JPS59111374A - Pressure sensor - Google Patents

Abstract

PURPOSE:To obtain the titled pressure sensor having little effect of residual distortion by a method wherein the cutting-out direction of a chip is selected in the direction having the smallest coefficient of piezoelectric resistance effect, and a diffused resistance is placed in parallel with the chip side, thereby enabling to suppress the effect of distortion without reducing the degree of integration. CONSTITUTION:When a chip 1 has a face <100>, its cut-out direction is set in the direction <100>. Both of the longitudinal and lateral piezoelectric resistance coefficient pil curved line 15 and pit curved line 16 in the face <100> are formed at the smallest value in the direction of <100>. If the resistor 12 for integrated circuit is arranged in the direction <100>, almost no change in resistance is generated even when the stress in parallel and orthogonal intersecting directions worked on the resistor 12. Pressure detecting resistors 3-6 are arranged in the direction where the largest piezoelectric resistance coefficient is obtained. The surface <100> has the direction in 45 deg. for the chip side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to pressure sensors, and more particularly to integrated pressure sensors.

[Prior art]

FIG. 1 shows a conventional example of a pressure sensor using integrated circuit technology. (a) is a top view of the chip, and (b) is a central sectional view.

1 is a pressure sensor chip whose surface is (100) and each side of the chip is parallel to the <110> direction.

2 is a diaphragm with the back side cut out and made thinner.
1) It is a part that bends under pressure. Diffusion resistors 3 to 6 for detecting strain or pressure are formed in the diaphragm portion.

Diffused resistance connections or lead-out portions 7 to 10 are formed and are not directly intended for detecting strain or pressure.

The chip part 11 other than the diaphragm 2 is a fixed part, which is a part that fixes the chip to another support body. Generally fixed part 11
A circuit for processing the signals obtained from the resistors 3 to 6 is formed using integrated circuit technology on the surface of the resistor. 12 shows a representative resistance used in the circuit. Further, 13 represents a transistor. Generally, resistors and transistors are connected by complicated At wiring, but in this application, these are omitted and are not shown in the drawings.

Generally, for reasons of layout and equipment, a layout is adopted in which resistors are arranged parallel to the sides of the chip. This layout method has the disadvantage that the resistance tends to change due to changes in residual stress, as described below. First, some explanation will be given about the piezoresistance effect of p-type silicon.

In FIG. 2, when a current i is flowing through the diffused resistance layer 14, a stress T5 is applied in the longitudinal direction and a stress Ts is applied in the perpendicular direction, and the resistance R of the diffused resistance layer is expressed by the following equation.

Here π1. π1 are the longitudinal and transverse piezoresistance coefficients, respectively. These coefficients exhibit anisotropy, and in the case of the (ioo) plane, they exhibit relative anisotropic properties as shown in FIG. Curves 15 and 16 indicate π1 and πt, respectively. In the example shown in Figure 1, the longitudinal direction of the resistor is parallel to (110), so π
Both 4 and π show maximum values, and resistance changes are most likely to occur when residual stress changes. Of course, it is effective to arrange pressure detection resistors 3 to 6 in the <110> direction. In this way, the general integrated circuit resistor and the pressure detection resistor must be arranged in different directions. If they are arranged in the same direction, there is a drawback that the residual stress is susceptible to changes in resistance value due to changes in temperature.

[Purpose of the invention]

The present invention provides a pressure sensor in which a resistor that is not affected by strain, such as a signal processing circuit, is arranged parallel to the side of a chip in a general integrated circuit and a pressure or strain sensor that applies integrated circuit technology and piezoresistive effect. There is something to do.

[Summary of the invention]

The present invention focuses on the fact that the resistors used in general integrated circuits are mainly p-type, and by selecting the direction in which the chip is cut out in the direction in which the coefficient of the piezoresistance effect is minimum, the p-type diffused resistor is placed on the side of the chip. This takes advantage of the fact that when placed parallel to , it is least susceptible to strain.

[Embodiments of the invention]

An embodiment of the invention is shown in FIG. This is the case when the chip (or wafer) plane is (100).

Since the same symbols as in FIG. 1 are used for each part, explanations thereof will be omitted. At this time, cutting the chip in the (100) direction is an essential condition for minimizing the influence of residual strain on the integrated circuit.

That is, as shown in Fig. 3, the piezoresistance coefficient in the (100) plane is πj (curve 1
5) and πt (curve 16) are both minimum. this is,
This is extremely convenient. This is because if the resistor is arranged in the <100> direction, even if stress in parallel and orthogonal directions is applied to the resistor, the resistance will hardly change. On the other hand, in integrated circuits, in order to increase integration within a fixed chip size, it is important to avoid using diffused resistors as much as possible, but in bipolar linear circuits,
It is an almost impossible technology to apply resistance. Therefore, it is necessary to increase the degree of integration of the diffused resistor arrangement. It is effective to arrange the resistors parallel to the sides of the chip. Therefore, when using the (10o) crystal plane, it is essential that the chip cutting direction be (100). Silicon generally has a property of being easily broken in the (11o> direction, so the chip cutting direction is currently set in the <110> direction.

However, at present, there is no longer a need for methods that use a dicer, etc., to reduce the tendency for silicon to break easily.
100> direction cutting is a possible technique.

However, in the pressure sensor shown in FIG. 4, pressure (or strain) detection resistors 3 to 6'! il - <100 as mentioned above
> cannot be placed in the direction. This is because resistance change sensitivity to pressure is lost. Therefore, it is important that the pressure detection resistor is placed in the direction where the piezoresistance coefficient is maximum. This is a necessary and sufficient condition, and does not necessarily mean that it has to be 45 degrees; it may be 40 degrees depending on the case. In short, it is meaningless to set the diffused resistance in the same direction as the diffused resistor used in the signal processing integrated circuit diffused in the fixed part 11.

In principle, it is conceivable to arrange the diffused resistors 12 at 45° in FIG. 1, but this is not a good idea from the point of view of the degree of integration.

In the case of FIG. 4, as in FIG. 1, the integrated circuit on the fixed part 11 is complicated, but the diffused resistor 12 and the transistor
Only 3 was expressed as a model. Also, all At wiring was omitted.

Generally, the pressure sensor shown in FIG.
6 to the Wheatstone bridge, and the integrated circuit has
Built-in bridge drive circuit, amplifier, and temperature compensation circuits. The diaphragm 2 is usually formed by chemical etching.

Another embodiment is shown in FIG. This is the case when the chip (or wafer plane) is a (110) plane. Since the same symbols as in FIG. 1 are used for each part, explanations thereof will be omitted. At this time, the chip cutting directions can be set in the <100> and (110) directions, and the diffused resistance in the integrated circuit can be set in the <100> direction.
This is a necessary and sufficient condition to minimize the effects of residual strain on integrated circuits. In other words, as shown in Figure 6, (11
0) plane is π in the <100> direction.
- (curve 15) and πt (curve 16) are both minimized. Therefore, it is essential to lay out the diffused resistance of the integrated circuit in the <100> direction, and as mentioned earlier,
To increase the degree of integration, the chip-side must be parallel to <ioo>.

Therefore, the other side inevitably becomes (110).

In this case, pressure detection resistors 3 to 6 on the diaphragm surface are
There are various types of arrangement. As shown in FIG. 5, there is a method in which resistors are arranged parallel to <110>, which has no sensitivity in the orthogonal direction. According to this, the resistor must be placed orthogonal to the resistor in a general integrated circuit.

FIG. 7 shows an embodiment in which the resistors are arranged in the <111> direction where πt is maximum and in the direction 45° from <100> where πt is maximum. Since it can be laid out in parallel with the resistor chips in the integrated circuit, the degree of integration can be increased, and since the pressure detection section has a small number of resistors, it can be placed on a special axis to increase sensitivity.

Although the explanation so far has been made with respect to a pressure sensor with a diaphragm, it is also applicable to a general sensor without a diaphragm or an IC.

〔Effect of the invention〕

According to the present invention, without reducing the degree of integration of the integrated circuit,
An integrated circuit or sensor that is less affected by residual strain can be obtained.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a conventional example, Figure 2 is a front view of a diffused resistor,
Fig. 3 is a diagram showing the piezoresistance coefficient, Fig. 4 is an explanatory diagram of one embodiment of the present invention, Fig. 5 is an explanatory diagram of another embodiment of the invention, and Fig. 6 is a diagram showing the piezoresistance coefficient. , FIG. 7 is an explanatory diagram of another embodiment of the present invention. 1...Silicon chip, 2...Diaphragm, 3~
6.°・Pressure detection resistor, 7-10...Connection diffusion layer, 1
DESCRIPTION OF SYMBOLS 1... Fixed part, 12... Integrated circuit resistance, 13...
Transistor, 14... Diffused resistance layer, 15... Piezoresistance coefficient chopsticks/IJ (a) (//l> /) 12m - Carving, 5B ((A) </10>

Claims (1)

[Claims] 1. In a pressure sensor in which a diffused resistor and a transistor are arranged on the same chip, the longitudinal direction of the resistor is parallel to the chip side, and the direction of the chip side is the minimum direction of the piezoresistance coefficient of the chip surface. A pressure sensor characterized in that the longitudinal direction of the diffusion resistance for detecting the pressure of the object to be measured is arranged in a direction different from that of the diffusion resistance.