JPS59114874A - Semiconductor pressure transducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor pressure transducers, and more particularly to semiconductor pressure transducers designed to compensate for signals generated when the pressure difference is zero. .

Conventional semiconductor pressure quadrature transducers employ a diaphragm that responds to a difference in pressure across two surfaces of the transducer. The diaphragm is formed of a single crystal semiconductor chip on one surface of which a stress sensor is arranged. Stress sensors widely used for this purpose exhibit piezoresistive properties. Since the stress generated within the chip changes depending on the differential pressure, the resistance value of the sensor is changed by the stress generated within the sensor. A circular cavity is formed on the other side of the chip to form a diaphragm, and one end of a cylindrical tube is joined to said other side to surround the cavity.

Typically, at least one pair of radial stress sensors and at least one pair of circumferential stress sensors are disposed on the surface of the chip.

Originally a circular tip with a circular diaphragm was employed so that the entire transducer was symmetrical about the tube, the cavity, and the common axis of the tip. However, recently, it has become common to use square chips because a plurality of square chips can be easily obtained by cutting the crystal way 1-.

However, such a semiconductor chip no longer exhibits symmetry about the axis of the cylindrical tube to which it is joined.

In these conventional cattle pressure quadrature transducers, the lack of axial symmetry and the different materials of the tube and tip result in static pressure (i.e., common pressure on both sides of the diaphragm) on the transducer. Changes in the pressure on the transducer or the temperature of the transducer will result in false or spurious signals, termed "zero shift". A signal that changes as a result of some action that occurs when the difference in pressure on both sides of the diaphragm is zero.Due to the zero shift phenomenon that occurs in conventional semiconductor pressure quadrature transducers, it is possible to measure the differential pressure with high accuracy. If required to be detected, the signal must be compensated electronically.

It is therefore an object of the present invention to provide an improved semiconductor pressure quadrature transducer.

Another object of the invention is to obtain a semiconductor pressure quadrature transducer with minimal zero shift percentage.

Another object of the invention is to obtain an innate body pressure quadrature transducer with very low spurious signals.

Yet another object of the invention is to provide a semiconductor pressure quadrature transducer that is capable of measuring pressure differences with greater accuracy than conventional ones.

According to the invention, a type of chip diaphragm having a square tip diaphragm with one edge of the tip forming a unique angle with respect to a given crystallographic axis of the tip or a particular sensor axis of a transducer is provided. By providing a semiconductor pressure quadrature transducer, the object is achieved.

According to one embodiment of the invention, one edge of the square chip is approximately 22.5
oriented at an angle of degrees. According to the invention, since the radial and circumferential stress changes induced in the diaphragm by temperature or static pressure changes are equal, the zero-shift signal caused by temperature or pressure changes is very be made smaller.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The semiconductor pressure quadrature transducer shown in FIG.
It has a thin square semiconductor chip 1.

This chip 1 is made of a single crystal semiconductor material such as silicon. Radial stress sensors 3, 4 are arranged on the first surface of the solid chip 1. A circumferential stress sensor 1, 8 is also arranged on the first surface thereof. These sensors 3, 4, 7.8 are integrated into the chip 1 by implanting impurities such as boron on the surface of the chip 1 in areas defined according to the desired shape of the sensor, for example by diffusion techniques. It is formed by becoming. The sensor exhibits piezoresistive properties, and the resistance of the sensor changes depending on the pressure applied to the sensor.

The circular cavity indicated by the dashed line in FIG.
formed on the surface of A cylindrical tube (not shown) is bonded to the second surface surrounding the cavity. The tube serves to transmit the pressure to be detected into the cavity. When pressure is transmitted to the cavity, the part of the chip 1 located above the cavity forms a diaphragm. The stress induced inside the diaphragm is related to the difference between the pressure carried by the tube and the pressure being applied to the first surface.

In FIG. 1, the sensor is shown as a strip.

However, in practice, certain sensors can be made in the form of a plurality of parallel strips connected in series. Traditionally, these sensors have been oriented to match the cylindrical coordinates of the cavity, or the cylindrical coordinates of the tube carrying the pressure. The sensors 3, 4 of FIG. 1 are therefore oriented with their longitudinal directions along the radial direction of the cylindrical coordinates. Senna 7. shown parallel to sensor 3.4.
8 is arranged so that its longitudinal direction is along the circumferential direction of the circular constrictor and is symmetrical about the radial direction of its cylindrical coordinates.

The stress induced inside the chip 1 is detected by a stress sensor. The resistance value of this sensor changes in response to the stress. Those stresses are generally described with respect to the axis of the sensor. A vector representing the direction of stress is shown in FIG. The amplitude of the stress represented by these vectors is denoted by the symbol σ, and its units are dynes per square centimeter. Therefore, the stress induced along the longitudinal direction of sensors 3,4 oriented in the radial direction is termed radial stress σr, and the stress in the direction perpendicular to the longitudinal direction of sensor 3.4 is termed circumferential stress. (sometimes referred to as tangential stress). Therefore, the stress caused along the longitudinal direction of the circumferential stress sensors 1, 8 is called the circumferential stress σ. The stress induced in the direction perpendicular to the direction is the radial stress σ.

It is called.

Four sensors 3, 4, 7.8 are constant current Wheatstone
The zero shift caused by the output signal produced when connected in a bridge configuration is given by:

e21/2i, Rπ44(σ1−σC) where l is the current supplied to the bridge and MRπ44 is a function that varies only with respect to the temperature of the transducer. It can be shown that in the case of a transducer that is completely axially symmetrical, no zero-shift signal will be generated even if the tip and tube are made of different materials. In that case, no bridge output is generated because the stress on the surface of the tip diaphragm is uniform and independent of direction. However, if the transducer tip is square rather than circular, and a cylindrical tube is joined, it will lack an axially symmetric structure.

The equation shown above shows that the difference in radial and circumferential pressure directly affects the zero shift signal. Furthermore, when such a pressure difference exists, temperature changes that affect (Rπ44) also contribute to the zero shift signal. However, the equation shown earlier is σ1 and σ. It is also shown that the zero shift signal can be minimized or even completely eliminated by making .

In conventional transducers, the sensor is oriented parallel or perpendicular to the edge of the chip, as shown in FIG. In general, when the sensor is placed in such an orientation, the stresses σ, and σ. are equal.

In order to solve such problems with conventional transducers, the present inventor conducted an experimental analysis to determine the stress σ and σ of a certain shape of transducer when the orientation of the sensor is changed. It was acknowledged that the difference in The results of this analysis are shown in FIG. 2 for various transducer models each having a silicon tip and a Pyrex tube. For each model analyzed, the difference between radial and circumferential stress was plotted when the radial and circumferential stress sensors were rotated about the edge of the square chip. For each model, the inner and outer diameters and lengths of the attached cylindrical tubes are listed near the curve of each model. The side length of the chip used was approximately 0.27 cm (approximately 0.10 finch). Three models used tips made of isotropic material and one type used tips made of rectangular material.

The inventors have observed that the radial and circumferential stresses are equal at an orientation angle of about 22.5 degrees for all model transducers analyzed. This orientation angle was the angle that the longitudinal axis of the sensor made with the straight edge of the chip. Also, this orientation angle is set to <110 of the chip.
> By matching the crystal orientation to the angle that it makes with the edge of the chip, the change in resistance of the sensor will be proportional to the difference between the radial and circumferential stresses.

An embodiment of the invention using the principle shown in FIG. 2 is shown in FIGS. 3 and 4. The semiconductor pressure quadrature transducer shown in FIGS. 3 and 4 has a square semiconductor chip 10 made from a single crystal of a semiconductor such as silicon. A pair of radial stress sensors 12, 13 are disposed through the center of the chip 10 along an axis forming an angle of approximately 22.5 degrees with respect to the pair of edges of the chip. A pair of circumferential stress sensors 16, 17 are disposed along another axis through the center of the chip 10 and at an angle of approximately 22.5 degrees with respect to the other two sides of the chip. The circumferential stress sensors are also parallel to the (110>crystalline direction of the chip. Each stress sensor makes an angle of 22.5 degrees with respect to one edge of the chip 10.

The sensors 12, 13, 16, 17 are manufactured by implanting an impurity, such as boron, into the surface of the chip 10 in areas defining the shape of their cells, by an implantation technique such as diffusion. It is made integrally with the chip 10. sensor 12,
13, 16, and 17 show piezoresistive characteristics. It is also within the scope of the invention that each sensor can be comprised of a plurality of parallel strips of piezoresistive material connected in series. The longitudinal direction of the strips is oriented parallel to the direction of the senna shown in FIG.

The circular cavity 21 shown in FIG. 4 is formed on the surface of the chip 1v opposite to the surface on which the stress sensors 12, 13, 16, 17 are arranged. A cylindrical tube 23, shown partially in cross section, is joined to said opposite surface of the chip 10.

The tube may be made of, for example, Pyrex and is bonded onto the surface of tube 10. Although tube 23 is shown surrounding cavity 21,
It is also within the scope of the present invention to make the inner diameter of the tube 23 larger or smaller than the diameter of the cavity 21.

Accordingly, the embodiment of the invention shown in FIGS. 3 and M4 has a radial sensor 12.13 and a circumferential sensor 16,1.
7, thereby substantially eliminating zero shifts due to changes in static pressure and changes in temperature of the transducer. For many practical applications of the invention, the effect of zero shift is effectively minimized for orientation angles θ selected in the range 15-30.

[Brief explanation of drawings]

Figure M1 is a schematic diagram of a conventional transducer, and Figure 2 shows the difference between radial stress and circumferential stress for various models of semiconductor pressure quadrature transducers composed of square chips, and the pressure applied to the chip. A curve drawn as a function of the angle between the orientation of the senna and the edge of the chip when the difference between It is a cross-sectional view along the -■ line. 1...chip, j, 4, 12, 13...
Radial direction sensor, 7, 8, 16. 17... Circumferential direction sensor, 21... Cavity, 23... Tube. Patent Applicant Honeywell Incorporated Territory Agent Kazuka Yamakawa (and 1 other person) 1'tG, 1 Etc, 3 F'tc;, 4

Claims (4)

[Claims] (1) a single crystal semiconductor chip having at least one straight edge; a pair of radial stress sensors disposed on one surface of the chip and having piezoresistive properties; and a pair of radial stress sensors having piezoresistive properties; a pair of circumferential stress sensors having piezoresistive properties disposed on top of the chip, wherein at least the linear edge of the chip has an I-t of 225 with respect to the (110) crystal direction of the chip; 2. A semiconductor pressure quadrature transducer oriented at an angle of 100 degrees, the sensor pair being oriented along the <110> crystal direction. (2) a single crystal semiconductor chip whose edges form a parallelogram', a pair of radial stress sensors arranged on one surface of this chip and having piezoresistive properties; a pair of circumferential stress sensors disposed on one surface and having piezoresistive characteristics, one of the sensor pairs being oriented parallel to the crystal direction of the chip; A semiconductor pressure quadrature transducer characterized in that one edge of said chip is oriented at an angle of approximately 22.5 degrees with respect to said <110> crystal direction. (3) one semiconductor chip having at least one linear edge and a circular cavity formed on one surface; a first semiconductor chip disposed on the other surface of the chip and having piezoresistive properties; and a second pair of sensors, wherein the first pair of sensors detects stress mainly along a first polar coordinate direction with respect to the cavity within the chip, and the second pair of sensors detects stress mainly along a first polar coordinate direction within the chip. a semiconductor pressure quadrature transducer for detecting stress along a second polar coordinate direction as the axis relative to the cavity, the second direction being perpendicular to the first direction; The direction is approximately 22.5 to said edge.
A semiconductor pressure quadrature transducer characterized by defining an axis forming an angle of degrees. (4) comprising one semiconductor chip on which at least one straight edge is formed and on one surface of which at least one sensor is arranged, said sensor having piezoresistive properties, so that said The resistance value of the sensor changes depending on the difference in mutually perpendicular stresses induced in the chips, and when the difference in pressure between the chips is zero, the difference between the mutually perpendicular stresses A semiconductor pressure quadrature transducer, characterized in that the sensor is disposed on the surface such that is zero.