CN112505354A

CN112505354A - MEMS accelerometer and method of formation

Info

Publication number: CN112505354A
Application number: CN202110141521.9A
Authority: CN
Inventors: 徐宝; 李森科·伊戈尔·叶夫根耶维奇; 徐元; 吴刚
Original assignee: Hangzhou Maixinmin Micro Technology Co Ltd
Current assignee: Hangzhou Maixinmin Micro Technology Co Ltd
Priority date: 2021-01-25
Filing date: 2021-02-02
Publication date: 2021-03-16
Anticipated expiration: 2041-02-02
Also published as: CN112505354B

Abstract

The invention relates to a MEMS accelerometer and a forming method, the MEMS accelerometer comprises a proof mass body and a plurality of tunnel tips, the tunnel tips are distributed on four sides of the proof mass body, at least two tunnel tips are correspondingly arranged on at least one of the four sides of the proof mass body, the plurality of tunnel tips are distributed on the four sides of the proof mass body, at least two tunnel tips are correspondingly arranged on at least one of the four sides of the proof mass body, so that when individual tunnel tips on the same side of the proof mass body are damaged, other tunnel tips can be used continuously, and the sensitivity and the reliability of the MEMS accelerometer are high.

Description

MEMS accelerometer and method of formation

Technical Field

The invention relates to the technical field of micro-electro-mechanical systems, in particular to a micro-electromechanical system (MEMS) accelerometer and a forming method thereof.

Background

An inertial sensor is a device capable of sensing and/or generating motion, including Micro-Electro-Mechanical systems (MEMS), examples of which include a MEMS accelerometer capable of sensing acceleration.

The MEMS accelerometer is one of main devices of an inertial navigation and guidance system, has the characteristics of low cost, small size, low power consumption, integration with an integrated circuit and the like compared with a traditional mechanical sensor or an optical sensor, is widely applied to the fields of consumer electronics, industrial manufacturing, medical electronics, automotive electronics, aerospace, military and the like, and has great development potential and commercial value.

MEMS accelerometers can be classified into capacitive type, field emission type, or tunneling current type, etc. according to their operating principles. MEMS accelerometers utilize the effect of inertia, and when an object moves, the suspended microstructure within the MEMS accelerometer is affected by inertial forces.

For example, capacitive MEMS accelerometers include capacitive planar MEMS accelerometers, in which movement of a proof mass brings an associated capacitive electrode closer to or farther from an opposing capacitive electrode, and capacitive lateral MEMS accelerometers, in which the capacitance produced by the accelerometers varies as a function of the acceleration applied to the proof mass, the variation in capacitance being inversely proportional to the square of the spacing between the capacitive electrodes; in a capacitive lateral MEMS accelerometer, the movement of the proof mass brings the associated comb electrode closer to or further from the opposite comb electrode, the capacitance produced by the accelerometer varies as a function of the acceleration applied to the proof mass, the variation in capacitance being proportional to the variation in the area of overlap between the capacitive comb electrodes.

Capacitive MEMS accelerometers have found widespread use in the industrial field, mainly because of their simple structure and their mode of operation compatible with semiconductor technology. Unlike capacitive accelerometers, tunnel current accelerometers (tunnel accelerometers for short) utilize the property that tunnel current varies exponentially with electrode spacing, and therefore tunnel accelerometers generally provide better sensitivity because relatively small acceleration changes produce a relatively large response in tunnel accelerometers compared to capacitive accelerometers.

In the related art, the structure of a tunnel accelerometer involves providing a tunnel gap between the tunnel tip and a proof mass that responds to acceleration applied to the proof mass by moving toward or away from the tunnel tip. A tunnel gap is formed between the tunnel tip and the proof mass by applying a bias voltage between the tunnel tip and the proof mass with appropriate flexure of the elastomeric suspension connecting the proof mass.

However, since the proof mass moves toward the tunnel tip, there may be a risk that a sufficiently strong acceleration will cause the proof mass to come into contact with the tunnel tip, and since the size of the tunnel tip apex is usually only about a few atoms, such contact easily damages the tunnel tip, resulting in a decrease in sensitivity or even an inability to continue use of the tunnel accelerometer, there is a problem in the related art that the reliability of the tunnel accelerometer is poor.

Disclosure of Invention

The invention aims to provide a MEMS accelerometer which is high in sensitivity and high in reliability.

In order to achieve the purpose, the invention adopts the following technical scheme: a MEMS accelerometer, comprising:

the proof mass is a mass of a material,

the tunnel tips are distributed on four sides of the proof mass, and at least two tunnel tips are correspondingly arranged on at least one of the four sides of the proof mass.

Preferably, the MEMS accelerometer further comprises a plurality of driving combs, and at least one of the driving combs is disposed on any one of four sides of the proof mass, and the driving combs include movable driving comb teeth and fixed driving comb teeth which are interdigitated to form an interdigital structure.

Preferably, the tunnel tips are arranged in four pairs, one to one correspondence with four sides of the proof mass, and the driving combs are arranged in four pairs, one to one correspondence with two of the tunnel tips of each pair of the tunnel tips.

Preferably, the movable drive combs are connected to the proof mass with a tunnel gap between the proof mass and the tunnel tips;

alternatively, the drive comb further comprises a movable frame integrating a plurality of the movable drive comb teeth, the movable frame being resiliently connected to the proof mass with a tunnel gap between the movable frame and the tunnel tip.

Preferably, the proof mass comprises a hollow portion penetrating through the inside of the proof mass block, the MEMS accelerometer further comprises a first substrate, anchor points and stoppers, the tunnel tip, the fixed driving comb teeth, the anchor points and the stoppers are all fixedly connected to the first substrate, the anchor points are multiple, the movable frame or the proof mass is elastically connected to at least one of the anchor points, and the stoppers are arranged in the hollow portion and used for limiting the movement range of the proof mass.

Preferably, the MEMS accelerometer further includes a second substrate disposed on a side of the proof mass away from the first substrate, wherein two ends of the first substrate and the second substrate are connected to form a cavity for placing the proof mass, the tunnel tip, the drive comb, the anchor point, and the stopper.

The invention also provides a forming method of the MEMS accelerometer, which comprises the step of etching a structure of the MEMS accelerometer on the polycrystalline silicon layer, wherein the structure comprises a proof mass and a plurality of tunnel tips, the plurality of tunnel tips are distributed on four sides of the proof mass, and at least two tunnel tips are correspondingly arranged on at least one of the four sides of the proof mass.

Preferably, after etching the structure of the MEMS accelerometer, the method comprises separating the proof mass and the tunnel tip to form a tunnel gap using focused ion beam techniques.

Preferably, before the etching the structure of the MEMS accelerometer, the method comprises:

depositing a silicon nitride layer on a first substrate, depositing a first phosphosilicate glass layer on the silicon nitride layer, and annealing;

etching an anchor hole in the first phosphosilicate glass layer;

and depositing the polycrystalline silicon layer on the first phosphorosilicate glass layer, depositing a second phosphorosilicate glass layer on the polycrystalline silicon layer, and annealing.

Preferably, after the forming of the tunnel gap, the method includes:

removing the first phosphorosilicate glass layer;

and encapsulating the proof mass and the tunnel tip in a cavity formed by the first substrate and the second substrate, and connecting two ends of the first substrate and the second substrate.

Compared with the prior art, the invention has the beneficial effects that:

in the MEMS accelerometer provided in the above technical solution, the tunnel tips are distributed on four sides of the proof mass, and at least two tunnel tips are correspondingly disposed on at least one of the four sides of the proof mass, so that when a single tunnel tip on the same side of the proof mass is damaged, other tunnel tips can be used continuously, thereby enabling the MEMS accelerometer to have high sensitivity and high reliability.

Drawings

Fig. 1 is a schematic structural diagram of a MEMS accelerometer according to an embodiment of the invention.

FIG. 2 is a schematic structural diagram of a MEMS accelerometer according to another embodiment of the invention.

FIG. 3 is a schematic diagram of reflecting the direction of the sensing signal of the MEMS accelerometer under the acceleration of the X axis according to the embodiment of the invention.

FIG. 4 is a schematic diagram of reflecting the direction of the sensing signal of the MEMS accelerometer under the acceleration of the Y axis according to the embodiment of the invention.

Fig. 5 is a flow chart illustrating a method for forming a MEMS accelerometer according to an embodiment of the invention.

Fig. 6 is a schematic view of the first substrate with the silicon nitride layer taken along a-a in fig. 1 in an embodiment of the present invention.

FIG. 7 is a schematic view of a first substrate with a first phosphosilicate glass layer taken along line A-A in FIG. 1 in an embodiment of the present invention.

Fig. 8 is a schematic view of the first substrate with the polysilicon layer taken along a-a in fig. 1 in an embodiment of the present invention.

Fig. 9 is a schematic view of a connection structure of the first substrate and the second substrate taken along a-a in fig. 1 in an embodiment of the present invention.

Fig. 10 is a schematic diagram of a first tunnel contact without the use of focused ion beam techniques in an embodiment of the present invention.

Fig. 11 is a schematic diagram of a first tunnel contact after using focused ion beam technology in an embodiment of the invention.

In the figure: 1. a proof mass; 11. a hollow-out section; 12. a through hole; 17. a silicon nitride layer; 2. a tunnel tip; 3. a drive comb; 31. the movable driving comb teeth; 32. fixing the driving comb teeth; 33. a movable frame; 4. a first substrate; 5. an anchor point; 6. a stopper; 7. a second substrate; 8. a polysilicon layer; 9. a first phosphosilicate glass layer; 91. an anchor eye; 10. a second phosphosilicate glass layer; 110. a first tunnel contact; 120. a second tunnel contact; 130. and a resilient suspension.

Detailed Description

The present invention will now be described in more detail with reference to the accompanying drawings, in which the description of the invention is given by way of illustration and not of limitation. The various embodiments may be combined with each other to form other embodiments not shown in the following description.

Referring to fig. 1 and 8, an embodiment of the invention provides a MEMS accelerometer, including: the MEMS accelerometer comprises a proof mass 1, a plurality of tunnel tips 2, a plurality of driving combs 3, a first substrate 4 and anchor points 5, wherein the plurality of tunnel tips 2 are distributed on four sides of the proof mass 1, at least two tunnel tips 2 are correspondingly arranged on at least one of the four sides of the proof mass 1, so that when the individual tunnel tips 2 on the same side of the proof mass 1 are damaged, other tunnel tips 2 can be used continuously, and the MEMS accelerometer has high sensitivity and high reliability.

It is noted that the top of the tunnel tip 2 may be triangular or have another shape, for example, in some of the embodiments, see fig. 2, the top of the tunnel tip 2 may also be rectangular.

Considering that the MEMS accelerometer needs to be calibrated during use, the driving comb 3 is provided in plurality, and at least one driving comb 3 is provided on any one of the four sides of the proof mass 1, the driving comb 3 includes a movable driving comb tooth 31 and a fixed driving comb tooth 32, the movable driving comb tooth 31 and the fixed driving comb tooth 32 are intersected with each other to form an interdigital structure, when calibrating, a dc bias voltage is applied to the fixed driving comb teeth 32 on one or more driving combs 3 to generate an electrostatic force, the electrostatic force drives the movable driving comb tooth 31 and the proof mass 1 to deflect along the tunnel tip 2 on the side where the two sensitive axial dc bias voltages are located, so that the distance between the tunnel tip 2 and the electrode (e.g., the proof mass 1) (i.e., the tunnel gap) is calibrated from a larger distance to a smaller distance (e.g., calibrated to about 4 nm), thereby creating conditions for generating tunnel current, in addition, the tunnel gap is calibrated by the driving comb, so that when different MEMS accelerometer manufacturing technologies are selected, although the manufactured tunnel gaps are different in size, the tunnel current can be generated through calibration.

Further, the tunnel tips 2 are arranged into four pairs, the four sides of the proof mass 1 are arranged in a one-to-one correspondence mode, the driving comb 3 is arranged into four pairs, the four pairs are arranged between the two tunnel tips 2 of each pair of the tunnel tips 2 in a one-to-one correspondence mode, each side of the proof mass 1 is provided with at least two tunnel tips 2, one tunnel tip 2 on any side is damaged, normal use of the MEMS accelerometer is not affected, meanwhile, the two tunnel tips 2 are arranged on the two sides of the driving comb 3 respectively, and the situation that when one tunnel tip 2 is damaged, the other tunnel tip 2 is damaged due to the fact that the two tunnel tips 2 are close to each other can be avoided, and therefore reliability of the MEMS accelerometer is further improved.

Electrodes are also required for generating the tunnel current, and optionally, proof mass 1 can be used as electrodes, movable drive comb 31 is connected to proof mass 1, and a tunnel gap is provided between proof mass 1 and tunnel tip 2, and proof mass 1 and tunnel tip 2 form first tunnel contact 110; alternatively, the drive comb 3 further comprises a movable frame 33 integrating a plurality of movable drive comb teeth 31, the movable frame 33 can be used as an electrode, the movable frame 33 is elastically connected with the proof mass 1, and the movable frame 33 and the tunnel tip 2 have a tunnel gap therebetween, the movable frame 33 and the tunnel tip 2 form a second tunnel contact 120; after applying a dc bias voltage across fixed drive comb 32 to calibrate the tunnel gap to a small distance (e.g., to about 4 nanometers), a voltage is applied across tunnel tip 2 and proof mass 1 or tunnel tip 2 and movable frame 33 to generate a tunnel current.

In addition, the possibility of damage to tunnel tip 2 by proof mass 1 or movable frame 33 can be further reduced by limiting the range of motion of proof mass 1, in this embodiment, proof mass 1 includes a hollow 11 passing through proof mass 1, the MEMS accelerometer further includes a stop 6 disposed in hollow 11, stop 6 and hollow 11 have a space between them, optionally, stop 6 can be disposed at the center of proof mass 1, since tunnel tip 2, fixed drive comb 32, anchor point 5 and stop 6 are all fixedly connected to the same side of first substrate 4, and anchor point 5 is provided in plurality, each movable frame 33 or proof mass 1 is elastically connected to at least one anchor point 5, so that stop 6 is stationary with respect to first substrate 4, proof mass 1 is movable with respect to first substrate 4, and stop 6 is embedded in proof mass 1, stops 6 can limit the range of motion of proof mass 1 under impact loads, further reducing the likelihood of tunnel tip 2 being damaged by proof mass 1 or moveable frame 33 under impact loads, thereby improving reliability of the MEMS accelerometer.

It should be noted that the elastic connection in the embodiment of the present invention may be implemented by providing elastic suspensions 130, and optionally, the number of elastic suspensions 130 between proof mass 1 and movable frame 33, between proof mass 1 and anchor point 5, and between movable frame 33 and anchor point 5 may be increased or decreased; there are several spring beams on each spring suspension 130, and the number of spring beams in each spring suspension 130 or part of the spring suspension 130 can be increased or decreased.

The proof mass 1, tunnel tip 2, drive comb 3, first substrate 4, anchor point 5, stops 6, and spring suspension 130 may comprise any suitable material known in the art, for example, a semiconductor material, including polysilicon, silicon carbide (SiC), gallium arsenide (GaAs), silicon (Si), or any other semiconductor material, or a conductive material, such as tungsten (W), gold (Au), aluminum (Al), copper (Cu), titanium (Ti), or any other conductive material; the proof mass 1, tunnel tip 2, drive comb 3 and spring suspension 130 may be of the same or different thickness, alternatively the thickness may be on the order of a few microns to 10 microns, for example on the order of 2 to 6 microns.

In some embodiments, the MEMS accelerometer further comprises a second substrate 7, see fig. 9, where the second substrate 7 is disposed on a side of the proof mass 1 away from the first substrate 4, and the first substrate 4 and the second substrate 7 are connected at opposite ends to form a cavity for placing the proof mass 1, the tunnel tip 2, the drive comb 3, the anchor point 5, and the stopper 6, the cavity containing, but not limited to, vacuum or other inert gas, such as nitrogen, etc.; by providing the second substrate 7, a hermetic environment can be formed in the MEMS accelerometer, and the MEMS accelerometer is packaged without being placed in a vacuum for packaging, but in other embodiments, the MEMS accelerometer may not include the second substrate 7, and in this case, the MEMS accelerometer is packaged by being placed in a vacuum for packaging.

The first substrate 4 may be comprised of any suitable substrate material known in the art, for example, silicon or any other semiconductor material, and if desired, the first substrate 4 may contain integrated circuits fabricated thereon; the second substrate 7 may be comprised of any suitable substrate material known in the art, including, for example, the semiconductor material silicon, or other semiconductor materials, or any other non-semiconductor material, such as glass, plastic, metal, or ceramic, etc., and the second substrate 7 may contain integrated circuits fabricated thereon, if desired.

The MEMS accelerometer provided by the invention has biaxial sensitivity, the output signal of the MEMS accelerometer contains the acceleration information of each axis, and the cost of the MEMS accelerometer manufactured according to the invention can be obviously lower than that of the MEMS accelerometer in the related art, because only a single MEMS accelerometer is needed for realizing the same function (simultaneously sensing the acceleration on two axes), the number of required devices is reduced; the present invention senses acceleration by configuring one or more tunnel tips 2 on each axis, and the tunnel current varies exponentially with the change of the distance between the proof mass 1 and the tunnel tip 2 or the movable frame 33 and the tunnel tip 2 under the acceleration, and compared to the capacitive MEMS accelerometer of the related art, the MEMS accelerometer provided by the present invention has better sensitivity because a relatively small change of acceleration causes a large change of the distance between the proof mass 1 and the tunnel tip 2, the movable frame 33 and the tunnel tip 2, and at the same time, the self noise level is low when operating.

The embodiment of the present invention further provides an operation principle of the MEMS accelerometer, which is only an illustrative, non-limiting illustration, and the operation principle is as follows:

in order to create the tunnel current, the tunnel gap must be reduced to around a few nanometers, for example to around 4 nanometers, for which, see figure 1, a dc bias voltage, which may be on the order of a few volts, e.g., on the order of 1 volt, is applied to one side drive combs 3 in the X-axis direction and one side drive combs 3 in the Y-axis direction of proof mass 1, the dc bias voltage generating sufficient electrostatic force, to move proof mass 1, movable drive combs 31, and movable frame 33, to reduce the tunnel gap from a larger distance (e.g., the distance is the tunnel gap width at the time of manufacture, 20 nanometers) to a smaller distance (e.g., to 4 nanometers), providing multiple tunnel tips 2 on the same side of the proof mass 1 allows for the generation of a tunnel current in at least one of the first tunnel contact 110 or the second tunnel contact 120.

To establish a tunneling current in the first tunnel contact 110 and in the second tunnel contact 120, a voltage of about 0.1 to 1 volt, for example about 0.2 volts, is applied to each of the first tunnel contact 110 and the second tunnel contact 120, in which case a tunneling current of about a few microamps, for example about 1 to 2 microamps, is established.

In the case of external linear acceleration along the X-axis of the MEMS accelerometer, the proof mass 1 will bear an inertial force, see fig. 1 and 3, the inertial force will move the proof mass 1 and thus the movable frame 33, and due to the deformation of the elastic suspension 130, the gap between one side of the movable frame 33 and the tunnel tip 2 is changed, and the tunnel current will change exponentially with the change of the contact gap of one side of the proof mass 1 in the X-axis direction.

In the case of applying linear acceleration to the MEMS accelerometer along the Y axis from the outside, the proof mass 1 will bear an inertial force, see fig. 1 and 4, the inertial force moves the proof mass 1, the gap between one side of the proof mass 1 and the tunnel tip 2 is changed due to the deformation of the elastic suspension 130, and the tunnel current changes exponentially with the change of the contact gap at one side of the proof mass 1 in the Y axis direction.

In this case, the sensitivity of the MEMS accelerometer based on the tunnel effect is about 0.9 microampere/g, which allows the measurement accuracy of the present invention to reach the micro-g level.

The embodiment of the present invention further provides a method for forming a MEMS accelerometer, please refer to fig. 5, which includes the following steps:

step S501, depositing a silicon nitride layer 17 on the first substrate 4, depositing a first phosphosilicate Glass (PSG) layer on the silicon nitride layer 17, and annealing, for example, an n-type silicon substrate may be used as the first substrate 4, a phosphosilicate Glass (PSG) layer may be used as the first phosphosilicate Glass layer 9, phosphorus may be doped in a standard diffusion furnace using the PSG layer as a doping source, after removing the PSG layer, depositing a 0.6 μm Low stress silicon nitride layer 17 as an electrical isolation layer on the first substrate 4, as shown in fig. 6, thereby reducing the influence of an electric field generated by the MEMS electrostatic device on the first substrate 4, and then depositing a 2 μm PSG layer by Low Pressure Chemical Vapor Deposition (LPCVD), and annealing in argon at 1050 ℃ for 1 hour;

step S502, etching an anchor hole 91 in the first phosphosilicate glass layer 9, for example, performing Reactive Ion Etching (RIE) after drawing by photolithography, as shown in fig. 7, forming the anchor hole 91, where the anchor hole 91 is filled with structures, such as the tunnel tip 2, the fixed driving comb 32, the anchor point 5, and the stopper 6, which need to be fixedly connected to the first substrate 4 in the subsequent steps;

step S503, depositing a polysilicon layer 8 on the first phosphosilicate glass layer 9, depositing a second phosphosilicate glass layer 10 on the polysilicon layer 8, and annealing, for example, as shown in fig. 8, after etching the first phosphosilicate glass layer 9, the polysilicon layer 8 (i.e. the structural layer) is deposited on the first phosphosilicate glass layer 9 with a thickness of 2 microns, then a 0.2 micron ultra-thin PSG layer is deposited on the surface of the polysilicon layer 8 as the second phosphosilicate glass layer 10, and the first substrate 4 is annealed at 1050 ℃ for 1 hour, wherein during the annealing, the surface and the lower part of the polysilicon layer 8 are doped with phosphorus from the first phosphosilicate glass layer 9 or the second phosphosilicate glass layer 10, and the annealing also helps to significantly reduce the net stress in the polysilicon layer 8;

step S504, etching a structure of the MEMS accelerometer on the polysilicon layer 8, wherein the structure includes a proof mass 1, a plurality of tunnel tips 2, a driving comb 3, an anchor point 5 and a stopper 6, the plurality of tunnel tips 2 are disposed on four sides of the proof mass 1, and at least two tunnel tips 2 are disposed on at least one of the four sides of the proof mass 1, as shown in fig. 8, after etching the polysilicon layer 8, the photoresist is stripped, the remaining second phosphor-silicon glass layer 10 is removed by RIE, forming a structure of the MEMS accelerometer, the second phosphor-silicon glass layer 10 deposited on the polysilicon layer 8 in step S503 may be annealed and performed one or more times together with step S504 to increase the thickness of the proof mass 1, the elastic suspension 130, the driving comb 3 and the tunnel tip 2 or increase the thickness of one of them, thereby forming an MEMS accelerometer with different structural thicknesses and realizing wide-range acceleration sensing;

step S505, using Focused Ion beam technology to separate the proof mass 1 and the tunnel tip 2 to form a tunnel gap, for example, after step S504 is finished, as shown in fig. 10, the tunnel tip 2 is still connected to the proof mass 1 (or the movable frame 33), in order to separate the tunnel tip 2 from the proof mass 1 (or the movable frame 33) and form the tunnel gap, a Focused Ion Beam (FIB) technology is required, the tunnel gap in the present invention is manufactured using standard semiconductor technology, when the first tunnel contact 110 (or the second tunnel contact 120) is formed using FIB technology, as shown in fig. 11, the proof mass 1 and the tunnel tip 2 are separated (or the movable frame 33 is separated from the tunnel tip 2), and the distance of the tunnel gap is about several to 100 nanometers, for example, 20 nanometers;

in step S506, the first phosphosilicate glass layer 9 is removed, for example, referring to fig. 9, the remaining first phosphosilicate glass layer 9, which is referred to as a sacrificial layer, is finally removed to release the structural layer of the MEMS accelerometer, and the method for removing the first phosphosilicate glass layer 9 is as follows: the first substrate 4 is immersed in a 49% hydrofluoric acid (HF) bath at 25 ℃ for 2 minutes, the remaining first phosphosilicate glass layer 9 is completely removed, and is immersed in distilled water and alcohol for 2 minutes respectively, and then is placed in an oven at 110 ℃ for at least 10 minutes to reduce viscosity, it should be noted that, in the embodiment of the present invention, as shown in fig. 1, the proof mass 1 includes a plurality of through holes 12 penetrating through the proof mass 1, and when the first phosphosilicate glass layer 9 is immersed in a 49% hydrofluoric acid (HF) bath at 25 ℃ for 2 minutes, the plurality of through holes 12 can increase the contact area of the first phosphosilicate glass layer 9 and the hydrofluoric acid (HF), thereby facilitating the first phosphosilicate glass layer 9 and the hydrofluoric acid (HF) to fully react, and accelerating the reaction speed;

step S507, encapsulating the proof mass 1, the tunnel tip 2, the driving comb 3, the anchor point 5 and the stopper 6 in a cavity surrounded by the first substrate 4 and the second substrate 7, and connecting two ends of the first substrate 4 and the second substrate 7, for example, referring to fig. 9, connecting the first substrate 4 and the second substrate 7 by anodic bonding to form a vacuum cavity of the MEMS accelerometer, which may include but is not limited to vacuum or other inert gas, such as nitrogen, etc., using a simple and effective substrate anodic bonding method to form the vacuum cavity of the MEMS accelerometer, thereby improving productivity while improving yield, and being suitable for mass production.

In other embodiments, the MEMS accelerometer of the present invention can also be fabricated using surface micromachining techniques and silicon-on-insulator (SOI) techniques.

The MEMS accelerometer provided by the invention is simple and effective in forming method, adopts standard equipment manufactured by semiconductors, improves the yield of devices, reduces the manufacturing cost of the devices, is suitable for batch production, effectively improves the sensitivity and reliability of measurement and improves the quality of the devices.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.

Claims

1. A MEMS accelerometer, comprising:

a proof mass (1) for the test element,

the tunnel tips (2) are distributed on four sides of the proof mass (1) in a plurality, and at least two tunnel tips (2) are correspondingly arranged on at least one of the four sides of the proof mass (1).

2. The MEMS accelerometer according to claim 1, further comprising a plurality of drive combs (3), and at least one of said drive combs (3) is provided on any of the four sides of said proof mass (1), said drive combs (3) comprising movable (31) and fixed (32) drive comb teeth interdigitated with each other to form an interdigitated structure.

3. The MEMS accelerometer according to claim 2, wherein the tunnel tips (2) are arranged in four pairs, one for each, on four sides of the proof mass (1), and the drive combs (3) are arranged in four pairs, one for each, between two of the tunnel tips (2) of each pair of tunnel tips (2).

4. The MEMS accelerometer according to claim 2, wherein the movable drive comb (31) is connected to the proof mass (1) with a tunnel gap between the proof mass (1) and the tunnel tip (2);

alternatively, the drive comb (3) further comprises a movable frame (33) integrating a plurality of the movable drive comb teeth (31), the movable frame (33) being elastically connected with the proof mass (1), and the movable frame (33) and the tunnel tip (2) having a tunnel gap therebetween.

5. The MEMS accelerometer according to claim 4, wherein the proof mass (1) comprises a hollow (11) passing through the proof mass (1), the MEMS accelerometer further comprising a first substrate (4), anchor points (5) and stoppers (6), the tunnel tip (2), the fixed drive comb (32), the anchor points (5) and the stoppers (6) all fixedly connected to the first substrate (4), the anchor points (5) being provided in plurality, the movable frame (33) or the proof mass (1) being elastically connected to at least one of the anchor points (5), the stoppers (6) being provided in the hollow (11) for limiting the range of movement of the proof mass (1).

6. The MEMS accelerometer according to claim 5, further comprising a second substrate (7) arranged on a side of the proof mass (1) remote from the first substrate (4), the first substrate (4) and the second substrate (7) being connected at both ends forming a cavity in which the proof mass (1), the tunnel tip (2), the drive comb (3), the anchor point (5) and the stopper (6) are placed.

7. A method for forming a MEMS accelerometer, the method comprising etching a structure of the MEMS accelerometer on a polysilicon layer (8), wherein the structure comprises a proof mass (1) and a plurality of tunnel tips (2), the plurality of tunnel tips (2) are distributed on four sides of the proof mass (1), and at least two tunnel tips (2) are correspondingly arranged on at least one of the four sides of the proof mass (1).

8. Method of forming a MEMS accelerometer according to claim 7, wherein after etching the structure of the MEMS accelerometer, the method comprises separating the proof mass (1) and the tunnel tip (2) using focused ion beam techniques to form a tunnel gap.

9. The method of forming a MEMS accelerometer of claim 8, wherein prior to etching the structure of the MEMS accelerometer, the method comprises:

depositing a silicon nitride layer (17) on a first substrate (4), depositing a first phosphosilicate glass layer (9) on the silicon nitride layer (17), and annealing;

-etching an anchor hole (91) in said first phosphosilicate glass layer (9);

-depositing the polycrystalline silicon layer (8) on the first phosphosilicate glass layer (9), -depositing a second phosphosilicate glass layer (10) on the polycrystalline silicon layer (8), and-annealing.

10. The method of forming a MEMS accelerometer according to claim 9, wherein after said forming a tunnel gap, the method comprises:

removing the first phosphosilicate glass layer (9);

and encapsulating the proof mass (1) and the tunnel tip (2) in a cavity enclosed by the first substrate (4) and the second substrate (7), and connecting two ends of the first substrate (4) and the second substrate (7).