JPH0465553B2 - - Google Patents

Description

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

Conventional semiconductor pressure 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 due to 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 chip with a circular diaphragm was employed so that the entire transducer was symmetrical about a common axis of the tube and cavity and the chip. However, recently, it has become common to use square chips because a plurality of square chips can be easily obtained by cutting a crystal wafer.
However, such a semiconductor chip no longer exhibits symmetry about the axis of the cylindrical tube to which it is joined.

In such conventional semiconductor pressure transducers, the lack of axial symmetry and the different materials of the tube and chip limit the static pressure (i.e., the static pressure applied commonly to both sides of the diaphragm) on the transducer. Due to changes in the pressure (pressure) or the temperature of the transducer, false or spurious signals, termed "zero cysts", will occur. In particular, a "zero shift" signal refers to a signal that changes as a result of some action that occurs when the pressure difference across the transducer diaphragm is zero. Because of this zero cyst phenomenon that occurs in conventional semiconductor pressure transducers, it is necessary to electronically compensate the signal when differential pressures are required to be detected with high accuracy.

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

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

Another object of the invention is to obtain a semiconductor pressure transducer with very low spurious signals.

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

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

According to one embodiment of the invention, one of the square chips
The two edges are oriented at approximately a 22.5 degree angle to the <110> crystal axis of the chip. According to the invention, since the radial and circumferential stress changes induced in the diaphragm by temperature changes or static pressure changes are equal, the zero shift signal caused by temperature or pressure changes is very small. be done.

Hereinafter, the present invention will be explained in detail with reference to the drawings. The semiconductor pressure transducer shown in FIG. 1 has a thin square semiconductor chip 1. The semiconductor pressure transducer shown in FIG. This chip 1 is made of a single crystal semiconductor material such as silicon. On the first surface of this chip 1 radial stress sensors 3, 4 are arranged. On its first surface there are circumferential stress sensors 7, 8.
will also be placed. These sensors 3, 4, 7, 8 are manufactured by implanting impurities such as boron into the chip 1 by implanting, for example by diffusion techniques, an impurity on the surface of the chip 1 in a region defined according to the desired shape of the sensor. It is formed integrally with. The sensor exhibits piezoresistive properties, and the resistance of the sensor changes depending on the pressure applied to the sensor.

A circular cavity, shown in broken lines in FIG. 1, is formed in the second surface of the chip 1. A cylindrical tube (not shown) is bonded to the second surface surrounding the cavity. The tube functions 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 imparted 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 pressure-carrying tube. The sensors 3, 4 of FIG. 1 are therefore oriented with their longitudinal directions along the radial direction of the cylindrical coordinates. Sensors 7, 8, which are shown parallel to sensors 3, 4, are arranged with their longitudinal directions along the circumferential direction of the cylindrical coordinates and symmetrically about the radial direction of the cylindrical coordinates. be done.

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 the sensors 3, 4 oriented in the radial direction is termed radial stress σ _r , and the stress in the direction perpendicular to the longitudinal direction of the sensors 3, 4 is termed circular. The circumferential stress (sometimes also called tangential stress) is named σ _c . Therefore, the stress induced along the longitudinal direction of the circumferential stress sensors 7, 8 is called circumferential stress σ _c , and the stress induced in the direction perpendicular to the longitudinal direction of the sensors 7, 8 is called circumferential stress σ c. The stress caused by this is called the radial stress σ _r .

The zero shift caused by the output signal generated when the four sensors 3, 4, 7, 8 are connected in a constant current Wheatstone bridge is given by the following equation.

e=1/2i _B Rπ ₄₄ (σ _r −σ _c ) where i is the current supplied to the bridge and the product Rπ ₄₄ is a function that varies only with respect to the temperature of the transducer. It can be shown that in the case of a completely axially symmetrical transducer, no zero shift signal is generated even if the tip and tube are made of different materials. In that case, the stress generated on the surface of the chip diaphragm is uniform and is not related to the direction, so
No bridge output is generated. However, if the transducer chip is square rather than circular and has a cylindrical tube attached, 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 (Rπ ₄₄ ) also contribute to the zero-shift signal. However, the equations presented above also show that the zero shift signal can be minimized or completely eliminated by making σ _r and σ _c equal.

In conventional transducers, the sensor is
Oriented parallel or perpendicular to the edge of the chip as shown. Generally, when the sensor is placed in such an orientation, the stresses σ _r and σ _c become equal.

In order to solve such problems with conventional transducers, the present inventor conducted an experimental analysis to determine the stress σ _r and σ _c of a transducer of a certain shape when the sensor orientation 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 chip and a Pyrex tube. For each model analyzed, the difference between the radial stress and the 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 chips used was approximately 0.27 cm (0.107 inch). Three types of models used chips made of isotropic materials and one type used chips made of orthotropic materials.

The inventors observed that the radial and circumferential stresses were equal at an orientation angle of approximately 22.5 degrees for the transducers of all models analyzed. This orientation angle was the angle that the longitudinal axis of the sensor made with the straight edge of the chip. Also, by matching this orientation angle to the angle that the <110> crystal orientation of the chip makes with the edge of the chip, the change in the resistance value of the sensor is proportional to the difference between the radial stress and the circumferential stress. I will do it.

An embodiment of the invention using the principle shown in FIG. 2 is shown in FIGS. 3 and 4. The semiconductor pressure transducer shown in FIGS. 3 and 4 includes a square semiconductor chip 10 made from a single crystal of a semiconductor such as silicon. A pair of radial sensors 12, 13 are arranged along an axis passing through the center of the chip 10 at an angle of 22.5 degrees with respect to the two parallel edges of the chip 10. A pair of circumferential sensors 16, 17 are located along another axis that is at an angle of 22.5 degrees to the remaining edges of the chip 10 and passes through the center of the chip 10. This other axis is parallel to the <110> crystal direction of the chip 10. Each stress sensor is one of ten chips.
It forms an angle of 22.5 degrees with the two edges. sensor 1
2, 13, 16, and 17 are integrated with the chip 10 by implanting an impurity, such as boron, into the surface of the chip 10 in the areas that define the shape of the sensors, by an implantation technique such as diffusion. Made. Sensors 12, 13, 16, 17 exhibit 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 sensor shown in FIG.

The circular cavity 21 shown in FIG.
0 on the surface opposite to the surface on which the stress sensors 12, 13, 16, and 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 Pyrex, for example, and is bonded onto the surface of the tube 10. Although the tube 23 is shown as surrounding the cavity 21, it is within the scope of the invention that the inner diameter of the tube 23 can be larger or smaller than the diameter of the cavity 21.

Accordingly, the embodiment of the invention shown in FIGS. 3 and 4 induces approximately equal stresses within the radial sensors 12, 13 and the circumferential sensors 16, 17, thereby causing changes in static pressure. Zero shifts due to changes in temperature and temperature changes in the transducer are almost eliminated. 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 the drawing]

Figure 1 is a schematic diagram of a conventional transducer;
Figure 2 shows the difference between radial stress and circumferential stress for various models of semiconductor pressure transducers constructed with square chips, depending on the orientation of the sensor and the stress on the chip when the difference in pressure on the chip is zero. curve drawn as a function of the angle between the edges of the third
The figure is a plan view of an embodiment of the present invention, and FIG. 4 is a sectional view taken along the - line in FIG. 3. 1... Chip, 3, 4, 12, 13... Radial direction sensor, 7, 8, 16, 17... Circumferential direction sensor, 2
1...Cavity, 23...Tube.

Claims (1)

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 sensors disposed on the one surface and having piezoresistive properties, at least the linear edge of the chip being substantially oriented with respect to the <110> crystallographic direction of the chip;
A semiconductor pressure transducer oriented at a 22.5 degree angle, each pair of sensors being oriented along the <110> crystal direction. 2. a single-crystal semiconductor chip whose edges form a parallelogram; a pair of radial stress sensors having piezoresistive properties disposed on one surface of the chip; a pair of circumferential stress sensors having piezoresistive characteristics, one of the pair of sensors being oriented parallel to the <110> crystal direction of the chip; And,
A semiconductor pressure 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. A semiconductor chip having at least one straight edge and a circular cavity formed in one surface, and first and second semiconductor chips disposed on the other surface of the chip and having piezoresistive properties. a pair of sensors, the first pair of sensors detects a stress mainly along a first polar coordinate direction with respect to the cavity within the chip, and the second pair of sensors detects a stress mainly along a first polar coordinate direction with respect to the cavity within the chip. a semiconductor pressure transducer for detecting stress primarily along a second polar coordinate direction, the second direction being perpendicular to the first direction, the first direction being <110 > A semiconductor pressure transducer, characterized in that it defines an axis parallel to the crystal direction and at an angle of approximately 22.5 degrees with respect to said edge.