can comprise electrically coupling the backplates to respective DC voltage sources that oppositely bias the backplates, and electrically coupling the diaphragm to an electronic amplifier that generates a buffered signal representing the acoustic pressure.

In another embodiment, the method can comprise modifying, via the respective DC voltage sources, a sensitivity of the MEMS microphone with respect to dBs of SPL that have been applied to the diaphragm.

In yet another embodiment, the method can comprise at least partially shielding, via the backplates, the diaphragm from electromagnetic radiation.

Furthermore, to the extent that the terms “includes,” “has,” “contains,” and other similar words are used in either the detailed description or the appended claims, such terms are intended to be inclusive—in a manner similar to the term “comprising” as an open transition word—without precluding any additional or other elements. Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

Aspects of MEMS microphones, apparatus, devices, processes, and process blocks explained herein can be embodied within hardware, such as an application specific integrated circuit (ASIC) or the like. Moreover, the order in which some or all of the process blocks appear in each process should not be deemed limiting. Rather, it should be understood by a person of ordinary skill in the art having the benefit of the instant disclosure that some of the process blocks can be executed in a variety of orders not illustrated.

Furthermore, the word “exemplary” and/or “demonstrative” is used herein to mean serving as an example, instance, or illustration. For the avoidance of doubt, the subject matter disclosed herein is not limited by such examples. In addition, any aspect or design described herein as “exemplary” and/or “demonstrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it meant to preclude equivalent exemplary structures and techniques known to those of ordinary skill in the art having the benefit of the instant disclosure.

Conventional microphone technologies have had some drawbacks with respect to being susceptible to EMI. On the other hand, various embodiments disclosed herein can improve noise rejection of a MEMS microphone by sandwiching, via air gaps, an acoustic membrane between oppositely biased backplates. In this regard, and now referring toFIG. 1, MEMS microphone100can comprise MEMS acoustic sensor110and electronic amplifier120. In this regard, MEMS acoustic sensor110comprises flexible diaphragm114, e.g., comprising a semiconductor material, a conductor, etc. that converts an acoustic pressure, e.g., sound pressure, sound wave, etc. into an electrical signal, and perforated backplates (112,116), e.g., comprising a conductor, semiconductor, etc. that are capacitively coupled to respective sides of flexible diaphragm114. As illustrated byFIG. 1, perforated backplate112is biased by positive DC source102, e.g., positive charge pump, switch capacitor voltage source, etc. at a positive DC voltage (+VDC). Further, perforated backplate116is biased, oppositely biased, etc. by negative DC source104, e.g., negative charge pump, switch capacitor voltage source, etc. at a negative DC voltage (−VDC), e.g., which is equal, substantially equal, etc. in magnitude, but opposite in polarity, to the positive DC voltage source.

In this regard, the positive/negative DC voltage facilitates measuring acoustic pressure induced deflections of flexible diaphragm114as a time varying voltage and/or current—such deflections generating a change in capacitance between flexible diaphragm114and the perforated backplates. In turn, electronic amplifier120can buffer the time varying voltage and/or current as a buffered output representing the acoustic pressure.

For example, in the embodiment illustrated byFIG. 1, as a positive going acoustic pressure wave first meets, and passes through, perforated backplate116, it can deflect flexible diaphragm114away from perforated backplate116and towards perforated backplate112—causing a time varying voltage and/or current that can be detected via electronic amplifier120. In this regard, the negative DC voltage on perforated backplate116enables electronic amplifier120to generate a non-inverted transfer function with respect to the positive input acoustic pressure wave first meeting perforated backplate116, e.g., generating a positive going buffered output that is in phase with, or of the same polarity as, the positive going acoustic pressure wave.

In one embodiment, electronic amplifier120can generate the non-inverted transfer function in response to detecting an increase in capacitance between flexible diaphragm114and positively biased perforated backplate112as flexible diaphragm114moves towards positively biased perforated backplate112. In another embodiment, electronic amplifier120can generate the non-inverted transfer function in response to detecting a decrease in capacitance between flexible diaphragm114and negatively biased perforated backplate116as flexible diaphragm114moves away from negatively biased perforated backplate116.

In embodiment(s), positively biased perforated backplate112and negatively biased perforated backplate116can at least partially shield flexible diaphragm114, e.g., comprising a high impedance node, from unwanted noise, electromagnetic radiation, etc. In this regard, the biased perforated backplates can effectively act, e.g., via small signal analysis, as respective ground potentials shunting externally generated electromagnetic radiation, EMI, noise, etc. to a small signal analysis alternating current (AC) ground.

In other embodiment(s), the oppositely biased perforated backplates112and116can generate opposing electric fields that can center flexible diaphragm114between perforated backplates112and116, e.g., to prevent, limit, etc. flexible diaphragm114from generating an asymmetrical buffered output.

Referring now to an embodiment illustrated byFIG. 2, MEMS microphone200can comprise MEMS acoustic sensor210and electronic amplifier120. In this regard, MEMS acoustic sensor210comprises flexible diaphragm114, perforated backplate116, and non-perforated backplate212. As illustrated byFIG. 2, flexible diaphragm114can be positioned closer to negatively biased perforated backplate116, and farther from positively biased non-perforated backplate212—such backplates at least partially shielding flexible diaphragm114from unwanted noise, EMI, etc. Further, to account for the offset positioning of flexible diaphragm114with respect to the backplates, negative DC source104can bias perforated backplate116at a negative DC voltage that is greater in magnitude than a positive DC voltage biasing non-perforated backplate212, e.g., such biases generating non-balanced and opposing electric fields that can prevent, limit, etc. flexible diaphragm114from generating an asymmetrical buffered output, a non-linear response, e.g., preventing, limiting, etc. flexible diaphragm114from impacting, contacting, etc. the perforated and/or non-perforated backplate, etc.

In an embodiment illustrated byFIG. 3, as a positive going acoustic pressure wave first meets, and passes through, perforated backplate112, it can deflect flexible diaphragm114away from perforated backplate112and towards perforated backplate114—causing a time varying voltage and/or current that can be detected via electronic amplifier120. In this regard, the positive DC voltage on perforated backplate112can enable electronic amplifier120to generate an inverted transfer function with respect to the positive input acoustic pressure wave first meeting perforated backplate112, e.g., generating a negative going buffered output that is 180 degrees out of phase with, or opposite in polarity to, the positive going acoustic pressure wave.

Now referring toFIG. 4, a block diagram of a MEMS microphone (400) biased with programmable voltage sources is illustrated, in accordance with various embodiments. In this regard, programmable voltage sources410, e.g., charge pumps, switched capacitor voltage sources, etc. can comprise programmable negative DC voltage source402that can bias perforated backplate112at a programmable negative DC voltage (−VDC). Further, programmable voltage sources410can comprise programmable positive DC voltage source404that can bias perforated backplate116at a programmable positive DC voltage (+VDC), e.g., equal, substantially equal (e.g., within a few μV), etc., and opposite in sign, to −VDC.

In this regard, programmable voltage sources410can be configured to control a sensitivity of MEMS microphone400with respect to dBs of SPL that have been applied to flexible diaphragm114. For example, the dynamic range of MEMS microphone400can be increased, e.g., to detect a large SPL, e.g., greater than 140 dB, by increasing respective gaps between flexible diaphragm114and perforated backplates112and116, e.g., to prevent flexible diaphragm114from impacting, contacting, etc. perforated backplates112and116during application of the large SPL. In this regard, voltages generated by programmable voltage sources410can be increased to maintain a constant sensitivity of MEMS microphone500in response to the respective gaps being increased.

Referring now toFIGS. 5 and 6, a block diagram of a MEMS microphone (500) comprising a programmable bias component (510), and a block diagram of a MEMS microphone system environment (600) are illustrated, respectively, in accordance with various embodiments. Programmable bias component510comprises positive DC source102and negative DC source104, which comprise respective memory components (520,530), e.g., a programmable fuse, a non-volatile memory, a volatile memory, etc. that can store data for trimming, controlling, etc. component(s) of positive DC source102and negative DC source104, e.g., for setting, defining, etc. output bias voltages coupled to MEMS acoustic sensor110, e.g., +VDC, −VDC. In an embodiment illustrated byFIG. 6, system controller610, e.g., a processor, microcontroller, etc. can be communicatively coupled to MEMS microphone500to program, set, etc. the data stored in memory components520and530.

FIGS. 7-10illustrate methodologies associated with a MEMS microphone, in accordance with various non-limiting aspects of the disclosed subject matter. In this regard, as illustrated byFIG. 7, a diaphragm, flexible acoustic membrane, etc. can be enclosed, sandwiched (e.g., via air), etc. between a pair of backplates of the MEMS microphone, at710, for conversion of an acoustic pressure into an electrical signal.

At720, the pair of backplates can be electrically coupled to respective DC voltage sources, e.g., a positive DC voltage source and a negative DC voltage, that oppositely bias the pair of backplates to at least partially shield the diaphragm, flexible acoustic membrane, etc. from electromagnetic radiation, EMI, etc.

At730, the diaphragm, flexible acoustic membrane, etc. can be electrically coupled to an electronic amplifier that generates a buffered output signal representing the acoustic pressure.

Referring now toFIG. 8, at810, respective gaps between the diaphragm, flexible acoustic membrane, etc. and the pair of backplates can be increased for tolerating application of higher sound pressure levels being applied to the diaphragm, flexible acoustic membrane, etc.

At820, a sensitivity of the MEMS microphone with respect to dBs of SPL that have been applied to the diaphragm, flexible acoustic membrane, etc. can be modified via the respective DC voltage sources.

Now referring toFIG. 9, at910, the MEMS microphone can receive data from a system controller. At920, the MEMS microphone can store the data, e.g., in memory device(s). At930, the MEMS microphone can set, based on the data, output bias voltages for oppositely biasing the pair of backplates.

In the subject specification, terms such as “memory” and substantially any other information storage component relevant to operation and functionality of MEMS microphones and/or devices disclosed herein, e.g., memory component520, memory component530, etc. refer to “memory components,” or entities embodied in a “memory,” or components comprising the memory. It will be appreciated that the memory can include volatile memory and/or nonvolatile memory. By way of illustration, and not limitation, volatile memory, can include random access memory (RAM), which can act as external cache memory. By way of illustration and not limitation, RAM can include synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct Rambus dynamic RAM (DRDRAM), and/or Rambus dynamic RAM (RDRAM). In other embodiment(s) nonvolatile memory can include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable ROM (EEPROM), or flash memory. Additionally, the MEMS microphones and/or devices disclosed herein can comprise, without being limited to comprising, these and any other suitable types of memory.