Patent Description:
A microphone is an acoustic sensor converting an acoustic pressure wave to an analog signal. The microphone includes a microelectromechanical system (MEMS) sensor and an application specific integrated circuit (ASIC). The MEMS sensor and the ASIC are disposed in a single package. The MEMS sensor and the ASIC are connected together through suitable electrical connections.

The MEMS sensor functions as a variable capacitor having a fixed plate and a movable plate. The movable plate is also known as a membrane. When an acoustic pressure wave is applied to the MEMS sensor, the membrane is able to move in response to the acoustic pressure wave. The movement of the membrane relative to the fixed plate varies the distance between the membrane and the fixed plate of the variable capacitor, which in turn varies the capacitance of the variable capacitor. The variation of the capacitance is determined by various parameters of the acoustic pressure wave such as sound pressure levels of the acoustic pressure wave. The variation of the capacitance of the MEMS sensor is converted into an analog signal, which is fed into the ASIC for further processing.

As semiconductor technologies further advance, a sealed dual-membrane MEMS silicon microphone has emerged to further improve key performance characteristics such as low noise and reliability. The sealed dual-membrane MEMS silicon microphone typically includes a top membrane, a bottom membrane, a perforated stator, a top isolation layer between the peripheral portions of the top membrane and the stator, a bottom isolation layer between the peripheral portions of the bottom membrane and the stator, and at least one pillar coupled between the top membrane and the bottom membrane.

The sealed dual-membrane MEMS silicon microphone is good for reducing noise. But there is still ASIC noise. More capacity is necessary to further reduce the ASIC noise. There is a need to increase the capacity of the MEMS silicon microphone so as to meet the requirements of the ever-changing MEMS microphone.

<CIT> relates to a MEMS microphone with a low pressure region between a first and second diaphragm.

<CIT> relates to a micromechanical microphone.

<CIT> relates to a MEMS device and a process.

<CIT> relates to a differential MEMS device.

In accordance with an embodiment, an MEMS apparatus comprises the features of claim <NUM>.

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present disclosure.

The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to preferred embodiments in a specific context, namely a triple-membrane MEMS microphone. The present disclosure may also be applied, however, to a variety of MEMS devices. Hereinafter, various embodiments will be explained in detail with reference to the accompanying drawings.

<FIG> illustrates a cross sectional view of a first implementation of the triple-membrane MEMS microphone in accordance with various embodiments of the present disclosure. The triple-membrane MEMS microphone <NUM> comprises a first membrane <NUM>, a second membrane <NUM> and a third membrane <NUM> spaced apart from one another. As shown in <FIG>, the second membrane <NUM> is between the first membrane <NUM> and the third membrane <NUM>. In some embodiments, the first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM> may be formed of conductive materials. Furthermore, the first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM> are movable membranes.

The triple-membrane MEMS microphone <NUM> further comprise a first low pressure region <NUM>, a second low pressure region <NUM>, a plurality of pillars <NUM> and a plurality of first stators <NUM> and a plurality of second stators <NUM>. As shown in <FIG>, the first low pressure region <NUM> is between the first membrane <NUM> and the second membrane <NUM>. The second low pressure region <NUM> is between the second membrane <NUM> and third second membrane <NUM>. The plurality of first stators <NUM> is in the first low pressure region <NUM>. The plurality of second stators <NUM> is in the second low pressure region <NUM>. It should be noted that the plurality of first stators <NUM> shown in <FIG> may be from a single stator plane having a plurality of openings. As such, the plurality of first stators <NUM> may be alternatively referred to as a first stator <NUM>. Likewise, the plurality of second stators <NUM> shown in <FIG> may be from another single stator plane having a plurality of openings. As such, the plurality of second stators <NUM> may be alternatively referred to as a second stator <NUM>.

The triple-membrane MEMS microphone <NUM> is formed over a support substrate <NUM>. As shown in <FIG>, the peripheral portions of the first membrane <NUM> are on the support substrate <NUM>. A backside cavity <NUM> may be formed in the support substrate <NUM>. The backside cavity <NUM> is employed to allow the first membrane <NUM> to oscillate in response to a sound wave. According to various embodiments, the backside cavity <NUM> may formed in the support substrate <NUM> through various etching techniques such as isotropic gas phase etching, vapor etching, wet etching, isotropic dry etching, plasma etching, any combinations thereof and the like.

In some embodiments, the support substrate <NUM> may be a silicon substrate. Alternatively, the support substrate <NUM> may be formed of any suitable semiconductor materials. For example, the support substrate <NUM> may be formed of semiconductor materials such as germanium, silicon germanium, silicon carbide, gallium nitride, indium, indium gallium nitride, indium gallium arsenide, indium gallium zinc oxide, any combinations thereof and the like. Furthermore, the support substrate <NUM> may be formed of suitable compound semiconductor materials such as III-V compound semiconductor materials and/or II-VI compound semiconductor materials.

As shown in <FIG>, the first membrane <NUM> and the third membrane <NUM> form a chamber. In some embodiments, the chamber is a sealed chamber. The chamber includes the first low pressure region <NUM> and the second low pressure region <NUM>. The pressure inside the chamber is lower than the pressure outside the chamber. In other words, the first low pressure region and the second low pressure region have a pressure less than an outer pressure. In some embodiments, the outer pressure is a pressure outside the membranes (outside the chamber). The outer pressure is equal to an atmospheric pressure or an ambient pressure.

In some embodiments, the pressure inside the chamber may be a vacuum. In some embodiments, the pressure in the first low pressure region <NUM> may be different from that of the second low pressure region <NUM>. In alternative embodiments, the second membrane <NUM> may have a plurality of openings. As a result of having the plurality of openings in the second membrane <NUM>, the pressure in the first low pressure region <NUM> is equal to the pressure of the second low pressure region <NUM>.

As shown in <FIG>, each stator (e.g., first stator <NUM>) may comprise a first counter electrode element <NUM> and a second counter electrode element <NUM>. The second counter electrode element <NUM> may be spaced apart from the first counter electrode element <NUM>. More particularly, a counter electrode isolating layer is formed between the first counter electrode element <NUM> and the second counter electrode element <NUM>. In some embodiments, the counter electrode isolating layer may be formed of suitable dielectric materials such as a silicon oxide, a silicon nitride and the like.

In some embodiments, the first counter electrode element <NUM> and the second counter electrode element <NUM> may be formed of various metals such as copper, aluminum, silver, nickel, and various suitable alloys. Alternatively, the first counter electrode element <NUM> and the second counter electrode element <NUM> may be formed of various semiconductor materials which may be doped such that they are electrically conductive (e.g., a polysilicon layer heavily doped with boron, phosphorus, or arsenic).

As shown in <FIG>, the first stator <NUM> is at least partially arranged in the first low pressure region <NUM> or extends in the first low pressure region <NUM>. Likewise, the second stator <NUM> is at least partially arranged in the second low pressure region <NUM> or extends in the second low pressure region <NUM>.

<FIG> shows some portions of the stators may be supported at its periphery or circumference by a support structure (e.g., membrane isolation layers <NUM>-<NUM>). <FIG> also shows some portions of the stators appear to be "floating" within the low pressure regions <NUM> and <NUM>. It should be noted that the "floating" portions of the stators may be typically attached to the circumference of the stators.

The plurality of pillars <NUM> extends between the first membrane <NUM> and the third membrane <NUM>. More particularly, a first terminal of each pillar extends through the first membrane <NUM>. A second terminal of each pillar extends through the third membrane <NUM>. In some embodiments, one or more pillars are electrically conductive. The conductive pillar provides a mechanical and electrical coupling between at least two membranes. In alternative embodiments, the pillars are electrically insulating. The non-conductive pillars provide a mechanical coupling between at least two membranes.

The plurality of pillars <NUM> is mechanically coupled to the first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM>. As shown in <FIG>, the pillars <NUM> typically do not contact or touch the first stator <NUM> and the second stator <NUM>. The pillars <NUM> may pass through the stators <NUM> and <NUM> through openings or holes in the stators <NUM> and <NUM>.

In the process of fabricating the triple-membrane MEMS microphone <NUM>, the pillars <NUM> may be integrally formed with the first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM>. Hence, the first membrane <NUM>, the second membrane <NUM>, the third membrane <NUM>, and the pillars <NUM> may form an integral structure of the same material such as polycrystalline silicon and the like. Alternatively, the membranes <NUM>, <NUM>, <NUM> and the pillars <NUM> may be formed of different materials. For example, the first membrane <NUM> may be formed first on a surface of the support substrate <NUM> during a first deposition process. Subsequently, the pillars <NUM> and eventually also the other membranes <NUM> and <NUM> may be formed during subsequent deposition processes. In some embodiments, the pillars <NUM>, which ensure a mechanical coupling among the membranes, do not provide an electrical connection between the two membranes. The pillars <NUM> can be made of an insulating material, like silicon, nitride, silicon oxide, a polymer or a combination of the former materials, or a combination of the former material.

The support structure of the triple-membrane MEMS microphone <NUM> may have a stacked configuration. The support structure of the triple-membrane MEMS microphone <NUM> includes the support substrate <NUM>, a first membrane isolation layer <NUM>, a second membrane isolation layer <NUM>, a third membrane isolation layer <NUM> and a fourth membrane isolation layer <NUM>. In some embodiments, the peripheral portions of the membranes <NUM>, <NUM> and <NUM>, and the stators <NUM>, <NUM> may be in contact with the support structure as shown in <FIG>. In particular, <FIG> shows the various membrane isolation layers of the support structure and the membranes may be arranged on top of each other in the following order, for example: the first membrane <NUM>, the first membrane isolation layer <NUM>, the first counter electrode element of the first stator <NUM>, the counter electrode isolating layer of the first stator <NUM>, the second counter electrode element of the first stator <NUM>, the second membrane isolation layer <NUM>, the second membrane <NUM>, the third membrane isolation layer <NUM>, the first counter electrode element of the second stator <NUM>, the counter electrode isolating layer of the second stator <NUM>, the second counter electrode element of the second stator <NUM>, the fourth membrane isolation layer <NUM> and the third membrane <NUM>.

It should be noted that while <FIG> shows the membrane isolation layer (e.g., the first membrane isolation layer <NUM>) is of a vertical sidewall, for achieving high robustness, the membrane isolation layer may be a tapered sidewall. For example, the first membrane isolation layer <NUM> may be of a tapered sidewall oriented in a first direction. The second membrane isolation layer <NUM> may be of a tapered sidewall oriented in a second direction. The first direction and the second direction are opposite to each other.

After having the support structure shown in <FIG>, each membrane (e.g., first membrane <NUM>) comprises a movable portion and a fixed portion. The fixed portion of the first membrane <NUM> is, for example, mechanically connected to the support substrate <NUM> and the first membrane isolation layer <NUM>.

<FIG> shows the triple-membrane MEMS microphone <NUM> at its rest position, e.g. when no sound wave arrives at the membranes. The sound wave could cause the membranes <NUM>, <NUM> and <NUM> to be deflected. As shown in <FIG>, the third membrane <NUM> may be exposed to an ambient pressure and potentially a sound pressure. This top side of the third membrane <NUM> may also be regarded as a sound receiving main surface of the triple-membrane MEMS microphone <NUM>. Alternatively, the first membrane <NUM> may be exposed to an ambient pressure and potentially a sound pressure. This bottom side of the first membrane <NUM> may also be regarded as a sound receiving main surface of the triple-membrane MEMS microphone <NUM>.

In some embodiments, when sound waves are incident on the membranes (e.g., the top side of the third membrane <NUM>), the membranes may deflect and/or oscillate. A displacement of one membrane (e.g., the third membrane <NUM>) may result in the corresponding displacements of the second membrane <NUM> and the first membrane <NUM> if they are mechanically coupled to each other. The third membrane <NUM> may deflect in a direction substantially toward the second stator <NUM> while the second membrane <NUM> may simultaneously be deflected in substantially the same direction as the third membrane <NUM> and therefore may move away from the second stator <NUM>. Likewise, the second membrane <NUM> may deflect in a direction substantially toward the first stator <NUM> while the first membrane <NUM> may simultaneously be deflected in substantially the same direction as the second membrane <NUM> and therefore may move away from the first stator <NUM>.

In some embodiments, the top side of the third membrane <NUM> at which the sound may arrive, the total pressure may be equal to the sum of the normal pressure (e.g., the atmospheric pressure) and the sound pressure. Within the backside cavity <NUM>, only the normal atmospheric pressure may be present.

In some embodiments, the first membrane <NUM> and the first stator <NUM> form a first capacitor. The first stator <NUM> and the second membrane <NUM> form a second capacitor. The second membrane <NUM> and the second stator <NUM> form a third capacitor. The second stator <NUM> and the third membrane <NUM> form a fourth capacitor.

It should be noted that the capacitor arrangement (first, second, third and fourth capacitors) described above is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the first membrane <NUM> and the third membrane <NUM> could be made of a non-conductive material and be used essentially to provide robustness against electrical leakage. The first membrane <NUM> and the third membrane <NUM> could be designed so as to satisfy the membrane compliance requirement. Under such a capacitor arrangement, the first membrane <NUM> and the third membrane <NUM> would not form capacitors with the corresponding stators, and only the second membrane <NUM> would form a capacitor or two capacitors with one or two stators, which would then work like a standard single backplate microphone or like a dual backplate microphone.

In operation, the capacitance variations of the four capacitors are observed. A first capacitance variation is based on the first capacitor, which is formed between the first membrane <NUM> and the first stator <NUM>. A second capacitance variation is based on the second capacitor, which is formed between the first stator <NUM> and the second membrane <NUM>. A third capacitance variation is based on the third capacitor, which is formed between the second membrane <NUM> and the second stator <NUM>. A fourth capacitance variation is based on the fourth capacitor, which is formed between the second stator <NUM> and the third membrane <NUM>. The capacitances of these four capacitors vary in relation to the movement of the movable portions of the first, second and third membranes <NUM>, <NUM> and <NUM> with respect to the stators <NUM> and <NUM>. The movement of the movable portions of the membranes <NUM>, <NUM> and <NUM> is generated by, for example, sound pressure changes caused by speech, music and the like.

<FIG> illustrates a cross sectional view of a second implementation of the triple-membrane MEMS microphone in accordance with various embodiments of the present disclosure. The triple-membrane MEMS microphone <NUM> shown in <FIG> is similar to the triple-membrane MEMS microphone <NUM> shown in <FIG> except that the peripheral portion of the second membrane <NUM> is not in contact with the support structure. As shown in <FIG>, the second membrane <NUM> is smaller than the first membrane <NUM> and the third membrane <NUM>. The second membrane <NUM> is mechanically coupled to the first membrane <NUM> and the third membrane <NUM> through the plurality of pillars <NUM>.

The support structure of the triple-membrane MEMS microphone <NUM> shown in <FIG> includes the support substrate <NUM>, the first membrane isolation layer <NUM>, the second membrane isolation layer <NUM> and the third membrane isolation layer <NUM>. In some embodiments, the peripheral portions of the first membrane <NUM>, the third membrane <NUM>, the stator <NUM> and the stator <NUM> may be in contact with the support structure as shown in <FIG>. In particular, <FIG> shows the various membrane isolation layers of the support structure and the membranes may be arranged on top of each other in the following order, for example: the first membrane <NUM>, the first membrane isolation layer <NUM>, the first counter electrode element of the first stator <NUM>, the counter electrode isolating layer of the first stator <NUM>, the second counter electrode element of the first stator <NUM>, the second membrane isolation layer <NUM>, the first counter electrode element of the second stator <NUM>, the counter electrode isolating layer of the second stator <NUM>, the second counter electrode element of the second stator <NUM>, the third membrane isolation layer <NUM> and the third membrane <NUM>.

<FIG> illustrates a cross sectional view of a third implementation of the triple-membrane MEMS microphone in accordance with various embodiments of the present disclosure. The triple-membrane MEMS microphone <NUM> shown in <FIG> is similar to the triple-membrane MEMS microphone <NUM> shown in <FIG> except that the second membrane <NUM> has a plurality of openings <NUM>. The plurality of openings <NUM> of the second membrane <NUM> forms perforation holes (not shown but illustrated in <FIG>). The perforation holes are configured to facilitate a releasing process after an etching process is applied to the triple-membrane MEMS microphone <NUM>.

<FIG> illustrates a cross sectional view of a fourth implementation of the triple-membrane MEMS microphone in accordance with various embodiments of the present disclosure. The triple-membrane MEMS microphone <NUM> shown in <FIG> is similar to the triple-membrane MEMS microphone <NUM> shown in <FIG> except that the second membrane <NUM> has a plurality of openings <NUM>. The plurality of openings <NUM> of the second membrane <NUM> forms perforation holes (not shown but illustrated in <FIG>). The perforation holes are configured to facilitate a releasing process after an etching process is applied to the triple-membrane MEMS microphone <NUM>.

<FIG> illustrates a top view of the second membrane shown in <FIG> and <FIG> in accordance with various embodiments of the present disclosure. In some embodiments, the second membrane <NUM> is substantially circular in shape by way of example. It is within the scope and spirit of the disclosure for the second membrane <NUM> to comprise other shapes, such as, but not limited to oval, square, rectangular and the like.

The plurality of openings <NUM> of the second membrane <NUM> forms perforation holes as shown in <FIG>. It should be noted while <FIG> shows the plurality of openings <NUM> is aligned with each other to form a straight dotted line, this is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

<FIG> below illustrate perspective views of various implementations of the triple-membrane MEMS microphone in accordance with various embodiments of the present disclosure. For simplicity, the stators <NUM> and <NUM> of the triple-membrane MEMS microphone are not included in the perspective views shown in <FIG>.

<FIG> illustrates a perspective view of the first implementation of the triple-membrane MEMS phone shown in <FIG> in accordance with various embodiments of the present disclosure. The first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM> spaced apart from one another. As shown in <FIG>, the second membrane <NUM> is between the first membrane <NUM> and the third membrane <NUM>. The plurality of pillars <NUM> extends from the first membrane <NUM> to the third membrane <NUM>. The plurality of pillars <NUM> extends through the second membrane <NUM>.

In some embodiments, the plurality of pillars <NUM> is formed of non-conductive materials.

Furthermore, at least one pillar of the plurality of pillars <NUM> is mechanically coupled to the first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM>. The first membrane <NUM>, the second membrane <NUM> and the third membrane <NUM> are supported around the circumference by a support structure <NUM>. In some embodiments, the support structure <NUM> is implemented as the membrane isolation layers <NUM>-<NUM> shown in <FIG>.

In some embodiments, the membranes <NUM>, <NUM> and <NUM> are deflected in response to a pressure change caused by the sound wave. Electrical signals may be generated by the deflection of the membranes <NUM>, <NUM> and <NUM>. The electrical signals may be read out by a plurality of read-out circuits. The read-out circuits process the electrical signals and convert the electrical signals into useable information.

As shown in <FIG>, the first membrane <NUM> is read out through a first read-out connection terminal <NUM>. The first read-out connection terminal <NUM> may be connected to any position of the circumference of the first membrane <NUM>. Likewise, the second membrane <NUM> is read out through a second read-out connection terminal <NUM>. The second read-out connection terminal <NUM> may be connected to any position of the circumference of the second membrane <NUM>. The third membrane <NUM> is read out through a third read-out connection terminal <NUM>. The third read-out connection terminal <NUM> may be connected to any position of the circumference of the third membrane <NUM>.

<FIG> illustrates a perspective view of the second implementation of the triple-membrane MEMS phone shown in <FIG> in accordance with various embodiments of the present disclosure. The second implementation of the triple-membrane MEMS microphone shown in <FIG> is similar to the first implementation of the triple-membrane MEMS microphone shown in <FIG> except that the second membrane <NUM> is a free-standing element. More particularly, the outer peripheral portion of the main portion of the second membrane <NUM> is not in contact with the support structure <NUM>. As shown in <FIG>, the second membrane <NUM> is smaller than the first membrane <NUM> and the third membrane <NUM>. The second membrane <NUM> is mechanically coupled to the first membrane <NUM> and the third membrane <NUM> through the plurality of pillars <NUM>.

The read-out connections of the first membrane <NUM> and the third membrane <NUM> are similar to those shown in <FIG>, and hence are not discussed again herein. The second membrane <NUM> comprises a main portion and a panhandle portion. As shown in <FIG>, the panhandle portion of the second membrane <NUM> is a protruding structure extending from the main portion of the second membrane <NUM>. The main portion of the second membrane <NUM> is connected to a read-out circuit through the panhandle portion.

In some embodiments, the main portion of the second membrane <NUM> is circular in shape. The panhandle portion of the second membrane <NUM> is rectangular in shape. This shape of the panhandle portion of the second membrane <NUM> is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the panhandle portion of the second membrane <NUM> can be any other appropriate shape, such as square, round, oval, any combinations thereof and the like.

<FIG> illustrates another perspective view of the second implementation of the triple-membrane MEMS phone shown in <FIG> in accordance with various embodiments of the present disclosure. The triple-membrane MEMS microphone shown in <FIG> is similar to the triple-membrane MEMS device shown in <FIG> except that at least one pillar is configured to provide an electrical coupling between two membranes.

As shown in <FIG>, the pillar <NUM> in the dashed rectangle includes two portions. A lower portion is placed between the first membrane <NUM> and the second membrane <NUM>. An upper portion <NUM> is placed between the second membrane <NUM> and the third membrane <NUM>. A middle point of the pillar <NUM> is mechanically coupled to the second membrane <NUM>. The middle point is the interface between the lower portion and the upper portion.

In some embodiments, the lower portion of the pillar <NUM> is formed of a non-conductive material. The lower portion of the pillar <NUM> is a non-conductive portion. The upper portion <NUM> is formed of a conductive material. The upper portion of the pillar <NUM> is a conductive portion. The conductive upper portion <NUM> is configured to electrically couple two membranes. In particular, the conductive upper portion <NUM> provides an electrical path between the second membrane <NUM> and the third membrane <NUM>.

The third membrane <NUM> is divided into two electrically isolating portions by an insulating structure <NUM>. The insulating structure <NUM> is formed of any suitable dielectric materials.

As shown in <FIG>, a first portion <NUM> of the third membrane <NUM> is read out by the third read-out connection terminal <NUM>. The second membrane <NUM> is read out by the second read-out connection terminal <NUM> through the electrical path formed by the upper portion <NUM> and a second portion <NUM> of the third membrane <NUM>. As such, signals generated by the MEMS microphone are configured to flow between the second membrane <NUM> and the third membrane <NUM> through the upper portion <NUM> of the pillar <NUM>.

It should be noted that the connection shown in <FIG> is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the lower portion of the pillar <NUM> may be formed of a conductive material. The upper portion of the pillar <NUM> may be formed of a non-conductive material. The conductive lower portion is configured to electrically couple two membranes. In particular, the conductive lower portion provides an electrical path between the second membrane <NUM> and the first membrane <NUM>.

<FIG> illustrates a cross sectional view of a fifth implementation of the triple-membrane MEMS microphone in accordance with various embodiments of the present disclosure. The triple-membrane MEMS microphone <NUM> shown in <FIG> is similar to the triple-membrane MEMS microphone <NUM> shown in <FIG> except that the first membrane <NUM> is not in direct contact with the support substrate <NUM>. As shown in <FIG>, a membrane isolation layer <NUM> is placed between the first membrane <NUM> and the support substrate <NUM>.

It should be noted that depending on design needs, the additional membrane isolation layer <NUM> may be implemented in other implementations of the triple-membrane MEMS microphone shown in <FIG>.

Although embodiments of the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the disclosure as defined by the appended claims.

Claim 1:
A microelectromechanical system (MEMS) apparatus (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a first membrane (<NUM>), a second membrane (<NUM>) and a third membrane (<NUM>) spaced apart from one another, wherein the second membrane (<NUM>) is between the first membrane (<NUM>) and the third membrane (<NUM>);
a first low pressure region (<NUM>) between the first membrane (<NUM>) and the second membrane (<NUM>);
a second low pressure region (<NUM>) between the second membrane (<NUM>) and the third membrane (<NUM>), wherein the first low pressure region (<NUM>) and the second low pressure region (<NUM>) have a pressure less than an outer pressure;
a first stator (<NUM>) in the first low pressure region (<NUM>);
a second stator (<NUM>) in the second low pressure region (<NUM>); and
a plurality of pillars (<NUM>) which extends between the first membrane (<NUM>) and the third membrane (<NUM>), wherein the plurality of pillars (<NUM>) is mechanically coupled to the first membrane (<NUM>), the second membrane (<NUM>) and the third membrane (<NUM>).