Resonator structure of pressure sensor and pressure sensitive chip and modulation method thereof

Abstract

The invention provides a resonator structure of a pressure sensor and a pressure sensitive chip and a modulation method thereof, the resonator structure comprises a piezoelectric substrate, an electrode and a SiO2 covering layer, the electrode is arranged on the piezoelectric substrate, and the SiO2 covering layer covers the electrode and the whole surface of the piezoelectric substrate. The temperature characteristic of the whole resonator is modulated by adjusting the thickness of the SiO2 covering layer. The thickness of the SiO2 covering layer is increased, so that the temperature characteristic curve moves in the direction that the frequency is increased along with the temperature, the optimal thickness of the covering layer is determined by combining simulation calculation with experimental measurement, the frequency deviation caused by the temperature is reduced to the minimum within the target temperature range, and the temperature compensation effect of the differential structure is enhanced. According to the invention, the electrodes are deposited on the wafer to form the resonator structure, then the SiO2 covering layer with the positive temperature coefficient is deposited on the resonator, and the temperature sensitivity of the resonator is modulated by adjusting the thickness of the covering layer, so that the temperature compensation effect is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure sensors, and in particular to a resonator structure of a pressure sensor and a pressure sensitive chip and a modulation method thereof, and in particular to a temperature characteristic modulation method of a high temperature resistant wireless passive pressure sensor based on a silicon dioxide cover layer. Background Art

[0002] The surface acoustic wave pressure chip analyzes the pressure through the different resonance frequencies of the chip under different pressures. However, its resonance frequency is also affected by temperature, and the effect of temperature on the resonance frequency is greater than that of pressure. Therefore, temperature compensation is necessary to accurately analyze the pressure value.

[0003] The temperature compensation methods and effects of existing surface acoustic wave wireless passive pressure sensors are as follows:

[0004] 1. Use a differential structure, place two resonators with the same temperature characteristics in different pressure areas for differential calculation, and cancel out the influence of temperature, thereby achieving temperature compensation. The key to designing a differential structure to offset the influence of temperature is to make the temperature-frequency characteristics of the two resonators completely consistent, and the temperature fields they are in are completely consistent. This is theoretically feasible, but it is difficult in engineering. Due to problems in processing technology and other aspects, the processed resonators are bound to be different, which in turn leads to deviations in the results after differential cancellation.

[0005] 2. Use a temperature sensor to first measure the ambient temperature, then bring it into the known temperature characteristic curve of the pressure sensor, eliminate the temperature effect, and then solve the pressure value. 2. When using crystalline materials such as lanthanum gallium silicate as the piezoelectric substrate, its temperature frequency coefficient usually increases with increasing temperature in the high temperature range (greater than 350°C), and the temperature frequency coefficient is much larger than the pressure frequency coefficient, and the frequency change caused by temperature fluctuations is much larger than the frequency deviation caused by pressure changes. Therefore, the method of first measuring the temperature value and then bringing it into the pressure sensor to eliminate the temperature effect requires extremely high accuracy in temperature detection. At the same time, due to the uneven distribution of the temperature field, it will significantly affect the effect of temperature compensation.

[0006] 3. By rotating the Euler angles of the piezoelectric crystal material, we can find a cut with a temperature coefficient as small as possible or even zero within the target operating temperature range, so that the pressure detection value is affected as little as possible by temperature. For example, when the temperature range of lanthanum gallium silicate crystal exceeds 350°C, no matter how the three Euler angles are rotated, we can no longer find a cut with a zero temperature coefficient. Summary of the invention

[0007] In view of the defects in the prior art, the present invention aims to provide a resonator structure of a pressure sensor and a pressure sensitive chip and a modulation method thereof.

[0008] A resonator structure of a pressure-sensitive chip provided by the present invention comprises a piezoelectric substrate, an electrode and a SiO2 covering layer, wherein the electrode is arranged on the piezoelectric substrate, and the SiO2 covering layer covers the electrode and the entire surface of the piezoelectric substrate;

[0009] By adjusting the thickness of the SiO2 capping layer, the temperature characteristics of the entire resonator are modulated.

[0010] Preferably, the SiO2 capping layer has a positive temperature coefficient.

[0011] Preferably, the method of generating the SiO2 capping layer with a positive temperature coefficient comprises PECVD, PVD or LPCVD.

[0012] Preferably, the material of the piezoelectric substrate includes lanthanum gallium silicate crystal, and the material of the electrode includes platinum.

[0013] According to a modulation method of a resonator structure of a pressure sensitive chip provided by the present invention, the resonator structure of the pressure sensitive chip is adopted, and the temperature characteristic curve is moved in the direction where the frequency increases with increasing temperature by increasing the thickness of the SiO2 covering layer, and then as the thickness of the SiO2 covering layer increases, the performance of the temperature characteristic curve is enhanced.

[0014] A pressure sensor provided by the present invention adopts the resonator structure of the pressure sensitive chip, and also includes a pressure sensor cover, a pressure sensor base and a radio frequency antenna;

[0015] The pressure sensor upper cover is connected to the pressure sensor base, the pressure sensitive chip is arranged between the pressure sensor upper cover and the pressure sensor base, the pressure sensitive chip and the pressure sensor upper cover form a high pressure cavity, and the pressure sensitive chip and the pressure sensor base form a sealed vacuum cavity;

[0016] And the pressure sensitive chip is electrically connected to the radio frequency antenna.

[0017] Preferably, the pressure sensor base is sleeved with a pressure sensor upper cover, and the pressure sensor base and the pressure sensor upper cover are threadedly connected.

[0018] Preferably, a sealing ring is provided between the pressure sensor upper cover and the pressure sensitive chip, and a sealing ring is provided between the pressure sensor base and the pressure sensitive chip.

[0019] Preferably, the sealing ring located on the side of the pressure sensitive chip close to the upper cover of the pressure sensor abuts against the upper cover of the pressure sensor;

[0020] The sealing ring located on the side of the pressure sensitive chip close to the pressure sensor base abuts against the pressure sensor base.

[0021] Preferably, the high-pressure chamber is in communication with the pressure to be measured, and the area of ​​the pressure-sensitive chip corresponding to the high-pressure chamber includes a pressure-sensitive area.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention utilizes photolithography, deposition, and stripping methods to deposit platinum electrodes on a lanthanum gallium silicate wafer to form a resonator structure, and then utilizes a PECVD method to deposit a SiO2 covering layer with a positive temperature coefficient on the resonator. The temperature sensitivity of the silicon dioxide layer is modulated by adjusting the thickness thereof, and the temperature coefficient is adjusted to be close to zero within a target operating temperature range, thereby improving the temperature compensation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0025] Figure 1 The figure is a schematic diagram of assembling a chip with a resonator structure into a pressure sensor according to the present invention.

[0026] Figure 2 It is a schematic diagram of the resonator structure on the pressure sensitive chip of the present invention.

[0027] Figure 3 Schematic diagram of the placement of two resonators to achieve temperature compensation using a differential structure.

[0028] Figure 4 3 is a graph showing the temperature characteristic modulation of a lanthanum gallium silicate surface acoustic wave resonator with an Euler angle of (0°, 0°, 30°) by a silicon dioxide layer with a thickness of 3% of the wavelength according to the present invention.

[0029] Figure 5 : This is a diagram showing the temperature characteristic modulation of a lanthanum gallium silicate surface acoustic wave resonator with an Euler angle of (0°, 0°, 30°) by a silicon dioxide layer with a thickness of 7% of the wavelength according to the present invention.

[0030] Figure numerals: 1. piezoelectric substrate; 2. electrode; 3. sealing ring; 4. pressure sensor base; 5. sealed vacuum chamber; 6. high-pressure chamber; 7. pressure sensor cover; 8. pressure sensor sensitive chip; 9. radio frequency antenna; 10. covering layer. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0032] According to a resonator structure of a pressure sensitive chip provided by the present invention, Figure 2 As shown, it includes a piezoelectric substrate, an electrode and a SiO2 covering layer, wherein the electrode is arranged on the piezoelectric substrate, and the SiO2 covering layer covers the electrode and the entire surface of the piezoelectric substrate. By adjusting the thickness of the SiO2 covering layer, the temperature characteristics of the entire resonator are modulated. The SiO2 covering layer has a positive temperature coefficient. The method of generating the SiO2 covering layer with a positive temperature coefficient includes PECVD, PVD or LPCVD. The material of the piezoelectric substrate includes lanthanum gallium silicate crystal, and the material of the electrode includes platinum. Specifically, a platinum electrode is deposited on the lanthanum gallium silicate wafer by photolithography, deposition, and stripping methods to form a resonator structure, and then a SiO2 covering layer with a positive temperature coefficient is deposited on the resonator by PECVD. After completion, a CMP process is used to flatten and adjust the thickness of the SiO2 layer to modulate the temperature characteristics of the entire resonator.

[0033] According to a pressure sensor provided by the present invention, the resonator structure of the pressure sensitive chip is adopted, and further includes a pressure sensor cover, a pressure sensor base and a radio frequency antenna. The pressure sensor cover is connected to the pressure sensor base, the pressure sensitive chip is arranged between the pressure sensor cover and the pressure sensor base, the pressure sensitive chip and the pressure sensor cover form a high pressure chamber, and the pressure sensitive chip and the pressure sensor base form a sealed vacuum chamber. And the pressure sensitive chip is electrically connected to the radio frequency antenna. The pressure sensor base is sleeved with the pressure sensor cover, and the pressure sensor base and the pressure sensor cover are threadedly connected. A sealing ring is arranged between the pressure sensor cover and the pressure sensitive chip, and a sealing ring is arranged between the pressure sensor base and the pressure sensitive chip. The sealing ring located on the side of the pressure sensitive chip close to the pressure sensor cover abuts against the pressure sensor cover. The sealing ring located on the side of the pressure sensitive chip close to the pressure sensor base abuts against the pressure sensor base. The high pressure chamber is connected to the measured pressure, and the area corresponding to the pressure sensitive chip and the high pressure chamber includes a pressure sensitive area.

[0034] like Figure 1 As shown, the chip with the resonator structure is not limited to Figure 1The pressure sensor is assembled in the form of a pressure sensor. The pressure sensor cover 7 is fastened to the pressure sensor base 4 by threads. The pressure sensor cover 7 and the pressure sensor base 4 are respectively sealed and fastened by a sealing ring 3, and a sealed vacuum chamber 5 and a high-pressure chamber 6 connected to the measured pressure are further formed on the upper and lower sides of the pressure sensitive chip 8. The pressure sensing chip 8 is electrically connected to the radio frequency antenna. Pressure sensing detection is performed by using the relationship between the resonant frequency of the resonator on the pressure sensitive chip 8 and the pressure applied in the high-pressure chamber 6.

[0035] According to a modulation method of a resonator structure of a pressure-sensitive chip provided by the present invention, the resonator structure of the pressure-sensitive chip is adopted, and the temperature characteristic curve is moved in the direction of increasing frequency with increasing temperature by increasing the thickness of the SiO2 covering layer, and then the optimal covering layer thickness is determined by simulation calculation combined with experimental measurement, so as to reduce the frequency deviation caused by temperature to a minimum within the target temperature range, thereby enhancing the temperature compensation effect of the differential structure. Specifically, the temperature characteristic curve is related to many factors, including the cut type of the lanthanum gallium silicate piezoelectric substrate, the electrode material, the thickness of the electrode material, and the thickness of the SiO2 covering layer. Qualitatively speaking, the SiO2 covering layer has a positive temperature coefficient, that is, the addition of a silicon dioxide layer will cause the original temperature characteristic curve to move in the direction of increasing frequency with increasing temperature, and this trend will increase with the increase of the thickness of the silicon dioxide layer.

[0036] The current method of obtaining the optimal SiO2 coating thickness includes using a finite element simulation model to perform complex load field theory calculations to obtain the modulation effect of SiO2 coatings of different thicknesses on the temperature characteristic curve. Depending on the thickness of the SiO2 coating deposition, the temperature characteristic curve of lanthanum gallium silicate can be adjusted to close to zero within the target operating range, thereby improving the temperature compensation effect of the pressure sensor. When affected by the combined effects of temperature and pressure, the relationship between the resonant frequency of the resonator and the temperature and pressure can be described as:

[0037] f-f0=S (压力) (P-P0)+S (温度) (T-T0)+Δ (T,P-T0,P0) (1)

[0038] Where f and f0 are the resonant frequencies of the resonator when the pressure and temperature are P, T and P0, T0 respectively. Δ(T, P-T0, P0) is the high-order small quantity generated by the combined effect of pressure and temperature. The principle of using differential structure to achieve temperature compensation is to place two resonators in a Figure 3 At the position shown, when subjected to the high pressure in the pressure chamber, the pressure sensitivity S of the two resonators is (压力) Not consistent, but S (温度)The sensitivity is consistent. After the resonant frequencies of the two resonators are differentially calculated, the frequency offset S caused by temperature can be eliminated. (温度) (T-T0) and the high-order small quantity Δ(T,P-T0,P0) of the composite action. After differential operation, formula (1) becomes

[0039] Δf-Δf0=ΔS (压力) (P-P0) (2)

[0040] Where Δf and Δf0 are the difference in the resonant frequencies of the two resonators when the pressure and temperature are P, T and P0, T0 respectively. ΔS (压力) is the difference in pressure sensitivity between the two resonators.

[0041] However, due to the inconsistency of the processing technology, the temperature sensitivity S of the two resonators is (温度) It is impossible to achieve consistency, and when the temperature sensitivity S (温度) The larger the value, the greater the deviation between the two. For high-temperature piezoelectric materials such as lanthanum gallium silicate, the temperature characteristics will not have a zero temperature coefficient after exceeding 350°C, no matter how the Euler angle is changed, and the temperature sensitivity S will continue to rise. (温度) The larger the value, the present invention adopts PECVD to deposit a silicon dioxide layer having a positive temperature coefficient, such as Figure 2 As shown, by adjusting the thickness of the silicon dioxide layer, the temperature sensitivity S (温度) By adjusting the temperature coefficient to close to zero within the target operating temperature range, the temperature compensation effect can be improved.

[0042] like Figure 4 and Figure 5 The figure shows the surface acoustic wave transducer prepared using platinum electrodes with a thickness of 3% and 7% of the wavelength on a lanthanum gallium silicate substrate with an Euler angle of (0°, 0°, 30°), and the change curve of its temperature characteristics after depositing silicon dioxide layers of different thicknesses. Figure 4 and Figure 5 In FIG. 8 , the abscissa represents the temperature, and the ordinate represents the thickness of the silicon dioxide layer.

[0043] Taking the electrode thickness of 7%λ on the (0°, 0°, 30°) cut as an example, a silicon oxide cover layer with a thickness of 15%λ can achieve a total frequency deviation of only 86ppm within the range of 550±50℃. For SAW devices without a silicon dioxide cover layer, the frequency deviation in this temperature range exceeds 5000ppm.

[0044] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", 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 application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0045] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A resonator structure of a pressure sensitive chip, characterized in that: It comprises a piezoelectric substrate, an electrode and a SiO2 covering layer, wherein the electrode is arranged on the piezoelectric substrate, and the SiO2 covering layer covers the electrode and the entire surface of the piezoelectric substrate; By adjusting the thickness of the SiO2 capping layer, the temperature characteristics of the entire resonator are modulated.

2. The resonator structure of a pressure sensitive chip according to claim 1, characterized in that: The SiO2 capping layer has a positive temperature coefficient.

3. The resonator structure of a pressure sensitive chip according to claim 1, characterized in that: Methods for producing the SiO2 capping layer with a positive temperature coefficient include PECVD, PVD or LPCVD.

4. The resonator structure of a pressure sensitive chip according to claim 1, characterized in that: The material of the piezoelectric substrate includes lanthanum gallium silicate crystal, and the material of the electrode includes platinum.

5. A method for modulating a resonator structure of a pressure sensitive chip, characterized in that: The resonator structure of the pressure sensitive chip described in claim 1 is adopted, and the temperature characteristic curve is moved in the direction where the frequency increases with increasing temperature by increasing the thickness of the SiO2 covering layer. The optimal covering layer thickness is determined by simulation calculation combined with experimental measurement, and the frequency deviation caused by temperature is reduced to a minimum within the target temperature range, thereby enhancing the temperature compensation effect of the differential structure.

6. A pressure sensor, characterized in that: The resonator structure of the pressure sensitive chip according to any one of claims 1 to 4 further comprises a pressure sensor cover, a pressure sensor base and a radio frequency antenna; The pressure sensor upper cover is connected to the pressure sensor base, the pressure sensitive chip is arranged between the pressure sensor upper cover and the pressure sensor base, the pressure sensitive chip and the pressure sensor upper cover form a high pressure cavity, and the pressure sensitive chip and the pressure sensor base form a sealed vacuum cavity; And the pressure sensitive chip is electrically connected to the radio frequency antenna.

7. The pressure sensor according to claim 6, characterized in that: The pressure sensor base is sleeved with a pressure sensor upper cover, and the pressure sensor base and the pressure sensor upper cover are threadedly connected.

8. The pressure sensor according to claim 6, characterized in that: A sealing ring is arranged between the pressure sensor upper cover and the pressure sensitive chip, and a sealing ring is arranged between the pressure sensor base and the pressure sensitive chip.

9. The pressure sensor according to claim 6, characterized in that: The sealing ring located on the side of the pressure sensitive chip close to the upper cover of the pressure sensor abuts against the upper cover of the pressure sensor; The sealing ring located on the side of the pressure sensitive chip close to the pressure sensor base abuts against the pressure sensor base.

10. The pressure sensor according to claim 6, characterized in that: The high-pressure chamber is in communication with the pressure to be measured, and the area of ​​the pressure-sensitive chip corresponding to the high-pressure chamber includes a pressure-sensitive area.

Images