JPH02234036A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To detect stress caused by pressure with high accuracy by detecting a difference between a 1st bridge circuit which detects the synthetic stress of pressure, temperature and inner stress and a 2nd bridge circuit which detects the synthetic stress of the temperature and the inner stress. CONSTITUTION:Four gauge resistances R1a-R4a are respectively formed on a surface inside the edge of a diaphragm part 2 responding to the pressure to form the 1st bridge circuit B1 which detects the output of the resistance change of the stress(sigma p+sigma t+sigma r) obtained by adding the stress sigma p caused by the pressure, the inner stress sigmat caused by the difference of thermal expansion and the inner stress sigma r caused by the difference of structure or materials. Then, four gauge resistances R1b-R4b are formed on the surface of a silicone substrate 1 which is the outside of the edge of the diaphragm part 2 to form the 2nd bridge circuit B which detects the resistance change of the stress(sigmat+sigma r)obtained by adding the stress sigmat and the stress sigma r. The output difference between the circuits B1 and B2, that is, (sigma p+sigma t+sigma r)-(sigma t+sigma r)=sigma p is detected. Thus, the stress caused by the pressure is detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor pressure sensor in which the effects of internal stress due to assembly and temperature are reduced.

[Conventional technology]

Figure 4 is a diagram showing the structure of a chip of a conventional semiconductor pressure sensor, where (a) is a plan view and (b) is a top view of the same figure (.).
-B' line sectional view. In the figure, a low-concentration silicon substrate 1K has its central portion removed by isotropic etching from the back side, and a nearly circular diaphragm portion 2 for sensing pressure is formed as a thin silicon substrate. ,ζ
On the inner surface of the edge of the diamond 7 ram part 2, there are gauge resistors Rla + R2a e which have a piezoresistance effect by diffusing high concentration impurities at positions K equally spaced at 90 degree intervals.
R3@*R4m are formed respectively. In addition, the silicon substrate 1 outside the edge of this diamond 72m portion 2
Wiring leads 3 made of Aj metal K are formed on the surface of each gauge resistor Rla w R2a + R3m described above.
+ "4m are bridge-connected to form a bridge circuit B as shown in the equivalent circuit K in Figure 5. Note that IP is the positive input terminal, IN is the negative input terminal, OP is the positive output terminal, ON is a negative output terminal, and these terminals IP, IN, OP, and ON are integrally formed on one end of the silicon substrate 1 by being connected to a wiring lead 3K.

Figure 6 shows the gauge resistance Rla * R2a shown in Figure 4.
+R3a * This shows the stress due to the pressure P generated in R4m. In the figure K, σp is the stress generated by the pressure PK, σt is the stress generated by the temperature, and σr is the assembly generated in the gauge resistance R1m+112a, R3a, R4m. This figure shows the stress caused by each stress.

Next, the operation will be explained.

In the semiconductor pressure sensor configured as above, the gauge resistance Rta+R2a+Raa+ on the diamond 7 ram part 2 is
Regarding the stress generated in the part K where R4m is formed, as shown in Figure 6, the stress σp generated by the pressure PK varies linearly with the pressure P, whereas the stress σt generated by the temperature changes with the pressure P according to the relationship table < , shows a constant value once the temperature is determined.

Furthermore, the stress σr caused by the difference in the thermal expansion coefficients of the materials exhibits a constant value regardless of the pressure once the structure and temperature are determined. For this reason, pressure. Once the temperature is determined, the gauge resistance R1
,,Rla e RSg * R4JlI K is σp+
(A stress equivalent to Ft+1fr is generated, and a resistance change occurs in accordance with that stress. Generally, the stress σr.#t is detected simultaneously with the stress σp proportional to the pressure P, so the pressure p
Even in the case of =o, a stress corresponding to σt+σr is applied and an offset output is generated.

[Problem to be solved by the invention]

However, in the semiconductor pressure sensor K configured in this way, the piezoresistance coefficient, stress (2t and stress ar
is a function of temperature, so the offset output changes according to the temperature change K), so the semiconductor pressure sensor has a series . It was necessary to connect resistors in parallel or both, perform trimming adjustments, and perform temperature compensation.

This invention has been made in order to solve the above-mentioned nine conventional problems, and its purpose is to provide a semiconductor pressure sensor in which the offset output is reduced and the temperature change in the K offset is reduced. .

[Means to solve the problem]

In the semiconductor pressure sensor according to the present invention, a first gauge resistor is formed on the inner surface of the edge of the diaphragm part, and σp+σt
A first bridge circuit detects a resistance change output due to a stress corresponding to and a second bridge circuit that detects the resistance change output due to the stress that overlaps with σt+σr without sensing σt+σr.

[Effect]

In this invention, the difference between the output of the first bridge circuit and the output of the second bridge circuit, that is, (1ν+#t0σ
Only r) - (at + σr) 10p is detected, and ζ is created in which the offset voltage is approximately zero at #1.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the structure of a chip according to an embodiment of the semiconductor pressure sensor according to the present invention, in which (.) is a plan view, and (b) is a line BB' in the figure (.). This is a sectional view, and the same parts as in the previous figures are given the same reference numerals.

In K in the same figure, each gauge resistor R111#R2JLIR3
On the surface of the silicon substrate 1 which is the outer edge of the diaphragm portion 2 where a+R41 is formed, each gauge resistor Rl1 is provided.
R2a # R3a * Gauge resistor Rib .Rib .Rib . R2b, R3b, and R4b are formed by diffusing high-concentration impurities, and are bridge-connected from the wiring lead 3K to form a first bridge circuit B1 and a second bridge circuit B2, as shown in the equivalent circuit in FIG. are connected in series. That is, on the edge inner surface K of the diaphragm part 2 that senses pressure, four gauge resistances Rlm + R2a + R3 @ t R4m are formed, and the stress σp generated by the pressure K, the internal stress σt due to the difference in thermal expansion, A first bridge circuit B1 is formed to detect a resistance change output corresponding to the stress (σp 10t 1σr) that is the sum of the internal stress σr caused by the different structures and materials K, and the outer edge of the diaphragm part 2 Each surface K of the silicon substrate 1 has four gauge resistors Rib.
421) +R3bsR4b is formed and the stress σp due to pressure is not sensed, and the resistance is equivalent to the stress (σt 10r) K, which is the sum of the internal stress σt due to the difference in thermal expansion and the internal stress σr caused by the difference in structure and material. A second bridge circuit B, which detects a changing output, is formed.

Next, the operation will be explained.

In the semiconductor pressure sensor configured as follows, a gauge resistance Rl formed on the surface of the diamond 7 ram portion 2
+ R2a I R3a l R4& are appropriately arranged from the crystal direction K of the silicon substrate 1, but since the formation positions are far from each other, the resistance values are not necessarily formed at all equivalent diffusion concentrations. Therefore, a first gauge resistor R1b t Rzb * R3b e R4b is placed on the surface of the silicon substrate 1 which is the outer edge of the diaphragm part 2.
Each gauge resistance R lg + R 2 a as shown in figure k
Each gauge resistor Rla l R2a # R3g +
Gauge resistor R1b+R2b*R3b I R4b having a diffusion concentration almost equal to that of R4a
is obtained. Similarly, the error from the center point of the diaphragm portion 2 formed by isotropic etching K of the silicon substrate 1, the rotation error of the silicon substrate crystal axis and the gauge resistance center axis are also the gauge resistance Rla + R2a + R
3a + each gauge resistor Rxb placed close to R4a
e Rzb + R3b * R4b is almost the same value. Also, the gauge resistance Rl @ s R2a l R3a l R4g inside the edge of the diaphragm part 2
Gauge resistance Rxb + R outside its edge with respect to K
2b * By providing Rab + Rab as congruent figures in shape, direction, and dimensions, the internal stress σr caused by the difference in structure and material is almost equal to the internal stress σt due to the difference in thermal expansion, and the gauge resistance Rla + R2
A first bridge circuit B.a + R3a + R4m. and the gauge resistance Rib + "2b
The output of the second bridge circuit B2 composed of +R3b*R4b is almost the same.

Therefore, the sensitivity to pressure is the gauge resistance R1. ．． R4
a # R3 @ * R4m is a gauge resistance R that is placed inside the edge of the diaphragm part 2 and can be sensitively detected.
ib + R2b + R3b * Since R4b is arranged on the outer edge VC of the diaphragm portion 2, it becomes insensitive in proportion to the square of the ratio between the thickness of the diaphragm portion 2 and the thickness of the silicon substrate 1. For example, if the thickness of the diaphragm portion 2 is about 40 μm and the thickness of the silicon substrate 1 is about 400 μm, the sensitivity can be reduced to 1/100. In other words, pressure sensitivity can be estimated.

According to such a configuration, the gauge resistance R1aeR2atR3@ formed on the inner surface of the edge of the diaphragm portion 2
First bridge circuit B composed of y R4a K
1 output and a gauge resistor R1b.1 formed on the surface of the silicon substrate 1 outside the edge of the diaphragm portion 2. R2b.
Second bridge circuit B.R3b l R4b. The difference between the output of
Only one (σt+σr)=−σp is detected, and the K offset output can be made zero as shown in FIG.

In addition, in the above-mentioned embodiment, stress σp due to pressure
Gauge resistance to detect "11 & + R2a + 9-
3@+R4m is placed inside the edge of the diamond 7 ram part 2, and the gauge resistance Rib"+R2b・' which does not detect pressure
Connect Rsb and R4b to the outside edge of diaphragm part 2,
, b is formed on the silicon substrate 1, but the present invention is not limited to this. Gauge resistors Rla e R2@v R3m l R4@ are formed on the silicon substrate 1, b*R2
Even if b + R3b and R4b are provided inside the edge of the diaphragm portion 2 to form a bridge circuit, the same effect as described above can be obtained.

Further, in the above embodiment, the diaphragm portion 2 is formed in a circular shape by isotropic etching on the silicon substrate 1, but it may be formed in a rectangular shape by anisotropic etching. However, the same effect as described above can be obtained.

Furthermore, in the embodiment described above, K on the silicon substrate 1 is
Although the case where the wiring lead 3 is made of At metal has been described, the same effect as described above can be obtained by forming it with a diffused conductor.

In addition, in the above-mentioned embodiment, the gauge resistance Rl @ + R28 e R inside the edge of the diamond 7 ram portion 2
3 @ #R4m and gauge resistance Rib on the outside of the edge
l R2b *Rs1) . We have explained the case K in which two sets of bridge circuits are formed by the R4b pair, but by forming a plurality of these pairs and connecting the plurality of sets in series]
, a pressure sensor with multiple times the sensitivity can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, the first bridge circuit detects the composite stress of pressure, temperature, and internal stress;
If the stress due to pressure K is detected rather than the difference K from the second bridge circuit that detects the composite stress of temperature and internal stress, the offset output will be extremely small and the temperature change in K offset will be small, so the accuracy will be improved. A semiconductor pressure sensor with high temperature can be obtained. In addition, conventional pressure sensors were subject to structural K limitations, which required consideration of the die bonding method and the shape of the die pad to minimize the effect on the chip part in order to minimize residual stress during assembly. According to the configuration according to the present invention, the pressure sensor can be selected regardless of structure, shape, material, etc., can be packaged with molded resin, and has extremely excellent effects such as being able to obtain an inexpensive and highly accurate semiconductor pressure sensor. is obtained.

[Brief explanation of drawings]

Figure 1 (.). (b) is a plan view of a pressure sensor chip showing an embodiment of the semiconductor pressure sensor according to the present invention, and a cross-sectional view thereof taken along the line BB'; FIG. 2 is an equivalent circuit A of the conductor pressure sensor chip of FIG. 1; Figure 3 is a diagram showing the internal composite stress that occurs when pressure is applied to the semiconductor pressure sensor chip in Figure 1, and Figures 4 (a) and (b) are plane views of the pressure sensor chip illustrating a conventional semiconductor pressure sensor. Figure, Part B
5 is an equivalent circuit diagram of the semiconductor pressure sensor chip shown in FIG. 4, and FIG. 6 is a diagram showing the internal composite stress that occurs when pressure is applied to the semiconductor pressure sensor chip K shown in FIG. 4. It is. 1●●●● silicon substrate, 2●gas diaphragm part,
3●●●●Wiring lead, Rla, RB), R2a+R2
b, R3a, R3b+R4awR4b ” “●● Gauge resistance, IP●・●● Positive side input terminal,! N●●war●
Negative side input terminal, OP●●●●Positive side output terminal, ON●
●...Negative output terminal. , Fig. 5

Claims (1)

[Claims] A diaphragm part consisting of a low concentration silicon substrate, a thin layer formed by etching a part of the silicon substrate from the back side, and a high concentration impurity diffused into four locations inside the edge of the surface of the diaphragm part. a first gauge resistor having a piezoresistance effect; and a piezoresistance effect formed by diffusing high concentration impurities on the silicon substrate surface outside the edge of the diaphragm portion in the vicinity of the first gauge resistor. a second gauge resistor formed on the silicon substrate and having a bridge connection between the first gauge resistor and the second gauge resistor, respectively.
A semiconductor pressure sensor comprising at least a bridge circuit and a wiring lead forming a second bridge circuit.