ULTRASONIC TRANSDUCER DEVICE

An ultrasonic transducer device includes a first electrode, an insulating layer, an oscillating membrane, a second electrode, and a third electrode. The insulating layer is disposed on the first electrode. The oscillating membrane is disposed over the insulating layer. A cavity is between the oscillating membrane and the insulating layer. The second electrode is disposed on the oscillating membrane. The third electrode is disposed in the cavity and has a plurality of first electrode openings overlapping the second electrode. The second electrode and the third electrode are each located at different sides of the oscillating membrane.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 111128897, filed on Aug. 2, 2022. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The disclosure relates to a transducer device, and more particularly, to an ultrasonic transducer device.

Description of Related Art

Ultrasound transducer devices are technology that obtains images by emitting and receiving ultrasound, which can be applied to measure distance, such as being installed in a car to provide judgment on driving distance, in daily life, or can be applied to a medical diagnosis to check the physical condition of a patient. Generally, an ultrasonic transducer device includes multiple ultrasonic transducer units. The cell density of the ultrasonic transducer device may affect the bandwidth and output power of the ultrasonic transducer device, which in turn affects the performance of the ultrasonic transducer device. How to improve the cell density of the ultrasonic transducer device is an issue to be overcome at present.

SUMMARY

The disclosure provides an ultrasonic transducer device with increased cell density, thereby improving the performance of the ultrasonic transducer device.

The ultrasonic transducer device of the disclosure includes a first electrode, an insulating layer, an oscillating membrane, a second electrode, and a third electrode. The insulating layer is disposed on the first electrode. The oscillating membrane is disposed over the insulating layer, and there is a cavity between the oscillating membrane and the insulating layer. The second electrode is disposed on the oscillating membrane. The third electrode is disposed in the cavity and has a plurality of first openings overlapping the second electrode, and the second electrode and the third electrode are each located on different sides of the oscillating membrane.

DESCRIPTION OF THE EMBODIMENTS

FIG.1Ais a schematic top view of an ultrasonic transducer device according to an embodiment of the disclosure.FIG.1BandFIG.1Care schematic cross-sectional views of an ultrasonic transducer device ofFIG.1Ataken along the section line A-A′.FIG.1Bis a schematic cross-sectional view of a third electrode160in a state where no bias voltage is applied.FIG.1Cis a schematic cross-sectional view of the third electrode160in a state where a bias voltage is applied. For clear illustration, an oscillating membrane140inFIG.1Ais shown in a perspective manner, and a first electrode110and an insulating layer120are omitted.

Referring toFIG.1AandFIG.1B, an ultrasonic transducer device10includes the first electrode110, the insulating layer120, the oscillating membrane140, a second electrode150, and the third electrode160.

The materials of the first electrode110, the second electrode150, and the third electrode160may be titanium (Ti), aluminum (Al), copper (Cu), tungsten (W), molybdenum (Mo), silver (Ag), an alloy thereof, a combination thereof, or other suitable conductive materials. In some embodiments, the first electrode110, the second electrode150, and the third electrode160may be a single-layer or multi-layer structure (e.g., each is a stacked structure of a titanium layer, an aluminum layer, and a titanium layer). In some embodiments, the materials of the first electrode110, the second electrode150, and the third electrode160may be the same or different, but the disclosure is not limited thereto. In some embodiments, the entire first electrode110may be disposed on the substrate (not shown) without being patterned.

The insulating layer120is disposed on the first electrode110. The material of the insulating layer120may be silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, organic insulating material, or other suitable insulating materials, and the disclosure is not limited thereto. In some embodiments, the insulating layer120is directly formed on the first electrode110and covers the first electrode110. The area of the insulating layer120may be the same as or different from the area of the first electrode110.

The oscillating membrane140is disposed over the insulating layer120, and there is a cavity130between the oscillating membrane140and the insulating layer120. In other words, at least part of the region between the oscillating membrane140and the insulating layer120is not in direct contact. The oscillating membrane140is a thin film, and the material of the oscillating membrane140may be silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, organic insulating material, or other suitable thin film materials. In some embodiments, the oscillating membrane140has a first surface140aand a second surface140bopposite to the first surface140a, and the second surface140bfaces the insulating layer120.

The second electrode150and the third electrode160are each located on different sides of the oscillating membrane140. For example, the second electrode150is disposed on the first surface140aof the oscillating membrane140, and the third electrode160is disposed on the second surface140bof the oscillating membrane140. That is, the third electrode160is disposed in the cavity130. In some embodiments, the third electrode160is a mesh structure. For example, the third electrode160includes multiple longitudinal portions162extending toward the second direction D2and arranged along the first direction D1, and multiple transverse portions164extending toward the first direction D1and arranged along the second direction D2, and the first direction D1and the second direction D2intersect. In some embodiments, the first direction D1orthogonally intersects the second direction D2. The third electrode160has multiple first openings OP1, and the first openings OP1are defined by multiple intersected longitudinal portions162and transverse portions164. In the embodiment, the first opening OP1is square, but the disclosure is not limited thereto. In other embodiments, the first opening OP1may be rectangular or in other suitable shapes.

The first openings OP1overlap the second electrode150. For example, the second electrode150may include multiple main parts152and multiple connecting parts154. The area of each main part152is greater than the area of each connecting part154. The main parts152are disposed in an array in the first direction D1and the second direction D2and overlap the first openings OP1of the third electrode160. In some embodiments, the projection of the main part152on the insulating layer120is square, but the disclosure is not limited thereto. The connecting parts154may be connected between adjacent main parts152in the first direction D1and between adjacent main parts152in the second direction D2. Accordingly, the connecting parts154and the main parts152may constitute multiple second openings OP2. In the embodiment, the second opening OP2is cross-shaped, but the disclosure is not limited thereto. In other embodiments, the second opening OP2may be rectangular, round, zigzag, or in other suitable shapes.

In some embodiments, the oscillating membrane140has multiple through holes V, and the through holes V penetrate through the oscillating membrane140. The through hole V is an etching hole configured to form the cavity130during the fabrication process of the ultrasonic transducer device10. For example, the method of forming the cavity130includes steps as follows. A sacrificial layer (not shown) is formed on the insulating layer120. Next, the third electrode160, the oscillating membrane140and the second electrode150are formed on the sacrificial layer. Through holes V exposing the sacrificial layer are formed on the oscillating membrane140. Finally, the sacrificial layer is etched through the through holes V to form the cavity130. After the cavity130is formed, a filling material170may be filled into the through hole V to close the cavity130. The filling material170is connected to the insulating layer120. In some embodiments, the filling material170includes, for example, cured photoresist, silicon-containing nitride, silicon-containing oxide, or other insulating materials.

Referring toFIG.1AandFIG.1C, when the third electrode160is applied with a bias voltage (e.g., a DC bias voltage may be applied to the third electrode160), a voltage difference is generated between the third electrode160and the first electrode110, and the third electrode160is brought close to the first electrode110. After the third electrode160is in direct contact with the insulating layer120, the third electrode160, the insulating layer120and the oscillating membrane140form multiple sub-cavities132, and the sub-cavities132are closed spaces and are separated from each other. Accordingly, the third electrode160, the insulating layer120, the oscillating membrane140and the sub-cavities132can constitute multiple ultrasonic transducer units100arranged in an array. The ultrasonic transducer units100substantially correspond to the first openings OP1of the third electrode160, that is, the third electrode160may define the dimension of the ultrasonic transducer unit100. The width W and the length L of the ultrasonic transducer unit100are substantially equal to the width and length of the first opening OP1. In the embodiment, the width W of the ultrasonic transducer unit100is the same as the length L, and the distance d1between the adjacent ultrasonic transducer units100in the first direction D1is the same as the distance d2between the adjacent ultrasonic transducer units100in the second direction D2, but the disclosure is not limited thereto. The dimension of the ultrasonic transducer unit100and the distances d1and d2in the first direction D1and the second direction D2may be adjusted according to actual requirements. In the specification, the distance d1refers to the distance between the centers of two adjacent ultrasonic transducer units in the first direction D1, and the distance d2refers to the distance between the centers of two adjacent ultrasonic transducer units in the second direction D2. Since the ultrasonic transducer unit100is formed by forming a sub-cavity132among the insulating layer120, the oscillating membrane140and the third electrode160when the third electrode160is applied with a bias voltage. Compared to other ultrasonic transducer devices in which the adjacent sub-cavities are filled with materials, in the embodiment, the smaller-sized sub-cavities132can be obtained by isolating the sub-cavities132through the third electrode160, thereby improving the cell density of the ultrasonic transducer unit100.

In some embodiments, the oscillating membrane140is wavy when the third electrode160is applied with a bias voltage. The crests of the oscillating membrane140may correspond to the sub-cavities132, and the troughs of the oscillating membrane140may correspond to the third electrode160.

In some embodiments, the ultrasonic transducer device10may have an active region R1and a peripheral region R2located outside the active region R1. The peripheral region R2may surround the active region R1or only be located on one or more sides of the active region R1, which is not limited in the disclosure. The ultrasonic transducer unit100is located in the active region R1to sense (e.g., receive or transmit) ultrasonic signals, so the first electrode110, the second electrode150and the third electrode160can be located in the active region R1. In some embodiments, some of the through holes V may be located in the peripheral region R2, so that the active region R1has more space for configuring the ultrasonic transducer units100, so as to increase the cell density of the ultrasonic transducer device10. In some embodiments, some of the through holes V may be located in the active region R1, and adjacent through holes V are separated by at least two first openings OP1, that is, at least two ultrasonic transducer units100are disposed between adjacent through holes V. Compared to other ultrasonic transducer devices having through holes between adjacent ultrasonic transducer units, the through holes V configured can be reduced in the embodiment, so as to increase the cell density of the ultrasonic transducer device10. In some embodiments, the through hole V located in the active region R1corresponds to the first opening OP1of the third electrode160.

In some embodiments, after applying a DC bias voltage to the third electrode160, in the ultrasonic transducer unit100, an AC bias voltage can be applied to the second electrode150so that the oscillating membrane140can oscillate back and forth to emit ultrasonic waves.

FIG.2is a schematic top view of an ultrasonic transducer device according to another embodiment of the disclosure. Note that the embodiment ofFIG.2adopts the reference numerals and part of the content of the embodiment ofFIG.1AtoFIG.1C, the same or similar reference numerals are used to represent the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, refer to the foregoing embodiments, which is not be repeated herein.

Referring toFIG.2, the difference between an ultrasonic transducer device20ofFIG.2and the ultrasonic transducer device10ofFIG.1Ais that the second opening OP2of the second electrode150of the ultrasonic transducer device20is zigzag. In detail, the adjacent main parts152in the second direction D2can be connected through the corresponding connecting parts154, but the adjacent main parts152in the first direction D1are not connected to each other. That is, the second electrode150is not a continuous structure and disconnected from each other in the first direction D1. Although in the embodiment, the second electrode150illustrated is discontinuous in the first direction D1, it is not intended to limit the disclosure. In other embodiments, the second electrode150may be discontinuous in the second direction D2but continuous in the first direction D1.

In some embodiments, the first opening OP1is rectangular, and the projection of the main part152on the insulating layer120is rectangular.

FIG.3is a schematic top view of an ultrasonic transducer device according to another embodiment of the disclosure. Note that the embodiment ofFIG.3adopts the reference numerals and part of the content of the embodiment ofFIG.1AtoFIG.1C, the same or similar reference numerals are used to represent the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, refer to the foregoing embodiments, which is not be repeated herein.

Referring toFIG.3, the difference between an ultrasonic transducer device30ofFIG.3and the ultrasonic transducer device10ofFIG.1Ais that the second opening OP2of the second electrode150of the ultrasonic transducer device30is rectangular.

FIG.4is a schematic top view of an ultrasonic transducer device according to another embodiment of the disclosure. Note that the embodiment ofFIG.4adopts the reference numerals and part of the content of the embodiment ofFIG.1AtoFIG.1C, the same or similar reference numerals are used to represent the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, refer to the foregoing embodiments, which is not be repeated herein.

Referring toFIG.4, the difference between an ultrasonic transducer device40ofFIG.4and the ultrasonic transducer device10ofFIG.1Ais that the second opening OP2of the second electrode150of the ultrasonic transducer device40is round or oval.

The following examples are given to verify the efficacy of the disclosure, but the disclosure is not limited to the followings. Note that the comparative examples ofFIG.5toFIG.7adopt the reference numerals and part of the content of the embodiments ofFIG.1AtoFIG.1C, and the same or similar reference numerals are used to represent the same or similar elements, and the description of the same technical content is omitted. For the description of the omitted part, refer to the foregoing embodiments, which is not be repeated herein.

In the case in which the following Embodiments 1-2 and Comparative examples 1-3 have the same overall area, that is, a length of 300 μm and a width of 4500 μm, the differences in cell density of the ultrasonic transducer units resulting from various configuration of the ultrasonic transducer units are compared.

The ultrasonic transducer device of Embodiment 1 is similar to that of the embodiment ofFIG.1AtoFIG.1C, and the ultrasonic transducer device of Embodiment 2 is similar to that of the embodiment ofFIG.2. The ultrasonic transducer devices of Comparative Examples 1 to 3 all include the first electrode110, the insulating layer120, the oscillating membrane140and the second electrode150but with no third electrode. There is a cavity between the oscillating membrane140and the insulating layer120, and there is the filling material170between adjacent ultrasonic transducer units100′, but the configuration between ultrasonic transducer units100′ and the filling material170of Comparative Examples 1 to 3 is different, as shown inFIG.5toFIG.7, respectively.

The relative dimensions, numbers, area ratios and cell densities of the ultrasonic transducer units of Embodiments 1-2 and Comparative examples 1-3 are listed in Table 1. The dimensions of the ultrasonic transducer units of Comparative examples 1-3 of Table 1 refer to the width W*length L of the oscillating membrane140corresponding to the main part152of the second electrode150. The distances d1and d2refer to the distance between the centers of two adjacent ultrasonic transducer units100/100′ in the first direction D1and the second direction D2. The area ratio refers to the ratio of the total area of the ultrasonic transducer unit to the overall area of the active region R1of the ultrasonic transducer device. The cell density is used to calculate the ratio of the area of the ultrasonic transducer unit to the area of the through hole. For example, in Comparative examples 1- 3, the number of ultrasonic transducer units is equal to the number of through holes, so the cell density is (the area of one ultrasonic transducer unit)/(the area of one ultrasonic transducer unit+the area of a through hole); for Embodiments 1-2, the number of ultrasonic transducer units is n times (e.g., 15 times) the number of through holes, so the cell density is (the area of n ultrasonic transducer units)/(the area of the n ultrasonic transducer units+the area of a through hole).

The ultrasonic transducer units100of Embodiments 1-2 are formed by forming the sub-cavity132among the insulating layer120, the oscillating membrane140and the third electrode160when the third electrode160is applied with a bias voltage, so more ultrasonic transducer units100can be configured in the same area, or the ratio of the area occupied by the ultrasonic transducer units100is relatively high, and the cell density is higher, thereby improving the bandwidth and the power output of the ultrasonic transducer device.