Novel structure for improving sensitivity and bandwidth of acoustic sensor

Abstract

The invention discloses a novel structure for improving sensitivity and bandwidth of an acoustic sensor. The novel structure comprises an upper cover plate layer, a sensitive structure layer and a substrate layer which are connected in sequence, a sound inlet hole is formed in the upper cover plate layer, so that sound in a sound field acts on the sensitive structure layer; two sensitive structures of the sensitive structure layer are symmetrically distributed on the left side and the right side of an anchor point, and a combination composed of two connecting beams and the two sensitive structures is elastically hung on the anchor point through two torsion beams. The base layer comprises a base anchor point, two lower electrodes, a buried oxide layer and a substrate layer, and the two lower electrodes are physically isolated from each other and symmetrically distributed on the left side and the right side of the base anchor point; and the anchor points of the sensitive structure layer are rigidly fixed on the anchor points of the substrate. A plurality of blind holes are evenly distributed in the bottoms of two sensitive structures of the sensitive structure layer, two cavities are symmetrically formed in the back face of the substrate layer, and the sensitivity and the bandwidth of the MEMS bionic microphone chip are improved under the condition that the size of the MEMS bionic microphone chip is not changed.

Description

Technical Field

[0001] The invention relates to the field of MEMS, and in particular to a novel structure for improving the sensitivity and bandwidth of an acoustic sensor. Background Art

[0002] Sensitivity and bandwidth are important performance parameters of microphones. Usually, the sensitivity and bandwidth of microphones are two mutually restrictive performance indicators. It is of great research significance to improve the sensitivity and bandwidth under the condition that the size of the MEMS microphone chip remains unchanged.

[0003] In some special application scenarios, the measurement of acoustic signals will be affected by vibration interference. How to measure acoustic signals under vibration interference conditions is a difficulty. Patent document 1 "Single-point differential structure anti-vibration interference chip and microphone with the chip" (Authorization number: ZL 2022 1 0064159.4) proposes a MEMS bionic microphone chip that is resistant to vibration interference. Since the working bandwidth and sensitivity of the sensor are two mutually restrictive properties, excessive working bandwidth usually leads to low sensitivity of the microphone. Patent document 1 fails to take into account both the working bandwidth and low sensitivity. The present invention is based on the above-mentioned patent for improvement and optimization to achieve the purpose of simultaneously improving sensitivity and bandwidth. Summary of the invention

[0004] The purpose of the present invention is: in order to solve the problems of low sensitivity and narrow bandwidth of the existing MEMS bionic microphone chip, the present invention proposes a new structure for improving the sensitivity and bandwidth of the sound sensor, and realizes the improvement of the sensitivity and working bandwidth indicators without changing the size of the MEMS bionic microphone chip.

[0005] The technical solution of the present invention is:

[0006] A novel structure for improving the sensitivity and bandwidth of an acoustic sensor comprises an upper cover layer, a sensitive structure layer and a base layer connected in sequence; wherein:

[0007] The upper cover layer is provided with a sound inlet hole so that the sound in the sound field acts on the sensitive structural layer;

[0008] The sensitive structure layer includes an anchor point, a torsion beam, a connecting beam and two sensitive structures. The number of the sensitive structures is two and they are symmetrically distributed on the left and right sides of the anchor point. The two connecting beams rigidly connect the two sensitive structures. The two torsion beams elastically suspend the assembly consisting of the two connecting beams and the two sensitive structures on the anchor point.

[0009] The base layer includes a base anchor point, two lower electrodes, a buried oxide layer and a substrate layer. The two lower electrodes are physically isolated from each other and symmetrically distributed on the left and right sides of the base anchor point to form a differential structure. The anchor point of the sensitive structure layer is rigidly fixed on the base anchor point. The two lower electrodes are insulated and isolated from the substrate layer by the buried oxide layer.

[0010] Preferably, the sound inlet hole provided on the upper cover layer corresponds to a sensitive structure of the sensitive structure layer and a lower electrode position of the base layer.

[0011] Preferably, a plurality of blind holes are evenly distributed on the bottom of the two sensitive structures of the sensitive structure layer.

[0012] Preferably, two second cavities are symmetrically arranged on the back side of the substrate layer.

[0013] Preferably, a first bonding area is arranged around the upper cover layer, which is bonded with the sensitive structure layer to form a whole, and a first cavity is formed in the middle to provide space for the movement of the sensitive structure layer.

[0014] Preferably, a plurality of damping adjustment holes are symmetrically distributed on the upper surfaces of the two lower electrodes of the substrate layer.

[0015] Preferably, a stop structure is also provided at the distal ends of the two lower electrodes to limit the physical displacement of the two sensitive structures.

[0016] The advantages of the present invention are:

[0017] 1. The present invention symmetrically arranges two cavities on the back side of the acoustic sensor substrate layer, and increases the volume of the air in the microphone back cavity, thereby reducing the stiffness effect of the air on the sensitive structure, thereby improving the sensitivity of the acoustic sensor and the acoustic performance of the MEMS bionic microphone chip.

[0018] 2. The present invention etches a plurality of blind holes on the back sides of the two sensitive structures of the acoustic sensor, which significantly reduce the effective mass of the sensitive structure. Since the first-order resonant frequency of the microphone is the square root of the ratio of the stiffness coefficient to the effective mass, the first-order natural frequency is increased, thereby improving the working bandwidth.

[0019] 3. The present invention symmetrically arranges two cavities on the back side of the substrate layer of the acoustic sensor, which, on the one hand, increases the force-bearing area of ​​the MEMS bionic microphone chip, and on the other hand, makes it difficult for sound waves to diffract to the back side of the sensitive structure, thereby increasing the sound pressure difference on both sides of the sensitive structure. Ultimately, the microphone sensitive structure is subjected to a greater force under the action of the same sound wave, that is, the displacement of the sensitive structure becomes larger.

[0020] The optimization of the above structural scheme has achieved the improvement of sensitivity and working bandwidth indicators without changing the size of the acoustic sensor chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0022] Figure 1 An exploded view of the 3D structure of the MEMS bionic differential microphone chip;

[0023] Figure 2 It is the three-dimensional model of the upper cover layer;

[0024] Figure 3 It is a three-dimensional model of the sensitive structural layer;

[0025] Figure 4 A three-dimensional model of a sensitive structural layer with metal pads;

[0026] Figure 5 It is a three-dimensional model of the basal layer;

[0027] Figure 6 The bottom of the basal layer Figure 3 dimensional model. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, the exploded diagram of the new structure proposed in this patent to improve the sensitivity and bandwidth of the acoustic sensor is as follows Figure 1 As shown, it is a sandwich structure, which is mainly composed of an upper cover layer 1, a sensitive structure layer 2 and a base layer 3 which are connected in sequence.

[0029] The upper cover layer Figure 2 As shown, it is mainly composed of a sound inlet hole 11, a first bonding area 12 and a first cavity 13. The function of the sound inlet hole 11 is to make the sound in the sound field act on the sensitive structure layer 2. The function of the first bonding area 12 is to bond with the sensitive structure layer 2 to form a whole. The function of the first cavity 13 is to provide space for the movement of the sensitive structure layer 2.

[0030] Sensitive structure layer 2 Figure 3 As shown, it mainly consists of an anchor point 21, a torsion beam 22, a connecting beam 23, sensitive structures 24 symmetrically distributed on the left and right sides of the anchor point 21, blind holes 25, a second bonding area 26 and a first silicon pad 27. The connecting beam 23 rigidly connects the two sensitive structures 24, and the two torsion beams 22 elastically suspend the assembly consisting of the two connecting beams 23 and the two sensitive structures 24 on the anchor point 21. Several blind holes 25 are evenly distributed on the two sensitive structures 24, and the second bonding area 26 rigidly bonds the sensitive structure layer 2 to the base layer 3. A first metal pad 28 is distributed on the surface of the first silicon pad 27, as shown in FIG. Figure 4 shown.

[0031] Basal layer 3 Figure 5As shown, it mainly includes two symmetrically distributed lower electrodes 31, a damping adjustment hole 32, a substrate anchor point 33, a silicon wire 34, a stop structure 35, a buried oxide layer 36, a second silicon pad 37 and a substrate layer 38. The two lower electrodes 31 are physically isolated from each other and are symmetrically distributed on the left and right sides of the substrate anchor point 33 to form a differential structure. The damping adjustment holes are symmetrically distributed on the two lower electrodes 31, and the substrate anchor point 33 rigidly fixes the sensitive structure layer (except the second bonding area 26) on the substrate layer 3. The silicon wire 34 electrically connects the sensitive structure and the lower electrode 31 with the second silicon pad 37. The stop structure 35 can limit the physical displacement of the sensitive structure and prevent excessive displacement of the sensitive structure from causing structural damage. The buried oxide layer 36 realizes the insulation isolation between the lower electrode 31 and the substrate layer 38. Two second metal pads 39 with the same function are set on the substrate layer. Two second cavities 40 are symmetrically set on the back side of the substrate layer, as shown in FIG. Figure 6 As shown, it is used to improve the acoustic performance of the MEMS bionic microphone chip.

[0032] The capacitive microphone uses the detection principle of charge pump power supply. The single-ended output voltage of the MEMS bionic differential microphone is shown in formula (1), where x is the displacement of the sensitive structure, V bias is the bias voltage, and d0 is the distance between the upper and lower electrodes.

[0033]

[0034] The average displacement of the sensitive structure is shown in formula (2), where T is the torque applied to the sensitive structure, L is the length of the sensitive structure, l is the length of the torsion beam, G is the shear modulus, β is a constant related to the structure of the torsion beam, t is the thickness of the torsion beam, w is the width of the torsion beam, and W is the width of the sensitive structure.

[0035]

[0036] The torque on the sensitive structure is as shown in formula (3), where p is the sound pressure difference on both sides of the sensitive structure.

[0037]

[0038] Substituting formula (2) and formula (3) into formula (1), we can get

[0039]

[0040] It can be seen from formula (4) that the longer the length L of the sensitive structure, the greater the sensitivity of the MEMS bionic microphone. Designing a damping hole on the sensitive structure is equivalent to reducing the effective length L of the sensitive structure. In addition, the damping hole opened on the sensitive structure will also cause the sound wave signal on the front of the sensitive structure to be diffracted to the back, thereby reducing the sound pressure difference p on both sides of the sensitive structure. Optimizing the design of the damping hole on the lower electrode can effectively improve the sensitivity of the MEMS bionic microphone chip.

[0041] The expression of the first-order natural frequency of the MEMS bionic microphone is formula (5), where k is the torsional stiffness, x is the coordinate, and d is m Represents the mass of the infinitesimal element at coordinate x.

[0042]

[0043] It can be seen from formula (5) that the smaller the mass of the sensitive structure, the larger the first-order natural frequency of the MEMS bionic microphone. By opening a blind hole on the sensitive structure, the mass of the sensitive structure is effectively reduced, thereby achieving the goal of increasing the first-order natural frequency.

[0044] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any modifications made according to the spirit of the main technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel structure for improving the sensitivity and bandwidth of an acoustic sensor, characterized in that: It includes an upper cover layer, a sensitive structure layer and a base layer connected in sequence; wherein: The upper cover layer is provided with a sound inlet hole so that the sound in the sound field acts on the sensitive structural layer; The sensitive structure layer includes an anchor point, a torsion beam, a connecting beam and two sensitive structures. The number of the sensitive structures is two and they are symmetrically distributed on the left and right sides of the anchor point. The two connecting beams rigidly connect the two sensitive structures. The two torsion beams elastically suspend the assembly consisting of the two connecting beams and the two sensitive structures on the anchor point. The base layer includes a base anchor point, two lower electrodes, a buried oxide layer and a substrate layer. The two lower electrodes are physically isolated from each other and symmetrically distributed on the left and right sides of the base anchor point to form a differential structure. The anchor point of the sensitive structure layer is rigidly fixed on the base anchor point. The two lower electrodes are insulated and isolated from the substrate layer by the buried oxide layer.

2. The novel structure for improving the sensitivity and bandwidth of an acoustic sensor according to claim 1 is characterized in that: The sound inlet hole arranged on the upper cover layer corresponds to a sensitive structure of the sensitive structure layer and a lower electrode position of the base layer.

3. The novel structure for improving the sensitivity and bandwidth of an acoustic sensor according to claim 1 is characterized in that: A number of blind holes are evenly distributed on the bottom of the two sensitive structures of the sensitive structure layer.

4. The novel structure for improving the sensitivity and bandwidth of an acoustic sensor according to claim 1 is characterized in that: Two second cavities are symmetrically arranged on the back side of the substrate layer.

5. The novel structure for improving the sensitivity and bandwidth of an acoustic sensor according to claim 1 is characterized in that: A plurality of damping adjustment holes are symmetrically distributed on the upper surfaces of the two lower electrodes of the substrate layer.

6. The novel structure for improving the sensitivity and bandwidth of an acoustic sensor according to claim 2 is characterized in that: The first bonding area is arranged around the upper cover layer, which is bonded with the sensitive structure layer to form a whole, and a first cavity is formed in the middle to provide space for the movement of the sensitive structure layer.

7. The novel structure for improving the sensitivity and bandwidth of an acoustic sensor according to claim 1 is characterized in that: A stop structure is also provided at the distal ends of the two lower electrodes to limit the physical displacement of the two sensitive structures.

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