Capacitive ultrasonic transducer

Abstract

The capacitive ultrasonic transducer comprises at least one sounding area and at least one collapse voltage adjusting area insulated and isolated from the sounding area, each of the sounding area and the collapse voltage adjusting area comprises a top electrode and a bottom electrode which are oppositely arranged up and down, and a communicated cavity is arranged between the top electrode and the bottom electrode. A driving voltage combined by a first direct current bias voltage and an alternating current voltage is connected between the top electrode and the bottom electrode of the sounding area, and a second direct current bias voltage is connected between the top electrode and the bottom electrode of the collapse voltage adjusting area. According to the utility model, under the condition of the same driving voltage, the collapse risk of the vibration layer of the sounding area is reduced, and the consistency of resonant frequencies during batch production can be improved.

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 that can improve the collapse voltage. 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, during mass production, the resonant frequency fc of the electrostatic thin-film ultrasonic transducer has a large tolerance due to the influence of material properties, dimensions, and assembly tolerances; and during long-term operation, the film is prone to fatigue, leading to its collapse.

[0005] Therefore, improving the consistency of the resonant frequency fc during mass production and preventing collapse during thin film fatigue are problems that need to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a capacitive ultrasonic transducer that can improve the consistency of resonant frequency during mass production and prevent collapse during thin film fatigue.

[0007] To achieve the above objectives, this utility model proposes a capacitive ultrasonic transducer, comprising at least one sound-emitting zone and at least one collapse voltage adjustment zone insulated from the sound-emitting zone. A communicating cavity exists between the sound-emitting zone and the collapse voltage adjustment zone. Both the sound-emitting zone and the collapse voltage adjustment zone include a top electrode and a bottom electrode arranged opposite each other, forming the cavity between the top and bottom electrodes. A driving voltage combining a first DC bias voltage and an AC voltage is connected between the top and bottom electrodes of the sound-emitting zone, and a second DC bias voltage is connected between the top and bottom electrodes of the collapse voltage adjustment zone.

[0008] In a preferred embodiment, the sound-emitting area and the collapse voltage adjustment area are distributed alternately in the left-right or inside-out direction.

[0009] In a preferred embodiment, a gap is provided between the sound-generating zone and the collapse voltage adjustment zone to insulate the two zones.

[0010] In a preferred embodiment, the width of the gap is 50µm to 200µm.

[0011] In a preferred embodiment, the withstand voltage of the gap is greater than the sum of the first DC bias voltage and the AC voltage and the difference between the first DC bias voltage and the second DC bias voltage.

[0012] In a preferred embodiment, the width of the gap is 100 μm.

[0013] In a preferred embodiment, the second DC bias voltage is less than the collapse voltage of the sound-generating region.

[0014] In a preferred embodiment, the capacitive ultrasonic transducer includes a vibrating layer, multiple support columns, and a non-vibrating layer. The vibrating layer includes a thin film and a first conductive layer, the first conductive layer being disposed on the bottom surface of the thin film near the non-vibrating layer. The non-vibrating layer 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 vibrating layer, and the insulating layer is disposed on the top surface of the second conductive layer near the vibrating layer. An air gap is formed between the first conductive layer and the insulating layer by the support columns, the air gap serving as a cavity communicating between the sound-generating area and the collapse voltage adjustment area. The first conductive layer is divided into at least two top electrodes, and / or the second conductive layer is divided into at least two bottom electrodes. The first conductive layer and / or the second conductive layer divide the capacitive ultrasonic transducer into at least one sound-generating area and at least one collapse voltage adjustment area.

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

[0016] In a preferred embodiment, the capacitive ultrasonic transducer is divided into multiple zones, all sound-emitting zones in the multiple zones are connected to the driving voltage, and all collapse voltage adjustment zones in the multiple zones are connected to the second DC bias voltage.

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

[0018] This invention divides a capacitive ultrasonic transducer into sections and connects some sections to a DC bias voltage. By adjusting the value of this DC bias voltage, the collapse voltage and resonant frequency of the sound-emitting section are adjusted, thereby increasing the collapse voltage. This reduces the risk of collapse of the vibration layer in the sound-emitting section under the same driving voltage conditions and improves the consistency of the resonant frequency during mass production. 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 structure of the capacitive ultrasonic transducer of this utility model, which is divided into two sections, left and right.

[0021] Figure 3 is a schematic diagram of the structure of the capacitive ultrasonic transducer of this utility model, which is divided into two collapse voltage adjustment areas on the left and right sides and a sound generation area in the middle.

[0022] Figure 4 is a schematic diagram of the capacitive ultrasonic transducer of this utility model, which is divided into two sections: inner and outer.

[0023] Figure 5 is a schematic diagram of the structure of the capacitive ultrasonic transducer of this utility model, which is divided into eight sections on the left and right.

[0024] Figure 6 is a schematic diagram of the stacked structure of a capacitive ultrasonic transducer according to a specific embodiment of the present invention.

[0025] Figure 7 is a schematic diagram of the stacked structure of a capacitive ultrasonic transducer according to another specific embodiment of the present invention.

[0026] The attached figures are labeled as follows:

[0027] 1. Sound-generating area; 11. Top electrode; 12. Bottom electrode; 2. Collapse voltage adjustment area; 3. Gap; 4. Vibration layer; 41. Thin film; 42. First conductive layer; 5. Support column; 6. Non-vibration layer; 61. Fixed base plate; 62. Second conductive layer; 63. Insulating layer; 7. Air gap. Detailed Implementation

[0028] 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.

[0029] 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.

[0030] As shown in Figures 2 to 7, the capacitive ultrasonic transducer disclosed in this utility model includes at least one sound-emitting zone 1 and at least one collapse voltage adjustment zone 2 that is insulated from and isolated from the sound-emitting zone 1. The sound-emitting zone 1 and the collapse voltage adjustment zone 2 have a communicating cavity, and both the sound-emitting zone 1 and the collapse voltage adjustment zone 2 include a top electrode 11 and a bottom electrode 12 arranged opposite to each other, with the cavity formed between the top electrode 11 and the bottom electrode 12.

[0031] Specifically, referring to Figures 2-5, the capacitive ultrasonic transducer is divided into multiple zones. These zones can be spaced apart in a left-right direction or an inside-outside direction, with each zone separated by a three-phase insulating gap. For example, if divided into two zones, one can be designated as the sound-generating zone 1 and the other as the collapse voltage adjustment zone 2. These two zones can be spaced apart laterally or longitudinally, i.e., one side as the sound-generating zone 1 and the other as the collapse voltage adjustment zone 2; or they can be spaced apart inside and out, i.e., the inner side as the sound-generating zone 1 and the outer side as the collapse voltage adjustment zone 2. Alternatively, if divided into three or more zones, specifically eight zones, these eight zones can be spaced apart laterally, longitudinally, or radially. Of these eight zones, the four on the left can be designated as collapse voltage adjustment zones 2, and the four on the right as sound-generating zones 1. Of course, the specific division of the multiple zones into sound-generating zones 1 and collapse voltage adjustment zones 2 can be determined according to actual needs and is not limited here.

[0032] Referring to Figure 6, in a specific embodiment, the capacitive ultrasonic transducer is a fully transparent capacitive ultrasonic transducer, which specifically includes a vibrating layer 4, multiple support columns 5, and a non-vibrating layer 6. The vibrating layer 4 includes a thin film 41 and a first conductive layer 42, with the first conductive layer 42 disposed on the bottom surface of the thin film 41 near the non-vibrating layer 6. The non-vibrating layer 6 includes a fixed base plate 61, a second conductive layer 62, and an insulating layer 63. The second conductive layer 62 is disposed on the top surface of the fixed base plate 61 near the vibrating layer 4, and the insulating layer 63 is disposed on the top surface of the second conductive layer 62 near the vibrating layer 4. An air gap 7 is formed between the first conductive layer 42 and the insulating layer 63 by the support columns 5. This air gap 7 serves as a cavity connecting the sound-generating area 1 and the collapse voltage adjustment area 2.

[0033] In this embodiment, the first conductive layer 42 is divided into at least two top electrodes 11, and / or the second conductive layer 62 is divided into at least two bottom electrodes 12. Specifically, the first conductive layer 42 is divided into two top electrodes 11, and the second conductive layer 62 is divided into two bottom electrodes 12. That is, in this embodiment, by partitioning the first conductive layer 42 and the second conductive layer 62, the entire capacitive ultrasonic transducer is divided into a sound-generating zone 1 and a collapse voltage adjustment zone 2. Specifically, in this embodiment, the thin film 41, one of the top electrodes 11, the air gap 7, the support column 5, the insulating layer 63, one of the bottom electrodes 12, and the fixed base plate 61 constitute a sound-generating zone 1. Similarly, the thin film 41, the other top electrode 11, the air gap 7, the support column 5, the insulating layer 63, the other bottom electrode 12, and the fixed base plate 61 constitute a collapse voltage adjustment zone 2. In other words, apart from the first conductive layer 42 and the second conductive layer 62, the two zones share the structures such as the thin film 41, the support column 5, the insulating layer 63, and the fixed base plate 61. Of course, the first conductive layer 42 can be divided into two top electrodes 11 that are spaced apart from each other, or the second conductive layer 62 can be divided into two bottom electrodes 12 that are spaced apart from each other. This embodiment does not limit this.

[0034] In another alternative embodiment, a support column 5 structure is also provided between the sound-emitting zone 1 and the collapse voltage adjustment zone 2, as shown in Figure 7, to increase the isolation between the two zones. However, the added support column 5 structure must ensure the connectivity of the cavity between the sound-emitting zone 1 and the collapse voltage adjustment zone 2. Therefore, holes can be opened on the added support column 5 or the support column can be set as a point, etc. This utility model does not limit this, as long as the added support structure does not affect the connectivity of the cavity between the two zones.

[0035] Of course, this utility model is not limited to the structure of the capacitive ultrasonic transducer described in the above embodiments. Other capacitive ultrasonic transducers with different structures are also applicable to this utility model, as long as they include the necessary top and bottom electrodes. It is also not limited to the partitioned structure of the transducer achieved by partitioning the conductive layer, such as dividing the transducer into multiple independent partitions, where each region does not share the vibrating diaphragm, fixed base plate, etc., but the cavities between the two regions are interconnected.

[0036] A driving voltage combining a first DC bias voltage and an AC voltage is applied between the top electrode 11 and the bottom electrode 12 in the sound-generating region 1, and a second DC bias voltage is applied between the top electrode 11 and the bottom electrode 12 in the collapse voltage adjustment region 2.

[0037] Specifically, as shown in Figure 6, a driving voltage combining a first DC bias voltage and an AC voltage (Vdc + Vac) is applied between the top electrode 11 and the second conductive layer 62 in the sound-emitting zone 1, and a second DC bias voltage (Vdc2) is applied between the top electrode 11 and the second conductive layer 62 in the collapse voltage adjustment zone 2. In other embodiments, such as a capacitive ultrasonic transducer divided into three or more zones, a driving voltage combining a first DC bias voltage and an AC voltage is applied between the top electrode 11 and the bottom electrode 12 of all sound-emitting zones 1 in the multiple zones, and the aforementioned second DC bias voltage is applied between the top electrode 11 and the bottom electrode 12 of all collapse voltage adjustment zones 2.

[0038] During implementation, the second DC bias voltage Vdc2 is less than the collapse voltage of the sound-generating area 1. This is because if it is greater than or equal to the collapse voltage, the diaphragm 41 will collapse. The collapse voltage refers to the critical voltage value in a capacitive ultrasonic transducer at which the applied DC bias voltage becomes too large, causing the diaphragm to be attracted to the back plate due to excessive electrostatic force, leading to device failure or damage.

[0039] Preferably, the sound-generating area 1 and the collapse voltage adjustment area 2 are insulated and isolated by a gap 3. In practice, the width of the gap 3 is 50um to 200um, preferably 100um. The withstand voltage value is greater than the sum of the first DC bias voltage and the AC voltage and the difference between the first DC bias voltage and the second DC bias voltage (i.e., the withstand voltage value is greater than Vdc + Vac - Vdc2), which means it needs to be greater than the maximum voltage difference between the two electrodes. Otherwise, the air will be broken down. The withstand voltage value can be adjusted by adjusting the width of the gap 3.

[0040] The resonant frequency and the magnitude of the collapse voltage in the sound-generating zone 1 can be dynamically adjusted by adjusting the magnitude of the second DC bias voltage.

[0041] Specifically, the formula for calculating the collapse voltage of sound-generating zone 1 is as follows:

[0042]

[0043] Among them, K ms K represents the mechanical stiffness of the vibrating layer 4 in the sound-generating zone 1. mb The additional mechanical stiffness formed by the air within the air gap 7 of the sound-generating zone 1, t g The initial thickness of air gap 7, ∈ g The dielectric constant of the air gap 7 (usually the dielectric constant in vacuum ∈ 0 ≈ 8.854 × 10⁻⁶) is given by the value of 7. -12 F / m (adjust accordingly if other media are present), S d The area of ​​the top electrode 11 in the sound-emitting region 1.

[0044] The additional mechanical stiffness K formed by the air within the air gap 7 of the sound-generating zone 1 is described above. mb The calculation formula is:

[0045]

[0046] Where ρ0 is the air density, c is the speed of sound, and V b The volume of the back cavity of vocalization zone 1.

[0047] By adjusting the magnitude of the second DC bias voltage Vdc2, the air density ρ0 of the sound-generating area 1 can be effectively changed. For example, increasing the air density ρ0 of the sound-generating area 1 can improve the mechanical stiffness K. mb According to the calculation formula, increasing the air density ρ0 in the sound-generating zone 1 can increase the additional mechanical stiffness K formed by the air in the air gap 7 of the sound-generating zone 1. mb Furthermore, the collapse voltage V of the aforementioned sound-generating area 1... coll The calculation formula shows that K mb The collapse voltage V of its sound-producing region 1 after improvement coll It will also improve, that is, under the same driving voltage conditions, the risk of collapse of the vibration layer 4 in the sound-generating zone 1 is reduced.

[0048] The formula for calculating the resonant frequency of sound-emitting region 1 is:

[0049]

[0050] Among them, f c K is the resonant frequency of sound-producing region 1. ms K represents the mechanical stiffness of the vibrating layer 4 in the sound-generating zone 1. mb M is the additional mechanical stiffness formed by the air within the air gap 7 of the sound-producing zone 1. ms The mass of the vibrating layer 4 in the sound-generating zone 1 and the mass of the air load added to its upper and lower surfaces.

[0051] The resonant frequency f of the aforementioned sound-emitting region 1 c From the calculation formula, we can see that K mb After the change, the resonant frequency f of its sound-producing region 1 c It will also change, thereby improving the consistency of the resonant frequency fc during mass production.

[0052] The advantage of this invention is that by dividing the capacitive ultrasonic transducer into sections and connecting some sections to a DC bias voltage, the collapse voltage and resonant frequency of the sound-emitting zone can be dynamically adjusted by adjusting the voltage value of the DC bias voltage, thereby increasing the collapse voltage. This reduces the risk of collapse of the vibration layer in the sound-emitting zone under the same driving voltage conditions and improves the consistency of the resonant frequency during mass production.

[0053] 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, The device includes at least one sound-generating area and at least one collapse voltage adjustment area that is insulated from the sound-generating area. The sound-generating area and the collapse voltage adjustment area have a communicating cavity. Both the sound-generating area and the collapse voltage adjustment area include a top electrode and a bottom electrode arranged opposite to each other. The cavity is formed between the top electrode and the bottom electrode. A driving voltage combining a first DC bias voltage and an AC voltage is connected between the top electrode and the bottom electrode of the sound-generating area. A second DC bias voltage is connected between the top electrode and the bottom electrode of the collapse voltage adjustment area.

2. The capacitive ultrasonic transducer as described in claim 1, characterized in that, The sound-emitting area and the collapse voltage adjustment area are distributed alternately in the left-right or inside-out direction.

3. A capacitive ultrasonic transducer as described in claim 1 or 2, characterized in that, There is a gap between the sound-emitting area and the collapse voltage adjustment area to insulate and isolate the two areas.

4. A capacitive ultrasonic transducer as described in claim 3, characterized in that, The width of the gap is 50um to 200um.

5. A capacitive ultrasonic transducer as described in claim 4, characterized in that, The withstand voltage of the gap is greater than the sum of the first DC bias voltage and the AC voltage, and the difference between the first DC bias voltage and the second DC bias voltage.

6. A capacitive ultrasonic transducer as described in claim 5, characterized in that, The width of the gap is 100 μm.

7. A capacitive ultrasonic transducer as described in claim 1 or 2, characterized in that, The second DC bias voltage is less than the collapse voltage of the sound-generating area.

8. A capacitive ultrasonic transducer as described in claim 1 or 2, characterized in that, The capacitive ultrasonic transducer includes a vibrating layer, multiple support columns, and a non-vibrating layer. The vibrating layer includes a thin film and a first conductive layer, with the first conductive layer disposed on the bottom surface of the thin film near the non-vibrating layer. The non-vibrating layer 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 vibrating layer, and the insulating layer is disposed on the top surface of the second conductive layer near the vibrating layer. An air gap is formed between the first conductive layer and the insulating layer by the support columns, and the air gap serves as a cavity communicating between the sound-generating zone and the collapse voltage adjustment zone. The first conductive layer is divided into at least two top electrodes, and / or the second conductive layer is divided into at least two bottom electrodes. The first conductive layer and / or the second conductive layer divide the capacitive ultrasonic transducer into at least one sound-generating zone and at least one collapse voltage adjustment zone.

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 capacitive ultrasonic transducer is divided into multiple zones, and all sound-emitting zones in the multiple zones are connected to the driving voltage, while all collapse voltage adjustment zones in the multiple zones are connected to the second DC bias voltage.

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