JP3580126B2 - Infrared sensor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an infrared sensor that measures an infrared amount, a temperature, a temperature change, and the like using a plurality of thermocouples connected in series.
[0002]
[Prior art]
2. Description of the Related Art In recent years, infrared sensors that detect infrared rays emitted from a human body or the like have been used in various fields such as security devices and ear thermometers.
[0003]
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 provided on the upper surface of the cavity 3 in the heat sink 2 having a frame shape, and two kinds of metals or semiconductors (from the upper surface of the heat sink 2 to the upper surface of the heat insulating thin film 4). A large number of first thermoelectric materials 5 and second thermoelectric materials 6) are wired, and the two metals are joined on the upper surface of the heat sink 2 to form the cold junction 7 of the thermocouple. A pair of hot junctions 8 is formed, and electrodes 10 are provided at both ends of a thermopile 9 in which thermocouples are connected in series. The hot junction 8 formed on the heat insulating thin film 4 is covered by a rectangular infrared absorber 11. An infrared filter 12 is provided above the thermopile 9 and the infrared absorber 11.
[0004]
Thus, when the infrared light transmitted through the infrared filter 12 is absorbed by the infrared absorber 11 and converted into heat, a temperature difference occurs between the cold junction 7 and the hot junction 8 formed on the heat sink 2, causing the thermopile 9 to move. An electromotive force is generated between the electrodes 10. That is, when the temperature of the junction (thermocouple) of the first and second thermoelectric materials 5 and 6 is T, the thermoelectromotive force generated at the junction is represented by φ (T). Is provided with m hot junctions 8, and m cold junctions 7 are also provided on the heat sink 22. If 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 can be measured in a non-contact manner by measuring the electromotive force V generated between the electrodes 10.
[0005]
[Problems to be solved by the invention]
In a conventional infrared sensor, the wavelength range of infrared light incident on the thermopile is determined by the transmittance characteristics of the infrared filter used. However, since the infrared filter is inexpensive, a silicon filter is 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 causes noise is also used. (JP-A-4-315927 and JP-A-7-120307). However, such an infrared sensor was very expensive.
[0006]
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]
DISCLOSURE OF THE INVENTION
The infrared sensor according to claim 1 includes an infrared absorber whose temperature changes depending on the intensity of infrared light, an element that converts the temperature of the infrared absorber into an electric signal, and a diffraction lens facing the infrared absorber. In the infrared sensor, the infrared absorber is formed in a ring shape and covers a temperature sensing portion of the conversion element, and the diffraction lens is formed in a ring shape so that an optical axis thereof coincides with a center axis of the infrared absorber. are formed on, the wavelength distance between the diffractive lens and the infrared-absorbing body is longer than the focal length of the diffractive lens against infrared wavelength to be detected, or so as to short be detected having passed through the diffraction lens The infrared ray is spread over a region coinciding with the infrared absorber and irradiated to the infrared absorber .
[0008]
In the infrared sensor according to the first aspect, since infrared rays are focused on the infrared absorber by a diffractive lens such as an annular Fresnel lens, sensitivity can be improved. Moreover, since the distance between the diffractive lens and the infrared absorber is set to be longer or shorter than the focal length of the diffractive lens for the infrared wavelength to be detected, the area of the infrared absorber can be increased, and the infrared absorber can be expanded. Can increase the efficiency of detecting infrared rays. In addition, the cost can be reduced by using a diffraction lens.
Furthermore, in the infrared sensor according to claim 1, since the infrared absorber is formed in a ring shape and covers the temperature sensing portion of the conversion element, the wavelength is shorter than the infrared wavelength to be detected. Light can escape to the inner peripheral side of the infrared absorber, and only infrared light in the wavelength range to be measured can be selectively detected.
[0009]
An embodiment according to claim 2 is the infrared sensor according to claim 1, wherein a distance between the diffraction lens and the infrared absorber is longer than a focal length of the diffraction lens with respect to an infrared wavelength to be detected. Light having a wavelength shorter than the infrared wavelength to be detected is transmitted through the diffractive lens and passes through the opening of the infrared absorber.
[0010]
Embodiment according to claim 3, Keru Contact the infrared sensor of claim 1 wherein said diffractive lens is characterized by a Fresnel lens of an annular shape is formed on the upper surface of the silicon substrate.
[0011]
An embodiment according to claim 4 is the infrared sensor according to claim 1, wherein the first silicon substrate provided with the infrared absorber and the conversion element and the second silicon substrate provided with the diffraction lens are provided. It is characterized by being stacked and integrated.
[0012]
Since the infrared sensor according to the third aspect is entirely laminated and integrated, the size of the infrared sensor can be reduced. In addition, alignment of the diffraction lens and the infrared absorber can be easily performed.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st 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 this 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. The thermal insulation 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 is joined to provide a thermocouple cold junction 27, and the first and second thermoelectric materials 25, 26 are joined on the upper surface of the heat insulating thin film 24 to provide a thermocouple hot junction 28, This forms a thermopile 29 for temperature measurement in which thermocouples are connected in series (FIG. 5). As shown in FIG. 5, the region on the heat insulating thin film 24 where the hot junction 28 is provided is annularly covered with an infrared absorber 30 made of metal black such as Au or Bi. Electrodes 31 are provided at both ends of the thermopile 29 for temperature measurement. In FIG. 5, the thermopile 29 in the shaded 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.
[0014]
Further, on the heat sink 22, a lens substrate 32 formed of a silicon substrate is bonded by silicon fusion bonding or the like. On the upper surface of the lens substrate 32, an annular Fresnel lens 33 as shown in FIG. 6 is formed. A concave portion 34 is provided on the lower surface of the lens substrate 32, and the periphery of the concave portion 34 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, so that a change in characteristics 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.
[0015]
When infrared light enters the infrared sensor 21, the infrared light is collected by the Fresnel lens 33, absorbed by the infrared absorber 30 formed on the hot junction 28, and converted into heat. Then, 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 on the heat sink 22.
[0016]
Here, for example, if the infrared absorber 30 is formed into a disk shape and the focal point of the Fresnel lens 33 is focused on one point of the infrared absorber 30 in a spot shape, the detection efficiency becomes higher, but the area of the infrared absorber 30 becomes smaller. The output is reduced because the number of thermocouples of the thermopile 29 cannot be increased. Also, high precision is required for alignment of the optical system.
[0017]
Therefore, in the present invention, as shown in FIG. 7, the focal point of the Fresnel lens 33 is deliberately shifted such that the infrared light of the wavelength λ to be detected is located in front of or behind the position of the infrared light receiving surface. It 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 increased, 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. 7 indicates the size of the Fresnel lens 33 for comparison (the shadow of the Fresnel lens 33).
[0018]
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 and the diameter of the annular zone of the infrared absorber 30 are increased. By adjusting the distance, only infrared rays in a specific wavelength range can be emitted. That is, the light outside the specific wavelength is deviated to the outer peripheral side or the inner peripheral side of the infrared absorber 30, so that 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 on 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).
[0019]
To achieve the same effect with an infrared filter, an expensive device is required because processing such as applying a multilayer film for anti-reflection to both sides of the filter is required, but this method is inexpensive and easily realized. can do. For example, a Si filter allows infrared rays of 1 to 15 μm to pass therethrough, but cuts out wavelengths of 5 μm or less, and when it is desired to mainly detect infrared rays having a wavelength of about 10 μm, as shown in FIG. The infrared light path may be removed from the infrared light absorber 30 and the infrared light absorber 30 may be arranged in the infrared light path portion having a wavelength of 10 μm (5 to 15 μm).
[0020]
According to this embodiment, the heat sink 22 on which the thermopile 29 and the infrared absorber 30 are formed and the lens substrate 32 on which the Fresnel lens 33 is formed are laminated to seal the thermopile 29 and the infrared absorber 30 inside. Therefore, alignment of the optical system can be easily performed. Further, since a metal stem, a can case, and the like are not required, cost can be reduced.
[0021]
Next, a method for manufacturing the thermopile infrared sensor 21 will be described with reference to FIG. First, heat insulating thin films 24a and 24b made of a nitride film or the like are coated on both surfaces of a silicon substrate 36 serving as the heat sink 22 (FIG. 10A). 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]. After the insulating film 37 formed on the infrared detecting surface side of the silicon substrate 36 is partially removed in accordance with the pattern of the infrared absorber 30 by a photolithography process, metal black such as gold or bismuth is deposited by vapor deposition or sputtering. Then, the infrared absorber 30 covering the hot junction 28 is patterned into an annular shape by the lift-off method, and the insulating film 37 is peeled off (FIG. 10D). Then, holes or slits are made 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 to form the hollow portion 23 and the air insulating heat insulating thin film 24 [FIG. 10 (e)].
[0022]
On the other hand, a silicon substrate 38 serving as the lens substrate 32 is anisotropically etched to form a hole 35 for taking out the electrode 31 [FIG. The recess 34 is formed by anisotropic etching [FIG. 10 (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. 10 (i)]. At this time, by using a double-sided aligner, the center of each of the Fresnel lens 33 and the infrared absorber 30 is formed to coincide. At the same time, the internal space between the lens substrate 32 and the heat sink 22 is sealed in a vacuum.
[0023]
The Fresnel lens 33 can be formed by isotropically etching the silicon substrate 38. Alternatively, a metal or organic thin film is formed on the lens substrate 32, and the Fresnel lens 33 is formed by etching the thin film. It may be formed.
[0024]
(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 serving as 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.
[0025]
According to such an embodiment, since the Fresnel lens 33, the thermopile 29, and the infrared absorber 30 are provided on the front and back of one silicon substrate, alignment of the optical system is facilitated and the cost is reduced. .
[0026]
(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 provided on a window 45 of a can case 44 mounted on the stem 43. A lens substrate 32 having a lens 33 is attached.
[0027]
According to such an embodiment, a package form of an existing infrared sensor can be used.
[0028]
The infrared absorber is preferably annular as described above, but may be in a disk shape. Further, the diffraction lens is not limited to the Fresnel lens, and a zone plate having an annular pattern may be used.
[0029]
Further, 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, but a thermistor bolometer or a pyroelectric infrared sensor may be used as this conversion element. .
[Brief description of the drawings]
FIG. 1 is a plan view showing a 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 of the above.
FIG. 6 is a plan view of the above infrared sensor.
FIG. 7 is an explanatory diagram of an operation of the infrared sensor.
FIG. 8 is a diagram illustrating the function of a Fresnel lens in the infrared sensor according to the first embodiment.
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.
[Explanation of symbols]
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 (4)

In an infrared sensor having an infrared absorber whose temperature changes depending on the intensity of infrared light, an element that converts the temperature of the infrared absorber into an electric signal, and a diffraction lens facing the infrared absorber,
The infrared absorber is formed in a ring shape and covers a temperature sensing portion of the conversion element,
The diffraction lens is formed in an annular shape so that its optical axis coincides with the central axis of the infrared absorber,
The distance between the diffractive lens and the infrared absorber is longer or shorter than the focal length of the diffractive lens for the infrared wavelength to be detected, and the infrared light of the wavelength to be detected transmitted through the diffractive lens is the infrared light. An infrared sensor, wherein the infrared sensor extends to a region coinciding with the absorber and irradiates the infrared absorber. The distance between the diffractive lens and the infrared absorber is longer than the focal length of the diffractive lens with respect to the infrared wavelength to be detected, and light having a wavelength shorter than the infrared wavelength to be detected passes through the diffractive lens. The infrared sensor according to claim 1, wherein the infrared light passes through an opening of the infrared absorber. The diffractive lens, characterized in that it is a Fureneruren's zonal formed on the upper surface of the silicon substrate, the infrared sensor according to claim 1. The infrared ray according to claim 1, wherein a first silicon substrate provided with the infrared absorber and the conversion element and a second silicon substrate on which the diffraction lens is formed are stacked and integrated. Sensors.

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