JPH0719963A - Ferroelectric thin film device - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To improve infrared absorption efficiency and heat conversion efficiency. [Structure] A film 15a in a region of the front surface side electrode 15 which overlaps with the ferroelectric thin film 2 has a thickness of 500 Å or more and 500 Å or more.
It is formed to a thickness of angstrom or less. The heat conduction of the thinly formed film 15b in the peripheral region is suppressed, and the heat converted by the absorption of infrared rays is not dissipated to all of the front surface side electrode 15 and the thickly formed film 15a of the front surface side electrode 15 is absorbed. Since heat is stored in the part, not only the infrared absorption efficiency is high, but also the heat conversion efficiency is the highest.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric thin film device (pyroelectric infrared sensor) for detecting infrared rays using a ferroelectric pyroelectric thin film.

[0002]

2. Description of the Related Art Usually, a ceramic or single crystal bulk material has been used for a pyroelectric element used in an infrared sensor, but in recent years, a ferroelectric thin film has been used for the purpose of downsizing the device and forming an array. Ferroelectric thin film devices using materials have been manufactured. Further, when a ferroelectric material was used for the above-mentioned application, polarization treatment was indispensable in order to align the polarization direction of the ferroelectric element in one direction. Ferroelectric device manufacturing technology that can achieve this has also been developed.

The structure of a conventional ferroelectric thin film device will be described below. FIG. 6 shows the structure of a conventional ferroelectric thin film device. 6A is a plan view, FIG. 6B is a sectional view taken along the line DD, and FIG. 7 is a process explanatory view showing a manufacturing process of a conventional ferroelectric thin film device. As shown in these drawings, in the conventional ferroelectric thin film device, the ferroelectric thin film 2 is sandwiched by the back surface side electrode 4 and the front surface side electrode 50, and the peripheral region thereof is formed by the organic thin film 3.
It is composed of a structure held by.

The pyroelectric infrared sensor detects a change in temperature of the ferroelectric thin film 2 due to infrared absorption, and it is necessary to suppress heat dissipation from the ferroelectric thin film 2 as much as possible and improve infrared absorption efficiency. Therefore, the structure is such that the MgO substrate 1 is removed and held only by the thin organic thin film 3. Further, the electrodes 4 and 50 connected to the ferroelectric thin film 2 are also thinned, and the rear surface side electrode lead-out portion 6 is thinly formed to thoroughly suppress heat dissipation.

Next, referring to FIGS. 7A to 7C,
A manufacturing process of a conventional ferroelectric thin film device will be described. First,
As shown in FIG. 7A, a lead titanate-based ferroelectric thin film 2 is formed on a single crystal MgO substrate 1 by an RF magnetron sputter method. By this film forming method and its optimum film forming conditions, it is possible to obtain the ferroelectric thin film 2 in which the polarization is aligned in one direction without the need for polarization treatment.

Next, as shown in FIG. 7B, the organic thin film 3 is formed into a desired shape by spin coating and a photolithography process, and is connected to the back surface side electrode 4 on the upper part of the ferroelectric thin film 2. The window is opened and the back surface side electrode 4 is formed. Next, the MgO substrate 1 is removed by etching, and a front surface side electrode 50 is formed on the surface of the ferroelectric thin film 2 facing the back surface side electrode 4, as shown in FIG. 7C.

In the ferroelectric thin film device, there are a case where all the MgO substrate 1 is removed and a case where only the effective region including the ferroelectric thin film 2 is removed in order to form the diaphragm. The case of removing the MgO substrate 1 has been described. This ferroelectric thin film device has a front surface electrode 5
The side where 0 is formed becomes the sensor surface, and the infrared rays to be detected first pass through the front surface side electrode 50 and enter. Normally, the front-side electrode 50 is formed of a metal material made of NiCr, but it is transparent to some extent even in the visible because of an extremely thin film thickness of 100 angstroms or less, and the wavelength of infrared rays has a long wavelength (of human body). Since it is about 10 μm in some cases, it can be easily transmitted.

The infrared light transmitted through the front surface side electrode 50 is transmitted through the ferroelectric thin film 2 and the back surface side electrode 4 in this order, but the back surface side electrode 4 is one digit larger than the front surface side electrode 50 due to structural strength. Since the thick film is used as described above, the surface thereof has a metallic luster similar to that of the NiCr bulk material, so that most of the light is reflected and the light is emitted in the route opposite to the incident. In these processes, the infrared rays absorbed by either of the electrodes 4 and 50 are converted into heat and detected.

[0009]

However, in the above-mentioned conventional ferroelectric thin film device, since the ferroelectric thin film 2 is a material transparent to infrared rays having a long wavelength, it cannot absorb infrared rays. It cannot function unless infrared rays are absorbed by the remaining electrodes 4 and 50. As described above, since the back surface side electrode 4 has a metallic luster similar to that of the NiCr bulk material, most of the back surface side electrode 4 is reflected and cannot contribute to the absorption of infrared rays, and functions by the absorption effect of the front surface side electrode 50. Is the current situation. However, a high absorption effect cannot be obtained only with the front surface side electrode 50, and a sufficient detection function has not yet been achieved.

Another problem is disconnection of the front surface side electrode 50. For example, a slight stress such as deformation of the organic thin film 3 causes a crack, which leads to disconnection. The extremely thin surface-side electrode 50 has a film thickness equal to the metal particle level, and the strength is determined by the bonding force of the metal grain boundaries. Therefore, in the state where the metal grain boundaries are extremely small, the strength is zero.

Therefore, an object of the present invention is to provide a ferroelectric thin film device having a structure having a high infrared absorption effect and an excellent detection function. Another object of the present invention is to provide a ferroelectric thin film device which prevents disconnection of the surface side electrode and has high reliability.

[0012]

According to another aspect of the present invention, there is provided a ferroelectric thin film device in which an organic thin film, a ferroelectric thin film whose peripheral region is held by the organic thin film, and the ferroelectric thin film are sandwiched therebetween. The front surface side electrode and the back surface side electrode that are formed are provided, and the thickness of the front surface side electrode is in the range of 150 angstroms or more and 300 angstroms or less.

A ferroelectric thin film device according to a second aspect of the present invention is an organic thin film, a ferroelectric thin film whose peripheral region is held by the organic thin film, and a surface side electrode formed so as to sandwich the ferroelectric thin film. And the back surface side electrode, and the thickness of the region of the front surface side electrode that overlaps the ferroelectric thin film is in the range of 150 angstroms or more and 500 angstroms or less.

A ferroelectric thin film device according to a third aspect of the present invention is an organic thin film, a ferroelectric thin film whose peripheral region is held by the organic thin film, and a surface side electrode formed so as to sandwich the ferroelectric thin film. And a back surface side electrode, the front surface side electrode is formed of a gold-based alloy material, and the infrared absorption film is formed in a region overlapping with the ferroelectric thin film of the front surface side electrode.

[0015]

According to the ferroelectric thin film device of the present invention, since the surface-side electrode is formed to have a thickness of 150 angstroms or more and 300 angstroms or less, the surface-side electrode has the highest infrared absorption efficiency. , Its effect, and excellent detection function can be obtained. Further, since the thickness of the front surface side electrode is increased, disconnection can be prevented.

According to the ferroelectric thin film device of the second aspect, since the region of the surface side electrode which overlaps with the ferroelectric thin film is formed to have a thickness of 150 angstroms or more and 500 angstroms or less, the peripheral region The heat conduction of the thinly formed surface side electrode is suppressed, and the heat converted by absorption of infrared rays is stored in the thickly formed part of the surface side electrode without being dissipated to all of the surface side electrode,
Not only the infrared absorption efficiency is high, but also the heat conversion efficiency is the highest, so that a more excellent detection function can be obtained.

According to the ferroelectric thin film device of the third aspect, since the front surface side electrode is formed of a gold-based alloy material with small metal particles, there are many film thicknesses similar to the conventional one. Since the metal grain boundary improves the bonding force between metal particles and has high strength, and because the material itself is rich in ductility, it can flexibly follow the deformation of the organic thin film,
It is possible to prevent disconnection due to the influence of stress. On the other hand, the gold-based alloy material is inferior in infrared absorption, but since the infrared absorption film is formed in the region overlapping the ferroelectric thin film of the surface side electrode,
The detection function is not impaired, but rather the detection function can be improved.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. 1A and 1B show the structure of a ferroelectric thin film device (a pyroelectric infrared sensor using a ferroelectric thin film) according to a first embodiment of the present invention. FIG. 1A is a plan view and FIG. FIG. Surface side electrode 5 made of NiCr
Is formed to have a film thickness of 150 angstroms or more and 300 angstroms or less, and has the same structure as the conventional ferroelectric thin film device and can be manufactured by the same manufacturing process.

FIG. 2 is a characteristic diagram showing the dependence of the infrared absorption rate and the pyroelectric sensitivity of the pyroelectric infrared sensor on the film thickness on the surface side electrode. As shown in this figure, the pyroelectric sensitivity of the pyroelectric infrared sensor greatly depends on the film thickness of the surface-side electrode 5,
In the region where the film thickness is thin, the pyroelectric sensitivity also changes with the infrared absorptivity, and the pyroelectric sensitivity also becomes maximum at a film thickness near 200 angstroms at which the infrared absorptivity becomes maximum. When the surface electrode 5 has a film thickness of 100 angstroms or less as in the conventional case,
Since the effect of infrared absorption cannot be effectively utilized, only low pyroelectric sensitivity can be obtained, and when the film thickness of the surface side electrode 5 is in the vicinity of 200 angstroms or more, the heat dissipated increases due to the effect of heat conduction. The pyroelectric sensitivity decreases more than the decrease in the rate. Therefore, considering the controllability of the film thickness of the front surface side electrode 5, the infrared absorption rate is high, and the heat dissipation is small, centered around 200 angstroms.
By selectively forming a film thickness of 0 angstroms or more and 300 angstroms or less, it is possible to obtain a structure having the highest pyroelectric sensitivity.

A second embodiment of the present invention will be described with reference to the drawings. 3A and 3B show the structure of a ferroelectric thin film device (a pyroelectric infrared sensor using a ferroelectric thin film) according to a second embodiment of the present invention. FIG. 3A is a plan view and FIG. It is a -B sectional view. Also in the second embodiment, as in the first embodiment, the front surface side electrode 15 is formed with a thicker film 15a than the conventional one.
However, the region is limited to a region overlapping with the ferroelectric thin film 2, and the other regions are formed with a film 15b having a thickness of 100 angstroms or less as in the conventional case.

With this configuration, as shown in the characteristic diagram of FIG. 4 showing the dependence of the infrared absorption rate and the pyroelectric sensitivity of the pyroelectric infrared sensor of the second embodiment on the thickness of the electrode on the surface side electrode, the peripheral region is thin. The heat conduction of the formed film 15b is suppressed, and the heat converted by the absorption of infrared rays is stored in the thickly formed film 15a of the front surface side electrode 15 without being dissipated to all of the front surface side electrode 15, Not only the infrared absorption efficiency is high, but also the heat conversion efficiency is the highest, and there is no rapid decrease in pyroelectric sensitivity even at a film thickness of around 200 angstroms at which both the pyroelectric sensitivity and the infrared absorption rate are maximum.
With a film thickness in the range of 150 angstroms or more and 500 angstroms or less, the same effect as that of the first embodiment can be obtained, and the selection range of the film thickness of the front surface side electrode 15 is widened, and
A better detection function can be obtained. Further, it has been confirmed that the heat conversion efficiency is also improved by reducing the heat capacity by reducing the area and the film thickness of the ferroelectric thin film 2, and the detection function is greatly improved accordingly.

A third embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows the structure of a ferroelectric thin film device (a pyroelectric infrared sensor using a ferroelectric thin film) according to a third embodiment of the present invention, (a) is a plan view, and (b) is its C. FIG. In the third embodiment, the front surface side electrode 9 is made of a gold-based alloy material such as a gold-paradium alloy. Since gold-based alloy materials have small metal particles, even if the film thickness is the same as the conventional one, the bonding force between metal particles is improved due to the many metal grain boundaries that exist, and the material itself has a high strength. Since it is rich in ductility, it can flexibly follow the deformation of the organic thin film 3, so that disconnection due to the influence of stress can be prevented.

On the other hand, the gold-based alloy material is inferior in absorption of infrared rays, but in the third embodiment, the infrared absorption film 10 is formed in the region of the surface side electrode 9 overlapping the ferroelectric thin film 2 to detect the infrared rays. However, the detection function can be improved. The infrared absorption film 10 may be made of a NiCr material having a film thickness of 150 angstroms or more and 500 angstroms or less, as in the second embodiment.

[0024]

According to the ferroelectric thin film device of the first aspect of the present invention, the surface side electrode has a thickness of 150 angstroms or more and 300 angstroms or more.
Since it is formed to have a thickness of less than angstrom, the infrared absorption efficiency can be improved and an excellent detection function can be realized. Further, it is possible to prevent disconnection of the front surface side electrode and ensure high reliability.

In the ferroelectric thin film device according to the second aspect of the present invention, since the region of the surface side electrode that overlaps with the ferroelectric thin film is formed to have a thickness of 150 angstroms or more and 500 angstroms or less, the infrared absorption efficiency is improved. It is possible to improve and realize an excellent detection function. According to the ferroelectric thin film device of the third aspect, since the front surface side electrode is formed of a gold-based alloy material having small metal particles, it is possible to prevent disconnection of the front surface side electrode and ensure high reliability. You can Further, since the infrared absorption film is formed in the region of the surface side electrode that overlaps with the ferroelectric thin film, the infrared absorption efficiency can be improved and an excellent detection function can be realized.

[Brief description of drawings]

FIG. 1A is a plan view of a ferroelectric thin film device according to a first embodiment of the present invention, and FIG. 1B is a sectional view taken along line AA of FIG.

FIG. 2 is a characteristic diagram showing the dependence of the infrared absorption rate and the pyroelectric sensitivity of the pyroelectric infrared sensor of the first embodiment on the film thickness on the surface side electrode.

3A is a plan view of a ferroelectric thin film device according to a second embodiment of the present invention, and FIG. 3B is a sectional view thereof.

FIG. 4 is a characteristic diagram showing the dependency of the infrared absorption rate and the pyroelectric sensitivity of the pyroelectric infrared sensor of the second embodiment on the film thickness on the surface side electrode.

5A is a plan view of a ferroelectric thin film device according to a third embodiment of the present invention, and FIG. 5B is a sectional view thereof.

FIG. 6A is a plan view of a conventional ferroelectric thin film device,
(B) is a sectional view.

7A to 7C are explanatory views showing a manufacturing process of a conventional ferroelectric thin film device.

[Explanation of symbols]

 1 MgO Substrate 2 Ferroelectric Thin Film 3 Organic Thin Film 4 Back Side Electrode 5 Front Side Electrode 9 Front Side Electrode 10 Infrared Absorption Film 15 Front Side Electrode

Claims (3)

[Claims] 1. An organic thin film, a ferroelectric thin film whose peripheral region is held by the organic thin film, a front surface side electrode and a rear surface side electrode formed so as to sandwich the ferroelectric thin film, and the front surface. A ferroelectric thin film device in which the thickness of the side electrode is in the range of 150 angstroms or more and 300 angstroms or less. 2. An organic thin film, a ferroelectric thin film whose peripheral region is held by the organic thin film, a front surface side electrode and a back surface side electrode formed so as to sandwich the ferroelectric thin film, and the front surface. A ferroelectric thin film device in which a thickness of a region of the side electrode overlapping with the ferroelectric thin film is set in a range of 150 angstroms or more and 500 angstroms or less. 3. An organic thin film, a ferroelectric thin film whose peripheral region is held by the organic thin film, a front surface side electrode and a back surface side electrode formed so as to sandwich the ferroelectric thin film, and the surface. The side electrode is made of a gold-based alloy material,
A ferroelectric thin film device in which an infrared absorbing film is formed in a region of the surface-side electrode that overlaps with the ferroelectric thin film.