Capacitive ultrasonic transducer

Abstract

The utility model discloses a capacitive ultrasonic transducer which comprises a top electrode, a bottom electrode and an air gap formed between the top electrode and the bottom electrode, the top electrode and / or the bottom electrode are / is provided with a non-conductive non-electrode area, and the non-electrode area is the area with the largest electric field intensity on the top electrode and / or the bottom electrode. Or is a part of an area with the maximum electric field intensity on the top electrode and / or the bottom electrode. According to the utility model, the electrode at the position with the maximum electric field intensity on the top electrode and / or the bottom electrode is removed, so that the accumulation of charges on the surface of the insulating layer can be reduced, the influence of the charges generated by air ionization on the air partial pressure is greatly reduced, and the reduction of the sound pressure level of the transducer during long-term work can be avoided.

Description

A capacitive ultrasonic transducer Technical Field

[0001] This utility model relates to the field of directional sound generation technology, specifically to a capacitive ultrasonic transducer. Background Technology

[0002] Electrostatic thin-film ultrasonic transducers, also known as capacitive thin-film ultrasonic transducers, utilize the electrostatic force generated by the upper and lower electrodes to drive the thin film to vibrate, thereby radiating ultrasonic waves.

[0003] A typical electrostatic thin-film ultrasonic transducer structure is shown in Figure 1. From top to bottom, it includes a thin film, a top electrode, a support column, an insulating layer, a bottom electrode, and a fixed base plate. An air gap is formed between the top electrode and the insulating layer. A DC bias voltage Vdc and an AC voltage Vac are applied between the top and bottom electrodes to drive the thin film to vibrate and produce sound.

[0004] However, when the DC bias voltage Vdc is applied, the top electrode and the thin film will be concave due to electrostatic force, and their center position will be closer to the bottom. When the electric field strength in the air gap is too large, the air may ionize under long-term operation, causing charge to accumulate on the top of the insulating layer, thereby reducing the electric field strength in the air gap, resulting in a decrease in amplitude and thus a decrease in sound pressure level. Once the air is ionized, the generated free electrons and positive ions will migrate in opposite directions under the action of the electric field force. Assuming that the bottom electrode (and the insulating layer on it) is at a positive potential relative to the top electrode (thin film) (usually the polarity of Vdc is set in this way to attract the negatively charged thin film), then the free electrons (negatively charged) will be attracted towards the positively charged bottom electrode. They will move to the surface of the insulating layer (i.e., the side facing the air gap) and accumulate there. Since the insulating layer is a poor conductor, these charges are difficult to flow through the insulating layer to the bottom electrode and be neutralized, thus forming surface bound charges. These charges accumulated on the top of the insulating layer (assuming they are mainly negative charges) will generate an additional electric field. The direction of this additional electric field is opposite to the direction of the main electric field generated by the applied voltages Vdc and Vac in the air gap. It can be understood that these accumulated charge layers are like inserting an extra thin layer with opposite polarization charge inside the capacitor, which serves to shield or weaken the original electric field.

[0005] Therefore, how to reduce the impact of air ionization on the reliability and sound pressure of electrostatic thin-film ultrasonic transducers is a problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a capacitive ultrasonic transducer that can effectively reduce the impact of air ionization on the reliability and sound pressure of electrostatic thin-film ultrasonic transducers.

[0007] To achieve the above objectives, this utility model proposes a capacitive ultrasonic transducer, including a top electrode, a bottom electrode, and an air gap formed between the top electrode and the bottom electrode. The top electrode and / or the bottom electrode are provided with a non-conductive electrode-free region, which is either the region with the largest electric field strength on the top electrode and / or the bottom electrode, or a part of the region with the largest electric field strength on the top electrode and / or the bottom electrode.

[0008] In a preferred embodiment, the region with the strongest electric field intensity is the central region on the top electrode and / or bottom electrode.

[0009] In a preferred embodiment, the area of ​​the electrode-free region accounts for 5% to 20% of the total electrode area.

[0010] In a preferred embodiment, when the electrode-free region is provided on both the top electrode and the bottom electrode, the position of the electrode-free region on the top electrode corresponds to the position of the electrode-free region on the bottom electrode.

[0011] In a preferred embodiment, the shape of the electrode-free region is at least circular, square, or elliptical.

[0012] In a preferred embodiment, the top electrode and / or bottom electrode includes an inner conductive layer and an outer conductive layer distributed inside and outside, with a gap between the inner conductive layer and the outer conductive layer serving as the electrode-free region.

[0013] In a preferred embodiment, the gap is annular and the gap width is 50µm to 200µm.

[0014] In a preferred embodiment, the withstand voltage of the gap is greater than the sum of the DC voltage and AC voltage applied between the top electrode and the bottom electrode.

[0015] In a preferred embodiment, the capacitive ultrasonic transducer is a fully transparent capacitive ultrasonic transducer.

[0016] In a preferred embodiment, the top electrode includes a thin film and a first conductive layer. The first conductive layer is disposed on the bottom surface of the thin film near the bottom electrode. The bottom electrode includes a fixed base plate, a second conductive layer, and an insulating layer. The second conductive layer is disposed on the top surface of the fixed base plate near the top electrode. The insulating layer is disposed between the first and second conductive layers. The electrode-free region is disposed on the first and / or second conductive layers. The top and bottom electrodes are edge-fitted together and supported by multiple support pillars to form an air gap. A driving voltage combining DC and AC voltages for driving the top electrode to vibrate and produce sound is connected between the first and second conductive layers.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention removes the electrodes at the positions with the greatest electric field intensity on the top and / or bottom electrodes, thereby reducing the accumulation of surface charge on the insulating layer. This significantly reduces the impact of charge generated by air ionization on air partial pressure, thus preventing a decrease in the transducer's sound pressure level during long-term operation. Attached Figure Description

[0019] Figure 1 is a schematic diagram of the structure of an existing electrostatic thin-film ultrasonic transducer;

[0020] Figure 2 is a schematic diagram of the stacked structure of the capacitive ultrasonic transducer of this utility model (with a no-electrode area set at the top electrode).

[0021] Figure 3 is a schematic diagram of the stacked structure of the capacitive ultrasonic transducer of this utility model (with an electrodeless area set at the bottom electrode).

[0022] Figure 4 is a schematic diagram of the stacked structure of the capacitive ultrasonic transducer of this utility model (both the bottom electrode and the top electrode are provided with electrode-free areas);

[0023] Figure 5 is a schematic diagram of a structure where the electrode-free region is circular;

[0024] Figure 6 is a schematic diagram of a square structure with no electrode region;

[0025] Figure 7 is a schematic diagram of a structure where the electrode-free region is elliptical;

[0026] Figure 8 is a schematic diagram of a structure where the electrode-free region is annular;

[0027] Figure 9 is a schematic diagram of the stacked structure of a capacitive ultrasonic transducer (both the bottom and top electrodes have electrode-free areas) in a specific embodiment of this utility model.

[0028] The attached figures are labeled as follows:

[0029] 1. Top electrode; 11. Thin film; 12. First conductive layer; 2. Bottom electrode; 21. Fixed base plate; 22. Second conductive layer; 23. Insulating layer; 3. Air gap; 4. Electrode-free area; 10. Inner conductive layer; 20. Outer conductive layer; 30. Gap; 5. Support column. Detailed Implementation

[0030] The specific embodiments of this utility model are described in detail below, but it should be understood that the protection scope of this utility model is not limited to the specific embodiments.

[0031] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprising" shall be understood to include the stated elements or components without excluding other elements or other components.

[0032] As shown in Figures 2-4, the capacitive ultrasonic transducer disclosed in this invention includes a top electrode 1 and a bottom electrode 2. The top electrode 1 and the bottom electrode 2 are fitted together with a frame, and an air gap 3 is formed between them to allow the top electrode 1 to vibrate. During operation, a DC bias voltage Vdc and an AC voltage Vac (i.e., Vdc + Vac) are applied between the top electrode 1 and the bottom electrode 2 to drive the top electrode 1 to vibrate and produce sound.

[0033] Preferably, the top electrode 1 and / or the bottom electrode 2 are provided with a non-conductive electrode-free region 4. This electrode-free region 4 is either the region with the highest electric field strength on the top electrode 1 and / or the bottom electrode 2, or a part of the region with the highest electric field strength on the top electrode 1 and / or the bottom electrode 2. Generally, the region with the highest electric field strength on the top electrode 1 and / or the bottom electrode 2 is in the central region. That is, the entire central region of the top electrode 1 and / or the bottom electrode 2 is used as the electrode-free region 4, or a part of the central region of the top electrode 1 and / or the bottom electrode 2 is used as the electrode-free region 4, to reduce the electric field strength at the center of the air gap 3. When electrode-free regions 4 are provided on both the top electrode 1 and the bottom electrode 2, the positions of the electrode-free regions 4 on the two electrodes correspond to each other. That is, when the electrode-free region 4 on the top electrode 1 is in its central region, the electrode-free region 4 on the bottom electrode 2 is also in its central region.

[0034] In implementation, the area of ​​the electrode-free region 4 preferably accounts for 5% to 20% of the total electrode area, and generally 10% is used. Furthermore, the shape of the electrode-free region 4 can be regular or irregular, and can be set according to actual needs, as shown in Figures 5 to 7, such as circular, square, elliptical, etc. This invention does not limit the shape in this respect.

[0035] Furthermore, if the capacitive ultrasonic transducer is entirely transparent, then for optical purposes, the electrode-free region 4 on the electrodes is preferably set as part of the region with the highest electric field strength. For example, the top electrode 1 and / or the bottom electrode 2 can be configured as having an inner conductive layer 10 and an outer conductive layer 20 distributed internally and externally. A gap 30, serving as the electrode-free region 4, is provided between the inner conductive layer 10 and the outer conductive layer 20, ensuring insulation between the inner and outer conductive layers. This gap 30 is preferably part of the central region of the top electrode 1 and / or the bottom electrode 2. In practice, as shown in Figure 8, the gap 30 can be annular, with a width preferably between 50 μm and 200 μm, typically 100 μm. The withstand voltage of the gap 30 must be greater than the sum of Vdc and Vac applied between the top electrode 1 and the bottom electrode 2.

[0036] As shown in Figure 9, in one specific embodiment, the top electrode 1 includes a thin film 11 and a first conductive layer 12, with the first conductive layer 12 disposed on the bottom surface of the thin film 11 near the bottom electrode 2. The bottom electrode 2 includes a fixed base plate 21, a second conductive layer 22, and an insulating layer 23, with the second conductive layer 22 disposed on the top surface of the fixed base plate 21 near the top electrode 1, and the insulating layer 23 disposed between the first conductive layer 12 and the second conductive layer 22. The top electrode 1 and the bottom electrode 2 are fitted together and supported by multiple support pillars 5 to form the aforementioned air gap 3. During operation, a driving voltage combining a DC voltage Vdc and an AC voltage Vac is applied between the first conductive layer 12 and the second conductive layer 22 to drive the top electrode 1 to vibrate and produce sound.

[0037] In this embodiment, the electrode-free region 4 can be disposed on the first conductive layer 12 and / or the second conductive layer 22, that is, a portion of the conductive layer is removed from the first conductive layer 12 and / or the second conductive layer 22 to form the electrode-free region 4. For example, the conductive layer in the central region of the first conductive layer 12 and the central region of the second conductive layer 22 can be removed to form the electrode-free region 4. The area and shape of the removed electrode can be referred to the above-described specifications, and will not be repeated here.

[0038] In addition, in order to consider the optical effect, in this embodiment, the conductive layers on the first conductive layer 12 and / or the second conductive layer 22 can be removed only in a ring shape, retaining part of the electrodes in the central region. The width of the ring gap and the withstand voltage can also be referred to the above-described limitation, and will not be repeated here.

[0039] The advantage of this invention is that by removing the electrodes at the positions with the greatest electric field intensity on the top electrode and / or bottom electrode, the accumulation of charge on the surface of the insulating layer can be reduced, thereby greatly reducing the impact of the charge generated by air ionization on the air partial pressure, and thus avoiding the reduction of the transducer sound pressure level during long-term operation.

[0040] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the present invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the present invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the present invention, as well as various different choices and variations. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A capacitive ultrasonic transducer, characterized in that, It includes a top electrode, a bottom electrode, and an air gap formed between the top electrode and the bottom electrode. The top electrode and / or the bottom electrode are provided with a non-conductive electrode-free region. The electrode-free region is the region with the largest electric field strength on the top electrode and / or the bottom electrode, or is a part of the region with the largest electric field strength on the top electrode and / or the bottom electrode.

2. The capacitive ultrasonic transducer as described in claim 1, characterized in that, The region with the strongest electric field intensity is the central region on the top electrode and / or bottom electrode.

3. A capacitive ultrasonic transducer according to claim 1 or 2, characterised in that, The area of ​​the electrode-free region accounts for 5% to 20% of the total electrode area.

4. A capacitive ultrasonic transducer as claimed in claim 1 or 2, characterized in that, When the electrode-free region is provided on both the top electrode and the bottom electrode, the position of the electrode-free region on the top electrode corresponds to the position of the electrode-free region on the bottom electrode.

5. A capacitive ultrasonic transducer as described in claim 1 or 2, characterized in that, The shape of the electrode-free region is at least circular, square, or elliptical.

6. A capacitive ultrasonic transducer as claimed in claim 1 or 2, characterized in that, The top electrode and / or bottom electrode include an inner conductive layer and an outer conductive layer distributed inside and outside, with a gap between the inner conductive layer and the outer conductive layer serving as the electrode-free region.

7. A capacitive ultrasonic transducer as described in claim 6, characterized in that, The gap is annular, and the gap width is 50um~200um.

8. A capacitive ultrasonic transducer as described in claim 6, characterized in that, The withstand voltage of the gap is greater than the sum of the DC voltage and AC voltage applied between the top electrode and the bottom electrode.

9. A capacitive ultrasonic transducer as described in claim 1, characterized in that, The capacitive ultrasonic transducer is a fully transparent capacitive ultrasonic transducer.

10. A capacitive ultrasonic transducer as described in claim 1 or 9, characterized in that, The top electrode includes a thin film and a first conductive layer. The first conductive layer is disposed on the bottom surface of the thin film near the bottom electrode. The bottom electrode includes a fixed base plate, a second conductive layer, and an insulating layer. The second conductive layer is disposed on the top surface of the fixed base plate near the top electrode. The insulating layer is disposed between the first conductive layer and the second conductive layer. The electrode-free region is disposed on the first conductive layer and / or the second conductive layer. The top electrode and the bottom electrode are edge-fitted together and supported by multiple support pillars to form the air gap. A driving voltage combining DC and AC voltages that drives the top electrode to vibrate and produce sound is connected between the first conductive layer and the second conductive layer.

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