An ultrasonic sensor with a sound absorption structure and a preparation method thereof

Abstract

The present invention provides an ultrasonic sensor with an acoustic absorption structure and a preparation method thereof. The ultrasonic sensor includes: a MEMS chip having a front cavity and a back cavity; a first wafer having at least one acoustic hole, the first wafer being disposed on the MEMS chip and the first wafer being located in the back cavity of the MEMS chip; and an acoustic absorption structure disposed on the first wafer, and the acoustic absorption structure being located on a side of the first wafer away from the MEMS chip. The present invention provides an ultrasonic sensor with an acoustic absorption structure and a preparation method thereof, which can effectively absorb the ultrasonic waves in the back cavity, thereby reducing the blind zone time of the ultrasonic sensor. By adopting a bonding process, the cost is low, the yield is high, the size is small, and the reliability is high.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic sensors, and particularly to an ultrasonic sensor with an acoustic absorption structure and a preparation method thereof. Background Art

[0002] The MEMS chip is processed by semiconductor etching technology. When an excitation voltage with a certain frequency is applied to the MEMS chip, the diaphragm will vibrate up and down to generate ultrasonic waves. The ultrasonic wave frequencies in front of and behind the diaphragm are the same, but the phases are opposite. If the ultrasonic waves in the back cavity of the MEMS chip are not processed, the ultrasonic waves will be emitted and superimposed in the back cavity, generating a reaction force on the diaphragm, increasing the blind zone time of the MEMS ultrasonic sensor, and directly affecting the ranging performance. Therefore, how to remove the ultrasonic waves in the back cavity is particularly important. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above problems existing in the prior art, and provide an ultrasonic sensor with an acoustic absorption structure and a preparation method thereof. An acoustic absorption structure is provided at the back cavity of the MEMS chip, which can effectively absorb the ultrasonic waves in the back cavity of the MEMS chip, reduce the reaction of the ultrasonic waves in the back cavity of the MEMS chip on the diaphragm, and thus reduce the blind zone time of the ultrasonic sensor.

[0004] To achieve the above technical purpose and reach the above technical effect, the present invention is realized through the following technical solutions:

[0005] The present invention provides an ultrasonic sensor with an acoustic absorption structure, and the ultrasonic sensor includes:

[0006] A MEMS chip having a front cavity and a back cavity;

[0007] A first wafer having at least one acoustic hole, the first wafer is disposed on the MEMS chip, and the first wafer is located in the back cavity of the MEMS chip; and

[0008] An acoustic absorption structure disposed on the first wafer, and the acoustic absorption structure is located on a side of the first wafer away from the MEMS chip.

[0009] In an embodiment of the present invention, the acoustic absorption structure includes:

[0010] A second wafer having at least one cavity and at least one acoustic hole, the second wafer is disposed on a side of the first wafer away from the MEMS chip; and

[0011] A third wafer having at least one cavity, the third wafer is disposed on a side of the second wafer away from the first wafer.

[0012] In an embodiment of the present invention, the sound absorption structure includes a fourth wafer having at least one cavity, and the fourth wafer is disposed on a side of the first wafer away from the MEMS chip.

[0013] In an embodiment of the present invention, the ultrasonic sensor further includes a friction material layer located on the surface of the first wafer, the inner wall of the sound hole, and the inner wall of the cavity.

[0014] In an embodiment of the present invention, the ultrasonic sensor further includes a metal bonding layer located at the connection between the MEMS chip and the first wafer and at the connection between the first wafer and the sound absorption structure.

[0015] The present invention also provides a method for manufacturing an ultrasonic sensor, and the manufacturing method includes the following steps:

[0016] Etch at least one through hole in the first wafer to form at least one of the sound holes;

[0017] Take one or more wafers and etch the sound absorption structure on the wafers;

[0018] Pressurize and heat bond the MEMS chip, the first wafer, and the sound absorption structure to obtain a wafer module; and

[0019] Slice the wafer module to obtain the ultrasonic sensor.

[0020] In an embodiment of the present invention, the etching step of the sound absorption structure includes:

[0021] Etch at least one groove and at least one through hole in the second wafer to form at least one of the cavities and at least one of the sound holes; and

[0022] Etch at least one groove in the third wafer to form at least one of the cavities.

[0023] In an embodiment of the present invention, the etching step of the sound absorption structure includes etching at least one groove in the fourth wafer to form at least one of the cavities.

[0024] In an embodiment of the present invention, before bonding the MEMS chip, the first wafer, and the sound absorption structure, a layer of the friction material layer is disposed on the surface of the first wafer, the inner wall of the sound hole, and the inner wall of the cavity.

[0025] In one embodiment of the present invention, the metal bonding layer includes a first patterned layer, and the first patterned layer is disposed at the connection between the MEMS chip and the first wafer and at the connection between the first wafer and the sound absorption structure.

[0026] In one embodiment of the present invention, the metal bonding layer further includes a second patterned layer, and the second patterned layer is disposed at the connection between the first wafer and the MEMS chip and at the connection between the sound absorption structure and the first wafer.

[0027] In summary, the present invention provides an ultrasonic sensor with a sound absorption structure and a preparation method. The ultrasonic sensor installs the sound absorption structure at the back cavity of the MEMS chip. When ultrasonic waves are emitted from the back cavity of the MEMS chip, the ultrasonic waves enter the sound absorption structure through the sound holes, and the sound absorption structure absorbs the ultrasonic waves, which can effectively absorb the ultrasonic waves in the back cavity, reduce the reaction of the ultrasonic waves in the back cavity on the diaphragm, thereby reducing the blind zone time of the ultrasonic sensor. By using a bonding process, the MEMS chip, the first wafer, and the sound absorption structure are bonded, which has low cost, high yield, small size, and high reliability, and is more attractive in MEMS packaging. Description of the Drawings

[0028] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of this application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 is a schematic structural diagram of an embodiment of the ultrasonic sensor of the present invention;

[0030] Figure 2 is the present invention Figure 1 exploded view of the structure;

[0031] Figure 3 is the present invention Figure 1 schematic diagram of the internal structure;

[0032] Figure 4 is a schematic structural diagram of an embodiment of the ultrasonic sensor of the present invention;

[0033] Figure 5 is the present invention Figure 4 schematic diagram of the internal structure;

[0034] Figure 6 is a schematic structural diagram of an embodiment of the ultrasonic sensor of the present invention;

[0035] Figure 7 is the present invention Figure 6 schematic diagram of the internal structure;

[0036] Figure 8 is an exploded view of the first wafer and the sound-absorbing structure in an embodiment of the present invention;

[0037] Figure 9 is an exploded view of the first wafer and the sound-absorbing structure in an embodiment of the present invention;

[0038] Figure 10 is an exploded view of the first wafer and the sound-absorbing structure in an embodiment of the present invention;

[0039] Figure 11 is an exploded view of the first wafer and the sound-absorbing structure in an embodiment of the present invention;

[0040] Figure 12 is an exploded view of the first wafer and the sound-absorbing structure in an embodiment of the present invention;

[0041] Figure 13 is an exploded view of the first wafer and the sound-absorbing structure in an embodiment of the present invention;

[0042] Figure 14 is a schematic diagram of a partial internal structure of the wafer module of the present invention;

[0043] Figure 15 is a process flow chart of the processing of the ultrasonic sensor of the present invention;

[0044] Figure 16 is a test result diagram of the blind area before adding the sound-absorbing structure to the MEMS chip of the present invention;

[0045] Figure 17 is a test result diagram of the blind area after adding the sound-absorbing structure to the MEMS chip of the present invention.

[0046] Explanation of the reference numerals in the figure: 1 - wafer module, 10 - MEMS chip, 101 - upper electrode layer, 102 - silicon layer, 103 - lower electrode layer, 104 - piezoelectric layer, 20 - first wafer, 30 - sound-absorbing structure, 301 - second wafer, 302 - third wafer, 303 - sound hole, 304 - fourth wafer, 305 - cavity, 40 - metal bonding layer, 50 - friction material layer, 60 - dividing line. Detailed implementation manners

[0047] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0048] It should be noted that the wafer in the present application can be single-crystalline silicon, polycrystalline silicon, or other types of silicon-based materials, Figure 16 and Figure 17 the board in is an obstacle during the test.

[0049] Please refer to Figures 1 to 7, the present invention provides an ultrasonic sensor with an acoustic absorption structure. The ultrasonic sensor is provided with an acoustic absorption structure 30 at the back cavity of the MEMS chip 10, which can effectively absorb the ultrasonic waves in the back cavity of the MEMS chip 10, reduce the reaction of the ultrasonic waves in the back cavity of the MEMS chip 10 on the diaphragm, and thus reduce the blind time of the ultrasonic sensor. Specifically, in an embodiment of the present invention, the ultrasonic sensor includes a MEMS chip 10, a first wafer 20, and an acoustic absorption structure 30. The MEMS chip 10 has a front cavity and a back cavity. The MEMS chip 10 includes a silicon layer 102, a lower electrode layer 103, a piezoelectric layer 104, and an upper electrode layer 101. The lower electrode layer 103 is disposed on the silicon layer 102 and is located in the front cavity of the MEMS chip 10. The piezoelectric layer 104 is disposed on the side of the lower electrode layer 103 away from the silicon layer 102. The upper electrode layer 101 is located on the side of the piezoelectric layer 104 away from the lower electrode layer 103.

[0050] Please refer to Figures 1 to 7 , in an embodiment of the present invention, the ultrasonic sensor further includes a first wafer 20 having at least one acoustic hole 303. The first wafer 20 is disposed on the MEMS chip 10 and is located in the back cavity of the MEMS chip 10. The first wafer 20 and the MEMS chip 10 may be connected by forming a metal bonding layer 40 through metal bonding. The metal bonding layer includes a first patterned layer and a second patterned layer. The first patterned layer is disposed at the connection between the MEMS chip and the first wafer, and the second patterned layer is disposed at the connection between the first wafer and the MEMS chip. The first patterned layer and the second patterned layer are pressurized and heated to form the metal bonding layer 40. Specifically, the metal bonding layer 40 may be, for example, a gold-tin bond or an indium-tin bond, but is not limited thereto. As Figures 8 to 13 shown, the present application does not limit the arrangement pattern of the acoustic holes 303. In an embodiment of the present invention, the acoustic holes 303 may be arranged singly and uniformly on the first wafer 20, or may be arranged as an acoustic hole group composed of a plurality of individual acoustic holes 303 on the first wafer 20. The acoustic holes 303 may be circular holes, but are not limited thereto.

[0051] Please refer to Figures 1 to 3 , Figure 12, in an embodiment of the present invention, the ultrasonic sensor further includes an acoustic absorption structure 30. The acoustic absorption structure 30 is disposed on the first wafer 20, and the acoustic absorption structure 30 is located on the side of the first wafer 20 away from the MEMS chip 10. The acoustic absorption structure 30 and the first wafer 20 can also be connected by forming a metal bonding layer 40 through metal bonding. The metal bonding layer includes a first patterned layer and a second patterned layer. The first patterned layer is disposed at the connection of the first wafer and the acoustic absorption structure, and the second patterned layer is disposed at the connection of the acoustic absorption structure and the first wafer. By pressurizing and heating the first patterned layer and the second patterned layer, the metal bonding layer 40 is formed. The metal bonding layer 40 can be, for example, a gold-tin bond or an indium-tin bond, but is not limited thereto. The present application does not limit the specific structure of the acoustic absorption structure 30. In an embodiment of the present invention, the acoustic absorption structure 30 can be composed of a second wafer 301 and a third wafer 302. The second wafer 301 has at least one acoustic hole 303 and at least one cavity 305. The second wafer 303 is disposed on the first wafer 20 on the side away from the MEMS chip 10. The second wafer 301 and the first wafer 20 can also be connected by forming a metal bonding layer 40 through metal bonding. The metal bonding layer 40 can be, for example, a gold-tin bond or an indium-tin bond, but is not limited thereto. The present application does not limit the shape of the acoustic hole 303 on the second wafer 301. In an embodiment of the present invention, the acoustic hole 303 can be circular, square, or wedge-shaped. The third wafer 302 has at least one cavity 305. The third wafer 302 is disposed on the second wafer 301 on the side away from the first wafer 20. The third wafer 301 and the second wafer 301 can also be connected by forming a metal bonding layer 40 through metal bonding. The metal bonding layer 40 can be, for example, a gold-tin bond or an indium-tin bond, but is not limited thereto. The ultrasonic waves transmitted from the back cavity of the MEMS chip 10 can enter the second wafer 301 through the acoustic hole 303. After being absorbed once by the cavity 305 in the second wafer 301, the remaining ultrasonic waves in the second wafer 301 enter the third wafer 302 through the acoustic hole 303 on the second wafer 301 and are absorbed twice by the cavity 305 in the third wafer 302, reducing the reaction of the ultrasonic waves in the back cavity on the diaphragm, thereby reducing the blind zone time of the ultrasonic sensor. The resonance frequencies of the second wafer 301 and the third wafer 302 can be calculated by the formula Calculation, where L is the height of the second wafer 301 or the third wafer 302, t is the thickness of the first wafer 20 or the second wafer 301, d is the aperture of the sound hole 303, S is the area of the first wafer 20 or the second wafer 301, and n is the number of sound holes 303. When the second wafer 301 or the third wafer 302 resonates, that is, when the resonance frequency of the second wafer 301 or the third wafer 302 is the same as the resonance frequency of the ultrasonic wave of the ultrasonic sensor, the sound absorption coefficient reaches the maximum value, and at this time the sound absorption coefficient xs is directly proportional to the acoustic resistance of the sound hole 303.

[0052] Please refer to Figures 4 to 11 、 Figure 13 In an embodiment of the present invention, the sound absorption structure 30 may also be composed of a fourth wafer 304. The fourth wafer 304 has at least one cavity 305, and the fourth wafer 304 is disposed on the first wafer 20 on the side away from the MEMS chip 10. The fourth wafer 304 and the first wafer 20 may also be connected by forming a metal bonding layer 40 through metal bonding. The metal bonding layer 40 may be, for example, a gold-tin bond or an indium-tin bond, but is not limited thereto. The present application does not limit the shape of the cavity either. In an embodiment of the present invention, the cavity 305 may be square or circular. The ultrasonic wave transmitted from the back cavity of the MEMS chip 10 can enter the fourth wafer 304 through the sound hole 303 and be absorbed by the cavity 305 in the fourth wafer 304, reducing the reaction of the ultrasonic wave in the back cavity on the diaphragm, thereby reducing the blind zone time of the ultrasonic sensor.

[0053] Please refer to Figure 2 、 Figure 3 、 Figure 5 and Figure 7 In an embodiment of the present invention, the ultrasonic sensor further includes a friction material layer 50. The friction material layer 50 is located on the inner wall of the sound hole 303, the surface of the first wafer 20, and the inner wall of the sound absorption structure 30. The friction material layer 50 is a thin film layer. The present application does not limit the specific type of the friction material layer 50. In an embodiment of the present invention, the friction material layer 50 may be a metal oxide thin film, a polytetrafluoroethylene thin film, or a PDMS thin film. The friction material layer 50 can further increase the friction of the ultrasonic wave in the sound absorption structure 30, thereby converting sound energy into heat energy and enhancing the sound absorption effect of the sound absorption structure 30. The thickness of the friction material layer 50 varies according to the type of the selected friction material. The thickness of the friction material layer 50 can be 0.1 - 50 um, for example, 0.8 um, 10 um, 20 um, 35 um, or 50 um.

[0054] Please refer to Figure 14 and Figure 15, the present invention also provides a method for manufacturing an ultrasonic sensor, and the manufacturing method includes the following steps S1 - S4:

[0055] S1 Etch at least one through - hole on the first wafer 20 to form a sound hole 303. Specifically, the sound hole 303 is etched on the first wafer 20 through a silicon etching process. The silicon etching process is carried out at a temperature of 5 - 15 °C, for example, it can be 10 °C, and a pressure environment of 2 - 4 MPa, for example, it can be 3 MPa. By introducing an etching gas into the etching machine, according to the required size, the sound hole 303 is etched on the first wafer 20. The etching gas can be SF6, but is not limited thereto. The flow rate of the introduced etching gas is 50 - 200 sccm, for example, it can be 100 sccm.

[0056] S2 Take one or more wafers, and etch an acoustic absorption structure 30 on the wafers. Specifically, at least one groove and at least one through - hole are etched on the second wafer 301 to form at least one cavity 305 and at least one sound hole 303. At least one groove is etched on the third wafer 302 to form at least one cavity 305. At least one groove is etched on the fourth wafer 304 to form at least one cavity 305. After the etching is completed, a friction material layer 50 is uniformly prepared on the surface of the first wafer 20, the sound hole 303, the inner walls of the second wafer 301, the third wafer 302, and the fourth wafer 304.

[0057] S3 bonds the MEMS chip 10, the first wafer 20, and the sound-absorbing structure 30 to obtain the wafer module 1. Specifically, a metal bonding layer 40 is formed by patterning at the connection between the MEMS chip 10 and the first wafer 20, and heating and pressurizing are performed at the metal bonding layer 40, so that bonding occurs between the MEMS chip 10 and the first wafer 20. A metal bonding layer 40 is formed by patterning at the connection between the first wafer 20 and the second wafer 301, and heating and pressurizing are performed at the metal bonding layer 40, so that bonding occurs between the second wafer 301 and the first wafer 20. A metal bonding layer 40 is prepared by patterning at the connection between the second wafer 301 and the third wafer 302, and heating and pressurizing are performed at the metal bonding layer 40, so that bonding occurs between the third wafer 302 and the second wafer 301, forming the wafer module 1. It is also possible to form a metal bonding layer 40 by patterning at the connection between the MEMS chip 10 and the first wafer 20, and heating and pressurizing are performed at the metal bonding layer 40, so that bonding occurs between the MEMS chip 10 and the first wafer 20. A metal bonding layer 40 is formed by patterning at the connection between the first wafer 20 and the fourth wafer 304, and heating and pressurizing are performed at the metal bonding layer 40, so that bonding occurs between the fourth wafer 304 and the first wafer 20, forming the wafer module 1. The temperature during the metal bonding process is 200 - 330 °C, for example, it can be 245 °C, the pressure is 15 - 50 MPa, for example, it can be 38 MPa, and the bonding time is 20 - 85 min, for example, it can be 30 min.

[0058] S4 dices the wafer module 1 to obtain the ultrasonic sensor. Specifically, the wafer module 1 is cut along the dividing line 60 by a cutting device to obtain the ultrasonic sensor.

[0059] Please refer to Figure 16 and Figure 17 , detect the blind zones before and after adding the sound-absorbing structure 30 to the MEMS chip 10. It can be seen that the blind zone distance before adding the sound-absorbing structure 30 to the MEMS chip 10 is 80 cm, and the blind zone distance after adding the sound-absorbing structure 30 to the MEMS chip 10 is 25 cm. Since the propagation speed of ultrasonic waves is constant, the blind zone time of the ultrasonic sensor can be effectively reduced after adding the sound-absorbing structure 30 to the MEMS chip 10.

[0060] In summary, the present invention provides an ultrasonic sensor with an acoustic absorption structure and a preparation method. The ultrasonic sensor installs the acoustic absorption structure at the back cavity of the MEMS chip. When ultrasonic waves are emitted from the back cavity of the MEMS chip, the ultrasonic waves enter the acoustic absorption structure through the sound holes, and the acoustic absorption structure absorbs the ultrasonic waves, which can effectively absorb the ultrasonic waves in the back cavity, reduce the reaction of the ultrasonic waves in the back cavity on the diaphragm, thereby reducing the blind area time of the ultrasonic sensor. By using the bonding process, the MEMS chip, the first wafer and the acoustic absorption structure are bonded, with low cost, high yield, small size and high reliability, which is more attractive in MEMS packaging.

[0061] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. An ultrasonic sensor with a sound-absorbing structure, characterized in that, The ultrasonic sensor includes: a MEMS chip having a front cavity and a back cavity; a first wafer having at least one acoustic hole, the first wafer being disposed on the MEMS chip and the first wafer being located in the back cavity of the MEMS chip; and an acoustic absorption structure disposed on the first wafer and the acoustic absorption structure being located on a side of the first wafer away from the MEMS chip; wherein the acoustic absorption structure includes: a second wafer having at least one cavity and at least one acoustic hole, the second wafer being disposed on a side of the first wafer away from the MEMS chip; and a third wafer having at least one cavity, the third wafer being disposed on a side of the second wafer away from the first wafer; the ultrasonic sensor further includes a friction material layer located on the surface of the first wafer, the inner wall of the acoustic hole, and the inner wall of the cavity.

2. The ultrasonic sensor according to claim 1, wherein, The acoustic absorption structure includes a fourth wafer having at least one cavity, the fourth wafer being disposed on a side of the first wafer away from the MEMS chip.

3. The ultrasonic sensor according to claim 1, characterized in that, The ultrasonic sensor further includes a metal bonding layer located at the connection between the MEMS chip and the first wafer and at the connection between the first wafer and the acoustic absorption structure.

4. The ultrasonic sensor according to claim 3, characterized in that, The metal bonding layer includes a first patterned layer disposed at the connection between the MEMS chip and the first wafer and at the connection between the first wafer and the acoustic absorption structure.

5. The ultrasonic sensor according to claim 4, characterized in that, The metal bonding layer further includes a second patterned layer disposed at the connection between the first wafer and the MEMS chip and at the connection between the acoustic absorption structure and the first wafer.

6. The preparation method of the ultrasonic sensor according to any one of claims 1-5, characterized in that, The manufacturing method includes the following steps: etching at least one through hole on the first wafer to form at least one of the acoustic holes; taking one or more wafers and etching the acoustic absorption structure on the wafers; pressing and heating to bond the MEMS chip, the first wafer, and the acoustic absorption structure to obtain a wafer module; and dicing the wafer module to obtain the ultrasonic sensor.

7. The preparation method according to claim 6, wherein The etching step of the acoustic absorption structure includes: etching at least one groove and at least one through hole on the second wafer to form at least one of the cavities and at least one of the acoustic holes; and etching at least one groove on the third wafer to form at least one of the cavities.

8. The preparation method according to claim 7, characterized in that, The etching step of the acoustic absorption structure includes etching at least one groove on a fourth wafer to form at least one of the cavities.

9. The preparation method according to claim 7 or 8, characterized in that, Before bonding the MEMS chip, the first wafer, and the acoustic absorption structure, a layer of the friction material layer is disposed on the surface of the first wafer, the inner wall of the acoustic hole, and the inner wall of the cavity.

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