Sensitive unit structure of piezoelectric-piezoresistive coupling electric field sensor and application

Abstract

A sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor and application, comprising a substrate, a cantilever beam structure is arranged on the substrate, a piezoelectric crystal block is bonded between the lower surface of the cantilever beam structure and the upper surface of the substrate, and a Wheatstone full-bridge structure is arranged on the upper surface of the cantilever beam structure; when the piezoelectric crystal block is subjected to the action of an electric field, the piezoelectric crystal block generates deformation along the Z-axis direction under the action of the inverse piezoelectric effect, so that the cantilever beam structure is deformed; in the Wheatstone full-bridge structure, the resistors arranged at the positions with the maximum stress difference generate deformation under stress, the stress directions of the resistors are opposite, and the resistance value changes are opposite; compared with the commonly used electric field sensor sensitive unit structures such as the electro-optic type and the mechanical type, the present application has the advantages of a larger range, a smaller size, lower power consumption and easy mass production.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and specifically relates to the sensitive unit structure and application of a piezoelectric-piezoresistive coupled electric field sensor. Background Technology

[0002] Electric field sensors have important applications in many fields, such as power systems and industrial production. In the power system field, electric field sensors can be used for electromagnetic environment assessment, condition sensing, defect detection, and evaluation and diagnosis of power transmission equipment and lines. In addition to power frequency and DC electric fields, power systems also have low-frequency, medium-high frequency, and high-frequency electric fields. With the expansion of power grid scale and the development of digital power systems, the demand for electric field sensors with a wider dynamic and static range and a wider frequency band is increasing.

[0003] Currently, commonly used miniature electric field sensors are mainly classified into several types according to their working principles, including electro-optic sensors, mechanical sensors, and D-dot sensors. Electro-optic electric field sensors, based on the electro-optic effect, modulate electric field signals into optical signals through energy coupling for sensing. They possess characteristics such as lossless transmission, wide measurement bandwidth, and fast dynamic response. However, optical electric field sensors require high laser stability, and the expensive and costly optical components, coupled with poor temperature stability, make miniaturization difficult, limiting their further development and application. Mechanical electric field sensors couple and modulate electric field signals into electrical signals through mechanical modulation and induced charges for sensing. They have advantages in ultra-high precision electrostatic field and extreme environment measurements; however, limited by the mechanical motion frequency, the detection range is generally 0~1kHz, unable to capture new voltage problems such as broadband oscillations and transient overvoltages, and their size is generally greater than 10cm². 3 Its power consumption is greater than 1W, which is not conducive to large-scale deployment.

[0004] Xue Fen et al. proposed a novel PE-PR MEMS sensor structure in their paper "Piezoelectric-Piezoresistive Coupled MEMS Sensor for Wide Bandwidth and Large Dynamic Range Electric Field Measurement" (IEEE Transactions on Industrial Electromagnets, Vol. 67, No. 1, January 2020). This structure has an hourglass-shaped cavity containing a piezoelectric crystal, allowing the piezoresistive membrane to vibrate freely. The composite structure, which couples the piezoelectric and piezoresistive effects, converts changes in electric field into changes in resistance through internal pressure. However, this scheme has a relatively small bandwidth, low sensitivity and resolution, and low mechanical strength and stability. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the present invention aims to provide a sensitive unit structure and application of a piezoelectric-piezoresistive coupled electric field sensor. The cantilever beam structure significantly amplifies the piezoresistive effect, and by coupling the piezoresistive and piezoelectric effects, the dynamic strain of the piezoelectric crystal block of the high-voltage coefficient material in the electric field is directly transmitted to the piezoresistive resistor, thus improving the measurement range. By setting the resistor of the Wheatstone full-bridge structure at the position of maximum stress extremum, the utilization rate of the piezoresistive effect is greatly improved, and the output signal of the full-bridge circuit is twice that of the half-bridge structure, thereby enhancing the sensitivity of the sensitive unit. The cantilever beam is a single-crystal SOI integrally etched double-ended beam, and the beam body and supporting structure are interface-free single-crystal continuums, significantly improving structural strength and stability. Furthermore, thanks to the integrated rigid support, thermal vibration noise is reduced, resulting in a significant improvement in resolution.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] A sensitive unit structure for a piezoelectric-piezoresistive coupled electric field sensor includes a substrate 4, on which a cantilever beam structure 1 is provided. A piezoelectric crystal block 3 is bonded between the lower surface of the cantilever beam structure 1 and the upper surface of the substrate 4. A Wheatstone full-bridge structure 2 is provided on the upper surface of the cantilever beam structure 1. Under the action of an electric field, the piezoelectric crystal block 3 generates Z-axis strain through the inverse piezoelectric effect. The strain is transmitted to the cantilever beam structure 1, causing the cantilever beam structure 1 to bend. The Wheatstone full-bridge structure 2 outputs a differential voltage signal proportional to the bending strain, realizing the conversion of electric field to electrical signal.

[0008] The cantilever beam structure 1 is a single-crystal SOI integral etching-formed double-end fixed beam. The fixed ends 12 on both sides of the cantilever beam structure 1 are etched from the bottom silicon layer of the single-crystal SOI wafer, and the beam body 11 between the two fixed ends 12 on both sides of the cantilever beam structure 1 is etched from the top silicon layer of the single-crystal SOI wafer.

[0009] The Wheatstone full-bridge structure 2 includes a first electrode 231, a second electrode 232, a third electrode 233, and a fourth electrode 234 respectively disposed at the four corners of the upper surface of the cantilever beam structure 1; the first electrode 231, the second electrode 232, the third electrode 233, and the fourth electrode 234 are respectively connected to the first resistor 211, the second resistor 212, the third resistor 213, and the fourth resistor 214 through the lead wire 22 to form a Wheatstone full-bridge circuit; wherein, the first electrode 231 is the voltage output terminal, the fourth electrode 234 is the ground terminal, and the second electrode 232 and the third electrode 233 are processed by an external differential circuit to form a signal output terminal.

[0010] The first electrode 231 to the fourth electrode 234 and the lead wire 22 are made by electron beam evaporation process to deposit chromium and gold.

[0011] The first resistor 211 to the fourth resistor 214 are all distributed along the length of the cantilever beam, and the first resistor 211 to the fourth resistor 214 are all varistors formed by ion implantation.

[0012] The first resistor 211 to the fourth resistor 214 are respectively arranged at the four positions with the largest stress difference along the length of the cantilever beam structure 1.

[0013] The piezoelectric crystal block 3 is a PMN-PT piezoelectric single crystal block, and the thickness ratio of the piezoelectric crystal block 3 to the thickness of the beam body 11 is 30:1.

[0014] A sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor is applied to electric field measurement: The electric field sensor is placed in the electric field to be measured, and an excitation voltage is applied to the Wheatstone full-bridge structure 2. The piezoelectric crystal block 3 undergoes a deformation proportional to the electric field under the action of the electric field. The strain is transmitted to the cantilever beam structure 1 of the single crystal SOI, causing the cantilever beam structure 1 to undergo bending deformation. The resistance values ​​of the piezoresistive resistors from the first resistor 211 to the fourth resistor 214 change proportionally to the deformation. A differential voltage signal proportional to the change in the resistance value of the piezoresistive resistor is output through the Wheatstone full-bridge structure 2, realizing the conversion of electric field to electrical signal and completing the electric field measurement.

[0015] Compared with existing electric field sensor sensing units, the beneficial effects of the present invention are as follows:

[0016] 1. The piezoelectric-piezoresistive electric field sensing unit with the stress-strain coupling composite structure of SOI cantilever beam piezoresistive film and piezoelectric material designed in this invention significantly amplifies the piezoresistive effect through the cantilever beam structure, and directly transmits the dynamic strain of the piezoelectric crystal block of the high-voltage coefficient material in the electric field to the piezoresistive resistor by coupling the piezoresistive effect and the piezoelectric effect, thereby improving the measurement range and greatly enhancing the electric field sensing performance compared with traditional electric field sensors.

[0017] 2. The cantilever beam structure designed in this invention is a single-crystal SOI integrally etched and molded double-ended fixed beam. Compared with the existing multi-structure bonded cantilever beam structure, there is no interface between the beam body and its supporting structure, and it is a continuous body, resulting in higher strength and better stability. At the same time, thanks to the integrated rigid support, thermal vibration noise is reduced, and the resolution is improved. Furthermore, compared with the common single-layer structure sensing unit, the buried oxide layer on the lower surface of the cantilever beam structure can block substrate leakage current, significantly reducing electrical signal transmission loss and lower power consumption of the sensing unit.

[0018] 3. The sensing element of the electric field sensor of this invention adopts a MEMS packaging structure, and the overall volume size is less than 0.05 cm. 3With a power consumption of less than 0.1W, it exhibits excellent frequency response characteristics in the range of 0~200kHz, a maximum operating bandwidth of 1.2MkHz, and a sensitivity of 190mV / (kV / m). It can sensitively capture complex waveforms such as wideband oscillations and transient overvoltages. Compared with electro-optic and mechanical electric field sensors, it has a smaller sensing element, lower power consumption, larger measurement range, and higher sensitivity. It also improves the uniformity of the sensing element, making it easy to mass-produce and deploy on a large scale. It is also convenient to deploy flexibly in complex environments to achieve large-scale, multi-point detection.

[0019] In summary, this invention has the advantages of large range, high precision, smaller size, lower power consumption, and mass production capability. Attached Figure Description

[0020] Figure 1 This is a three-dimensional schematic diagram of the sensitive unit structure of the piezoelectric-piezoresistive coupled electric field sensor of the present invention.

[0021] Figure 2 for Figure 1 Schematic diagram of cross-section of the medium-sensitive unit structure.

[0022] Figure 3 for Figure 1 Top view of the structure of the medium-sensitive unit.

[0023] Figure 4 This is a schematic diagram of the equivalent circuit connection of the Wheatstone full-bridge structure in this embodiment.

[0024] The components are: 1. Cantilever beam structure; 2. Wheatstone full-bridge structure; 3. Piezoelectric crystal block; 4. Substrate; 11. Beam body; 12. Fixed end; 211. First resistor; 212. Second resistor; 213. Third resistor; 214. Fourth resistor; 22. Lead wire; 231. First electrode; 232. Second electrode; 233. Third electrode; 234. Fourth electrode. Detailed Implementation

[0025] To make the technical solution of the present invention clearer, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0026] like Figure 1 As shown, a sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor includes a substrate 4, on which a cantilever beam structure 1 is provided, such as... Figure 2As shown, a piezoelectric crystal block 3 is bonded between the lower surface of the cantilever beam structure 1 and the upper surface of the substrate 4. The piezoelectric crystal block 3 is a PMN-PT piezoelectric single crystal block. A Wheatstone full-bridge structure 2 is provided on the upper surface of the cantilever beam structure 1. Under the action of an electric field, the piezoelectric crystal block 3 generates Z-axis strain through the inverse piezoelectric effect. The strain is transmitted to the cantilever beam structure 1, causing the cantilever beam structure 1 to bend. The Wheatstone full-bridge structure outputs a differential voltage signal that is proportional to the bending strain, realizing the conversion of electric field to electrical signal.

[0027] The cantilever beam structure 1 is a single-crystal SOI integral etching-formed double-end fixed beam. The fixed ends 12 on both sides of the cantilever beam structure 1 are formed by etching the bottom silicon layer of the SOI wafer, and the beam body 11 between the two fixed ends 12 on both sides of the cantilever beam structure 1 is formed by etching the top silicon layer of the SOI wafer.

[0028] like Figure 3 As shown, the Wheatstone full-bridge structure 2 includes a first electrode 231, a second electrode 232, a third electrode 233, and a fourth electrode 234 respectively disposed at the four corners of the upper surface of the cantilever beam structure 1; the first electrode 231, the second electrode 232, the third electrode 233, and the fourth electrode 234 are respectively connected to the first resistor 211, the second resistor 212, the third resistor 213, and the fourth resistor 214 through the lead wire 22 to form a Wheatstone full-bridge circuit; wherein, the first electrode 231 is the voltage output terminal, the fourth electrode 234 is the ground terminal, and the second electrode 232 and the third electrode 233 are processed by an external differential circuit to form a signal output terminal.

[0029] The first electrode 231 to the fourth electrode 234 and the lead wire 22 are made by electron beam evaporation process to deposit chromium and gold.

[0030] The first resistor 211 to the fourth resistor 214 are all distributed along the length of the cantilever beam, and the resistors are varistors formed by ion implantation.

[0031] The first resistor 211 to the fourth resistor 214 are respectively arranged at the four positions with the largest stress difference along the length of the cantilever beam structure 1.

[0032] The piezoelectric crystal block 3 is a PMN-PT piezoelectric single crystal block, and its thickness ratio to the thickness of the beam body 11 is 30:1.

[0033] A sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor is applied to electric field measurement: The electric field sensor is placed in the electric field to be measured, and an excitation voltage is applied to the Wheatstone full-bridge structure 2. The piezoelectric crystal block 3 undergoes a deformation proportional to the electric field under the action of the electric field. The strain is transmitted to the cantilever beam structure 1 of the single crystal SOI, causing the cantilever beam structure 1 to undergo bending deformation. The resistance values ​​of the piezoresistive resistors from the first resistor 211 to the fourth resistor 214 change proportionally to the deformation. A differential voltage signal proportional to the change in the resistance value of the piezoresistive resistor is output through the Wheatstone full-bridge structure 2, realizing the conversion of electric field to electrical signal and completing the electric field measurement.

[0034] The working principle of this invention is as follows:

[0035] Figure 3 This is a schematic diagram of the sensitive element when it is at rest. The upper surface of the beam body 11 is flush with the upper surfaces of the two fixed ends 12, and the piezoelectric crystal block 3 does not deform. When the piezoelectric crystal block 3 is subjected to an electric field, under the action of the inverse piezoelectric effect, the piezoelectric crystal block 3 deforms along the Z-axis, causing the beam body 11 to deform. The two pairs of resistors (first resistor 211, fourth resistor 214, second resistor 212, and third resistor 213) arranged at the position of maximum strain difference are deformed under force. The forces on the two pairs of resistors are in opposite directions, and the resistance values ​​change in opposite directions.

[0036] Figure 4 This is the equivalent circuit diagram of the Wheatstone bridge structure 2 in this sensitive unit structure. Vin is the input voltage, Vout is the output voltage, and R1~R4 are the initial resistance values ​​of the first resistor 211 to the fourth resistor 214. According to the Wheatstone bridge principle, the bridge output signal is proportional to the change in resistance value, and thus proportional to the electric field to be measured, thereby realizing the measurement of the electric field. The electric field strength E can be calculated by S=Vout / E, thus obtaining the electric field value. The sensitivity S can be obtained by calibration experiments under a standard electric field.

[0037] The cantilever beam structure 1 of the sensitive unit structure disclosed in this invention has higher sensitivity, mechanical strength, and stability, and better impact resistance compared to membrane structure electric field sensor sensitive unit structures. By adjusting the length, width, and thickness of the cantilever beam structure, the frequency and mode of the sensitive unit structure can be modulated, improving the frequency response range and mode matching accuracy of the sensitive unit structure. The resonant frequency formula of the cantilever beam structure is shown below.

[0038]

[0039] in, , For the vibration of the first Vibration mode number, Mass per unit volume A For cross-sectional area,L Let be the length of the beam. Let J be the bending stiffness, and J be the moment of inertia of the cross section about the x and y axes that are perpendicular to the centroidal axis of the cross section.

[0040] Optimization enables electric field sensors to respond effectively over a wider frequency range, better adapting to the complex and variable voltage signal characteristics in ultra-high voltage flexible DC systems, while ensuring optimal performance within the target monitoring frequency band, thereby improving the measurement accuracy and reliability of electric field sensors.

[0041] The embodiments described above are merely illustrative of the technical concept of this invention, intended to enable those skilled in the art to understand the invention, and are not intended to limit the scope of protection of this invention. It should be noted that any modifications to the technical solutions of this invention that do not depart from the spirit and essence of this invention should be covered within the scope of protection of this invention.

Claims

1. A sensitive unit structure for a piezoelectric-piezoresistive coupled electric field sensor, comprising a substrate (4), characterized in that, The substrate (4) is provided with a cantilever beam structure (1). A piezoelectric crystal block (3) is bonded between the lower surface of the cantilever beam structure (1) and the upper surface of the substrate (4). A Wheatstone full-bridge structure (2) is provided on the upper surface of the cantilever beam structure (1). The piezoelectric crystal block (3) generates Z-axis strain through the inverse piezoelectric effect under the action of the electric field. The strain is transmitted to the cantilever beam structure (1) to cause the cantilever beam structure (1) to bend. The Wheatstone full-bridge structure (2) outputs a differential voltage signal that is proportional to the bending strain, thereby realizing the conversion of electric field to electrical signal. The cantilever beam structure (1) is a double-ended fixed beam formed by single-crystal SOI integral etching. The fixed ends (12) on both sides of the cantilever beam structure (1) are etched from the bottom silicon layer of the single-crystal SOI wafer. The main beam body (11) between the fixed ends (12) on both sides of the cantilever beam structure (1) is etched from the top silicon layer of the single-crystal SOI wafer.

2. The sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor according to claim 1, characterized in that, The Wheatstone full-bridge structure (2) includes a first electrode (231), a second electrode (232), a third electrode (233), and a fourth electrode (234) respectively set at the four corners of the upper surface of the cantilever beam structure (1); the first electrode (231), the second electrode (232), the third electrode (233), and the fourth electrode (234) are respectively connected to the first resistor (211), the second resistor (212), the third resistor (213), and the fourth resistor (214) through the lead wire (22) to form a Wheatstone full-bridge circuit; wherein, the first electrode (231) is the voltage output terminal, the fourth electrode (234) is the ground terminal, and the second electrode (232) and the third electrode (233) are processed by an external differential circuit to form a signal output terminal.

3. The sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor according to claim 2, characterized in that, The first electrode (231) to the fourth electrode (234) and the lead wire (22) are made by electron beam evaporation process to deposit chromium and gold.

4. The sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor according to claim 2, characterized in that, The first resistor (211) to the fourth resistor (214) are all distributed along the length of the cantilever beam, and the first resistor (211) to the fourth resistor (214) are all piezoresistors formed by ion implantation.

5. The sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor according to claim 4, characterized in that, The first resistor (211) to the fourth resistor (214) are respectively arranged at the four positions with the largest stress difference along the length of the cantilever beam structure (1).

6. The sensitive unit structure of a piezoelectric-piezoresistive coupled electric field sensor according to claim 1, characterized in that, The piezoelectric crystal block (3) is a PMN-PT piezoelectric single crystal block, and the thickness ratio of the piezoelectric crystal block (3) to the thickness of the beam body (11) is 30:

1.

7. The application of the sensitive unit structure of the piezoelectric-piezoresistive coupled electric field sensor according to any one of claims 1 to 6, for electric field measurement, characterized in that: The electric field sensor is placed in the electric field to be measured, and an excitation voltage is applied to the Wheatstone full-bridge structure (2). The piezoelectric crystal block (3) undergoes a deformation proportional to the electric field under the action of the electric field. The strain is transmitted to the cantilever beam structure (1) of the single crystal SOI, causing the cantilever beam structure (1) to bend. The resistance values ​​of the varistors of each resistor in the Wheatstone full-bridge structure (2) change proportionally to the deformation. The differential voltage signal output by the Wheatstone full-bridge structure (2) is proportional to the change in the resistance value of the varistor. The electric field is converted into an electric signal and the electric field measurement is completed.

Images