JP3555052B2 - Pyroelectric infrared thin film element - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to an infrared detection device in which an infrared detection section comprising a pyroelectric thin film and an upper electrode and a lower electrode provided on the upper and lower surfaces thereof is formed above the concave portion of a substrate having a concave portion in a surface layer portion. And a pyroelectric infrared thin film element.
[0002]
[Prior art]
One of the pyroelectric infrared thin film elements is disclosed in Japanese Patent Application Laid-Open No. 7-55577. As shown in FIGS. 8A and 8B, this pyroelectric infrared thin-film element uses an MgO (100) single crystal substrate as a substrate 51, and a lower electrode 52 made of a Pt thin film, A body thin film 53 and an upper electrode 54 made of a NiCr thin film are provided in this order, and the pyroelectric thin film 53 and the infrared detecting portion 55 where the upper and lower electrodes 54 and 52 overlap each other are held by an organic holding film 56, and then the infrared detecting portion The microcavity 57 is formed by etching the surface layer portion of the substrate 51 below 55.
[0003]
[Problems to be solved by the invention]
According to the pyroelectric infrared thin film element having the above-described structure, the microcavity 55 is formed below the infrared detecting section 56 where the lower electrode 52, the pyroelectric thin film 53, and the upper electrode 54 overlap each other. Although the heat capacity is small and the thermal response is excellent, it has the following disadvantages.
[0004]
That is, as understood from FIG. 8A, the thin lead-out portion 52a of the lower electrode 52 is symmetrically provided between the infrared detection section 55 and the substrate 51 with the infrared detection section 55 as the center. In order to increase the strength of the infrared detection unit 55 after the substrate is etched, the extraction unit 52a is made of Pt.
[0005]
However, Pt has a small ductility and malleability, and its coefficient of thermal expansion has a great difference from that of the organic retaining film.
[0006]
The present invention has been made in consideration of the above-mentioned matter, and adopts a structure having as little mechanical stress as possible in connection between a lower electrode and a lower extraction electrode, thereby providing a robust pyroelectric infrared thin film element. It is intended to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a pyroelectric thin film, and an infrared detecting portion comprising an upper electrode and a lower electrode provided on the upper surface and the lower surface, respectively, are provided above the concave portion of the substrate having the concave portion in the surface layer portion. In the formed pyroelectric infrared thin film element, the lower electrode is formed of Pt, and a lower extraction electrode connected to the lower electrode is formed of a gold-based material. The extraction protrusion as a connection portion was positioned so as not to exceed the edge of the recess , and the extraction protrusion and the lower extraction electrode were formed on an insulating thin film interposed therebetween. Electrical connection is made through the holes .
[0008]
In the pyroelectric infrared thin film element having the above-described structure, the lower electrode made of Pt has a short lead-out protrusion, and the lower lead electrode connected to this lower electrode is made of a gold-based material (pure gold or gold) that is highly ductile and malleable. (A gold alloy as a main component), the lead-out configuration of the lower electrode can be made as small as possible with mechanical stress.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the details of the present invention will be described with reference to the drawings.
[0010]
1 to 3 show an example of a pyroelectric infrared thin film element S according to the present invention. FIG. 1 is a diagram showing a planar shape of the pyroelectric infrared thin film element S. FIG. FIG. 3 is a cross-sectional view showing a cross-sectional shape along line I along with an enlarged view, and FIG. 3 is an exploded perspective view of a pyroelectric infrared thin film element S.
[0011]
1 to 3, reference numeral 1 denotes a single crystal substrate made of MgO (magnesium oxide), and reference numeral 2 denotes a minute concave portion formed in a surface layer portion of the substrate 1 by etching. Reference numeral 3 denotes a pyroelectric thin film, for example, a PZT-based ferroelectric thin film or a PLZT ferroelectric thin film. An upper electrode 4 and a lower electrode 5 made of, for example, Pt (platinum) are provided on both upper and lower surfaces of the pyroelectric thin film 3 so as to correspond to each other. Reference numeral 4a denotes a plurality of etching holes formed in the upper electrode 4, and 5a denotes a lead-out projection formed in the lower electrode 5. When viewed in the direction of the arrow A, a portion where the electrodes 4 and 5 and the pyroelectric thin film 3 overlap each other is referred to as an infrared detector 6.
[0012]
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 unit 6. An infrared absorbing material such as carbon black is appropriately mixed into a photosensitive organic thin film capable of photolithography. It is. Reference numeral 8 denotes an insulating thin film formed around the infrared detecting unit 6 and holding the infrared detecting unit 6 with respect to the substrate 1, and an organic insulating thin film such as a polyimide resin thin film or an inorganic insulating thin film such as a SiO ₂ thin film. Consists of a thin film. Reference numeral 8a denotes an etching hole formed in the insulating 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 unit 6. Reference numeral 8b denotes a through hole provided on the insulating thin film 8 at a position corresponding to the extraction protrusion 5a of the lower electrode 5. Reference numerals 9 and 10 denote an upper extraction electrode and a lower extraction electrode electrically connected to the upper electrode 4 and the lower electrode 5, respectively.
[0013]
A method for forming the pyroelectric infrared thin film element S will be described with reference to FIGS. 5 to 7, a diagram schematically illustrating a cross-sectional shape and a diagram schematically illustrating a planar shape are respectively shown in parallel. In addition, reference numerals indicating portions corresponding to the respective members before the final shape are denoted by '(dash).
[0014]
(1) An MgO (100) single crystal substrate 1 having an appropriate thickness (for example, 500 μm) is prepared (see FIG. 4A).
[0015]
(2) Pt is formed as a lower electrode 5 'to a thickness of 0.2 μm on the upper surface of the substrate 1 by, for example, sputtering (see FIG. 4B).
[0016]
(3) On the upper surface of the lower electrode 5 ', a PZT-based ferroelectric thin film (or a PLZT ferroelectric thin film) is formed as a pyroelectric thin film 3' by about 2 μm by MOCVD (metal organic chemical vapor deposition), for example. (See FIG. 4C).
[0017]
(4) On the upper surface of the pyroelectric thin film 3 ', Pt is formed as an upper electrode 4' to a thickness of 0.2 μm by sputtering (see FIGS. 4D, 5A, and 5B). ).
[0018]
(5) A resist is applied to the upper electrode 4 ', and the resist is patterned by photolithography. Then, after patterning the upper electrode 4 by etching, the resist is removed to form a shape having a plurality of holes 4a (see FIGS. 5C and 5D).
[0019]
(6) Next, a resist is applied to the pyroelectric thin film 3 ', and the resist is patterned by photolithography. Then, after patterning the pyroelectric thin film 3 by etching, the resist is removed, and the upper electrode 4 is formed into a shape having a plurality of holes at positions corresponding to the holes 4a (see FIGS. 5E and 5F). ). In this embodiment, the pyroelectric thin film 3 is formed to have a slightly larger diameter than the upper electrode 4.
[0020]
(7) Next, a resist is applied to the lower electrode 5 ', and the resist is patterned by photolithography. Then, after patterning the lower electrode 5 'by etching, the resist is removed, and the lower electrode 5 and the lead-out protrusion 5a connected thereto are formed (see FIGS. 6A and 6B). In this case, the draw-out protrusion 5a is formed as short as possible (this will be described later). In this embodiment, the lower electrode 5 is formed to have the same diameter as the pyroelectric thin film 3, but may have a slightly larger diameter.
[0021]
(8) An insulating thin film 8 having a thermal conductivity smaller than that of a metal is formed around the infrared detecting section 6 and the upper surface of the substrate 1 (see FIGS. 6C and 6D). The insulating thin film 8 may be either an organic insulating thin film or an inorganic insulating thin film. A polyimide resin thin film is suitable as the organic insulating thin film, and a SiO ₂ thin film is preferable as the inorganic insulating thin film.
[0022]
(9) The upper electrode lead portion 9 and the lower lead portion 10 made of Au are formed by, for example, sputtering (see FIGS. 6E and 6F). At this time, a part of Au flows into the through-hole 8b formed in the insulating thin film 8.
[0023]
(10) Then, a photosensitive organic thin film such as a negative resist material mixed with about 3 wt% of an infrared absorbing material such as carbon black is coated on the upper surface of the upper electrode 4 of the infrared detecting section 6 as appropriate. After that, by patterning, the upper surface of the upper electrode 4 is covered with the infrared absorbing film 7 (see FIGS. 7A and 7B).
[0024]
A phosphoric acid solution having a predetermined concentration is injected as an etching solution through the holes 8a of the insulating thin film 8, and the substrate 1 immediately below the infrared detecting unit 6 is removed by etching to form a concave portion (microcavity) 2 (FIG. 7 ( C) and (D)). In this case, the concave portion 2 is formed so as to be larger than the infrared detecting portion 6, but since the insulating thin film 8 is formed around the infrared detecting portion 6 and over the upper surface of the substrate 1, the infrared detecting portion 6 It is held in a state of floating on the upper surface of the concave portion 2 by the insulating thin film 8. That is, a pyroelectric infrared thin film element S as shown in FIGS. 1 to 3 and FIGS. 7C and 7D is obtained.
[0025]
Here, the connection structure between the lower electrode 5 and the lower extraction electrode 10 will be described. The lower electrode 5 is made of Pt, and the extraction protrusion 5a formed on the lower electrode 5 is formed to be quite short. As shown, the tip is formed so as not to exceed the recess 2 formed in the substrate 1 by etching. The lower extraction electrode 10 connected to the extraction projection 5a is made of a gold-based material such as pure gold or a gold alloy, which is highly ductile and malleable.
[0026]
As understood from FIGS. 2 and 3, the positional relationship between the lower electrode 5 and the lower extraction electrode 10 is such that the insulating thin film 8 is located above the lower electrode 5, and the lower insulating film 8 is located above the insulating thin film 8. The extraction electrode 10 is located. That is, the insulating thin film 8 is interposed between the lower electrode 5 and the extraction protrusion 5 a connected to the lower electrode 5. Therefore, in this embodiment, as shown in FIGS. 2 and 3, the projection 5a and the lower part are formed through the through holes 8b formed in the insulating thin film 8 so as to correspond to the projections 5a. The extraction electrode 10 is electrically connected. That is, a part of Au flows into the through hole 8b formed in the insulating thin film 8 when the lower extraction electrode 10 is formed, and the lower extraction electrode 10 and the extraction protrusion 5a are electrically connected.
[0027]
The constituent material of the lower extraction electrode 10 may be pure gold, or may be a gold alloy mainly composed of gold.
[0028]
【The invention's effect】
The present invention is embodied in the form described above, and has the following effects.
[0029]
The lead-out protrusion of the lower electrode made of Pt is short, and the lower lead-out electrode connected to this lower electrode is made of a gold-based material having excellent ductility and malleability. Can be smaller. Therefore, a robust pyroelectric infrared thin film element can be obtained.
[Brief description of the 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 sectional view taken along line II of FIG. 1 and a partially enlarged view thereof.
FIG. 3 is an exploded perspective view of the pyroelectric infrared thin film element S.
FIG. 4 shows a manufacturing process of the pyroelectric infrared thin film element together with FIGS. 5 to 7 and shows an initial part of the manufacturing process.
FIG. 5 is a view showing a manufacturing step following FIG. 4;
FIG. 6 is a view showing a manufacturing step following FIG. 5;
FIG. 7 is a view showing a manufacturing step following FIG. 6;
FIGS. 8A and 8B are diagrams for explaining a conventional technique, wherein FIG. 8A is a plan view and FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... recessed part, 3 ... pyroelectric thin film, 4 ... upper electrode, 5 ... lower electrode, 5a ... protrusion protrusion, 6 ... infrared detection part, 7 ... infrared absorption film, 8 ... insulator thin film, 8b: hole, 10: lower extraction electrode, S: pyroelectric infrared thin film element.

Claims (1)

In a pyroelectric infrared thin-film element in which a pyroelectric thin film and an infrared detecting portion comprising an upper electrode and a lower electrode provided on the upper and lower surfaces thereof are formed above the concave portion of a substrate having a concave portion in a surface layer portion, The lower electrode is formed of Pt, a lower extraction electrode connected to the lower electrode is formed of a gold-based material, and an extraction protrusion, which is a connection portion of the lower electrode with the lower extraction electrode, is formed in the recess. And the extraction protrusion and the lower extraction electrode are electrically connected to each other through a hole formed in the insulator thin film interposed therebetween. A pyroelectric infrared thin film element characterized by the following.

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