JPH0581666U - Chip type infrared sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] By eliminating the temperature difference between the various packages enclosing the thermopile element and eliminating the output error due to the radiation from the infrared transmission window, etc., reliability can be improved even in environments with large temperature changes. An infrared sensor capable of obtaining high output is provided. [Structure] A thermopile element formed on a substrate using a silicon wafer was sandwiched between another silicon wafer substrate provided with a groove, and the substrates were bonded together by an anodic bonding method for sealing. [Effect] Since the substrate on which the thermopile element is formed and the substrate serving as the infrared ray transmitting window are in close contact with each other at a very close distance, heat transfer between the two substrates is performed quickly and the temperature of both substrates is always kept at the same temperature. Be done. As a result, the radiation from each part of the package does not change the temperature of the thermopile element, and it is possible to construct a highly reliable infrared sensor that responds only to infrared rays coming from the outside even if the environmental temperature changes greatly.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an infrared sensor using a thermopile element, and more particularly to a structure for sealing a thermopile element.

[0002]

[Prior Art]

 An infrared sensor using the conventional thermopile element 3 will be described with reference to FIG. First, in the thermopile element 3, a pit 30 is provided on the base plate 10 serving as a heat sink 34 coated with an insulating film to form a diaphragm 33, and a thermocouple is formed so that the diaphragm 33 has a hot junction 38 and the heat sink 34 has a cold junction 39. Many 35 are arranged. The substrate 10 is made of a material having a good thermal conductivity such as a silicon wafer.

The thermopile element 3 is generally mounted on a header 90 for a hermetic seal and wire-bonded to take out an output to the outside. The thermopile element 3 has a structure in which the cap 62 is covered and sealed in consideration of temporal stability and physical protection. An inert gas is used as the internal gas at the time of sealing, and usually nitrogen is used. The cap 62 is provided with an infrared transmitting window 6 for introducing infrared rays, and a silicon wafer is used as a material.

The operation of the infrared sensor in which the thermopile element 3 is sealed is as follows. First, the infrared rays emitted from the detection object existing outside the sensor pass through the infrared transmission window 6 and reach the thermopile element 3. Since the diaphragm 33 has a small heat capacity, the temperature of the diaphragm 33 instantly rises due to the infrared rays absorbed, but the heat sink 34 has a large heat capacity and is in contact with the header 90, so that it cannot be easily warmed up. There is a temperature difference. Accordingly, a temperature difference also occurs between the hot junction 38 and the cold junction 39 of the thermocouple 35, so that a DC voltage output can be obtained. Here, it is known that the amount of infrared rays emitted from the detection target is correlated with the temperature of the detection target. Since the thermopile element 3 also emits infrared rays correlated with its own temperature, the temperature rise of the diaphragm 33 is determined by the temperature difference between the object to be detected and the thermopile element 3. In other words, the temperature of the object to be detected can be known using this infrared sensor, and this infrared sensor functions as a radiation thermometer.

By the way, infrared rays reaching the thermopile element 3 are not only from the outside of the infrared sensor. As a matter of course, the infrared transmitting window 6 or the cap 62, which constitutes the infrared sensor, also has a certain temperature, so that the infrared radiation emitted therefrom reaches the thermopile element 3. However, the thermopile element 3, the head 90, the cap 62, and the infrared transmitting window 6 which normally form the infrared sensor are in close contact with each other, and it is considered that all parts have the same temperature due to heat conduction in the steady state. Therefore, the temperature of the diaphragm 33 is not raised by the infrared rays emitted from the infrared ray transmitting window 6 and the cap 62, and the output is not generated. However, this is not the case when a sudden temperature change is given to the infrared sensor from the outside, for example, when the cap 62 is touched with a finger. When the cap 62 is touched, the temperature of the portion in the very vicinity touched first rises, and the heat is transmitted to warm the header 90 and the thermopile element 3. However, in the current infrared sensor having an outer diameter of 4 to 5 mm, no matter how closely the components are in contact, heat cannot be transferred instantaneously, and a temperature difference occurs between the cap portion and the thermopile element 3. Once there is a temperature difference, the infrared radiation emitted from the cap 62 cannot be ignored, that is, the infrared radiation emitted from the cap 62 changes the temperature of the diaphragm 33. This change appears in the form of noise in the output, which makes it impossible for the infrared sensor to correctly measure the temperature of the detection target.

[0006]

[Problems to be solved by the device]

 As described above, in the infrared sensor using the conventional thermopile element 3, when a rapid temperature change is applied, an error occurs in the output due to the radiation from the cap 62 or the infrared transmission window 6, and it is used as a radiation thermometer. There was a problem that I could not do it. Therefore, conventionally, when this infrared sensor was used as a radiation thermometer, the entire sensor was protected by a metal block with a large heat capacity to prevent sudden temperature changes. However, a very large block is necessary to completely eliminate the influence of external temperature changes. Therefore, at present, when this infrared sensor is used as an accurate radiation thermometer, a block of an appropriate size is used, but in the end it is necessary to limit the operating environment. Further, in order to further correct the error, a complicated structure of monitoring the temperature of the infrared transmission window 6 and the cap 62 with another temperature sensor is necessary.

Therefore, an object of the present invention is to solve the above problems, eliminate the temperature difference between the thermopile element 3 and the other parts of the package, and eliminate the output error due to the radiation from the package components such as the infrared transmission window 6. Therefore, it is possible to provide an infrared sensor that can obtain a stable output even in an environment where the temperature changes drastically without the need for a block or the like.

[0008]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, in the present invention, a first substrate made of a silicon wafer having a thermopile element for infrared detection formed on the front surface and a sealing groove on the back surface are provided. A glass substrate is formed on the back surface, a mask made of a metal film is formed on the front surface, and a portion other than the mask is an infrared transparent window. Since the front surface of the first substrate and the back surface of the second substrate are bonded and in close contact with each other by using the anodic bonding technique, the thermopile element on the front surface of the first substrate is sealed between the two substrates. A chip-type infrared sensor having the above structure was manufactured.

[0009]

[Action]

 According to the present invention, since the substrate on which the cold junction of the thermopile element is formed and the substrate serving as the infrared transparent window are in direct contact with each other, the heat transfer between them becomes very fast and the temperature difference hardly occurs. Here, the infrared rays emitted from the infrared transmission window do not change the temperature of the diaphragm of the thermopile element, and the output obtained from the thermopile element is affected only by the infrared rays emitted from the external detection target. Become. Therefore, if this infrared sensor is used for a radiation thermometer, stable and reliable temperature measurement can be performed even in an environment where the temperature changes greatly.

[0010]

【Example】

 An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a main part of a chip type infrared sensor of the present invention, and FIG. 2 is a plan view of a front surface of a first substrate constituting the chip type infrared sensor.

The chip type infrared sensor of the present invention is composed of a first substrate 1 and a second substrate 2 which are two silicon wafers each processed into a unique shape. First, the thermopile element 3 is formed on the front surface of the first substrate 1, and the structure of the thermopile element 3 is as follows. An insulating coating 31 is formed on the front surface of the first substrate 1, and the insulating coating 31 floats up near the center of the first substrate 1 and is spatially separated from the first substrate 1 to form a cavity. The part 32 is made up. Regarding the fabrication of the structure having the cavity 32, first, a metal such as an aluminum film which is easily dissolved is formed on the first substrate 1 and then patterned into the desired shape of the cavity 32. Then, the insulating film 31 made of a SiO ₂ film or a Si ₃ N ₄ film is formed and patterned, and then the aluminum film is melted from the through hole 37. From now on, the insulating coating film 31 at the location corresponding to the cavity 32 becomes the diaphragm 33, and at the portion in contact with the first substrate 1 it becomes the heat sink 34.

A large number of thermocouples 35 are formed on the insulating film 31 so as to form hot contacts 38 on the diaphragm 33 and cold contacts 39 on the heat sink 34. Bismuth and antimony were mainly used for the thermocouple 35. An extraction electrode 36 is formed of aluminum or the like at the end of the thermocouple 35. Although not shown in the figure, a black body using gold black or the like may be formed on the diaphragm to enhance the infrared absorption efficiency.

Next, the second substrate 2 will be described. On the back surface of the second substrate 2, the substrate material silicon itself is processed by etching to form the sealing groove 4. Since the sealing groove 4 needs to have a size in which the thermopile element 3 can be accommodated when the first substrate 1 and the second substrate 2 are bonded together later, its planar shape is larger than that of the insulating film 31 and its depth is large. Needs to be larger than the thickness of the thermopile element 3. Silicon of the substrate material is also etched from the front surface of the second substrate 2 to form an electrode take-out hole 5 penetrating the front surface. An infrared transmitting window 6 is provided on the front surface of the second substrate 2. This is manufactured by forming a mask 61 of a metal film such as chromium on the entire front surface of the second substrate 2 and removing the chromium film by etching to a required size. Therefore, the film thickness of the mask 61 may be opaque to infrared light. Furthermore, a glass film 7 is formed by a method such as sputtering on the back surface of the second substrate 2 at a place which does not correspond to the sealing groove 4 or the electrode lead-out hole 5. Here, low melting point glass was used for the glass film 7.

The first substrate 1 and the second substrate 2 configured as described above are aligned with each other and bonded by an anodic bonding method. With this method, first, the first substrate 1 and the second substrate 2 are brought into contact with each other so that the front surface 11 and the back surface 22 of the second substrate 2 come into contact with each other. At this time, the thermopile element 3 excluding a part of the extraction electrode 36 comes to a position to be housed in the sealing groove 4. Further, the electrode lead-out hole 5 of the second substrate 2 must be sized or positioned so as to be within the surface of the lead-out electrode 36. The contacting portion of both substrates is the contact surface 8 shown in FIG. 2, which corresponds to the portion of the second substrate on which the glass film 7 is formed. After combining, both substrates are heated to about 150 ° C., and a DC voltage of about 100 V is applied so that the first substrate 1 is negative and the second substrate 2 is positive. As a result, the metal ions in the glass film 7 move to the vicinity of the surface, and a large electrostatic attractive force is generated between the two substrates to reach the bonding. Anodic bonding can be performed between glass and silicon, or glass and a metal such as aluminum that easily forms an oxide on the surface, so that both substrates are bonded at the contact surface and are stored in the sealing groove 4. The ill element 3 is completely sealed.

Since this anodic bonding is usually performed in a nitrogen atmosphere, the inside of the sealing groove 4 is filled with nitrogen, and the thermopile element 3 can be kept stable because the influence of oxidation or the like is avoided. Further, the thermopile element 3 can be vacuum-sealed by performing the joining in a vacuum atmosphere, and thereby the output can be greatly improved.

In the present embodiment, a silicon wafer is used for the first substrate 1, but this may be replaced by another metal substrate as long as it has good thermal conductivity and the surface is polished and smooth. Further, a low melting point glass was formed on the second substrate 2, but other materials may be used as long as it is a glass containing an ion component, and the film forming method is not limited to the sputtering method but a vacuum evaporation method, a CVD method. Further, spin coating may be used. . However, in that case, the temperature and voltage, which are the conditions for anodic bonding, change depending on the glass material. For example, when Pyrex glass is used, the temperature is about 400 ° C and the voltage is about 50V. Further, although aluminum is used for the extraction electrode 36 involved in the bonding, other materials such as titanium, nickel, chromium, and iron whose surface is easily oxidized can be used.

[0017]

[Effect of the device]

 As apparent from the embodiments, according to the present invention, since the first substrate, which is a heat sink on which the thermopile element is formed, and the second substrate, which forms the infrared transmitting window, are in close contact, both substrates are The heat transfer between them is rapid and both substrates are always kept at the same temperature. As a result, there is almost no temperature difference between the cold junction temperature and the infrared transmission window, so that radiation from other parts of the package such as the infrared transmission window does not affect the diaphragm temperature of the thermopile element. Disappear. That is, the thermopile element responds only to infrared rays coming from the outside and produces an output. If the infrared sensor of the present invention is used for a radiation thermometer, stable and reliable non-contact temperature measurement can be performed at all times, and it can withstand use especially in a place where environmental temperature changes greatly. Moreover, since it is not necessary to protect with a metal block having a large heat capacity as in the past, it is very advantageous for downsizing the radiation thermometer.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a chip type infrared sensor of the present invention.

FIG. 2 is a plan view of the front surface of the first substrate of the chip type infrared sensor of the present invention.

FIG. 3 is a sectional view of a main part of a conventional infrared sensor.

[Explanation of symbols]

 1 First Substrate 11 First Substrate Front Surface 2 Second Substrate 21 Second Substrate Front Surface 3 Thermopile Element 30 Pit 31 Insulating Film 32 Cavity 33 Diaphragm 34 Heat Sink 35 Thermocouple 36 Extraction Electrode 37 Through Hole 38 Hot junction 39 Cold junction 4 Sealing groove 5 Electrode extraction hole 6 Infrared transmission window 61 Mask 62 Cap 7 Glass film 8 Contact surface 90 Header

Claims (1)

[Scope of utility model registration request] 1. A first substrate made of a silicon wafer having a thermopile element for infrared detection formed on the front surface, a sealing groove formed on the back surface, and a glass film formed on the back surface. And a second substrate made of a silicon wafer in which a mask made of a metal film is formed on the front surface and the portion other than the mask serves as an infrared transmission window, the front surface of the first substrate and the second substrate By using the anodic bonding technology, the back surface is bonded and in close contact,
A chip-type infrared sensor having a structure in which a thermopile element on the front surface of a first substrate is sealed between two substrates.