JP6971109B2 - Sensor element - Google Patents

Description

The present disclosure relates to sensor elements.

Conventionally, a sensor that detects a specific substance in a sample has been known. For example, Patent Document 1 discloses a sensor including a diaphragm portion and a piezo resistance element that detects bending of the diaphragm portion.

Japanese Unexamined Patent Publication No. 10-22511

In such a sensor, it is required to improve the detection accuracy.

The sensor element according to the embodiment of the present disclosure includes a substrate containing a first conductive type first impurity and a second conductive type second impurity. The substrate has at least one piezo resistance portion, a first region, and a second region. The piezo resistance portion contains the second impurity. The first region surrounds the piezo resistance portion in a state of being in contact with the side portion and the bottom portion of the piezo resistance portion and contains the first impurity. The second region surrounds the first region and contains the first impurity. The concentration of the first impurity in the first region is higher than the concentration of the first impurity in the second region. The substrate has a diaphragm, and a deformable sensitive film is located on the diaphragm. The piezo resistance portion is located outside the sensitive membrane and around the diaphragm.

According to the sensor element according to the embodiment of the present disclosure, the detection accuracy can be improved.

It is a top view which shows the schematic structure of the sensor element which concerns on one Embodiment of this disclosure. It is sectional drawing of the sensor element along the line I-I shown in FIG. It is sectional drawing of the sensor element which concerns on a comparative example.

Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings. In the following, the sensor element according to the embodiment of the present disclosure shall be adopted for a gas sensor. However, the sensor element according to the embodiment of the present disclosure is not limited to the gas sensor, and may be adopted for any sensor using the piezo resistance portion. For example, the sensor element according to one embodiment of the present disclosure may be adopted as a pressure sensor, an acceleration sensor, or an odor sensor.

[Sensor element configuration]
FIG. 1 is a top view showing a schematic configuration of a sensor element 1 according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view of the sensor element 1 along the line I-I shown in FIG.

The sensor element 1 is used in, for example, a gas sensor. The subject of the sensor element 1 is, for example, human exhaled breath, but is not limited thereto. When the subject is human exhaled breath, the detection target of the sensor element 1 is, for example, acetone, ethanol, carbon monoxide, or the like.

The sensor element 1 includes a substrate 10. In the following, it is assumed that the substrate 10 is a Si substrate. However, the substrate 10 does not have to be a Si substrate as long as it is a semiconductor substrate.

As shown in FIG. 2, the substrate 10 includes an n-type region such as the first regions 13 and 14 and the second region 15, and a p-type region such as the piezo resistance portion 20. That is, the substrate 10 contains an n-type first impurity as the first conductive type and a p-type second impurity as the second conductive type. The first impurity is, for example, phosphorus (P) or arsenic (As). The second impurity is, for example, boron (B) or the like. In this embodiment, the first conductive type is n-type and the second conductive type is p-type. However, the first conductive type may be p type and the second conductive type may be n type.

As shown in FIG. 1, the substrate 10 has a diaphragm 11 and piezo resistance portions 20, 21, 22, and 23. The sensor element 1 shown in FIG. 1 includes four piezo resistance portions 20 to 23. However, the number of piezo resistance portions included in the sensor element 1 is not limited to four. The sensor element 1 may include at least one piezo resistance unit.

The diaphragm 11 is a deformable member. The diaphragm 11 is, for example, a thin n-type Si substrate. The diaphragm 11 has a circular shape when viewed from above. A sensitive film 12 is arranged on the diaphragm 11. When the sensitive film 12 arranged on the upper surface of the diaphragm 11 is deformed, the diaphragm 11 is deformed according to the degree of deformation of the sensitive film 12.

The sensitive film 12 has a circular shape when viewed from above. When a substance to be detected is adsorbed on the sensitive film 12, the sensitive film 12 expands and contracts and deforms due to physical contact with the substance or a chemical reaction with the substance. For the sensitive film 12, a material corresponding to the substance to be detected is used.

The piezo resistance portions 20 to 23 are p-type Si. That is, the piezo resistance portions 20 to 23 contain the second impurity. The piezo resistance portions 20 to 23 can be formed, for example, by diffusing a second impurity to a high concentration. The piezo resistance portions 20 to 23 are, for example, high-concentration p-type Si.

The piezo resistance portions 20 and 21 are formed on the substrate 10 as shown in FIG. Similar to the piezo resistance portions 20 and 21, the piezo resistance portions 22 and 23 are formed on the substrate 10. As shown in FIG. 2, a wiring 30 is formed on the piezo resistance portion 20. As shown in FIG. 2, a wiring 31 is formed on the piezo resistance portion 21. Similar to the piezo resistance portions 20 and 21, the wiring 32 is formed on the piezo resistance portions 22. Similar to the piezo resistance portions 20 and 21, the wiring 33 is formed on the piezo resistance portions 23. As shown in FIG. 1, the wiring 30 is electrically connected to the wiring 30A from the outside. The wiring 31 is electrically connected to the wiring 31A from the outside. The wiring 32 is electrically connected to the wiring 32A from the outside. The wiring 33 is electrically connected to the wiring 33A from the outside.

As shown in FIG. 1, the piezo resistance portions 20 to 23 are arranged at equal intervals around the diaphragm 11 in a top view. The piezo resistance portion 20 and the piezo resistance portion 21 are arranged at positions facing each other with the sensitive film 12 interposed therebetween. The piezo resistance portion 22 and the piezo resistance portion 23 are arranged at positions facing each other with the sensitive film 12 interposed therebetween.

The resistance values of the piezo resistance portions 20 to 23 vary depending on the stress received by the piezo resistance portions 20 to 23, respectively. In the present embodiment, the resistance values of the piezo resistance portions 20 to 23 change due to the bending of the diaphragm 11 and the stress applied to the piezo resistance portions 20 to 23, respectively. The change in the resistance value of the piezo resistance portions 20 to 23 is output to the outside as an electric signal via the wirings 30 to 33 and the wirings 30A to 33A. By detecting the change in the resistance value of the piezo resistance portions 20 to 23 as an electric signal, it is possible to detect the adsorption of the substance to be detected on the sensitive film 12.

The piezo resistance portions 20 to 23 may form a Wheatstone bridge circuit. By detecting the change in the resistance value of the piezo resistance portions 20 to 23 as an electric signal from the Wheatstone bridge circuit composed of the piezo resistance portions 20 to 23, the adsorption of the substance to be detected to the sensitive film 12 is detected. It's okay.

As shown in FIG. 2, the wiring 30 is formed on the piezo resistance portion 20 as, for example, an electrode layer. The wiring 30 is electrically connected to the piezo resistance portion 20. As shown in FIG. 2, the wiring 31 is formed on the piezo resistance portion 21 as, for example, an electrode layer. The wiring 31 is electrically connected to the piezo resistance portion 21. Similar to the wirings 30 and 31, the wiring 32 is formed on the piezo resistance portion 22 as, for example, an electrode layer. The wiring 32 is electrically connected to the piezo resistance portion 22. Similar to the wirings 30 and 31, the wiring 33 is formed on the piezo resistance portion 23, for example, as an electrode layer. The wiring 33 is electrically connected to the piezo resistance portion 23.

The first region 13 surrounds the piezo resistance portion 20 and contains the first impurities. That is, the first region 13 is an n-type region surrounding the piezo resistance portion 20. The first region 14 surrounds the piezo resistance portion 21 and contains the first impurities. That is, the first region 14 is an n-type region surrounding the piezo resistance portion 21. In the present embodiment, the substrate 10 further includes a first region surrounding the piezo resistance portion 22 and a first region surrounding the piezo resistance portion 23.

The second region 15 surrounds the first regions 13 and 14 and contains the first impurities. That is, the second region 15 is an n-type region surrounding the first regions 13 and 14. Further, the second region 15 may be grounded via wiring or the like.

Here, in the present embodiment, the concentration of the first impurity in the first regions 13 and 14 is higher than the concentration of the first impurity in the second region 15. For example, the concentration of the first impurity in the first regions 13 and ¹⁴ may be 1.0 × 10 14 cm ^{3 to} 1.0 × 10 ¹⁹ cm ^3. For example, the concentration of the first impurity in the second region 15 may be ^{1.0 × 10 13} cm ^{3 to} 1.0 × 10 ¹⁵ cm ^3. In this case, the concentration of the first impurity in the first regions 13 and 14 is 10 to 10,000 times higher than the concentration of the first impurity in the second region 15. That is, the first regions 13 and 14 are high-concentration n-type regions with respect to the second region 15. Further, the second region 15 is a low-concentration n-type region with respect to the first regions 13 and 14.

With such a configuration, the sensor element 1 according to the present embodiment can improve the detection accuracy as described below.

FIG. 3 is a cross-sectional view of the sensor element 1A according to the comparative example. Among the components shown in FIG. 3, the same components as those shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

The sensor element 1A according to the comparative example includes a substrate 10A. The substrate 10A does not include the first region. Therefore, the high-concentration p-type piezo resistance portions 20 and 21 are surrounded by the second region 15 as shown in FIG.

In the sensor element 1A according to the comparative example, the high-concentration p-type piezo resistance portions 20 to 23 come into contact with the low-concentration n-type second region 15 on the substrate 10A. Therefore, the diffusion potential of the pn junction (for example, arrow B) between the piezo resistance portion 20 and the like and the second region 15 becomes large. When the diffusion potential of the pn junction becomes large, the depletion layer formed at the pn junction becomes thick. When the depletion layer formed at the pn junction becomes thick, there is a high possibility that external light will enter the depletion layer during the detection process using the sensor element 1A. When external light enters the depletion layer, a photovoltaic current is generated by the photovoltaic power, and this current may become a noise source.

On the other hand, in the sensor element 1 according to the present embodiment, the high-concentration p-type piezo resistance portions 20 to 23 have high-concentration n-type first regions 13, 14 and the like on the substrate 10, as shown in FIG. Contact with. Therefore, the diffusion potential of the pn junction (for example, arrow A shown in FIG. 2) between the piezo resistance portion 20 and the like and the first region 13 and the like can be smaller than that of the comparative example. By reducing the diffusion potential of the pn junction, the depletion layer formed at the pn junction can be narrower than in the comparative example. By narrowing the depletion layer formed at the pn junction, the probability that external light will enter the depletion layer can be reduced. By reducing the probability that external light will enter the depletion layer, the sensor element 1 according to the present embodiment can reduce the generation of a current that becomes a noise source. Therefore, the sensor element 1 according to the present embodiment can improve the detection accuracy.

In addition, gas sensors are often used by users in their daily lives. That is, gas sensors are often exposed to light because they are often used during the day when the user is active. Here, the sensor element 1 according to the present embodiment can reduce the probability that external light enters the depletion layer and reduce the generation of a current that becomes a noise source, as described above. Therefore, the sensor element 1 according to the present embodiment can improve the detection accuracy even if it is adopted in a gas sensor that a user uses in daily life.

In addition, in the present embodiment, when the sensor element 1 includes two piezo resistance portions 20 and 21 facing each other as shown in FIG. 2, the first region 13 surrounding the piezo resistance portion 20 and the piezo resistance portion 21 are provided. The second region 15 is located between the surrounding first region 14 and the surrounding first region 14. With such a configuration, it is possible to prevent the piezo resistance portion 20 and the piezo resistance portion 21 from being short-circuited.

Although the present disclosure has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and modifications based on the present disclosure. Therefore, it should be noted that these modifications and modifications are included in the scope of the present invention. For example, the functions included in each functional unit, each means, etc. can be rearranged so as not to be logically inconsistent, and a plurality of functional units, etc. can be combined or divided into one. .. Further, each of the above-described embodiments of the present disclosure is not limited to faithful implementation of each of the embodiments described above, and each of the features may be combined or partially omitted as appropriate. You can also do it.

For example, in the above-described embodiment, the sensor element 1 has been described as being adopted for a gas sensor. However, the sensor element 1 may be adopted for a sensor other than the gas sensor as long as it is a sensor that utilizes the piezo resistance portion. For example, the sensor element 1 may be adopted as a pressure sensor, an acceleration sensor, or an odor sensor.

For example, in the above-described embodiment, the first conductive type is n-type and the second conductive type is p-type. However, the first conductive type may be p type and the second conductive type may be n type. In this case, when the substrate 10 is a Si substrate, the first impurity is, for example, boron (B) or the like. The second impurity is, for example, phosphorus (P) or arsenic (As).

1,1A Sensor element 10,10A Board 11 Diaphragm 12 Sensitive film 13,14 First area 15 Second area 20,21,22,23 Piezo resistance part 30,31,32,33 Wiring 30A, 31A, 32A, 33A Wiring

Claims (3)

A substrate containing a first conductive type first impurity and a second conductive type second impurity is provided.
The substrate comprises at least one piezo resistance portion containing the second impurity, and a first region containing the first impurity while surrounding the piezo resistance portion in contact with the side portion and the bottom portion of the piezo resistance portion. It has a second region that surrounds the first region and contains the first impurity.
The concentration of the first impurity in the first region is higher than the concentration of the first impurity in the second region.
The substrate has a diaphragm, and a deformable sensitive film is located on the diaphragm.
The piezo resistance portion is a sensor element located outside the sensitive film and around the diaphragm. The sensor element according to claim 1.
The substrate has two piezo resistance portions facing each other.
A sensor element in which the second region is located between the first regions surrounding the two piezo resistance portions. The sensor element according to claim 1 or 2.
A sensor element further comprising wiring electrically connected to the piezo resistance portion.

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