JPS581550B2 - semiconductor pressure transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor pressure transmitter, and more particularly to a piezoresistive element for output compensation on a diaphragm made of a semiconductor single crystal.

FIG. 1 shows a top view of a known silicon diaphragm, and the surface of the diaphragm is a (100) plane.

4 is a thin part, and 5 is a fixed part.

71 is a radius gauge, 72 is a tangent gauge, and gauge 71
, 72 constitute a Wheatstone bridge, and a compensation resistor 8 is provided to compensate for the output of this Wheatstone bridge.

This compensation resistor 8 is formed near the radius gauge 71 and the tangent gauge 720 primarily to make the resistance values the same, and as can be seen from the curve of the sensitivity coefficient πl regarding resistance change in FIG. 2, the sensitivity is the minimum. It is arranged along the <100> axis.

Here, πl is the piezoresistance coefficient when the current direction and the stress direction are parallel.

However, even if the piezoresistance coefficient πl is arranged in the <100> axis direction, its value does not become exactly zero, so the first
When the compensation resistor is formed across the fixed part and the thin part as shown in the figure, the compensation resistor has the disadvantage that its resistance changes slightly due to deformation due to pressure.

Specific resistance σ - 7.8Ω・πl in the <100> axis direction calculated from the basic piezoresistance coefficient for my sample is 0. 0
7 X 1 0-2ym? t/kg, πt is -0.0
3×10'mm/kg, and π2 becomes zero.

Here, πt is the piezoresistance coefficient when the current direction and the stress direction are perpendicular to each other, and π7 is the piezoresistance coefficient perpendicular to the plane of the diffusion gauge.

The resistance change rate of the compensation resistor when stress is applied - is 1 = πlσ
l + πtσt 1π2σ2 (1).

When the resistance change rate of the compensation resistor is calculated for a 100 kg/cm silicon diaphragm from equation (1), the resistance change rate is 0.8% in the example shown in FIG.

It goes without saying that it is desirable that the rate of change in resistance of the compensation resistor for output compensation be as small as possible.

Next, there is a third method for reducing the resistance change rate of the compensation resistor.
It is conceivable to provide a compensation resistor in the fixed part as shown in the figure.

In the example shown in Fig. 3, a thin-walled portion 4 is formed by concave processing in a part of an N-type silicon single crystal plate having a (110) plane, and the crystal axis is aligned with the <1 1 1> axis in the radial direction of this circular hole. A configuration is shown in which two radius gauges 71 are arranged in a P-shape, two tangential resistors 72 are arranged at an angle of 45° from the <1 0 0> axis, and a compensation resistor is arranged in the fixed part 5.

This compensation resistor constitutes a part of a zero point transition compensation gauge which will be described later.

Here, zero point transition refers to readjusting the bridge output to zero under a certain measurement distortion state.

Ideally, a compensation gauge for zero-point transition should not change resistance when pressure is applied, but we have taken into consideration the following points: uniformity of resistance values, simplicity of the manufacturing process, and transient response of output due to changes in ambient temperature. , are formed on the silicon diaphragm at the same time as the gauges 71 and 72, so a slight change in resistance is unavoidable.

Therefore, in the example shown in FIG. 3, a compensation resistor 8 is installed along the <110> axis in a portion near the gauges 71 and 72 in the fixed part 5, which is considered not to be deformed by pressure, and in consideration of the fact that the resistance values are the same. This minimizes resistance changes due to pressure.

In the example shown in Fig. 3, this is not a particular problem for a diaphragm for low pressure measurement, but for a diaphragm for high pressure exceeding 100 kg/crA, it is difficult to strictly separate the thin part 4 and the fixed part 5, and the so-called elastic support model is used. Therefore, there is a disadvantage that even in the fixed part, a portion near the thin wall part undergoes local deformation, and the compensation resistor 8 is also subjected to strain, causing a change in resistance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor pressure transmitter in which a change in resistance due to pressure in an output compensation resistor of a Wheatstone bridge constituted by a semiconductor gauge is reduced.

In the present invention, the output compensation resistors connected between the gauges on two adjacent sides between the bridge output terminals are arranged in the crystal orientation with the minimum piezoresistance coefficient on the fixed part of the silicon diaphragm.

According to an embodiment of the present invention, it has been confirmed that the compensation resistors arranged along each crystal axis of the (110) plane high voltage silicon diaphragm exhibit a distribution corresponding to the sensitivity curve shown in FIG. By arranging the compensation resistor in the fixed part along the <100> axis where the resistance change is the smallest among them, the bridge output is prevented from being adversely affected.

The pressure transmitter can instruct you to expand a part of the measurement range,
There is a unique way to use it to make the output voltage full scale for a certain part of the pressure range.

At this time, a zero point transition mechanism is required to transition the output zero point to an arbitrary point within the measurement range.

FIG. 6 shows an example of this circuit.

In pressure transmitters using conventional metal wire strain gauges, the temperature coefficient of resistance of the strain gauge is small, so by connecting a resistor with a low temperature coefficient of resistance in series or parallel to one side of the bridge, a wide range of zero point transitions can be achieved. It is possible and
There was no adverse effect on temperature characteristics or static characteristics.

When a semiconductor gauge is used, its temperature coefficient of resistance is extremely large, so a simple method such as the above-mentioned metal strain gauge causes a large change in the zero point due to temperature.

Therefore, we created a zero point transition circuit network as shown at 10 and 10' in Fig. 6, and calculated the resistance temperature coefficient of this circuit by the temperature change of the resistance change ΔR due to the pressure of the strain gauges 71, 72 or 71', 72'. If it is set equal to , there is no change in zero point due to temperature regardless of the amount of zero point transition.

Since this temperature coefficient of resistance includes a large quadratic term, the transition circuits 10 and 10' are connected to thermistors 91 and 91 having negative temperature coefficients.
91', a compensating resistor 8L81' having the same large positive temperature coefficient of resistance as the semiconductor gauge, and a resistance element having a small temperature coefficient of resistance, and the values of each table are selected to appropriate values.

If this transition circuit is used, the zero point change due to temperature change will be eliminated, but as mentioned above, since the compensation resistors 81 and 81' are formed on a part of the silicon diaphragm at the same time as the strain gauge, when the measurement pressure increases, There is a problem in that a large resistance change occurs, which adversely affects the static characteristics of pressure and output.

Particularly in recent years, where high-precision pressure transmitters are required, a non-linear error of about 0.1% becomes a problem, and this adverse effect is an important issue that must be avoided at all costs.

FIG. 4 is a diagram showing one embodiment of the present invention.

1 is a fixing plate made of silicone with a hole 11 in the center. Ru.

2 is made of N-type conductivity type silicon, and the crystal plane is (110).
It is a silicon diaphragm with a concave notch 3 in the center of the surface.

The thin part 4 is provided with a radial gauge 71 along the <1 1 1> axis, and two tangential gauges 72 are each spread out along an angle of 45° from the <1 1 0> axis. There is.

The silicon diaphragm 2 and the silicon plate 1 are bonded together at a bonding portion 6 using a gold-silicon eutectic alloy or the like.

The compensation resistor 8 in FIG. 4, which corresponds to 81 and 81' in FIG. , the resistance change is small even in the case of a high-voltage silicon diaphragm, as will be described later.

When pressure P is applied in the direction of the arrow, the thin wall portion 4 is deformed, the resistance of the radius gauges 71, 71' diffused thereon increases, and the resistance of the tangential gauges 72, 72' decreases.

These gauges are wired as shown in FIG. 6, and are connected to, for example, a constant current source Ix, so that the zero point transition circuits 10, 10'
A voltage proportional to the pressure is obtained from the sliders of the variable resistors 1 1 and 1 1', that is, the output terminals e and e'.

As mentioned above, the compensation resistor 8 is placed in a position where it is not susceptible to resistance changes due to pressure, so if you compare it with a silicon diaphragm for 100 kg/cm, the resistance change rate ΔR/R in the one in Figure 1 is While it was 6%, in the embodiment shown in FIG. 4, it can be reduced to 1/20 of this (ie, 0.3%) or less.

As a result, the zero point transition circuits 10 and 10' can be considered to be insensitive to pressure, and even if the left and right variable resistors are made unbalanced and the zero point is shifted, the output voltage taken out from the output terminals e and e' will be adversely affected. I won't give it.

When the example shown in Fig. 4 is incorporated into the circuit shown in Fig. 6, the influence of the resistance change rate on the output voltage is approximately 1/10 of 0.3%.
It will be about.

Therefore, according to the present invention, the most important static characteristics of the pressure transmitter can maintain the high accuracy obtained by the strain gauges 71 and 72.

Furthermore, since the circuit configuration of the zero-point transition circuit takes temperature compensation into consideration, it is necessary that it not be affected by pressure.

When the resistance value of the compensation resistor 8 changes due to pressure, the temperature coefficient of resistance of the zero point transition circuit 10 changes, so it is possible to prevent the disadvantage that the output voltage fluctuates with changes in ambient temperature.

If the temperature compensation is completely compensated by the circuit shown in FIG. 6, the adverse effect on the output due to the pressure change of the compensation resistor will be about <0.03% as described above.

Although the above embodiment shows an example in which a P-type strain gauge is diffused in an N-type silicon diaphragm, the same concept can be applied to a case where the conductivity type is reversed, and the same effect can be achieved.

This is because although the P-type and N-type have different crystal orientations that exhibit maximum sensitivity and have opposite signs of resistance change (ΔR/R),
This is because other characteristics are similar.

For example, when a diaphragm is made of P-type silicon and an N-type strain gauge is diffused, the <111> axis has the lowest sensitivity, so compensation resistors may be arranged along this direction.

1 Note that the present invention is not limited to the above embodiments, and for example, when diffusing a P-type strain gauge, a fixed part on the <100> axis on the (100) plane or (110) plane of the silicon diaphragm. A compensation resistor may also be provided.

Further, when diffusing the N-type strain gauge, a compensation resistor may be provided at a fixed portion on the <111> axis on the (110) plane or the (211) plane.

According to the present invention, it is possible to reduce the resistance change due to pressure in the compensation resistor diffused on the silicon diaphragm, so that static characteristics and temperature characteristics are not adversely affected, and it is possible to provide a pressure transmitter that maintains the high accuracy of a strain gauge. I can do it.

Further, since the resistance temperature coefficient of the zero point transition circuit is not changed, the output zero point does not fluctuate due to changes in ambient temperature.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional semiconductor pressure transmitter, Fig. 2 is a sensitivity characteristic diagram of the transmitter shown in Fig. 1, Fig. 3 is an improvement proposal proposed by the present inventor, and Fig. 4 is a diagram of the present invention. FIG. 5 is a sensitivity characteristic diagram of the transmitter shown in FIG. 4, and FIG. 6 is an example diagram of the connection of compensation resistors included in the bridge circuit and zero point transition circuit of the strain gauge. 1... fixed end, 2... silicon diaphragm, 3... recessed part, 4... thin wall part, 5... fixed part , 71 , 71', 72
, 72'...Strain gauge, 8,8L81'
...Compensation resistance, 1 0, 1 0'...
・Zero point transition circuit.

Claims (1)

[Scope of Claims] 1. A diaphragm made of silicon single crystal, a strain gauge diffused on the diaphragm, a Wheatstone bridge formed by the gauge, and two adjacent sides between at least one output end of the bridge. A semiconductor pressure transmitter comprising a resistor for compensating the output of the bridge connected between the gauges of the semiconductor pressure transmitter, characterized in that the compensating resistor is arranged in a crystal orientation in which the piezoresistance coefficient on the fixed part of the silicon diaphragm is substantially minimum. Semiconductor pressure transmitter. 2. In the semiconductor pressure transmitter according to item 1, when a P-type strain gauge is diffused into an N-type silicon diaphragm, the surface of the diaphragm is a (110) plane, and the compensation resistors are arranged in the 100> axis direction. A semiconductor pressure transmitter featuring: 3. The semiconductor pressure transmitter according to item 1, wherein the compensation resistor includes a temperature compensation resistor and a zero point transition compensation variable resistor connected in parallel.