CN113884701A

CN113884701A - Wind speed and direction sensor for improving measurement range and full-range precision

Info

Publication number: CN113884701A
Application number: CN202111142905.9A
Authority: CN
Inventors: 齐博; 秦明; 王振军; 易真翔; 黄庆安
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2021-09-28
Filing date: 2021-09-28
Publication date: 2022-01-04
Anticipated expiration: 2041-09-28
Also published as: CN113884701B; WO2023050908A1

Abstract

The invention provides a wind speed and direction sensor for improving the measurement range and the full-range precision. Then, double-sided silicon wafers are oxidized, silicon nitride is deposited to be used as passivation layer protection, and the back surfaces of the silicon wafers are windowed and corroded to form a back cavity and a silicon film. And finally, removing the silicon nitride protective layer, etching the lead hole, sputtering metal and stripping redundant parts to realize the metal lead and the electrode. According to the method, the heating element, the temperature measuring element and the silicon piezoresistor are simultaneously prepared on the silicon film, and the air deflector is additionally arranged above the chip to realize air pressure measurement, so that the defects of low heat distribution measurement range and low high air speed measurement sensitivity are overcome, and the measurement range and full-range precision of the sensor are effectively improved.

Description

Wind speed and direction sensor for improving measurement range and full-range precision

Technical Field

The invention relates to a two-dimensional wind speed and direction sensor with a thin film structure manufactured based on a micro-machining technology, in particular to a high-precision wide-range wind speed and direction sensor which combines wind pressure measurement and heat distribution measurement.

Background

With the rapid development of micro-electro-mechanical systems (MEMS) technology, wind speed and direction sensors are gradually developing toward miniaturization, integration and intelligence. The MEMS thermal type wind speed and direction sensor has no movable part, has the advantages of small volume, low power consumption and the like, gradually becomes the mainstream of the research of the wind sensor, and has high application value. The MEMS thermal type wind speed and direction sensor is generally composed of a heating element and a temperature measuring element and is limited by the working principle, and the output sensitivity of the sensor is gradually reduced along with the increase of the wind speed. Although increasing the heating power can improve the overall sensitivity of the sensor, due to the characteristics of the heating element material, the heating temperature cannot be increased without limit, and cannot play an effective role in the process of measuring the ultra-high wind speed. Therefore, how to improve the wind speed measurement accuracy and widen the range on the basis of keeping the advantages of the original thermal wind speed sensor is a key problem to be overcome urgently.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the problems, the invention provides a wind speed and direction sensor structure for improving the measurement range and the full-range precision. The characteristics that the heat distribution measurement principle is high in measurement sensitivity in a low wind environment and the wind pressure measurement principle is high in sensitivity in a high wind environment are utilized, and the heat distribution measurement and the wind pressure measurement are ingeniously combined in the same structure.

The technical scheme is as follows:

the sensor structure is manufactured on a silicon film and consists of a heating element, four temperature measuring elements which are centrosymmetrically distributed and four silicon piezoresistors which are centrosymmetrically distributed, the sensor realizes low wind speed measurement by measuring the surface heat distribution deviation of the silicon film in work, and the silicon piezoresistors measure the whole compression condition of the silicon film to realize high wind speed detection. In the chip packaging process, an air deflector is added above the silicon film, due to the special structure of the air deflector, incoming air in each horizontal direction is deflected downwards at a certain angle and blows towards the central surface of the silicon film, the larger the deflection angle is, the larger the longitudinal and transverse stresses borne by the silicon piezoresistor on the surface of the silicon film are, and the higher the sensitivity of wind pressure measurement is. However, the range and sensitivity of the heat distribution measurement can be reduced while the deflection angle is increased, and the selection of the proper deflection angle is crucial to ensure the sensitivity of the two measurement schemes.

In a low wind speed range, the heat distribution measurement is used for indirectly representing a wind speed and wind direction value mainly by monitoring the temperature distribution condition of the surface of the chip. The heating element in the center of the chip generates joule heat after supplying power, so that the surface temperature of the chip is higher than the ambient temperature, the thermal field on the surface of the sensor chip is uniformly distributed by the symmetrical structure of the sensor chip in a windless state, the temperature of the temperature measuring elements in four directions is the same, and the temperature difference is zero. When wind blows on the front surface of the chip film, the distribution of the thermal field changes along with the wind speed and the wind direction, and the larger the wind speed is, the larger the offset of the thermal field relative to the center of the chip is. The temperature difference in the horizontal direction and the vertical direction is respectively detected by two pairs of temperature measuring elements which are mutually orthogonally distributed, and the two groups of temperature difference signals are subjected to vector synthesis to be used for representing wind speed and direction information.

In a high wind speed range, wind pressure measurement is used for indirectly representing a wind speed and wind direction value mainly by monitoring the edge pressure condition of a silicon film. The wind pressure formula under the standard state is

Wherein W₀Dynamic pressure and wind speed. According to the formula, the wind pressure is proportional to the square of the wind speed, namely the larger the wind speed is, the higher the sensitivity of representing the wind speed by measuring the pressure difference between two sides of the silicon film is.

The stress is greatest at the midpoint of the silicon film edge, and the greatest measurement sensitivity is obtained by fabricating the silicon piezoresistors at these locations. And under the windless state, the front pressure of the film is zero. When wind blows, the wind deflector above the chip enables the wind direction to deflect at a certain angle in the vertical direction, so that the film is deformed, the two groups of silicon piezoresistors are subjected to horizontal stress and vertical stress respectively to generate resistance value change, and the stress difference of the two pairs of silicon piezoresistors can be used for representing the wind speed change condition.

In order to realize the wind sensing structure design of the wind speed and direction sensor combining the heat distribution measurement and the differential pressure measurement, the following steps are required to be completed. Firstly, the sensor chip is injected in the center of the circular heat insulation ring to ensure good heat insulation, and is bonded on the plastic base. And finally, a fairing comprising an arc-shaped air deflector and a fairing column is additionally arranged above the sensor plastic package chip so as to realize the wind sensing structure design combining the wind pressure measurement and the heat distribution measurement.

Has the advantages that: 1) the method for measuring the thermal distribution indicates that the change rate of the heating power increases along with the increase of the wind speed when the wind speed is high, namely, the method for measuring the thermal distribution indicates that the method has lower energy efficiency ratio when the wind speed is high. The combination of the thermistor and the silicon piezoresistor obviously improves the measuring range of wind speed measurement by introducing differential pressure detection on the premise of ensuring the sensitivity of wind direction measurement; 2) it can be seen from the square of the wind speed that the pressure difference across the silicon thin film is proportional to the wind speed, and the greater the wind speed, the higher the sensitivity. The sensitivity of the thermal field for detecting the characteristic wind speed at low wind speed is high, the sensitivity of the wind pressure for measuring the characteristic wind speed at high wind speed is high, and the two are complementary to each other, so that the high-sensitivity wind speed and wind direction sensor structure is obtained. 3) Wind flows through the wind deflector to deflect at a certain angle in the vertical direction to act on the silicon film, and the pressure difference between the two sides of the silicon film is changed. The larger the deflection angle, the larger the force acting on the silicon membrane, and the higher the sensitivity of the wind pressure measurement.

Drawings

FIG. 1 is a cross-sectional view of a sensor chip of the present invention;

FIG. 2 is a top view of a sensor chip of the present invention;

FIG. 3 is a cross-sectional view of the central axis location of the overall structure of the present invention;

fig. 1 and 2 have the same reference numerals. Wherein the sensor chip 10: 11. a silicon substrate; 12. a substrate surface oxidation layer; 13. a metal electrode and a metal lead; 14. silicon piezoresistance; 15. a temperature measuring element; 16. a heating element; 17. a silicon thin film; 18. a sensor back cavity;

the labels in fig. 3 are: 10. a sensor chip; 20. an air deflector; 30. a rectifying grid; 40. a bottom cover is arranged; 50. an insulating ring.

Detailed Description

The technical solution of the present invention is described below with reference to the accompanying drawings and examples.

As shown in FIG. 1 and FIG. 2, the chip 10 of the anemorumor and wind direction sensor for improving the measurement range and the full-scale accuracy of the invention is composed of a silicon substrate 11, a substrate surface oxide layer 12, a metal electrode and metal lead 13, a silicon piezoresistor 14, a temperature measuring element 15, a heating element 16, a silicon film 17 and a sensor back cavity 18.

The heating element 16 is positioned in the center of the silicon film 17, the four temperature measuring elements 15 are arranged on the silicon film 17 and are distributed around the heating element 16 in a central symmetry manner, and the four silicon piezoresistors 14 are arranged at the edge of the silicon film 17 and are also distributed around the heating element 16 in a central symmetry manner. When no wind exists, the heating element 16 forms a centrosymmetric temperature field, and the positions of the four temperature measuring elements 15 have the same temperature, so that the output temperature difference signal is zero; the pressure difference between the two sides of the silicon film is zero, and the longitudinal stress and the transverse stress borne by the four silicon piezoresistors are zero, so that the output of the wind pressure signal is zero.

When wind blows, heat is brought to the downstream by the wind from the upstream, the temperature of the corresponding positions of the four temperature measuring elements 15 which are symmetrically distributed in the center changes, the temperature difference on the surface of the sensor can be orthogonally decomposed into temperature differences in the east-west direction and the south-north direction by the two groups of temperature measuring elements 15 which are orthogonal to each other, and wind speed and wind direction information can be obtained through vector synthesis; the airflow is deflected by a certain angle through the air deflector 20 and then acts on the silicon film 17, the two groups of silicon piezoresistors 14 which are orthogonal to each other are respectively subjected to longitudinal stress and transverse stress, the stress is increased along with the increase of the wind speed, and the magnitude of the pressure difference at the two sides of the silicon film 17 can reflect the wind speed information.

A wind speed and wind direction sensor for improving measurement range and full-range precision is manufactured by the following steps:

(1) and preparing sensitive elements such as a heating element 16, a temperature measuring element 15, a silicon piezoresistor 14 and the like by ion implantation.

(2) And oxidizing the silicon wafer on the double surfaces, depositing silicon nitride through LPCVD to protect the passivation layer, and etching and windowing the back surface of the silicon wafer by taking the photoresist as a mask.

(3) And etching the wafer by a wet method to form a back cavity and a silicon film 17, and removing the silicon nitride protective layer.

(4) And etching the lead holes by taking the photoresist as a mask.

(5) Metal is sputtered and excess metal is stripped to realize the metal lead and electrode 13.

The above is the basic manufacturing process of the wind speed and direction sensor.

Claims

1. The utility model provides an improve wind speed and direction sensor of measuring range and full-scale range precision which characterized in that: the sensor chip (10) comprises a silicon film (17) and a sensor back cavity (18), wherein the silicon film (17) is provided with a central heating element (16), four centrosymmetric temperature measuring elements (15), four centrosymmetric silicon piezoresistors (14), an air deflector (20), a rectifying grid (30), a lower bottom cover (40) and a heat insulation ring (50).

2. The wind speed and direction sensor for improving the measurement range and the full-scale accuracy of claim 1, wherein: the shape of the silicon thin film (17) is arbitrary centrosymmetric.

3. The wind speed and direction sensor for improving the measurement range and the full-scale accuracy of claim 1, wherein: the shape of the air deflector (20) is a centrosymmetric shape which can deflect the wind direction to the front silicon film (17).

4. The wind speed and direction sensor for improving the measurement range and the full-scale accuracy of claim 1, wherein: the rectifying grid (30) is cylindrical or mesh in shape.

5. The wind speed and direction sensor for improving the measurement range and the full-scale accuracy of claim 1, wherein: the insulating ring (50) is composed of any low thermal conductivity material.