JPH04350978A - Pyroelectric infrared array sensor - Google Patents

Abstract

PURPOSE:To enhance the performance of a sensor by increasing the absorption of infrared rays by a pyroelectric thin film. CONSTITUTION:An optical element 5 which is provided with a function to reflect infrared rays is formed on the face in one part of an organic thin film 4 formed on a pyroelectric thin film 2. Thereby, after irifrared rays which are incident on the pyroelectric thin film 2 and which are indicated by arrows (a) have been transmitted through the pyroelectric thin film 2, they are refletced by a face 5a faced with the pyroelectric thin film 2 of the optical element 5 and are incident again on the pyroelectric thin films 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric infrared array sensor using a pyroelectric thin film.

0002

BACKGROUND OF THE INVENTION Conventionally, pyroelectric infrared detectors are thermal infrared detectors that can operate at room temperature, have low sensitivity dependence on wavelength, and are highly sensitive among thermal detectors. In principle, pyroelectric infrared detectors use the pyroelectric effect, which is a phenomenon in which a temperature change is applied to a pyroelectric material to generate an electric charge on the surface of the material depending on the rise and fall of the temperature, to detect infrared rays. This is to detect. The detection process includes the following three processes.

(1) First, the temperature (T) of the pyroelectric material increases by ΔT by absorbing the incident light (intensity L). (2) Next, an electric charge (ΔQ) is generated on the surface of the pyroelectric material through a change ΔPs in the polarization (Ps) of the pyroelectric material due to a rise in temperature.

(3) Furthermore, charge (Δ
Take out Q) as current or voltage. In this way, in a pyroelectric infrared detector, the temperature rise of the pyroelectric material, which is the cause of charge generation, is important. Then, it is given by ηL (L is the incident light intensity). Furthermore, due to the temperature increase ΔT, heat of GΔT is lost from the pyroelectric material. Here, G is thermal conductivity. That is, the time change in temperature rise of the pyroelectric material is expressed by the following equation.

[0005]

[Math 1]

From the above equation, the temperature rise ΔT is

[0007]

[Math 2]

[0008] Here, H is the heat capacity of the pyroelectric material,
ω is the angular frequency of the incident light. That is, the greater the absorption of incident light, the greater the temperature rise of the pyroelectric material, and as a result, the greater the charge generated on the surface of the pyroelectric material.

[0009] Materials used in pyroelectric detectors include single crystals such as TGS and LiTaO3, Pb
Examples include TiO3-based/PbX Zr1-X TiO3-based ceramics, and organic films such as PVF2-based.

[0010] This PbTiO3 has the figure of merit of pyroelectric material Fv (=γ/εCv) and Fm (=γ/Cv√
εdtanδ) is high. Here, γ is the pyroelectric coefficient, ε is the dielectric constant, Cv is the volumetric specific heat, and d is the thickness. Also, PbT
iO3 has features such as a small temperature change in the pyroelectric coefficient γ and a sufficiently high Curie point. PbTiO3 porcelain is often used in pyroelectric detectors. Porcelain is polycrystalline, and there is no directionality in the arrangement of crystal axes, so the spontaneous polarization Ps is also arranged randomly. As described above, the pyroelectric material extracts the change in the spontaneous polarization Ps as an output, so the maximum output is obtained when the spontaneous polarization Ps is aligned in one direction. Therefore, it is necessary to apply a high electric field to the ceramic to perform polarization treatment to align the direction of the spontaneous polarization Ps.

Furthermore, when using pyroelectricity generated in the orientation axis direction of a C-axis oriented PbTiO3 thin film, the dielectric constant ε in the C-axis direction decreases and the pyroelectric coefficient γ increases.
It is reported in Proceedings of the 30th Applied Physics Association Lecture Proceedings 7P-z-2 that it is possible to realize a highly sensitive pyroelectric material exhibiting an Fv approximately three times higher than that of O3 porcelain.

Further, it is desirable that the infrared array sensor be arranged in a fine array in order to improve the spatial resolution in relation to the optical system.

[0013]

[Problems to be Solved by the Invention] As the thickness of the pyroelectric material becomes thinner, the noise becomes smaller and the detectability (D*) increases. When constructing an array with PbTiO3 porcelain, there is a limit to how thin the porcelain film can be, and there is a limit to how much the detectability (D*) can be improved by reducing the thickness. Further, crosstalk between each element increases depending on the distance between each element, and spatial resolution decreases. Therefore, it is necessary to separate each element. Furthermore, if the area is made smaller, the capacitance becomes smaller, so miniaturization becomes difficult due to the effects of external capacitance and stray capacitance. Furthermore, the following problem occurs when polarizing a pyroelectric material.

(1) First, dielectric breakdown may occur due to polarization treatment. (2) Next, in high-resolution array elements arranged at high density, it is difficult to uniformly polarize them.

On the other hand, the pyroelectric thin film solves the problems described above when using porcelain. Pyroelectric thin films are created at high temperatures by thin film forming methods such as sputtering. However, since the pyroelectric thin film has a thickness of several micrometers, its absorption of infrared rays is small. Furthermore, a pyroelectric thin film such as PbTiO3 is transparent up to a wavelength of about 10 μm. For this reason, a detector using a pyroelectric thin film has a problem in that its absorption of infrared rays is small, resulting in poor performance as a pyroelectric infrared sensor.

The present invention solves the above-mentioned conventional problems, and aims to provide a pyroelectric infrared array sensor with excellent performance by increasing the absorption of infrared rays by a pyroelectric thin film.

[0017]

[Means for Solving the Problems] In order to solve the above problems, a pyroelectric infrared array sensor of the present invention includes a pyroelectric thin film,
a first electrode thin film formed on the first surface of the pyroelectric thin film; a second electrode thin film formed on the second surface of the pyroelectric thin film; and a first electrode thin film formed on the first surface of the pyroelectric thin film. This is a pyroelectric infrared array sensor having a covering organic thin film, and an optical element having a function of reflecting infrared rays is provided on a part of the surface of the organic thin film.

The pyroelectric infrared array sensor of the present invention also includes a pyroelectric thin film, a first electrode thin film formed on a first surface of the pyroelectric thin film, and a second electrode thin film formed on a second surface of the pyroelectric thin film. A pyroelectric infrared array sensor comprising a second electrode thin film formed on the pyroelectric thin film and an organic thin film covering a first surface of the pyroelectric thin film, the optical element having a function of reflecting infrared rays is It is provided in a part of the organic thin film parallel to the surface of the pyroelectric thin film.

Further, the optical element of the pyroelectric infrared array sensor of the present invention is constructed of a metal thin film.

[0020]

[Operation] With the above configuration, an optical element having the function of reflecting infrared rays is provided on a part of the surface of the organic thin film covering the pyroelectric thin film, so that the infrared rays incident on the pyroelectric infrared array sensor are The infrared rays that have passed through the pyroelectric thin film and the organic thin film are reflected by the surface of the optical element facing the pyroelectric thin film, and then enter the pyroelectric thin film again.

In addition, since an optical element having a function of reflecting infrared rays is provided in a part of the organic thin film covering the pyroelectric thin film parallel to the surface of the pyroelectric thin film, the optical element which is a metal thin film is replaced by an organic thin film. The reflective surface of the optical element is parallel to and close to the surface of the pyroelectric thin film, and the infrared rays are efficiently incident from the reflective surface of the optical element to the pyroelectric thin film. It turns out.

Furthermore, since the optical element is a metal thin film,
This results in high reflection of infrared rays onto the pyroelectric thin film.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing the structure of a pyroelectric infrared array sensor according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA' in FIG. 1 and 2, a pyroelectric thin film 2 of Pb1-X LaX Ti1-0 . 75X
An O3 (PLT) thin film was grown to a thickness of 3 μm. Each element of this pyroelectric thin film 2 is separated by a metal mask. A mixed gas of Ar and O2 was used as the atmospheric gas. (Table 1) shows the sputtering conditions.

[0024]

[Table 1]

Next, on this pyroelectric thin film 2, a film with a thickness of about 0.2 μm is deposited.
An Au electrode thin film 3 having a thickness of m was formed by vapor deposition. This Au electrode thin film 3 is separated and arranged in a grid pattern according to the pitch of the array by photolithography. Furthermore, an organic thin film 4 was provided on these. This organic thin film 4 is coated with photosensitive polyimide resin using a spinner.
After being irradiated with ultraviolet rays, it was heat-treated at 200 degrees Celsius. The film thickness is 3.0 μm. Then, an optical element 5 having a function of reflecting infrared rays was provided on a part of the surface of this organic thin film 4. In this optical element 5, an Al thin film, which is a metal thin film, was formed on the organic thin film 4, that is, about 20 μm above the pyroelectric thin film 2 by vapor deposition. This Al thin film reflects approximately 97% or more of infrared rays with a wavelength of 6 μm to 10 μm.

Furthermore, a contact hole 6 was formed in a part of the electrode thin film 3 to bring the electrode thin film 3 and the extraction electrode 7 into contact. The extraction electrode 7 and the optical element 5 are formed so as to be electrically insulated by an insulating mask or the like. Then, the optical element 5 and the other electrode thin film are electrically insulated. Furthermore, Mg in the lower part of the pyroelectric thin film 2
The O substrate 1 was etched to form an opening 8, and a NiCr electrode thin film 9 was formed through the opening 8 on the substrate side surface of the pyroelectric thin film 2 by vapor deposition.

Here, 75 of the polarization axis of the PLT pyroelectric thin film 2
% or more is oriented in one direction, the pyroelectric coefficient γ is 5×
10C/cmK, and this value is 100kV at 200℃
This is considerably larger than that of PbTiO3 ceramics (γ=1.8×10C/cmK), which was polarized by applying a voltage of /cm. In addition, when the orientation rate is 90%, the pyroelectric coefficient is 6.8×
10C/cmK. Moreover, not only is it almost the same as the value after polarization treatment, but it is also larger than the value after polarization when the orientation rate is small. The dielectric constant ε is when the orientation rate is 90%,
The value is about 200, which is almost the same as that of ceramics.

As described above, in the PLT pyroelectric thin film 2 used in this example, if the thin film is sufficiently oriented along the c-axis at the time of film formation, the spontaneous polarization is uniform even without polarization treatment.
It was found that the effect is large for thin films with an orientation rate of 75% or more. In addition, Fv (=
The value of γ/εCv) also increases, and when heated at 200℃ for 10 minutes,
PbTiO3 subjected to polarization treatment by applying 00 kV/cm
Compared to the value of ceramics, the PLT thin film showed a value more than three times higher. The c-axis orientation rate of this PLT pyroelectric thin film 2 is higher when it is formed directly on the MgO substrate 1 than on the base electrode formed on the Mg substrate, which is advantageous both in terms of the figure of merit and in that polarization treatment is not required. .

With the above configuration, the optical element 5 having the function of reflecting infrared rays is connected to the organic thin film 4 covering the pyroelectric thin film 2.
By providing it on a part of the upper surface, a part of the infrared rays shown by the arrow a in FIG.
After passing through the pyroelectric thin film 2 and further through the organic thin film 4, the light is reflected by the surface 5a of the optical element 5 facing the pyroelectric thin film 2, and then enters the pyroelectric thin film 2 again. Thereby, the incident infrared rays can be effectively used without escaping, and the absorption of infrared rays in the pyroelectric thin film 2 is increased, so that the performance of the sensor can be improved. Therefore, the characteristics as a pyroelectric infrared array sensor are improved in sensitivity and detectability (D*) by about 70% compared to a sensor not provided with the optical element 5 having the function of reflecting infrared rays.

FIG. 3 is a plan view showing the structure of a pyroelectric infrared array sensor according to a second embodiment of the present invention, and FIG.
It is a BB' sectional view in . 3 and 4, the process up to the formation of the Au electrode thin film 3 is the same as that of the first embodiment. An organic thin film 11 is provided on this Au electrode thin film 3, and this organic thin film 11 is made by coating a photosensitive polyimide resin with a spinner, irradiating it with ultraviolet light, and then heat-treating it at 200 degrees Celsius. The film thickness is 1.5 μm. Then, an optical element 12 having a function of reflecting infrared rays was provided on a part of the surface of the organic thin film 11. For this optical element 12, a thin Al film of about 20 μm was formed by vapor deposition. This Al thin film reflects approximately 97% or more of infrared rays with a wavelength of 6 μm to 10 μm. Thereafter, the organic thin film 13 was again formed to a thickness of 1.5 μm in the same manner as in the previous step. A contact hole 14 was provided in a part of the electrode thin film 3 and brought into contact with an extraction electrode 15 . The extraction electrode 15 and the optical element 12 are formed to be electrically insulated.

Furthermore, MgO in the lower part of the pyroelectric thin film 2
The substrate 1 was etched to form an opening 8, and a NiCr electrode thin film 9 was formed through the opening 8 on the substrate side surface of the pyroelectric thin film 2 by vapor deposition. This is similar to the first embodiment.

With the above configuration, the optical element 12 having the function of reflecting infrared rays is provided in a part of the organic thin films 11 and 13 covering the pyroelectric thin film 2 in parallel to the surface of the pyroelectric thin film 2. A part of the infrared rays shown by arrow b in FIG. 4 that entered the pyroelectric infrared array sensor was absorbed by the pyroelectric thin film 2, and the other incident infrared rays passed through the electrode 9, the pyroelectric thin film 2, and further the organic thin film 11. Thereafter, the light is reflected by the surface 12a of the optical element 12 facing the pyroelectric thin film 2, and then enters the pyroelectric thin film 2 again. Thereby, the incident infrared rays can be effectively used without escaping, and the absorption of infrared rays in the pyroelectric thin film 2 is increased, so that the performance of the sensor can be improved. This is the same as in the first embodiment. In the case of the second embodiment, since the optical element 12, which is a thin film, is covered with the organic thin films 11 and 13, the optical element 12, which is a metal thin film, is protected from damage by the organic thin films 11 and 13, and Optical element 12 and other electrode thin films are reliably electrically insulated. Further, the reflective surface 1 of the optical element 12
2a is provided parallel to and close to the surface of the pyroelectric thin film 2, the incidence efficiency of infrared rays reflected from the reflective surface of the optical element 12 and incident on the pyroelectric thin film 2 is further improved.

In the first and second embodiments, Al material was used for the optical elements 5 and 12 having the function of reflecting infrared rays, but the material is not limited to Al material, and Ag, Al
Any metal having a high reflectance of infrared rays such as u or Cu may be used.

[0034]

As described above, according to the pyroelectric infrared array sensor of the present invention, an optical element having the function of reflecting infrared rays is provided on a part of the surface of the organic thin film covering the pyroelectric thin film. By doing so, it is possible to effectively utilize the incident infrared rays without letting them escape, and increase the absorption of the infrared rays in the pyroelectric thin film, thereby improving the performance of the sensor.

Furthermore, by providing an optical element having the function of reflecting infrared rays in a part of the organic thin film covering the pyroelectric thin film parallel to the surface of the pyroelectric thin film, the optical element can be protected by the organic thin film. Furthermore, by bringing the reflective surface of the optical element close to the surface of the pyroelectric thin film, the absorption of infrared rays by the pyroelectric thin film can be increased, and the performance of the sensor can be improved.

Furthermore, by configuring the optical element with a metal thin film, a high reflection of infrared rays can be obtained, thereby increasing the absorption of infrared rays in the pyroelectric thin film, and improving the performance of the sensor. It is something.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the structure of a pyroelectric infrared array sensor according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA' in FIG. 1;

FIG. 3 is a plan view showing the structure of a pyroelectric infrared array sensor according to a second embodiment of the present invention.

FIG. 4 is a BB' cross-sectional view in FIG. 3;

[Explanation of symbols]

2 Pyroelectric thin film 3 First electrode thin film 4, 11, 13 Organic thin film 5, 12 Optical element having the function of reflecting infrared rays 9 Second electrode thin film

Claims (3)

[Claims] 1. A pyroelectric thin film, a first electrode thin film formed on a first surface of the pyroelectric thin film, and a second electrode thin film formed on a second surface of the pyroelectric thin film, The first of the pyroelectric thin films
1. A pyroelectric infrared array sensor comprising: an organic thin film covering a surface of the pyroelectric infrared array sensor, wherein an optical element having a function of reflecting infrared rays is provided on a part of the surface of the organic thin film. 2. A pyroelectric thin film, a first electrode thin film formed on a first surface of the pyroelectric thin film, and a second electrode thin film formed on a second surface of the pyroelectric thin film, The first of the pyroelectric thin films
A pyroelectric infrared array sensor having an organic thin film covering a surface of the pyroelectric thin film, wherein an optical element having a function of reflecting infrared rays is provided in a part of the organic thin film parallel to the surface of the pyroelectric thin film. Pyroelectric infrared array sensor. 3. The pyroelectric infrared array sensor according to claim 1, wherein the optical element is composed of a metal thin film.