CN114339557B - MEMS microphone chip, preparation method thereof and MEMS microphone - Google Patents
MEMS microphone chip, preparation method thereof and MEMS microphone Download PDFInfo
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Abstract
The embodiment of the invention discloses an MEMS microphone chip and a preparation method thereof, and an MEMS microphone, wherein the MEMS microphone chip comprises a substrate with a back cavity and a piezoelectric diaphragm positioned on one side of the substrate, and the orthographic projection of the piezoelectric diaphragm on the substrate covers the back cavity; the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along the direction parallel to the substrate; the main vibrating diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are positioned between two adjacent auxiliary vibrating diaphragms, and the main body part is connected with each first fixed end and is suspended on the back cavity; at least the primary diaphragm is adapted to convert incident acoustic pressure into a voltage signal. The technical scheme of the embodiment of the invention can improve the sensitivity of the MEMS microphone and broaden the frequency response range of the MEMS microphone under the condition of not increasing the size of the MEMS microphone chip, thereby being beneficial to the miniaturization design of the MEMS microphone chip.
Description
Technical Field
The embodiment of the invention relates to the technical field of microphones, in particular to an MEMS microphone chip, a preparation method of the MEMS microphone chip and an MEMS microphone.
Background
The MEMS microphone is a microphone manufactured based on the MEMS (Micro-Electro-Mechanical Systems) technology, has the characteristics of small size, light weight, simple installation, easy formation of an array, low cost, mass manufacturing and the like, and is widely applied to products such as mobile phones and notebook computers in the consumer electronics field, hands-free phones in the automobile field, hearing aids in the medical field and the like.
The MEMS microphone includes a capacitive MEMS microphone and a piezoelectric MEMS microphone. Wherein, piezoelectric type MEMS microphone uses the piezoelectric diaphragm as the pickup transducer, and its theory of operation is: the incident sound pressure generates in-plane stress in the piezoelectric film, and due to the piezoelectric effect, the two surfaces of the film generate output voltage, so that sound signals are converted into electric signals, and the reading of the sound signals is realized.
Compared with the traditional capacitance type MEMS microphone, the piezoelectric type MEMS microphone eliminates the air gap between the diaphragm and the back plate in the double-membrane and three-membrane structures in the capacitance type MEMS microphone, so that the piezoelectric type MEMS microphone has many advantages including dust resistance, water resistance, high-fidelity output characteristic, ultralow starting current, zero-power quick awakening and the like, and has gained wide attention in the industry. However, the sensitivity of the piezoelectric MEMS microphone is positively correlated with the area of the piezoelectric film receiving the sound pressure, and how to make the MEMS microphone have the advantages of both miniaturization and high sensitivity is a problem to be solved.
Disclosure of Invention
The embodiment of the invention provides an MEMS microphone chip, a preparation method thereof and an MEMS microphone, so that the sensitivity and the frequency response range of the MEMS microphone are improved under the condition of not increasing the size of the MEMS microphone chip, and the miniaturization design of the MEMS microphone chip is facilitated.
In a first aspect, an embodiment of the present invention provides a MEMS microphone chip, including:
a substrate having a back cavity;
the piezoelectric vibrating diaphragm is positioned on one side of the substrate, and the orthographic projection of the piezoelectric vibrating diaphragm on the substrate covers the back cavity;
the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along the direction parallel to the substrate; the main vibrating diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are positioned between two adjacent auxiliary vibrating diaphragms, and the main body part is connected with each first fixed end and is suspended on the back cavity;
at least the primary diaphragm is adapted to convert incident acoustic pressure into a voltage signal.
Optionally, the piezoelectric diaphragm includes a first electrode layer, a first piezoelectric layer, a second electrode layer, a second piezoelectric layer, and a third electrode layer, which are sequentially stacked along a first direction; the first direction is vertical to the plane of the substrate;
the first electrode layer comprises a first main end electrode positioned at the first fixed end, the second electrode layer comprises a second main end electrode positioned at the first fixed end, the third electrode layer comprises a third main end electrode positioned at the first fixed end, and the first main end electrode is electrically connected with the third main end electrode; along a first direction, the first main end electrode and the third main end electrode are respectively at least partially overlapped with the second main end electrode to form a first capacitor;
the first capacitors corresponding to the first fixed ends are connected in series.
Optionally, the first electrode layer further includes a first main body part electrode located on the main body part, and the first main body part electrode and the first main end part electrode are separately disposed; the second electrode layer also comprises a second main body part electrode positioned on the main body part, and the second main body part electrode and the second main end part electrode are separately arranged; the third electrode layer also comprises a third main body part electrode positioned on the main body part, and the third main body part electrode and the third main end part electrode are separately arranged;
the first main body electrode is electrically connected with the third main body electrode; along the first direction, the first main body part electrode and the third main body part electrode are at least partially overlapped with the second main body part electrode respectively to form a second capacitor.
Optionally, the second capacitor is connected in series with each first capacitor.
Optionally, the second main body portion electrode is electrically connected to a second main end portion electrode of the first capacitor located at the end portion in the first capacitors connected in series.
Optionally, the auxiliary diaphragm includes a second fixed end and a free end, and the free end is located at one side of the second fixed end close to the main body portion and is suspended on the back cavity;
the first electrode layer further comprises a first auxiliary end electrode positioned at the second fixed end, the second electrode layer further comprises a second auxiliary end electrode positioned at the second fixed end, the third electrode layer further comprises a third auxiliary end electrode positioned at the second fixed end, and the first auxiliary end electrode is electrically connected with the third auxiliary end electrode; the first auxiliary end electrode and the third auxiliary end electrode are respectively at least partially overlapped with the second auxiliary end electrode along the first direction to form a third capacitor;
and the third capacitors corresponding to the second fixed ends are connected in series.
Optionally, the third capacitor is connected in series with the first capacitor.
Optionally, the first auxiliary tip electrode is electrically connected to the second main tip electrode, and/or the second auxiliary tip electrode is electrically connected to the first main tip electrode.
In a second aspect, an embodiment of the present invention further provides a method for manufacturing an MEMS microphone chip, where the method for manufacturing an MEMS microphone chip provided in the first aspect includes:
providing a substrate;
forming a piezoelectric diaphragm on one side of a substrate; the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along the direction parallel to the substrate; the main vibrating diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are positioned between two adjacent auxiliary vibrating diaphragms, and the main body part is connected with each first fixed end;
forming a back cavity on a substrate; the orthographic projection of the piezoelectric diaphragm on the substrate covers the back cavity, and the main body part is suspended on the back cavity.
In a third aspect, an embodiment of the present invention further provides an MEMS microphone, including an ASIC chip and the MEMS microphone chip provided in the first aspect, where the ASIC chip is electrically connected to the MEMS microphone chip and is configured to amplify a voltage signal output by the MEMS microphone chip.
According to the MEMS microphone chip provided by the embodiment of the invention, the piezoelectric diaphragm is divided into the main diaphragm and the at least two auxiliary diaphragms, and the gap is arranged between the main diaphragm and the auxiliary diaphragms, so that the main diaphragm and the auxiliary diaphragms are separated, the rigidity of the main diaphragm can be reduced, the sensitivity of the main diaphragm to incident sound pressure is improved, the sensitivity and the frequency response range of the MEMS microphone can be further improved under the condition that the size of the MEMS microphone chip is not increased, and the miniaturization design of the MEMS microphone chip is facilitated.
Drawings
Fig. 1 is a schematic top view of an MEMS microphone chip according to an embodiment of the present invention;
FIG. 2 is a schematic cross-sectional view of a MEMS microphone chip taken along AA' in FIG. 1;
FIG. 3 is a schematic cross-sectional view of a MEMS microphone chip taken along line BB' in FIG. 1;
FIG. 4 is a schematic diagram of an equivalent structure of a first capacitor in a MEMS microphone chip;
FIG. 5 is a schematic cross-sectional view of another MEMS microphone chip taken along AA' in FIG. 1;
fig. 6 is a schematic cross-sectional view of another MEMS microphone chip taken along BB' in fig. 1;
FIG. 7 is a schematic diagram of an equivalent structure of a second capacitor in the MEMS microphone chip;
fig. 8 is a schematic cross-sectional view of still another MEMS microphone chip taken along BB' in fig. 1;
FIG. 9 is an equivalent structure diagram of a third capacitor in the MEMS microphone chip;
fig. 10 is a schematic cross-sectional view of still another MEMS microphone chip taken along BB' in fig. 1;
FIG. 11 is a graph of output voltage versus acoustic frequency for a first fixed end of the main diaphragm at a sound pressure of 1 Pa;
FIG. 12 is a graph of output voltage versus acoustic frequency for an auxiliary diaphragm at a sound pressure of 1 Pa;
FIG. 13 is a graph of total output voltage versus acoustic frequency at a sound pressure of 1Pa for the first fixed end and the main body portion of the main diaphragm;
fig. 14 is a schematic flow chart of a method for manufacturing a MEMS microphone chip according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for convenience of description, only a part of the structure related to the present invention is shown in the drawings, not the whole structure, and the shapes and sizes of the respective elements in the drawings do not reflect the true scale thereof, and are only for schematically illustrating the contents of the present invention.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application cover the modifications and variations of this application provided they come within the scope of the corresponding claims (the claimed technology) and their equivalents. It should be noted that the embodiments provided in the embodiments of the present application can be combined with each other without contradiction.
The embodiment of the invention provides an MEMS microphone chip, which comprises: the piezoelectric vibration film comprises a substrate with a back cavity and a piezoelectric vibration film positioned on one side of the substrate, wherein the orthographic projection of the piezoelectric vibration film on the substrate covers the back cavity; the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along the direction parallel to the substrate; the main vibrating diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are positioned between two adjacent auxiliary vibrating diaphragms, and the main body part is connected with each first fixed end and is suspended on the back cavity; at least the primary diaphragm is adapted to convert incident acoustic pressure into a voltage signal.
By adopting the technical scheme, the main vibrating diaphragm and the auxiliary vibrating diaphragm can be separated, so that the rigidity of the main vibrating diaphragm can be reduced, the sensitivity of the main vibrating diaphragm to incident sound pressure can be improved, the sensitivity and the frequency response range of the MEMS microphone can be improved under the condition that the size of the MEMS microphone chip is not increased, and the miniaturization design of the MEMS microphone chip is facilitated.
The above is the core idea of the present application, and based on the embodiments in the present application, a person skilled in the art can obtain all other embodiments without making creative efforts, which belong to the protection scope of the present application. The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.
Fig. 1 is a schematic top view of an MEMS microphone chip according to an embodiment of the present invention, fig. 2 is a schematic cross-sectional view of the MEMS microphone chip taken along AA 'in fig. 1, and fig. 3 is a schematic cross-sectional view of the MEMS microphone chip taken along BB' in fig. 1. Referring to fig. 1 to 3, a MEMS microphone chip provided by an embodiment of the present invention includes: a substrate 10 having a back cavity 110 and a piezoelectric diaphragm 20 located at one side of the substrate 10, wherein an orthographic projection of the piezoelectric diaphragm 20 on the substrate 10 covers the back cavity 110; the piezoelectric diaphragm 20 includes a main diaphragm 21 and at least two auxiliary diaphragms 22 (fig. 1 shows 6 auxiliary diaphragms 22), and a gap 23 (air gap) is provided between the main diaphragm 21 and the auxiliary diaphragms 22 in a direction parallel to the substrate 10; the main diaphragm 21 includes a main body portion 211 and at least two first fixed ends 212, the first fixed ends 212 are located between two adjacent auxiliary diaphragms 22, the main body portion 211 is connected to each first fixed end 212 and is suspended on the back cavity 110; at least the main diaphragm 21 is used to convert incident sound pressure into a voltage signal.
The MEMS microphone generally includes a MEMS microphone chip and an ASIC (Application Specific Integrated Circuit) chip electrically connected to each other. The piezoelectric diaphragm 20 is a core pickup structure of a piezoelectric MEMS microphone chip, and the back cavity 110 is configured to provide a vibration space for the piezoelectric diaphragm 20. After the incident sound pressure enters the MEMS microphone chip, the piezoelectric diaphragm 20 converts the incident sound pressure into a voltage signal based on the piezoelectric effect, thereby reading the sound signal. Further, the ASIC chip is used to further process, for example, amplify, the voltage signal output by the MEMS microphone chip.
In this embodiment, the piezoelectric diaphragm 20 includes a main diaphragm 21 and at least two auxiliary diaphragms 22 that are separated from each other, and fig. 1 illustrates that the piezoelectric diaphragm 20 includes six auxiliary diaphragms 22, and correspondingly, the first fixed end 212 is located between two adjacent auxiliary diaphragms 22, and therefore, the number of the first fixed ends 212 is also six. The number of the auxiliary diaphragms 22 may be set according to actual requirements, and is not limited in the embodiment of the present invention. Illustratively, the width of the gap 23 may be less than or equal to 2 μm.
As can be seen from fig. 1 to fig. 3, in the embodiment of the present invention, the piezoelectric diaphragm 20 includes the main diaphragm 21 and the auxiliary diaphragm 22, a gap 23 is formed between the main diaphragm 21 and the auxiliary diaphragm 22, the first fixed end 212 of the main diaphragm 21 is located between two adjacent auxiliary diaphragms 22, and the main body portion 211 is connected to each first fixed end 212, so that the root portion of the main diaphragm 21 is fixed on the substrate 10 by a plurality of symmetrical cantilevers (i.e., the first fixed ends 212), and the main body portion 211 is suspended on the back cavity 110, thereby reducing the rigidity of the main diaphragm 21 by using the design of the auxiliary diaphragm 22, and improving the sensitivity of the main diaphragm 21 to incident sound pressure. Therefore, under the same device size and the same incident sound pressure, the MEMS microphone chip provided by the embodiment of the invention has larger output voltage compared with the existing product, so that the sensitivity of the MEMS microphone can be improved. Under the same sensitivity requirement, the technical scheme of the embodiment of the invention can reduce the size of the MEMS microphone chip, thereby being beneficial to the miniaturization design of products.
Further, in the present embodiment, at least the main diaphragm 21 is used to convert the incident sound pressure into a voltage signal. In other words, the auxiliary diaphragm 22 may be used only to reduce the stiffness of the main diaphragm 21, and at this time, the area of the auxiliary diaphragm 22 may be reduced appropriately to increase the area ratio of the main diaphragm 21, thereby increasing the output voltage and further increasing the sensitivity. In other embodiments, the auxiliary diaphragm 22 may also serve as a sound pickup structure, respond to the incident sound pressure and output a voltage signal, so as to achieve the effects of increasing the total output voltage and increasing the spectral bandwidth, which will be described in detail later.
Alternatively, the piezoelectric diaphragm 20 may be a piezoelectric bimorph (bimorph) or a piezoelectric unimorph (unimorph) formed by a piezoelectric film to convert the incident sound pressure into a voltage signal, which is not limited in the embodiment of the present invention and can be set by a person skilled in the art as required.
Alternatively, the material of the substrate 10 may be silicon. As shown in fig. 2, an insulating layer 80, such as silicon dioxide, may be disposed between the substrate 10 and the piezoelectric diaphragm 20.
To sum up, the embodiment of the present invention divides the piezoelectric diaphragm into the main diaphragm and the at least two auxiliary diaphragms, and sets the gap between the main diaphragm and the auxiliary diaphragms to separate the main diaphragm from the auxiliary diaphragms, so as to reduce the rigidity of the main diaphragm, improve the sensitivity of the main diaphragm to the incident sound pressure, further improve the sensitivity and the frequency response range of the MEMS microphone without increasing the size of the MEMS microphone chip, and facilitate the miniaturization design of the MEMS microphone chip.
On the basis of the above-described embodiment, the structure of the piezoelectric diaphragm 20 will be described in further detail below.
Referring to fig. 2, optionally, the piezoelectric diaphragm 20 includes a first electrode layer (e.g., a film layer where the first main end electrode 301 is located), a first piezoelectric layer 40, a second electrode layer (e.g., a film layer where the second main end electrode 501 is located), a second piezoelectric layer 60, and a third electrode layer (e.g., a film layer where the third main end electrode 701 is located), which are sequentially stacked along the first direction x; the first direction x is perpendicular to the plane of the substrate 10. Illustratively, the material of the first electrode layer may be AlN/Mo, the material of the second electrode layer and the third electrode layer may be Mo, and the thickness of the first electrode layer, the thickness of the second electrode layer and the thickness of the third electrode layer may be 50nm to 200 nm. The material of the first piezoelectric layer 40 and the second piezoelectric layer 60 can be AlN, and the thickness can be 300 nm-800 nm.
With this configuration, a piezoelectric diaphragm of a piezoelectric bimorph structure can be formed, and when the piezoelectric diaphragm 20 is bent due to incident sound pressure, the first electrode layer and the third electrode layer at the same position due to the piezoelectric effect have the same charge polarity, and form an output voltage with the second electrode layer. Furthermore, different patterning designs are performed on the first electrode layer, the second electrode layer and the third electrode layer, so that the piezoelectric diaphragms at different positions can respond to incident sound pressure and output voltage signals, further, the voltage signals output by the piezoelectric diaphragms at different positions can be mutually superposed to realize the adjustment of output voltage, and several alternatives are provided below.
As a first possible embodiment, referring to fig. 2 and 3, the first electrode layer may alternatively include a first main terminal electrode 301 at the first fixed end 212, the second electrode layer includes a second main terminal electrode 501 at the first fixed end 212, the third electrode layer includes a third main terminal electrode 701 at the first fixed end 212, and the first main terminal electrode 301 is electrically connected to the third main terminal electrode 701 (not shown); along the first direction x, the first main terminal electrode 301 and the third main terminal electrode 701 respectively at least partially overlap with the second main terminal electrode 501 to form a first capacitor; the first capacitors corresponding to the first fixing terminals 212 are connected in series.
Fig. 4 is an equivalent structure diagram of the first capacitor in the MEMS microphone chip, and referring to fig. 2 and fig. 4, the first main end electrode 301, the first piezoelectric layer 40, and the second main end electrode 501 form one capacitor, the third main end electrode 701, the second piezoelectric layer 60, and the second main end electrode 501 form another capacitor, and the first capacitor C1 is equivalent to two capacitors connected in parallel. When the incident sound pressure causes the main diaphragm 21 to bend, the first main end electrode 301 and the third main end electrode 701 have the same charge polarity, and form an output voltage with the second main end electrode 501, the output voltage is the voltage across the first capacitor C1, and thus the sound signal can be read according to the output voltage of the first capacitor C1. In this embodiment, since the main diaphragm 21 has low rigidity and the middle portion of the main diaphragm 21 has a large pressure-bearing area, the output voltage of the microphone chip is higher and the sensitivity is higher under the same sound pressure. Also, there is no gap in the middle portion of the main diaphragm 21, so that the low frequency response is good.
It should be noted that the areas and relative positions of the first main end electrode 301, the second main end electrode 501, and the third main end electrode 701 may be set according to actual requirements, and fig. 2 is only an illustration and is not a limitation. Illustratively, the areas of the first, second and third main end electrodes 301, 501 and 701 respectively account for 50% to 90% of the area of the first fixed end 212.
Further, compared with the method of reading the sound signal according to the output voltage of each first capacitor C1, the present embodiment can increase the output voltage of the MEMS microphone chip by connecting the first capacitors C1 corresponding to the respective first fixed ends 212 in series, thereby increasing the sensitivity. Illustratively, referring to fig. 1 and 4, six first capacitors C1 corresponding to the six first fixed terminals 212 are connected in series as follows: the first pole P of the first capacitor C1 is electrically connected to the second pole N of the second first capacitor C1, the first pole P of the second first capacitor C1 is electrically connected to the second pole N of the third first capacitor C1 … …, the first pole P of the fifth first capacitor C1 is electrically connected to the second pole N of the sixth first capacitor C1, and the second pole N of the first capacitor C1 and the first pole P of the sixth first capacitor C1 are respectively used as two output electrode terminals of the MEMS microphone chip and are electrically connected to the ASIC chip.
For example, the first main terminal electrode 301 and the third main terminal electrode 701 may be electrically connected by a via or a lead, the first main terminal electrode 301 and the third main terminal electrode 701 corresponding to each first capacitor C1 may be led out to a first pad or connected by a via, the second main terminal electrode 501 may be led out to a second pad or connected to the first main terminal electrode 301 of an adjacent capacitor by a via, and the first pad and the second pad of different capacitors may be electrically connected by a lead to realize the series connection of each first capacitor C1. In the following embodiments, the connection manner of the second capacitor C2 and the third capacitor C3 is the same, and is not described again.
As a second possible implementation, fig. 5 is a schematic cross-sectional structure of another MEMS microphone chip taken along AA 'in fig. 1, and fig. 6 is a schematic cross-sectional structure of another MEMS microphone chip taken along BB' in fig. 1. Referring to fig. 5 and 6, optionally, the first electrode layer further includes a first main body portion electrode 302 located on the main body portion 211, and the first main body portion electrode 302 is separately disposed from the first main end portion electrode 301; the second electrode layer further comprises a second main body part electrode 502 positioned on the main body part 211, and the second main body part electrode 502 and the second main end part electrode 501 are separately arranged; the third electrode layer further includes a third main body portion electrode 702 located on the main body portion 211, and the third main body portion electrode 702 and the third main end portion electrode 701 are separately disposed; the first body portion electrode 302 is electrically connected to the third body portion electrode 702 (not shown); along the first direction x, the first and third body portion electrodes 302 and 702 at least partially overlap the second body portion electrode 502, respectively, forming a second capacitance.
Fig. 7 is an equivalent structure diagram of a second capacitor in the MEMS microphone chip, and referring to fig. 5 and 7, the first body portion electrode 302, the first piezoelectric layer 40, and the second body portion electrode 502 form one capacitor, the third body portion electrode 702, the second piezoelectric layer 60, and the second body portion electrode 502 form another capacitor, and the second capacitor C2 is equivalent to two capacitors connected in parallel. When the incident sound pressure causes the main diaphragm 21 to bend, the first body portion electrode 302 and the third body portion electrode 702 have the same charge polarity, and form an output voltage with the second body portion electrode 502, that is, a voltage across the second capacitor C2. Since the main body portion 211 has a large area and a high sensitivity to incident sound pressure, the main body portion 211 may be provided with the first, second, and third electrode layers, the first, second, and third main body portion electrodes 302, 502, and 702 being left in part, so as to obtain the second capacitor C2, and read a sound signal based on an output voltage of the second capacitor C2, thereby improving the sensitivity of the MEMS microphone chip.
It should be noted that the areas and relative positions of the first main body electrode 302, the second main body electrode 502, and the third main body electrode 702 may be set according to actual requirements, and fig. 5 is only an illustration and is not a limitation. Illustratively, the area of the first, second, and third body portions 302, 502, and 702 respectively accounts for 50% to 90% of the area of the body portion 211.
Further, an optional second capacitor C2 is connected in series with each first capacitor C1, i.e., the second capacitor C2 is connected in series with each first capacitor C1. Therefore, the total output voltage of the MEMS microphone chip can be improved, and the sensitivity is improved.
It should be noted that, when the main diaphragm 21 is bent due to the incident sound pressure, the polarities of the first main body portion electrode 302 (third main body portion electrode 702) and the first main end portion electrode 301 (third main end portion electrode 701) are opposite due to the different directions of the stresses applied to the main body portion 211 and the first fixed end portion 212, and therefore, the second capacitor C2 and the first capacitor C1 need to be connected in series as follows: the second body portion electrode 502 is electrically connected to the second main terminal electrode 501 of the first capacitor C1 located at the end of the first capacitors C1 connected in series. Thus, the output voltage can be prevented from being reduced due to the cancellation of positive and negative charges.
Specifically, referring to fig. 1, 4 and 7, after the six first capacitors C1 are connected in series, the first pole P (i.e., the first main terminal electrode 301 and the third main terminal electrode 701) of the first capacitor C1 at one end is in a floating state, the second pole N (i.e., the second main terminal electrode 501) of the first capacitor C1 at the other end is in a floating state, and the second body electrode 502 is electrically connected to the floating second main terminal electrode 501, so that the first pole P of the second capacitor C2 is electrically connected to the floating second pole N of the first capacitor C1 after being connected in series, and the second capacitor C2 is connected in series to each of the first capacitors C1. The first pole P (i.e. the first main terminal electrode 301 and the third main terminal electrode 701) floating in the first capacitor C1 and the second pole N (i.e. the first main body part electrode 302 and the third main body part electrode 702) floating in the second capacitor C2 after being connected in series are respectively used as two output electrode terminals of the MEMS microphone chip and are electrically connected with the ASIC chip.
For example, referring to fig. 4 and 7, in the embodiment of receiving the above-mentioned first capacitors in series, after six first capacitors C1 are connected in series, the second pole N (i.e., the second main end electrode 501) of the first capacitor C1 is suspended, so that the first pole P (i.e., the second body electrode 502) of the second capacitor C2 can be electrically connected to the second main end electrode 501 of the first capacitor C1, and the second pole N (i.e., the first body electrode 302 and the third body electrode 702) of the second capacitor C2 and the first pole P (i.e., the first main end electrode 301 and the third main end electrode 701) of the last first capacitor C1 are respectively used as two output electrode terminals of the MEMS microphone chip and are electrically connected to the ASIC chip.
Fig. 8 is a schematic cross-sectional structure diagram of another MEMS microphone chip taken along BB' in fig. 1 as a third possible embodiment. Referring to fig. 1 and 8, optionally, the auxiliary diaphragm 22 includes a second fixed end 221 and a free end 222, and the free end 222 is located at a side of the second fixed end 221 close to the main body portion 211 and is suspended on the back cavity 110; the first electrode layer further includes a first sub tip electrode 303 at the second fixed end 221, the second electrode layer further includes a second sub tip electrode 503 at the second fixed end 221, the third electrode layer further includes a third sub tip electrode 703 at the second fixed end 221, the first sub tip electrode 303 is electrically connected to the third sub tip electrode 703 (not shown); the first auxiliary tip electrode 303 and the third auxiliary tip electrode 703 respectively overlap the second auxiliary tip electrode 503 at least partially in the first direction x to form a third capacitance; the third capacitors C3 corresponding to the second fixed terminals 221 are connected in series.
Fig. 9 is an equivalent structure diagram of a third capacitor in the MEMS microphone chip, and referring to fig. 8 and 9, the first auxiliary end electrode 303, the first piezoelectric layer 40, and the second auxiliary end electrode 503 constitute one capacitor, the third auxiliary end electrode 703, the second piezoelectric layer 60, and the second auxiliary end electrode 503 constitute another capacitor, and the third capacitor C3 is equivalent to two capacitors connected in parallel. When the incident sound pressure causes the free end 222 of the auxiliary diaphragm 22 to bend, the first auxiliary end electrode 303 and the third auxiliary end electrode 703 have the same charge polarity, and constitute an output voltage, i.e., a voltage across the third capacitor C3, with the second auxiliary end electrode 503. By forming the first auxiliary tip electrode 303, the second auxiliary tip electrode 503, and the third auxiliary tip electrode 703 while leaving a part of the first electrode layer, the second electrode layer, and the third electrode layer at the second fixed end 221, a third capacitance C3 is obtained, and an acoustic signal can be read from the output voltage of the third capacitance C3.
Because the pressure area of the auxiliary diaphragm 22 is small, the sensitivity to high-frequency sound pressure is higher, so that high-frequency output can be enhanced, the bandwidth of the frequency spectrum of the MEMS microphone (the bandwidth of 20Hz to 20kHz can be approximately realized), and the frequency response range of the MEMS microphone is improved. In addition, the main diaphragm 21 and the auxiliary diaphragm 22 respond to the same sound pressure movement direction, and the gap 23 is close to the root of the main diaphragm 21, so that when the main diaphragm 21 and the auxiliary diaphragm 22 vibrate synchronously, the gap 23 is not widened, and the low-frequency performance of the microphone can be ensured.
In addition, referring to fig. 8 and 3, when the auxiliary diaphragm 22 is configured to output a voltage signal in response to an incident sound pressure, the area of the auxiliary diaphragm 22 may be increased appropriately so that the free end 222 of the auxiliary diaphragm 22 is suspended above the back chamber 110, and the back chamber 110 is used to provide a vibration space for the auxiliary diaphragm 22.
It should be noted that the areas and relative positions of the first auxiliary tip electrode 303, the second auxiliary tip electrode 503 and the third auxiliary tip electrode 703 may be set according to actual requirements, and fig. 8 is only an illustration and is not a limitation. Illustratively, the areas of the first auxiliary end electrode 303, the second auxiliary end electrode 503 and the third auxiliary end electrode 703 respectively account for 30% to 60% of the area of the auxiliary diaphragm 22.
Further, compared with the method of reading the sound signal according to the output voltage of each third capacitor C3, the present embodiment can increase the output voltage of the auxiliary diaphragm 22 by connecting the third capacitors C3 corresponding to the respective second fixed ends 221 in series, thereby increasing the sensitivity of the MEMS microphone to the high-frequency sound signal. Illustratively, referring to fig. 1 and 9, the six third capacitors C3 corresponding to the six second fixed terminals 221 are connected in series as follows: the first pole P of the first third capacitor C3 is electrically connected to the second pole N of the second third capacitor C3, the first pole P of the second third capacitor C3 is electrically connected to the second pole N of the third capacitor C3 … …, the first pole P of the fifth third capacitor C3 is electrically connected to the second pole N of the sixth third capacitor C3, and the second pole N of the first third capacitor C3 and the first pole P of the sixth third capacitor C3 are respectively used for electrically connecting to the ASIC chip.
Furthermore, the optional third capacitor C3 is connected in series with the first capacitor C1, so as to increase the total output voltage of the MEMS microphone chip, and further increase the sensitivity.
Specifically, when the incident sound pressure causes the main diaphragm 21 and the auxiliary diaphragm 22 to bend, since the directions of the stresses applied to the first fixed end 212 and the second fixed end 221 are the same, the polarities of the first auxiliary end electrode 303 (the third auxiliary end electrode 703) and the first main end electrode 301 (the third main end electrode 701) are the same, and therefore, the third capacitor C3 and the first capacitor C1 may be connected in series as follows: the first auxiliary tip electrode 303 is electrically connected to the second main tip electrode 501, and/or the second auxiliary tip electrode 503 is electrically connected to the first main tip electrode 301.
With reference to fig. 9 and 4, the first auxiliary end electrode 303 is electrically connected to the second main end electrode 501, that is, the first pole P of the third capacitor C3 is electrically connected to the second pole N of the first capacitor C1; the second auxiliary end electrode 503 is electrically connected to the first main end electrode 301, that is, the second pole N of the third capacitor C3 is electrically connected to the first pole P of the first capacitor C1, and specifically, the first auxiliary end electrode 303 may be electrically connected to the second main end electrode 501 according to the serial position of the third capacitor C3, and/or the second auxiliary end electrode 503 may be electrically connected to the first main end electrode 301.
For example, when the third capacitor C3 is connected in series between two adjacent first capacitors C1, it is necessary that the first pole P of the third capacitor C3 is electrically connected to the second pole N of the previous first capacitor C1, i.e., the first auxiliary end electrode 303 is electrically connected to the second main end electrode 501, and it is necessary that the second pole N of the third capacitor C3 is electrically connected to the first pole P of the next first capacitor C1, i.e., the second auxiliary end electrode 503 is electrically connected to the first main end electrode 301. When the series-connected third capacitor C3 is connected in series with the series-connected first capacitor C1, it is necessary to electrically connect the first pole P (i.e., the first auxiliary end electrode 303 and the third auxiliary end electrode 703) floating in the series-connected third capacitor C3 with the second pole N (i.e., the second main end electrode 501) floating in the series-connected first capacitor C1, or to electrically connect the second pole N (i.e., the second auxiliary end electrode 503) floating in the series-connected third capacitor C3 with the first pole P (i.e., the first main end electrode 301 and the third main end electrode 703) floating in the series-connected first capacitor C1. In summary, when the first capacitor C1 is connected in series with the third capacitor C3, it is sufficient that the first pole P of the capacitor (the first capacitor C1 or the third capacitor C3) is electrically connected to the second pole N of the previous capacitor, and the second pole N of the capacitor is electrically connected to the first pole P of the next capacitor. The first pole P (second pole N) of the first capacitor and the second pole N (first pole P) of the last capacitor are respectively used as two output electrode terminals of the MEMS microphone chip for electrically connecting with the ASIC chip.
Fig. 8 corresponds to the structure shown in fig. 2, and shows only a cross-sectional structure of the body portion 211 without an electrode. Without limitation, as a fourth possible embodiment, fig. 10 is a schematic cross-sectional structure of another MEMS microphone chip taken along BB' in fig. 1, and with reference to fig. 5 and 10, the first electrode layer optionally includes a first main end electrode 301, a first main body portion electrode 302, and a first auxiliary end electrode 303, the second electrode layer includes a second main end electrode 501, a second main body portion electrode 502, and a second auxiliary end electrode 503, and the third electrode layer includes a third main end electrode 701, a third main body portion electrode 702, and a third auxiliary end electrode 703, in this case, a first capacitor C1 may be formed at the first fixed end 212, a second capacitor C2 may be formed at the main body portion 211, and a third capacitor C3 may be formed at the second fixed end 221, and by connecting the first capacitor C1, the second capacitor C2, and the third capacitor C3 in series, the total output voltage of the MEMS chip may be increased to a greater extent, the sensitivity is improved. For a specific serial connection manner, reference may be made to the description of the above embodiments, which are not repeated herein.
To sum up, the embodiment of the present invention exemplarily provides four possible structures of the piezoelectric diaphragm 20, which can be respectively described with reference to fig. 1, fig. 2 and fig. 3, fig. 1, fig. 2 and fig. 8, fig. 1, fig. 5 and fig. 6, and fig. 1, fig. 5 and fig. 10, of course, the technical solution of the embodiment of the present invention is not limited to the above 4 embodiments, and other combination manners are also possible, which are not described herein again, and specifically, at least one of the first capacitor C1, the second capacitor C2 and the third capacitor C3 may be formed according to requirements, and the voltage signal is independently output by each of the first capacitor C1, the second capacitor C2 and each of the third capacitors C3 or output by being connected in series with each other, which is not limited in the embodiment of the present invention.
The output voltage of the current typical size MEMS microphone chip is smaller than mV/Pa, and the output voltage needs to be further amplified by a high-performance ASIC chip. Under the same chip size, fig. 11 is a relationship curve of an output voltage of the first fixed end in the main diaphragm under a sound pressure of 1Pa and an audio frequency, and fig. 12 is a relationship curve of an output voltage of the auxiliary diaphragm under a sound pressure of 1Pa and an audio frequency, and it can be seen from fig. 11 and fig. 12 that the output voltages of the main diaphragm and the auxiliary diaphragm under a unit sound pressure of the MEMS microphone chip provided by the embodiment of the present invention can reach the magnitude of 1mV/Pa, so that the sensitivity of the MEMS microphone can be improved. Further, fig. 13 is a graph showing a relationship between a total output voltage and an acoustic frequency of the first fixed end and the main body portion of the main diaphragm under a sound pressure of 1Pa, taking the structure shown in fig. 1 as an example, showing a relationship between a total output voltage and an acoustic frequency of the main diaphragm after 6 first capacitors C1 corresponding to the 6 first fixed ends are connected in series with the second capacitor C2 corresponding to the main body portion, as can be obtained by comparing fig. 13 and fig. 11, by connecting the second capacitor C2 in series with the six first capacitors C1, the total output voltage can be increased by nearly 7 times compared with the output voltage of the single first capacitor C1, and the sensitivity of the MEMS microphone is significantly improved. When the capacitors on the main diaphragm and the auxiliary diaphragm are connected in series and are used for responding to the sound pressure output voltage signal, the total output voltage is larger, so that the sensitivity of the MEMS microphone can be obviously improved, the performance requirement on an ASIC chip is reduced, and the cost is reduced.
Based on the same inventive concept, the embodiment of the invention also provides a preparation method of the MEMS microphone chip, which is used for preparing the MEMS microphone chip provided by any one of the embodiments. Fig. 14 is a schematic flow chart of a method for manufacturing an MEMS microphone chip according to an embodiment of the present invention, and referring to fig. 14, the method includes the following steps:
s101, providing a substrate.
Illustratively, the material of the substrate 10 may be silicon. The thickness of the silicon substrate 10 may be set according to actual requirements. In addition, referring to fig. 2, before the piezoelectric diaphragm 20 is prepared, an insulating layer 80 may be formed on the silicon substrate 10, and the insulating layer 80 may be, for example, silicon dioxide and may have a thickness of 1 μm to 2 μm.
S102, forming a piezoelectric diaphragm on one side of a substrate; the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along the direction parallel to the substrate; the main vibrating diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are located between two adjacent auxiliary vibrating diaphragms, and the main body part is connected with the first fixed ends.
As shown in fig. 1, the piezoelectric diaphragm 20 includes a main diaphragm 21 and at least two auxiliary diaphragms 22 (fig. 1 shows 6 auxiliary diaphragms 22), and a gap 23 (air gap) is provided between the main diaphragm 21 and the auxiliary diaphragms 22 in a direction parallel to the substrate 10; the main diaphragm 21 includes a main body portion 211 and at least two first fixed ends 212, the first fixed ends 212 are located between two adjacent auxiliary diaphragms 22, and the main body portion 211 connects the first fixed ends 212.
Specifically, referring to fig. 2, the piezoelectric diaphragm 20 includes a first electrode layer, a first piezoelectric layer 40, a second electrode layer, a second piezoelectric layer 60, and a third electrode layer deposited in a stacked manner. When each electrode layer is prepared, different electrode structures may be obtained by performing patterning (e.g., etching) on the first electrode layer, the second electrode layer, and the third electrode layer to form at least one of the first capacitor C1, the second capacitor C2, and the third capacitor C3, and those skilled in the art may design the electrode structures according to actual requirements. The gap 23 can be obtained by forming through holes in the first piezoelectric layer 40 and the second piezoelectric layer 60, the main diaphragm 21 and the auxiliary diaphragm 22 which are separated from each other are formed, the rigidity of the main diaphragm 21 is reduced by using the design of the auxiliary diaphragm 22, the sensitivity of the main diaphragm 21 to incident sound pressure is improved, the output voltage of the MEMS microphone chip is improved, and the sensitivity of the MEMS microphone is further improved.
Illustratively, the material of the first electrode layer may be AlN/Mo, Pt, Ru and W, the material of the second and third electrode layers may be Mo, W, Ru, Pt, Au and Al, and the thickness of the first, second and third electrode layers may be 50nm to 200 nm. The material of the first piezoelectric layer 40 and the second piezoelectric layer 60 can be any piezoelectric material, such as AlN and PZT, and the thickness can be 300nm to 800 nm.
S103, forming a back cavity on the substrate; the orthographic projection of the piezoelectric diaphragm on the substrate covers the back cavity, and the main body part is suspended on the back cavity.
As shown in fig. 2, the orthographic projection of the piezoelectric diaphragm 20 on the substrate 10 covers the back cavity 110, and at least the main body portion 211 of the main diaphragm 21 is suspended on the back cavity 110, and in other embodiments, the free end 222 of the auxiliary diaphragm 22 may also be suspended on the back cavity 110 (see fig. 8). The back cavity 110 may provide a vibration space for the piezoelectric diaphragm 20, so that the piezoelectric diaphragm 20 may output a voltage signal in response to the incident sound pressure, thereby implementing reading of the sound signal.
According to the preparation method of the MEMS microphone chip provided by the embodiment of the invention, the piezoelectric diaphragm is formed on one side of the substrate and comprises the main diaphragm and the auxiliary diaphragm which are separated from each other, so that the rigidity of the main diaphragm can be reduced, the sensitivity of the main diaphragm to incident sound pressure can be improved, the sensitivity and the frequency response range of the MEMS microphone can be further improved under the condition that the size of the MEMS microphone chip is not increased, and the miniaturization design of the MEMS microphone chip is facilitated.
Based on the same inventive concept, an embodiment of the present invention further provides an MEMS microphone, which includes an ASIC chip and the MEMS microphone chip provided in any of the above embodiments, and thus has the same beneficial effects as the MEMS microphone chip, and the same points can be understood with reference to the above embodiment of the MEMS microphone chip, and are not described herein again. In the MEMS microphone, the ASIC chip is electrically connected to the MEMS microphone chip, and specifically, may be electrically connected to a pad on the MEMS microphone chip, for amplifying a voltage signal output by the MEMS microphone chip. The MEMS microphone chip provided by the embodiment of the invention has larger output voltage, so that the performance requirement on an ASIC chip can be reduced, and the cost of a device is reduced.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (9)
1. A MEMS microphone chip, comprising:
a substrate having a back cavity;
the piezoelectric diaphragm is positioned on one side of the substrate, and the orthographic projection of the piezoelectric diaphragm on the substrate covers the back cavity;
the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along the direction parallel to the substrate; the main diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are positioned between two adjacent auxiliary diaphragms, and the main body part is connected with each first fixed end and is suspended on the back cavity;
at least the main diaphragm is used for converting incident sound pressure into a voltage signal;
the piezoelectric diaphragm comprises a first electrode layer, a first piezoelectric layer, a second electrode layer, a second piezoelectric layer and a third electrode layer which are sequentially stacked along a first direction; an orthographic projection of the first piezoelectric layer on the base and an orthographic projection of the second piezoelectric layer on the base overlap; the first direction is vertical to the plane of the substrate;
the first electrode layer comprises a first main end electrode at the first fixed end, the second electrode layer comprises a second main end electrode at the first fixed end, the third electrode layer comprises a third main end electrode at the first fixed end, and the first main end electrode is electrically connected with the third main end electrode; along the first direction, the first main end electrode and the third main end electrode are respectively at least partially overlapped with the second main end electrode to form a first capacitor;
the first capacitors corresponding to the first fixed ends are connected in series.
2. The MEMS microphone chip of claim 1, wherein the first electrode layer further comprises a first body portion electrode on the body portion, the first body portion electrode being separate from the first main tip electrode; the second electrode layer further comprises a second main body part electrode positioned on the main body part, and the second main body part electrode and the second main end part electrode are separately arranged; the third electrode layer further comprises a third main body electrode positioned on the main body, and the third main body electrode and the third main end electrode are separately arranged;
the first body portion electrode is electrically connected to the third body portion electrode; along the first direction, the first main body part electrode and the third main body part electrode are at least partially overlapped with the second main body part electrode respectively to form a second capacitor.
3. The MEMS microphone chip of claim 2, wherein the second capacitance is in series with each of the first capacitances.
4. The MEMS microphone chip of claim 3, wherein the second body portion electrode is electrically connected to a second main terminal electrode of the first capacitor located at an end portion of the first capacitors after being connected in series.
5. The MEMS microphone chip of claim 1 or 3, wherein the auxiliary diaphragm comprises a second fixed end and a free end, the free end is located at a side of the second fixed end close to the main body part and is suspended on the back cavity;
the first electrode layer further comprises a first auxiliary end electrode positioned at the second fixed end, the second electrode layer further comprises a second auxiliary end electrode positioned at the second fixed end, the third electrode layer further comprises a third auxiliary end electrode positioned at the second fixed end, and the first auxiliary end electrode is electrically connected with the third auxiliary end electrode; in the first direction, the first auxiliary end electrode and the third auxiliary end electrode are respectively at least partially overlapped with the second auxiliary end electrode to form a third capacitor;
and the third capacitors corresponding to the second fixed ends are connected in series.
6. The MEMS microphone chip of claim 5, wherein the third capacitance is in series with the first capacitance.
7. The MEMS microphone chip of claim 6, wherein the first auxiliary tip electrode is electrically connected to the second main tip electrode, and/or wherein the second auxiliary tip electrode is electrically connected to the first main tip electrode.
8. A method for manufacturing a MEMS microphone chip, for manufacturing the MEMS microphone chip of any one of claims 1 to 7, comprising:
providing a substrate;
forming a piezoelectric diaphragm on one side of the substrate; the piezoelectric vibrating diaphragm comprises a main vibrating diaphragm and at least two auxiliary vibrating diaphragms, and a gap is formed between the main vibrating diaphragm and the auxiliary vibrating diaphragms along a direction parallel to the substrate; the main diaphragm comprises a main body part and at least two first fixed ends, the first fixed ends are positioned between two adjacent auxiliary diaphragms, and the main body part is connected with each first fixed end;
forming a back cavity on the substrate; the orthographic projection of the piezoelectric diaphragm on the substrate covers the back cavity, and the main body part is suspended on the back cavity;
the piezoelectric diaphragm comprises a first electrode layer, a first piezoelectric layer, a second electrode layer, a second piezoelectric layer and a third electrode layer which are sequentially stacked along a first direction; an orthographic projection of the first piezoelectric layer on the base and an orthographic projection of the second piezoelectric layer on the base overlap; the first direction is vertical to the plane of the substrate; the first electrode layer comprises a first main end electrode at the first fixed end, the second electrode layer comprises a second main end electrode at the first fixed end, the third electrode layer comprises a third main end electrode at the first fixed end, and the first main end electrode is electrically connected with the third main end electrode; along the first direction, the first main end electrode and the third main end electrode are respectively at least partially overlapped with the second main end electrode to form a first capacitor; the first capacitors corresponding to the first fixed ends are connected in series.
9. A MEMS microphone comprising an ASIC chip and the MEMS microphone chip of any of claims 1-7, the ASIC chip being electrically connected to the MEMS microphone chip for amplifying a voltage signal output by the MEMS microphone chip.
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| CN108337617A (en) * | 2018-03-02 | 2018-07-27 | 上海微联传感科技有限公司 | Piezoelectric microphone |
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Effective date of registration: 20240424 Address after: 214135 China Sensor Network International Innovation Park F2, 200 Linghu Avenue, Xinwu District, Wuxi City, Jiangsu Province Patentee after: SV SENSTECH (WUXI) CO.,LTD. Country or region after: China Address before: 2 / F, building 3, 439 Chunxiao Road, China (Shanghai) pilot Free Trade Zone, Pudong New Area, Shanghai, 201203 Patentee before: Maigan Microelectronics (Shanghai) Co.,Ltd. Country or region before: China |