JPH01227929A - Thermal infrared sensor - Google Patents

Abstract

PURPOSE:To improve the output sensitivity of the title sensor in an intermediate infrared band by forming the infrared ray absorbing film of the sensor of a precious-metal film provided with numerous projections of precious-metal particles whose diameters and intervals are within prescribed value ranges. CONSTITUTION:This thermal infrared sensor is provided with an infrared detecting body 1 which absorbs the light energy of infrared rays as heat energy and generates an electric output corresponding to the heat energy and an infrared ray absorbing film 4 formed on the light receiving surface side of the detecting body 1. The film 4 is constituted of a precious-metal film provided with numerous projection of precious-metal particles on its surface on the light receiving side, with the diameters of the projections being set to 0.1-5.0mum and intervals between each particle being set to 0.1-1.5mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a mature light receiving element, and particularly to a thermal infrared sensor that detects infrared light.

[Conventional branch j4 near 1 There are various types of infrared sensors depending on their detection principles, and they are generally divided into two types: aspirational and quantum types. Thermal infrared sensors include pyroelectric infrared sensors, conductive infrared sensors, thermoelectromotive infrared sensors, and thermal expansion infrared sensors. There are conductive infrared sensors, photoelectromagnetic infrared sensors, etc.

Thermal infrared sensors utilize the temperature change of the element itself due to the heat ray action of infrared rays, while quantum infrared sensors treat infrared rays as light and convert them into carriers (based on the photoelectric effect).
It utilizes the excitation of electrons.

Comparing the characteristics of a thermal infrared sensor and a quantum infrared sensor, the thermal infrared sensor has relatively low sensitivity, but its sensitivity does not depend on wavelength, and it can be operated at room temperature, etc., making it practical -1-
There are many advantages.

A pyroelectric infrared sensor is a type of thermal infrared sensor.
Thermal infrared sensors have high sensitivity, so they can be used, for example, for non-contact temperature measurement of high-temperature objects, household cooking devices (microwave ovens,
It is expected to be used in a variety of applications, including intrusion alarms (e.g., ovens).

The pyroelectric infrared sensor will be explained below.

In a pyroelectric infrared sensor, a pyroelectric body, which is an infrared detection body, has spontaneous polarization, and under steady state, it captures floating charges on its surface and maintains electrical neutrality. When infrared light is irradiated here, the infrared light is absorbed as thermal energy, the temperature of the pyroelectric body rises, and the spontaneous polarization inside the pyroelectric body changes.

At this time, the surface charge cannot quickly respond to this change, so if electrodes are formed on both sides of the pyroelectric material, the charge corresponding to the change in spontaneous polarization on the pyroelectric material surface can be extracted as an infrared light signal. Can be done.

By the way, as can be seen from the above-mentioned principle, in order to improve the output sensitivity of an infrared sensor, it is important that there is sufficient absorption of incident infrared rays. Formation of an infrared absorbing film made of platinum or the like has been carried out. Recently, a thin film pyroelectric infrared sensor using a pyroelectric thin film has been developed as an image sensor with multiple elements arranged. As it turns out,
As the amount of transmitted infrared light increases and the absorption decreases,
The role of the infrared absorbing film is important.

[Problems to be Solved by the Invention] A noble metal film constituting a conventional infrared absorbing film has a characteristic that it has a high absorption rate in the near-infrared region, but a high reflectance for light in the mid-infrared region. Therefore, excellent results have been obtained in non-contact temperature measurement of high-temperature objects, that is, sensing in the near-infrared region of around 1 to 2 μm, but the specific temperature of cooking equipment (microwaves, ovens), etc. For use (3 to 15 such as front sensor, flame detection, human body detection, etc.)
There was a problem in that the sensitivity was low even in the mid-infrared region of about μn1.

The present invention has been made to solve the above problems, and its eleventh objective is to provide a thermal infrared sensor having excellent output sensitivity in the mid-infrared region of about 3 to 1.5 It m. .

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to FIG. 1. A thermal infrared sensor absorbs infrared light energy as thermal energy N-, and generates an electrical output corresponding to this thermal energy. The apparatus includes an infrared detecting body 1 that generates infrared rays, and an infrared absorbing film 4 formed on the light receiving surface side of the infrared detecting body.

As shown in FIG. 3, the infrared absorbing film 4 is composed of a noble metal film in which a large number of projections 11 of noble metal particles are formed on the light-receiving surface, and the diameter of the projections is 01 to 5.0 μm. The interval between them is set to 0.1 to 1.5 μm.

[Function] As a result of examining the reasons for whether the noble metal film constituting the conventional infrared absorbing film 4 has a characteristic of having a high absorption rate in the near-infrared region or a high reflectance for light in the mid-infrared region, it was found that It was discovered that since the absorption film 4 has a surface structure as shown in FIG. 4, the reflection becomes thicker. Therefore, since the infrared absorbing film 4 of the present invention has a large number of protrusions 41 on its surface (FIG. 3), the reflected light is not dispersed as it is, but is repeatedly injected and reflected between adjacent protrusions. Therefore, the absorption opportunities (interaction opportunities) of infrared light and infrared absorption yA4 increase, and the formation of the protrusions 41 also increases the light-receiving surface area as a whole, so that the absorption efficiency is improved.

Therefore, in addition to pyroelectric infrared sensors, thermal infrared sensors that absorb infrared light energy as thermal energy and detect infrared light using changes in the temperature of the element, such as conductive infrared sensors, thermoelectromotive infrared sensors, etc. It can also be used in sensors, thermal expansion type infrared sensors, etc.

"Example" FIGS. 1 and 2 show an example in which the present invention is applied to a bulk pyroelectric infrared sensor. In the figure, l is an infrared detector made of a bulk type pyroelectric material, and an upper electrode 2 and an upper electrode 3 made of a metal film are formed on the lower surface of F. Lines -1 to 21.31 extend from the electrodes 2.3 (FIG. 1), and their outputs are input to the circuit on the circuit support board 5 and taken out to the outside.

An infrared absorbing film 4 is formed on the upper surface of the upper electrode 2.

The infrared absorbing film 4 is made of a noble metal film such as platinum or gold, and has a large number of noble metal particle projections 41 on its upper surface.
is formed (Figure 3).

The protrusion 41 has a diameter of 0.1 to 5.0 knots, preferably 0.
．． 3 to 1.6 nozm, the distance between each protrusion is 0.1 to 1.5μ
m, preferably in the range of 0.2 to 0.6 Bm. When the diameter of the protrusion 41 exceeds 5°0 μm, or when the diameter is 0.1. smaller than ilm, the interval is 0.1μ
If it is smaller than m, a sufficient effect on absorption in the mid-infrared region cannot be obtained. Further, even if the diameter is within the above range, if the distance exceeds 1.5 μm, the protrusions are so small that the desired effect cannot be obtained.

The infrared absorbing film 4 having the above-mentioned surface structure can be formed by forming noble metals such as platinum and gold into ultrafine particles by sputtering, vapor deposition in gas, or the like. For example, when the sputtering method is adopted, the introduced gas is argon/oxygen -1/1
The infrared absorption pA4 of the above-mentioned surface structure can be obtained by using the mixed dregs of 1 and adjusting the sputtering gas pressure to 10 Pa and the mixed gas introduction amount to a range of 0.4 to 0.7 Pa.

An example of the manufacturing method is shown below.

As a pyroelectric material, PZ of PbO, ZrO2, TiO2
5n-3b was obtained by baking at 1280°C using a T composition with a small amount of S n O2 and 5b203 added.
A PZT-based ceramic bulk was used as an infrared detector 1.

As a pyroelectric material, NiO2, Nb2 is used for PZTII.
Ni-Nb series)) Z'r ceramics to which O3 is added may also be used. The size of the detection object 1 is 5 mm in diameter,
The thickness was 0.1 mm, the dielectric constant was about 340±20, and the pyroelectric coefficient was 1O±0.5×10 −8 C/cJ −deg.

A film with a thickness of 5000 mm is applied to the upper and lower surfaces of the detection object 1 by sputtering.
A platinum metal film having a diameter of 6000A and a diameter of 4ITtlT+ was formed to serve as an upper electrode 2 and a lower electrode 3, respectively.

The input power was 120 to 130 W, the substrate temperature was 600 °C, the sputtering time was 10 minutes, the introduced gas was 100% argon, and the sputtering gas pressure was 1. This was done while adjusting the displacement so that OPa remained constant.

In the experiment, platinum was used as the electrode material, but an aluminum metal film made by vapor deposition may also be used.

Next, using a platinum target, by sputtering,
A platinum ultrafine particle film was formed on the upper electrode 2 to form an infrared absorbing film 4. The sputtering conditions were: input power 170W;
The substrate temperature was kept constant at room temperature, and a mixed gas of argon/oxygen = 1/1 was used as the gas introduced. Sputter gas) EE
] Sputtering was performed for 30 minutes while adjusting the exhaust volume so that the OPa remained constant, and the diameter was 2ITII1.
1. An infrared absorbing film 4 having a thickness of 3 μm was produced. At this time,
The amount of waste introduced is appropriately selected within the range of 0°4 to 0.7 Pa.

Infrared absorption Jl! FIG. 5 shows the relationship between the amount of gas introduced and the infrared light absorption rate during the production of J4. As a measurement sample, the 6th
As shown in the figure, a glass substrate (NA-40: ) (OY
An aluminum metal film 6 was vapor-deposited as a metal reflection film on 7 made by A Co., Ltd., and an infrared absorption film 4 was formed on the upper surface of the aluminum metal film 6. The film thickness of aluminum metal 11Q6 is 1
[mu]m, and the infrared absorbing film 4 was measured under the above-mentioned conditions, with the amount of gas introduced being varied in the range of 34 to 1°6 Pa, and the respective absorption rates were measured.

The measurement was carried out by a reflection method using a Fourier transform spectrophotometer (FT-IR). As a reference, a glass substrate 7-1 on which only the aluminum metal film 6 was deposited was used, and the reflectance was assumed to be 100%, that is, the absorption rate was 0%.

Further, when this reference was calibrated using a standard mirror, a reflectance value of approximately 100% was obtained. The absorption rate (%) of the sample is determined by the amount of light reflected by the sample...the light reflected on the surface of the infrared absorbing film.
It is defined as the amount of reflected light at the joint surface of the infrared absorbing film and the metal film, and the measurement wavelength range of FT-I (2.5 to 25 μm)
The average value of the absorption rate was adopted. In addition, the amount of sludge introduced was measured using a Schulz vacuum gauge using a sputtering device 5PF21011 (manufactured by TL Dens Anelva Co., Ltd.) by introducing a mixed gas of argon/oxygen-171 during exhaust with the main bulk fully open. Expressed in chamber gas pressure.

As is clear from FIG. 5, the absorption rate has a peak near 0.56 Pa and shows high values in the range of 0.4 to 0.7 Pa.

In addition, if the thickness of the absorbing film is thin, the absorption opportunity will decrease, and if the film is thick, the desired effect cannot be obtained due to the relationship between the heat capacity and heat conduction of the absorbing film itself. It turns out that there are no practical problems.

Next, waste introduction u 0 , 4 P a , 0 , 54
P 21.0.56Pa, 0.6Pa, 0.7P 21
The surface of the infrared absorbing film 4 was observed using a scanning electron microscope (SEM) for five samples prepared under the following conditions, and photographs were taken. As shown in Figure 7, on the surface of the infrared absorbing film 1, there are particles (%vl product) 4
It was found that the four protrusions were lined up at predetermined intervals and had an uneven surface. On the other hand, a similar surface observation of a sample prepared under the condition of 1°Of-)εI revealed that the infrared absorbing film 4 had a surface structure in which particles were densely stacked, as shown in FIG. was. From these comparisons, it became clear that the presence or absence of protrusions was significantly involved in improving the absorption rate.

Furthermore, for the above five samples, SEMff; from the truth,
The diameter of the protrusions and the distribution of the spacing between each protrusion were investigated. SEM
The photographs were taken at arbitrary positions for each of the five samples and taken from directly above.

The diameter of the protrusion was expressed as the diameter of a circle with an area equal to the cross-sectional area of the protrusion. High-speed color image/analysis device 5PI
Image processing was performed using CCA (manufactured by Ichiki Avionics Co., Ltd.) to measure the diameter of the protrusions and the distribution of the distance between each protrusion. It was confirmed that the particles were distributed in the range of .1 to 1.5 μm (7). Note that gas introduction amounts of 0.54 Pa, 0, 56 Pa, 0, 6 show particularly high absorption rates.
Similar measurements were performed on three samples of P a, and the diameter was 0.3 to 1.6 μm, and the distance between protrusions was 0.2 to 0.6
It was Nozm.

Next, a bulk type pyroelectric infrared sensor was manufactured using the manufacturing method described above, and its evaluation was performed. Note that the infrared absorbing film 4
The manufacturing conditions were gas introduction MO and 56 Pa. For comparison, the manufacturing conditions for the infrared absorbing film 4 were set to 1.
I decided to change it to OPa.

The two pyroelectric infrared sensors thus produced were subjected to polarization treatment for 150 cm and 30 minutes, and then the infrared absorbing film 4 was evaluated.

Near L as a light source for measurement system? A 7 μm cross-pass filter was used as a filter to serve as an infrared light source. The output signal was detected as a voltage signal by connecting a load resistance of 1011Ω between the electrodes. Note that since the pyroelectric material and load resistance have high impedance, F
Impedance conversion was performed using ET (K30A, manufactured by Toshiba Corporation). Since the pyroelectric infrared sensor is a differential type detector, the incident light was irradiated through a chopper whose frequency could be varied in the range of 1 to several hundred H7.

The output waveform obtained by irradiating with infrared light was observed using an oscilloscope. As a result of the measurement, it was found that the pyroelectric infrared sensor having the infrared absorbing film 4 manufactured under the conditions of a dust introduction MO of 456 Pa had a dust introduction amount of 1. An output voltage approximately twice as high as that produced under OPa conditions was obtained.

From the above results, the infrared absorbing film 4 has a dramatic absorption rate in the mid-infrared region by forming a large number of noble metal particle protrusions on the surface and setting the diameter of the protrusions and the interval between each protrusion within the range of the present invention. It can be seen that the output sensitivity of the sensor is greatly improved as a result.

In the above embodiment, a bulk pyroelectric infrared sensor using a bulk pyroelectric body was described, but as shown in FIGS. 9 and 10, a pyroelectric thin film is used as the infrared detecting body 1, and It is also possible to have a structure in which the electrode 3, the infrared detector 1, and the upper electrode 2 are laminated in this order. An example of a method for manufacturing a thin film pyroelectric infrared sensor will be described below.

A platinum metal film was formed on the MgO substrate S by sputtering to form the lower electrode 3. The size of the board 8 is 4.5/4
mr+1', the sputtering conditions were an input power of 20 W, a substrate temperature of 600° C., and an introduced gas of 100% argon. The exhaust volume was adjusted so that the sputtering gas pressure was constant at 0.5 Pa, and the film thickness was 1,000 to 20 mm with a sputtering time of 40 minutes.
A metal film of 0OA was formed. At this time, the metal film is
epitaxial growth was performed on top.

On one upper surface of the lower electrode 3, 5n-3 with 10% excess Pb
Using a b-based PZ'F ceramic sputtering target, a film thickness of 8,000 to 100 mm was formed by sputtering.
A 00 size pyroelectric thin film was formed to serve as an infrared detector 1.

Sputtering conditions are input power 100W, substrate temperature 600°.
A mixture of argon/oxygen (1/1) was used as the C1 introduction gas, and the exhaust amount was adjusted so that the sorrel-ivy gas pressure remained constant at 0.3 Pa. Sputtering time is 1
The duration was 20 minutes. Furthermore, formation rIAf&, 900°C1
Annealing was performed in a Pb atmosphere for 2 hours.

On the upper surface of the infrared detector 1, an aluminum electrode with a film thickness of 10,000 A is formed by vapor deposition, and on the upper surface of the aluminum electrode, an infrared absorbing film 4 with a film thickness of 3 μm is formed in the same manner as in the above embodiment. A plurality of elements were formed thereon.

Next, a polarization treatment was performed for 5 seconds and 30 minutes to obtain a thin film pyroelectric infrared sensor. In this case as well, as in the above embodiment, higher output sensitivity than before was obtained.

[Effects of the Invention] In the thermal infrared sensor of the present invention, the infrared absorbing film is composed of a noble metal film in which a large number of projections of noble metal particles are formed on the light-receiving surface, and the diameter of the projections is 0.1 to 5°0 μm. , by setting the interval between each protrusion to 0.1 to 1.5 μm, especially 3 to 1 μm.
The absorption rate of infrared light in the mid-infrared region of about 5 μm increases dramatically. Therefore, the output sensitivity to infrared light in the mid-infrared region is improved, and excellent effects are exhibited in non-contact temperature measurement near room temperature, such as human body detection.

Therefore, in addition to pyroelectric infrared sensors, thermal infrared sensors that absorb infrared light energy as thermal energy and detect infrared light using changes in the temperature of the element, such as conductive infrared sensors, thermoelectromotive infrared sensors, etc. It can also be used in sensors, thermal expansion type infrared sensors, etc.

[Brief explanation of the drawing]

Figures 1 to 3 show one embodiment of the present invention, Figure 1 is a schematic diagram of a bulk pyroelectric infrared sensor, Figure 2 is a partially enlarged sectional view of Figure 1, and Figure 3 is an infrared absorption FIG. 4 is an enlarged sectional view of the surface of the membrane, FIG. 4 is an enlarged sectional view of the surface of a conventional infrared absorbing membrane, and FIG. 5 is a diagram showing the change in absorption rate with respect to the amount of gas introduced.
Figure 6 is a cross-sectional view of the sample used to measure the absorption rate of the infrared absorbing film, Figure 7 is an electron micrograph showing the particle structure of the infrared absorbing film of the present invention, and Figure 8 is the grain structure of a conventional infrared absorbing film. FIG. 9 is a schematic diagram of a thin film pyroelectric infrared sensor showing another embodiment of the present invention, and FIG. 10 is an enlarged sectional view of section A in FIG. 9. 1... Infrared detector 4... Infrared absorbing film 41... Protrusion Figure 1 Figure 4 Figure 3! J! , 5 Figure 6 Figure 7R □)-□Heshi Figure 8 prn

Claims (2)

[Claims] (1) Absorbs infrared light energy as thermal energy,
A thermal infrared sensor comprising an infrared detector that generates an electrical output corresponding to this thermal energy, and an infrared absorbing film formed on the light receiving surface side of the infrared detector, the infrared absorbing film being formed on the light receiving surface side. It is composed of a noble metal film with many noble metal particle protrusions formed on its surface, and the diameter of the protrusions is 0.1 to 5.
．． A thermal infrared sensor characterized in that the distance between each projection is 0.1 to 1.5 μm. (2) The infrared detector comprises a pyroelectric infrared detecting element having at least one pair of electrodes on both sides, and the infrared absorbing film is formed adjacent to the electrode on the light receiving surface side of the pyroelectric infrared detecting element. The thermal infrared sensor according to claim 1.