JP3084616B2 - Diffusion type pressure transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a diffusion pressure transducer employing an N-type silicon substrate as the 0) plane, and more particularly, to an arrangement of a piezoresistive element of the diffusion pressure transducer which has improved offset and offset temperature characteristics.

[0002]

2. Description of the Related Art A conventional diffusion type pressure transducer employing an N-type silicon substrate having a (100) crystal orientation will be described with reference to FIGS.

In general, the stress distribution is specified by the crystal orientation plane of the silicon substrate to be used and the shape of the diaphragm, and therefore, the optimum arrangement of the piezoresistive element is almost determined. FIG. 9 shows N (100) plane of crystal orientation.
FIG. 10 is a plan view showing the front surface side of the diaphragm portion of a conventional diffusion type pressure transducer in which a substantially rectangular diaphragm portion is formed on a silicon substrate. FIG. It is sectional drawing of a container. In the conventional diffusion type pressure transducer, one end piezoresistive element is arranged on the surface side of the strain-generating region located on each long side of the diaphragm, and the strain-generating element located substantially in the center of the diaphragm is arranged. Two central piezoresistive elements are arranged in parallel on the surface side of the region.

[0004]

However, in such a conventional diffusion type pressure transducer, with the downsizing of the chip,
The distance between the respective piezoresistive elements shown by a, b, and b ′ in FIG. 9 is reduced, and especially in the central piezoresistive elements 31 and 33 provided close to each other, the influence of the diffusion step and the photolithographic step is strongly increased. This causes variations in individual resistance values and their temperature characteristics (TCR), thereby deteriorating offset and offset temperature characteristics. Also,
The proximity of the central piezoresistive elements 31 and 33 causes a problem such as a leak current, and has a problem that the energization drift and the temperature reproducibility are deteriorated. On the other hand, when a silicon substrate having another crystal orientation plane is adopted, each central piezoresistive element can be arranged linearly in the longitudinal direction of the diaphragm portion. If an N-type silicon substrate with a (100) plane is adopted,
Due to the relationship of the stress distribution, it was impossible to achieve this without sacrificing various characteristics such as sensitivity and linearity.

[0005] In view of the above-mentioned conventional disadvantages, the present invention has
This was done to eliminate these drawbacks, without sacrificing various characteristics such as sensitivity and linearity, suppressing variations due to manufacturing processes such as diffusion and photolithography, and improving offset and offset temperature characteristics. It is an object of the present invention to obtain a diffusion type pressure transducer which is excellent in current drift and temperature reproducibility and can easily perform temperature compensation.

[0006]

In order to achieve the above object, according to the present invention, a substantially rectangular diaphragm portion is formed on an N-type silicon substrate having a (100) crystal orientation, and a long side of each of the diaphragm portions is formed. 1 each on the surface side of the strain generating region
One end piezoresistive element is formed, and two central piezoresistive elements are formed on the surface side of the strain-generating region located substantially at the center of the diaphragm, and each end piezoresistive element and each central piezoresistive element are formed. 2 along the longitudinal direction of the diaphragm portion on the back side of the diaphragm portion located between the
A diffused pressure transducer is formed by forming two rigid portions and arranging two central piezoresistive elements in a region where the stress value is constant by the two rigid portions in parallel with the rigid portions and linearly. Is composed. The crystal orientation (10
A substantially rectangular diaphragm portion is formed on the N-type silicon substrate on the 0) plane, and one end piezoresistive element is formed on each of the strain-generating regions located on the long side of each of the diaphragm portions. Two central piezoresistive elements are formed on the surface side of a strain generating region located substantially at the center of the diaphragm section, and the diaphragm section located between each end piezoresistive element and each central piezoresistive element On the back side of the diaphragm, two rigid portions are formed along the longitudinal direction of the diaphragm portion.
Two central piezoresistive elements are arranged in a region where the stress value is constant by the two rigid parts in parallel with the rigid part and in a straight line, and one end piezoresistive element is arranged from the center of the diaphragm part. A diffusion type pressure transducer is configured by arranging the distance in the Y-axis direction to the center and the distance in the X-axis direction from the center of the diaphragm to the center of one central piezoresistive element to be substantially equal. .

[0007]

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

FIG. 1 is a plan view of a diaphragm portion of a diffusion type pressure transducer according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the diffusion type pressure transducer viewed from II-II in FIG. FIG. Reference numeral 1 denotes a substrate made of N-type silicon having a crystal orientation (100) plane.
A substantially rectangular diaphragm portion 3 which is a strain generating portion is formed. Two end piezoresistive elements 21a and 23a are formed by diffusion on the surface side of the strain generating region located on the long side of each of the diaphragm portions 3, and are formed at substantially the center of the diaphragm portion 3. On the surface side of the strain region, two central piezoresistive elements 11a and 13a are formed linearly with respect to the longitudinal direction of the diaphragm part 3, similarly to the end piezoresistive elements 21a and 23a. On the back side of the diaphragm portion 3 between the end piezoresistive element 21a and the central piezoresistive elements 11a and 13a and between the central piezoresistive elements 11a and 13a and the end piezoresistive element 23a, a diaphragm portion is provided. Rigid bodies 5a, 5a each having the shape shown in FIGS. 1 and 2 are formed along the longitudinal direction of 3.

FIG. 3 schematically shows an effective stress value of the diffusion type pressure transducer according to the first embodiment of the present invention, and schematically shows the stress distribution. Similarly, FIG. 4 shows the effective stress value of the conventional diffusion type pressure transducer, and schematically shows the stress distribution as in FIG. In the conventional diffusion type pressure transducer having no rigid parts 5a, 5a, DD ′ in FIG.
As can be seen from the stress distribution and the EE ′ stress distribution, the stress value is not constant in the longitudinal direction of the diaphragm 51, and in order to maximize the pressure detection sensitivity, two central piezoresistive elements are required. Cannot be arranged linearly in the longitudinal direction of the diaphragm 51. On the other hand, in the first embodiment of the present invention, A in FIG.
As can be seen from the −A ′ stress distribution and the BB ′ stress distribution, there is a region where the stress value is constant in the longitudinal direction of the diaphragm portion 3 (see α, β, γ in FIG. 5). In the region, two central piezoresistive elements 11a, 13
a can be arranged linearly in the longitudinal direction of the diaphragm 3. The region where the stress value is constant is determined by the length of the rigid portion 5a in the longitudinal direction. Here, the length is determined by two central piezoresistive elements arranged linearly with respect to the longitudinal direction of the diaphragm portion 3. 11a, 13a
By forming longer than the combined length of
The two central piezoresistive elements 11a and 13a can be arranged in parallel and linearly with the rigid portion 5a in a region where the stress value is constant. Further, in the case where the distance at which the two central piezoresistive elements 11a and 13a approach each other at substantially the center of the diaphragm portion 3 is equal to the distance between the conventional central piezoresistive elements 31 and 33 arranged in parallel. Also, the smaller the area (volume) facing, is advantageous for leak current and the like. By arranging the central piezoresistive element in the optimum region in this way, the resistance values and TCRs of the individual piezoresistive elements can be made substantially the same, so that the two central piezoresistive elements are close to each other. Therefore, it is possible to prevent offset and offset temperature characteristics from deteriorating, thereby suppressing various problems such as leak current. In addition, it is effective in reducing linearity, current drift, and temperature reproducibility, and is very effective in reducing the size of the diffusion type pressure transducer. Note that substantially the same effect can be obtained if a substantial portion of the central piezoresistive elements 11a and 13a is arranged in a region where the stress value is constant.

Next, as can be seen from the CC ′ stress distribution in FIG. 3, in the diffusion pressure transducer according to the first embodiment of the present invention, the rigid members 5a, 5a act to Stress concentration occurs in the diaphragm portion 3 where the portions 5a and 5a are not formed, and this region (for example, α,
By forming each piezoresistive element in β, γ), a highly sensitive diffusion type pressure transducer can be obtained. Also, sensitivity and linearity can be improved by reducing the distance between the rigid portions 5a, 5a. However, since the central piezoresistive element is linearly arranged, it can be easily realized. Is very effective in obtaining an optimal diffusion pressure transducer especially for micro pressure.

In the meantime, in the diffusion type pressure transducer for minute pressure, the thickness of the diaphragm portion 3 needs to be extremely thin. At this time, the thickness of the diaphragm portion 3 is reduced by using an SOI silicon substrate. Since the control of the pressure is easy, it is very effective in obtaining a high-precision micro pressure diffusion type pressure transducer.

Further, in the conventional diffusion type pressure transducer, due to the influence of the alignment accuracy in the photolithography process, etc.
When the arrangement of the central piezoresistive elements 31 and 33 is shifted with respect to the widthwise direction of the diaphragm 51, the central piezoresistive elements 31 and 33 are arranged in parallel. The stress value of the element (for example, 31) shifts to the positive side, and the stress value of the other central piezoresistive element (for example, 33) shifts to the negative side. Different directions (+
(See FIG. 4 FF ′ stress distribution). Similarly, the end piezoresistive elements 41 and 43 also shift in different directions (+ side, − side). Usually, these four piezoresistive elements (central piezoresistive element, end piezoresistive element) improve the output sensitivity by bridge connection. Therefore, the product of the change in the resistance value of each piezoresistive element (for example, center The output value changes with respect to the product of the partial piezoresistive element 31 and the end piezoresistive element 41 (the product of the central piezoresistive element 33 and the end piezoresistive element 43). Therefore, a slight misalignment greatly affects the linearity. On the other hand, in the diffusion pressure transducer according to the first embodiment of the present invention, the center piezoresistive element 11a, Even if the arrangement of the piezoresistive element 11a is shifted,
Since the a and 13a are arranged in parallel and linearly with respect to the rigid portion 5a, the stress values of the two central piezoresistive elements 11a and 13a shift from the peak values to the negative side. Piezoresistive element 2
The stress values of 1a and 23a are determined by the central piezoresistive element 11.
Similarly to FIGS. 13a and 13a, the peak values are both shifted to the minus side, but the respective stress values are substantially the same (see the CC ′ stress distribution in FIG. 3). In this case, the change in the output value can be minimized, which is very effective in improving the linearity.

FIG. 6 is a plan view showing a front surface side of a diaphragm portion of a diffusion type pressure transducer according to a second embodiment of the present invention.
One end piezoresistive element 21b is arranged on the left side of the diaphragm section 3, and the other end piezoresistive element 23b is arranged on the right side of the diaphragm section 3. As described above, by providing the end piezoresistive elements at arbitrary locations within the region where the stress values indicated by β and γ in FIG. 5 are constant, the same effect as in the first embodiment of the present invention can be obtained. In addition to this, the end piezoresistive element can be provided at an arbitrary position, so that the degree of freedom in pattern design including the wiring pattern can be increased.

FIGS. 7 and 8 are plan views showing the front side of the diaphragm portion of the diffusion type pressure transducer according to the third and fourth embodiments of the present invention. The first and second embodiments of the present invention are shown in FIGS. The main difference from the diffusion type pressure transducer of the embodiment is that the arrangement of the central piezoresistive element in the X-axis direction is limited.

The distance Y in the Y-axis direction from the center of the diaphragm 3 to the center of one end piezoresistive element 21a.
1 is substantially equal to the distance X1 in the X-axis direction from the center of the diaphragm section 3 to the center of one center piezoresistive element 13b, and similarly, the other end piezoresistor from the center of the diaphragm section 3 The distance -Y1 (≒ Y1) in the Y-axis direction to the center of the element 23a and the distance -X1 (≒) in the X-axis from the center of the diaphragm 3 to the center of the other central piezoresistive element 11b. By arranging X1) approximately equal to each other, it is possible to reduce variations in the diffusion process and the photolithography process, and to further improve the offset and the offset temperature characteristics as compared with the first and second embodiments of the present invention. .

[0016]

As described in detail above, the present invention can provide the following effects.

(1) Since the two central piezoresistive elements are arranged linearly in the longitudinal direction of the diaphragm, the two piezoresistive elements do not come close to each other.
Adverse effects in the diffusion and photolithography steps can be avoided, offset and offset temperature characteristics can be improved, and leak current and the like can be reduced. In addition, since linearity, conduction drift, and temperature reproducibility can be reduced, temperature compensation can be easily and accurately performed, and a diffusion pressure transducer with good temperature characteristics and high accuracy can be easily obtained. In addition, it is possible to easily obtain a diffusion pressure transducer that is optimal for miniaturization and micro pressure.

(2) Since the influence of misalignment in the photolithographic process in the formation of the piezoresistive element and the diaphragm can be minimized, a diffusion pressure transducer having excellent linearity can be obtained and the temperature can be reduced. A diffusion pressure transducer with good characteristics and high accuracy can be obtained.
Further, the product yield can be improved.

(3) Since the arrangement of the end piezoresistive elements can be arbitrarily set, the degree of freedom in pattern design is increased.

(4) The distance in the Y-axis direction from the center of the diaphragm to the center of one end piezoresistive element, and the distance X from the center of the diaphragm to the center of one center piezoresistive element. By disposing the distances in the axial direction substantially equal to each other, it is possible to reduce variations in the diffusion step and the photolithography step, and to further improve offset and offset temperature characteristics.

(5) By using a silicon substrate having an SOI structure, it is possible to easily control the thickness of the diaphragm portion, and to obtain a diffusion pressure transducer which is optimal for a minute pressure.

[Brief description of the drawings]

FIG. 1 is a plan view showing a front surface side of a diaphragm portion of a diffusion type pressure transducer according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the diffusion pressure transducer according to the first embodiment of the present invention as viewed from II-II in FIG.

FIG. 3 is a schematic diagram showing a stress distribution of the diffusion type pressure transducer according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram showing a stress distribution of a conventional diffusion type pressure transducer.

FIG. 5 is a bottom view of the diffusion type pressure transducer according to the first embodiment of the present invention.

FIG. 6 is a plan view showing a front surface side of a diaphragm portion of a diffusion type pressure transducer according to a second embodiment of the present invention.

FIG. 7 is a plan view showing a front surface side of a diaphragm of a diffusion pressure transducer according to a third embodiment of the present invention.

FIG. 8 is a plan view showing a surface side of a diaphragm of a diffusion pressure transducer according to a fourth embodiment of the present invention.

FIG. 9 is a plan view showing a surface side of a diaphragm of a conventional diffusion type pressure transducer.

FIG. 10 is a cross-sectional view of the conventional diffusion type pressure transducer viewed from XX in FIG. 9;

[Explanation of symbols]

1: board, 3, 51: diaphragm portion, 5a, 5b: rigid portion, 7: thick portion, 11a, 11b, 31, 13a, 13b, 33:
Central piezoresistive element, 21a, 21b, 21c, 4
1, 23a, 23b, 23c, 43: end piezoresistive elements.

Claims (2)

(57) [Claims] 1. A substantially rectangular diaphragm portion is formed on an N-type silicon substrate having a (100) crystal orientation, and one end portion is formed on each surface side of a strain generating region located on each long side of the diaphragm portion. A piezoresistive element is formed, and two central piezoresistive elements are formed on the surface side of a strain generating region located substantially at the center of the diaphragm, and each end piezoresistive element and each central piezoresistive element are formed. Two rigid portions are formed along the longitudinal direction of the diaphragm portion on the back side of the diaphragm portion located between the two rigid portions, and two central piezoresistive elements are provided in a region where the stress value is constant by the two rigid portions. A diffusion type pressure transducer, wherein the pressure transducer is arranged in parallel with the rigid part and linearly. 2. A substantially rectangular diaphragm portion is formed on an N-type silicon substrate having a (100) crystal orientation, and one end portion is formed on the surface side of a strain generating region located on each long side of the diaphragm portion. A piezoresistive element is formed, and two central piezoresistive elements are formed on the surface side of a strain generating region located substantially at the center of the diaphragm, and each end piezoresistive element and each central piezoresistive element are formed. Two rigid portions are formed along the longitudinal direction of the diaphragm portion on the back side of the diaphragm portion located between the two rigid portions, and two central piezoresistive elements are provided in a region where the stress value is constant by the two rigid portions. It is arranged in parallel with the rigid part and linearly, and the distance in the Y-axis direction from the center of the diaphragm to the center of one end piezoresistive element, and one center from the center of the diaphragm Pi A diffusion-type pressure transducer, wherein the distances in the X-axis direction to the center of the piezoresistive element are substantially equal.