JPH03146831A - Infrared detector - Google Patents

Abstract

PURPOSE: To obtain sufficiently high absorption even if the optical thickness of the film between first and second conductors is smaller than 1/4 a selected wavelength by allowing a reflector to be spaced apart from the third conductor on the second surface of the film along a radiation passage. CONSTITUTION: A detection element is composed of a multilayered structure consisting of a film 10, conductors 21, 22 and a gap 28. The film 10 has temp. dependence and is constituted of a solid liquid crystal substance changing the polarizing mode of light passed through or reflected from the film 10. The opposed surface 26 of a mount device 25 spaced apart from the conductor 22 is made reflective with respect to a predetermined range of radiation and the optical thickness n.t of the film 10 between the conductors 21, 22 is set to 1/4 the selected wavelength λS within a predetermined wavelength range or less and the optical thickness n.t of the film 10 and the conductor 22 on the side opposed to a reflecting surface 26 are constituted of a resistance layer showing sufficient effective area resistance Z2 to almost absorb reflected radiation within the predetermined wavelength range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an infrared detection device for detecting infrared radiation within a predetermined wavelength range (e.g. 8-14 μm wavelength) comprising a flexible film having temperature-dependent properties. It is related to.

The film can for example have pyroelectric and/or ferroelectric properties or comprise a liquid crystal material. Such a device according to the invention can be used, for example, in thermal radiation sensing systems for intruder detection or in relatively inexpensive infrared cameras or other thermal imaging devices.

BACKGROUND OF THE INVENTION One problem associated with such infrared radiation detection devices is the need to ensure sufficient absorption of incident radiation at the wavelength of interest. Pyroelectric and/or ferroelectric materials (and also liquid crystals) suitable for sensing elements often exhibit relatively low absorption over at least a portion of the wavelength range in which these sensing elements are to operate.

It is desirable to make the film (and its support layer) very thin, especially in order to reduce its heat capacity and its heat transfer to the surroundings. However, the thinner the film material, the lower the overall absorption of incident radiation by the film material.

European Patent Application Publication No. 0269161 (JP-A-63-134921) discloses an infrared detection device that detects infrared radiation within a predetermined wavelength range, and this device is a (pyroelectric) ) at least one sensing element having a multilayer structure comprising a flexible film having temperature-dependent properties along the radiation path, the first and second electrical conductors of the sensing element being connected to the first and second opposing surfaces of the film a first conductor on a first surface facing the incident radiation, comprising a resistive layer providing a sufficient sheet resistance to absorb a large portion of the incident radiation within a predetermined wavelength range; A reflector facing the second surface of the film is provided behind the film to reflect radiation transmitted through the film.

In the device disclosed in EP-A-0269161, the reflector is formed by a second conductor having a sufficiently low sheet resistance so that the radiation is reflected back to the absorbing first conductor layer at the second surface of the film. ing. The film is supported on a mounting device such that at least a majority of the area of the second surface of the sensing element is not in contact with the mounting device and is spaced apart from an opposing surface of the mounting device by an air gap. This mounting arrangement reduces heat transfer to and from the sensing element, thereby increasing the temperature responsiveness of the film to incident absorbed radiation.

In this known device of [EP-A-0269161] the radiation absorption of the pyroelectric polymer film is increased in order to improve the sensitivity of the device. This is achieved by providing the first conductor with a suitable sheet resistance to provide sufficient absorption of the incident radiation and selecting the thickness of the film such that reflection of the radiation is reduced. Reflection occurs when the optical thickness of the film (i.e. the product of its physical thickness and its refractive index) is 1/4
It reaches its minimum at a wavelength that is an odd multiple of the wavelength. The maximum wavelength bandwidth over which reflection is reduced is approximately 1 wavelength at which the optical thickness is selected.
/4. This choice of wavelength is based on the fact that reflection increases fairly rapidly as the wavelength of the incident radiation decreases from the selected value to half its value, but increases fairly slowly as the wavelength increases from the selected value and that the film material and device window It is necessary to take into consideration the spectral absorption characteristics of the front optical element such as: When the detection device is adapted for use in detecting infrared radiation of a human body (e.g. in an intruder detection device) or other room temperature objects, the wavelength of interest is approximately 5-15 μm, and the radiation by the resistive conductor layer is The absorption is chosen to be maximum at a wavelength of 8 μm. In this case, the optical thickness of the film is selected to be about 1/4 of this wavelength, ie about 2 μm.

The conductor on the first surface of the film of the device of EP-A-0269161 faces free space and is chosen to have a sheet resistance of approximately 377 Ω/mouth (this is the characteristic impedance of free space). Optimal absorption of radiation. The conductive layer on the second surface of the pyroelectric film is reflective with a sheet resistivity on the order of 5 Ω/hole or less adjacent to the film.

British Patent Application Publication (GB-^) No. 2173038 (JP 61-226623) European Patent Application Publication (EP-
A) No. 0272731 (Unexamined Japanese Patent Publication No. 61149525)
discloses another construction of an infrared detection device in which the first conductor is provided with an appropriate sheet resistance to absorb the incident radiation and is preceded by one or more 174 wavelength thick dielectric support layers. .

UP-^-0269161, EP-A-0272
The structures disclosed in No. 731 and GB-A21-3038 provide very efficient absorption of the infrared radiation to be detected. In a particular example, the optical thickness of the pyroelectric material is EP-A
-0269161, it is about 2 μm (1/4 wavelength), and BP -A -0272731 and GB -A
-2173038 is one order of magnitude larger.

In order to produce infrared detection elements with low thermal mass, short response time, wide spectral response and high sensitivity, Langmuir Blodgett films and liquid crystal films with ferroelectric and/or pyroelectric properties are used. Its use is receiving considerable attention. Unlike conventional ferroelectric and/or pyroelectric materials, Lang's Broget film does not require a poling process.

PCT Publication No. 87100347 discloses specific examples of Lang's Brosier films with pyroelectric and ferroelectric properties, and GB-^216356
No. 6 discloses some examples of liquid crystal films for infrared detection devices. In either case, the optical thickness of the film is much smaller than 174 wavelengths to be detected. For example, typically Langmuir-Prosch films and liquid crystal films can have a physical thickness of 0.05 μI11 to 0.5 μm, and therefore their optical thickness is One order of magnitude from polymer film, GB-A-2173038 and E
It can be made two orders of magnitude thinner than the pyroelectric element of P-A-0272731.

In an attempt prior to inventing the present invention, the applicant attempted to increase the radiation absorption of a thin film detector by adjusting the sheet resistance of the first conductor facing the radiation. . Figure 1 is 37
The first (front) conductor has a sheet resistance of 7 ohms/mouth and 2 ohms/
Figure 3 shows the radiation absorption properties calculated for a 0.5 μm thick film (with an optical thickness of 0.9 μm) with a reflective second (back) conductor with a sheet resistance of the mouth. As shown in FIG. 1, absorption is low in the wavelength range of 5 μm to 15 μm, and particularly low in the wavelength band of 8 μm to 14 μm.

The applicant attempted to improve this absorption by adjusting the resistance values of the first and second conductors. Figure 2 shows the first and second
The calculated properties are shown for the same film whose conductors both have a sheet resistance of 400 Ω/hole. In the best case, such attempts still result in an absorption of about 52 μm between 8 and 14 μm.
%. Furthermore, these results are 0.5
This is for a .mu.m thick film, and as the film thickness is further reduced, the absorption becomes even worse.

SUMMARY OF THE INVENTION The present invention comprises at least one detection element having along a radiation path a multilayer structure with a flexible film having (pyroelectric) temperature-dependent properties, a first and a second electrical conductor on the first and second opposing surfaces of the film, respectively, a first electrical conductor on the first surface facing the incident radiation.
The conductor is constructed with a resistive layer providing sufficient sheet resistance to absorb a large portion of the incident radiation within a predetermined wavelength range, and a reflector is provided behind the film facing the second surface of the film. In an infrared detection device for detecting infrared radiation within a predetermined wavelength range adapted to reflect radiation transmitted through a film, the reflector is arranged at a second surface on a second surface of the film.
the multilayer structure ( (including the film and the separation part)
to the reflector equal to about 174 of the selected wavelength, and a second conductor facing the reflector has a thickness sufficient to absorb a majority of the reflected radiation within the wavelength range. It is characterized by being composed of a resistance layer that provides effective area resistance.

Even if the optical thickness of the film between the first and second conductors is less than 1/4 of the selected wavelength, the detection device can be configured as described above according to the invention to provide a sufficiently high absorption (1/4 of the conventional
It was confirmed that it is possible to achieve a value close to that obtained with a configuration with a thickness of /4 wavelength. The separation between the second conductor and the reflector may be approximately 1/4 the optical thickness of the selected wavelength, but the optical thickness of the film and the support in front of the film may be reduced to achieve optimal absorption. It can be made thinner depending on whether there are layers or not. Calculations show that in this device structure with remote reflectors, the sheet resistance of the resistive layers of the first and second conductors is approximately 2.Z instead of ZoO.

(where Zo is the characteristic impedance of free space) has been found to give optimum absorption, and in this calculation the resistive layers of the first and second conductors are placed in front of them in the respective directions of the incident and reflected radiation. It was assumed that free space (vacuum or gas depending on the atmosphere inside the device) existed. Several examples are provided below to illustrate the consequences of varying these resistance layer resistance, void thickness, and film thickness parameters. These parameters are not critical and fairly large tolerances may exist to achieve very good radiation absorption in the 8 μm-14 μm wavelength band.

These parameters of the structure of the device according to the invention can therefore be selected to adapt to different technical requirements and preferences.

The temperature-dependent film may be freely supported within the mounting arrangement such that at least a major portion of the resistive layer of the first and second conductors faces free space in the respective directions of incident and reflected radiation. The space in front of the second conductor may be an air gap separating the second conductor from the reflector, in which case the optical thickness of the film between the first and second conductors and the gap between the second conductor and the reflector The sum of the optical thicknesses of the air gaps can be approximately 1/4 of the selected wavelength in the wavelength range.

However, in variants it is also possible to incorporate one or more support layers for the film. In this case, at least one of the first and second conductors is provided immediately in front of it in the direction of incident or reflected radiation with an electrically insulating support layer supporting the film, which support layer is part of the multilayer structure. It may be made to constitute a section. Such a support layer may have a thickness greater than the thickness of the film (e.g. it may be up to 0.5 μm).
The multilayer structure preferably also includes a space-defining cavity in front of the reflector. Providing air gaps within the mounting device and keeping the film and support layer at a small thickness (less than 0.5 μm) reduces the heat capacity and heat transfer to and from the sensing element, reducing the incident absorbed radiation of the film. improve temperature response to

The present invention is a film (with or without a support layer).
It also provides an advantageous structure for supporting and mounting the reflector above the reflector while also making an electrical connection to the second N body on the second surface of the film. In this preferred device construction according to the invention, spaced support elements are present below the film to support the film above the reflector via a gap, which gap allows at least one connection between the reflector and the second conductor. providing the separation between the bulk and supporting at least one of the support elements an electrical connection to a second conductor below the film; This structure can be used for films with a single sensing element or a small number of sensing elements.

However, this structure forms individual lower connections to a large two-dimensional array of sensing elements and supports a large area of film with a small well-defined air gap as a separation between the sensing elements and the reflector. It is particularly useful for

The air gap can be formed in four parts of the substrate, with the upright part of the substrate forming a support element onto which the film of the sensing element can be mounted. Depending on the nature of the substrate material, this recess can be etched or otherwise formed. In order to support large film areas with gaps of desired optical thickness, at least some support elements can be formed on the reflector as bumps distributed along the second surface of the film. These bumps can be deposited on the substrate, or formed by cutting, etching, or molding the substrate surface or surface layer; in the case of an array, at least some of these bumps It can be manufactured to support an electrical connection to the second conductor.

The support layer and/or the substrate can be made of an electrically and thermally insulating material, for example when supporting a liquid crystal film that does not require electrical connections. In the case of pyroelectric and/or ferroelectric films, the support layer and/or the substrate may be made of an electrically and thermally insulating material, which may include one or more conductors to the second conductor of the film. Can support electrical connections. but,
The mounting device can also be designed such that the substrate is not made of conductive material.

〔Example〕

The present invention will be described below by way of example with reference to the drawings.
First of all, each figure is shown schematically.
It should be noted that the cross-sectional views of FIGS. 7, 8, 12, and 13 are shown in relatively enlarged or reduced sizes for the convenience of explanation, and are not shown to scale. In addition, the characteristic diagrams shown in Figures 1, 2° 4-6.9-11 and Figure 14 (these characteristic diagrams are plotted with absorbance as a percentage and plotted against wavelength λ) are simplified. It should also be noted that the calculations are based on computer models. In this computer model,
Although it is assumed that both the spectral transmission/absorption characteristics of the radiation by the film 10 and the refractive index of the film 10 (and the support layer 15) are constant over a given wavelength range, these simplifying assumptions are not used in the present invention. In the modeling example, film 10 (and support layer 15) is so thin that it can be legally accepted.

Figures 7 and 8 show a predetermined wavelength range, e.g. 5μm to 15μm.
2 shows two special infrared detection devices for detecting infrared radiation in the range of m, in particular in the wavelength band from 8 μm to 14 μm. Figures 3, 12 and 13 briefly show the detection element of this type of infrared detection device according to the present invention.

The infrared detection device includes a flexible film 10 that exhibits temperature-dependent characteristics using, for example, pyroelectric and/or ferroelectric properties.
It is equipped with Film E0 forms part of a multilayer structure constituting at least one sensing element. film 10
There are first and second conductors 21 and 22 of each sensing element on each first and second surface 11 and 12 of the sensor. The first conductor 21 facing the incident radiation 31 has a sufficient effective area resistance 2. to absorb a large portion of the incident radiation 31 (and 32) in the predetermined wavelength range. It consists of a resistive layer that exhibits Film 10 is supported on a mounting device 25. 3rd and 1st
In the apparatus having the configuration shown in FIG. 2, the second surface 1 of the film 10
2 does not come into contact with the mounting device 24 and is spaced apart from the opposing surface 26 of this mounting device 25 by a gap 28 . In the apparatus having the configuration shown in FIG.
A gap 28 exists between the supporting layer 15 of the 0 and the facing surface 26 of the mounting device 25. 3.12 and 13, t is the physical thickness of the film, n is the refractive index of the film, and therefore nt is the optical thickness of the film. be.

The physical thickness of the air gap 28 is d, and the air gap is assumed to be a vacuum or air or other gas having a refractive index of 1, and the optical thickness of the air gap is d. The optical thickness of the extremely thin conductors 21 and 22 can be ignored.

FIG. 3 shows the simplest infrared detection device in which each detection element has a multilayer structure consisting of a film 10, its conductors 21 and 22, and a gap 28. According to the invention, the facing surface 26 of the mounting device 25 remote from the conductor 22 is reflective for a predetermined range of radiation; the optical thickness n of the film IO between the conductors 21 and 222 〇- −t is 174 or less of the selected wavelength (λ, , ) within a predetermined wavelength range; the optical thickness nt of the film 10, the second conductor 22 and the reflective surface 2;
The sum of the optical thickness d of the air gap 28 between the
Further, the second conductor 22 (the conductor on the side facing the reflective surface 26) is configured with a resistive layer exhibiting a sufficient effective area resistance Z2 so as to absorb most of the reflected radiation 32 within a predetermined wavelength range. do.

The film lO of FIG. 3 has, for example, molecular orientation and refractive index n
is a solid liquid crystal material which changes with temperature fluctuations (due to local heating by absorbed radiation 31.32) in a known manner and changes the polarization mode of the light transmitted through or reflected from the film 10. Can be configured. Since the output of such a liquid crystal detection element can be read optically using an external polarizer, in this case, the film 1
The electrical connection to o can be eliminated, and the conductors 21 and 22 can act simply as optical elements for radiation absorption. Conductors 21 and 22 (e.g. capacitor 2 formed on pyroelectric and/or ferroelectric film 10)
In the case of a detection element that is electrically connected (with a radiation element), these electrodes 21 and 22 are also important as optical elements for absorbing radiation. Therefore, in any of the above cases, the optical thickness n·t of the specific film 10 that constitutes the detection device is 1
74 wavelength (λ5/4) or less, the resistance value Z of the two layers 21 and 22, the value of Z2, and the air gap 28
The thickness d is an important parameter.

4 to 6 show the effects of varying the above parameters on the radiation absorption characteristics of the device of FIG. 3. 4-6, the radiations 31 and 32 are approximately perpendicular to the exposed surface, and each successive layer of the device of FIG. 3 that interacts with the radiation is all parallel, with free space in front of the resistive layer 21. The plots are based on computer calculations assuming that the air gap 28 is also a free space. The sheet resistance value of the reflective surface layer 26 was arbitrarily selected to be 2Ω/hole, and the value of the refractive index n of the film 10 was arbitrarily selected to be 1.8.

In both cases of the film 10 of liquid crystal material and the Langmuir Blodgett pyroelectric and/or ferroelectric film 10, the physical thickness of the film IO is, for example, between 0.05 μm and 0.5 μm.
The thickness can be within the range of m. For example, in FIGS. 4 and 5, the physical thickness t of the film 10 is 0.1 μm.
(In other words, the optical thickness is 0.18 μm), but in Figure 6, the physical thickness t of the film IO is 0.5 μm.
(That is, when the optical thickness is 0.9 μm).

Values for various parameters are listed below.

(i) Film thickness t of 0.1 μm (Figures 4 and 5) Curve 4 a: d = 2.22 μm Z+ =zz=
754Ω curve 4 b: d = 2.22μm Z
I=Z2=400Ω curve 5 a : d = 1.8 u
m Z+ = Z2 = 754Ω curve 5 b : d
-3, Oum Z+ =Zz=754Ω(ii)
0.5 Bn film thickness t (Figure 6) curve 6a:
d=1.5, //DI Z+=Zz=75
4Ω curve 6 b: d=1. o μm Z+ =
Zz=754Ω curve 6 c: d=2.5 am
Z+ = Zz = 754 Ω It is clear from these curves that the resistance value of layers 21 and 223 is 754 Ω, that is, 2·20 (here 2
is the characteristic impedance of free space), the maximum absorption approaches 100%. This sets the optimum resistance value for a similar layer 21 to Z. If the conductor 22 on the back side is also resistive, the resistance value of these conductor layers is further reduced (EP-^-0
269161. BP-A-0272731 and GB-
〉as disclosed in A-2173038
This is different from the case of the /4 wavelength structure.

For absorption within the wavelength band of 8 μm to 14 μm,
As is clear from these curves, the optimum value of the air gap 28 for a film 10 with a thickness of 0.1 μm is the case of curve 4a (d = 2.22 μm), and the optimum value of the air gap 28 for a film 10 with a thickness of 0.5 μm is the case of curve 4a (d = 2.22 μm). The optimum value of is for curve 6a (d=1.5 μm). Therefore, the optimum thickness d of the void 28 depends on the thickness t of the film IO, but in general the optimum optical thickness d is usually within a predetermined wavelength range (8μ in this example).
174 or less of the selected wavelength (λ5) at m to 14 μm). This makes the optimal optical thickness for each dielectric film/layer equal to 1/4 of the selected wavelength (e.g. EP-^-02
69161゜EP-A-0272731 and Gto^-2
173,038)). curve 4a
and curve 6a both correspond to the case where the sum of the optical thicknesses (n-L+d) of the film 10 and the air gap 28 is equal to 1/4 of the wavelength λ5, which is chosen to be 9.6 μm. This 9.6μm
As the wavelength λ of the radiations 31 and 32 decreases from this selected value, the reflection increases rapidly to a maximum value, and for wavelengths above the selected value the reflection again (usually very slowly) In view of this increase, it is suitable for the wavelength band of 8 μI and 11 to 14 μm as shown in FIGS. 4 to 6. In this situation, it is usually preferable to select the wavelength of λ8 to be within the predetermined wavelength range of 172 or less. For the spectral absorption characteristics of the film 10, the optical thickness nt of the film 10 is very thin in most cases, so the influence of this film hardly matters; however, usually nt is the optical thickness of the gap 2B. It is also necessary to take into account that it is smaller than d (by about an order of magnitude in the case of an extremely thin film 10). In determining the selected wavelength λ5, the spectral absorption of the optical element in front of the detection element (for example, a lens, a window of the device, or a filter) is also taken into account, together with the absorption characteristics of the configuration shown in Figure 3. In most cases, the selected wavelength λ9 is set to a value within a predetermined wavelength range, but in some cases, the selected wavelength λ5 may be selected to a value slightly lower than the predetermined wavelength range. Curve 6b in FIG. 6 is just below the wavelength range of 8μ111 to 14μm and is an example of the case where 4(nt+d) is equal to 7.6μm.

As is clear from curves 4a and 6a, 4(n・t+d
) is selected to be equal to the selected wavelength of 9.6 μm, the absorption of the radiations 31 and 32 over the wavelength range 8 μI11-14 μm is approximately maximum and amounts to more than 90%.

Each of the curves in FIGS. 4-6 shows the optimum absorption of infrared radiation 31 and 32 when the sheet resistance of each layer 21 and 22 is approximately equal to 2.Zo, or about 754 ohms/hole. In reality, it is necessary to consider the stability of the resistance value of the metal film used as the conductors 21 and 22. Although this stability is a function of the method of depositing the metal film and the surface of the film 10 and its volumetric characteristics, it is assumed that the resistance of the metal film becomes less stable and generally increases over time. Therefore, it is academically advantageous to explore tolerances in resistance values in order to further increase absorption efficiency.

Curve 4b in FIG. 4 has a resistance value of 2. The effect of lowering Z2 from 754 ohms (FIG. 4a) to a value as low as 400 ohms (ie, a value as low as Z0) is shown. As is clear from this curve 4b, the absorption efficiency still exhibits an extremely high value over the wavelength range of 8 μm to 14 μm. Resistance values Z1 and z2 for the case of Fig. 6
When the curve 6a is lowered, the absorption characteristic becomes similar to the absorption characteristic of curve 6a, and is slightly lower than that of curve 6a.

Therefore, from the viewpoint of increasing stability, zl and Z
A value of 2 can in practice be chosen much lower than 754 ohms, which provides optimum absorption. In order to maintain a high absorption efficiency, a value of 7 is preferably in the range between the sheet resistance Z0 of the resistive layers 21 and 22 facing the space and approximately 2Z. The value of Zl is not necessarily always Z2
It does not have to be the same as the value of . Zl and Z2 are for example conductors 21 and 22 as described below with respect to FIGS. 12 and 13.
If one of the conductors 22 or 21 faces the space and the other conductor 22 or 21 faces the support layer 15, it is advantageous to make them different from each other.

Since the thickness of the void 28 is small (generally λ5/4 or less), it is difficult to control the optical thickness d of the void over at least a large area of the film 10.

This allows the void thickness d to still achieve high absorption efficiency.
It is advantageous to explore the intersection of Comparing curves 5a and 5b with curve 4a and comparing [11+ lines 6b and 6c] shows the influence that a change in the thickness d of the void 28 has on the average absorption. It can be concluded from these comparisons that even if d changes by approximately ±50% from its optimal value, it still exhibits high absorption, which is acceptable for many applications of infrared detection devices. It is. Therefore, in the configuration shown in FIG. 3, the optical maximum thickness of the gap 28 itself is 1/1/2 of the optimal wavelength λ5 selected for a predetermined wavelength range.
It can be an even multiple of 4, 8.

The absorbance shown by the curves in FIGS. 4-6 relates to the absorbance of the complete optical path including the reflective layer 26.

Absorption of radiation in the reflective layer 26 is undesirable since it reduces the energy available for absorption of radiation in the detection element layers 10.21 and 22. The resistance value of the reflective layer 26 was arbitrarily chosen to be 2 ohms because such a low resistance value can be easily achieved in practice using, for example, a thin vapor deposited gold layer. According to computer analysis, 8
The maximum absorption in a 2 ohm layer of radiation over the wavelength range μm = 14 μm is only 0.6%, 4μ111~
In the range of 5 μm, the maximum absorption for the wavelength λ increases to about 2%. Therefore, a 2 ohm metal film has a wavelength range of 5
It functions very satisfactorily as a reflective layer with negligible radiation absorption in the wavelength band of μm to 15 μm, particularly 8 μm to 14 μm.

FIG. 7 does not show an example in which, for example, the structure shown in FIG. 3 is used as an individual pyroelectric detection element in a conventional To-5 type device so that it can be used as a home intruder detection device. The void 28 is formed by a recessed portion of the substrate 251, and the pyroelectric film 10 is attached onto this substrate.

A film 10 with an optical thickness of λ,/4 or less is glued around the periphery of the film 10 to the ring 100 (for example, rather than being stretched taut and supported over an insulating ceramic or glass ring 100). For a typical home intruder detector, the outer diameter of ring 100 and film 10 may be several 59 meters;
The width of the radiation-absorbing conductors 21 and 22 defining the active detection region in the center of 0 can be, for example, about 0.5 ns or less. The conductors 21 and 22 may have a rectangular shape of, for example, 0.5 trm square defining a rectangular pyroelectric detection element, or they may have a circular shape of similar dimensions. Both conductors 21 and 22 may be constructed of, for example, a nickel-chromium alloy, such that they are deposited directly on each surface 11 and 12 of film 10. These conductors are deposited by sputtering or evaporation to a sufficient thickness to exhibit sheet resistance values in the 0 range of 400 ohms to 760 ohms/hole.

Film 10 is supported on mounting device 25 by an annular peripheral rim extending around a recess in substrate 251 and along at least a large portion of one side of the recess. Substrate 251, which may be made of molded plastic, for example, is also provided with a plurality of bumps 252 distributed over second surface 12 of film 10 to define the entire sensing element area as desired in air gap 28. It is supported above the reflective surface 26 with an optical thickness d. Although only two bumps 252 are shown in FIG. 7, normally a large number of these bumps 252 are provided.
Provide adequate support for the large active detection area in the center of the film IO. Reflective surface 26 may be formed of gold or other metal film at the bottom of recess 28.

The film IO disposed on the substrate 251 is attached to the header 256 of the TO-5 shaped cap 261 such that the film is supported within the enclosing cavity 260 of this cap 261. The enclosed cavity 260 can be inflated, evacuated, or filled with other gases. The cap 261 has a window 300,
This window can be, for example, a germanium window for daylight filtering, through which the infrared radiation to be detected passes. Therefore, window 300 passes almost all of the incident radiation in the intended operating wavelength range of 8 μm to 14 μm.

When the temperature of the pyroelectric filter 10 changes locally due to absorption of thermal energy from the incident radiation 31, changes occur on both sides 11 and 12 of the film 10 at that location. Conductor 21
and 22 function as an optical element involved in absorbing the radiation 31 as described with reference to FIG. 3, and also function electrically as a capacitor electrode for detecting the above change. Electrodes 21 and 22 are supported by the film 10 in a superimposed and coextensive relationship with each other, and are located away from the peripheral edges of the film. Since the generation of charge within the pyroelectric film 10 depends on the temperature change of the film, the incident radiation 31 needs to vary with time in order to detect it.

This may be the case when the detection device is made to respond to changes in a situation that would otherwise hardly change over time, such as for intruder detection purposes. Alternatively, this can be done by scanning the detection device across the viewing scene or by chopping the incident radiation 31.

Electrical connections to the resistive electrodes 1!21 and 22 are made by forming relatively narrow conductive tracks 121 and 122 on each side 11 and 12 of the film 10. These tracks 121 and 122 have one end connected to the resistive electrode layer 2.
1 and 22, and the other end is electrically connected to the header 256 and the field effect transistor T in a known manner. This NET forms part of an impedance matching circuit. The FET is a sensing element 10.2 in a circuit containing a nonlinear network that protects the gate of this NET from overvoltage.
1.22. For details of this type of circuit, please refer to British Patent Specification GB-1580403. This circuit is attached to header 256 and located within enclosing cavity 260, but this is not shown in FIG. 7 as the space in the drawing is too narrow. For example, in FIG. 7, the electrical connection to the conductive track 121 is made by a metallized track 121 extending on side 3 of the insulating ring 100. Optionally, electrical connections to conductive tracks 122 are provided by substrate 25.
This can take place via a metal track extending on one side, which metallization track can also be an integral layer with the reflective film 26. Additionally, if desired, the metallization tracks can extend over the bumps 252 located on the underside of the resistive electrode layer 22 to provide a connection to the layer 22 (instead of providing conductive tracks 122). Such a connection is also advantageous for the individual bottom conductors 22 of the sensing element array.

FIG. 8 shows another example of FIG. 3, in this example film 1
0 to form an array of pyroelectric detection elements used, for example, as image sensors in inexpensive infrared cameras. This array has a common first electrode 2 on the upper side of the film 10.
1 and an individual second electrode 22 for each sensing element on the underside 12 of the film 10. These electrodes 21 and 22 can be made of, for example, a nickel-chromium alloy, and are sufficiently thin to have a sheet resistance of 400Ω.
/Ro~760Ω/mouth. Optical thickness is λ
5/4 or more The lower film 10 is attached onto the bumps 252 of the substrate 25. In this case, the bumps 252 electrically contact the individual electrodes 22 and establish electrical connections to each sensing element. Also, these bumps 252 connect the electrode 22 and the reflective surface 26.
and maintains the optical thickness of the air gap 28 at a desired value.

Substrate 251 is a conductive material in this example (e.g., silicon) and forms the interface between the sensing element array and the underlying semiconductor circuit board 255, which is not a semiconductor circuit board (e.g., a monolithic silicon integrated circuit). )
The signal from the detection element is processed by. Thus, for example, the semiconductor circuit board trF1.255 can be provided with a field effect transistor T, a nonlinear network and a switching matrix, so that the signals from the individual detection elements of the array can be read out sequentially. In order to make individual connections between each sensing element and circuit board 255, conductive substrate 251 is divided into an array of conductive pillars by grooves 258. Note that this method is a relatively simple connection method. The array of conductive pillars is held together by an insulating material 259 at least in part of the grooves 258 before the substrate 251 is attached to a circuit board 255 (=L 4J5 ) to form a substrate unit. The substrate unit can be handled together with the film 10 mounted thereon.

The mounting device 25 of the device shown in FIG. 8 can be manufactured by the following steps. First, a continuous silicon wafer is bonded to a continuous insulating film (eg, polyimide resin material). Next, hole 257 is made in the boria resin film.
The array is etched to expose areas of the silicon wafer. The top side of the silicon wafer is then etched to form a recess of depth d to define an array of bumps 252, the height of which is the depth d of the desired void 28.

Next, a metal film having, for example, a sheet resistance of 2 Ω/hole is deposited on the upper etched surface of the silicon wafer (including the bumps 252) to form a reflective surface 26.

Next, the silicon wafer is cut into strips by sawing to form grooves 258 to form conductive pillars 251.

Next, the pyroelectric film 10 with thin electrodes is attached to the steel strip substrate 2.
51 &-1, bringing the electrode 22 into contact with the metallized bump 6 252 .

Next, an easy-to-handle film 1 is placed on the steel strip substrate 251.
0 assembly with circuit board 255.

This hybrid attachment attaches the film board assembly to the solder bumps 2 on top of the contact pads 254 of the circuit board 255.
53 or other connection bumps such that these contact pads 254 are connected to each sensing element via conductive pillars 251.

Figures 7 and 8 show a pyroelectric detection device in which the thin pyroelectric film can be formed by the Langmuir proge process or as a very thin copolymer, for example by solution casting. In the latter case, it is necessary to apply an electric field to the film in a known manner for poling. The advantage of using the Rangku Your Blog method is that the film material (supporting material)
Second, in a multilayer structure), the film can be spontaneously polarized (by an internally generated dipole moment) to have a polar axis perpendicular to the plane of the film 10. Even when cumulative deposition is used to grow thick Languyou 7 Arbrosier films on a support, the internally generated dipole moment can be maintained throughout the thickness of the grown film.

The characteristic diagrams in Figures 4 to 6 show the first and second characteristics as shown in Figure 3.
This is relevant when the conductors 21 and 22 face a cavity in the direction in which the incident radiation 31 and the reflected radiation 32 arrive, respectively. However, it may be desirable to support the active film 10 with an electrically insulating support layer, for example when using a very thin film 10, a Lang's Brosier film 10, or a liquid crystal film 10, and in some cases. Sometimes you have to do it that way. Such a support layer 15 can be, for example, a polyimide resin film or a silicon nitride layer. Thus, for example, the Langmuir-Bloger film 10 can be deposited on an insulating support layer that forms either the first conductor or the second conductor 22 thereon before depositing the film. .

During this deposition, the support layer itself can be supported 8 on a thick substrate (eg, a glass slide) to further increase the rigidity of the support layer, after which the substrate can be removed.

Such a support layer 15 may be part of a multilayer structure of the finished infrared detection device and thus in this case one of the first and second conductors 21 and 22 in the direction of the incident radiation 31 and the direction of the reflected radiation 32. are applied directly to the dielectric support layer 15 as shown in FIGS. 12 and 13, respectively. Conductor 2 in the example of Figure 12
1 and to conductor 22 in the example of FIG.
This can be done by metallization at the location of the holes through the support layer 15. The device structure shown in FIGS. 12 and 13 is the seventh
It can also be modified so as to be incorporated into a device as shown in FIGS.

The characteristic diagrams of FIGS. 9-11 relate to the sensing element of FIGS. 12 and 13 having a dielectric support layer 15 and an air gap 28. FIG. 14 relates to a modification in which the void 28 is eliminated. The simple computer model used to generate these profiles shows that the radiation due to the support layer is 31.32
Both the spectral transmission/absorption of and the refractive index of the support layer were assumed to be constant over a given wavelength range. A value of 1.8 was arbitrarily selected as the value of the refractive index 9 (N) of the support layer.

In plotting the characteristics in FIGS. 9-11 and 14, the following parameters were kept constant.

Thickness to of active film 10: 1 μm Refractive index of active film 10: 1.8 Conductors 21 and 2
In the case of FIG. 9, the thickness d of the void 28 and the thickness T of the support layer 15 were set as follows.

d=2.14 μm T=0.1 μm Curve 9a in FIG.
This is related to the case shown in FIG. 12, which is sandwiched between .

Curve 9b provides a support layer 15 behind the active film IO, placing this support layer in the optical path of the reflected radiation 32;
This relates to the case of FIG. 13, in which the rear conductor 22 is sandwiched between the support layer 15 and the film 10.

It can be seen that the curves 9a and 9b are slightly shifted in the lateral direction, but the absorbance over the wavelength range of 8 μm to 14 μm is extremely good. , or the support layer is made of film IO (which has little bearing on the absorbance. In this case, the sum of the optical thicknesses (n - t + N - T + d) of the multilayer structure including the voids 28 is 10 μm. 1/ of the wavelength of
4, and it can be seen that the absorbance is maximum around 10 μm.

In the example of FIG. 9, the thickness of the support layer 15 is the same as the thickness of the active film IO. However, the support layer 1 for the film 10
It is often desirable that the thickness of film 5 be greater than the thickness of film 10. For example, FIGS. 10 and 11 are plots for the support layer 15 having a thickness of 0.5 μm. The thickness of the support layer can be increased further depending on the material properties of the layer, but to reduce heat capacity and heat conduction laterally along the support layer, the thickness of the support layer is at most about 0. It is said that it is desirable to set the thickness to .5 μm.

FIG. 10 relates to the case of FIG. 12 in which a 0.5 μm thick support layer 15 is provided in front of the active film 10 and the top conductor 21 is sandwiched between the support layer 15 and the film IO. be.

The curves 10a to 10c in FIG. 1O are obtained when the thickness d of the void 28 is set to the following values.

Curve 10a: d=2.14μm Curve 10b: d-1,50,czm Curve 10c
: d=1. Since the OOμm curve 10a is provided with a thick front support layer, unless the thickness of the gap 28 is made thin to compensate for this, the absorption over the wavelength band 8μI from 11 to 14μm will be poor, especially at the edge of 8μm. This shows that it is considerably inferior. In this case, the sum of the optical thicknesses of the multilayer structure (n - t + N - T + d) corresponds to a wavelength of 10.3 pm, which is in the lower half of the range from 8 μm to 14 μm.

When the thickness of the air gap 28 is made considerably thinner, curve 10c), 8
Although the absorbance over the upper half of the wavelength range of μm=12 μm is somewhat low, the absorbance is good overall.

In this case, the sum of the optical thicknesses of the multilayer structure (n・t+2 N-T+d) corresponds to 1/4 of the wavelength of 8.3 μm.

Figure 11 shows 0.5μ111 on the back side of the active film 10.
This relates to the case of FIG. 13 in which a thick support layer 15 is provided and a back conductor 22 is sandwiched between the support layer 15 and the film 10. In this case, the support layer 15 is in the optical path of the reflected radiation 32 and a gap 28 of thickness d exists between the support layer 15 and the reflective surface 2.
It exists between 6 and 6. The thickness d of this gap 28 is made thinner to compensate for the provision of the support layer 15. The curves 11a to lid in FIG. 11 are obtained when the thickness d of the void 28 is set to the following values.

Curve 11a: d = 1.46 μm Curve 11b:
d = 1.20 μm curve 11c: d = 0.
90 μm curve 11d: d = 0, that is, the three curves 11a to 11c with no void, the maximum absorption shifts toward the lower wavelength end as the thickness d of the void becomes thinner, but the absorption over 8μI11 to 14 μm All grades are good. The sum of the optical thicknesses of the multilayer structure (n-10N-T+d) for both curves 11a and llb is between 8 μm and 14 μm.
Corresponding to 1/4 of the length of wave 3 in the lower half of the μm range, the sum of the optical thicknesses of the multilayer structure (n − 10 N − T 1 d) for curve 11c is 8 μm −
1/ of the wavelength just below the 14 μm range (7,92 μm)
Corresponds to 4.

The curve lid is for the case not according to the present invention.

In this case, the reflective surface 26 is provided directly on the back side of the 0.5 μm thick support layer, and no void 28 is present.

As is clear from the curve lid, the absorbance in this case is 8
It is extremely inferior to the wavelength band of μm to 14 μm.

For this reason, it is important to provide the air gap 28 in the device of FIG. 13 so that the sum of the optical thicknesses over the entire multilayer structure up to the reflective layer 26 is approximately 1/4 of λ5. It turns out that. However, as shown in FIG. 14, very good absorption can also be achieved by eliminating the void 28 from the device structure of FIG. 13 and increasing the thickness of the back side support layer 15 to compensate for it. Obtainable.

Therefore, the characteristics shown in FIG. 14 are obtained by changing the characteristics shown in FIG. 13 as follows.

Thickness to of the film 10, 1 μm4 Refractive index of the film 10 1.8 Refractive index of the support layer 15 1.8 Resistance value of the conductors 21 and 22 Z754Ω Reflective layer on the back surface of the support layer 15 2Ω In the case of curve 14a The thickness T of the support layer 15 is 1,38
Assuming 9 μm, its optical thickness is 17 of λ5 of 10 μm.
4 (at this point the absorbance is almost at its maximum), and the sum of the optical thicknesses (N-T-1-nt) is about 1/4 of the wavelength of 10.7 μm. In the case of curve 14b, support layer 15
Assuming that the thickness T of
174. However, increasing the material thickness of the element structure with respect to curves 14a and 14b is disadvantageous, since it would significantly increase the heat capacity of the sensing element and the heat conduction to and from the sensing element.

In most infrared detection devices manufactured according to the present invention, the material of the film 10, the configuration of the detection element, and the circuit operation are selected to be the same, so as to utilize the conventional pyroelectric effect, and the spontaneous When a temperature change occurs in a polar crystal (structure) material exhibiting a typical polarization (eg, upon absorption of incident infrared radiation 31), charges are generated on both sides of the material. The pyroelectric material is connected to a suitable amplifier circuit as a capacitor in a known manner (electrodes 21 and 22 on both sides).
By arranging (with) a current or voltage signal can be generated and detected. The most effective pyroelectric materials are also ferroelectric, and they exhibit pyroelectric properties in the ferroelectric phase below their cue transition temperature. However, the dielectric constant of infrared detectors changes rapidly with temperature. It can also be constructed in known manner using ferroelectric polymeric materials that actuate at the cue points. This type of ferroelectric infrared detection element can also be configured as a capacitor by connecting electrodes to both surfaces 11 and 12.

Both pyroelectric and ferroelectric polymer type sensing elements can be manufactured and installed in accordance with the present invention. Other types of infrared detection devices, such as polymer liquid crystal devices, can also be manufactured according to the invention.

It goes without saying that the present invention is not limited to the above-mentioned examples, but can be modified in many ways.

6

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing the radiation absorption characteristics of a new detection device structure invented by the present inventor, but which does not have the features of the present invention. Figure 3 is a schematic diagram showing a part of the infrared detector of the present invention. Figures 4 to 6 are graphs showing radiation absorption characteristics for various parameter values of the detection device of the present invention, and Figure 7 is a circuit diagram of a part of an embodiment of the detection device of the present invention having a single detection element. FIG. 8 is a sectional view of a portion of another embodiment of a detection device according to the invention having an array of detection elements; FIGS. Graphs showing the radiation absorption characteristics of the device. Figures 12 and 13 are schematic diagrams showing part of an infrared detection device of the invention having a film supported by such a support layer. DESCRIPTION OF SYMBOLS 10... Film 11... First surface 7 of film 12... Second surface of film 15... Support layer 21... First conductor 22... Second conductor 25... Mounting device 26... Reflective surface 28... Gap 31... Incident radiation 32... Reflected radiation 100... Glass rings 121, 122... Conductive track 251... Substrate (conductive pillar) 252... - Bump 253... Solder bump 254... Contact pad 255... Semiconductor circuit board 256... Header 257... Hole 258... Groove 259... Insulating layer 8 260... Vacant space 261 ...Gap 300...Window

Claims (1)

Claims: 1. At least one sensing element having a multilayer structure comprising a flexible film with temperature-dependent properties along the radiation path, the first and second electrical conductors of the sensing element being connected to the film. on first and second opposing surfaces respectively, the first conductor on the first surface facing the incident radiation comprising a resistive layer providing sufficient sheet resistance to absorb a majority of the incident radiation within a predetermined wavelength range; and a reflector facing the second surface of the film is provided behind the film to reflect the radiation transmitted through the film. , the reflector is spaced along a radiation path from a second conductor on the second surface of the film by a spacing, and an optical thickness of the film between the first and second conductors is selected within the wavelength range. and the sum of the optical thicknesses of the multilayer structure (including the film and the standoff) along the radiation path to the reflector is equal to about 1/4 of the selected wavelength. , and wherein the second conductor facing the reflector is constituted by a resistive layer that provides an effective sheet resistance sufficient to absorb most of the reflected radiation within the wavelength range. 2. A resistive layer of one or both of the first and second conductors faces free space in each direction of incident radiation and reflected radiation, and the resistive layer has a characteristic impedance of free space, Zo, of approximately 2.Zo. 2. A device according to claim 1, characterized in that it provides a sheet resistance in the range between . 3. A plurality of spaced apart support elements are present below the film to support the film above the reflector through an air gap, the air gap providing at least a major portion of the reflector and the second conductor. 3. A device according to claim 1 or 2, characterized in that the spacing is provided between the support elements and at least one of these support elements supports an electrical connection to the second conductor below the film. 4. The resistive layers of both the first and second conductors face free space in respective directions of incident and reflected radiation, and the free space of the second conductor provides an air gap separating the second conductor from the reflector. and the sum of the optical thickness of the film between the first and second conductors and the optical thickness of the gap between the second conductor and the reflector is about 1/4 of the selected wavelength. The device according to item 3. 5. The device of claim 4, wherein the film is at most 0.5 micrometers thick. 6. At least one of said first and second conductors comprises an electrically insulating support layer supporting a film immediately in front thereof in each direction of incident radiation and reflected radiation, said support layer being part of said multilayer structure. The apparatus according to any one of claims 1 to 3, characterized in that it comprises a. 7. The thickness of the support layer is greater than the thickness of the film and is at most 0.5 micrometers, and the multilayer structure includes a space-forming void in front of the reflector. The device described. 8. The device according to claim 3, 4 or 7, wherein the gap is formed by a recess provided in a substrate supporting the film. 9. The film comprises an array of detection elements, and the reflector is provided with bumps distributed along the second surface of the film to place the detection elements above the reflector in a gap of desired optical thickness. and each sensing element has an individual second conductor, and the electrical connections to the individual second conductors are each supported on one bump.
or the device described in 8. 10. The substrate is formed of a conductive material to constitute an interface between the array of sensing elements and a lower semiconductor circuit for processing the signals from these sensing elements, and the substrate is divided by grooves into an array of conductive pillars. 10. A conductive conductor according to claim 9, wherein the conductive pillar array is held together by an insulating material within at least a portion of the groove. equipment. 11. Claim 6, wherein the support layer provides the separation between the second conductor and the reflector, and the reflector is formed by a reflective surface layer on one surface of the support layer. The device described in. 12. The selected wavelength is selected such that absorption of the incident radiation is substantially maximal over the wavelength range, and the wavelength range is approximately 8 μm to 14 μm.
12. The device according to any one of 11. 13. The device according to any one of claims 1 to 12, characterized in that the temperature-dependent film is a Langmuir-Bloger film having ferroelectric and/or pyroelectric properties.