CN103398806B - Chip of 6H-SiC high-temperature pressure sensor - Google Patents

Abstract

The invention discloses a chip of a 6H-SiC high-temperature pressure sensor, which belongs to the technical field of sensor chips. The chip comprises four sensitive piezoresistors and a sensitive membrane, which jointly form a bridge circuit, wherein the sensitive membrane is a sensitive round membrane which has the advantages of uniform stress distribution and low stress concentration. Specific to the isotropy of the piezoresistive coefficient of the 6H-SiC material and the characteristic of different trends of radial and tangential stress coefficients changing along with temperature change, two of the four piezoresistors are distributed in the center of the sensitive round membrane, the other two piezoresistors are distributed symmetrically on the edges of the sensitive round membrane relative to the sensitive piezoresistors in the center, the four piezoresistors are distributed along a radial direction, and the signal output of the chip is realized through the bridge circuit. According to the chip, the piezoresistive effect of a doped 6H-SiC material can be utilized to the maximum extent, and the sensitivity of the 6H-SiC high-temperature pressure sensing chip is increased.

Description

A chip of 6H-SiC high temperature pressure sensor

technical field

The invention relates to a chip structure of a MEMS sensor, in particular to a chip structure made of 6H-SiC material for high-temperature pressure measurement, and belongs to the technical field of sensor structure design.

Background technique

Compared with traditional silicon materials, SiC has more stable physical and chemical properties at high temperatures, and is a very promising semiconductor material for high temperature and harsh conditions. Some research results at home and abroad have shown that electronic devices made of SiC materials, especially 6H-SiC materials, can directly work in an environment of 600 °C without cooling. Among the existing high-temperature devices made of SiC materials, piezoresistive high-temperature pressure sensors have been extensively studied due to their simple structure and wide application range. In the process of designing the 6H-SiC high temperature pressure sensor chip, the structural design must be carried out according to the characteristics of the piezoresistive pressure sensor and the material properties of 6H-SiC itself, including the following points:

First, the need for a specific structure sensitive to changes in external pressure.

2. The sensitive piezoresistor should be arranged according to the isotropic characteristic of the 6H-SiC piezoresistive coefficient.

3. As the temperature increases, the gauge factor of 6H-SiC will change, and the trend of the gauge factor changing with temperature in the radial and tangential directions is different.

Only by designing the structure of the 6H-SiC high-temperature pressure sensor chip according to the above-mentioned points can the pressure-sensitive characteristics of the sensitive piezoresistor be utilized to the greatest extent, the sensitivity of the device can be improved, and the performance of the device in high-temperature environments can be guaranteed.

Contents of the invention

The purpose of the present invention is to propose a structure of a 6H-SiC high temperature pressure sensor chip, on the basis of ensuring the stable operation of the 6H-SiC pressure sensor at high temperature, to maximize the use of the pressure sensitive characteristics of the sensitive piezoresistor, and to improve the performance of the device at high temperature. lower sensitivity.

Technical scheme of the present invention is as follows:

A 6H-SiC high-temperature pressure sensor chip, the chip structure includes a sensitive circular film and four sensitive piezoresistors required to form a bridge circuit: the first long piezoresistor, the second long piezoresistor, the third long piezoresistor and The fourth long piezoresistor; the above four long piezoresistors are obtained by etching the doped 6H-SiC epitaxial layer, and the circuit formed by patterning after sputtering connects these four long piezoresistors to form a complete The bridge circuit is characterized in that: the first long piezoresistor and the second long piezoresistor are arranged at the center of the sensitive circular membrane, the two are parallel to each other, and are aligned on both sides in the radial direction; the third long piezoresistor and the second long piezoresistor The four long piezoresistors are radially arranged at the edge of the sensitive circular membrane, symmetrically arranged with respect to the first long piezoresistor and the second long piezoresistor, and are on the same straight line as the first long piezoresistor and the second long piezoresistor.

The above-mentioned 6H-SiC high-temperature pressure sensor chip is characterized in that: the third long piezoresistor is formed by connecting the first short piezoresistor and the second short piezoresistor in series through metal strips, the two are equal in length, parallel to each other, and aligned on both sides; The four long piezoresistors are formed by connecting the third short piezoresistor and the fourth short piezoresistor in series through the two metal strips, the two are equal in length, parallel to each other, and aligned on both sides.

The above 6H-SiC high temperature pressure sensor chip is characterized in that: the first short piezoresistor, the third short piezoresistor and the first long piezoresistor are on the same straight line; The piezoresistance is on the same straight line.

The present invention has the following advantages and outstanding effects: 1. The force distribution of the sensitive circular film is uniform and the stress concentration is less, so the upper limit of the work is higher; 2. Since the piezoresistive coefficient of 6H-SiC is isotropic, it is arranged in the The sensitive piezoresistance at the center and edge of the membrane can obtain the maximum piezoresistive effect, and at the same time, the direction of stress on the center of the sensitive circular membrane is opposite to that at the edge. The above structure can ensure the differential output of the bridge circuit, further improving the performance of 6H-SiC Sensitivity of the high temperature pressure sensor chip; 3. The tangential gauge coefficient of the 6H-SiC wafer in the high temperature environment decreases faster than the radial one, so the sensitive piezoresistor arranged in the radial direction is conducive to improving the sensitivity of the chip working at high temperature, and also The stability of the 6H-SiC pressure sensor at high temperature is guaranteed.

Description of drawings

Fig. 1 is a schematic diagram of the chip structure principle of the 6H-SiC high temperature pressure sensor provided by the present invention.

Fig. 2 is a schematic diagram of a long piezoresistive structure arranged at the edge of a circular membrane.

Fig. 3 is a schematic diagram of a long piezoresistive structure arranged at the center of a circular membrane.

In the figure: 1-the first long piezoresistive; 2-the second long piezoresistive; 3-the first metal bar; 4-the first short piezoresistive; 5-the second short piezoresistive; 6-the second metal bar; 7-the first Three short piezoresistive; 8-fourth short piezoresistive; 9-sensitive circular membrane; 10-third long piezoresistive; 11-fourth long piezoresistive.

Detailed ways

The structure, principle and working process of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a schematic diagram of the chip structure principle of a 6H-SiC high-temperature pressure sensor provided by the present invention, including a sensitive circular membrane and four sensitive piezoresistors required to form a complete bridge circuit: the sensitive circular membrane structure is evenly distributed in force, and the stress The concentration is less, so the upper limit of work is higher; the first long piezoresistor 1 and the second long piezoresistor 2 are arranged in the center of the sensitive circular membrane, and they are parallel to each other and aligned on both sides in the radial direction; the third long piezoresistor 10 and The fourth long piezoresistor 11 is radially arranged at the edge of the sensitive circular membrane, and is arranged symmetrically with respect to the first long piezoresistor 1 and the second long piezoresistor 2, and is connected to the first long piezoresistor 1 and the second long piezoresistor 2 on the same line. Since the piezoresistive coefficient of 6H-SiC is isotropic, the center and edge of the sensitive circular film are the regions with the largest piezoresistive effect, and the above-mentioned chip structure can obtain the maximum sensitivity. At the same time, the tangential strain coefficient of the 6H-SiC wafer drops faster than the radial one in a high temperature environment, so the arrangement of four sensitive piezoresistors along the radial direction can ensure that there is still a large piezoresistive effect at a very high working temperature. Then the sensitivity of the 6H-SiC pressure sensor chip working at high temperature is improved.

Fig. 2 is a schematic diagram of a long piezoresistive structure in which a 6H-SiC high temperature pressure sensor chip is arranged at the edge of a circular membrane provided by the present invention, the first short piezoresistor 4 and the second short piezoresistor 5 are connected in series through a metal strip 3, so that The final formed first long piezoresistor 10 is as close as possible to the edge of the sensitive circular membrane, while the first short piezoresistor 4 and the second short piezoresistor 5 are arranged radially along the circular membrane, which also improves the temperature of the 6H-SiC pressure sensor chip at high temperature. Lower working sensitivity.

Fig. 3 is a schematic diagram of the long piezoresistive structure of a 6H-SiC high temperature pressure sensor chip provided by the present invention at the center of the circular membrane, in which the first long piezoresistor 1 and the second long piezoresistor 2 are arranged at the center of the sensitive circular membrane , both parallel to each other and aligned along the radial direction.

Claims (3)

1. A 6H-SiC high-temperature pressure sensor chip, the chip structure includes a sensitive circular film (9) and four sensitive piezoresistors required to form a bridge circuit: the first long piezoresistor (1), the second long piezoresistor (2), the third long piezoresistor (10) and the fourth long piezoresistor (11); the above four long piezoresistors are obtained by etching the doped 6H-SiC epitaxial layer, after sputtering The patterned circuit connects these four long piezoresistors to form a complete bridge circuit, which is characterized in that: the first long piezoresistor (1) and the second long piezoresistor (2) are arranged in the sensitive circle At the center of the membrane (9), the two are parallel to each other and aligned on both sides in the radial direction; the third long piezoresistor (10) and the fourth long piezoresistor (11) are arranged radially at the edge of the sensitive circular membrane (9), And arranged symmetrically with respect to the first long piezoresistor (1) and the second long piezoresistor (2), and on the same straight line as the first long piezoresistor (1) and the second long piezoresistor (2). 2. The chip of 6H-SiC high-temperature pressure sensor according to claim 1, characterized in that: the third long piezoresistor (10) is passed by the first short piezoresistor (4) and the second short piezoresistor (5) Metal strip one (3) is formed in series, the two lengths are equal, parallel to each other, and the two sides are aligned; the fourth long piezoresistor (11) is formed by the third short piezoresistor (7) and the fourth short piezoresistor (8) through the metal strip Two (6) are formed in series, both of equal length, parallel to each other and aligned on both sides. 3. The 6H-SiC high temperature pressure sensor chip according to claim 2, characterized in that: the first short piezoresistor (4), the third short piezoresistor (7) and the first long piezoresistor (1) are in the same on a straight line; the second short piezoresistor (5), the fourth short piezoresistor (8) and the second long piezoresistor (2) are on the same straight line.