JPH04313276A - Semiconductor strain gauge - Google Patents

Abstract

PURPOSE:To provide a semiconductor strain gauge where a gauge element with a small change in output characteristics due to temperature increase is formed regarding a semiconductor strain gauge which is obtained by forming the gauge element with a piezo resistance effect on an Si single-crystal substrate as a high-impurity concentration region. CONSTITUTION:A high-impurity concentration region (low specific resistance) is provided at (high specific resistance) Si single-crystal substrates 2 and 7 which contain an n-type impurity at low concentration, thus forming gauge elements 3 and 8. Namely, the gauge elements 3 and 8 are formed according to a difference in specific resistance instead of pn junction, thus eliminating poor influence to output characteristics at a high-temperature region. Also, even if a high-impurity concentration region is formed at the Si single-crystal substrate which does not contain impurities at all, semiconductor strain gauges 1 and 6 with less change in output characteristics due to temperature increase are obtained.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a semiconductor strain gauge used in a semiconductor pressure sensor that detects compressive force by utilizing the piezoresistance effect of a gauge element, and more particularly, the present invention relates to a semiconductor strain gauge for use in a semiconductor pressure sensor that detects compressive force by utilizing the piezoresistance effect of a gauge element. The present invention relates to a semiconductor strain gauge formed as a high impurity concentration region.

0002

[Prior Art] Conventional pressure sensors use adhesives to form a Wheatstone bridge circuit by attaching a plurality of strain-generating bodies to a strain-generating body using an adhesive to measure the distortion of a strain-generating body that occurs in response to an applied compressive force. The voltage was transmitted to an electrically connected strain gauge, and the magnitude of the voltage output generated based on the resistance change of the strain gauge was detected. In recent years, the strain gauges used for this purpose have also been made of silicon (Silicon,
Semiconductor strain gauges made of semiconductor single crystals, mainly Si (hereinafter referred to as Si), have become mainstream. However, semiconductor pressure sensors, which are made by attaching multiple semiconductor strain gauges to a strain-generating body using an adhesive and connecting them to form a Wheatstone bridge circuit, are complicated and require a high level of know-how, especially when attaching them. The disadvantages are that the characteristics vary widely and the cost is high, and the adhesive used for pasting causes negative effects such as creep and hysteresis, and does not ensure strain transmission, which significantly reduces the reliability of the semiconductor pressure sensor. there were. Therefore,
Semiconductor strain gauges used in semiconductor pressure sensors are made of Si
Formation has been carried out by doping impurities into a single crystal substrate.

FIG. 2 shows an example of the structure of a semiconductor strain gauge used in a conventional diaphragm type semiconductor pressure sensor. Input electrodes and output electrodes are omitted. As shown in the figure, the semiconductor strain gauge 11 includes a pressure receiving diaphragm 12 made of a Si single crystal substrate made by processing a portion of single crystal Si into a thin layer (several tens of μm), doped with impurities, and integrated with a gauge element 13. It is formed. This gauge element 13 is formed by doping an n-type Si single crystal substrate with a p-type impurity such as boron using an ion implantation method, a diffusion method, or the like. The pressure receiving diaphragm 12 is joined to the support portion 14. Conversely, the gauge element 13 may be formed by doping a p-type Si single crystal substrate with an n-type impurity.

Gas or liquid is introduced into the pressure introduction part 12a of the pressure receiving diaphragm 12 through the pressure introduction port 12b, and the strain caused by the received pressure is measured from the resistance change of the gauge element 13. The diaphragm 12 is deformed by the pressure received by the pressure introduction part 12a, and stress is also generated in the gauge element 13 formed on the diaphragm 12. The piezoresistance effect of the semiconductor element changes the electrical resistance due to the change in resistivity caused by this stress, that is, due to the force applied from the outside,
It utilizes the phenomenon that the energy structure within a semiconductor crystal changes and the specific resistance changes based on the relative change in carriers.

FIG. 3 shows an example of the structure of a semiconductor strain gauge used in a conventional orthogonal semiconductor pressure sensor. The input electrode, output electrode, and upper pedestal are omitted. As shown in the figure, the semiconductor strain gauge 16 has a gauge element 18 formed integrally with a monocrystalline Si substrate 17 that is formed thick and also serves as a support base, doped with impurities. Similar to the diaphragm type gauge element 13, this orthogonal type gauge element 1
8 is also formed by doping an n-type Si single crystal substrate with a p-type impurity such as boron using an ion implantation method, a diffusion method, or the like. Conversely, a p-type Si single crystal substrate may be doped with an n-type impurity.

In the case of the semiconductor strain gauge 16 used in an orthogonal type semiconductor pressure sensor, since the direction of the crystal axis of the gauge element 18 affects the sensitivity, it is formed in advance so that the upper surface 18a is a crystal plane that meets the purpose. be done. For example, a p-type impurity layer (or an n-type impurity layer) that becomes the gauge element 18
is formed so that its upper surface 18a is a (110) plane, and then 45
Input electrode and output in the direction of °

[0007]

[Outside 1]

A pair of electrodes is provided, and a compressive force is applied perpendicularly to the upper surface 18a of the gauge element 18 while a current is flowing through the input electrode, and a voltage corresponding to the compressive force is extracted from a direction perpendicular to the direction in which the current flows. That's what I do.

The gauge element of the semiconductor strain gauge formed as described above, regardless of whether it is a diaphragm type or an orthogonal type semiconductor sensor, is produced by doping an n-type Si single crystal substrate with a p-type impurity or Since it is formed by doping an n-type impurity into a p-type Si single crystal substrate, a pn junction is formed. Therefore, an n-type Si single crystal substrate and a p-type impurity region or a p-type S
i A potential barrier is formed by a pn junction at the boundary between the single crystal substrate and the n-type impurity region, and the current flowing through the gauge element, which is normally a current flow path, flows through the bulk (n-type S
There is no leakage into the i-single crystal substrate or p-type Si-type crystal substrate.

0010

In the semiconductor strain gauge having the above structure, a pn junction is formed by doping impurities, and a potential barrier generated at the boundary is used to form a gauge element. However, the potential barrier that occurs at the boundary of this pn junction decreases as the temperature rises, so in high-temperature regions (above about 150°C), the leakage current increases and the potential barrier becomes less effective. This has the disadvantage that it has a large adverse effect on the output characteristics.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide a semiconductor strain gauge in which a gauge element is formed whose output characteristics do not change much even when the temperature rises.

0012

[Means for Solving the Problems] In order to achieve the above object, the semiconductor strain gauge of the present invention includes a gauge element formed by providing a high impurity concentration region in a Si single crystal substrate, and a piezoresistance that the gauge element has. In a semiconductor strain gauge that detects compressive force by utilizing the effect, the gauge element is formed on a low impurity concentration Si single crystal substrate as a high impurity concentration region having the same type of impurity as the impurity contained in the Si single crystal substrate. and the gauge element is made of impurity-free Si.
It is formed as a high impurity concentration region on a single crystal substrate.

[0013]

[Operation] The gauge element is made of S with low impurity concentration (high specific resistance).
A high impurity concentration (low resistivity) region of the same type as the impurity contained in the Si single crystal substrate is formed in the i single crystal substrate due to the difference in resistivity. When a gauge element is formed by a p-n junction, a rise in temperature has an adverse effect on the output characteristics, but since a gauge element is formed by a difference in resistivity, the difference between the gauge element and the Si single-crystal substrate can be affected even by a rise in temperature. Since the resistance ratio between the two does not change much, there is little change in output characteristics due to temperature changes. Further, a Si single crystal substrate containing no impurities can be considered as a case in which the concentration of impurities contained at a low concentration in the above case becomes zero, and the effect is the same.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1(a) and (b) are diagrams each showing the configuration of a semiconductor strain gauge according to a first embodiment of the present invention, and FIG. ) indicates the case where it is used in an orthogonal type semiconductor pressure sensor.

In FIG. 1(a), a semiconductor strain gauge 1 has a pressure receiving diaphragm 2 made of a Si single crystal substrate containing a low concentration of n-type impurities (high specific resistance) doped with a high concentration of n-type impurities. As a result, a gauge element 3 having an n-type impurity region (low resistivity) is formed and is bonded to the support portion 4. Gas or liquid is introduced into the pressure introduction portion 2a of the pressure receiving diaphragm 2 through the pressure introduction port 2b. As another example, there is a method in which the inside of the pressure receiving diaphragm 2 is sealed as a reference pressure and the external pressure applied to the diaphragm 2 is sensed.

[0016] The impurity doping is performed using an ion implantation method or a diffusion method, but it is needless to say that it is not limited to these methods, and the same method can be used hereinafter. In addition, in FIG. 1(b), the semiconductor strain gauge 6 has a thick Si single crystal substrate 7 containing a low concentration of n-type impurities (high specific resistance) that also serves as a support base, and a semiconductor strain gauge 6 that has a high concentration of n-type impurities. By doping to a concentration n
A gauge element 8 of type impurity region (low resistivity) is formed. At this time, the upper surface of the gauge element 8 is formed to be a predetermined crystal plane. For example, the gauge element 8 is (11
0) The surface is the top surface, and the <001> direction, and the outer 2
Input electrodes and output electrodes (not shown) are formed at 45 degrees from the direction.

[0017]

[Outside 2]

[0018] The operation of the semiconductor strain gauge shown in FIGS. 1(a) and 1(b) is similar to that of the conventional example. As described above, in the first embodiment of the present invention, the gauge elements 3 and 8, which are current flow paths, are connected to the Si single-crystal substrate 2 by the difference in resistivity.
, 7. In this case, there is some leakage current at the boundary even at room temperature, but the resistance ratio between the two does not change much even when the temperature rises, so it is more effective than when the gauge element is formed using a pn junction as in the past. It is possible to form a gauge element on a Si single crystal substrate by doping with the same type of impurity, and due to the difference in the impurity concentration (due to the difference in specific resistance), which has little change in output characteristics due to temperature changes. Compared to forming a gauge element, the number of steps does not increase and it can be said to be relatively easy.

Although not shown, the following example can be considered as a second embodiment. In FIGS. 1(a) and 1(b), the Si single crystal substrates 2 and 7 are substrates containing p-type impurities at a low concentration (high specific resistance), and the gauge elements 3 and 8 are substrates containing p-type impurities at a low concentration. This is an example of forming a p-type impurity region (low resistivity) by doping at a high concentration. This is an example in which the p-type and n-type are reversed compared to the first embodiment.

Furthermore, although not shown, the following example can be considered as a third embodiment. In the first embodiment, the Si single crystal substrates 2 and 7 are replaced with impurity-free S
i This is an example of a single crystal substrate. This corresponds to the case where the n-type impurity concentration, which was originally a low concentration, in the Si single crystal substrate in the first embodiment is made infinitely close to zero.

Furthermore, although not shown, the following example may be considered as a fourth embodiment. This is an example in which the Si single crystal substrates 2 and 7 in the second embodiment are Si single crystal substrates containing no impurities. This corresponds to the case where the p-type impurity concentration, which was originally low in the Si single crystal substrate in the second embodiment, is made infinitely close to zero.

As described above, the second to fourth aspects of the present invention
In the semiconductor pressure sensor of the embodiment, the gauge element is also formed by providing a high impurity concentration (low resistivity) region of the same type in a Si single crystal substrate with a low impurity concentration (high resistivity) including zero concentration. be. In other words, the gauge element is formed based on the difference in specific resistance without using a pn junction.

Therefore, in any of the first to fourth embodiments described above, since the structure does not utilize the potential barrier generated at the boundary of the pn junction, there is little adverse effect on the output characteristics due to temperature rise.

[0024]

As described above, according to the present invention, since the gauge elements of the semiconductor strain gauge are formed by differences in specific resistance, there is little change in output characteristics due to temperature changes. Furthermore, the process of forming the gauge element becomes relatively easy.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a configuration example of a semiconductor strain gauge according to an embodiment of the present invention, in which (a) shows a diaphragm type, and (b) shows a case where it is used in an orthogonal type semiconductor pressure sensor.

FIG. 2 is a sectional view of a configuration example of a semiconductor strain gauge used in a conventional diaphragm type semiconductor pressure sensor.

FIG. 3 is a diagram showing an example of the configuration of a semiconductor strain gauge used in a conventional orthogonal semiconductor pressure sensor, in which (a) is a plan view;
(b) is a cross-sectional view.

[Explanation of symbols]

1,6 Semiconductor strain gauge 2,7 Si single crystal substrate 3,8 Gauge element

Claims (2)

[Claims] 1. A semiconductor strain gauge in which a gauge element is formed by providing a high impurity concentration region on a Si single crystal substrate, and compressive force is detected by utilizing the piezoresistance effect of the gauge element, the gauge element being A semiconductor strain gauge characterized in that it is formed in a low impurity concentration Si single crystal substrate as a high impurity concentration region of the same type as the impurity contained in the Si single crystal substrate. 2. A semiconductor strain gauge in which a gauge element is formed by providing a high impurity concentration region on a Si single crystal substrate, and compressive force is detected by utilizing the piezoresistance effect of the gauge element, wherein the gauge element is , impurity-free Si
A semiconductor strain gauge characterized by forming a high impurity concentration region on a single crystal substrate.