Curved piezoelectric micro-machined ultrasonic transducer element and method for manufacturing same

Abstract

A piezoelectric ultrasonic transducer element according to an embodiment of the present invention includes: a semiconductor substrate provided with a cavity; a diaphragm disposed to cover the upper surface of the cavity; a lower electrode disposed on the diaphragm; a piezoelectric layer disposed on the lower electrode; an upper electrode disposed on the piezoelectric layer; and a sealing substrate disposed to cover the lower surface of the cavity and bonded to the lower surface of the semiconductor substrate. The cavity is in a vacuum state, and the diaphragm is bent toward the sealing substrate by a pressure difference therebetween.

Description

Curvature piezoelectric micromachined ultrasonic transducer element and manufacturing method thereof

[0001] The present invention relates to a piezoelectric ultrasonic transducer element using semiconductor process technology and a method for manufacturing the same, and more specifically, to a piezoelectric ultrasonic transducer element employing anodic bonding.

[0002] Ultrasonic transducers manufactured using conventional ceramic processing methods are difficult to mass-produce because they are made by mechanical processing (dicing) of piezoelectric materials, which leads to an increase in product price.

[0003] A piezoelectric micro-machined ultrasonic transducer (PMUT) has a lower electrode, a piezoelectric layer, and an upper electrode, sequentially arranged on a diaphragm floating on a substrate. When a voltage (or electric field) is applied between the lower and upper electrodes, the piezoelectric layer deforms, generating ultrasonic waves. Conversely, when ultrasonic waves vibrate the piezoelectric layer, the piezoelectric layer converts the vibration energy into electrical energy, inducing a potential difference between the upper and lower electrodes, and detecting the potential difference to detect the ultrasonic waves.

[0004] Piezoelectric micromachined ultrasonic transducers (PMUTs) are manufactured using micro electro mechanical systems (MEMS) processes and have the advantages of integration and mass production, making them attractive as next-generation ultrasonic transducers.

[0005] The conventional PMUT structure requires an upper electrode, a piezoelectric layer, a lower electrode, and a passive support layer. In particular, the passive support layer consumes a significant amount of vibration energy, which degrades the PMUT's performance. To develop a PMUT that does not utilize a passive support layer, a curved piezoelectric micromachined ultrasonic transducer (curved PMUT) was proposed.

[0006] A dome-shaped PMUT was proposed through residual stress control. (Akhbari, S.; Sammoura, F.; Yang, C.; Heidari, A.; Horsley, D.; Lin, L. Self-Curved Diaphragms by Stress Engineering for Highly Responsive PMUT. In Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), Estoril, Portugal, 18-22 January 2015; Volume 2015.)

[0007] Curved PMUTs, a micromachined ultrasonic transducer with a curvature controlled by residual stress, have a high manufacturing complexity, and it is difficult to manufacture PMUTs with a constant curvature. Curved PMUTs, using silicon-on-insulator (SOI) substrates, are therefore expensive.

[0008] Furthermore, a silicon patterning process was used to fabricate curved pMUTs, but this has the limitation of making it very difficult to uniformly create the same pattern on a wafer. (Hajati, Arman, Dimitre Latev, and Deane Gardner. "3D MEMS piezoelectric ultrasound transducer technology." 2013 Joint IEEE International Symposium on Applications of Ferroelectric and Workshop on Piezoresponse Force Microscopy (ISAF / PFM). IEEE, 2013.)

[0009] Therefore, a curvature piezoelectric micromachined ultrasonic transducer using a low cost and simple process is required.

[0010] The technical problem to be solved by the present invention is to provide a curvature piezoelectric micromachined ultrasonic transducer that implements curvature by utilizing the pressure difference between vacuum and atmospheric pressure.

[0011] The technical problem to be solved by the present invention is to provide a method for manufacturing a curvature piezoelectric micro-machined ultrasonic transducer that implements curvature by utilizing the pressure difference between vacuum and atmospheric pressure.

[0012] A piezoelectric ultrasonic transducer element according to one embodiment of the present invention comprises: a semiconductor substrate having a cavity; a diaphragm arranged to cover an upper surface of the cavity; a lower electrode arranged on the diaphragm; a piezoelectric layer arranged on the lower electrode; an upper electrode arranged on the piezoelectric layer; and a sealing substrate arranged to cover a lower surface of the cavity and bonded to a lower surface of the semiconductor substrate. The cavity is in a vacuum state, and the diaphragm is bent in the direction of the sealing substrate due to a pressure difference.

[0013] In one embodiment of the present invention, the thickness of the sealing substrate may be tens of micrometers or more.

[0014] In one embodiment of the present invention, the material of the diaphragm may be a silicon oxide film, the material of the lower electrode and the upper electrode may be Mo, and the piezoelectric layer may be AlN.

[0015] In one embodiment of the present invention, the thickness of the diaphragm may be 100 nm to 300 nm, the thickness of the lower electrode may be 100 nm to 300 nm, the thickness of the upper electrode may be 100 nm to 300 nm, and the thickness of the piezoelectric layer may be 500 nm to 2000 nm.

[0016] In one embodiment of the present invention, the pressure of the cavity may be 1 Torr to 600 Torr.

[0017] In one embodiment of the present invention, the sealing substrate is a glass substrate, and the semiconductor substrate and the sealing substrate can be bonded by anodic bonding.

[0018] In one embodiment of the present invention, the diameter of the cavity may be 100 micrometers to 600 micrometers.

[0019] A method for manufacturing a micro-machined piezoelectric ultrasonic transducer element according to one embodiment of the present invention comprises the steps of: forming an upper silicon oxide film and a lower silicon oxide film on an upper surface and a lower surface of a semiconductor substrate, respectively; sequentially depositing a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the upper silicon oxide film; patterning the upper electrode layer to form an upper electrode and patterning the piezoelectric layer to form a contact hole to expose the lower electrode layer; grinding to remove the lower silicon oxide film formed on the lower surface of the semiconductor substrate and then etching to expose the upper silicon oxide film on the lower surface of the semiconductor substrate to form a cavity; and bonding the lower surface of the semiconductor substrate and a sealing substrate in a vacuum atmosphere.

[0020] In one embodiment of the present invention, the vacuum atmosphere may be 1 Torr to 600 Torr.

[0021] In one embodiment of the present invention, the sealing substrate is a glass substrate, and the lower surface of the semiconductor substrate and the sealing substrate can be bonded by anodic bonding.

[0022] A piezoelectric ultrasonic transducer element according to one embodiment of the present invention includes: a semiconductor substrate having a cavity; a diaphragm arranged to cover an upper surface of the cavity; a lower electrode arranged on the diaphragm; a piezoelectric layer arranged on the lower electrode; an upper electrode arranged on the piezoelectric layer; and a sealing substrate arranged to cover the upper electrode and bonded to an upper surface of the semiconductor substrate. The sealing substrate includes a sunken auxiliary cavity formed on a lower surface of the sealing substrate. The auxiliary cavity is in a vacuum state, and the diaphragm is bent in the direction of the sealing substrate due to a pressure difference.

[0023] In one embodiment of the present invention, the material of the diaphragm may be a silicon oxide film, the material of the lower electrode and the upper electrode may be Mo, and the piezoelectric layer may be AlN.

[0024] In one embodiment of the present invention, the thickness of the diaphragm may be 100 nm to 300 nm, the thickness of the lower electrode may be 100 nm to 300 nm, the thickness of the upper electrode may be 100 nm to 300 nm, and the thickness of the piezoelectric layer may be 500 nm to 2000 nm.

[0025] In one embodiment of the present invention, the pressure of the auxiliary cavity may be 1 Torr to 600 Torr.

[0026] In one embodiment of the present invention, the sealing substrate is a glass substrate, and the semiconductor substrate and the sealing substrate can be bonded by anodic bonding.

[0027] In one embodiment of the present invention, the diameter of the cavity may be 100 micrometers to 600 micrometers.

[0028] A micro-machined ultrasonic transducer (PMUT) according to one embodiment of the present invention can provide curvature to a diaphragm using a pressure difference between vacuum and atmospheric pressure.

[0029] A micro-machined ultrasonic transducer (PMUT) according to one embodiment of the present invention can change its resonant frequency by changing the degree of vacuum within a cavity.

[0030] A micromachined ultrasonic transducer (PMUT) according to one embodiment of the present invention can improve the electromechanical coupling coefficient of the pMUT by changing the curvature.

[0031] By utilizing the present invention, non-uniformity in device performance caused by residual stress of a thin film can be compensated for using vacuum.

[0032] By utilizing the present invention, contamination (dust, water, etc.) occurring in the rear cavity can be prevented.

[0033] FIG. 1 is a conceptual diagram illustrating a piezoelectric ultrasonic transducer element according to one embodiment of the present invention.

[0034] FIGS. 2A to 2G are drawings showing a method for manufacturing a piezoelectric ultrasonic transducer according to one embodiment of the present invention.

[0035] FIG. 3 is a result of a computer simulation of a piezoelectric ultrasonic transducer element according to one embodiment of the present invention.

[0036] FIG. 4 is a conceptual diagram illustrating a piezoelectric ultrasonic transducer element according to another embodiment of the present invention.

[0037] According to one embodiment of the present invention, the PMUT can form a curvature using an anodic bonding process of a silicon substrate and a glass substrate.

[0038] According to one embodiment of the present invention, the degree of bending can be controlled by utilizing the difference between the atmospheric pressure acting on the upper portion of the PMUT and the vacuum level within the cavity formed in the silicon substrate.

[0039] A PMUT according to one embodiment of the present invention can be utilized as an ultrasonic distance sensor (or motion sensor) in the air.

[0040] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosure is thorough and complete and to sufficiently convey the spirit of the present invention to those skilled in the art. In the drawings, components are exaggerated for clarity. Parts denoted by the same reference numerals throughout the specification represent the same components.

[0041] FIG. 1a is a plan view illustrating a piezoelectric ultrasonic transducer element according to one embodiment of the present invention.

[0042] Figure 1b is a cross-sectional view taken along line AA' of Figure 1a.

[0043] Referring to FIGS. 1A and 1B, a piezoelectric ultrasonic transducer element (100) includes a semiconductor substrate (110) having a cavity (110a); a diaphragm (112) arranged to cover an upper surface of the cavity (110a); a lower electrode (122) arranged on the diaphragm (112); a piezoelectric layer (124) arranged on the lower electrode (122); an upper electrode (126a) arranged on the piezoelectric layer (124); and a sealing substrate (130) arranged to cover a lower surface of the cavity (110a) and bonded to a lower surface of the semiconductor substrate. The cavity (110a) is in a vacuum state, and the diaphragm (112) is bent in the direction of the sealing substrate (130) due to a pressure difference.

[0044] The semiconductor substrate (110) may be a silicon semiconductor substrate. The semiconductor substrate (110) may include a vacuum cavity. The cavity may penetrate the semiconductor substrate (110). The radius of the cavity may be on the order of several hundred micrometers. More specifically, the radius of the cavity may be on the order of 100 micrometers (μm) to 600 micrometers. The thickness of the semiconductor substrate (110) may be on the order of about 450 μm. The vacuum degree of the cavity (110a) may be 1 Torr or less. The resonant frequency may vary depending on the vacuum degree of the cavity.

[0045] The diaphragm (112) is arranged to cover the upper surface of the cavity (110a), and the diaphragm (112) may be fixed to the semiconductor substrate (110). The diaphragm (112) may be a silicon oxide film. The thickness of the diaphragm may be 100 to 300 nm. The thickness of the diaphragm (112) may be about 200 nm.

[0046] The lower electrode (122) is formed on the diaphragm (112) and may be made of molybdenum. The material of the lower electrode (122) may be modified into a metal or a metal alloy. The thickness of the lower electrode may be 100 nm to 300 nm. The thickness of the lower electrode (122) may be about 200 nm.

[0047] The piezoelectric layer (124) may be disposed on the lower electrode (122). The piezoelectric layer (124) may include a contact hole for electrical connection between the lower electrode (124) and an external power source. The piezoelectric layer (124) may be a piezoelectric material. The material of the piezoelectric layer (124) may be AlN. The thickness of the piezoelectric layer may be 500 nm to 2000 nm. The thickness of the piezoelectric layer (124) may be about 2000 nm.

[0048] The upper electrode (126a) may be formed on the piezoelectric layer (124). The upper electrode (126a) may be patterned to cover all or part of the cavity (110a). The material of the upper electrode (126a) may be the same as the material of the lower electrode (122). The thickness of the upper electrode may be 100 nm to 300 nm. The thickness of the upper electrode (126a) may be about 200 nm. The upper electrode (126a) may have a disc shape. The upper electrode (126a) may further include a connection pad connected to a power source (140).

[0049] The power source (140) can apply a voltage between the upper electrode (126a) and the lower electrode (122) to apply an electric field to the piezoelectric layer (124) to generate ultrasonic waves. The resonant frequency of the piezoelectric ultrasonic transducer is determined by the diameter and thickness of the diaphragm, the hardness of the material, the residual stress, and the vacuum level of the cavity, and can be on the order of several kHz to several MHz.

[0050] The above piezoelectric ultrasonic transducer elements (100) can be arranged one-dimensionally or two-dimensionally.

[0051] The sealing substrate (130) may be a glass substrate, a semiconductor substrate, or a dielectric substrate. When the sealing substrate (130) is a glass substrate, the semiconductor substrate (110) and the sealing substrate (130) may be bonded to each other by anodic bonding. Meanwhile, when the sealing substrate is a silicon substrate, the semiconductor substrate (110) and the sealing substrate may be bonded to each other by van der Waals bonding. Meanwhile, the sealing substrate (130) and the semiconductor substrate (110) may be bonded to each other by a bonding pad and solder (eutectic bonding) or an adhesive. The sealing substrate (130) may have a thickness that does not bend due to a pressure difference between vacuum and atmospheric pressure. For example, the thickness of the sealing substrate (130) may be tens of micrometers or more. Preferably, the thickness of the sealing substrate (130) may be hundreds of micrometers.

[0052] The difference between the pressure of the cavity (110a) and the atmospheric pressure can apply pressure to the diaphragm (112) to bend the diaphragm (112). The bent curvature can depend on the diameter of the cavity (110a), the structure of the diaphragm, the lower electrode, the piezoelectric layer, and the upper electrode, and the pressure difference. The diaphragm (112) can be bent to have a dome shape. The height difference between the lowermost surface of the dome and the arrangement plane of the unbent diaphragm can be on the order of several micrometers.

[0053] FIGS. 2A to 2G are drawings showing a method for manufacturing a piezoelectric ultrasonic transducer according to one embodiment of the present invention.

[0054] Referring to FIGS. 2a to 2g, a method for manufacturing a piezoelectric ultrasonic transducer element includes: forming an upper silicon oxide film (112) and a lower silicon oxide film (114) on the upper and lower surfaces of a semiconductor substrate (110), respectively; depositing a lower electrode layer (122), a piezoelectric layer (124), and an upper electrode layer (126) sequentially on the upper silicon oxide film (112); patterning the upper electrode layer (126) to form an upper electrode (126a) and patterning the piezoelectric layer (124) to form a contact hole (124a) to expose the lower electrode layer (122); grinding to remove the lower silicon oxide film (114) formed on the lower surface of the semiconductor substrate (110), and then etching to expose the upper silicon oxide film (112) on the lower surface of the semiconductor substrate (110) to form a cavity (110a); And a step of bonding the lower surface of the semiconductor substrate (110) and the sealing substrate (130) in a vacuum atmosphere. The vacuum atmosphere may be 1 Torr or less.

[0055] Referring to FIG. 2a, an upper silicon oxide film (112) and a lower silicon oxide film (114) are formed on the upper and lower surfaces of a semiconductor substrate (110), respectively. The semiconductor substrate (110) may be a silicon semiconductor substrate. The upper silicon oxide film (112) and the lower silicon oxide film (114) may be a thermal oxide film or a plasma-assisted silicon oxide film. The thickness of the upper silicon oxide film (112) and the lower silicon oxide film (114) may be about 200 nm. The upper silicon oxide film (112) may be replaced with a silicon nitride or aluminum nitride layer.

[0056] Referring to FIG. 2b, a lower electrode layer (122), a piezoelectric layer (124), and an upper electrode layer (126) may be sequentially deposited on the upper silicon oxide film (112). The lower electrode layer (122) and the upper electrode layer (126) may be deposited by a sputtering method. The thickness of the lower electrode layer (122) may be about 200 nm. The thickness of the upper electrode layer (126) may be about 200 nm. The piezoelectric layer (124) is a piezoelectric material, and may be AlN, for example. The AlN may be deposited by a pulsed laser deposition method or an atomic layer deposition method. The thickness of the piezoelectric layer (124) may be about 500 to 2000 nm.

[0057] Referring to Fig. 2c, the upper electrode layer (126) can be patterned. The upper electrode layer (126) can be patterned through a photolithography process and an etching process to provide an upper electrode (126a). Alternatively, the upper electrode (126a) can be directly formed through a leaf-off process. Fig. 2c can be performed after Fig. 2d depending on the process conditions.

[0058] Referring to FIG. 2d, the piezoelectric layer (124) can be patterned to form a contact hole (124a). The piezoelectric layer (124) can be patterned through a photolithography process and an etching process.

[0059] Referring to FIG. 2e, grinding may be performed to remove the lower silicon oxide film (114) formed on the lower surface of the semiconductor substrate (110). The grinding may be performed through a chemical mechanical polishing (CMP) process. After the grinding process is performed, the thickness of the semiconductor substrate (110) may be reduced to about 450 μm. The lower surface of the semiconductor substrate (110) may be etched to expose the upper silicon oxide film (112) to form a cavity (110a). In order to form the cavity, a photolithography process and an etching process may be performed on the lower surface of the semiconductor substrate (110). The etching process may expose the upper silicon oxide film (112). The contact hole (124a) may be arranged on the outside of the cavity (110a).

[0060] Referring to FIGS. 2f and 2g, the lower surface of the semiconductor substrate (110) and the sealing substrate (130) are bonded in a vacuum atmosphere. Accordingly, the interior of the cavity (110a) may be in a vacuum state. When the sealing substrate is a glass substrate, the cavity (110a) is vacuum-sealed by the anodic bonding. The pressure of the cavity (110a) may be 1 Torr or less.

[0061] FIG. 3 is a result of a computer simulation of a piezoelectric ultrasonic transducer element according to one embodiment of the present invention.

[0062] Referring to FIGS. 1B and 3, the thickness of the semiconductor substrate (110) is 450 μm, the thickness of the upper electrode (Mo) is 200 nm, the thickness of the piezoelectric layer (AlN) is 1 μm, the thickness of the lower electrode (Mo) is 200 nm, and the diameter of the cavity is 400 μm. The thickness of the diaphragm (112) is 200 nm. In this case, the diaphragm (112) sags downward by 35 μm at a pressure of 1 ATM. Accordingly, a curvature piezoelectric micromachined ultrasonic transducer element is formed.

[0063] FIG. 4 is a conceptual diagram illustrating a piezoelectric ultrasonic transducer element according to another embodiment of the present invention.

[0064] Referring to FIG. 4, a piezoelectric ultrasonic transducer element (200) includes a semiconductor substrate (110) having a cavity (110a); a diaphragm (112) arranged to cover an upper surface of the cavity (110a); a lower electrode (122) arranged on the diaphragm (112); a piezoelectric layer (124) arranged on the lower electrode (122); an upper electrode (126a) arranged on the piezoelectric layer (124); and a sealing substrate (230) arranged to cover the upper electrode (126a) and bonded to an upper surface of the semiconductor substrate. The sealing substrate (230) includes a sunken auxiliary cavity (230a) formed on a lower surface of the sealing substrate. The auxiliary cavity (230a) is in a vacuum state, and the diaphragm (112) is bent in the direction of the sealing substrate (230) due to a pressure difference.

[0065] The material of the diaphragm (112) may be a silicon oxide film, the material of the lower electrode (122) and the upper electrode (126a) may be Mo, and the piezoelectric layer (122) may be AlN. The thickness of the diaphragm (112) may be 100 nm to 300 nm, the thickness of the lower electrode (122) may be 100 nm to 300 nm, the thickness of the upper electrode (126a) may be 100 nm to 300 nm, and the thickness of the piezoelectric layer (124) may be 500 nm to 2000 nm.

[0066] The pressure of the auxiliary cavity (230a) may be 1 torr to 600 torr. The sealing substrate (230) is a glass substrate, and the semiconductor substrate and the sealing substrate may be bonded by anodic bonding. The diameter of the cavity (110a) may be 100 micrometers to 600 micrometers.

[0067] The sealing substrate (230) may be a glass substrate, a semiconductor substrate, or a dielectric substrate. When the sealing substrate (230) is a glass substrate, the semiconductor substrate (110) and the sealing substrate (130) may be bonded to each other by anodic bonding. Meanwhile, when the sealing substrate is a silicon substrate, the semiconductor substrate (110) and the sealing substrate (230) may be bonded to each other by van der Waals bonding. Meanwhile, the sealing substrate (230) and the semiconductor substrate (110) may be bonded to each other by a bonding pad and solder (eutectic bonding) or an adhesive.

[0068] Although the present invention has been illustrated and described with respect to preferred embodiments of the features, the present invention is not limited to these embodiments, and includes various forms of embodiments that can be implemented by a person having ordinary skill in the art to which the invention pertains without departing from the technical spirit of the present invention claimed in the claims.

Claims

1. A semiconductor substrate having a cavity; A diaphragm arranged to cover the upper surface of the cavity; A lower electrode disposed on the above diaphragm; A piezoelectric layer disposed on the lower electrode; an upper electrode disposed on the piezoelectric layer; and A sealing substrate is disposed to cover the lower surface of the cavity and is bonded to the lower surface of the semiconductor substrate, The above cavity is in a vacuum state, A piezoelectric ultrasonic transducer element characterized in that the diaphragm is bent in the direction of the sealing substrate due to a pressure difference.

2. In paragraph 1, A piezoelectric ultrasonic transducer element characterized in that the thickness of the sealing substrate is tens of micrometers or more.

3. In paragraph 1, The material of the above diaphragm is silicon oxide film, The material of the lower electrode and the upper electrode is Mo, A piezoelectric ultrasonic transducer element characterized in that the piezoelectric layer is made of AlN.

4. In paragraph 3, The thickness of the above diaphragm is 100 nm to 300 nm, The thickness of the above lower electrode is 100 nm to 300 nm, The thickness of the upper electrode is 100 nm to 300 nm, A piezoelectric ultrasonic transducer element characterized in that the thickness of the piezoelectric layer is 500 nm to 2000 nm.

5. In paragraph 1, A piezoelectric ultrasonic transducer element characterized in that the pressure of the cavity is 1 Torr to 600 Torr.

6. In paragraph 1, A piezoelectric ultrasonic transducer element characterized in that the sealing substrate is a glass substrate, and the semiconductor substrate and the sealing substrate are joined by anodic bonding.

7. In paragraph 1, A piezoelectric ultrasonic transducer element characterized in that the diameter of the cavity is 100 micrometers to 600 micrometers.

8. In a method for manufacturing a micro-machined piezoelectric ultrasonic transducer element, A step of forming an upper silicon oxide film and a lower silicon oxide film on the upper and lower surfaces of a semiconductor substrate, respectively; A step of sequentially depositing a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the upper silicon oxide film; A step of patterning the upper electrode layer to form an upper electrode and patterning the piezoelectric layer to form a contact hole to expose the lower electrode layer; A step of forming a cavity by grinding to remove the lower silicon oxide film formed on the lower surface of the semiconductor substrate and then etching to expose the upper silicon oxide film on the lower surface of the semiconductor substrate; and A method for manufacturing a piezoelectric ultrasonic transducer element, characterized by comprising a step of bonding a lower surface of the semiconductor substrate and a sealing substrate in a vacuum atmosphere.

9. In paragraph 8, A method for manufacturing a piezoelectric ultrasonic transducer element, characterized in that the vacuum atmosphere is 1 Torr to 600 Torr.

10. In paragraph 8, The above sealing substrate is a glass substrate, A method for manufacturing a piezoelectric ultrasonic transducer element, characterized in that the lower surface of the semiconductor substrate and the sealing substrate are bonded by anodic bonding.

11. Semiconductor substrate having a cavity; A diaphragm arranged to cover the upper surface of the cavity; A lower electrode disposed on the above diaphragm; A piezoelectric layer disposed on the lower electrode; an upper electrode disposed on the piezoelectric layer; and A sealing substrate is disposed to cover the upper electrode and is bonded to the upper surface of the semiconductor substrate, The sealing substrate includes a sunken auxiliary cavity formed on the lower surface of the sealing substrate, The above auxiliary cavity is in a vacuum state, A piezoelectric ultrasonic transducer element characterized in that the diaphragm is bent in the direction of the sealing substrate due to a pressure difference.

12. In paragraph 11, The material of the above diaphragm is silicon oxide film, The material of the lower electrode and the upper electrode is Mo, A piezoelectric ultrasonic transducer element characterized in that the piezoelectric layer is made of AlN.

13. In paragraph 11, The thickness of the above diaphragm is 100 nm to 300 nm, The thickness of the above lower electrode is 100 nm to 300 nm, The thickness of the upper electrode is 100 nm to 300 nm, A piezoelectric ultrasonic transducer element characterized in that the thickness of the piezoelectric layer is 500 nm to 2000 nm.

14. In paragraph 11, A piezoelectric ultrasonic transducer element characterized in that the pressure of the auxiliary cavity is 1 Torr to 600 Torr.

15. In paragraph 11, A piezoelectric ultrasonic transducer element characterized in that the sealing substrate is a glass substrate, and the semiconductor substrate and the sealing substrate are joined by anodic bonding.

16. In paragraph 11, A piezoelectric ultrasonic transducer element characterized in that the diameter of the cavity is 100 micrometers to 600 micrometers.

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