JP2005207830A - Infrared sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared sensor for detecting an infrared ray in a wavelength band wherein a cut wavelength of a long-wavelength cut filter is approximately a lower limit, without being influenced by a background temperature of a detection object without using an interference filter having a complicated manufacturing method. <P>SOLUTION: A pair is formed by the first infrared ray receiving element wherein filters for cutting infrared rays over a specific wavelength are combined and the second infrared ray receiving element wherein filters are not combined, and this infrared sensor having sensitivity to the infrared ray in the wavelength band wherein the cut wavelength of the filter is approximately the lower limit is constituted by using the difference of the output signals of the two infrared ray receiving elements. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an infrared sensor that detects infrared light in a wavelength band whose cut wavelength is approximately the lower limit of a filter that cuts infrared light of a specific wavelength or more.

Conventionally, pyroelectric elements, thermopiles, and the like have been mainly used as light receiving elements of infrared sensors that can operate at room temperature. However, these light receiving elements absorb infrared rays and then detect infrared rays according to the pyroelectric effect and thermoelectromotive force caused by the heat converted in the light receiving elements, so the selectivity of the detection sensitivity to the infrared wavelength is low, and the human body is more In the case of efficient detection, an interference filter that transmits only a band of 8 to 14 μm far-infrared as a transmission wavelength band is necessary. This interference filter is complicated and difficult to manufacture, which contributes to increasing the cost of the human sensor.
The pyroelectric element utilizes a change in spontaneous polarization accompanying a change in the amount of incident infrared rays. This method has a disadvantage that it is vulnerable to fluctuations in the background temperature of the detection target because a signal is output even when the temperature inside the pyroelectric element changes. Therefore, in order to reduce the influence, an infrared sensor is formed by combining two or four pyroelectric elements, and the change in the amount of infrared rays due to the movement of the detection object is taken as the difference in output signal between the pyroelectric elements. This is suitable for detecting a moving human body. However, when the human body is stationary, there is a problem that the difference between the output signals between the elements is zero and cannot be detected, which is not suitable for use as a human sensor.

  The thermopile can directly detect the temperature of incident infrared rays, and is therefore suitable for detecting a stationary human body. However, since the detection level changes when the background temperature changes as in the pyroelectric element, it is necessary to change the threshold value for identifying the presence or absence of a human body, and there is a problem that the control method becomes complicated. In order to solve this problem, as disclosed in Patent Document 1, an infrared sensor that detects a human body by combining two elements, a dielectric multilayer film interference filter, a differential amplifier, and a reference voltage comparator is disclosed. . However, according to the present invention, two dielectric multilayer interference filters having a complicated manufacturing method are required, and the thermopile has low selectivity for the infrared wavelength as described above. Since a plurality of interference filters are necessarily required, the manufacturing method becomes a factor.

JP-A-5-256698

  An object of this invention is to provide the infrared sensor which detects the infrared rays of the wavelength band which makes the cut wavelength of a long wavelength cut filter the lower limit about.

As a result of intensive studies to solve the above-mentioned problems, the present inventor found that the infrared light-receiving element and the filter that cuts infrared light having a specific wavelength or more are combined, and that the above-mentioned purpose is met. The present invention has been made.
That is, as described in claim 1, a filter that cuts infrared light having a specific wavelength λ ₁ or more, a first infrared light receiving element that detects infrared light that has passed through the filter, and direct infrared light that does not pass through the filter. A second infrared light receiving element that detects the difference between the output signal of the first infrared light receiving element and the output signal of the second infrared light receiving element, thereby reducing the cut wavelength of the filter to about An infrared sensor having sensitivity to infrared rays in the wavelength band λ _{1 to} λ _{2 as} a lower limit is configured.

According to a second aspect of the present invention, in the infrared sensor according to the first aspect, the first and second infrared light receiving elements are both compound semiconductor light receiving elements.
According to a third aspect of the present invention, the first and second infrared light receiving elements are compound semiconductor light receiving elements made of InAs _x Sb _1-x (0 ≦ x ≦ 0.75). The infrared sensor according to claim 1 or claim 2 is configured.
4. The filter according to claim 1, wherein the filter has a characteristic of cutting infrared rays having a specific wavelength λ ₁ of about 5 μm or more. 5. The described infrared sensor is configured.

The infrared sensor according to claim 4, wherein the filter is selected from silicate glass, borosilicate glass, phosphate glass, or soda glass. To do.
The infrared ray according to any one of claims 1 to 5, wherein a filter for cutting visible light is attached to the front surfaces of the first and second infrared light receiving elements. Configure the sensor.

  According to the present invention, it is possible to produce an infrared sensor that is sensitive to infrared rays in a wavelength band that does not use an interference filter and is not affected by the background temperature of the detection target and that has a cut wavelength of the long wavelength cut filter as a lower limit.

The best mode for carrying out the present invention will be specifically described below.
First infrared light receiving element detects the infrared by placing a filter for cutting a specific wavelength lambda ₁ or more infrared to the front of the light receiving element, an infrared second infrared receiving elements directly without passing through the filter An infrared sensor having sensitivity to infrared rays in a wavelength band whose cut wavelength of the filter is approximately the lower limit by detecting and inputting the output signals of the first and second infrared light receiving elements to a differential amplifier to obtain a difference Configure.
As another method for obtaining a difference between output signals of the first and second infrared light receiving elements, a bridge is formed by electrically connecting the first and second infrared light receiving elements in series, You may output from the midpoint.

Here, the specific wavelength λ ₁ indicates the cut wavelength of the filter, and is the approximate lower limit of the detection wavelength band of the infrared sensor in the present invention. The wavelength λ ₂ is the upper limit value of the wavelength at which the infrared light receiving element used in the present invention has light receiving sensitivity.
Next, an embodiment in which the present invention is applied to detect a human body will be described.
A compound semiconductor is preferably used as the infrared light receiving element having good sensitivity in the infrared wavelength range emitted by the human body for the following reasons. As a specific example of the compound semiconductor, InAs _x Sb _1-x ( x is preferably a composition ratio). However, although not limited thereto, Hg _1-x Cd _x Te and Pb _1-x Sn _x Te can be similarly used for the same purpose as other semiconductors.

The light receiving sensitivity distribution of the infrared light receiving element can be determined so as to respond more strongly according to the infrared wavelength distribution emitted when the human body is regarded as a black body of 310 ° K. as shown in FIG. That is, as shown in FIG. 2, the wavelength indicating the maximum detection sensitivity is included in the region of 6 to 14 μm and is determined to have good sensitivity. In order to achieve this object, it is preferable to use a compound semiconductor capable of controlling a desired sensitivity distribution by the composition ratio x as a thin film. When the compound semiconductor is InAs _x Sb _1-x , the composition ratio x is set to 0 ≦ x ≦ 0.75. In this case, the upper limit wavelength λ _{2 at} which the infrared light receiving element has light receiving sensitivity is approximately 6.9 to 11.5 μm. Furthermore, in order to improve the selectivity of infrared rays emitted by the human body more efficiently, it is preferable to set the wavelength indicating the maximum detection sensitivity in the vicinity of the maximum value of the infrared wavelength distribution emitted by the human body. For this purpose, the composition is determined so that the upper limit wavelength λ ₂ having light receiving sensitivity is preferably 9.0 to 11.5 μm. In order to satisfy this condition, the composition ratio x of InAs _x Sb _1-x is more preferably selected from 0.13 ≦ x ≦ 0.58.

When InAs _x Sb _1-x is used as the compound semiconductor, a compound semiconductor thin film can be formed on the substrate using a vacuum deposition apparatus or an MBE (Molecular Beam Epitaxy) apparatus. As the substrate used for this purpose, a GaAs substrate or a Si substrate is preferable. It is also preferable that the compound semiconductor thin film previously formed on the mica substrate is bonded to a GaAs substrate, Si substrate, or glass or plastic substrate using an adhesive, and then the mica is peeled off. This is one of the manufacturing methods.
The thickness of the thin film of InAs _x Sb _1-x is set between 0.1 to 10.0 μm so that infrared rays of the above conditions are absorbed more strongly. As described above, because a compound semiconductor thin film is manufactured on a GaAs substrate or Si substrate using a vacuum evaporation apparatus or an MBE apparatus, a too thin film takes a long time to manufacture and is not practical. Defects generated at the interface tend to adversely affect the characteristics when operated as a light receiving element. Therefore, the thickness of the compound semiconductor thin film is more preferably optimized in the range of 0.5 to 5.0 μm.

As described above, when a compound semiconductor thin film is used as the infrared light receiving element, the infrared light having a wavelength longer than the wavelength corresponding to the band gap energy of the compound semiconductor has no sensitivity. Therefore, the upper limit value on the long wavelength side is naturally set by using a compound semiconductor, and the cutoff characteristic at the upper limit value λ ₂ is a relatively steep characteristic.
The infrared light receiving element of the present invention has light in the near-infrared region having a wavelength of 0.7 to 5 μm and the visible region having a wavelength of 0.4 to 0.7 μm as well as the far infrared region having a wavelength of 5 μm or more on the short wavelength side. However, it will have a slight sensitivity to light. In order to allow light having a wavelength of 6 to 14 μm to be incident on the infrared light receiving element so as to selectively react with far infrared rays emitted by the human body, it is necessary to use the filter in combination with a filter that cuts infrared rays having the specific wavelength or more. In other words, an infrared sensor having a maximum sensitivity in a wavelength region of 6 to 14 μm, using two compound semiconductor infrared light receiving elements as a pair and using one of them as shown in FIG. 4 for cutting infrared light having a wavelength of 5 μm or more. It is a preferable form for the present invention to constitute.

As the filter having the characteristic of cutting infrared rays having a wavelength of 5 μm or more, glass can be used. For example, silicate glass, borosilicate glass, phosphate glass and the like can be preferably used. Furthermore, soda glass having transmission characteristics as shown in FIG. 4 is one of the preferred glasses. However, other materials can be used as long as they can achieve transmission characteristics as shown in FIG.
The thickness of the glass can be freely selected as long as the characteristics as shown in FIG. 4 can be achieved as a filter, but a range of 0.05 to 5.0 mm is preferable. If the thickness is too small outside this range, the mechanical strength is insufficient, and there is a risk of cracking due to an impact such as dropping during the manufacturing process or during use. On the other hand, if it is too thick, it is not preferable from the viewpoint of reducing the thickness and size of the sensor. Accordingly, the thickness of the glass is more preferably selected from the range of 0.1 to 1.0 mm.

By arranging the filter as described above on the front surface of one of the infrared light receiving elements forming a pair, there is no difference in the output of each infrared light receiving element with respect to light in the wavelength region that passes through the filter. Even if it is very small, there is a large difference in the output of the infrared light receiving element with respect to infrared light in a wavelength region that does not pass through the filter. Therefore, by inputting the outputs of the infrared light receiving elements forming a pair to the differential amplifier 3 to obtain the difference, it is possible to configure as a human sensor.
FIG. 5 shows a combination of an infrared light receiving element using a compound semiconductor and a filter that cuts infrared light of a specific wavelength or more, and the infrared sensor of the present invention having sensitivity to infrared light in a wavelength band whose cut wavelength is approximately the lower limit. It is a figure showing a sensitivity characteristic. In other words, by multiplying the sensitivity characteristic of the compound semiconductor infrared light receiving element having a specific composition and the transmission characteristic of the filter that cuts the specific wavelength or more, the cut wavelength λ _{1 of the} filter as shown by the oblique line in the figure is obtained. It is shown that an infrared sensor having sensitivity to infrared rays in the wavelength band λ _{1 to} λ _{2 that} is approximately the lower limit is configured.

Also, the order filter is not 100% transmission at a particular wavelength lambda ₁ or less in the region, even for the original difference not want to occur a specific wavelength lambda ₁ or less of the incident light, the output of the two infrared light-receiving element Although a difference may occur, it can be configured as a human sensor by subsequently attaching a reference comparator that is set to output an on / off signal by identifying with a threshold value. However, if light in the visible region with a large absolute intensity is incident, a difference larger than this threshold value may be generated, and it is possible to set the threshold value so that it does not occur. The sensitivity to light in the detection wavelength band that should have high sensitivity may be lowered, and it is necessary to perform complicated processing to vary the threshold value. Therefore, by arranging the visible light cut filter in front of the two infrared light receiving elements, it is possible to more accurately detect infrared rays in the detection wavelength band, and to provide a human sensor having good sensitivity to far infrared rays emitted by the human body. Is possible. For this purpose, a silicon substrate can be suitably used as a filter that cuts visible light having a wavelength of about 1 μm or less.

  Next, the present invention will be described by Embodiments 1 to 5.

Embodiment 1
As shown in FIG. 1, a filter 2 that cuts infrared light of a specific wavelength or more, a first infrared light receiving element 1 a that detects infrared light that has passed through the filter 2, and a second that directly detects infrared light without passing through the filter. Filter 2 by inputting the output signal of the first infrared light receiving element 1a and the output signal of the second infrared light receiving element 1b to the differential amplifier 3 to obtain a difference. An infrared sensor having sensitivity to infrared rays in a wavelength band whose cut wavelength is approximately the lower limit is configured.

[Embodiment 2]
In order to further reduce the influence of light in the visible region, it is also one of preferable modes of the present invention to use a filter that cuts visible light on two infrared light receiving elements. As shown in FIG. 6, a first infrared light receiving element 1 a that detects infrared light that has passed through a filter 2 that cuts infrared light of a specific wavelength or more, and a second infrared light reception that directly detects infrared light without passing through the filter 2. The visible light cut filter 4 is provided in front of the element 1b and the two infrared light receiving elements 1a and 1b, and signals output from the two infrared light receiving elements 1a and 1b are input to the differential amplifier 3 to obtain a difference. Thus, an infrared sensor having sensitivity to infrared rays in a wavelength band whose cut wavelength of the filter 2 is approximately the lower limit is configured.

[Embodiment 3]
As shown in FIG. 7, a filter that cuts visible light is used as a fixed substrate 5 so as to have a function of fixing the infrared light receiving element, and two infrared light receiving elements 1 a and 1 b are provided on the fixed substrate 5. The filter 2 that cuts infrared light of a specific wavelength or more is attached only to the front surface of one of the infrared light receiving elements 1a, and signals output from the two infrared light receiving elements 1a and 1b are sent to the differential amplifier 3. A difference is obtained by inputting, and an infrared sensor having sensitivity to infrared rays in a wavelength band whose cut wavelength of the filter 2 is approximately the lower limit is configured. At this time, as the fixed substrate 5, a substrate that can be used as a filter for cutting visible light, such as a GaAs substrate, an Si substrate, or a plastic substrate, can be preferably used.

[Embodiment 4]
When a filter that cuts off a specific wavelength or more can be used as the fixed substrate 5 for fixing the two infrared light receiving elements 1a and 1b, as shown in FIG. 8, the two infrared light receiving elements 1a and 1b One infrared light receiving element 1b is fixed to the front surface of the filter with the light receiving surface facing the light source, and the other infrared light receiving element 1a is fixed to the back surface of the fixed substrate 5 with the light receiving surface facing the fixed substrate 5. An infrared sensor having sensitivity to infrared rays in a wavelength band whose cut wavelength of the filter 2 is approximately the lower limit is obtained by inputting the signals output from the two infrared light receiving elements 1a and 1b to the differential amplifier 3 to obtain a difference. To do.

[Embodiment 5]
An InAs _0.35 Sb _0.65 thin film was grown on a GaAs substrate to a thickness of 1.25 μm using an MBE apparatus, and a protective film was formed by element isolation by a semiconductor manufacturing process, and then a two-terminal electrode was attached. An infrared light receiving element chip is manufactured. As shown in FIG. 9, two cut out infrared light receiving elements 1a and 1b are attached to the glass epoxy support package 9 so that the respective light receiving elements 1a and 1b are close to each other, and are directed from the same object in the same direction. It is installed so that the infrared rays of. One infrared light receiving element 1a is provided with a soda glass filter 2 having a thickness of 0.5 mm on the front surface and attached without touching the infrared light receiving element 1a.

The two infrared light receiving elements 1a and 1b are electrically connected in series, and a power source and a ground are connected to both ends thereof. The midpoint potential point is connected to the voltage amplifier 6 through the low-pass filter 8. The output signal of the voltage amplifier 6 is input to a reference comparator 7 in which a threshold value is set in advance. The reference comparator 7 is set so as to output an on signal when the output signal of the voltage amplifier 6 is larger than the threshold value, and an off signal when the output signal is smaller than the threshold value. An infrared sensor having sensitivity to infrared rays is configured.
In addition, when the operation of this infrared sensor was checked, an on signal was output when an infrared ray radiated from a human body at a distance of 1 m from the front end of the sensor was incident. The on signal was not output even when light from the lamp was incident or sunlight was incident.

  The present invention can be suitably used as a human sensor for detecting the presence of a human body.

It is a figure which shows Embodiment 1 of the infrared sensor of this invention description. It is a figure which shows the relative sensitivity distribution of the infrared light receiving element used for this invention. It is a figure which shows 310 degree K black body radiation distribution. It is a figure which shows the transmittance | permeability of soda glass. It is a figure which shows the relative sensitivity and transmittance | permeability in the structure of the infrared sensor of this invention. It is a figure which shows Embodiment 2 of the infrared sensor of this invention description. It is a figure which shows Embodiment 3 of the infrared sensor of this invention description. It is a figure which shows Embodiment 4 of the infrared sensor of this invention description. It is a figure which shows Embodiment 5 of the infrared sensor of this invention description.

Explanation of symbols

1a, 1b Infrared light receiving element 2 Filter 3 Differential amplifier 4 Visible light cut filter 5 Fixed substrate 6 Voltage amplifier 7 Reference comparator 8 Low pass filter 9 Glass epoxy support package

Claims (6)

It comprises a filter that cuts infrared light having a specific wavelength λ ₁ or more, a first infrared light receiving element that detects infrared light that has passed through the filter, and a second infrared light receiving element that directly detects infrared light without passing through the filter. By taking the difference between the output signal of the first infrared light receiving element and the output signal of the second infrared light receiving element, the infrared light in the wavelength band λ _{1 to} λ ₂ having the cut wavelength of the filter as a lower limit. An infrared sensor characterized by having a sensitivity.   The infrared sensor according to claim 1, wherein the first and second infrared light receiving elements are both compound semiconductor light receiving elements. 3. The infrared ray according to claim 1, wherein the first and second infrared light receiving elements are compound semiconductor light receiving elements made of InAs _x Sb _1-x (0 ≦ x ≦ 0.75). Sensor. 4. The infrared sensor according to claim 1, wherein the filter is a filter having a characteristic of cutting infrared rays having a specific wavelength λ ₁ of about 5 μm or more. 5.   The infrared filter according to claim 4, wherein the filter is selected from silicate glass, borosilicate glass, phosphate glass, or soda glass.   The infrared sensor according to claim 1, wherein a filter for cutting visible light is attached to the front surfaces of the first and second infrared light receiving elements.

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