JPH0629781B2 - Pyroelectric infrared imaging device - Google Patents

Description

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

2. Description of the Related Art Infrared imaging devices that measure the temperature distribution of an object in a non-contact manner include quantum detectors that detect infrared rays as photons, or thermal detectors that absorb temperature changes and convert element temperature changes into electrical signals. Is adopted. The former has a high response speed and high sensitivity, but requires cooling to the liquid nitrogen temperature, and the sensitivity has a large wavelength dependence. The latter has a slow response, but has the characteristics that it can operate at room temperature and has high sensitivity at long wavelengths, and is expected to be used for households and general consumers.

At present, a large number of infrared imaging devices that have been put into practical use are combined with a linear array type detector consisting of points or a small number of elements and mechanical scanning of an optical system. Recently, a two-dimensional infrared imaging device in which a Schottky barrier is formed as a detection unit and is electronically scanned by a charge-coupled device (CCD) has been put into practical use. On the other hand, a vacuum tube type pyroelectric vidicon has already been put to practical use in an infrared imaging device using a thermal detector. Pyroelectric infrared detector and CC
A solid-state pyroelectric CCD in which D and D are integrated is under research and development, and a method of coupling the pyroelectric element and the CCD with an In bump has been proposed in infrared physics (Infrared Phys.) 22, 259 (1982).

The material used for the pyroelectric infrared imaging device is TGS
System / LiTaO ₃ system single crystal, PbTiO ₃ system / PbZr _x Ti
_{There are 1-x} O ₃ based ceramics, PVF ₂ based organic films, and the like. Fv (= γ / (εCv)) and Fm (= γ / (Cv (εdtanδ) ^1/2 )), which are performance indexes of pyroelectric materials, are generally high in inorganic materials and low in organic materials. Here, γ is the pyroelectric coefficient, ε is the dielectric constant, Cv is the specific heat of deposition, and d is the thickness. It is necessary to reduce the thickness of the pyroelectric material in order to reduce the heat capacity of the pyroelectric element itself, to speed up the response, and to increase the sensitivity. In particular, for high-density one-dimensional and two-dimensional detectors, a pyroelectric thin film material having a high figure of merit is required.

Further, since the pyroelectric material takes out the change of the spontaneous polarization Ps as an output, when Ps is aligned in one direction, the maximum output can be obtained. Therefore, by applying a high electric field to the pyroelectric material, Ps
It is necessary to perform polarization processing to align the directions. However,
The c-axis oriented PbTiO ₃ -based thin film prepared by the rf macnetron sputtering method can be used for PbT without polarization treatment.
It has been reported in the 30th Joint Lecture on Applied Physics, Proceedings 7P-z-2 that a highly sensitive pyroelectric material exhibiting Fv about three times that of io ₃ ceramics can be realized.

Therefore, in order to improve sensitivity, detectability, spatial resolution, and responsiveness, it is important to reduce the thickness of the pyroelectric material used in the infrared imaging device. Therefore, a polishing process is required, and control must be performed to prevent cracking of the pyroelectric material. Further, there is a limit to thinning a single crystal or ceramics, and there is a limit to reducing the thickness to improve the detectability: D ‡. As the thickness decreased, it became difficult to control the film thickness, causing sensitivity variations.

Furthermore, when the pyroelectric material is polarized, dielectric breakdown occurs, and it is difficult to uniformly polarize them in a high-resolution array element arranged at high density. Therefore, a pyroelectric CCD with high sensitivity and small variation in sensitivity has not yet been developed.

On the other hand, when the pyroelectric thin film showing a high performance index and the CCD are joined by bumps or the like, the pyroelectric thin film is required to have mechanical strength, and the pyroelectric thin film is cracked or broken. In addition, contact failure and cracks occurred due to thermal expansion of the CCD and the sensor section.

It is an object of the present invention to provide a pyroelectric infrared imaging device that solves the above problems of the prior art.

Means for Solving the Problems The present invention has a chemical formula (Pb _x La _y ) (Ti _z
Zr _w ) O ₃ represented by a pyroelectric thin film, an electrode thin film group two-dimensionally arranged on the pyroelectric thin film, and an input diode of each element of the charge transfer device on the electrode thin film group so as to be connected. And a resin filled between the pyroelectric thin film and the charge transfer element, and the pyroelectric thin film is fixed to the charge transfer element. Further, the pyroelectric thin film is highly oriented in the <001> direction or the <111> direction, and the polarization direction is uniform in one direction. However, it is assumed that x, y, z and w in the above equation satisfy the above condition of a, b or c.

a) 0.7 ≦ x ≦ 1 0.9 ≦ x + y ≦ 1 0.95 ≦ z ≦ 1 w = 0 b) x = 1 y = 0 0.1 ≦ z ≦ 1 z + w = 1 c) 0.83 ≦ x ≦ 1 x + y = 1 0.3 ≦ z ≦ 1 0.96 ≦ z + w ≦ 1 Action In the pyroelectric infrared imaging device using the above-mentioned pyroelectric thin film and structure, since the pyroelectric thin film has a high performance index, high sensitivity is achieved. Not only is it possible to peel off the thin film,
Can prevent cracking. In addition, the above-mentioned pyroelectric thin film is sufficiently <001> when it is produced by the sputtering method.
Alternatively, if it is oriented in the <111> direction, spontaneous polarization is uniform without polarization treatment (JP-A-62-2).
No. 05266). Therefore, by using this pyroelectric thin film, spontaneous polarization in which spontaneous polarization has already been obtained is obtained,
It is possible to provide a high-performance pyroelectric infrared imaging device with high yield without the need for polarization processing.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 are views showing the structure and manufacturing process of the pyroelectric infrared imaging device of the present invention.

Pb _0.9 La _0.1 Ti _0.975 O ₃ (PLT) was grown to a thickness of _{3 μm} as a pyroelectric thin film 2 on a MgO single crystal substrate 1 cleaved by (100) and mirror-polished by a high frequency magnetron sputtering method ( FIG. 2 (a)). A for atmosphere gas
Using a mixed gas of r and O ₂ , the sputtering target is a powder of {0.8PLT + 0.2PbO}. Table 1 shows the sputtering conditions.

A plurality of CrAu having a thickness of about 0.2 μm are formed on the pyroelectric thin film 2.
The electrode thin film group 3 was produced by vapor deposition (FIG. 2 (b)).
The CrAu electrode thin film group 3 is two-dimensionally arranged by a photolithography method. Further, a CrAu vapor deposition film (not shown) is formed, and after electrically connected to each other,
Forming a resist except a part on the electrode thin film group 3;
Au bumps 4 are formed on the electrode thin film group 3 by electroplating.
Of 5 μm was produced (FIG. 2 (c)). Next, the CrAu
After removing the vapor deposition film by etching and separating the electrode thin film group 3, a resin 5 is applied on the pyroelectric thin film (FIG. 2 (d)). The Au bump 4 and the Al electrode group 8 provided on the input diode 7 of the charge transfer device 6 are aligned and M
UV rays are irradiated from the gO substrate 1 side to cure the resin 5,
The electrode thin film group 3 and the Al electrode group 8 of the charge transfer element 6 were joined via the Au bumps 4 (FIG. 2 (e)).
After that, a part or the whole of the MgO substrate 1 below the pyroelectric thin film 2 is etched with hot concentrated phosphoric acid to form an opening 9, and a NiCr light receiving electrode thin film 10 is formed on the substrate-side surface of the pyroelectric thin film 2. (Fig. 2 (f)).

An ultraviolet curable resin such as epoxy, silicone, or acrylic was used as the resin 5, but a thermosetting resin may be used as long as the heating temperature is lower than the Curie temperature of the pyroelectric thin film 2.

The PLT pyroelectric thin film used in this example has a polarization axis (<001>
Direction) is 90% oriented in one direction, the pyroelectric coefficient:
γ is 6.8 × 10 ^-8 C / cm ² k, which is 100 kV /
PbTiO ₃ ceramics (γ
= 1.8x10 ^-8 C / cm ² k), which is considerably larger. In addition, it is almost the same as the value after the polarization treatment, and is larger than the value after the polarization when the orientation ratio is small. When the orientation rate is 90%, the dielectric constant is about 200, which is almost the same value as that of ceramics. Therefore, the values of F _v and F _m , which are the performance indexes as a pyroelectric material, were also large, showing a value slightly more than three times the value of PbTiO ₃ ceramics.

As the pyroelectric material, a PbTiO ₃ -based thin film is given, and it is represented by the chemical formula (Pb _x La _y ) (Ti _z Zr _w ) O ₃ , and a) 0.7 ≦ x ≦ 1 0.9 ≦ x + y ≦ 1 0.95 ≦ z ≦ 1 w = 0 b) x = 1 y = 0 0.1 ≦ z ≦ 1 z + w = 1 c) 0.83 ≦ x ≦ 1 x + y = 1 0.3 ≦ z ≦ 1 0.96 ≦ z + w ≦ Also for the pyroelectric thin film material having any one of the compositions 1), the high performance index and the effect that the polarization treatment is unnecessary can be obtained. By using a pyroelectric thin film that exhibits a high performance index in this way and by fixing the charge transfer element and the pyroelectric thin film with resin, it is possible to achieve high sensitivity and high spatial resolution, and to crack and destroy the pyroelectric thin film. Could be prevented. Further, it was possible to prevent contact failure and cracks due to the difference in thermal expansion of the CCD sensor unit.

EFFECTS OF THE INVENTION The pyroelectric infrared imaging device according to the present invention uses a pyroelectric thin film that exhibits a high performance index and does not require polarization treatment, and has a structure in which the charge transfer device and the pyroelectric thin film are fixed by a resin.
By increasing the sensitivity and spatial resolution, it is possible to prevent the pyroelectric thin film from cracking or breaking. Further, it is possible to prevent contact failure and crack due to the difference in thermal expansion between the CCD and the sensor section. Further, it is possible to prevent cracking of the pyroelectric thin film due to the polarization treatment and nonuniformity of polarization, and it is possible to remarkably improve the yield.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a pyroelectric infrared imaging device according to an embodiment of the present invention, and FIG. 2 is a simplified diagram showing the manufacturing process of the pyroelectric infrared imaging device. 1 ... MgO substrate, 2 ... pyroelectric thin film, 3 ... electrode thin film group, 4 ... Au bump, 5 ... resin, 6 ... charge transfer element, 8 ... Al electrode group, 9 ... opening 10 ... Light receiving electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunihito Ogawa, 1006, Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Atsushi Abe, 1006, Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A pyroelectric thin film formed on a substrate, an electrode thin film group two-dimensionally arranged on the pyroelectric thin film, and an input diode of each element of a charge transfer device on the electrode thin film group. And a resin filled between the pyroelectric thin film and the charge transfer element, wherein the pyroelectric thin film is fixed to the charge transfer element. Pyroelectric infrared imaging device. 2. A pyroelectric thin film is represented by the chemical formula (Pb _x La _y ) (Ti _z Zr _w ) O ₃ , and a) 0.7 ≦ x ≦ 1 0.9 ≦ x + y ≦ 1 0.95 ≦ z ≦ 1 w = 0 b) x = 1 y = 0 0.1 ≦ z ≦ 1 z + w = 1 c) 0.83 ≦ x ≦ 1 x + y = 1 0.3 ≦ z ≦ 1 0.96 ≦ z + w ≦ 1 , <001> direction or <1
The pyroelectric infrared imaging device according to claim 1, wherein the pyroelectric infrared imaging device is highly oriented in the 11> direction, and the polarization directions are also aligned in one direction. 3. The pyroelectric infrared imaging device according to claim 1, wherein an ultraviolet curable resin is used.