JPH11258038A - Infrared sensor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a thermopile infrared sensor with high sensitivity and low cost. A thermopile is formed on an upper surface of a heat sink, and each hot junction of the thermopile is covered by an annular infrared absorber. Lens substrate 32 having Fresnel lens 33 on heat sink 22
Are laminated, and the Fresnel lens 33 and the infrared absorber 30 are aligned. Thermopile 29 and infrared absorber 30
Is sealed between the heat sink 22 and the lens substrate 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared sensor for measuring an infrared ray amount, a temperature, a temperature change, and the like using a plurality of thermocouples connected in series.

[0002]

2. Description of the Related Art In recent years, infrared sensors for detecting infrared rays emitted from the human body or the like have been used in various fields such as security devices and ear thermometers.

FIGS. 1 and 2 are a plan view and a partially cutaway perspective view showing the structure of a conventional general thermopile infrared sensor 1 used as a thermal infrared sensor. In the thermopile type infrared sensor 1, a heat insulating thin film 4 is stretched on the upper surface of the cavity 3 in the heat sink 2 having a frame shape. A large number of first thermoelectric materials 5 and second thermoelectric materials 6) are wired, and the heat sink 2
By joining both metals on the upper surface, a cold junction 7 of a thermocouple is formed,
The two metals are joined on the upper surface of the heat insulating thin film 4 to form a hot junction 8 of a thermocouple, and a thermopile 9 in which thermocouples are connected in series
Are provided at both ends. Thermal insulation thin film 4
The hot junction 8 formed on the top is covered with an infrared absorber 11 formed in a rectangular shape. In addition, thermopile 9
Above the infrared absorber 11, an infrared filter 12
Are arranged.

When the infrared light transmitted through the infrared filter 12 is absorbed by the infrared absorber 11 and converted into heat, the cold junction 7 and the hot junction 8 formed on the heat sink 2 are formed.
, A temperature difference is generated between the electrodes 10 of the thermopile 9 to generate an electromotive force. That is, the first and second thermoelectric materials 5,
6, when the temperature of the junction (thermocouple) is T, the thermoelectromotive force generated at the junction is represented by φ (T).
Assuming that m hot junctions 8 are provided on the upper side and m cold junctions 7 are also provided on the heat sink 22, when the temperature of the hot junction 8 is Tw and the temperature of the cold junction 7 is Tc ,
An electromotive force V represented by the following equation (1) is generated between the electrodes 10 at both ends of the thermopile 9. V = m [φ (Tw) −φ (Tc)] Therefore, assuming that the temperature Tc of the heat sink 2 is known, the temperature Tw of the measurement object is measured by measuring the electromotive force V generated between the electrodes 10. It can be measured by contact.

[0005]

In the conventional infrared sensor, the wavelength range of the infrared light incident on the thermopile is determined by the transmittance characteristics of the infrared filter used. Filters are often used. However, the silicon filter has a disadvantage that the sensor easily malfunctions because visible light and near infrared light are transmitted relatively well. For this reason, an infrared filter that cuts off light having a wavelength of 5 μm or less by forming an anti-reflection film (multilayer film) on one or both sides of the filter to cut off light in a wavelength range that becomes noise is also used. (JP-A-4-315927 and JP-A-7-120307). However, such an infrared sensor was very expensive.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and has as its object to provide a highly sensitive and inexpensive infrared sensor.

[0007]

The infrared sensor according to claim 1, wherein the infrared sensor has an infrared absorber whose temperature changes depending on the intensity of infrared light, and an element for converting the temperature of the infrared absorber into an electric signal. A diffraction lens facing the absorber is provided, and the distance between the diffraction lens and the infrared absorber is longer or shorter than the focal length of the diffraction lens for a predetermined wavelength of infrared light.

In the infrared sensor according to the first aspect, since infrared rays are focused on the infrared absorber by a diffractive lens such as a Fresnel lens, the sensitivity can be improved. Moreover, since the distance between the diffractive lens and the infrared absorber is longer or shorter than the focal length of the diffractive lens for a predetermined wavelength of infrared light,
The area of the infrared absorber can be increased, and the efficiency of infrared detection by the infrared absorber can be increased. In addition, the cost can be reduced by using the diffraction lens.

According to a second aspect of the present invention, in the infrared sensor according to the first aspect, the infrared absorber is formed in a ring shape.

In the infrared sensor according to the second aspect of the invention, since the infrared absorber is formed in a ring shape, light outside the predetermined wavelength range can be released to the outer peripheral side and the inner peripheral side of the infrared absorber. Can be selectively detected.

According to a third aspect of the present invention, in the infrared sensor according to the first aspect, the first substrate provided with the infrared absorber and the conversion element and the second substrate provided with the diffraction lens are provided. It is characterized by being stacked and integrated.

Since the infrared sensor according to the third aspect is entirely laminated and integrated, the size of the infrared sensor can be reduced. Further, alignment of the diffraction lens and the infrared absorber can be easily performed.

[0013]

(First Embodiment) FIG. 3 is a partially cutaway perspective view of a thermopile infrared sensor 21 according to an embodiment of the present invention, and FIG. 4 is a sectional view thereof. In the thermopile type infrared sensor 21, a cavity 23 is opened in the upper surface of a central portion of a heat sink 22 formed of a silicon substrate, and a heat insulating thin film 24 is formed on the upper surface of the cavity 23. This heat insulating thin film 24
Is formed by a Si0 ₂ or SiN, is a few microns thick to reduce the heat capacity. At the boundary between the heat sink 22 and the heat insulating thin film 24, the first thermoelectric material 25 and the second thermoelectric material 26 are alternately wired over the upper surface of the heat sink 22 and the upper surface of the heat insulating thin film 24. And the second thermoelectric material 25, 26 are joined to provide a cold junction 27 of a thermocouple, and the first and second thermoelectric materials 25,
26 are joined to provide a thermocouple hot junction 28, thereby forming a thermopile 29 for temperature measurement in which the thermocouples are connected in series (FIG. 5). The region where the hot junction 28 is provided on the heat insulating thin film 24 is, as shown in FIG.
It is annularly covered with an infrared absorber 30 made of black metal such as u or Bi. Electrodes 31 are provided at both ends of the thermopile 29 for temperature measurement. In FIG. 5, the thermopile 29 in the hatched area represents the first thermoelectric material 25, the thermopile 29 in the non-hatched area represents the second thermoelectric material 26, and the shaded area represents the infrared absorbing material. The area where the body 30 is provided is shown.

Further, on the heat sink 22, a lens substrate 32 formed of a silicon substrate is bonded by silicon fusion bonding or the like. An annular Fresnel lens 33 as shown in FIG. 6 is formed on the upper surface of the lens substrate 32. A concave portion 34 is provided on the lower surface of the lens substrate 32, and the concave portion 3 is provided.
4 is joined to the heat sink 22. Therefore, the thermopile 29 and the infrared absorber 30 are hermetically sealed between the heat sink 22 and the lens substrate 32, and the characteristic change of the thermopile 29 and the like is reduced. Further, a nitrogen gas or an inert gas can be sealed inside. Further, a hole 35 for exposing the electrode 31 to the outside is formed in the lens substrate 32 so as to face the position of the electrode 31.

When infrared rays enter the infrared sensor 21, the infrared rays are condensed by the Fresnel lens 33, absorbed by the infrared absorber 30 formed on the hot junction 28, and converted into heat. Then, the heat sink 22
An electromotive force is output between the electrodes 31 of the thermopile 29 due to a temperature difference between the cold junction 27 and the hot junction 28 formed above.

Here, for example, the infrared absorber 30 is formed in a disk shape, and the focal point of the Fresnel lens 33 is set to the infrared absorber 30.
If the light is condensed in a spot at one point, the detection efficiency is increased, but the area of the infrared absorber 30 is reduced and the number of thermocouples of the thermopile 29 cannot be increased, so that the output decreases. Also, high precision is required for the alignment of the optical system.

Therefore, in the present invention, as shown in FIG. 7, the focal point of the Fresnel lens 33 is deliberately shifted so that the infrared ray of the wavelength λ to be detected is located before or behind the position of the infrared ray receiving surface. The light receiving surface is designed so that the infrared ray of the wavelength λ spreads slightly in a ring shape. By determining the position and size of the infrared absorber 30 in accordance with the infrared region slightly expanding in a ring shape on the infrared light receiving surface, the area of the infrared absorber 30 can be enlarged, and the number of thermocouples of the thermopile 29 (temperature The efficiency of detecting infrared rays by the infrared absorber 30 can be increased without reducing the number of contacts. Note that 33A shown in FIG.
Shows the size of the Fresnel lens 33 for comparison (the shadow of the Fresnel lens 33).

Further, as shown in FIG. 8, since the focal length of the Fresnel lens 33 varies depending on the wavelength, the Fresnel lens 33 and the annular infrared absorber 30 are combined, and the width of the annular zone of the infrared absorber 30 is reduced. By adjusting the size of the diameter, it is possible to emit only infrared light in a specific wavelength range. That is, light outside the specific wavelength is deviated to the outer peripheral side or the inner peripheral side of the infrared absorber 30,
The infrared absorber 30 is not irradiated. More specifically, the light of the maximum wavelength in the infrared wavelength region to be detected is irradiated to the outer peripheral edge (or inner peripheral circle) of the infrared absorber 30, and the light of the minimum wavelength is emitted from the infrared absorber 30. Irradiation is performed on the periphery (or outer circumference circle).

If the same effect is to be realized by an infrared filter, processing such as applying a multilayer film for antireflection to both surfaces of the filter is necessary, which is an expensive device. However, if this method is used, it is inexpensive. It can be easily realized. For example, a Si filter allows infrared rays of 1 to 15 μm to pass therethrough.
When it is desired to mainly detect an infrared ray near 0 μm, as shown in FIG. 9, the optical path of the infrared ray having a wavelength of 1 to 5 μm is removed from the infrared absorber 30, and the optical path of the infrared ray having a wavelength of 10 μm (5 to 15 μm) is removed. What is necessary is just to arrange | position the infrared absorber 30.

Further, according to this embodiment, the heat sink 2 having the thermopile 29 and the infrared absorber 30 formed thereon
2 and the lens substrate 32 on which the Fresnel lens 33 is formed, and the thermopile 29 and the infrared absorber 30 are sealed inside, so that alignment of the optical system can be easily performed. Further, since a metal stem, a can case, and the like are not required, the cost can be reduced.

Next, the thermopile type infrared sensor 2
1 will be described with reference to FIG. First, both surfaces of a silicon substrate 36 serving as the heat sink 22 are coated with heat insulating thin films 24a and 24b made of a nitride film or the like [FIG.
(A)]. Next, a plurality of thermocouples made of different kinds of thermoelectric materials such as bismuth and antimony are connected in series on the infrared detection surface side of the silicon substrate 36 to form a thermopile 29 having a plurality of hot junctions 28 and cold junctions 27. At this time, the conductive lines of bismuth and antimony are patterned by a vapor deposition method, a photolithography step, and a lift-off method, respectively (FIG. 10B). Thereafter, an insulating film 37 made of an oxide film or the like is coated on both surfaces of the silicon substrate 36 by sputtering or the like [FIG. 10C]. Silicon substrate 3
6, after partially removing the insulating film 37 formed on the infrared detection surface side according to the pattern of the infrared absorber 30 by a photolithography process, depositing metal black such as gold or bismuth by vapor deposition or sputtering, The infrared absorber 30 covering the hot junction 28 is patterned in a ring shape by a lift-off method, and the insulating film 37 is peeled off (FIG. 10D). Then, holes or slits are formed in the heat insulating thin film 24, and the silicon substrate 36 is anisotropically etched from the infrared detection surface side with a KOH solution or the like, thereby forming the hollow portion 23 and the air insulating heat insulating thin film 24 [FIG. 10 (e)].

On the other hand, a silicon substrate 38 serving as the lens substrate 32 is anisotropically etched to make a hole 35 for taking out the electrode 31 [FIG. A recess 34 is formed by anisotropically etching the surface of FIG.
(G)]. The heat sink 22 thus manufactured and the lens substrate 32 are overlapped, and the electrodes 31 and the holes 35 are aligned and joined [FIG. 10 (h)]. Thereafter, a metal film of Au or Al is deposited or sputtered on the infrared detecting surface side of the lens substrate 32, and a pattern of the Fresnel lens 33 is formed by a photolithography process [FIG.
(I)]. At this time, by using a double-sided aligner, the center of the Fresnel lens 33 and the center of the infrared absorber 30 are formed to coincide. At the same time, the lens substrate 32
The interior space between the heat sink 22 and the heat sink 22 is sealed in a vacuum.

The Fresnel lens 33 includes a silicon substrate 38
Can be formed by isotropic etching, or a Fresnel lens 33 can be formed by forming a metal or organic thin film on the lens substrate 32 and etching it.

(Second Embodiment) FIG. 11 is a sectional view showing a thermopile type infrared sensor 41 according to another embodiment of the present invention. In this embodiment, a thermopile 29, an infrared absorber 30, and a Fresnel lens 33 are formed on one silicon substrate. That is, a cavity 23 is formed on a lower surface of a heat sink (also a lens substrate) 22 formed of a silicon substrate, and a heat insulating thin film 24 is provided on a lower surface of the cavity 23. A thermopile 29 is provided on the lower surface of the heat insulating thin film 24, and an annular heat insulating thin film 24 is formed on the lower surface (or upper surface) of the thermopile 29. The Fresnel lens 33 is formed directly on the upper surface of the heat sink 22 by etching or the like.

According to this embodiment, the Fresnel lens 33 and the thermopile 2 are placed on the front and back of one silicon substrate.
9 and the infrared absorber 30, the alignment of the optical system is facilitated and the cost is reduced.

(Third Embodiment) FIG. 12 is a sectional view showing a thermopile type infrared sensor 42 according to another embodiment of the present invention. In this embodiment, a heat sink 22 on which a thermopile 29 and an annular infrared absorber 30 are formed is formed on a stem 43, and a Fresnel lens is formed on a window 45 of a can case 44 mounted on the stem 43. A lens substrate 32 having a lens substrate 33 is attached.

According to such an embodiment, an existing infrared sensor package can be used.

The infrared absorber is preferably annular as described above, but may be a disk.
In addition, the diffraction lens is not limited to the Fresnel lens,
A zone plate having an annular pattern may be used.

In the above embodiment, the case where a thermopile is used as an element for converting the temperature of the infrared absorber into an electric signal has been described.
A thermistor bolometer or a pyroelectric infrared sensor may be used.

[Brief description of the drawings]

FIG. 1 is a plan view showing the structure of a conventional thermopile infrared sensor.

FIG. 2 is a partially broken perspective view of the infrared sensor according to the first embodiment;

FIG. 3 is a partially broken perspective view showing a structure of a thermopile infrared sensor according to an embodiment of the present invention.

FIG. 4 is a sectional view of the infrared sensor according to the first embodiment;

FIG. 5 is a plan view showing a heat sink of the infrared sensor.

FIG. 6 is a plan view of the above infrared sensor.

FIG. 7 is a diagram illustrating the operation of the above infrared sensor.

FIG. 8 is a view for explaining the function of a Fresnel lens in the infrared sensor of the above.

FIG. 9 is a diagram illustrating a design example of a Fresnel lens and an infrared absorber in the infrared sensor according to the first embodiment.

FIGS. 10A to 10I are manufacturing process diagrams of the infrared sensor according to the first embodiment.

FIG. 11 is a cross-sectional view illustrating a thermopile infrared sensor according to another embodiment of the present invention.

FIG. 12 is a sectional view showing a thermopile infrared sensor according to still another embodiment of the present invention.

[Description of Signs] 22 Heat sink 24 Heat insulating thin film 27 Cold junction 28 Hot junction 29 Thermopile 30 Heat absorber 32 Lens substrate 33 Fresnel lens

Claims (3)

[Claims] 1. An infrared sensor having an infrared absorber whose temperature changes depending on the intensity of infrared light and an element for converting the temperature of the infrared absorber into an electric signal, comprising: a diffraction lens facing the infrared absorber; An infrared sensor wherein the distance between the diffraction lens and the infrared absorber is longer or shorter than the focal length of the diffraction lens for a predetermined wavelength of infrared light. 2. The infrared sensor according to claim 1, wherein the infrared absorber is formed in a ring shape. 3. The apparatus according to claim 1, wherein the first substrate provided with the infrared absorber and the conversion element and the second substrate provided with the diffraction lens are integrated with each other. Infrared sensor.