WO2013183453A1

WO2013183453A1 - Thermopile, thermopile sensor using same, and infrared sensor

Info

Publication number: WO2013183453A1
Application number: PCT/JP2013/064327
Authority: WO
Inventors: 恭輔尾崎; 宏行朝比奈
Original assignee: アルプス電気株式会社
Priority date: 2012-06-08
Filing date: 2013-05-23
Publication date: 2013-12-12
Also published as: JP2015155797A

Abstract

[Problem] To provide a thermopile capable of reducing the difference in impedance and the difference in resistor temperature coefficient as viewed from each of a pair of terminals. [Solution] The thermopile includes a semiconductor substrate (20) and a plurality of thermocouples (21) formed on the semiconductor substrate (20). The plurality of thermocouples (21) are connected in series to form a series circuit. The series circuit has a pair of terminals (31, 32) for connecting to an external circuit. A reference potential is connected between the pair of terminals (31, 32).

Description

Thermopile, thermopile sensor and infrared sensor using the same

The present invention relates to a thermopile, a thermopile sensor using the thermopile, and an infrared sensor, and more particularly, a thermopile capable of reducing a difference in impedance and a difference in temperature coefficient of resistance viewed from each of a pair of terminals, and The present invention relates to a thermopile sensor and an infrared sensor using the same.

As temperature sensors used in industrial equipment and thermometers, and sensor elements that measure various heat related physical quantities such as thermal analysis, fluid flow, impurity concentration, and atmospheric pressure, those using thermopiles are known.

FIG. 7 shows a plan view of a conventional thermopile 110. As shown in FIG. 7, the conventional thermopile 110 is configured on a semiconductor substrate 120 in which first thermoelectric material layers 122 and second thermoelectric material layers 123 are alternately connected in series. The first thermoelectric material layer 122 and the second thermoelectric material layer 123 are formed using different materials. The pair of the first thermoelectric material layer 122 and the second thermoelectric material layer 123 includes the thermocouple 121. Configure. The thermopile 110 is configured by connecting a plurality of thermocouples 121 in series. Each thermocouple 121 generates a thermoelectromotive force corresponding to the temperature difference between the first contact 124 and the second contact 125, and the thermopile 110 sums the thermoelectromotive forces of the thermocouples 121 to the same temperature. It is possible to obtain a larger thermoelectromotive force with respect to the difference. And the thermoelectromotive force of the thermopile 110 is taken out from the 1st terminal 131 and the 2nd terminal 132 provided in the both ends of the series circuit.

In recent years, mounting of the thermopile 110 to mobile devices and the like has been studied, and a reduction in size is desired. When the thermopile 110 is downsized, the temperature difference between the first contact 124 and the second contact 125 is reduced, and the electromotive force of each thermocouple 121 tends to be reduced. Therefore, it is necessary to increase the sensitivity of the thermopile 110 by increasing the thermocouples 121 connected in series. However, in this case, increasing the number of thermocouples 121 increases the resistance value between the first terminal 131 and the second terminal 132.

FIG. 8 shows an equivalent circuit diagram of a thermopile sensor 111 in which an instrumentation amplifier 135 is connected to the first terminal 131 and the second terminal 132 of the thermopile 110. As shown in FIG. 8, an external resistor 140 provided outside the semiconductor substrate 120 is connected to one input terminal of the instrumentation amplifier 135. When the thermopile 110 and the instrumentation amplifier 135 are connected without providing the external resistor 140, the resistance 150, which is the resistance component of the thermopile 110, has a large value as described above. The impedance difference when viewed from each of the above becomes large. In this case, an offset of the output V _0ut of the instrumentation amplifier 135 occurs, and an accurate sensor output cannot be obtained. The external resistor 140 is provided to adjust the difference in impedance when viewed from each of the pair of input terminals of the instrumentation amplifier 135, thereby suppressing the occurrence of offset in the instrumentation amplifier 135. Thus, the thermoelectromotive force from the thermopile 110 can be output accurately.

Patent Document 1 discloses an infrared detector using a thermal resistance element such as a thermopile or a bolometer. In the infrared detector of Patent Document 1, an external circuit for adjusting the occurrence of offset due to self-heating of the thermosensitive resistor element is connected.

JP 2005-221264 A

However, in the conventional thermopile sensor 111, it is necessary to provide an external resistor 140 to adjust the impedance difference as shown in FIG. Furthermore, an external resistor 140 having a resistance value equivalent to the resistor 150, which is a resistance component of the thermopile 110, must be provided, and the material selectivity of the external resistor 140 and the design flexibility of the thermopile sensor 111 are reduced.

Further, the resistance 150 of the thermopile 110 and the external resistance 140 have different temperature coefficients, and it is difficult to match them. Therefore, when a temperature change occurs in the usage environment, the resistance value between the resistor 150 of the thermopile 110 and the external resistor 140 changes, and the difference in input impedance when viewed from the instrumentation amplifier 135 becomes large. In this case, a drift occurs in the output V _out from the instrumentation amplifier 135, causing a problem that an accurate sensor output cannot be obtained.

The present invention solves the above-described problem, and can reduce a difference in impedance and a difference in temperature coefficient of resistance when viewed from each of a pair of terminals, a thermopile sensor using the thermopile, and An object is to provide an infrared sensor.

The thermopile of the present invention includes a semiconductor substrate and a plurality of thermocouples formed on the semiconductor substrate, and the plurality of thermocouples are connected in series to form a series circuit, and the series circuit Is provided with a pair of terminals for connection to an external circuit, and a reference potential is connected between the pair of terminals.

According to this, in the series circuit composed of a plurality of thermocouples, the resistance value is divided at the location where the reference potential is connected. Assuming that the divided thermocouples are a first thermocouple group and a second thermocouple group, respectively, the resistance values when viewed from one pair of terminals are the resistance values of the first thermocouple group and the second thermocouple group, respectively. The resistance value of the thermocouple group. Therefore, the impedance difference when viewed from each of the pair of terminals can be reduced as compared with the thermopile of the conventional example. Further, since the first thermocouple group and the second thermocouple group are composed of thermocouples formed of the same material, they have the same temperature coefficient. Therefore, it is possible to reduce the difference in temperature coefficient of resistance when viewed from each of the pair of terminals, and even when a temperature change occurs, the difference in impedance can be reduced as compared with the conventional thermopile. .

According to the thermopile of the present invention, it is possible to reduce the difference in impedance and the difference in temperature coefficient of resistance when viewed from each of the pair of terminals.

In the thermopile of the present invention, it is preferable that the reference potential is connected to a midpoint of the series circuit. According to this, in the series circuit, the impedance and the temperature coefficient of resistance when viewed from each of the pair of terminals can be made equal. In addition, when a thermopile sensor is formed using the thermopile of the present invention, it is not necessary to provide an external resistor for impedance adjustment, so that the size can be reduced. Furthermore, it is possible to suppress the occurrence of drift due to a temperature coefficient shift and obtain an accurate output.

In the thermopile of the present invention, it is preferable that a voltage dividing resistor for generating the reference potential is formed on the semiconductor substrate. According to this, since the voltage dividing resistor can be formed by a thin film process in the same manner as each thermocouple, the resistance value is more accurate than when a voltage dividing resistor (external resistor) is provided outside the semiconductor substrate. Control can be performed, and the size of the sensor can be reduced.

The thermopile sensor of the present invention is characterized by using any one of the above thermopile. According to this, since the difference in impedance when viewed from each of the pair of terminals of the thermopile and the difference in temperature coefficient of resistance are small, impedance adjustment can be easily performed when an external circuit such as an instrumentation amplifier is connected. Or impedance adjustment is not necessary. Furthermore, since the impedance difference can be reduced even when a temperature change occurs, the occurrence of drift can be suppressed and an accurate sensor output can be obtained.

The infrared sensor of the present invention is characterized by using the above-described thermopile sensor. According to this, by reducing the difference in impedance and the temperature coefficient of resistance when viewed from a pair of terminals of the thermopile, the occurrence of offset and temperature drift is suppressed and the measurement accuracy of the infrared sensor is improved. Can be made.

According to the thermopile of the present invention, the resistance value of the series circuit composed of a plurality of thermocouples is divided at the location where the reference potential is connected. Assuming that the divided thermocouples are a first thermocouple group and a second thermocouple group, respectively, the resistance values when viewed from one pair of terminals are the resistance values of the first thermocouple group and the second thermocouple group, respectively. The resistance value of the thermocouple group. Therefore, the impedance difference when viewed from a pair of terminals can be reduced as compared with the conventional thermopile. Further, since the first thermocouple group and the second thermocouple group are composed of thermocouples formed of the same material, they have the same temperature coefficient. Therefore, it is possible to reduce the difference in temperature coefficient of resistance when viewed from each of the pair of terminals, and even when a temperature change occurs, the difference in impedance can be reduced as compared with the conventional thermopile. .

It is a top view of the thermopile in the embodiment of the present invention. FIG. 2 is a cross-sectional view of a thermopile when cut along line II-II in FIG. 1. It is an equivalent circuit diagram of the thermopile of this embodiment. It is an equivalent circuit diagram of the thermopile sensor in the embodiment of the present invention. It is an equivalent circuit diagram which shows the modification of a thermopile, and a thermopile type sensor using the same. It is sectional drawing of the infrared sensor of this invention. It is a top view of the thermopile of a prior art example. It is an equivalent circuit diagram of a thermopile sensor of a conventional example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the top view of the thermopile 10 in this embodiment is shown. FIG. 2 is a cross-sectional view of the thermopile 10 taken along the line II-II in FIG.

As shown in FIG. 1, the thermopile 10 includes a plurality of thermocouples 21 connected in series. Each thermocouple 21 is configured by connecting a first thermoelectric material layer 22 and a second thermoelectric material layer 23 by a first contact 24. The plurality of thermocouples 21 are connected by the second contact 25. Thereby, the some thermocouple 21 is connected in series and comprises a series circuit. A first terminal 31 and a second terminal 32 are connected to the plurality of thermocouples 21 and can be connected to an external circuit.

The first thermoelectric material layer 22 and the second thermoelectric material layer 23 are formed using different materials. In the present embodiment, polysilicon is used as the first thermoelectric material layer 22, and the second thermoelectric material is used. The layer 23 is formed using aluminum. The first thermoelectric material layer 22 and the second thermoelectric material layer 23 are formed by a thin film method such as sputtering, and are patterned by photolithography. Thereby, the thermocouple 21 connected in series as shown in FIG. 1 is formed.

As shown in FIG. 2, the thermopile 10 includes a semiconductor substrate 20, and the semiconductor substrate 20 has a through hole 28 that opens up and down. In the present embodiment, a silicon substrate can be used as the semiconductor substrate 20, and the through hole 28 can be formed by etching from the lower surface of the semiconductor substrate 20. An insulating film 27 formed as a thin film is provided on the upper surface of the semiconductor substrate 20 so as to cover the through hole 28, and a plurality of thermocouples 21 are formed on the upper surface of the insulating film 27. As shown in FIG. 1, the plurality of thermocouples 21 are formed so as to surround the through hole 28, the first contact 24 is in a position overlapping the through hole 28, and the second contact 25 is the semiconductor substrate 20. It is formed in the position which overlaps with the thick part.

As the insulating film 27, a silicon nitride film, a silicon oxide film, or the like can be used. In the present embodiment, the through hole 28 is formed in the semiconductor substrate 20. However, the present invention is not limited to this mode, and a configuration in which a cavity is formed on the upper surface or the lower surface of the semiconductor substrate 20 by etching may be used.

As shown in FIGS. 1 and 2, the first contact 24 is formed on the insulating film 27 located in the through hole 28 having a small heat capacity, and the second contact 25 is a thick wall of the semiconductor substrate 20 having a large heat capacity. It is formed on the insulating film 27 located in the part. Thereby, when a temperature difference arises between the 1st contact 24 and the 2nd contact 25, a thermoelectromotive force generate | occur | produces in the thermocouple 21 by Seebeck effect. As shown in FIG. 1, the thermopile 10 has a plurality of thermocouples 21 connected in series, and the total electromotive force of each thermocouple 21 is output from the first terminal 31 and the second terminal 32 as the output of the thermopile 10. It is taken out.

The electromotive force of each thermocouple 21 is small, and it is difficult to increase the temperature difference between the first contact 24 and the second contact 25 when the thermopile 10 is downsized. The electromotive force of the pair tends to be small. Therefore, in order to increase the output of the thermopile 10, the total sum of electromotive forces of the thermocouple 21 is increased by usually connecting several tens to several hundreds of thermocouples 21 in series. Therefore, the sum total of the resistance values of the plurality of thermocouples 21 also increases. In the thermopile 10 of this embodiment, as shown in FIG. 1, the lead-out wiring layer 26 is led out from the midpoint 34 between the first terminal 31 and the second terminal 32 and connected to the reference potential connection terminal 33. Yes. A reference potential is connected via a reference potential connection terminal 33 to the middle point 34 of the series circuit composed of a plurality of thermocouples 21.

In FIG. 3, the equivalent circuit schematic of the thermopile 10 of this embodiment is shown. Here, a plurality of thermocouples 21 between the first terminal 31 and the midpoint 34 shown in FIG. 1 are defined as a first thermocouple group 21a, and a plurality of thermocouples 21 between the midpoint 34 and the second terminal 32 are provided. The thermocouple 21 is defined as a second thermocouple group 21b. As shown in FIG. 3, the reference potential V _ref is connected to the reference potential connection terminal 33 drawn from the midpoint 34, and the plurality of thermocouples 21 are connected to the first thermocouple group 21 a and the second thermocouple 21 at the midpoint 34. The thermocouple group 21b is divided.

Thus, the resistance values when viewed from the first terminal 31 and the second terminal 32 are the resistance component 50 of the first thermocouple group 21a and the resistance component of the second thermocouple group 21b, respectively. The resistance 51 is as follows. Each thermocouple 21 is formed on the same semiconductor substrate 20 in the same process and has very little variation. Therefore, the resistance 50 of the first thermocouple group 21a and the resistance 51 of the second thermocouple group 21b. The resistance value is almost equal. Therefore, the impedance when viewed from the first terminal 31 and the second terminal 32 can be made substantially equal. As a result, when an external circuit is connected to the first terminal 31 and the second terminal 32 to form a sensor, the influence of the impedance difference between the terminals can be reduced and the offset of the sensor output can be suppressed. it can.

Further, since the first thermocouple group 21a and the second thermocouple group 21b are made of the same material, the resistance 50 of the first thermocouple group 21a and the resistance 51 of the second thermocouple group 21b. And the temperature coefficient can be made substantially equal. Therefore, the temperature coefficient of the impedance when viewed from the first terminal 31 and the second terminal 32 is also equal, and it is possible to suppress the occurrence of a difference in impedance when a temperature change occurs. Thereby, when it is set as a sensor using the thermopile 10, it becomes possible to obtain the exact sensor output, suppressing generation | occurrence | production of the drift by a temperature change.

FIG. 4 shows an equivalent circuit diagram of the thermopile sensor 11 in which the instrumentation amplifier 35 is connected to the thermopile 10 of the present embodiment. As shown in FIG. 4, the first terminal 31 and the second terminal 32 are each connected to an input terminal pair of the instrumentation amplifier 35. A reference potential V _ref is connected to the midpoint 34 of the thermopile 10, and each thermocouple 21 is divided into a first thermocouple group 21a and a second thermocouple group 21b. Thus, to one input terminal of the instrumentation amplifier 35, the thermoelectromotive force of the first thermocouple group 21a is input the reference potential V _ref as a reference, based on the reference potential V _ref to the other input terminal The thermoelectromotive force of the second thermocouple group 21b is input. Then, the voltage input to the input terminal pair is amplified and output as the output voltage _Vout .

In the thermopile sensor 11 shown in FIG. 4, the impedance when viewed from the first terminal 31 and the second terminal 32 of the thermopile 10 is substantially equal, and therefore when viewed from each input terminal of the instrumentation amplifier 35. The impedance is almost equal.

Thereby, it is possible to suppress the occurrence of the offset of the output voltage _Vout caused by the difference in input impedance, and an accurate sensor output can be obtained. Further, since it is not necessary to adjust the impedance, it is not necessary to connect the external resistor 140 for impedance adjustment to the outside of the semiconductor substrate 120 as shown in the conventional thermopile sensor 111 of FIG. The type sensor 11 can be downsized.

In addition, since the temperature coefficient of the impedance when viewed from each input terminal of the instrumentation amplifier 35 can be made equal, even when a temperature change occurs, the occurrence of variations in impedance viewed from each of the input terminal pairs is prevented. can do. Thereby, it is possible to obtain an accurate sensor output by suppressing the occurrence of drift of the output voltage _Vout that occurs when a temperature change occurs.

In the thermopile 10 and the thermopile sensor 11 using the same according to the present embodiment, the middle point 34 of the series circuit composed of a plurality of thermocouples 21, that is, the middle of the first terminal 31 and the second terminal 32. Although a configuration in which the reference potential V _ref is connected to the point 34 is shown, the present invention is not limited to this. A configuration in which the reference potential connection terminal 33 is provided at any location between the first terminal 31 and the second terminal 32 and the reference potential V _ref is connected may be employed.

Even in this case, the impedance difference when viewed from the first terminal 31 and the second terminal 32 of the thermopile 10 can be reduced as compared with the thermopile 110 and the thermopile sensor 111 of the conventional example. As a result, when the thermopile sensor 11 is used, the impedance difference between the input terminals can be easily adjusted, and the material selectivity can be expanded even when an external resistor is provided, and the design flexibility of the thermopile sensor 11 can be increased. it can. Moreover, since each thermocouple 21 has the same temperature coefficient, it is possible to reduce the difference in temperature coefficient when viewed from the first terminal 31 and the second terminal 32 of the thermopile 10. Therefore, when the thermopile sensor 11 is used, it is possible to suppress the occurrence of drift due to a temperature change and obtain an accurate sensor output.

In FIG. 5, the modification of the thermopile 10 of this embodiment and the equivalent circuit schematic of the thermopile sensor 11 using the same are shown. In the thermopile 10 of this modification, a voltage _dividing resistor 41 and a voltage _dividing resistor 42 for generating the reference potential V _ref are formed. As shown in FIG. 5, the voltage dividing resistor 41 and the voltage dividing resistor 42 are connected in series, the supply voltage Vs is applied to one end, and the GND is connected to the other end and grounded. A reference potential is extracted from between the voltage dividing resistor 41 and the voltage dividing resistor 42 and connected to the reference potential connection terminal 33. When the resistance value of the voltage _dividing resistor 41 is R1 and the resistance value of the voltage _dividing resistor 42 is R2, V _ref = V _s × R2 / (R1 + R2) is applied as the reference potential V _ref . By appropriately setting the voltage _dividing resistor 41 and the voltage _dividing resistor 42, the reference potential V _ref can be set with high accuracy. For example, if the voltage dividing resistor 41 and the voltage dividing resistor 42 are formed to have the same resistance value, a value that is ½ of the supply voltage V _s is applied as the reference potential V _ref .

In the present modification, the voltage dividing resistor 41 and the voltage dividing resistor 42 are preferably formed on the semiconductor substrate 20 shown in FIG. According to this, as with each thermocouple 21, the voltage dividing resistor 41 and the voltage dividing resistor 42 can be formed by a thin film process, and the resistance value can be adjusted easily and accurately by trimming with a laser or the like. Is possible. Therefore, the reference potential V _ref can be set by controlling the resistance value with high accuracy.

Although the material used for the voltage dividing resistors 41 and 42 is not particularly limited, it can be formed using the same material as the first thermoelectric material layer 22 or the second thermoelectric material layer 23. In this modification, the voltage dividing resistor 41 and the voltage dividing resistor 42 can be formed using, for example, polysilicon. In this case, the voltage dividing resistor 41 and the voltage dividing resistor 42 and the thermocouple 21 of the thermopile 10 can be formed in the same process, and the manufacturing cost can be reduced.

Further, by forming the voltage dividing resistors 41 and 42 on the semiconductor substrate 20, each thermocouple 21 and the voltage dividing resistors 41 and 42 can be configured as one sensor chip 12, and the reference potential V _ref is set as the reference potential V _ref . There is no need to provide an external resistor to generate. Therefore, miniaturization of the thermopile sensor 11 can be realized.

FIG. 6 shows a cross-sectional view of an infrared sensor 13 using the thermopile sensor 11 of the present invention. In the infrared sensor 13 of the present embodiment, the thermopile sensor 11 is housed in a package. In FIG. 6, sectional drawing of the thermopile 10 used for the infrared sensor 13 of this embodiment is shown.

As shown in FIG. 6, in the infrared sensor 13, an infrared absorption film 29 is formed across the insulating film 27 and each thermocouple 21. The infrared absorption film 29 is formed at a position where the heat capacity overlapping with the through hole 28 is small, and is formed so as to overlap with the first contact 24 of the thermocouple 21 and not overlap with the second contact 25. ing.

When the infrared sensor 13 is irradiated with infrared rays, the infrared absorption film 29 absorbs the infrared rays and the temperature rises. As a result, the temperature of the first contact 24 of the thermocouple 21 increases. On the other hand, since the second contact 25 is formed on the thick part of the semiconductor substrate 20 having a large heat capacity, and the thick part of the semiconductor substrate 20 functions as a heat sink, the temperature of the second contact 25 does not increase. . In this way, a temperature difference is generated between the first contact 24 and the second contact 25 due to infrared irradiation, and an electromotive force is generated in each thermocouple 21 by the Seebeck effect. The sum of the electromotive forces becomes the output of the infrared sensor 13, and the infrared rays can be detected by the change in the electromotive force.

In the infrared sensor 13 of the present embodiment, the thermopile sensor 11 shown in FIG. 4 or 5 is used. Even in this case, since the impedance when viewed from each input terminal of the instrumentation amplifier 35 can be made substantially equal, it is not necessary to provide an external resistor for impedance adjustment outside the semiconductor substrate 20. Therefore, the infrared sensor 13 can be downsized.

Also, the temperature coefficients of the first thermocouple group 21a and the second thermocouple group 21b when viewed from each input terminal of the instrumentation amplifier 35 are substantially equal. Therefore, when the temperature of the thermocouple 21 rises due to the absorption of infrared rays, it is possible to suppress the occurrence of drift due to temperature changes and obtain the highly accurate output of the infrared sensor 13.

In addition, in this embodiment, although the case where the infrared sensor 13 was comprised using the thermopile type sensor 11 was shown, it is not limited to this. For example, the present invention can be applied as a temperature sensor or a flow rate sensor, and the same effect can be obtained when a catalyst layer that reacts with a specific gas is provided to form a gas sensor.

DESCRIPTION OF SYMBOLS 10 Thermopile 11 Thermopile type sensor 13 Infrared sensor 20 Semiconductor substrate 21 Thermocouple 21a 1st thermocouple group 21b 2nd thermocouple group 22 1st thermoelectric material layer 23 2nd thermoelectric material layer 24 1st contact 25 25th 2 contacts 26 Lead-out wiring layer 27 Insulating film 28 Through-hole 29 Infrared absorbing film 31 First terminal 32 Second terminal 33 Reference potential connection terminal 34 Middle point 35 Instrumentation amplifier 41, 42 Voltage dividing resistor 50, 51 Resistance

Claims

A semiconductor substrate;
A plurality of thermocouples formed on the semiconductor substrate;
The plurality of thermocouples are connected in series to form a series circuit,
The series circuit is provided with a pair of terminals for connection to an external circuit,
A thermopile, wherein a reference potential is connected between the pair of terminals.
The thermopile according to claim 1, wherein the reference potential is connected to a midpoint of the series circuit.
3. The thermopile according to claim 1 or 2, wherein a voltage dividing resistor for generating the reference potential is formed on the semiconductor substrate.
A thermopile sensor using the thermopile according to any one of claims 1 to 3.
An infrared sensor using the thermopile sensor according to claim 4.