JP3431764B2 - Pyroelectric infrared thin film element - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pyroelectric thin film,
The present invention relates to a pyroelectric infrared thin film element for infrared detection, in which an infrared detecting section composed of an upper electrode and a lower electrode respectively provided on the upper surface and the lower surface is formed above the concave portion of a substrate having a concave portion on the surface layer portion.

[0002]

2. Description of the Related Art One of the pyroelectric infrared thin film elements is disclosed in Japanese Patent Application Laid-Open No. 7-55577. In this pyroelectric infrared thin film element, as shown in FIGS. 8A and 8B, an MgO (100) single crystal substrate is used as a substrate 51, and a lower electrode 52 and a pyroelectric thin film 53 are provided on the surface layer portion thereof. The upper electrode 54 and the upper electrode 54 are provided in this order to make the lower electrode 52 smaller than the minute cavity 55 formed in the surface layer of the substrate 51. Therefore, the pyroelectric thin film 53 and the infrared detecting section 56 where the upper and lower electrodes 54, 52 overlap each other. Are supported by the organic support film 57.

[0003]

In the pyroelectric infrared thin film element having the above structure, the lower electrode 52 and the pyroelectric thin film 53 are provided.
Since the micro-cavity 55 is formed below the infrared detection section 56 where the upper electrode 54 and the upper electrode 54 overlap with each other, the heat capacity of the substrate 51 is reduced and the thermal response is excellent. There is.

That is, even with the above structure, even if infrared rays are incident on the infrared detecting section 56 and the temperature thereof rises, the heat in the infrared detecting section 56 is diffused to the surroundings, so that the sensitivity and high-speed response are improved. There was room for improvement in terms. Also,
As can be seen from FIG. 8A, the thin lead-out portion 52a of the lower electrode 52 is symmetrically provided between the infrared detecting portion 55 and the substrate 51 with the infrared detecting portion 55 as the center. Although the strength of the infrared detecting portion 55 after etching is to be increased, the lead-out portion 52a is made of Pt.

However, since Pt has low ductility and malleability and its coefficient of thermal expansion has a large difference from that of the organic holding film, it is susceptible to mechanical stress to cause wire breakage.

The present invention has been made in consideration of the above matters, and has a high sensitivity and a high-speed responsiveness by preventing the heat in the infrared detecting section by the incident infrared rays from being diffused to the outside as much as possible. Moreover, it is an object of the present invention to provide a robust pyroelectric infrared thin film element by adopting a structure with the least mechanical stress in the connection between the lower electrode and the lower extraction electrode.

[0007]

In order to achieve the above object, according to the present invention, an infrared detecting portion comprising a pyroelectric thin film and an upper electrode and a lower electrode respectively provided on the upper surface and the lower surface of the thin film is recessed in the surface layer portion. In a pyroelectric infrared thin film element formed on the concave portion of the substrate having, the concave portion is formed larger than the infrared detecting portion,
The infrared detector is held on the substrate only by an insulator thin film having a thermal conductivity lower than that of metal , and
The lower electrode is made of Pt and the lower electrode is
The lower extraction electrode to be connected is made of a gold-based material .

In the pyroelectric infrared thin film element having the above-mentioned structure, the infrared detecting portion does not come into direct contact with the substrate, and the infrared detecting portion is insulated with a thermal conductivity smaller than that of metal. Since it is held on the substrate only by the body thin film, when infrared rays are incident on the infrared detection section and its temperature rises, it is difficult for that heat to be transmitted to the substrate, and the heat associated with the incidence of the infrared rays is efficiently transmitted by the infrared detection section. Be absorbed. Therefore, the sensitivity and responsiveness of the pyroelectric infrared thin film element are improved.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below with reference to the drawings.

1 to 3 show an example of a pyroelectric infrared thin film element S of the present invention, FIG. 1 is a plan view of the pyroelectric infrared thin film element S, and FIG. I in 1
FIG. 4 is a cross-sectional view showing a cross-sectional shape taken along line I along with an enlarged view, and FIG. 3 is an exploded perspective view of a pyroelectric infrared thin film element S.

In FIGS. 1 to 3, 1 is a single crystal substrate made of MgO (magnesium oxide), and 2 is a minute recess formed in the surface layer of the substrate 1 by etching. Reference numeral 3 denotes a pyroelectric thin film, which is made of, for example, a PZT-based ferroelectric thin film or a PLZT ferroelectric thin film. This pyroelectric thin film 3
An upper electrode 4 and a lower electrode 5 made of, for example, Pt (platinum) are provided on the upper and lower surfaces of the so as to correspond to each other. 4a is a plurality of holes for etching formed in the upper electrode 4, and 5a is a protrusion formed in the lower electrode 5. The portion where the electrodes 4, 5 and the pyroelectric thin film 3 overlap each other when viewed in the direction of the arrow A is referred to as an infrared detection unit 6.

Reference numeral 7 denotes an infrared absorbing film provided so as to cover the upper surface of the upper electrode 4 serving as a light receiving electrode of the infrared detecting section 6. The photosensitive organic thin film capable of photolithography is provided with an infrared absorbing material such as carbon black. It is appropriately mixed. 8 is formed around the infrared detector 6,
An insulator thin film that holds the infrared detection unit 6 on the substrate 1, and is made of an organic insulator thin film such as a polyimide resin thin film or an inorganic insulator thin film such as a SiO ₂ thin film. 8a
Is a hole for etching formed in the insulator thin film 8, which is provided corresponding to the hole 4a of the upper electrode 4, and is provided so as to surround the infrared detecting section 6. 9, 10
Is an upper extraction electrode and a lower extraction electrode connected to the upper electrode 4 and the lower electrode 5, respectively, and is made of, for example, Au.

A method of forming the pyroelectric infrared thin film element S will be described with reference to FIGS. 5 to 7, a diagram schematically showing a cross-sectional shape and a diagram schematically showing a planar shape are shown in parallel. In addition, a symbol ('dash) is attached to a code representing a portion corresponding to each member before the final shape.

(1) M having an appropriate thickness (for example, 500 μm)
A gO (100) single crystal substrate 1 is prepared (see FIG. 4A).

(2) Pt of 0.2 μm is formed as the lower electrode 5 ′ on the upper surface of the substrate 1 by, for example, sputtering.
A film having a thickness of m is formed (see FIG. 4B).

(3) A PZT-based ferroelectric thin film (or PL) is formed on the upper surface of the lower electrode 5'as a pyroelectric thin film 3'by, for example, MOCVD (metalorganic chemical vapor deposition).
A ZT ferroelectric thin film) is formed to a thickness of about 2 μm (FIG. 4).
(See (C)).

(4) On the upper surface of the pyroelectric thin film 3 ', 0.2 Pt is formed as the upper electrode 4'by sputtering.
A film having a thickness of μm is formed (FIG. 4 (D) and FIG. 5 (A),
(See (B)).

(5) A resist is applied to the upper electrode 4 ', and the resist is patterned by photolithography.
After that, the upper electrode 4 is patterned by etching, and then the resist is removed to form a shape having a plurality of holes 4a (see FIGS. 5C and 5D).

(6) Next, a resist is applied to the pyroelectric thin film 3 ', and the resist is patterned by photolithography. Then, the pyroelectric thin film 3 is patterned by etching, the resist is removed, and the holes 4a of the upper electrode 4 are removed.
Is formed in a shape having a plurality of holes at positions corresponding to (see FIGS. 5E and 5F). In this embodiment, the pyroelectric thin film 3 has a diameter slightly larger than that of the upper electrode 4.

(7) Next, a resist is applied to the lower electrode 5 ', and the resist is patterned by photolithography. After that, the lower electrode 5'is patterned by etching, and then the resist is removed to form the lower electrode 5 and the lower electrode protrusion 5a continuous with the lower electrode 5 (FIG. 6 (A),
(See (B)). In this embodiment, the lower electrode 5 is formed to have the same diameter as the pyroelectric thin film 3, but the diameter may be slightly larger than this.

(8) An insulator thin film 8 having a thermal conductivity smaller than that of metal is formed around the infrared detecting section 6 and the upper surface of the substrate 1 (see FIGS. 6C and 6D). The insulator thin film 8 may be either an organic insulator thin film or an inorganic insulator thin film. A polyimide resin thin film is suitable as the organic insulator thin film, and a SiO ₂ thin film is suitable as the inorganic insulator thin film. And 8a is a hole provided at a position corresponding to the hole 4a of the upper electrode 4 and on the outer circumference of the infrared detecting section 6.

(9) Au by, for example, sputtering
An upper electrode lead-out portion 9 and a lower electrode lead-out portion 10 are formed (see FIGS. 6E and 6F).

(10) Then, a photosensitive organic thin film such as a negative resist material mixed with an infrared absorbing material such as carbon black of about 3 wt% is appropriately provided on the upper surface of the upper electrode 4 of the infrared detecting section 6. After being applied to a thickness, patterning is performed to cover the upper surface of the upper electrode 4 with the infrared absorbing film 7 (see FIGS. 7A and 7B).

A phosphoric acid solution having a predetermined concentration is injected as an etching solution from the hole 8a of the insulator thin film 8 to remove the substrate 1 immediately below the infrared detecting section 6 by etching to form a recess (microcavity) 2 ( See FIGS. 7C and 7D). In this case, the recess 2 is formed so as to be larger than the infrared detector 6, but since the insulator thin film 8 is formed over the periphery of the infrared detector 6 and the upper surface of the substrate 1, the infrared detector 6 is The insulator thin film 8 holds the upper surface of the recess 2 in a state of being levitated. That is, FIG. 1 to FIG. 3 and FIG.
A pyroelectric infrared thin film element S as shown in (C) and (D) is obtained.

By the way, in this embodiment, as shown in FIGS. 1 to 3, a plurality of holes 8a are formed in the insulator thin film 8 around the infrared detecting section 6. These holes 8a
Prevents the heat generated in the infrared detecting section 6 when infrared rays are incident on the infrared detecting section 6 from being easily transmitted to the surrounding area other than the infrared detecting section 6, and injects the etching solution when the MgO substrate 1 is etched. Used to do.

In the pyroelectric infrared thin film element S having the above-mentioned structure, the infrared detecting section 6 is made of the insulating thin film 8 for the substrate 1.
Since it is held on the substrate 1, it does not come into contact with the surface of the substrate 1 or the surface of the recess 2 formed in the surface layer thereof. Since the insulator thin film 8 holding the infrared detecting section 6 has a thermal conductivity smaller than that of metal, the infrared detecting section 6 is
When infrared rays are incident on and the temperature rises, the heat is hard to be transmitted to the direction of the substrate 1, and the heat associated with the incidence of infrared rays is efficiently absorbed by the infrared detecting section 6. Therefore, the sensitivity and responsiveness of the pyroelectric infrared thin film element S are improved.

Particularly, by providing a plurality of holes 8a around the infrared detecting portion 6 of the insulator thin film 8, the propagation of the heat can be prevented more effectively. Further, although this hole 8a can be used as an etching solution injection hole at the time of etching the substrate 1, a plurality of holes 8a are evenly provided around the infrared detecting portion 6 from the viewpoint of favorably forming the concave portion 2 by etching. Is good. Further, this hole 8a may be provided in the infrared detecting section 6.

By the way, although the lower electrode 5 is made of Pt,
The protrusion 5a for extraction formed on this is formed to be considerably short, and as shown in FIGS. 1 and 2, the tip thereof is formed so as not to exceed the recess 2 formed on the substrate 1 by etching. Further, the lower extraction electrode 10 connected to the extraction protrusion 5a has a ductility and malleability of A.
It is made of gold-based material such as u or gold alloy.

Then, the lower electrode 5 and the lower extraction electrode 10
As will be understood from FIGS. 2 and 3, the positional relationship of
The insulator thin film 8 is located above the lower electrode 5, and the lower extraction electrode 10 is located above this insulator thin film 8. That is, the insulator thin film 8 is interposed between the extraction protrusion 5 a connected to the lower electrode 5 and the lower extraction electrode 10. In view of this, in this embodiment, as shown in FIGS. 2 and 3, the pull-out protrusion 5a and the lower portion are connected via the through hole 8b formed in the insulator thin film 8 so as to correspond to the pull-out protrusion 5a. The extraction electrode 10 is electrically connected. That is, when the lower extraction electrode 10 is formed, Au is used.
Is partially formed on the through hole 8b formed in the insulator thin film 8 to electrically connect the lower extraction electrode 10 and the extraction projection 5a.

As described above, since the extraction protrusion 5a of the lower electrode 5 is short and the lower extraction electrode 10 connected to the lower electrode 5a is made of a gold-based material having high ductility and malleability, the extraction of the lower electrode 5 is performed. The configuration can be as mechanically stressed as possible. Therefore, a robust pyroelectric infrared thin film element S can be obtained.

The constituent material of the lower extraction electrode 10 is
Although Au may be used, a gold alloy mainly containing gold may be used.

[0032]

The present invention is implemented in the above-described modes and has the following effects.

It is possible to effectively prevent the heat generated in the infrared detecting section due to the infrared rays incident on the infrared detecting section from propagating to the outside of the infrared detecting section, especially to the substrate side. It is efficiently absorbed by the parts. Therefore, the sensitivity and responsiveness of the pyroelectric infrared thin film element are improved, and a more excellent pyroelectric infrared thin film element can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a pyroelectric infrared thin film element of the present invention.

FIG. 2 is a cross-sectional view taken along the line I-I in FIG. 1 and a partially enlarged view thereof.

3 is an exploded perspective view of the pyroelectric infrared thin film element S. FIG.

FIG. 4 shows a manufacturing process of the pyroelectric infrared thin film element together with FIGS. 5 to 7, and shows a beginning portion thereof.

FIG. 5 is a diagram showing a manufacturing process following FIG. 4;

FIG. 6 is a diagram showing the manufacturing process following FIG. 5;

FIG. 7 is a diagram showing a manufacturing process that follows FIG. 6;

8A and 8B are views for explaining a conventional technique, where FIG. 8A is a plan view and FIG. 8B is a sectional view.

[Explanation of symbols]

1 ... Substrate, 2 ... Recess, 3 ... Pyroelectric thin film, 4 ... Upper electrode,
Reference numeral 5 ... Lower electrode, 5a ... Extraction protrusion, 6 ... Infrared detector, 7 ... Infrared absorbing film, 8 ... Insulator thin film, 8a ... Hole, 1
0 ... Lower extraction electrode, S ... Pyroelectric infrared thin film element.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Matsumoto, 2 Higashimachi, Kichijoin-miya, Minami-ku, Kyoto-shi, Kyoto (56) References Japanese Patent Laid-Open No. 1-136035 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01J 1/00-1/60 G01J 5/00-5/62

Claims (4)

(57) [Claims] 1. A pyroelectric film comprising an infrared detecting section comprising a pyroelectric thin film and an upper electrode and a lower electrode respectively provided on the upper surface and the lower surface of the pyroelectric thin film, which is formed above the concave portion of a substrate having a concave portion in the surface layer portion. Type infrared thin film element, the recess is formed to be larger than the infrared detecting portion, and the infrared detecting portion is held on the substrate only by an insulating thin film having a thermal conductivity smaller than that of metal , and the lower portion
The electrode is made of Pt and is connected to this lower electrode.
A pyroelectric infrared thin film element, wherein the lower extraction electrode is formed of a gold-based material . 2. The pyroelectric infrared thin film element according to claim 1, wherein the insulator thin film is made of an organic resin material. 3. The pyroelectric infrared thin film element according to claim 1, wherein a plurality of holes are formed around the infrared detecting portion of the insulating thin film. 4. The upper electrode is covered with an infrared absorbing film.
Pyroelectric infrared thin film element according to any one of claims 1 to 3 that.