Non-radio frequency piezoelectric acoustic device and earphone

Abstract

The application provides a non-radio frequency piezoelectric acoustic device and earphone. The non-radio frequency piezoelectric acoustic device comprises a substrate, an insulating layer and a piezoelectric functional layer. The substrate is made of a low-resistance material, so that the loss of the non-radio frequency piezoelectric acoustic device during operation can be effectively reduced. The substrate with low resistivity has a large number of free carriers. When the electric field in the piezoelectric functional layer changes, the free carriers can quickly respond and move to form effective mirror charges, which can play a good electromagnetic shielding effect, reflect the energy back to the piezoelectric functional layer, and prevent the energy from leaking and dissipating to the deeper and farther substrate.

Description

Technical Field

[0001] This application relates to the field of microelectromechanical devices (MEMS) technology, and more specifically, to a non-radio frequency piezoelectric acoustic device and headphones. Background Technology

[0002] Piezoelectric acoustic devices in Micro-Electromechanical Systems (MEMS) mainly consist of piezoelectric units and application-specific integrated circuits (ASICs). The piezoelectric unit includes a substrate, a support structure, and a cantilever diaphragm structure. When sound is applied to the diaphragm, it vibrates under the sound pressure, generating corresponding strain. At this time, the piezoelectric layer, due to the strain, generates charges on its upper and lower sides, outputting an electrical signal to achieve sensing. In piezoelectric devices, device loss is one of the key performance indicators, directly affecting the device's efficiency, signal quality, and energy conversion capability. Therefore, the loss of piezoelectric devices is crucial.

[0003] Existing methods for reducing device losses include introducing high-resistivity silicon into the device, but these methods are not applicable to piezoacoustics. Summary of the Invention

[0004] The purpose of this application is to address the shortcomings of the prior art by providing a non-RF piezoelectric acoustic device and headphones, which effectively reduces the loss of the non-RF piezoelectric acoustic device.

[0005] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows: In a first aspect, embodiments of this application also provide a non-radio frequency piezoelectric acoustic device, comprising: Base; An insulating layer is disposed on the upper part of the substrate; And a piezoelectric functional layer, disposed on the upper part of the insulating layer; The substrate is a low-resistivity material, and the ratio of the resistivity of the substrate to the resistivity of the insulating layer is less than 0.2 × 10⁻⁶. -12 .

[0006] In one embodiment, the substrate is low-resistivity silicon with a resistivity of less than 2000 Ω·cm.

[0007] In one embodiment, the resistivity of the insulating layer is: 10. 16 ~10 19 Within the range of Ω·cm, the relative permittivity of the insulating layer is in the range of 3.7 to 4.2.

[0008] In one embodiment, the operating frequency of the non-RF piezoacoustic device is less than 100MHz.

[0009] In one embodiment, the piezoelectric functional layer includes: a first metal electrode, a second metal electrode, and a first piezoelectric layer located between the first metal electrode and the second metal electrode.

[0010] In one embodiment, it further includes a third metal electrode and a second piezoelectric layer located between the third metal electrode and the second metal electrode.

[0011] In one embodiment, the piezoelectric functional layer is a cantilever structure.

[0012] In one embodiment, the cantilever structure includes one or more cantilever beams.

[0013] In one embodiment, the piezoelectric functional layer is a diaphragm structure.

[0014] Secondly, embodiments of this application also provide an earphone, including any of the non-RF piezoelectric acoustic devices described above.

[0015] The beneficial effects of this application are: 1. This application provides a non-RF piezoelectric acoustic device and headphones. By using a low-resistivity substrate, the loss of the non-RF piezoelectric acoustic device during operation can be effectively reduced. When the non-RF piezoelectric acoustic device is working, sound acts on the diaphragm, and the diaphragm begins to vibrate under the action of sound pressure, generating corresponding strain. At this time, the piezoelectric functional layer is subjected to strain, generating charges on its upper and lower sides, and outputting an electrical signal to achieve sensing. The low-resistivity substrate contains a large number of free carriers (electrons or holes). When the electric field in the piezoelectric functional layer changes, these free carriers can respond quickly and move, forming an effective mirror charge, which plays a good electromagnetic shielding role, reflecting energy back to the working area of ​​the device (piezoelectric functional layer), preventing energy from leaking and dissipating to deeper and farther substrates.

[0016] 2. The ratio of the resistivity of the substrate to the resistivity of the insulating layer is less than 0.2*10. -12This ratio is not an arbitrarily set value, but a stringent, quantifiable requirement for the performance of the substrate and insulating layer. It ensures that the "near-ideal conductor" effect of low-resistivity silicon can be truly realized. The numerator (substrate resistivity) is extremely low: the substrate resistivity must be low enough to ensure sufficient free carriers to quickly form mirror charges. The denominator (insulator resistivity) is extremely high: the insulating layer resistivity must be extremely high to ensure that the insulating layer itself is almost non-conductive, perfectly providing electrical isolation and preventing signal current from leaking directly to the substrate. Simultaneously, a high-quality insulating layer is also crucial for supporting the cavity and forming the acoustic reflection boundary. The above ratio is less than 0.2 * 10⁻⁶. -12 The system comprehensively constrains both the conditions that "the substrate must be sufficiently conductive" and "the insulating layer must be sufficiently insulating." Only when this ratio is extremely small can it be proven that, from an electrical perspective, the substrate is almost in a "short-circuit" state relative to the insulating layer, while the insulating layer is almost in an "open-circuit" state. This extreme contrast ensures that the electric field is completely confined within the piezoelectric functional layer.

[0017] 3. The substrate is low-resistivity silicon with a resistivity of less than 2000 Ω·cm. Compared with the existing technology that uses high-resistivity silicon to reduce the loss of non-RF piezoacoustic devices, the effect is more significant. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The graph shows the trend of loss of non-RF piezoacoustic devices as a function of resistivity of high-resistivity silicon. Figure 2 This is a schematic diagram of the structure of a non-RF piezoelectric acoustic device provided in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of a second type of non-RF piezoelectric acoustic device provided in the embodiments of this application; Figure 4 This is a schematic diagram of the structure of a third type of non-RF piezoelectric acoustic device provided in the embodiments of this application; Figure 5 This is a schematic diagram of the structure of the fourth non-RF piezoelectric acoustic device provided in the embodiments of this application; Figure 6 The piezoelectric functional layer provided in this application embodiment includes a structural diagram of four series cantilever beams; Figure 7 A schematic diagram of the membrane structure of each cantilever beam provided in the embodiments of this application; Figure 8 Equivalent circuit diagram of a non-RF piezoelectric acoustic device provided in the embodiments of this application; Figure 9 The equivalent circuit diagram of the membrane structure of the cantilever beam in the non-RF piezoacoustic device provided in the embodiments of this application after being equivalent to C0 and R0; Figure 10 This is a schematic diagram illustrating the relationship between low-resistivity silicon and loss, provided in an embodiment of this application. Figure 11 The simulation cloud diagram is for the existing high-resistivity silicon. Figure 12 A simulation contour plot of low-resistivity silicon is introduced for the embodiments of this application.

[0020] Explanation of reference numerals in the attached figures: Non-RF piezoelectric acoustic devices 100: 10 substrate, 20 insulating layer, 30 piezoelectric functional layer; Support layer 31, piezoelectric layer 32: first piezoelectric layer 32-1, second piezoelectric layer 32-2; metal electrode 33: first metal electrode 33-1, second metal electrode 33-2, third metal electrode 33-3, fourth metal electrode 33-4, fifth metal electrode 33-5. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the accompanying drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0022] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] It should be noted that the term "comprising" will be used in the embodiments of this application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.

[0024] In piezoelectric devices, device loss is one of the key performance indicators, typically including dielectric loss and mechanical loss. Device loss directly affects the device's operating efficiency, signal quality, and energy conversion efficiency. The loss tangent, also known as the dielectric loss factor or tanδ, represents the ratio of active power loss to reactive power storage in a dielectric material under an alternating electric field. It is a key parameter for measuring energy loss in dielectric materials (Loss Tan). In some non-RF piezoelectric acoustic devices, such as microphones, loss is one of the main sources of the device's inherent noise; in other devices, such as loudspeakers, loss is a source of heat generation.

[0025] In existing technologies, high-resistivity silicon (Si) is introduced into the bottom of piezoelectric devices to reduce losses. With other materials remaining constant, the introduction of high-resistivity silicon effectively reduces leakage current in the substrate, thereby lowering the overall device loss. This method has been widely applied to radio frequency (RF) non-RF piezoelectric acoustic devices such as filters and duplexers. After introducing high-resistivity silicon, the losses of RF non-RF piezoelectric acoustic devices can typically be controlled to below 0.2%. The operating frequency range of RF non-RF piezoelectric acoustic devices is above 100 MHz.

[0026] However, when this conventional method of reducing device losses by introducing high-resistivity silicon is applied to non-RF piezoelectric acoustic devices, the losses of the acoustic devices are relatively high. For example, when high-resistivity silicon with a resistivity of 100,000 Ω·cm is introduced into a non-RF piezoelectric acoustic device, there is a significant horizontal potential difference in the underlying silicon of the non-RF piezoelectric acoustic device, i.e., the high-resistivity silicon. This potential difference can drive the movement of charge carriers in the high-resistivity silicon, thereby forming leakage current and causing losses in the acoustic device.

[0027] When simulating non-RF piezoacoustic devices that do not yet include silicon, the loss of the non-RF piezoacoustic devices is less than 0.2%. Comparing the loss results before and after introducing high-resistivity silicon, it can be seen that the loss of the non-RF piezoacoustic devices with high-resistivity silicon is significantly increased compared to those without, and this increase is mostly due to the introduced underlying high-resistivity silicon. Therefore, the effect of introducing high-resistivity silicon to reduce the loss of non-RF piezoacoustic devices is not significant; a large leakage current still exists in the high-resistivity silicon, and the loss remains substantial. Table 1 below shows the loss results of non-RF piezoacoustic devices before and after introducing high-resistivity silicon.

[0028] Table 1

[0029] Figure 1 The graph shows the trend of loss of non-RF piezoelectric acoustic devices as a function of the resistivity of high-resistivity silicon. Figure 1 As can be seen, the higher the resistivity of high-resistivity silicon, the lower the loss of non-RF piezoacoustic devices. Figure 1 It can be seen from this that the resistivity of high-resistivity silicon needs to be increased to 1×10⁻⁶. 9 For non-RF piezoelectric acoustic devices, the loss can only be reduced to two-thousandths of an Ω·cm. However, the resistivity of intrinsic silicon at room temperature can only reach a maximum of 2.3 × 10⁻⁶ Ω·cm. 5 Ω·cm, where intrinsic silicon is high-purity, undoped silicon. Therefore, the resistivity of high-resistivity silicon that meets the loss condition is 1×10⁻⁶. 9 The resistivity of Ω·cm is four orders of magnitude higher than that of intrinsic silicon at room temperature; therefore, silicon substrates under conventional conditions simply cannot achieve 1×10⁻⁶ Ω·cm. 9 The resistivity is Ω·cm. Therefore, it is not feasible to reduce the loss of non-RF piezoacoustic devices by introducing high-resistivity silicon.

[0030] The reason why introducing high-resistivity silicon into non-RF piezoelectric acoustic devices cannot solve the loss of non-RF piezoelectric acoustic devices is that the working principle and loss mechanism of high-frequency devices are different from those of low-frequency devices. High-frequency devices include radio frequency devices such as filters, while low-frequency devices include acoustic devices such as sensors.

[0031] The main losses in high-frequency devices originate from the dynamic losses caused by parasitic capacitance during charging and discharging. Using high-resistivity silicon as the device substrate can reduce the coupling capacitance between the substrate and the device, thereby reducing energy loss during charging and discharging. Furthermore, high-frequency signals easily couple to the substrate through capacitance, forming unnecessary current paths (such as eddy currents). The poor conductivity of high-resistivity silicon can significantly reduce the current amplitude in the silicon substrate, reducing signal crosstalk and eddy current losses. Moreover, the skin effect at high frequencies concentrates current on the conductor surface; high-resistivity silicon substrates reduce the penetration of electromagnetic fields into the substrate, thus lowering the dielectric loss of the substrate.

[0032] In contrast, the losses of low-frequency piezoelectric sensors, such as non-RF piezoacoustic devices, mainly come from ohmic losses. When high-resistivity silicon is used at the bottom layer of the device, the series resistance of the equivalent capacitance at the bottom layer is increased, leading to a significant increase in conduction losses. Moreover, dynamic losses account for a small proportion at low frequencies, such as the charging and discharging of parasitic capacitances. This means that the improvement of dynamic losses by high-resistivity silicon is limited, and the overall loss is worsened due to the increased conduction resistance.

[0033] Therefore, based on the aforementioned technical problems, this application provides a non-radio frequency piezoelectric acoustic device 100. Figure 2 This is a schematic diagram of the structure of a non-RF piezoelectric acoustic device 100 provided in an embodiment of this application, as shown below. Figure 2 As shown, the non-RF piezoelectric acoustic device 100 may include a substrate 10, an insulating layer 20, and a piezoelectric functional layer 30.

[0034] Reference Figure 2 The diagram shows the structure of a non-RF piezoelectric acoustic device 100. The substrate 10 may include low-resistivity silicon with a resistivity within a target resistivity range, so that the loss of the non-RF piezoelectric acoustic device 100 meets a preset condition.

[0035] Continue to refer to Figure 2 The piezoelectric functional layer 30 is disposed on top of the insulating layer 20, which is disposed on top of the substrate 10. Figure 2 As can be seen, a cavity is formed between the piezoelectric functional layer 30 and the substrate 10. Therefore, the non-RF piezoelectric acoustic device 100, from bottom to top, consists of: substrate 10, insulating layer 20, and piezoelectric functional layer 30. The substrate 10 is a low-resistance material, and the ratio of the resistivity of the substrate 10 to the resistivity of the insulating layer 20 is less than 0.2 × 10⁻⁶. -12 Specifically, the ratio of the maximum resistivity of the substrate 10 to the minimum resistivity of the insulating layer 20 is less than 0.2 × 10⁻⁶. -12 .

[0036] It is worth noting that Figure 2 The layers and relationships between the layers in the non-RF piezoacoustic device 100 are merely illustrative and may include other structural layers and relationships, which are not limited in this embodiment.

[0037] In this embodiment, by setting the substrate 10 as a low-resistivity material, the loss of the non-RF piezoelectric acoustic device 100 during operation can be effectively reduced. When the non-RF piezoelectric acoustic device 100 is working, sound acts on the diaphragm, and the diaphragm begins to vibrate under the action of sound pressure, generating corresponding strain. At this time, the piezoelectric functional layer 30, due to the strain, generates charges on its upper and lower sides, outputting as an electrical signal to achieve sensing. The low-resistivity substrate 10 has a large number of free carriers (electrons or holes). When the electric field in the piezoelectric functional layer 30 changes, these free carriers can respond quickly and move, forming an effective mirror charge, which plays a good electromagnetic shielding role, reflecting energy back to the working area of ​​the device (piezoelectric functional layer 30), preventing energy from leaking and dissipating to deeper and farther substrates. More specifically, the ratio of the resistivity of the substrate 10 to the resistivity of the insulating layer 20 is less than 0.2*10. -12This ratio condition is not an arbitrarily set value, but a stringent, quantitative requirement for the performance of substrate 10 and insulating layer 20. It ensures that the "near-ideal conductor" effect of low-resistivity silicon can be truly realized. The numerator (resistivity of substrate 10) is extremely low: the resistivity of substrate 10 must be sufficiently low (e.g., <100 Ω·cm) to ensure enough free carriers to quickly form mirror charges. The denominator (resistivity of insulating layer 20) is extremely high: the resistivity of insulating layer 20 (typically silicon dioxide SiO2) must be extremely high (e.g., >10 Ω·cm). 16 The insulation layer 20 is approximately Ω·cm high, ensuring that it is virtually non-conductive and perfectly provides electrical isolation, preventing signal current from leaking directly to the substrate 10. Simultaneously, the high-quality insulation layer 20 is crucial for supporting the cavity and forming the acoustic reflection boundary. The aforementioned ratio is less than 0.2*10. -12 The conditions of "substrate 10 must be sufficiently conductive" and "insulating layer 20 must be sufficiently insulating" are combined. Only when this ratio is very small can it be proven that, from an electrical point of view, substrate 10 is almost in a "short-circuit" state relative to insulating layer 20, while insulating layer 20 is almost in an "open-circuit" state. This extreme contrast ensures that the electric field is completely confined within the piezoelectric functional layer 30.

[0038] In one embodiment, the substrate 10 is a low-resistivity silicon with a resistivity of less than 2000 Ω·cm. In this embodiment, setting the resistivity of the low-resistivity silicon to less than 2000 Ω·cm is more effective in reducing the loss of the non-RF piezoacoustic device 100 compared to the use of high-resistivity silicon in the prior art.

[0039] In one embodiment, the resistivity of the insulating layer 20 is: 10. 16 ~10 19 Within the Ω·cm range, the insulating layer 20 effectively prevents the working signal current from leaking longitudinally from the piezoelectric functional layer 30 into the underlying low-resistivity substrate 10. Without this high-quality insulating layer 20, even if the substrate 10 has a very low resistance, some signal current will flow directly into the substrate 10, causing ohmic loss and increasing the overall insertion loss of the non-RF piezoelectric acoustic device 100. The relative permittivity of the insulating layer 20 is in the range of 3.7 to 4.2. Optionally, the insulating layer 20 contains an insulating material, or the insulating layer 20 is silicon dioxide (SiO2). A core function of the insulating layer 20 structure located between the piezoelectric functional layer 30 and the substrate 10 is to confine the acoustic wave energy within the piezoelectric functional layer 30, preventing it from leaking into the high-loss substrate 10. The principle is based on the reflection of acoustic waves at the interface between different materials. In this embodiment, the acoustic impedance of the low-resistivity silicon is very high (~20 × 10⁻⁶). 6 kg / m 2 s), while silicon dioxide (SiO2) has a very low acoustic impedance (~13×10 s), 6 kg / m2 There is a significant acoustic impedance mismatch between them. This significant difference in acoustic impedance results in strong acoustic wave reflections at the interface between the piezoelectric functional layer 30 and the insulating layer 20, and at the interface between the insulating layer 20 and the substrate 10. The insulating layer 20, together with the underlying structure (such as a cavity or another reflective layer), forms a Bragg acoustic mirror, which efficiently reflects the downward-propagating acoustic wave energy back into the piezoelectric resonant cavity, greatly reducing acoustic energy loss.

[0040] In one embodiment, the non-RF piezoelectric acoustic device 100 operates at a frequency less than 100MHz. Some non-RF piezoelectric acoustic devices 100 operate in the frequency range of 500kHz to 1MHz. Others operate in the frequency range of 200kHz to 20kHz.

[0041] In one specific embodiment, the substrate 10 is a low-resistivity silicon with a resistivity of 800 Ω·cm, and the insulating layer 20 has a resistivity of 1*10⁻⁶. 19 The resistivity of the substrate 10 is Ω·cm, and the ratio of the resistivity of the insulating layer 20 to the resistivity is 800 / (1*10). 19 ) = 0.8 * 10 -16 In another specific embodiment, the substrate 10 is a low-resistivity silicon with a resistivity of 800 Ω·cm, and the insulating layer 20 has a resistivity of 1*10⁻⁶. 16 The resistivity of the substrate 10 is Ω·cm, and the ratio of the resistivity of the insulating layer 20 to the resistivity is 800 / (1*10). 19 ) = 0.8 * 10 -13 .

[0042] Figure 3 This is a schematic diagram of the structure of the second type of non-RF piezoelectric acoustic device 100 provided in the embodiments of this application, as shown below. Figure 3 As shown, the piezoelectric functional layer 30 in the non-RF piezoelectric acoustic device 100 may include: a support layer 31, a piezoelectric layer 32, and a metal electrode 33, wherein the piezoelectric functional layer 30 includes at least one piezoelectric structural layer and at least two metal electrode layers.

[0043] Continue as Figure 3 As shown, the piezoelectric layer 32 is disposed on top of the support layer 31, and the support layer 31 is disposed on top of the insulating layer 20.

[0044] Optionally, one or more piezoelectric layers may be disposed between at least two metal electrode layers.

[0045] Figure 4 This is a schematic diagram of the structure of the third non-RF piezoelectric acoustic device 100 provided in the embodiments of this application, as shown below. Figure 4As shown, there is one piezoelectric layer 32 (i.e., the first piezoelectric layer 32-1), and the metal electrode layer may include a first metal electrode 33-1 and a second metal electrode 33-2.

[0046] In one embodiment, such as Figure 4 As shown, the first piezoelectric layer 32-1 is disposed between the first metal electrode 33-1 and the second metal electrode 33-2. Specifically, the first metal electrode 33-1 is disposed on top of the insulating layer 20, the first piezoelectric layer 32-1 is disposed on top of the first metal electrode 33-1, and the second metal electrode 33-2 is disposed on top of the piezoelectric layer 32-2. Therefore, the structure of the piezoelectric functional layer 30 from bottom to top is as follows: first metal electrode 33-1, first piezoelectric layer 32-1, and second metal electrode 33-2. The first metal electrode 33-1 is disposed on top of the support layer 31.

[0047] Figure 5 This is a schematic diagram of the structure of the fourth non-RF piezoelectric acoustic device 100 provided in the embodiments of this application. Figure 5 As shown, the piezoelectric functional layer 30 includes a third metal electrode 33-3 and a second piezoelectric layer 32-2 located between the second metal electrode 33-2 and the third metal electrode 33-3. Specifically, the piezoelectric functional layer 30 includes: a first piezoelectric layer 32-1 and a second piezoelectric layer 32-2, a first metal electrode 33-1, a second metal electrode 33-2, and a third metal electrode 33-3.

[0048] like Figure 5 As shown, the first piezoelectric layer 32-1 is disposed between the first metal electrode 33-1 and the second metal electrode 33-2, and the second voltage layer 32-2 is disposed between the second metal electrode 33-2 and the third metal electrode 33-3. The first metal electrode 33-1 is the bottom electrode layer, and the third metal electrode 33-3 is the top electrode layer. Figure 5 The piezoelectric functional layer 30 has the following structure from bottom to top: a first metal electrode 33-1, a first piezoelectric layer 32-1, a second metal electrode 33-2, a second piezoelectric layer 32-2, and a third metal electrode 33-3. Furthermore, the first metal electrode 33-1 is disposed on top of the support layer 31, the support layer 31 is disposed on top of the insulating layer 20, and the insulating layer 20 is disposed on top of the substrate 10. Figure 5 A gap is formed in the middle of the piezoelectric functional layer 30, and a cavity is formed between the piezoelectric functional layer 30 and the substrate 10.

[0049] In one embodiment, the piezoelectric functional layer 30 is a cantilever structure, comprising one or more cantilever beams. The specific number of cantilever beams is not limited and can be 1, 2, 3, 4, 5, 6, 8, 9, 10, or more. The piezoelectric functional layer 30 includes several cantilever beams connected in series (e.g., Figure 6The diagram shows the case with four cantilever beams (the number of cantilever beams can also be 2, 6, 8, 10, etc.). The membrane structure (section) corresponding to each cantilever beam can be as follows: Figure 5 The piezoelectric stack structure shown, consisting of three layers of electrodes and two layers of piezoelectric thin films, can also be as follows: Figure 4 The diagram shows a single-layer piezoelectric structure consisting of two electrode layers and one layer of piezoelectric material. During fabrication, the thin film structure is first deposited, followed by deep trench etching of the back cavity to form a cantilever beam.

[0050] In one embodiment, the piezoelectric functional layer 30 is a diaphragm structure, the substrate 10 is a low-resistivity material, and the ratio of the resistivity of the substrate 10 to the resistivity of the insulating layer 20 is less than 0.2 × 10⁻⁶. -12 .

[0051] This application also provides an earphone, which includes the non-RF piezoelectric acoustic device 100 described in the foregoing specific embodiments.

[0052] In one embodiment, Figure 7 This is a schematic diagram of the membrane structure of each cantilever beam in the piezoelectric functional layer 30 of the non-RF piezoelectric acoustic device 100. (See diagram for example.) Figure 7 As shown, in the non-RF piezoacoustic device 100, each cantilever beam is connected in series through a beam-to-beam connection structure. Figure 7 The membrane structure within the red dashed box refers to a cantilever beam membrane structure. Figure 7 As can be seen, the membrane structures of multiple cantilever beams are connected in series, and each conical cantilever beam membrane structure includes a piezoelectric layer 32 and a metal electrode 33. The green area in the red dashed box is the piezoelectric layer 32, and the blue area is the metal electrode 33.

[0053] The membrane structure of each cantilever beam in the non-RF piezoelectric acoustic device 100 has an equivalent circuit. This equivalent circuit is used to represent the connection relationship of all cantilever beams in the non-RF piezoelectric acoustic device 100. In one embodiment, it can be based on... Figure 7 The membrane structure of all cantilever beams determines the equivalent circuit of the non-RF piezoacoustic device 100, such as... Figure 8 As shown in the diagram, this equivalent circuit represents the connections between the equivalent input terminals, output terminals, and the underlying silicon. Figure 8 In the diagram, the piezoelectric functional layer 30 in the membrane structure of each cantilever beam is equivalent to a first capacitor C, and the piezoelectric layer 32 in the piezoelectric functional layer 30 is equivalent to a first resistor R. Each cantilever beam can be equivalently represented as a cantilever equivalent circuit consisting of a first capacitor C and a first resistor R connected in parallel, as shown below. Figure 8 The equivalent circuits of each cantilever are connected in series. Furthermore, the structure of the insulating layer 20 between the electrode layer at the input terminal and the corresponding bottom silicon layer at the input terminal is equivalent to... Figure 8 and Figure 9The capacitor C1 in the middle. The structure of the electrode layer at the output terminal and the insulating layer 20 between the electrode layer at the output terminal and the corresponding bottom silicon at the output terminal can be equivalent to as follows: Figure 8 and Figure 9 The other capacitor C1 in the process. The underlying silicon in the non-RF piezoacoustic device 100 is equivalent to, as shown in the figure. Figure 8 and Figure 9 The circuit in which capacitor C2 and resistor R2 are connected in parallel.

[0054] based on Figure 8 The equivalent circuit structure in the diagram, since the piezoelectric layer 32 itself is a large resistor, can be further equivalent to a structure of a capacitor and a resistor connected in parallel, such as... Figure 8 The structure of C and R in parallel. When each cantilever beam film layer structure consists of three electrode layers sandwiching two piezoelectric layers 32, this parallel equivalent circuit still holds, only the capacitance and resistance values ​​of the equivalent capacitor will change. That is, for different cantilever beam film layer structures, they can all be equivalent to a structure of capacitor and resistor in parallel, and the capacitance and resistance values ​​change with the number of layers in the cantilever beam film layer. Therefore, the equivalent circuit of different cantilever beam film layer structures can be equivalent to a structure such as Figure 9 The circuit is a capacitor C0 connected in parallel with a resistor R0. Where C0 = C / number of cantilever beams, and R0 = number of cantilever beams * R.

[0055] like Figure 8 In the equivalent circuit, as the resistivity of R2 gradually increases, Figure 8 The losses in the equivalent circuit gradually increase, and when the resistivity of the underlying silicon increases without limit, it tends to 1×10⁻⁶. 9 When the resistivity of R2 approaches infinity (Ω·cm), it is equivalent to R2 being in an open-circuit state. At this point, the loss on R2 almost disappears, and the overall equivalent circuit loss decreases. To minimize the loss caused by R2, its resistivity needs to be reduced, making R2 approach a short-circuit state. Therefore, the resistivity of the underlying silicon must continuously decrease to achieve the equivalent of R2 approaching infinity, i.e., R2 approaching a short-circuit state. The equivalent circuit then becomes as follows: Figure 9 The structure shown, with capacitor C0 connected in parallel with R0, introduces zero loss in the low-resistivity silicon, and the non-RF piezoacoustic device 100 only contains intrinsic losses. Compared to the equivalent circuit with resistor R2 present, the losses also include heat loss through R2. When R2 approaches zero, the heat loss caused by R2 decreases, resulting in a reduction in the overall loss of the equivalent circuit. Based on this, the adjustment direction is determined to be to decrease the resistance value.

[0056] After the underlying silicon is introduced, a capacitor is formed between the electrode layer at the input end of the acoustic device and the underlying silicon through the intermediate insulating layer 20. Figure 9In C1, the electrode layer at the output terminal and the underlying silicon are connected by an intermediate insulating layer 20 to form another capacitor, such as... Figure 9 In the C1 configuration, the input and output electrode plates and their corresponding underlying silicon layers form two C1 capacitors through the intermediate insulating layer 20. Since there is a potential difference between the underlying silicon layers corresponding to the input and output terminals in the horizontal plane, the path between the two C1 capacitors on the underlying silicon layer, which are equivalent to capacitors C2 and resistor R2 connected in parallel, can be considered equivalent to a structure where C2 is connected in parallel with R2. Therefore, based on the input and output film structure of the non-RF piezoacoustic device 100, taking f=1kHz in the audio frequency range, the circuit can be simplified to the equivalent configuration. Figure 9 In the target equivalent circuit, the change in resistivity of the silicon substrate is equivalent to the change in resistance R2.

[0057] By inputting an electrical signal with a frequency f = 1 kHz and a voltage of 1 V into the target equivalent circuit, and changing the resistivity of the low-resistivity silicon introduced into the bottom layer of the non-RF piezo-acoustic device 100, the following can be obtained: Figure 10 The result in Figure 10 This diagram illustrates the relationship between low-resistivity silicon and loss, as provided in an embodiment of this application. Figure 10 As can be seen, after introducing low-resistivity silicon into the non-RF piezoacoustic device 100, the loss of the non-RF piezoacoustic device 100 remains at a very low level until the resistivity of the low-resistivity silicon reaches 500 Ω·cm, at which point the loss of the non-RF piezoacoustic device 100 begins to increase. When the resistivity of the low-resistivity silicon increases to 2000 Ω·cm, the device loss increases to 20% of the device's intrinsic value, where the intrinsic value refers to the loss of the non-RF piezoacoustic device 100 without the underlying silicon. At this point, the preset threshold is not met. Therefore, resistivity greater than or equal to 2000 Ω·cm is discarded, and resistivity less than 2000 Ω·cm is used as the target resistivity. Therefore, the resistivity of the low-resistivity silicon introduced in this embodiment is less than 2000 Ω·cm. The frequency range of the electrical signal can be 20Hz to 20kHz.

[0058] Since the resistivity of the equivalent resistor in the equivalent circuit of the non-RF piezoelectric acoustic device 100 is variable, the current loss of the equivalent circuit at the current variable resistivity can be detected by changing the resistivity of the equivalent resistor. The variable resistivity of the equivalent resistor can be changed in ascending order. After each change in the variable resistivity, the loss of the equivalent circuit of the non-RF piezoelectric acoustic device 100 is measured to obtain the current loss at the current variable resistivity. The process continues until the current loss at the current variable resistivity does not meet a preset loss threshold, at which point the process ends.

[0059] For example, if the resistivity of the equivalent resistor in the equivalent circuit is set to the current variable resistivity 1, and a 1kHz audio signal is input into the equivalent circuit of the non-RF piezoelectric acoustic device 100, and the loss of the equivalent circuit of the non-RF piezoelectric acoustic device 100 is detected to obtain the current loss 1, then the current loss 1 is the current loss under the current variable resistivity 1; if the resistivity of the equivalent resistor is set to the current variable resistivity 2, and a 1kHz audio signal is input into the equivalent circuit of the non-RF piezoelectric acoustic device 100, and the loss of the equivalent circuit of the non-RF piezoelectric acoustic device 100 is detected to obtain the current loss 2, then the current loss 2 is the current loss under the current variable resistivity 2. The current loss is calculated as follows: The resistivity of the equivalent resistor is set to the current variable resistivity 3. A 1kHz audio signal is input into the equivalent circuit of the non-RF piezoelectric acoustic device 100, and the loss of the equivalent circuit is detected to obtain the current loss 3. The current loss 3 is the current loss under the current variable resistivity 3. The resistivity of the equivalent resistor is set to the current variable resistivity 4. A 1kHz audio signal is input into the equivalent circuit of the non-RF piezoelectric acoustic device 100, and the loss of the equivalent circuit is detected to obtain the current loss 4. The current loss 4 is the current loss under the current variable resistivity 4. This process continues.

[0060] Optionally, if the preceding loss meets a preset loss threshold (i.e., the current loss is less than the preset loss threshold), then the current variable resistivity corresponding to the current loss is taken as the target resistivity within the target resistivity range. If the preceding loss does not meet the preset loss threshold (i.e., the current loss is greater than the preset loss threshold), then the current variable resistivity corresponding to the current loss is not taken as the target resistivity within the target resistivity range, and the process ends.

[0061] The target resistivity is used to indicate how low-resistivity silicon can reduce the loss of the non-RF piezoacoustic device 100 at that target resistivity.

[0062] For example, if the current loss 1 is less than the preset loss threshold, then the current variable resistivity 1 corresponding to the current loss 1 is taken as the target resistivity within the target resistivity range; if the current loss 2 is less than the preset loss threshold, then the current variable resistivity 2 corresponding to the current loss 2 is taken as the target resistivity within the target resistivity range; if the current loss 3 is less than the preset loss threshold, then the current variable resistivity 3 corresponding to the current loss 3 is taken as the target resistivity within the target resistivity range; if the current loss 4 is less than the preset loss threshold, then the current variable resistivity 4 corresponding to the current loss 4 is taken as the target resistivity within the target resistivity range.

[0063] It is worth noting that the method used in this application to determine the target resistivity range can also be used by other methods, and no limitation is made here.

[0064] Table 2 below shows the loss comparison results before and after the introduction of low-resistivity silicon in this application. As shown in Table 2, when the resistivity of low-resistivity silicon is 1 Ω·cm, the difference in loss between the non-RF piezoacoustic device 100 and the device without low-resistivity silicon is small. At this time, the non-RF piezoacoustic device 100 is an equipotential body, there is no potential difference in the entire substrate, and both leakage current and loss are reduced.

[0065] Table 2

[0066] Figure 11 The existing simulation contour plot shows the results after introducing high-resistivity silicon. Figure 12 This application introduces a simulation contour plot of low-resistivity silicon for its embodiments, from... Figure 12 As can be seen, the non-RF piezoacoustic device 100 is an equipotential body, and there is no potential difference in the entire substrate (substrate 10), which reduces leakage current and loss.

[0067] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems and devices described above can be referred to the corresponding processes in the method embodiments, and will not be repeated here. In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection can be through some communication interfaces; the indirect coupling or communication connection of devices or modules can be electrical, mechanical, or other forms.

[0068] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A non-radio frequency piezoelectric acoustic device, comprising: Base; An insulating layer is disposed on the upper part of the substrate; And a piezoelectric functional layer, disposed on the upper part of the insulating layer; Its features are, The substrate is a low-resistivity material, specifically low-resistivity silicon with a resistivity of less than 2000 Ω·cm. The ratio of the resistivity of the substrate to the resistivity of the insulating layer is less than 0.2 × 10⁻⁶. -12 ; The operating frequency of the non-RF piezoelectric acoustic device is less than 100MHz.

2. The non-RF piezoelectric acoustic device according to claim 1, characterized in that, The resistivity of the insulating layer is:

10. 16 ~ 10 19 Within the range of Ω·cm, the relative permittivity of the insulating layer is in the range of 3.7 to 4.

2.

3. The non-RF piezoelectric acoustic device according to claim 1, characterized in that, The piezoelectric functional layer includes: a first metal electrode, a second metal electrode, and a first piezoelectric layer located between the first metal electrode and the second metal electrode.

4. The non-RF piezoelectric acoustic device according to claim 3, characterized in that, It also includes a third metal electrode and a second piezoelectric layer located between the third metal electrode and the second metal electrode.

5. The non-RF piezoacoustic device according to claim 3 or 4, characterized in that, The piezoelectric functional layer has a cantilever structure.

6. The non-RF piezoelectric acoustic device according to claim 5, characterized in that, The cantilever structure includes one or more cantilever beams.

7. The non-RF piezoelectric acoustic device according to claim 3 or 4, characterized in that, The piezoelectric functional layer is a diaphragm structure.

8. An earphone, characterized in that, Includes the non-RF piezoacoustic device according to any one of claims 1-7.

Images