JP7562930B2 - Thermopile Sensor - Google Patents

Description

The present invention relates to a thermopile sensor.

Conventionally, as a type of thermopile sensor, a flow sensor has been proposed that has a heater that is placed in a flow path through which a fluid flows and heats the fluid, a first temperature-sensing element (thermopile) that is placed upstream of the heater in the flow path, and a second temperature-sensing element (thermopile) that is placed downstream (see, for example, Patent Document 1).

As a thermopile type sensor, an infrared sensor is known in which a first temperature-sensing element (thermopile) and a second temperature-sensing element (thermopile) are arranged with the rows of their hot junctions facing each other, and an electromotive force is generated according to the temperature difference between the cold junction and the hot junction. Among these, an infrared sensor has been proposed that has a structure in which aluminum wiring is layered over p-type or n-type polysilicon (for example, Non-Patent Document 1).

Patent No. 5112728 European Patent Application Publication No. 1092962 European Patent Application Publication No. 2930475 Patent No. 5861497

Zhou, Huchuan, et al. "Development of a thermopile infrared sensor using stacked double polycrystalline silicon layers based on the CMOS process." Journal of Micromechanics and Microengineering 23.6 (2013): 065026.

In general, high sensitivity is required for the above-mentioned thermopile-type sensors when measuring temperature. However, for example, due to variations in the dimensions of the cavity area, which is a recess formed under the thermopile and opens to a specific surface side of the substrate, differences in sensitivity may occur for each thermopile, reducing the reliability of the sensitivity to temperature. In addition, when a temperature distribution occurs on the substrate due to the external environment, differences in temperature around the cold junctions may occur for each thermopile, reducing the stability of the sensitivity to temperature. As a result, there are inconveniences such as a decrease in the measurement accuracy of the thermopile-type sensor and a decrease in productivity in order to improve the dimensional accuracy of the cavity area.

In response to this, a thermopile-type sensor has been proposed in which at least a portion of the circuit section, including the integrated circuit, is covered with a metal protective film (see Patent Document 2). In such a thermopile-type sensor, the metal protective film provides an electromagnetic shielding effect and is thought to improve resistance to electromagnetic noise. However, because the parts involved in temperature detection are not covered with a metal protective film, the cold junctions in the thermopile are also heated when the substrate is heated due to the influence of heat from an internal heater or external infrared rays, etc., which can result in the same problem as above of reduced reliability in sensitivity.

The ultimate objective of the present invention is to improve the resistance of thermopile sensors to electromagnetic noise, or to improve measurement accuracy or productivity.

To solve the above problems, the present invention provides:
a cavity area which is a recessed portion opening to a predetermined surface side of the substrate;
a thin film portion formed to cover an opening of the cavity area;
a sensor portion formed on the thin film portion and related to detecting temperature;
a circuit portion formed on a predetermined surface of the substrate and constituting an electric circuit;
the sensor portion includes two or more thermopiles arranged side by side and including a plurality of thermocouples arranged in parallel at a predetermined interval on the thin film portion;
each of the thermocouples has a hot junction formed at an end closer to an adjacent thermopile and a cold junction formed at an end farther from the adjacent thermopile, the hot junction being located on the cavity area and the cold junction being located on a region of the substrate other than the cavity area;
the circuit section, the cold junction, and a part of the area of the thermopile on the cold junction side that overlaps with the cavity area in a plan view are covered with a metal protective film.
It is a thermopile type sensor.

According to the present invention, the thermopile sensor has a monolithic structure with a sensor section and a circuit section on the same substrate, making it easy to realize a small module, and complex signals from the sensor section can be processed in the circuit section. In addition, a hot junction and a cold junction are formed at both ends of the thermocouple, respectively, and by creating a temperature difference between them, an electromotive force can be generated by the Seebeck effect. In addition, the circuit section, the cold junction, and a portion of the area on the cold junction side of the part of the thermopile that overlaps with the cavity area in a plan view are covered with a metal protective film, which provides the effects of improving resistance to electromagnetic noise, improving the measurement accuracy of temperature measurement, and improving productivity.

The present invention may also be a thermopile sensor characterized in that the metal protective film is connected to the ground of the circuit section. In this way, the metal protective film is electrically connected to the ground of the circuit section, making it possible to improve electromagnetic shielding.

In addition, in the present invention, a thermopile sensor may be provided in which a plurality of metal terminals are formed on the substrate, the plurality of metal terminals are exposed to the outside through an opening on the thin film side, some of the plurality of metal terminals are connected to the metal protective film, and the remaining metal terminals of the plurality of metal terminals other than the some of the metal terminals are formed of a metal film and connected to a predetermined signal line of the circuit section, and the metal film has the same thickness as the metal protective film. This allows the metal film forming the metal terminals and the metal protective film to be formed in the same process, simplifying the manufacturing process.

The present invention may also provide a thermopile sensor characterized in that an area of 40 μm or less from the outer periphery of the substrate is not covered by the metal protective film. In this way, laser dicing is applied to the thermopile sensor when it is made into chips in the manufacturing process, but since a laser cannot be incident from above the metal protective film, the application of laser dicing is made possible by leaving an appropriate space that is not covered by the metal protective film.

In addition, the present invention may be a thermopile sensor characterized in that the distance from the end of the opening of the cavity area to the end of the hot junction side of the partial region is 5 μm or more and 100 μm or less. This makes it possible to prevent problems that may occur when the distance from the end of the opening of the cavity area to the end of the hot junction side of the region is too small or too large. Specifically, when the distance from one end of the opening of the cavity area to the other end is 1000 μm, if the distance is 0 μm or more and less than 5 μm, it is difficult to ensure a margin when the dimensions of the cavity area vary. In addition, in the manufacturing process of the thermopile sensor, it is difficult to keep the distance to 0 μm or more and less than 5 μm by etching. In addition, if the distance exceeds 100 μm, the heat of the heater is transmitted through the metal protective film and escapes to the substrate, resulting in a decrease in sensitivity.

In addition, the present invention may be a thermopile sensor in which the main component of the metal protective film is aluminum, a surface protective layer containing a silicon-based material is formed on the surface of the metal protective film, and the surface protective layer is not formed on the multiple metal terminals. According to this, aluminum is relatively inexpensive among metals, so it is possible to reduce manufacturing costs, and since it is a metal that is commonly used when forming integrated circuits, it is easy to manufacture. Furthermore, aluminum has a relatively high ionization tendency among metals and is easily corroded, but the corrosion can be prevented by the surface protective layer. Furthermore, since the surface protective layer is not formed on the metal terminals, the connectivity between the external wiring and the metal terminals can be ensured.

The present invention may also provide a thermopile sensor in which the main component of the metal protective film is gold. This makes it possible to eliminate the need to form a surface protective layer, as gold is less susceptible to corrosion than aluminum. In addition, since gold has high electrical conductivity and thermal conductivity, it is possible to obtain a higher shielding effect and a higher uniform heating effect. Furthermore, gold is also a metal to which external wiring can be connected by wire bonding or the like.

In a modified example of the present invention, a thermopile sensor may be provided on the substrate, and the temperature sensor may be characterized in that the temperature sensor is covered by the metal protective film. This allows the temperature sensor to improve measurement accuracy. Specifically, the temperature sensor can detect the temperature of the cold junction. The absolute value of the temperature of the object can be expressed as the sum of the temperature difference between the hot junction and the cold junction and the temperature of the cold junction. In addition, since the temperature sensor is covered by the metal protective film, heat from the outside is less likely to be transmitted to the temperature sensor, and the temperature sensor itself is prevented from being heated. The modified example of the present invention is often applied to infrared sensors.

In addition, in the present invention, the means for solving the above problems can be used in combination as much as possible.

According to the present invention, in a thermopile sensor having a monolithic structure, the circuit section, the cold junction, and a portion of the area on the cold junction side of the thermopile that overlaps with the cavity area in a plan view are covered with a metal protective film, thereby making it possible to improve resistance to electromagnetic noise, reduce measurement errors in the flow rate of fluids, and improve productivity.

FIG. 2 is a schematic diagram showing an example of a sensor element constituting a flow sensor in an embodiment. FIG. 2 is a cross-sectional view for explaining the mechanism of a sensor element constituting the flow sensor in the embodiment. FIG. 1 is a perspective view illustrating an example of a flow sensor in an embodiment. FIG. 4 is a cross-sectional view for explaining a schematic configuration of an example of the flow sensor shown in FIG. 3 . FIG. 4 is a perspective view showing a modified example of the flow sensor shown in FIG. 3 . FIG. 2 is a cross-sectional view for explaining a schematic configuration of an infrared sensor in an embodiment.

[Application example]
In this application example, a case where the thermopile sensor is applied to a thermal flow sensor will be described. The thermopile sensor according to this application example has a thermopile, and the thermopile is composed of a plurality of thermocouples. Each thermocouple has a hot junction located on the heater side and a cold junction located on the opposite side of the heater and paired with the hot junction.

When the hot junction of a thermocouple senses the heat of the heater, an electromotive force is generated due to the temperature difference with the cold junction, due to the Seebeck effect. When an electromotive force is generated, it becomes possible to detect the temperature difference between the thermopiles, and to observe the value of the fluid flow rate. Here, as the value of the fluid flow rate increases, the value of the temperature difference between the thermopiles also increases, and since the two values are individually correlated, it is possible to obtain the fluid flow rate by measuring the temperature difference between the thermopiles.

The thermopile is placed symmetrically on either side of the heater, with the side where the fluid flows along the flow path during flow rate detection being the upstream side, and the opposite side being the downstream side. The thermopile and heater are also placed on a thin insulating film, with part of the insulating film formed to cover a cavity area, which is a recess that opens onto a specified surface side of the substrate.

A circuit section constituting an electronic circuit is provided on the substrate so as to be adjacent to the area in which the thermopile, heater, and cavity area are located. By providing the circuit section on the substrate, the signal derived from the temperature difference detected by the thermopile can be processed in the vicinity of the thermopile, making it possible to improve noise resistance.

However, the above-mentioned thermopile-type sensor has drawbacks, such as the circuit section being exposed to electromagnetic noise and being affected by it, or a temperature distribution on the board caused by the external environment resulting in a temperature difference between the cold junctions of the thermopile, or an offset voltage being generated when the dimensions of the cavity area vary. As a result, inconveniences may arise, such as a decrease in the measurement accuracy of the thermopile-type sensor or a decrease in productivity in order to improve the dimensional accuracy of the cavity area.

Therefore, in the thermopile sensor of the present invention, the circuit section, the cold junctions located on the substrate in areas other than the cavity area, and a portion of the area on the cold junction side of the thermopile that overlaps with the cavity area in a plan view are covered with a metal protective film. This makes it possible to improve the above-mentioned drawbacks.

Example 1
A thermopile-type sensor according to a first embodiment of the present invention will be described in detail below with reference to the drawings. In the following embodiment, an example in which the present invention is applied to a flow sensor will be described, but the present invention may also be applied to other thermopile-type sensors such as an infrared sensor. The flow sensor according to the present invention is not limited to the following configuration.

<Device configuration>

1 is a schematic diagram showing an example of a sensor element 2 constituting a flow sensor 1 in this embodiment. The flow sensor 1 is a thermal flow sensor that is incorporated in, for example, a gas meter, a combustion device, an internal combustion engine such as an automobile, a fuel cell, other industrial equipment such as medical equipment, and built-in equipment to measure the amount of fluid passing through a flow path. Here, the flow sensor 1 corresponds to a thermopile sensor in the present invention.

Figure 1(a) is a perspective view of a sensor element 2 constituting a flow sensor 1 in this embodiment, and Figure 1(b) is a cross-sectional view of the cross section X-X of Figure 1(a). The sensor element 2 includes a heater (heating portion) 3 and a thermopile (temperature detection portion) 4 arranged symmetrically on either side of the heater 3. The heater 3 is a resistor made of, for example, polysilicon. The shape of the thermopile 4 is approximately rectangular in a plan view. The heater 3 and the thermopile 4 are formed in an insulating thin film 5, which is provided on a silicon substrate 6. Here, the heater 3 and the thermopile 4 correspond to the sensor portion in this invention. The insulating thin film 5 and the silicon substrate 6 correspond to the thin film portion and the substrate in this invention, respectively.

The sensor element 2 detects a value indicating the flow rate of the fluid to be measured based on the temperature detection signals output from the two thermopiles 4. Specifically, the sensor element 2 calculates the difference between the temperature detection signal output from one thermopile 4 and the temperature detection signal output from the other thermopile 4, and obtains a value indicating the flow rate of the fluid to be measured based on the difference. The sensor element 2 then outputs the value indicating the flow rate to an electronic circuit section (described below). Note that although two thermopiles 4 are shown in FIG. 1(a), there is no limit to the number of thermopiles 4 as long as there are two or more.

Although shown in a simplified manner in FIG. 1(a), each thermopile 4 is composed of multiple thermocouples 7 arranged side by side at a predetermined interval on the insulating thin film 5. Each pair of thermocouples 7 has a metal thin film formed on polysilicon wiring, and the polysilicon wiring is connected to the metal thin film at both ends of the thermocouple 7. Of these, the point connected on the same side as the heater 3 is the hot junction 8, and the point connected on the opposite side to the heater 3 is the cold junction 9. In other words, between the two thermopiles 4, the hot junctions 8 are relatively close to each other, and the cold junctions 9 are relatively far from each other.

In addition, a cavity area 10, which is a recess, is provided on the silicon substrate 6 below the heater 3 and thermopile 4 on the insulating thin film 5. The hot junctions 8 are located next to each other on the upper part of the cavity area 10, and the cold junctions 9 are located in the silicon substrate 6 in an area other than the cavity area 10. Heat generated from the heater 3 is released to the cavity area 10, so the diffusion of heat into the silicon substrate 6 is suppressed. Therefore, the temperature of the cold junctions 9 located in the area other than the cavity area 10 on the silicon substrate 6 hardly increases, and a temperature difference with the hot junctions 8 located around the heater 3 is more likely to occur. The temperature difference between the hot junctions 8 and the cold junctions 9 allows for efficient generation of electromotive force.

Figure 2 is a cross-sectional view for explaining the mechanism of the sensor element 2 constituting the flow sensor 1 in this embodiment. In Figure 2, the temperature distribution when the heater 3 generates heat is shown by a dotted ellipse. Note that the temperature distribution closer to the heater 3 is higher. Figure 2(a) shows an example of the temperature distribution when electricity is applied to the heater 3 with no fluid flowing. On the other hand, Figure 2(b) shows an example of the temperature distribution when electricity is applied to the heater 3 with fluid flowing in the direction of the dotted arrow. The heater 3 and the thermopile 4 are arranged side by side in the sensor element 2 along the direction of the dotted arrow. The longitudinal direction of each of the heater 3 and the thermopile 4 is perpendicular to the flow direction of the fluid.

When no fluid is flowing, the heat of the heater 3 is diffused symmetrically around the heater 3. Therefore, in the orientation of FIG.
The temperatures of the heater 3 and the heater 3 are the same. That is, no output voltage is generated from the thermopile 4. On the other hand, when a fluid is flowing, the heat of the heater 3 is affected by the flow of the fluid and does not diffuse symmetrically around the heater 3, but diffuses asymmetrically along the flow of the fluid. Therefore, a difference occurs between the temperature of the hot junction 8 on the left side of the heater 3 and the temperature of the hot junction 8 on the right side of the heater 3 in the orientation shown in FIG. 2(b). Then, an output voltage is generated from the thermopile 4 in proportion to the temperature difference. In addition, since the temperature difference increases according to the flow speed, the magnitude of the flow speed can be detected based on the electromotive force of the thermopile 4. In addition, the positive and negative of the temperature difference between the two hot junctions 8 shown in FIG. 2(b) is reversed depending on the direction of the fluid flow, and the positive and negative of the electromotive force are also reversed, so the direction of the fluid flow can be detected. The sensor element 2 uses this bias in the distribution of heat from the heater 3 to output a value indicating the flow rate.

・・・（１）
なお、Ｔ_ｈはヒータ３の温度、Ｔ_ａはサーモパイル４外側に設けられる周囲温度センサが測定した温度、Ｖ_ｆは流速の平均値、Ａとｂは所定の定数である。 The output voltage ΔV of the sensor element 2 is expressed, for example, by the following equation (1).

...(1)
Here, _Th is the temperature of the heater 3, _Ta is the temperature measured by an ambient temperature sensor provided outside the thermopile 4, _Vf is the average value of the flow velocity, and A and b are predetermined constants.

Figure 3 is a perspective view showing an example of the flow sensor 1 in this embodiment. The flow sensor 1 has a monolithic structure in which the sensor element 2 and the electronic circuit section 11 that constitutes the circuit are provided on the same chip. Note that in Figure 3, a part of the structure of the sensor element 2, i.e., the structure around the heater 3 and the thermopile 4, is shown in a simplified manner. The thermopile 4 is also shown in a simplified manner. The insulating thin film 5 is formed so as to cover the upper surface of the cavity area 10 and the upper surface of the silicon substrate 6 on which the electronic circuit section 11 is formed. The structure shown in Figure 3 includes a metal protective film 12, and in Figure 3, the dotted lines R and S represent the boundaries of the metal protective film 12, and the area surrounded by the dotted lines R and S represents the area covered by the metal protective film 12. The thermal conductivity of the metal protective film 12 provides a uniform heating effect against heat from the outside of the flow sensor 1 and the electric circuit section 11. The electronic circuit section 11 is formed below the metal protective film 12 and is not visible on the surface of the chip, so it is shown by a roughly rectangular dotted line in Figure 3.

An area with a width of 0 μm to 40 μm from the edge of the flow sensor 1 is not covered by the metal protective film. That is, the value of W in Fig. 3 is at least 40 μm. In the manufacturing process of the flow sensor 1, laser dicing is applied when it is made into chips, but since a laser cannot be incident from above on the part covered by the metal protective film 12, it is necessary to leave an appropriate amount of space that is not covered by the metal protective film 12.

The structure shown in FIG. 3 also includes metal terminals 13a to 13e. The metal terminals 13a to 13e are exposed to the outside through openings on the insulating thin film 5 side, and can be connected to external terminals. The metal terminals 13a, 13b, 13d, and 13e are terminals for input and output of the electronic circuit section 11, and are not connected to the metal protective film 12. In this embodiment, the electronic circuit section 12 is formed below the metal protective film 12 between the row of metal terminals 13a to 13e and the thermopile 4 close to the row of metal terminals 13a to 13e, but it may be formed in other parts. For example, it may be formed in the lower part of the metal protective film 12 around the cavity area 10. The areas around the metal terminals 13a, 13b, 13d, and 13e do not have to be covered by the metal protective film 12.

Figure 4 is a cross-sectional view for explaining the schematic configuration of an example of the flow sensor 1 shown in Figure 3. Figure 4(a) is a cross-sectional view of the section Y-Y in Figure 3, and Figure 4(b) is a cross-sectional view of the section Z-Z in Figure 3. In Figure 4(b), the silicon substrate 6 below the electronic circuit section 11 is omitted, and the upper part above the silicon substrate 6 is illustrated in an enlarged vertical direction. As shown in Figure 4(a), the electronic circuit section 11, the cold junction 9, and a part of the area of the thermocouple 7 on the cold junction 9 side of the part overlapping with the cavity area 10 in a plan view are covered by a metal protective film 12. By covering the electronic circuit section 11 with the metal protective film 12, an electromagnetic shielding effect is obtained, and resistance to electromagnetic noise is improved. By covering the cold junction 9 with the metal protective film 12, a temperature difference is less likely to occur between the cold junctions 9 of the two pairs of thermocouples 7, and the measurement error of the flow rate is reduced. By covering a portion of the thermocouple 7 on the cold junction 9 side of the portion that overlaps with the cavity area 10 in a plan view with a metal protective film 12, offset voltage is less likely to occur even if there is variation in the dimensions of the cavity area 10, improving productivity. Here, the electronic circuit section 11 corresponds to the circuit section in this invention.

Also, the distance from one end of the opening of the cavity area 10 to the other end, i.e., the value of Φ in FIG. 4(a) is 1000 μm. In this case, the distance from the end of the opening of the cavity area 10 to the direction from the cold junction 9 side to the hot junction 8 side to the distance covered by the metal protective film 12, i.e., the value of D in FIG. 4(a) is 5 μm or more and 100 μm or less. Here, if the value of D in FIG. 4(a) is less than 5 μm, when the dimensions of the cavity area 10 vary, there is a risk that the part of the thermocouple 7 that overlaps with the cavity area 10 in a plan view cannot be covered by the metal protective film 12. Also, in the manufacturing process of the flow sensor 1, it is difficult to keep the range less than 5 μm by etching. Also, if the value of D in FIG. 4(a) exceeds 100 μm, the heat of the heater 3 is transmitted through the metal protective film 12 and escapes to the silicon substrate 6, so that the sensitivity may decrease. Therefore, by setting the value of D to 5 μm or more and 100 μm or less as in this embodiment, the cavity area 10
Since it is not necessary to strictly control the dimensional variation and it is possible to maintain the sensitivity, the productivity is improved.

The main component of the metal protective film 12 is aluminum or gold. When the main component is aluminum, it is relatively inexpensive among metals, so it is possible to reduce manufacturing costs, and aluminum is a metal that is commonly used when forming the electronic circuit section 11, so the formation of the metal protective film 12 is easy. However, since aluminum has a relatively high ionization tendency among metals and is easily corroded, when it is used as the main component of the metal protective film 12, it is necessary to form a surface protective layer containing a silicon-based material on the surface. The surface protective layer is not formed on the metal film that constitutes the metal terminals 13a, 13b, 13d, and 13e, or on the metal protective film 12 in the metal terminal 13. When the main component is gold, it is not necessary to form a surface protective layer because gold has high corrosion resistance. In this case, the main component of the metal film that constitutes the metal terminals 13a, 13b, 13d, and 13e is also gold, in accordance with the main component of the metal protective film 12.

The cross-sectional view of FIG. 4(b) shows the configuration of the insulating thin film 5, electronic circuit section 11, metal protective film 12, and metal terminals 13a to 13e. The metal terminals 13a to 13e are exposed to the outside through openings on the insulating thin film 5 side. The metal terminal 13c is electrically connected to the metal protective film 12. The metal terminals 13a, 13b, 13d, and 13e are electrically connected to predetermined signal lines of the electronic circuit section 11 formed below the metal protective film 12. Here, the predetermined signal lines include input/output lines, or power supplies and grounds. The thickness T of the metal protective film 12 is equal to the thicknesses T1 to T4 of the metal films constituting the metal terminals 13a, 13b, 13d, and 13e.

[Modification 1]
Next, a first modified example of the present invention will be described. In this modified example, a flow sensor having a different configuration from the flow sensor 1 shown in the first embodiment will be described.

Figure 5 is a perspective view showing a modified example of the flow sensor 1 shown in Figure 3. Note that Figure 5 shows only a simplified view of part of the structure of the sensor element 2, i.e., the structure around the heater 3 and thermopile 4. The thermopile 4 is also shown in a simplified manner. Compared to Figure 3, the arrangement angle of the heater 3, thermopile 4, and cavity area 10 differs by 90 degrees. What is similar is that it has a monolithic structure, the area surrounded by dotted lines R and S is covered by a metal protective film 12, and metal terminals 13a to 13e are formed.

In the configuration shown in FIG. 5, compared to the configuration shown in FIG. 3, the cold junctions 9 are formed at a position away from the electronic circuit section 11, so the cold junctions 9 are less susceptible to the heat generated by the electronic circuit section 11, and temperature differences are less likely to occur between the cold junctions 9 in the two pairs of thermopiles 4. Also, in the configuration shown in FIG. 5, compared to the configuration shown in FIG. 3, the arrangement direction of the heaters 3 and thermopiles 4 is rotated 90 degrees, and the direction in which the flow rate is detected is the short side direction of the chip 1. This makes the fluid to be measured less susceptible to airflow disturbances caused by wire bonding connected to the metal terminals 13a to 13e, improving the detectability of the flow rate. The configuration shown in FIG. 5 can actually be designed.

Example 2
Next, a second embodiment of the present invention will be described. In the first embodiment, an example in which a thermopile sensor is applied to a flow sensor 1 is described, but in this embodiment, an example in which a thermopile sensor is applied to an infrared sensor is described.

Figure 6 is a cross-sectional view for explaining the schematic configuration of the infrared sensor 15 in this embodiment. The basic configuration is similar to that of the flow sensor 1, so a plan view is omitted. Compared to the cross-sectional view of Figure 4 (a), the heater 3 is not provided in Figure 6. Also, an infrared absorbing film or an infrared absorber is applied to the area of the hot junction 8 of the thermocouple 7 as necessary, but is omitted in Figure 6. Infrared rays are irradiated from the outside as a heat source in the direction of the arrow in Figure 6, and the thermocouple 7 is heated. Although the range where the infrared rays hit is wide due to irradiation from the outside, most of the silicon substrate 6 is covered by the metal protective film 12, which prevents the infrared rays from entering, and therefore the temperature rise of the silicon substrate 6 is suppressed. Also, the cold junction 9 is covered by the metal protective film 12, but the hot junction 8 is not covered, so it is possible to generate a larger temperature difference between the hot junction 8 and the cold junction 9 by irradiation with infrared rays.

6A, the infrared sensor 15 of this embodiment is provided with a temperature sensor 14 on the silicon substrate 6 between the electronic circuit section 11 and the cold junction 9. The temperature sensor 14 is capable of measuring the ambient temperature. Here, the ambient temperature refers to the temperature of the cold junction 9 near the temperature sensor 14. By measuring the temperature difference ΔT between the hot junction 8 and the cold junction 9 caused by irradiation of infrared rays and the ambient temperature T _atm , the temperature T of the object can be expressed, for example, by the following formula (2).
... (2)
By using the infrared sensor 15 in this embodiment, it is possible to measure T _atm in addition to ΔT, so that T can be calculated directly.

Furthermore, when the temperature sensor 14 is provided, being covered with the metal protective film 12 improves the thermal conductivity between the cold junction 9 and the temperature sensor 14, making the temperature around them uniform and reducing the error in the calculated value of T. Furthermore, since the temperature sensor 14 is covered with the metal protective film 12, it is possible to prevent the temperature sensor 14 from being heated by infrared radiation. Since the temperature sensor 14 functions as a part of the electronic circuit, it may be built into the electronic circuit section 11 as a part constituting the electronic circuit section 11.

Also, as shown in FIG. 6(b), the electronic circuit section 11 may not be formed on the silicon substrate 6, but may be formed outside the area of the silicon substrate 6. In this configuration, only the temperature sensor 14 is covered by the metal protective film 12. In this case, it is possible to say that the temperature sensor 14 corresponds to the circuit section.

In this embodiment, the temperature sensor 14 may be of a resistance change type, a diode type, a thermistor type, or the like. In addition, in this embodiment, an example in which the temperature sensor 14 is applied to an infrared sensor 15 is shown, but the temperature sensor 14 may also be applied to a flow sensor 1.

In the following, the components of the present invention will be described with reference to the reference numerals in the drawings in order to make it possible to compare the components of the present invention with the configurations of the embodiments.
<Invention 1>
A cavity area (10) which is a recessed portion opening to a predetermined surface side on the substrate (6);
A thin film portion (5) formed so as to cover the opening of the cavity area;
A sensor portion (4) formed on the thin film portion and related to detecting temperature;
A circuit portion (11) formed on a predetermined surface of the substrate and constituting an electric circuit,
The sensor unit includes a plurality of thermocouples (7) arranged in parallel at a predetermined interval on the thin film unit, and has two or more thermopiles (4) arranged side by side;
Each of the thermocouples has a hot junction (8) formed at an end closer to an adjacent thermopile and a cold junction (9) formed at an end farther from the adjacent thermopile, the hot junction being located on the cavity area and the cold junction being located on an area of the substrate other than the cavity area;
the circuit section, the cold junction, and a part of the area of the thermopile on the cold junction side that overlaps with the cavity area in a plan view are covered with a metal protective film (12).
Thermopile type sensor (1).

1: Flow sensor 2: Sensor element 3: Heater 4: Thermopile 5: Insulating thin film 6: Silicon substrate 7: Thermocouple 8: Hot junction 9: Cold junction 10: Cavity area 11: Electronic circuit section 12: Metal protective film 13a-13e: Metal terminal 14: Temperature sensor 15: Infrared sensor

Claims (8)

a cavity area which is a recessed portion opening to a predetermined surface side of the substrate;
a thin film portion formed to cover an opening of the cavity area;
a sensor portion formed on the thin film portion and related to temperature detection;
a circuit portion formed on a predetermined surface of the substrate and constituting an electric circuit;
the sensor unit is a flow sensor having a heater disposed on the thin film portion, and two or more thermopiles , each consisting of a plurality of thermocouples arranged in parallel at a predetermined interval on the thin film portion, arranged symmetrically with the heater in between,
each of the thermocouples has a hot junction formed at an end closer to an adjacent thermopile and a cold junction formed at an end farther from the adjacent thermopile, the hot junction being located on the cavity area and the cold junction being located on a region of the substrate other than the cavity area;
the circuit section, the cold junction, and a part of an area of the thermopile on the cold junction side of a portion overlapping with the cavity area in a plan view , the part being symmetrical with respect to the heater , are covered with a metal protective film.
Thermopile type sensor. The metal protective film is connected to a ground in the circuit portion.
2. The thermopile sensor according to claim 1. A plurality of metal terminals are formed on the substrate,
the plurality of metal terminals are exposed to the outside through openings on the thin film portion side,
Some of the plurality of metal terminals are connected to the metal protective film;
Among the plurality of metal terminals, the metal terminals other than the part of the metal terminals are formed of a metal film and connected to a predetermined signal line of the circuit portion,
The metal film has the same thickness as the metal protective film.
3. The thermopile sensor according to claim 1 or 2. An area having a width of 40 μm or less from the outer periphery of the substrate is not covered by the metal protective film.
The thermopile sensor according to claim 1 . A distance from an end of the opening of the cavity area to an end of the hot junction side of the partial region is 5 μm or more and 100 μm or less.
The thermopile sensor according to any one of claims 1 to 4. The main component of the metal protective film is aluminum,
a surface protection layer including a silicon-based material is formed on a surface of the metal protection film,
The surface protection layer is not formed on the plurality of metal terminals.
The thermopile sensor according to any one of claims 1 to 5. The main component of the metal protective film is gold.
The thermopile sensor according to any one of claims 1 to 5. A temperature sensor is provided on the substrate;
The temperature sensor is covered with the metal protective film.
2. The thermopile sensor according to claim 1.

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