CN114604817A

CN114604817A - Micro-electromechanical device and method of forming the same

Info

Publication number: CN114604817A
Application number: CN202011413995.6A
Authority: CN
Inventors: 夏佳杰
Original assignee: Vanguard International Semiconductor Corp
Current assignee: Vanguard International Semiconductor Corp
Priority date: 2020-12-07
Filing date: 2020-12-07
Publication date: 2022-06-10
Anticipated expiration: 2040-12-07
Also published as: CN114604817B

Abstract

The invention provides a micro-electromechanical device and a forming method thereof. The composite substrate includes a first semiconductor layer, an adhesive layer and a second semiconductor layer stacked in sequence from bottom to top. The cavity is arranged in the composite substrate, extends from the second semiconductor layer to the first semiconductor layer and does not penetrate through the first semiconductor layer. The piezoelectric stack structure is arranged on the composite substrate and comprises a suspension area positioned above the cavity. The mass block is arranged in the cavity and connected with the piezoelectric stack structure.

Description

Micro-electromechanical device and method of forming the same

Technical Field

The present invention relates to a micro-electromechanical device and a method for forming the same, and more particularly, to a micro-electromechanical device and a method for forming the same, which are applied to the field of acoustics.

Background

Micro-electromechanical system (MEMS) devices are micro mechanical elements manufactured by conventional semiconductor processes, and mechanical elements having micron dimensions are completed by semiconductor techniques such as deposition or selective etching of material layers. The mems device can operate by using electromagnetic (electromagnetic), electrostrictive (electrostrictive), thermoelectric (pyroelectric), piezoelectric (piezoelectric), or piezoresistive (piezoresistive) and has dual functions of electronics and mechanics, so it is commonly used in microelectronics, such as an accelerator (accelerometer), a gyroscope (gyroscope), a mirror (mirror), or an acoustic sensor (acoustic sensor).

In recent years, due to the rapid development of wireless bluetooth (TWS) headsets, mems accelerator products have been used to sense the vibration of sound, bringing a new field of view to acoustic transducers. The accelerator product of the micro electro mechanical system is arranged in the wireless Bluetooth headset, so that the wireless Bluetooth headset can still effectively capture sound even in the surrounding environment with high noise or more noise. However, since the mems accelerator products are commonly used in the field of mobile phones, the structural design is biased to be thick and large, so that the design requirement of the miniaturization of the wireless bluetooth headset cannot be satisfied. Thus, there is still a need for a new design of accelerator for use in the acoustic field.

Disclosure of Invention

The present invention provides a microelectromechanical device having a miniaturized proof mass (proof mass) that occupies a relatively small area relative to suspended structures such as cantilevers (cantilevers), diaphragms (diaphragms), and the like, and a method of forming the same. Through the arrangement mode, the micro-electromechanical device can be applied to a wireless Bluetooth headset, so that the voice vibration of a microphone is assisted.

To achieve the above objective, an embodiment of the present invention provides a mems device, which includes a composite substrate, a cavity, a piezoelectric stack structure, and a mass. The composite substrate comprises a first semiconductor layer, an adhesive layer and a second semiconductor layer which are stacked from bottom to top in sequence. The cavity is arranged in the first semiconductor layer, extends from the second semiconductor layer to the first semiconductor layer and does not penetrate through the first semiconductor layer. The piezoelectric stack is disposed on the composite substrate, the piezoelectric stack including a suspended region over the cavity. The mass block is disposed within the cavity and connected to the piezoelectric stack.

To achieve the above objective, an embodiment of the present invention provides a method for forming a micro-electromechanical device, comprising the following steps. Firstly, a composite substrate is provided, wherein the composite substrate comprises a first semiconductor layer, an adhesive layer and a second semiconductor layer which are sequentially stacked from bottom to top. And forming a cavity in the composite substrate, wherein the cavity extends from the second semiconductor layer to the first semiconductor layer and does not penetrate through the first semiconductor layer. Then, a piezoelectric stack structure is formed on the composite substrate, wherein the piezoelectric stack structure comprises a suspension area positioned above the cavity. Then, a mass is formed within the cavity, the mass being coupled to the piezoelectric stack.

Drawings

FIG. 1 is a top view of a micro-electromechanical device (MEMS device) after forming a cavity (cavity) according to the present invention.

Fig. 2 is a schematic sectional view taken along the line a-a' in fig. 1.

FIG. 3 is a cross-sectional view of a micro-electromechanical device of the present invention after trench formation.

FIG. 4 is a schematic top view of a MEMS device after an oxidation process is performed thereon.

Fig. 5 is a cross-sectional view of the micro-electromechanical device of fig. 4 along a cut line a-a'.

FIG. 6 is a top view of a MEMS device after forming a piezoelectric stack structure according to the present invention.

Fig. 7 is a cross-sectional view of the micro-electromechanical device of fig. 6 along a cut line a-a'.

FIG. 8 is a cross-sectional view of a micro-electromechanical device according to the present invention after thinning of the composite substrate.

FIG. 9 is a top view of a MEMS device after release of the piezo-electric stack structure in accordance with the present invention.

Fig. 10 is a cross-sectional view of the micro-electromechanical device of fig. 9 along a cut line a-a'.

FIG. 11 is a top view of a MEMS device in accordance with another embodiment of the present invention.

FIG. 12 is a cross-sectional schematic view of a MEMS device in accordance with another embodiment of the present invention.

The reference numerals are explained below:

200: piezoelectric stack structure

201 a: first piezoelectric layer

201 b: second piezoelectric layer

202: insulating layer

203 a: a first metal layer

203 b: second metal layer

203 c: a third metal layer

205 a: connecting pad

205 b: connecting pad

207: perforation

210: suspension area

210 a: half of the suspension region adjacent to the anchoring end

210 f: half part of the suspension area adjacent to the free end

211: connecting pad

300. 500: micro-electromechanical device

310: substrate

310 a: first surface

310 b: second surface

311. 312: first semiconductor layer

311 a: initial cavity

313: adhesive layer

313 a: undercut portion

315: a second semiconductor layer

315 a: groove

315 b: grid

315 c: area of mass

316: oxide region

317: insulating layer

320: hollow cavity

330: insulating layer

330 a: undercut portion

331: insulating layer

350: protective layer

370: oxide layer

390: covering layer

450: cover layer

450 a: hollow cavity

AE: anchoring end

d1, d2, d 3: size of

FE: free end

T1, T2, T4: thickness of

T3: total thickness of

x, y: direction of rotation

Detailed Description

In order to make the present invention more comprehensible to those skilled in the art, several embodiments accompanied with figures are described in detail below to explain the present invention and its intended effects. Furthermore, those skilled in the art will be able to make substitutions, rearrangements, and combinations of features from several different embodiments without departing from the spirit of the invention.

In the present invention, the description "the first member is formed on or above the second member" may mean "the first member is in direct contact with the second member", or "another member is present between the first member and the second member", so that the first member is not in direct contact with the second member. In addition, various embodiments of the present invention may use repeated reference numerals and/or text labels. These repeated use of reference characters and letters are intended to provide a concise and definite description, and are not intended to indicate any relationship between the various embodiments and/or configurations. In addition, for spatially related descriptive words mentioned in the present invention, for example: the use of "below," "above," "lower," "upper," "lower," "below," "above," "below," "over," "bottom," "top," and the like in describing, for purposes of convenience, the relative relationship of one component or feature to another component(s) or feature in the drawings is for convenience. In addition to the orientations shown in the drawings, these spatially relative terms are also used to describe possible orientations of the semiconductor device during fabrication, during use, and during operation. For example, when the semiconductor device is rotated 180 degrees, some components that were originally disposed "above" other components become disposed "below" the other components. Therefore, as the swing direction of the semiconductor device changes (rotates by 90 degrees or other angles), the spatially related descriptions for describing the swing direction should be interpreted in a corresponding manner.

Although the present invention has been described using terms such as first, second, third, etc. to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by such terms. Such terms are only used to distinguish one element, component, region, layer and/or block from another element, component, region, layer and/or block, and do not denote any order or importance, nor do they denote any order or importance, unless otherwise indicated. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the scope of embodiments of the present invention.

The term "about" or "substantially" as used herein generally means within 20%, preferably within 10%, and more preferably within 5%, or within 3%, or within 2%, or within 1%, or within 0.5% of a given value or range. It should be noted that the amounts provided in the specification are approximate amounts, that is, the meaning of "about" or "substantially" may still be implied without specific recitation of "about" or "substantially".

Fig. 1 to 10 are schematic diagrams illustrating a process of a micro-electromechanical device 300 according to a first embodiment of the invention, in which fig. 1, 4, 6, and 9 respectively illustrate a top view of the micro-electromechanical device during the process, and other figures respectively illustrate a cross-sectional view of the micro-electromechanical device during the process. First, as shown in fig. 1 and fig. 2, a composite substrate 310, such as a silicon-on-insulator (SOI) substrate, is provided for manufacturing the mems device 300. The composite substrate 310 further includes a first semiconductor layer 311 made of a material such as single crystal silicon (Si-Si), polysilicon, amorphous silicon (A-Si) or other suitable materials, an adhesive layer 313 made of a material such as silicon monoxide (SiO), silicon oxynitride (SiON) or silicon dioxide (SiO)₂) And a second semiconductor layer 315, which is made of, for example, monocrystalline silicon, polycrystalline silicon, amorphous silicon, or other suitable materials. The first semiconductor layer 311, the adhesive layer 313 and the second semiconductor layer 315 are sequentially stacked from bottom to top to form a compositeA substrate 310. In the present embodiment, the thickness T1 of the second semiconductor layer 315 is preferably smaller than the thickness (not shown) of the first semiconductor layer 311, for example, the thickness of the first semiconductor layer 311 is about 400 micrometers (μm) to 500 μm, and the thickness T1 of the second semiconductor layer 315 may be about 50 μm to 100 μm, but not limited thereto. Preferably, the thickness T1 of the second semiconductor layer 315 may be equal to a predetermined thickness of the subsequently formed mass, such as 50 μm, but is not limited thereto. It should be easily understood by those skilled in the art that the thickness of the second semiconductor layer 315 can be further adjusted according to the sensing accuracy required by the actual product, and the following formula (I) is referred to.

Formula (I):

wherein, κ_BBoltzmann's constant (Boltzmann's constant); t is the absolute temperature; omega₀Is the resonant frequency; m is_iIs the mass of the sensor; q is a mass coefficient.

An initial cavity 311a is formed in the composite substrate 310, the initial cavity 311a extends from the top surface of the first semiconductor layer 311 to the inside of the first semiconductor layer 311, as shown in fig. 2, and the adhesive layer 313 covers the top surface of the first semiconductor layer 311 and the inner surface of the initial cavity 311 a. In one embodiment, the composite substrate 310 may be formed, for example, by the following steps. First, two semiconductor layers (not shown) having a thickness of about 400 to 500 μm are provided, an initial cavity 311a is formed on one of the two semiconductor layers, a surface of the one of the two semiconductor layers is oxidized to form an adhesive layer 313, and the two semiconductor layers are bonded to each other by the adhesive layer 313. The other of the two semiconductor layers is then thinned to a thickness, such as thickness T1, to obtain composite substrate 310. In another embodiment, the adhesive layer 313 may be disposed directly on the semiconductor layer and the initial cavity 311a, and the adhesive layer 313 may include an organic material, such as polyimide (polyimide), photoresist, or other suitable materials.

In detail, the composite substrate 310 has two opposite surfaces, such as a first surface 310a and a second surface 310b shown in fig. 2, wherein the initial cavity 311a is formed at a position adjacent to the first surface 310a, that is, the initial cavity 311a is formed at the front side of the composite substrate 310, such that the size (e.g., aperture) d1 thereof is, for example, about 100 microns to 150 microns, but is not limited thereto. In other words, the initial cavity 311a is used to preliminarily define the size and position of the cavity to be formed subsequently, so as to further adjust the dimension d1 of the initial cavity 311a according to the predetermined size of the cavity to be formed subsequently. On the other hand, an insulating layer 317 is formed on the second surface 310b (i.e., the backside of the composite substrate 310), and the insulating layer 317 may include, but is not limited to, silicon oxide or silicon dioxide. In one embodiment, the insulating layer 317 may be formed by an oxidation process, such as, but not limited to, the same oxidation process used to form the adhesion layer 313.

Next, as shown in fig. 3, a plurality of trenches 315a are formed in the composite substrate 310 such that each trench 315a penetrates through two opposite surfaces of the second semiconductor layer 315. The slots 315a are spaced apart from each other at a position corresponding to the lower initial cavity 311a to define at least one mass region 315c within the initial cavity 311a, as shown in fig. 3. Preferably, the dimension (width) d3 of the mass region 315c may be substantially equal to a predetermined dimension of a subsequently formed mass, and the predetermined dimension of the mass may be determined according to a sensing accuracy required by an actual product, for example, according to the aforementioned formula (I). In one embodiment, a plurality of gates 315b are spaced between each trench 315a, and the dimension (width) d2 of each trench 315a is preferably determined by the oxidation rate required in the subsequent oxidation process. In one embodiment, each trench 315a and each gate 315b may have the same dimension (width) d2, such as about 0.5 to 2.5 microns, preferably about 0.6 to 0.8 microns, but is not limited thereto. In another embodiment, the trench 315a and the gate 315b may have different sizes, or a plurality of trenches with different sizes or a plurality of gates with different sizes may be formed, so that different oxidation rates may be achieved in a practical process.

Then, as shown in fig. 4 and 5, an oxidation process, such as a wet oxidation process or a dry oxidation process, is performed to form an oxidation region 316 in the second semiconductor layer 315. In one embodiment, the oxidized region 316 preferably comprises the same material as the adhesion layer 313, or comprises the same etching selectivity ratio as the adhesion layer 313, but not limited thereto. In detail, the oxidized region 316 is formed by oxidizing the gate 315b, and since the volume of the oxidized gate 315b is increased compared to the original volume of the gate 315b, the oxidized region 316 can be filled in the adjacent trench 315a and further combines all the oxidized gates 315b to form the oxidized region 316. In an embodiment, the second semiconductor layer 315 includes, for example, silicon, and the volume of the oxidized gate 315b (including, for example, silicon oxide or silicon dioxide) can be increased by about two times, so as to fill the trench 315a and combine with each other, but the material of the second semiconductor layer 315 is not limited to the foregoing. It should be noted that, since the oxidation process is performed uniformly on all exposed surfaces of the second semiconductor layer 315, as shown in fig. 5, the bottom surface of the mass region 315c is also oxidized, and an insulating layer 330 may be further formed on the top surface of the second semiconductor layer 315 (i.e., the first surface 310a of the composite substrate 310). In this case, the mass region 315c may be surrounded by the oxidized portions, such as the oxidized region 316 and the insulating layer 330. It should be noted that, in an embodiment, one or more mass regions may be selectively defined at positions corresponding to the initial cavities 311 a. For example, as shown in fig. 4, three mass regions 315c may be defined in the same initial cavity 311a, but not limited thereto. It should be understood that any number of mass regions may be formed in the initial cavity 311a to meet different product requirements.

Then, as shown in fig. 6 and 7, a piezoelectric stack structure 200 is further formed on the insulating layer 330, wherein the piezoelectric stack structure 200 is disposed on the front side of the composite substrate 310. The piezoelectric stack 200 may be formed by depositing and/or selectively etching a material layer or the likeAny suitable semiconductor structure formed by a conductor process. In one embodiment, the piezoelectric stack 200 includes at least one piezoelectric layer, such as two

piezoelectric layers

201a and 201b, and at least one metal layer 203, such as three

metal layers

203a, 203b and 203c, which are alternately stacked on an insulating layer 202 above an insulating layer 330. The piezoelectric layer includes, for example, a piezoelectric material, such as aluminum nitride (AlN), doped aluminum nitride (doped aluminum nitride), scandinium nitride (ScAlN), doped scandinium aluminum nitride (doped scandium aluminum nitride), lead zirconate titanate (PZT), zinc oxide (ZnO), polyvinylidene fluoride (PVDF), lead manganese niobate-lead titanate (lead manganese niobate-lead titanate), lithium niobate (LiNbO)₃) Or lithium tantalate (LiTaO)₃) The metal layer includes, for example, but not limited to, copper (Cu), molybdenum (Mo), tungsten (W), titanium (Ti), platinum (Pt), or aluminum (Al). In detail, the first piezoelectric layer 201a is stacked on the first metal layer 203a above the insulating layer 202, the second piezoelectric layer 201b is stacked on the second metal layer 203b above the first piezoelectric layer 201a, and then, the third metal layer 203c is stacked on the second piezoelectric layer 201b, as shown in fig. 7, but not limited thereto. In another embodiment, two metal layers and one piezoelectric layer stacked on each other may also be formed. In addition, the piezo-electric stack 200 further includes at least one connecting pad, such as two connecting

pads

205a, 205b passing through the piezo-electric stack 200 to electrically connect different metal layers (e.g., the second metal layer 203b and the first metal layer 203a), respectively. Wherein the connecting pad may comprise a conductive material, such as copper or aluminum. In order to clearly illustrate the arrangement position between the piezoelectric stack 200 and the elements (such as the mass region 315c) therebelow, the detailed elements of the piezoelectric stack 200, such as the connecting

pads

205a, 205b, etc., are omitted in fig. 6.

The piezo-electric stack 200 further includes at least one suspension region 210 corresponding to the lower initial cavity 311a, and at least one through hole 207 is formed on the piezo-electric stack 200 adjacent to the suspension region 210, as shown in fig. 7, so that the structure disposed in the suspension region 210 can be partially separated from the composite substrate 310 in a subsequent process to form a suspension structure like a cantilever or a diaphragm (not shown). The suspension structure includes, for example, a top electrode (e.g., the second metal layer 203b), a piezoelectric layer (e.g., the second piezoelectric layer 201a), and a bottom electrode (e.g., the first metal layer 203a) stacked in sequence from top to bottom, so as to be capable of vibrating at a specific frequency in a subsequent process. In one embodiment, one or more suspension regions 210 may be optionally formed within the piezoelectric stack 200 and above the initial cavity 311 a. For example, three suspension regions 210 may be formed at the same time, and three mass regions 315c are respectively disposed under the three suspension regions 210, as shown in fig. 6, so that the vibration frequency of each suspension structure can be adjusted to meet the product requirement.

Then, as shown in fig. 8, a protective layer 350 is formed on the piezoelectric stack 200 for protecting the elements disposed in the piezoelectric stack 200. The passivation layer 350 may comprise the same material as the adhesion layer 313 and the insulation layer 330, or a material having the same etching selectivity as the adhesion layer 313 and the insulation layer 330, such as silicon oxide or silicon dioxide, but is not limited thereto. Then, a thinning process of the composite substrate 310 is performed, for example, from the back side (i.e., the side where the second surface 310b is located) of the composite substrate 310. Thereby, the insulating layer 317 disposed on the second surface 310b is completely removed, and a portion of the first semiconductor layer 311 is also removed, so that the remaining first semiconductor layer 312 has a smaller thickness T2. In an embodiment, the thickness T2 of the remaining first semiconductor layer 312 (i.e., the thinned first semiconductor layer) is, for example, about 200 microns to 300 microns, and thus, the total thickness T3 of the composite substrate 310 may be about 300 microns to 400 microns, but not limited thereto.

Thereafter, as shown in fig. 9 to 10, an etching process, such as an isotropic wet etching process, is performed from the front side of the composite substrate 310 to completely remove the passivation layer 350 and the oxide region 316, and partially remove the insulating layer 330 and the adhesive layer 313 which are made of similar materials or materials with similar etching selectivity. In this manner, the suspending region 210 within the piezoelectric stack 200 can be released to form the micro-electromechanical device 300. As shown in fig. 10, when the oxide region 316 is removed, the insulating layer 330 and the portion of the adhesion layer 313 near the oxide region 316 are also removed, thereby exposing a portion of the bottom surface of the suspension region 210, as shown in fig. 10. In this case, the space created by removing the oxidized region 316 and the initial cavity 311a may together form a cavity 320 within the composite substrate 310. The cavity 320 extends from the top surface of the second semiconductor layer 315 into the thinned first semiconductor layer 312 and connects to the exposed bottom surface of the hanging region 210, and the cavity 320 may have an opening with a uniform dimension d1, as shown in fig. 10.

On the other hand, after removing the oxide region 316, the mass region 315c in the second semiconductor layer 315 may be separated from the remaining portion of the second semiconductor layer 315. In this way, the mass region 315c is connected to the bottom surface of the suspension region 210 only through the insulating layer 330, and can serve as a mass of the micro-electromechanical device 300. Therefore, the thickness of each mass block may be substantially equal to the thickness T2 of the second semiconductor layer 315, for example, about 50 microns to 100 microns, preferably 50 microns. As shown in fig. 10, a portion of the insulating layer 331 is sandwiched between each of the suspension regions 210 and each of the proof masses (i.e., each of the proof mass regions 315c), and when the etching process is performed, the sidewalls of the portion of the insulating layer 331, the sidewalls of the remaining portions of the insulating layer 330 and the adhesive layer 313 are slightly removed together, so as to form undercut

portions

330a and 313a near the cavity 320, as shown in fig. 10.

The mems device 300 according to the first embodiment of the invention is formed by the aforementioned processes, and the mems device 300 includes the piezoelectric stack 200, the cavity 320, and at least one mass (i.e., the mass region 315c of the second semiconductor layer 315) disposed inside the cavity 320. It is noted that, due to the formation of the through hole 207, after the passivation layer 350 and the oxidized region 316 are removed, one end of each of the suspending regions 210 can be separated from the composite substrate 310, such that the end of each of the suspending regions 210 adjacent to the through hole 207 is a Free End (FE). On the other hand, the other end of the suspended region 210 remains connected to the composite substrate 310 as an anchored end (anchor end) AE of the suspended region 210, as shown in fig. 9-10. With this arrangement, each suspension region 210 may be suspended above the composite substrate 310, with the suspension structure within each suspension region 210 producing a corresponding vibration upon receiving a sound wave or electrical signal, and further with the mass adjusting the suspension structure so that the suspension structure may have a resonant frequency that may be in accordance with the desired sensed audio frequency range.

Furthermore, each of the masses has a relatively small size compared to the size of each of the suspension regions 210, for example, the coverage area of each of the masses can be reduced by about 10% to 90%, preferably by about 25% to 50%, relative to the coverage area of each of the suspension regions 210. In the present embodiment, each of the masses is preferably disposed on a half portion 210f of the suspension region 210 adjacent to the free end FE, as shown in fig. 9. Therefore, each mass block can effectively improve the sensing accuracy of the micro-electromechanical device 300 on the premise of not causing rigid impact on the suspension structure. In a preferred embodiment, each of the masses only partially overlaps a half portion 210f of the suspension region 210 adjacent to the free end FE, but does not overlap a half portion 210a of the suspension region 210 adjacent to the anchoring end AE, but is not limited thereto. With this configuration, the MEMS device 300 of the present embodiment can be used as a MEMS accelerometer (micro electro mechanical system device), and thus can be applied to a wireless bluetooth headset to assist the voice vibration of a microphone.

The main feature of the process of the micro-electromechanical device 300 of the present embodiment is to form trenches 315a in the composite substrate 310, and then oxidize the gates 315b between the trenches 315a, thereby forming the oxidized region 316 and defining a quality block region 315c in the second semiconductor layer 315. With this arrangement, the proof-mass (i.e., the proof-mass region 315c) and the cavity 320 of the microelectromechanical device 300 may be conveniently and accurately formed by removing the oxide region 316 in a subsequent process. In this manner, cavity 320 may have an opening with a uniform dimension d1, and the dimensions of the mass and the position at which the mass is disposed within cavity 320 may also be accurately defined at the same time. It should be readily understood by those skilled in the art that although the trench 315a or the oxide region 316 is formed after the formation of the soi substrate in the above embodiments, other variations or other process sequences may be implemented in the actual process. For example, in another embodiment (not shown), a plurality of trenches may be formed on one of the two semiconductor layers constituting the SOI substrate (e.g., the trenches 315a shown in FIG. 3, not shown), and then the gate between the trenches may be oxidized before or after bonding the two semiconductor layers. Subsequently, said one of said two semiconductor layers is thinned, still obtaining a similar structure as shown in fig. 5.

Furthermore, although the above-mentioned fabricating process of the micro-electromechanical device 300 is described as an embodiment in which the three suspension regions 210 extend in the same direction (e.g., y-direction, as shown in fig. 9) and are respectively connected to the corresponding masses, the present invention is not limited to the above-mentioned manner. In another embodiment, the number of suspension regions 210 and masses and their arrangement can be further adjusted according to the sensing accuracy required by the mems device. For example, as shown in fig. 11, a smaller number of suspension regions 210 and masses can be selected according to the formula (I) to obtain different detection signals. Alternatively, the hanging region 210 may extend in another direction, such as the x-direction shown in fig. 11, so that signals from different directions can be sensed. In another embodiment, suspension regions (not shown) extending in different directions may be further formed, so that signals from different directions can be sensed to further meet actual product requirements.

Other embodiments or variations of the microelectromechanical device of the invention and methods of forming the same will be described below. For simplicity, the following description mainly refers to the differences of the embodiments, and the description of the same parts is not repeated. In addition, the same elements in the embodiments of the present invention are denoted by the same reference numerals to facilitate the comparison between the embodiments.

Referring to FIG. 12, a schematic diagram of a micro-electromechanical device 500 according to a second embodiment of the present invention is shown. The structure of the micro-electromechanical device 500 in this embodiment is substantially similar to that in the previous embodiments, and is not repeated here. The difference between the present embodiment and the previous embodiment is that a cap layer 450 is additionally formed on the piezoelectric stack structure 200 to form a vacuum cavity (vacuum cavity) in the mems device 500.

Specifically, the cover layer 450 includes a rigid substrate material such as silicon, glass, etc., and the cover layer 450 is bonded to the front side of the composite substrate 310, such that a cavity 450a is formed between the cover layer 450 and the piezoelectric stack 200 disposed above the composite substrate 310. Preferably, the cavity 450a has a thickness T4 of about 5 to 20 microns, and the cavity 450a may be set in a vacuum (vacuum) state for further application in a high-gravity environment. It is noted that the cover layer 450 is bonded to the bonding pad 211 on the piezoelectric stack 200 by a protruding structure disposed thereon. In one embodiment, the protrusion structure may be disposed around the periphery of the cap layer 450, so that the protrusion structure may have a ring shape when viewed from a top view (not shown) and may have two protrusion structures separated from each other when viewed from a side cross-sectional view as shown in fig. 12. The protrusion structure may include an oxide layer 370 and a capping layer 390 overlying the oxide layer 370, wherein the oxide layer 370 may include silicon oxide or silicon dioxide, and the capping layer 390 may include a metal material, such as aluminum germanium (AlGe), but not limited thereto. Preferably, the thickness of the oxide layer 370 may be about 2 microns to about 10 microns, so that the cavity 450a formed inside the micro-electromechanical device 500 may have enough space.

Thus, the mems device 500 according to the second embodiment of the invention is completed, and the mems device 500 includes the piezoelectric stack 200, the cavity 320, the mass (i.e., the mass region 315c of the second semiconductor layer 315) disposed inside the cavity 320, and the cover layer 450. Thus, a vacuum cavity 450a may be additionally formed between the cover layer 450 and the piezoelectric stack structure 200, so that the mems device 500 may be applied to a high-impact state as a high-gravity accelerometer (e.g., about 10g to 300g), thereby achieving a better sensing effect.

In general, it is an object of the present invention to provide a micro-electromechanical device having a mass that is miniaturized and has precise dimensions, such that the coverage area of the mass can be reduced by about 10% to 90%, preferably by about 25% to 50%, relative to the coverage area of a correspondingly disposed suspension region. But is not limited thereto. In addition, one or more masses can be optionally provided on the microelectromechanical device corresponding to one or more suspension regions, respectively, such that each mass can be connected to each suspension region, respectively, thereby further adjusting the vibration frequency. Under the arrangement, the micro-electromechanical device can be used as an accelerator of the micro-electromechanical system and can be applied to a wireless Bluetooth headset, so that the voice vibration of a microphone is assisted.

Another objective of the present invention is to provide a process for fabricating a micro-electromechanical device, which comprises forming a plurality of trenches in a composite substrate, and oxidizing gates between the trenches to define regions and dimensions of a mass block by the oxidized gates. Then, the mass block with accurate position and size, that is, the cavity with uniform opening size, can be obtained by means of simply removing the oxidized region in the subsequent process. Thus, the formed micro-electromechanical device can have more improved functions and effects.

The above-mentioned embodiments are merely preferred embodiments of the present invention, and all equivalent changes and modifications made by the claims of the present invention should be covered by the scope of the present invention.

Claims

1. a microelectromechanical device, is characterized in that, comprises:

a composite substrate, comprising a first semiconductor layer, an adhesive layer and a second semiconductor layer sequentially stacked from bottom to top;

a cavity disposed in the first semiconductor layer, the cavity extending from the second semiconductor layer to the first semiconductor layer and not passing through the first semiconductor layer;

a piezoelectric stack disposed on the composite substrate, the piezoelectric stack including a suspended region on the cavity; and

A mass is arranged in the cavity and connected to the piezoelectric stack structure.

2 . The MEMS device of claim 1 , wherein the material of the mass is the same as the material of the second semiconductor layer. 3 .

3 . The MEMS device of claim 2 , wherein the thickness of the proof mass is the same as the thickness of the second semiconductor layer. 4 .

4 . The MEMS device of claim 1 , wherein the coverage area of the proof mass is reduced by about 10% to 90% compared to the coverage area of the suspension region. 5 .

5 . The MEMS device of claim 1 , further comprising an insulating layer disposed between the second semiconductor layer and the piezoelectric stack structure. 6 .

6. The MEMS device of claim 5, wherein the piezoelectric stack structure further comprises:

a metal layer disposed on the insulating layer;

a first piezoelectric layer disposed on the metal layer; and

A second metal layer is disposed on the first piezoelectric layer.

7 . The MEMS device of claim 1 , further comprising a cover layer disposed on the piezoelectric stack structure, wherein a vacuum cavity is disposed on the cover layer and the piezoelectric layer. 8 . between stacked structures.

8 . The MEMS device of claim 7 , wherein the cap layer is connected to the piezoelectric stack structure through a protruding structure. 9 .

9 . The MEMS device of claim 1 , wherein the piezoelectric stack structure comprises a plurality of the suspension regions, and a plurality of the mass blocks are arranged in the cavity to connect the suspensions. 10 . area.

10. A method for forming a microelectromechanical device, comprising:

A composite substrate is provided, the composite substrate includes a first semiconductor layer, an adhesive layer and a second semiconductor layer sequentially stacked from bottom to top;

forming a cavity in the first semiconductor layer, the cavity extending from the second semiconductor layer to the first semiconductor layer and not passing through the first semiconductor layer;

forming a piezoelectric stack on the composite substrate, the piezoelectric stack including a suspended region above the cavity; and

A mass is formed in the cavity, and the mass is connected to the piezoelectric stack structure.

11. The method for forming a microelectromechanical device according to claim 10, further comprising:

forming a plurality of trenches in the second semiconductor layer to define a plurality of gates and the mass between the trenches;

oxidizing the gate to form an oxidized region, wherein the oxidized region surrounds the proof mass; and

The oxidized region is removed to form a portion of the cavity, wherein the proof-mass is connected to the piezoelectric stack.

12 . The method of claim 11 , wherein the piezoelectric stack structure is formed after the oxidation region is formed, and the piezoelectric stack structure is formed on the oxidation region. 13 . .

13. The method for forming a microelectromechanical device as claimed in claim 11, further comprising:

before forming the piezoelectric stack structure, forming an insulating layer on a surface of the second semiconductor layer, the insulating layer being disposed between the oxidized region and the proof mass; and

After the piezoelectric stack structure is formed, the insulating layer is removed to partially expose a bottom surface of the piezoelectric stack structure.

14. The method of claim 13, wherein the insulating layer is removed when the oxidized region is removed.

15. The method for forming a microelectromechanical device according to claim 13, further comprising:

When the piezoelectric stack structure is formed, an initial cavity is formed in the first semiconductor layer, and the insulating layer is formed on the surface of the first semiconductor layer and the initial cavity.

16 . The method of claim 11 , wherein the trench is formed between two opposite surfaces of the second semiconductor layer. 17 .

17. The method of claim 10, wherein the proof-mass is formed from a portion of the second semiconductor layer.

18. The method for forming a microelectromechanical device according to claim 10, wherein the coverage area of the mass block is about 10% to 90% smaller than the coverage area of the suspension region.

19. The method for forming a microelectromechanical device according to claim 10, further comprising:

A cover layer is formed on the piezoelectric stack structure, wherein a vacuum cavity is disposed between the cover layer and the piezoelectric stack structure.

20. The method for forming a microelectromechanical device according to claim 10, further comprising:

forming a plurality of the suspension regions within the piezoelectric stack, the suspension regions extending in a same direction; and

A plurality of the mass blocks are formed in the cavity to connect the suspension regions respectively.