Ultrasonic wave sensor and manufacturing method thereof

Abstract

The invention provides an ultrasonic sensor and a manufacturing method thereof. The ultrasonic sensor is provided with a capacitive ultrasonic transducer, and the capacitive ultrasonic transducer is provided with three metal layers and four insulating layers. The first metal layer receives a reference voltage, the second metal layer receives a DC voltage, and the third metal layer receives an AC voltage. A cavity formed between the first metal layer and the second metal layer allows the capacitive ultrasonic transducer to mechanically vibrate, thereby generating an ultrasonic wave.

Description

Technical Field

[0001] The invention relates to an ultrasonic sensor and a manufacturing method thereof. Background Art

[0002] The operation mode of the capacitive ultrasonic transducer (CMUT) is mainly to generate sound waves through the change of capacitance. The CMUT is mainly composed of a ground electrode and a diaphragm, and another electrode is provided in the diaphragm. When the CMUT is in the transmission stage, its ground electrode is grounded, and the electrodes in the diaphragm are applied with DC voltage and AC voltage. Among them, the applied DC voltage will make the diaphragm approach the ground electrode, causing the diaphragm to bend. The applied AC voltage will excite the diaphragm to vibrate, thereby generating sound waves. However, when only AC voltage is applied without applying DC voltage, the vibration of the diaphragm will not be large enough. Therefore, in order to make the diaphragm vibrate sufficiently large, DC voltage and AC voltage must be applied at the same time. However, because the applied DC voltage and AC voltage are applied to the same electrode in the diaphragm, the applied DC voltage and AC voltage cannot be controlled separately.

[0003] When the CMUT is in the receiving stage, its ground electrode is grounded, and a DC voltage is applied to the electrodes in the diaphragm. The distance between the diaphragm and the ground electrode changes due to the sound wave, which causes the capacitance between the diaphragm and the ground electrode and the amount of charge stored in the electrodes in the diaphragm to change accordingly, thereby causing the electrodes in the diaphragm to output a corresponding AC voltage. However, when the CMUT is in the receiving stage, if a DC voltage is not applied to the electrodes in the diaphragm, the diaphragm cannot generate a large enough vibration in the receiving stage of the CMUT, which results in the AC voltage output by the electrodes in the diaphragm not having a large enough amplitude, thereby increasing the difficulty of its measurement. Therefore, in order to enable the diaphragm to generate a large enough vibration in the receiving stage of the CMUT, a DC voltage must be applied to the electrodes in the diaphragm. However, since the application of the DC voltage and the output of the AC voltage are both through the same electrode in the diaphragm, and it takes a certain switching time for the electrodes in the diaphragm to switch from the state where the DC voltage is applied to the state where the DC voltage is not applied, when the state switching cannot be completed immediately, it will cause serious distortion of the CMUT imaging.

[0004] Therefore, it is necessary to design a new type of ultrasonic sensor and a manufacturing method thereof to overcome the above-mentioned defects. Summary of the invention

[0005] The object of the present invention is to provide an ultrasonic sensor and a manufacturing method thereof, which can accurately control the time point of applying a DC voltage so that the ultrasonic sensor can receive sound waves more accurately to improve the signal-to-noise ratio of the ultrasonic sensor.

[0006] To achieve the above-mentioned object, the present invention provides an ultrasonic sensor, comprising: a substrate; a first metal layer formed on the substrate, a first portion of the first metal layer being used to receive a reference voltage; a first insulating layer formed on the first metal layer; a second insulating layer located above the first insulating layer and forming a first cavity between the second insulating layer and the first insulating layer; a second metal layer formed on the second insulating layer, a third portion of the second metal layer being used to receive a direct current voltage, which is not equal to the reference voltage; a third insulating layer formed on the second metal layer; a third metal layer formed above the third insulating layer, a sixth portion of the third metal layer being used to receive an alternating current voltage; and a fourth insulating layer formed on the third metal layer; wherein the first portion of the first metal layer, the first cavity, the third portion of the second metal layer and the sixth portion of the third metal layer form a capacitive ultrasonic transducer.

[0007] Preferably, it further comprises a semiconductor layer formed between the substrate and the second metal layer, wherein the semiconductor layer, the second portion of the first metal layer, the third portion of the second metal layer and the fourth portion of the second metal layer form a thin film transistor.

[0008] Preferably, the fourth portion of the second metal layer is coupled to the third portion of the second metal layer, the fifth portion of the second metal layer is used to receive the DC voltage, and the second portion of the first metal layer controls the electrical connection between the fourth portion of the second metal layer and the fifth portion of the second metal layer according to a control signal.

[0009] Preferably, the first portion of the first metal layer, the third portion of the second metal layer, the sixth portion of the third metal layer, and the first cavity at least partially overlap in a top-view direction of the ultrasonic sensor.

[0010] Preferably, it also includes a fifth insulating layer, which is formed under the third metal layer and forms a second cavity between the third insulating layer, and the first part of the first metal layer, the third part of the second metal layer, the sixth part of the third metal layer, the first cavity and the second cavity at least partially overlap in the top-down direction.

[0011] Preferably, the reference voltage is a ground voltage.

[0012] The present invention also provides a method for manufacturing an ultrasonic sensor, which comprises providing a substrate; forming a first metal layer on the substrate, the first metal layer comprising a first portion and a second portion; forming a first insulating layer on the first metal layer; forming a semiconductor layer on the substrate and the second portion of the first metal layer; forming a first sacrificial layer on the first insulating layer; forming a second insulating layer on the first sacrificial layer; removing the first sacrificial layer to form a first cavity between the first insulating layer and the second insulating layer; forming a second metal layer on the second insulating layer; forming a third insulating layer on the second metal layer; forming a third metal layer above the third insulating layer; and forming a fourth insulating layer on the third metal layer.

[0013] Preferably, the first sacrificial layer is formed before forming the semiconductor layer.

[0014] Preferably, the first sacrificial layer is formed after forming the semiconductor layer.

[0015] Preferably, the first portion of the first metal layer, the first cavity, the third portion of the second metal layer and the sixth portion of the third metal layer form a capacitive ultrasonic transducer; and

[0016] The second portion of the first metal layer, the semiconductor layer, the fourth portion of the second metal layer and the fifth portion of the second metal layer form a thin film transistor.

[0017] Preferably, the fourth portion of the second metal layer is coupled to the third portion of the second metal layer, the fifth portion of the second metal layer is used to receive a DC voltage, and the second portion of the first metal layer is used to control the electrical connection between the fourth portion of the second metal layer and the fifth portion of the second metal layer according to a control signal.

[0018] Preferably, the first portion of the first metal layer, the third portion of the second metal layer, the sixth portion of the third metal layer, and the first cavity at least partially overlap in a top-view direction of the ultrasonic sensor.

[0019] Preferably, the method further comprises: forming a second sacrificial layer on the third insulating layer; forming a fifth insulating layer on the second sacrificial layer; and removing the second sacrificial layer to form a second cavity between the third insulating layer and the fifth insulating layer.

[0020] Preferably, the first cavity and the second cavity at least partially overlap in a top-view direction of the ultrasonic sensor.

[0021] Compared with the prior art, an ultrasonic sensor and a manufacturing method thereof are provided in an embodiment of the present invention. The ultrasonic sensor comprises a substrate, a first metal layer, a first insulating layer, a second insulating layer, a second metal layer, a third insulating layer, a third metal layer and a fourth insulating layer. The first metal layer is formed on the substrate, and a first portion of the first metal layer is used to receive a reference voltage. The first insulating layer is formed on the first metal layer. A first cavity is formed between the second insulating layer and the first insulating layer. The second metal layer is formed on the second insulating layer, and a third portion of the second metal layer is used to receive a direct current voltage, which is not equal to the reference voltage. The third insulating layer is formed on the second metal layer. The third metal layer is formed above the third insulating layer, and a sixth portion of the third metal layer is used to receive an alternating current voltage. The fourth insulating layer is formed on the third metal layer. The first portion of the first metal layer, the first cavity, the third portion of the second metal layer and the sixth portion of the third metal layer form a capacitive ultrasonic transducer. In this way, the time point of applying the direct current voltage can be accurately controlled so that the ultrasonic sensor can receive sound waves more accurately to improve the signal-to-noise ratio of the ultrasonic sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 FIG. 4 is a top view of an ultrasonic sensor according to an embodiment of the present invention.

[0023] Figure 2 yes Figure 1 A cross-sectional view of the ultrasonic sensor along section line 2-2'.

[0024] Figure 3 yes Figure 1 Schematic diagram of the connection between the control circuit of the ultrasonic sensor and the related metal layers.

[0025] Figures 4 to 11 FIG. 4 is a schematic diagram for explaining the manufacturing of an ultrasonic sensor according to an embodiment of the present invention.

[0026] Figure 12 to Figure 13 FIG. 4 is a schematic diagram for explaining the manufacturing of an ultrasonic sensor according to another embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention can be understood by referring to the following detailed description in conjunction with the accompanying drawings. It should be noted that in order to facilitate the reader's understanding and simplify the drawings, the multiple drawings in the present invention only depict a portion of the electronic device, and the specific components in the drawings are not drawn according to the actual scale. In addition, the number and size of each component in the drawings are only for illustration and are not intended to limit the scope of the present invention.

[0028] Certain words are used throughout the specification of the present invention to refer to specific components. It should be understood by those skilled in the art that electronic equipment manufacturers may refer to the same components by different names. This document does not intend to distinguish between components that have the same function but different names. In the following specification and claims, the words "including" and "comprising" are open-ended words and should therefore be interpreted as "including but not limited to...".

[0029] It should be understood that when an element or film layer is referred to as being "on", "disposed on" or "connected to" another element or film layer, it may be directly on or directly connected to the other element or layer, or there may be an intervening element or film layer between the two (indirect case). Conversely, when an element is referred to as being "directly on", "disposed directly on" or "directly connected to" another element or film layer, there may be no intervening element or film layer between the two.

[0030] Electrical connection can be direct or indirect. Electrical connection between two components can be direct contact to transmit electrical signals without any other components between them. Electrical connection between two components can be bridged by a conductive medium between the two components to transmit electrical signals. Coupling between two components can be without a conductive medium between the two components, but the two components can form a capacitor through the medium.

[0031] Although the terms first, second, third, etc. can be used to describe a variety of components, the components are not limited to these terms. These terms are only used to distinguish a single component from other components in the specification. Please refer to Figure 1 and Figure 2 . Figure 1 is a top view of an ultrasonic sensor 10 according to an embodiment of the present invention, and Figure 2 yes Figure 1The ultrasonic sensor 10 is a cross-sectional view along the section line 2-2'. The ultrasonic sensor 10 includes a substrate 12, a first metal layer M1, a first insulating layer PV1, a second insulating layer PV2, a second metal layer M2, a third insulating layer PV3, a third metal layer M3 and a fourth insulating layer PV4. The first metal layer M1 is formed on the substrate 12, and the first metal layer M1 can be divided into a plurality of parts by etching, for example, a first part M11 and a second part M12. The first insulating layer PV1 is formed on the first metal layer M1, and a first cavity G1 is formed between the second insulating layer PV2 and the first insulating layer PV1. The second metal layer M2 is formed on the second insulating layer PV2, and the second metal layer M2 can be divided into a plurality of parts by etching, for example, a third part M21, a fourth part M22 and a fifth part M23. The third insulating layer PV3 is formed on the second metal layer M2. The third metal layer M3 is formed on the third insulating layer PV3, and the third metal layer M3 can be etched to retain the required portion, such as the sixth portion M31. The fourth insulating layer PV4 is formed on the third metal layer M3. The first portion M11 of the first metal layer M1, the first cavity G1, the third portion M21 of the second metal layer M2, and the sixth portion M31 of the third metal layer M3 form a capacitive ultrasonic transducer (CMUT) 20 of the ultrasonic sensor 10. Figure 1 It can be seen that the first portion M11 of the first metal layer M1 , the third portion M21 of the second metal layer M2 , the sixth portion M31 of the third metal layer M3 and the first cavity G1 at least partially overlap in the top view direction of the ultrasonic sensor 10 .

[0032] In one embodiment of the present invention, the ultrasonic sensor 10 further includes a semiconductor layer 15 formed between the substrate 12 and the second metal layer M2. The semiconductor layer 15 and the second portion M12 of the first metal layer M1, the fourth portion M22 of the second metal layer M2, and the fifth portion M23 of the second metal layer M2 form a thin film transistor (TFT) 30. An insulating layer 14 is provided between the second portion M12 of the first metal layer M1 and the semiconductor layer 15, and an ohmic contact layer 16 is provided between the semiconductor layer 15 and the fourth portion M22 and the fifth portion M23 of the second metal layer M2, respectively. The second portion M12 of the first metal layer M1 constitutes a gate of the thin film transistor 30, the fourth portion M22 of the second metal layer M2 constitutes a drain of the thin film transistor 30, and the fifth portion M23 of the second metal layer M2 constitutes a source of the thin film transistor 30.

[0033] Please refer to Figure 3 , and match Figure 2 . Figure 3 yes Figure 1 Schematic diagram of the connection between the control circuit 40 and the relevant metal layers of the ultrasonic sensor 10. The control circuit 40 can generate a control signal Vg, a reference voltage Vgn, a DC voltage Vdc and an AC voltage Vac. The control signal Vg is applied to the second part M12 of the first metal layer M1 to control the electrical connection between the fourth part M22 of the second metal layer M2 and the fifth part M23 of the second metal layer M2. The reference voltage Vgn can be a ground voltage, and the reference voltage Vgn is not equal to the DC voltage Vdc, and the reference voltage Vgn is applied to the first part M11 of the first metal layer M1. The DC voltage Vdc is applied to the third part M21 of the second metal layer M2, and the AC voltage Vac is applied to the sixth part M31 of the third metal layer M3.

[0034] When the ultrasonic sensor 10 is in the transmitting stage, the reference voltage Vgn is applied to the first portion M11 of the first metal layer M1, the DC voltage Vdc is applied to the third portion M21 of the second metal layer M2, and the control signal Vg is applied to the second portion M12 of the first metal layer M1 to turn on the thin film transistor 30, thereby making the fourth portion M22 of the second metal layer M2 electrically connected to the fifth portion M23 of the second metal layer M2. Due to the conduction of the thin film transistor 30, the DC voltage Vdc is transmitted to the third portion M21 of the second metal layer M2 via the fifth portion M23 and the fourth portion M22 of the second metal layer M2. At this time, since the third portion M21 of the second metal layer M2 is applied with the DC voltage Vdc, the third portion M21 of the second metal layer M2 will approach the first portion M11 of the first metal layer M1, thereby causing the third portion M21 of the second metal layer M2 to bend. Then, the AC voltage Vac is applied to the sixth portion M31 of the third metal layer M3, so that the third portion M21 of the second metal layer M2 and the sixth portion M31 of the third metal layer M3 vibrate, thereby generating sound waves. Since the DC voltage Vdc can be controlled to be supplied to the third portion M21 of the second metal layer M2 by controlling whether the thin film transistor 30 is turned on, when the transmission phase of the ultrasonic sensor 10 is to be ended, the DC voltage Vdc can be immediately stopped from being supplied to the third portion M21 of the second metal layer M2 by turning off the thin film transistor 30. When the third portion M21 of the second metal layer M2 is not provided with the DC voltage Vdc, even if the sixth portion M31 of the third metal layer M3 may still receive other noise or the AC voltage Vac, the vibration generated by the third portion M21 of the second metal layer M2 and the sixth portion M31 of the third metal layer M3 will be very small and can be ignored. In one embodiment of the present invention, when the transmission phase of the ultrasonic sensor 10 is to be terminated, the control circuit 40 simultaneously turns off the thin film transistor 30 and stops supplying the AC voltage Vac to the third portion M21 of the second metal layer M2. Since the DC voltage Vdc and the AC voltage Vac are applied to the third portion M21 of the second metal layer M2 and the sixth portion M31 of the third metal layer M3, respectively, and the DC voltage Vdc is supplied to the third portion M21 of the second metal layer M2 through the thin film transistor 30, the time point of applying the DC voltage Vdc and the AC voltage Vac can be accurately controlled, so that the ultrasonic sensor 10 can generate sound waves more accurately.

[0035] When the ultrasonic sensor 10 is in the receiving stage, the reference voltage Vgn is applied to the first portion M11 of the first metal layer M1, the DC voltage Vdc is applied to the third portion M21 of the second metal layer M2, and the control signal Vg is applied to the second portion M12 of the first metal layer M1 to turn on the thin film transistor 30, thereby making the fourth portion M22 of the second metal layer M2 electrically connected to the fifth portion M23 of the second metal layer M2. Due to the conduction of the thin film transistor 30, the DC voltage Vdc is transmitted to the third portion M21 of the second metal layer M2 via the fifth portion M23 and the fourth portion M22 of the second metal layer M2. At this time, the sixth portion M31 of the third metal layer M3 can be used to sense external sound waves. Furthermore, the distance between the sixth portion M31 of the third metal layer M3 and the first portion M11 of the first metal layer M1 changes due to the sound wave, so that the capacitance between the sixth portion M31 of the third metal layer M3 and the first portion M11 of the first metal layer M1 and the amount of charge stored in the sixth portion M31 of the third metal layer M3 change accordingly, thereby causing the sixth portion M31 of the third metal layer M3 to output a corresponding AC voltage. Therefore, by detecting the change in the AC voltage output by the sixth portion M31 of the third metal layer M3, the ultrasonic sensor 10 can complete the corresponding ultrasonic imaging. Since the DC voltage Vdc can be controlled to be supplied to the third portion M21 of the second metal layer M2 by controlling whether the thin film transistor 30 is turned on, when the receiving phase of the ultrasonic sensor 10 is to be ended, the DC voltage Vdc can be immediately stopped from being supplied to the third portion M21 of the second metal layer M2 by turning off the thin film transistor 30. When the third portion M21 of the second metal layer M2 is not provided with the DC voltage Vdc, even if the sixth portion M31 of the third metal layer M3 may still receive subsequent sound waves, the vibration generated by the sixth portion M31 of the third metal layer M3 will be very small and can be ignored. Since the DC voltage Vdc and the AC voltage Vac are applied to the third portion M21 of the second metal layer M2 and the sixth portion M31 of the third metal layer M3 respectively, and the DC voltage Vdc is supplied to the third portion M21 of the second metal layer M2 through the thin film transistor 30, the time point of applying the DC voltage Vdc can be accurately controlled, so that the ultrasonic sensor 10 can receive sound waves more accurately, thereby improving the signal-to-noise ratio (SNR) of the ultrasonic sensor 10.

[0036] Please refer to Figure 1In one embodiment of the present invention, the ultrasonic sensor 10 further includes a plurality of capacitive ultrasonic transducers 20'. The structure of each capacitive ultrasonic transducer 20' is the same as that of the capacitive ultrasonic transducer 20. The first portion M11 of the capacitive ultrasonic transducer 20 and the plurality of capacitive ultrasonic transducers 20' is formed on the first metal layer M1, the third portion M21 thereof is formed on the second metal layer M2, the sixth portion M31 thereof is formed on the third metal layer M3, and each capacitive ultrasonic transducer 20' also includes a first cavity G1 formed between the first metal layer M1 and the second metal layer M2. The ultrasonic sensor 10 can simultaneously control the capacitive ultrasonic transducer 20 and the plurality of capacitive ultrasonic transducers 20', so that the capacitive ultrasonic transducer 20 and the plurality of capacitive ultrasonic transducers 20' simultaneously generate sound waves, or output an AC voltage generated by receiving the sound waves. When the thin film transistor 30 is turned on, the DC voltage Vdc is applied to the third portion M21 of the capacitive ultrasonic transducer 20 and the plurality of capacitive ultrasonic transducers 20' through the second metal layer M2. In addition, during the transmission phase, the ultrasonic sensor 10 applies the AC voltage Vac to the sixth portion M31 of the capacitive ultrasonic transducer 20 and the plurality of capacitive ultrasonic transducers 20' through the third metal layer M3. During the reception phase of the ultrasonic sensor 10, the capacitive ultrasonic transducer 20 and the plurality of capacitive ultrasonic transducers 20' output the AC voltage generated by the received sound waves through the third metal layer M3.

[0037] Please refer to Figures 4 to 11 , Figures 4 to 11 FIG. 1 is a schematic diagram for illustrating the manufacturing of an ultrasonic sensor according to an embodiment of the present invention. First, a substrate 12 is provided, and a first metal layer M1 is formed on the substrate 12. Then, the first metal layer M1 is etched to generate a first portion M11 and a second portion M12 (such as Figure 4 Afterwards, Figure 5 As shown in FIG. 1 , a first insulating layer PV1 is formed on the first metal layer M1. Figure 6 As shown, an insulating layer 14, a semiconductor layer 15, and an ohmic contact layer 16 are formed on the substrate 12 and the second portion M12 of the first metal layer M1, and a first sacrificial layer S1 is formed on the first insulating layer PV1. The insulating layer 14, the semiconductor layer 15, and the ohmic contact layer 16 may be formed first, and then the first sacrificial layer S1 may be formed; or the first sacrificial layer S1 may be formed first, and then the insulating layer 14, the semiconductor layer 15, and the ohmic contact layer 16 may be formed. In addition, in one embodiment of the present invention, the insulating layer 14 and the first insulating layer PV1 may be formed simultaneously. Afterwards, as Figure 7As shown, a second insulating layer PV2 is formed on the first sacrificial layer S1, and the ohmic contact layer 16 is partially etched. The second insulating layer PV2 may be formed first, and then the ohmic contact layer 16 is partially etched; or the ohmic contact layer 16 may be partially etched first, and then the second insulating layer PV2 is formed. Figure 8 As shown, a second metal layer M2 is formed on the second insulating layer PV2 and the ohmic contact layer 16, and the second metal layer M2 is etched to separate the fourth portion M22 and the fifth portion M23 of the second metal layer M2. Fig. 9 As shown in FIG. 1 , a third insulating layer PV3 is formed on the second metal layer M2. Fig.10 As shown, the first sacrificial layer S1 is removed to form a first cavity G1 between the first insulating layer PV1 and the second insulating layer PV2. In order to remove the first sacrificial layer S1, a through hole connected to the space where the first sacrificial layer S1 is located can be formed in the third insulating layer PV3 and the second insulating layer PV2, and then an etching material (such as hydrochloric acid, nitric acid, sulfuric acid, etc.) can be used to etch the first sacrificial layer S1 through the through hole to remove the first sacrificial layer S1, thereby forming the first cavity G1. Then, as Fig.11 As shown, a third metal layer M3 is formed above the third insulating layer PV3, and a fourth insulating layer PV4 is formed on the third metal layer M3. Among them, the materials of the first insulating layer PV1, the second insulating layer PV2, the third insulating layer PV3, the fourth insulating layer PV4 and the insulating layer 14 can be, but not limited to, silicon oxide (SiO2), silicon nitride (SiNx), hafnium oxide (HfO2), zirconium oxide (ZrO2) and tantalum oxide (Ta2O5). The materials of the first metal layer M1, the second metal layer M2, the third metal layer M3 and the first sacrificial layer S1 can be, but not limited to, aluminum, copper, gold and silver. The material of the semiconductor layer 15 can be, but not limited to, amorphous silicon (Amorphous silicon; a-Si for short), microcrystalline silicon (Microcrystalline silicon; mc-Si for short), germanium (Ge), gallium arsenide (GaAs) and gallium nitride (GaN). The material of the ohmic contact layer 16 can be, but not limited to, aluminum, gold, silver, tungsten and magnesium. Since the manufacturing process of the capacitive ultrasonic transducer 20 is compatible with the manufacturing process of the thin film transistor 30 , the number of process steps for simultaneously manufacturing the ultrasonic transducer 20 and the thin film transistor 30 is less than the total number of process steps required for separately manufacturing the ultrasonic transducer 20 and the thin film transistor 30 .

[0038] In the above embodiment, the capacitive ultrasonic transducer 20 has a single cavity (ie, the first cavity G1), but the present invention is also applicable to each capacitive ultrasonic transducer having a plurality of cavities. Figure 12 to Figure 13 , Figure 12 to Figure 13FIG. 1 is a schematic diagram for illustrating another embodiment of the present invention when manufacturing an ultrasonic sensor 10B. In this embodiment, a second sacrificial layer S2 is first formed on the third insulating layer PV3, and then a third metal layer M3 is formed. Fig.12 As shown, the second sacrificial layer S2 is formed on the third insulating layer PV3, and a fifth insulating layer PV5 is formed on the second sacrificial layer S2. The third metal layer M3 is formed on the fifth insulating layer PV5, and the fourth insulating layer PV4 is formed on the third metal layer M3. Fig.13 As shown, the second sacrificial layer S2 is removed, and a second cavity G2 is formed between the third insulating layer PV3 and the fifth insulating layer PV5. The method of removing the second sacrificial layer S2 is similar to the method of removing the first sacrificial layer S1. A through hole connected to the space where the second sacrificial layer S2 is located can be formed in the fourth insulating layer PV4 and the fifth insulating layer PV5, and then the etching material can etch the second sacrificial layer S2 through the through hole to remove the second sacrificial layer S2, thereby forming the second cavity G2. The second cavity G2 and the first cavity G1 at least partially overlap in the top view direction of the ultrasonic sensor 10B, and the first portion M11 of the first metal layer M1, the first cavity G1, the third portion M21 of the second metal layer M2, the second cavity G2, and the sixth portion M31 of the third metal layer M3 form a capacitive ultrasonic transducer 20B of the ultrasonic sensor 10B. The control method of the ultrasonic sensor 10B is the same as that of the ultrasonic sensor 10. For this part, please refer to the above description of applying the control signal Vg, the reference voltage Vgn, the DC voltage Vdc and the AC voltage Vac, which will not be repeated here. Compared with the single-cavity capacitive ultrasonic transducer 20, the capacitive ultrasonic transducer 20B with a double cavity has a larger amplitude of the sound wave generated, and the amplitude of the AC voltage generated during the receiving stage is also larger.

[0039] In summary, the ultrasonic sensor in the embodiment of the present invention, because the DC voltage and AC voltage used for driving are respectively applied to the first part of the second metal layer and the sixth part of the third metal layer, and the DC voltage is supplied to the third part of the second metal layer through the thin film transistor, when the ultrasonic sensor is in the sending stage, the time point of applying the DC voltage and the AC voltage can be accurately controlled, so that the ultrasonic sensor can accurately generate sound waves. In addition, when the ultrasonic sensor is in the receiving stage, because the time point of applying the DC voltage can be accurately controlled, the ultrasonic sensor can receive sound waves more accurately, thereby improving the signal-to-noise ratio of the ultrasonic sensor.

[0040] Although the present invention is described in conjunction with the accompanying drawings, the embodiments disclosed in the drawings are intended to exemplify the preferred embodiments of the present invention and should not be construed as limiting the present invention. In order to clearly describe the required components, the proportions in the schematic drawings do not represent the proportional relationship of the actual components.

[0041] The present invention has been described by the above-mentioned relevant embodiments, however, the above-mentioned embodiments are only examples for implementing the present invention. It must be pointed out that the disclosed embodiments do not limit the scope of the present invention. On the contrary, changes and modifications made without departing from the spirit and scope of the present invention are all within the scope of patent protection of the present invention.

Claims

1. An ultrasonic sensor, characterized in that: include: substrate; A first metal layer is formed on the substrate, and a first portion of the first metal layer is used to receive a reference voltage; A first insulating layer formed on the first metal layer; A second insulating layer, located above the first insulating layer, and forming a first cavity between the second insulating layer and the first insulating layer; A second metal layer is formed on the second insulating layer, and a third portion of the second metal layer is used to receive a DC voltage, and the DC voltage is not equal to the reference voltage; A third insulating layer formed on the second metal layer; A third metal layer is formed above the third insulating layer, and a sixth portion of the third metal layer is used to receive an alternating voltage; as well as a fourth insulating layer formed on the third metal layer; The first portion of the first metal layer, the first cavity, the third portion of the second metal layer, and the sixth portion of the third metal layer form a capacitive ultrasonic transducer.

2. The ultrasonic sensor according to claim 1, wherein: The invention also comprises a semiconductor layer formed between the substrate and the second metal layer. The semiconductor layer, the second part of the first metal layer, the third part of the second metal layer and the fourth part of the second metal layer form a thin film transistor.

3. The ultrasonic sensor according to claim 2, characterized in that: The fourth part of the second metal layer is coupled to the third part of the second metal layer, the fifth part of the second metal layer is used to receive the DC voltage, and the second part of the first metal layer controls the electrical connection between the fourth part of the second metal layer and the fifth part of the second metal layer according to a control signal.

4. The ultrasonic sensor according to claim 1, wherein: The first portion of the first metal layer, the third portion of the second metal layer, the sixth portion of the third metal layer, and the first cavity at least partially overlap in a top-view direction of the ultrasonic sensor.

5. The ultrasonic sensor according to claim 4, characterized in that: It also includes a fifth insulating layer, which is formed under the third metal layer and forms a second cavity between the third insulating layer. The first part of the first metal layer, the third part of the second metal layer, the sixth part of the third metal layer, the first cavity and the second cavity at least partially overlap in the top-down direction.

6. The ultrasonic sensor according to claim 1, wherein: The reference voltage is ground voltage.

7. A method for manufacturing an ultrasonic sensor, characterized in that: providing a substrate; forming a first metal layer on the substrate, the first metal layer comprising a first portion and a second portion; forming a first insulating layer on the first metal layer; forming a semiconductor layer on the substrate and the second portion of the first metal layer; forming a first sacrificial layer on the first insulating layer; forming a second insulating layer on the first sacrificial layer; removing the first sacrificial layer to form a first cavity between the first insulating layer and the second insulating layer; forming a second metal layer on the second insulating layer; forming a third insulating layer on the second metal layer; forming a third metal layer above the third insulating layer; and A fourth insulating layer is formed on the third metal layer.

8. The method for manufacturing an ultrasonic sensor according to claim 7, wherein: The first sacrificial layer is formed before forming the semiconductor layer; Alternatively, the first sacrificial layer is formed after forming the semiconductor layer.

9. The method for manufacturing an ultrasonic sensor according to claim 7, wherein: The first portion of the first metal layer, the first cavity, the third portion of the second metal layer, and the sixth portion of the third metal layer form a capacitive ultrasonic transducer; as well as The second portion of the first metal layer, the semiconductor layer, the fourth portion of the second metal layer and the fifth portion of the second metal layer form a thin film transistor.

10. The method for manufacturing an ultrasonic sensor according to claim 9, wherein: The fourth part of the second metal layer is coupled to the third part of the second metal layer, the fifth part of the second metal layer is used to receive a DC voltage, and the second part of the first metal layer is used to control the electrical connection between the fourth part of the second metal layer and the fifth part of the second metal layer according to a control signal.

11. The method for manufacturing an ultrasonic sensor according to claim 9, wherein: The first portion of the first metal layer, the third portion of the second metal layer, the sixth portion of the third metal layer, and the first cavity at least partially overlap in a top-view direction of the ultrasonic sensor.

12. The method for manufacturing an ultrasonic sensor according to claim 7, wherein: Also includes: forming a second sacrificial layer on the third insulating layer; forming a fifth insulating layer on the second sacrificial layer; as well as The second sacrificial layer is removed to form a second cavity between the third insulating layer and the fifth insulating layer.

13. The method for manufacturing an ultrasonic sensor according to claim 12, wherein: The first cavity and the second cavity at least partially overlap in a top-view direction of the ultrasonic sensor.

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