Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – Measuring or testing system or device
Reexamination Certificate
2002-09-24
2004-12-28
Kopec, Mark (Department: 1751)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
Measuring or testing system or device
C374S032000, C374S176000, C250S336100, C250S336200
Reexamination Certificate
active
06836677
ABSTRACT:
TECHNICAL FIELD
This invention relates to a bolometer material and a bolometer thin film that are suitable for use in a non-cooled infrared sensing element which reads signals on radiation intensity of infrared radiation by the use of a material that absorbs incident infrared radiation, changes its temperature to thereby change its electrical resistance with the temperature change, as well as to a method for producing a bolometer thin film and an infrared sensing element utilizing these techniques.
BACKGROUND ART
In typical bolometer-type infrared sensing elements, a photoreceptor absorbs incident infrared radiation to thereby change its temperature, the temperature change of the photoreceptor then causes a change in electrical resistance of a material in the photoreceptor, and the radiation intensity of the infrared radiation is detected as an electrical signal based on the change in electrical resistance. The sensitivity of detection increases with an increasing temperature-dependency (temperature coefficient of resistance; TCR) of the electrical resistance change. Thin films for use in bolometer-type non-cooled infrared sensing elements are thin films which absorb infrared radiation at room temperature to change their temperatures to thereby change their electrical resistance. As such thin films, thin films made of silicon (Si), germanium (Ge), or divanadium trioxide (V
2
O
3
) used as semiconductor materials have been used in practice. Silicon (Si) has a |TCR| of about 1.5%/deg., and the divanadium trioxide (V
2
O
3
) thin film having a relatively high sensitivity has a |TCR| at room temperature of about 2.0%/deg.
To further improve the sensitivity of such non-cooling infrared sensing elements, an infrared sensing element using a bolometer having a temperature coefficient of resistance (|TCR|) at 20° C. of 0.4 to 3.9%/K has been proposed. The bolometer material for use in the infrared sensing element in question is a semiconductor including a crystalline or polycrystalline oxide or fine-structured amorphous substance comprising (1) one or more elements selected from barium, strontium, and calcium, (2) one or more elements selected from yttrium, lanthanum, and rare earth elements, (3) copper, and (4) oxygen. More specifically, the material is a yttrium (Y)-barium (Ba)-copper (Cu)-oxygen (O) system (hereinafter briefly referred to as “YBCO”) material having a compositional ratio of Y:Ba:Cu:O of 1:1.2-2.1:3:7-9 (Japanese Unexamined Patent Application Publication No. 11-500578).
FIG.
4
(A) illustrates an example of a configuration of an infrared sensing element using such a conventional YBCO thin film as described in Japanese Unexamined Patent Application Publication No. 11-500578 as a bolometer thin film. FIG.
4
(A) is a cross sectional view of the infrared sensing element. FIG.
4
(A) shows that the conventional infrared sensing element comprises a silicon (Si) substrate
100
and a monolithic transducer structure
108
floated over a cavity
107
. FIG.
4
(B) is a top view of the silicon substrate
100
. In FIG.
4
(B), the top of the cavity
107
is almost continuously formed along the outer periphery of the monolithic transducer structure
108
except for part of the outer periphery. A portion remaining after etching serves as a support
109
and fixes the monolithic transducer structure
108
to the silicon substrate
100
. The monolithic transducer structure
108
has a multilayer structure as shown in FIG.
4
(A). Specifically, the monolithic transducer structure
108
comprises a first silicon nitride layer
101
, a first yttrium-stabilized zirconia layer
102
, a YBCO layer
103
, a second yttrium-stabilized zirconia layer
104
, and a second silicon nitride layer
105
. A metallic lead
106
is electrically connected with the YBCO layer
103
. The second silicon nitride layer
105
plays roles as a protecting film and as the support
109
.
The sensitivity of such infrared sensing elements is proportional to the temperature coefficient of resistance (TCR) and is inversely proportional to voltage noise induced by various causes occurring upon the manufacture of the infrared sensing elements. The resistance increases or decreases with temperature change, but the temperature coefficient of resistance is evaluated on the basis of the absolute value of the change of the resistance and is hereinafter referred to as “|TCR|”.
To increase the sensitivity of non-cooled infrared sensing elements, |TCR| at room temperature should be equal to or more than 2.5%/deg. and should preferably be equal to or more than 3.0%/deg. As is described above, conventional silicon (Si), germanium (Ge) or divanadium trioxide (V
2
O
3
) thin films each have |TCR| less than 2.5%/deg., and resulting infrared sensing elements cannot have high sensitivity, as long as they include these thin films as a bolometer.
The YBCO thin film has a high |TCR| at room temperature, exhibits a low noise voltage and is a promising bolometer thin film to increase the sensitivity of infrared sensing elements. However, YBCO materials are apt to absorb moisture and carbon dioxide gas upon manufacture and, when they are used as a sputtering target, the resulting target splits in some cases. In addition, the YBCO thin film exhibits an increased electric resistance when it is left in the air, thus causing variations and deterioration upon handling.
The present invention has been accomplished to solve these problems, and it is an object of the present invention to provide a bolometer material having a high temperature coefficient of resistance (|TCR|), to provide a bolometer thin film exhibiting low voltage noise and a small variation in electric resistance and a method for producing the same, and to provide a highly sensitive infrared sensing element using the bolometer thin film.
DISCLOSURE OF INVENTION
To achieve the above objects, the present invention provides a bolometer material mainly comprising an oxide represented by formula: Z
y
CuO
x
, wherein Z is one or more of alkaline earth metals, one or more of rare earth elements selected from yttrium and lanthanoid elements, one or more of elements belonging to Period 5 or Period 6 of the Periodic Table selected from bismuth, lead, thallium, mercury and cadmium, or potassium or sodium; y is a number satisfying the following condition: 0<y≦2; and x is a number satisfying the following condition: 0.5y≦x≦1.5+2y.
The bolometer material of the present invention may mainly comprise CuO
x
wherein y in the elemental compositional formula equals zero.
In the bolometer material of the present invention just mentioned above, x in CuO
x
may satisfy the following condition: 0.5<x<1.2
In the bolometer material of the present invention, x in CuO
x
may satisfy the following condition: 0.6≦x<1.0
In the bolometer material of the present invention, Z may be an element selected from alkaline earth metals.
In the bolometer material of the present invention, it is preferred that Z is an alkaline earth metal, y satisfies the following condition: 0<y<1.2, and x satisfies the following condition: y<x≦1.5+y
In the bolometer material of the present invention, Z may be a rare earth element selected from yttrium and lanthanoid elements.
Z in the bolometer material of the present invention may be an element belonging to Period 5 or Period 6 of the Periodic Table selected from bismuth, lead, thallium, mercury and cadmium.
Z in the bolometer material of the present invention may also be an alkali metal selected from potassium and sodium.
In the bolometer material, Z in the elemental compositional formula may be a rare earth element selected from yttrium and lanthanoid elements, and the bolometer material may further comprise an oxide of an alkaline earth metal selected from beryllium and magnesium.
The bolometer material mainly comprising the oxide according to the invention may further comprise lithium or gold as an accessory component.
The p
Higuma Hiroko
Miyashita Shoji
Kopec Mark
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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