A piezoelectric-electrostatic dual-regulation electric field sensor based on silicon-on-insulator

Abstract

The application belongs to the technical field of electric field sensing, and specifically discloses a piezoelectric-electrostatic double-regulation electric field sensor based on silicon-on-insulator, which comprises a silicon-on-insulator substrate, a piezoelectric driving unit, a composite sensing electrode plate and a signal detection circuit; the silicon-on-insulator substrate is composed of a substrate layer, a buried oxygen layer and a device layer, the substrate layer is provided with a back cavity, the device layer forms a center suspended plate and a support beam through a releasing groove, and the center suspended plate and the support beam form a sensitive thin film structure; the piezoelectric driving unit is embedded in the back cavity and is fixed to the lower surface of the sensitive thin film structure, the composite sensing electrode plate is attached to the upper surface of the center suspended plate, and the stress concentration area of the support beam is integrated with a piezoresistance element and forms a Wheatstone bridge. Through the piezoelectric-electrostatic double-regulation mechanism and the optimized structure design, the application realizes electric field detection with high sensitivity, low noise and good temperature stability, has strong process compatibility, and can be widely applied to scenes with high requirements for electric field measurement, such as power equipment monitoring and thunderstorm early warning.

Description

Technical Field

[0001] This invention belongs to the field of electric field sensing technology, and specifically relates to a piezoelectric-electrostatic dual-controlled electric field sensor based on silicon-on-insulator. Background Technology

[0002] Electric field measurement technology is crucial in fields such as online monitoring of power systems, atmospheric physics research, aerospace safety, and industrial electrostatic protection. Accurate electric field detection is a core support for achieving functions such as equipment fault early warning and thunderstorm forecasting. With the development of the Internet of Things and intelligent sensing technology, the demand for miniaturized, highly sensitive, and highly reliable electric field sensors is becoming increasingly urgent.

[0003] Currently, mainstream electric field sensors are based on a single physical mechanism, which has obvious performance bottlenecks: electrostatic induction sensors (especially microelectromechanical system vibration modulation type) rely on external bias voltage, which increases system complexity and power consumption, and metal components are prone to performance drift due to charge accumulation, resulting in insufficient stability; piezoelectric effect sensors do not require external bias and have fast response, but the output signal is weak when measuring weak static or quasi-static electric fields, which is easily affected by noise interference, and the sensitivity is limited by the dielectric properties of piezoelectric materials; microelectromechanical system sensors based on silicon-on-insulator technology have the advantages of low power consumption and low parasitic capacitance, but they mostly adopt a single electrostatic drive and piezoresistive detection scheme, which limits the sensitivity and dynamic range, and improper matching design between the piezoresistive strip and the stress concentration area can easily cause signal loss.

[0004] In summary, existing sensors, due to their single driving mechanism and structural design defects, are unable to meet the requirements of high-precision measurement in terms of sensitivity, stability, and anti-interference capability. There is an urgent need for a new type of sensor that integrates the advantages of multiple sensing mechanisms and optimizes structural design to achieve efficient and stable detection of electric fields. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a piezoelectric-electrostatic dual-controlled electric field sensor based on silicon-on-insulator. Through the synergistic effect of the piezoelectric and electrostatic dual driving mechanisms, combined with an optimized structural design, it achieves high sensitivity, low noise, and high reliability in electric field detection.

[0006] The technical solution of the present invention is: a piezoelectric-electrostatic dual-controlled electric field sensor based on silicon-on-insulator, comprising a silicon-on-insulator substrate, a piezoelectric driving unit, a composite sensing plate, and a signal detection circuit.

[0007] The silicon-on-insulator substrate comprises, from bottom to top, a substrate layer, a buried oxide layer, and a device layer. A back cavity is located in the central region of the substrate layer. Multiple release grooves are located in the region of the device layer above the back cavity. The lower ends of the release grooves extend through the buried oxide layer and communicate with the back cavity. The release grooves divide the device layer above the back cavity into a central suspension plate and multiple support beams connecting the central suspension plate to other regions of the device layer. A piezoresistive element is integrated in the stress concentration area of ​​each support beam. These piezoresistive elements are connected by metal interconnects to form a Wheatstone bridge structure. The central suspension plate and support beams together constitute a vertically vibrating sensitive thin-film structure. A piezoelectric drive unit is located within the back cavity, with its upper end fixed to the lower end of the buried oxide layer, and is used to apply a piezoelectric driving force to the central suspension plate. A composite sensing plate is attached to the upper surface of the central suspension plate to sense an external electric field and generate electrostatic force. A signal detection circuit is electrically connected to the Wheatstone bridge structure.

[0008] Furthermore, the cross-section of the release groove is L-shaped.

[0009] Furthermore, there are four release slots arranged in a matrix, the central suspension plate has a square cross-section, and there are four support beams.

[0010] Furthermore, the two sides of the L-shaped release groove structure are equal, and the four support beams are distributed at the center of the four sides of the central suspension plate.

[0011] Furthermore, the composite inductive electrode plate includes a first metal layer and a second metal layer from bottom to top. The first metal layer is laid on the upper surface of the central suspension plate and is connected to the metal interconnection line. The second metal layer is stacked on the upper surface of the first metal layer, and the first metal layer is controlled to be grounded so that the lower surface of the second metal layer is at the ground potential.

[0012] Furthermore, the thickness of the first metal layer is less than the thickness of the second metal layer.

[0013] Furthermore, the piezoelectric driving unit is a piezoelectric single crystal block polarized along the 001 crystal direction, and the piezoelectric single crystal block has a low dielectric constant characteristic in the polarization direction.

[0014] Furthermore, the piezoresistive element includes a lightly doped piezoresistive strip and a heavily doped connecting region; the piezoresistive element is disposed on the side of the support beam away from the central suspension plate.

[0015] Furthermore, the substrate layer is made of silicon and has a thickness of 450μm to 500μm; the buried oxide layer is made of silicon dioxide and has a thickness of 0.8μm to 1.2μm; and the device layer is made of single-crystal silicon and has a thickness of 18μm to 22μm.

[0016] Furthermore, the piezoelectric drive unit is bonded to the lower end of the buried oxide layer.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention has a compact structure and high driving efficiency: It creatively integrates the piezoelectric driving unit into the back cavity of the silicon-on-insulator substrate and adopts a vertical stacking structure of "back driving and top sensing". This not only avoids the driving unit occupying the valuable surface area of ​​the device layer, but also realizes the coaxial coupling of driving force and induced electrostatic force, effectively improving driving efficiency and energy transfer ratio, and simplifying the overall structure.

[0018] High sensitivity and low stiffness design: By setting an L-shaped release groove in the device layer, a support beam structure with low mechanical stiffness is formed, which enables the central suspension plate to produce significant displacement under the action of weak electrostatic force (electric field force), greatly improving the sensor's detection sensitivity to low frequency or weak electric field.

[0019] Good process compatibility and high consistency: Using silicon-on-insulator as the substrate material, and taking advantage of the excellent mechanical properties of single-crystal silicon in the device layer and the self-stopping etching characteristics of the buried oxide layer, the thickness and size of the sensitive structure can be precisely controlled, ensuring the consistency and yield of sensor processing and reducing the difficulty of mass production.

[0020] The signal readout has good linearity and strong anti-interference ability: the Wheatstone bridge piezoresistive readout structure located at the root of the support beam can linearly convert the vibration displacement of the central suspension plate into a voltage signal and is easy to integrate with external circuits; the grounding adhesion interconnection layer of the composite induction plate can effectively shield interference and improve signal stability and anti-electromagnetic interference ability.

[0021] Wide range of applications: Through the dual control mechanism of piezoelectric and electrostatic, it takes into account the active response characteristics of piezoelectric drive and the high sensitivity of electrostatic induction. It can adapt to the measurement needs of electric fields of different frequencies and intensities, and is suitable for many occasions with high requirements for electric field measurement, such as partial discharge monitoring of power equipment and early warning of atmospheric electric field thunderstorms. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a top view of the present invention; Figure 3 This is a schematic diagram of the process structure for an application example of the present invention.

[0023] Among them, 1-substrate layer, 10-back cavity, 2-buried oxide layer, 3-device layer, 30-release groove, 31-central suspension plate, 32-support beam, 33-piezoresistive element, 330-metal interconnect line, 4-piezoelectric drive unit, 5-composite sensing electrode plate, 51-first metal layer, 52-second metal layer. Detailed Implementation

[0024] The following is in conjunction with the appendix Figure 1 To the attached Figure 3 The specific embodiments of the present invention will be described in detail below. In the description of the present invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0025] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0026] It should be noted that the circuit connections involved in this invention all adopt conventional circuit connection methods and do not involve any innovation.

[0027] Example like Figure 1 , Figure 2 The piezoelectric-electrostatic dual-tunable electric field sensor based on silicon-on-insulator (SiO2) includes a SiO2 substrate, a piezoelectric driving unit 4, a composite sensing plate 5, and a signal detection circuit.

[0028] The silicon-on-insulator substrate comprises, from bottom to top, a substrate layer 1, a buried oxide layer 2, and a device layer 3. A back cavity 10 is located in the central region of the substrate layer 1. Multiple release grooves 30 are located in the region of the device layer 3 above the back cavity 10. These release grooves divide the region of the device layer 3 above the back cavity 10 into a central suspension plate 31 and multiple support beams 32 connecting the central suspension plate 31 to other regions of the device layer 3. A piezoresistive element 33 is integrated into the stress concentration area of ​​each support beam 32. These piezoresistive elements 33 are connected by metal interconnects 330 to form a Wheatstone bridge structure. The central suspension plate 31, support beams 32, and the buried oxide layer 2 together constitute a sensitive thin film structure capable of vertical vibration. A piezoelectric drive unit 4 is located within the back cavity 10. The upper end of the piezoelectric drive unit 4 is fixed to the lower end of the buried oxide layer 2 and is used to apply a piezoelectric driving force to the central suspension plate 31, causing the sensitive thin film structure to be in a resonant or forced vibration state. The composite induction plate 5 is attached to the upper surface of the central suspension plate 31 to sense an external electric field and generate electrostatic force. This electrostatic force acts on the central suspension plate 31 and modulates its vibration state. The signal detection circuit is electrically connected to the Wheatstone bridge structure.

[0029] Preferably, the release groove 30 has an L-shaped cross-section.

[0030] Preferably, there are four release slots 30 arranged in a matrix, the central suspension plate 31 has a square cross-section, and there are four support beams 32.

[0031] Preferably, the two sides of the L-shaped release groove 30 are equal, and the four support beams 32 are distributed at the center of the four sides of the central suspension plate 31.

[0032] Preferably, the composite induction plate 5 includes a first metal layer 51 and a second metal layer 52 from bottom to top. The first metal layer 51 is laid on the upper surface of the central suspension plate 31 and is connected to the metal interconnection line 330. The second metal layer 52 is stacked on the upper surface of the first metal layer 51. The first metal layer 51 is controlled to be grounded so that the lower surface of the second metal layer 52 is at the ground potential.

[0033] Preferably, the thickness of the first metal layer 51 is less than the thickness of the second metal layer 52.

[0034] Preferably, the piezoelectric driving unit 4 is a piezoelectric single crystal block polarized along the 001 crystal direction, and the piezoelectric single crystal block has a low dielectric constant in the polarization direction, thereby improving the driving efficiency by utilizing its low dielectric constant in the polarization direction.

[0035] Preferably, the piezoresistive element 33 includes a lightly doped piezoresistive strip and a heavily doped connecting region; the piezoresistive element 33 is disposed on the side of the support beam 32 away from the central suspension plate 31.

[0036] Preferably, the substrate layer 1 is made of silicon with a thickness of 450μm to 500μm; the buried oxide layer 2 is made of silicon dioxide with a thickness of 0.8μm to 1.2μm; and the device layer 3 is made of single-crystal silicon with a thickness of 18μm to 22μm.

[0037] Preferably, the piezoelectric drive unit 4 is bonded to the lower end of the buried oxide layer 2.

[0038] Application examples The embodiment 1 presents a piezoelectric-electrostatic dual-controlled micro electric field sensor based on silicon-on-insulator (SiO2) technology. The core of this technology lies in precisely matching the layer thickness characteristics of the SiO2 wafer with the dimensions of the piezoelectric element. Figure 3 As shown, the specific implementation plan is as follows: I. Selection of Silicon-on-Insulator Substrate: Customized silicon-on-insulator wafers are selected as the substrate for fabrication.

[0039] The device layer 3 has a thickness of 20 μm and is made of low-resistivity n-type single crystal silicon. It serves as the main material for forming the central suspension plate 31, the support beam 32, and the piezoresistive detection structure. This thickness ensures that the sensitive structure has sufficient mechanical strength and moderate mass.

[0040] The buried oxide layer 2 has a thickness of 1 μm and plays a crucial role in electrical insulation and mechanical connection, while also serving as a self-stopping layer for back cavity etching.

[0041] The substrate layer 1 has a thickness of 480 μm, which directly determines the depth of the back cavity 10, providing a precise vertical spatial reference for the embedding of the piezoelectric unit.

[0042] II. Sensitive Structure Geometry: A vibratory mechanical structure is released in device layer 3 through deep reactive ion etching.

[0043] The central suspension plate 31 is designed as a square with a side length ranging from 250μm to 300μm, preferably 280μm.

[0044] The composite induction plate 5 has an Au / Ti metal film deposited on the upper surface of the central suspension plate 31. The film is square in shape with a side length ranging from 230μm to 275μm. The size of the metal film is slightly smaller than that of the central suspension plate 31 to prevent short circuits or stress concentrations at the edges due to process errors.

[0045] Cantilever support system: The central suspension plate 31 is supported by an L-shaped microbeam structure. The length or span of the support beam 32 is designed to be 600μm. The reasonable length-to-diameter ratio design ensures that the first natural frequency of the structure falls within the target operating frequency band, which not only ensures the suppression of low-frequency noise, but also has sufficient mechanical sensitivity.

[0046] III. Zero-gap embedding and size mapping of piezoelectric drive unit 4: A unique "embedded size mapping" design is adopted to achieve optimal electromechanical coupling efficiency.

[0047] Thickness matching: A piezoelectric ceramic block or single crystal block with a thickness strictly controlled at 480μm is selected as the piezoelectric driving unit 4. Since the thickness of the silicon substrate layer 1 on the insulator is also 480μm, when the piezoelectric driving unit 4 is embedded in the back cavity 10 and rests against the lower surface of the buried oxide layer 2, the bottom of the piezoelectric driving unit 4 and the bottom of the silicon chip on the insulator are at the same level, which greatly simplifies the subsequent chip packaging process. There is no need to reserve additional protrusion space for the piezoelectric driving unit 4, thus realizing the flattening of the sensor.

[0048] Precise area mapping: The width of the piezoelectric drive unit 4 is designed to be consistent with that of the composite induction plate 5, i.e., 230μm-275μm. This "one-to-one correspondence" geometric design ensures that the piezoelectric drive force in the vertical direction only acts on the effective area of ​​the induction capacitor, i.e., the area of ​​the central suspension plate 31, avoiding the drive force from being dispersed to the root of the support beam 32, thereby eliminating the common-mode interference of the piezoelectric drive on the piezoresistive detection bridge and improving the signal-to-noise ratio.

[0049] It should be noted that sensor performance can be optimized by adjusting key parameters to adapt to different application scenarios.

[0050] Low-frequency electric field measurement optimization: To improve the sensitivity of low-frequency electric field measurement, the stiffness of the support beam 32 can be optimized, such as by reducing the beam width or increasing the beam length, and by adjusting the size and position of the piezoelectric drive unit 4 accordingly, to ensure that the piezoelectric drive force and electrostatic induction force are optimally coupled on the movable structure, thereby enhancing the response to weak low-frequency electric fields. High-frequency electric field measurement optimization: To adapt to high-frequency electric field measurement, a piezoelectric material with high frequency response can be selected as the piezoelectric driving unit 4. Specifically, the piezoelectric material can be a PIN-PMN-PT single crystal. The modes of the movable structure are optimized so that its resonant frequency avoids the main interference frequency band, thereby improving the accuracy and stability of high-frequency electric field detection.

[0051] Lightly doped piezoresistive strips Figure 3 Lightly to moderately p-type doped piezoresistive silicon is the piezoresistive sensitive region, used to sense stress and output signals; the heavily doped junction region is... Figure 3 Medium to heavy P-type doped piezoresistive silicon is a low-resistance connection region used to reduce contact resistance and improve bridge stability.

[0052] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the protection scope of the present invention.

Claims

1. A piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator, characterized in that, include: The silicon-on-insulator substrate comprises, from bottom to top, a substrate layer, a buried oxide layer, and a device layer. A back cavity is provided in the central region of the substrate layer. Multiple release grooves are provided in the region of the device layer above the back cavity. The lower ends of the release grooves extend through the buried oxide layer and communicate with the back cavity. The release grooves divide the device layer above the back cavity into a central suspension plate and multiple support beams connecting the central suspension plate to other regions of the device layer. A piezoresistive element is integrated in the stress concentration area of ​​each support beam. The piezoresistive elements are connected by metal interconnects to form a Wheatstone bridge structure. The central suspension plate and the support beams together constitute a sensitive thin-film structure capable of vertical vibration. A piezoelectric drive unit is located inside the back cavity. The upper end of the piezoelectric drive unit is fixed to the lower end of the buried oxygen layer and is used to apply piezoelectric driving force to the central suspension plate. Composite induction plates are attached to the upper surface of the central suspension plate and are used to sense external electric fields to generate electrostatic forces. The signal detection circuit is electrically connected to the Wheatstone bridge structure.

2. The piezoelectric-electrostatic dual-tunable electric field sensor based on silicon-on-insulator as described in claim 1, characterized in that, The release groove has an L-shaped cross-section.

3. The piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 2, characterized in that, There are four release slots arranged in a matrix, the central suspension plate has a square cross-section, and there are four support beams.

4. The piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 3, characterized in that, The two sides of the L-shaped release groove are equal, and the four support beams are distributed at the center of the four sides of the central suspension plate.

5. The piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 1, characterized in that, The composite induction plate includes a first metal layer and a second metal layer from bottom to top. The first metal layer is laid on the upper surface of the central suspension plate and is connected to the metal interconnection line. The second metal layer is stacked on the upper surface of the first metal layer. The first metal layer is controlled to be grounded so that the lower surface of the second metal layer is at the ground potential.

6. The piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 5, characterized in that, The thickness of the first metal layer is less than the thickness of the second metal layer.

7. The piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 1, characterized in that, The piezoelectric driving unit is a piezoelectric single crystal block polarized along the 001 crystal direction, and the piezoelectric single crystal block has a low dielectric constant characteristic in the polarization direction.

8. The piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 1, characterized in that, The piezoresistive element is located on the side of the support beam away from the central suspension plate.

9. A piezoelectric-electrostatic dual-modulation electric field sensor based on silicon-on-insulator as described in claim 1, characterized in that, The substrate is made of silicon and has a thickness of 450μm to 500μm. The embedded oxide layer is made of silicon dioxide and has a thickness of 0.8 μm to 1.2 μm. The device layer is made of monocrystalline silicon and has a thickness of 18μm to 22μm.

10. A piezoelectric-electrostatic dual-tunable electric field sensor based on silicon-on-insulator as described in claim 1, characterized in that, The piezoelectric drive unit is bonded to the lower end of the buried oxide layer.

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