Coating processes – Electrical product produced – Metallic compound coating
Reexamination Certificate
1999-06-28
2002-08-13
Jones, Deborah (Department: 1775)
Coating processes
Electrical product produced
Metallic compound coating
C427S376200, C427S376400
Reexamination Certificate
active
06432474
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thin-film of manganese oxide having a perovskite type crystal structure exhibiting metal-insulator phase transition and a process for producing the same thin film and also relates to a thermal type far-infrared sensor (bolometer) having high sensitivity and a wide band of effective wavelengths, which is produced by using the same thin-film material.
Materials having a large change in resistivity, which are well-known as metal-insulator phase transition (Physics of Metal and Non-metal (2nd ed.), written by Mott, translated by Ono and Otsuki and published by Maruzen in Japan, 1998) have been studied for possible various applications. Typical examples of those materials are high-temperature superconductors or transition metal oxides such as V
2
O
3
and so on. The former has been developed for past ten several years to possess high quality and an improved transition range of 0.1K (90% of the temperature width from a maximal value to a least value in resistivity). However, a highest transition temperature is 136K for HgBa
2
Ca
2
Cu
3
O
y
, which is far from a room temperature. The latter include V
2
O
3
doped with Cr by 1%, which has a transition temperature close to a room temperature and exhibits a change of 2 orders of magnitude in resistivity. However, the transition is first-order and has a large hysteresis.
A thermal far-infrared sensing element is one of the devices using material having a big change in resistivity at a phase transition point. Conventional infrared sensing elements that have been developed are classified mainly into quantum type elements and thermal type elements. The quantum type elements use inner quantum effects such as photoconductive effect, photoelectric effect and photomagnetic effect of semiconductors, while the thermal type elements are used for detection of a temperature change occurred by conversion infrared rays into heat energy. The infrared sensing elements are widely used for transmission of signals between electronic devices, detection of a human body, monitoring of food cooking temperatures, medical diagnostics, security and crime prevention systems, thermal management, volcano monitoring, earth environmental monitoring, resource investigation, space observation and so on. Recently, many studies have been actively conducted for application of a wavelength band from infrared to middle millimeter waves (ultra-far-infrared rays) for communications.
However, the above quantum type infrared sensing elements have a narrow usable wavelength band since a detectable infrared wavelength band is limited by a used semiconductor. For detecting a long far-infrared of about 10 microns in wavelength, it is necessary to reduce bandgap energy or impurity ionization potential of the semiconductor used. Therefore, the sensing elements are required to be cooled down to the liquid helium temperature (4.2K) to prevent the increase of carriers that may be produced in a semiconductor from thermal excitation. The thermal type sensing elements have wide effective wavelengths but low detection sensitivity.
Recently, there have been studied infrared sensing elements using insulator-metal phase transition (or semiconductormetal phase transition) of compound perovskite type structure manganese oxide (for example, p. 593, Extended Abstracts (The Autumn Meeting, 1997); The Japan Society of Applied Physics). The infrared sensing element of this type has a large figure of merit (|d log &rgr;/dT |), where &rgr; is electrical resistivity and T is absolute temperature, since the phase transition from insulator (or semiconductor) to metal can occur abruptly for a temperature change. Furthermore, it has a wide effective wavelength band relative to incident infrared radiation.
However, a normal compound perovskite type manganese oxide can maintain a large figure of merit merely within a low temperature range and has a decreased figure of merit at temperatures achieved by thermoelectric cooling means or at a room temperature. For example, a representative perovskite type manganese oxide La
0.7
Ca
0.3
MnO
3
has a merit figure of about 0.16K
−1
at a temperature of 255K. A merit figure of manganese oxide La
0.7
Ba
0.3
MnO
3
having a transition point of 340K is decreased to 0.04 and a merit figure of manganese oxide La
0.7
Sr
0.3
MnO
3
having a transition 380K is decreased to 0.02.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thin film of manganese oxide, which has a metal-insulator phase transition obtainable at a higher temperature than i-conventional material and is based upon the inventor's studies on doping of the above material with carrier supplying alkali earth metals (such as Sr and Ca) and oxygen.
Another object of the present invention is to provide a process of producing the above manganese oxide thin-film.
Still another object of the present invention is to provide an infrared sensor made of the above manganese oxide thinfilm, which has the increased detection sensitivity and does not require cooling or requires a small cooling load. Means for solving problems
For accomplishing the above objects, inventors of the present invention have advanced studies on doping with alkali earth metals (Sr, Ca and so on) and oxygen, which are elements composing a perovskite type manganese oxide and supply with carriers and found thin film of perovskite type structure manganese oxide whose metal-insulator transition point obtainable within a very high temperature range.
The inventors have also found the fact that perovskite type manganese thin film prepared by a sol-gel process is given a higher phase transition temperature in comparison with a thin film prepared by an other method or has a metal-insulator transition range extended into a light dope side.
A thin film of perovskite type manganese oxide containing an element Ca or Sr and elements La, Mn and O, which is a first aspect of the present invention, is characterized in that a metal-insulation phase transition point of the thin film exists within a range of temperatures obtainable by a thermoelectric cooling method.
The range of thermoelectrically obtainable temperatures is a range of temperatures of −60° C. (low temperature) to room temperature that can be achieved by thermoelectric cooling method using a thermoelectric cooler such as a Peltier element.
A thin film of perovskite type manganese oxide containing an element Ca or Sr and elements La, Mn and O, which is a second aspect of the present invention, is characterized in that an oxygen component ratio is homogeneous in the film owing to inhibition of diffusion of oxygen elements.
A thin film of perovskite type manganese oxide whose composition is expressed as La
1−x
Ca
x
MnO
3+&dgr;
and which is a third aspect of the present invention, is characterized in that the Ca-component ratio x lies in a range of 0.1-0.2 and metal-to-insulator phase transition can occur within a temperature range obtained by thermoelectrically cooling method. The film thus constructed can work effectively at a room temperature or with a Peltier cooler having a small cooling load. The use of this film can create a high sensitivity infrared sensor having a high figure of merit.
A thin film of perovskite type manganese oxide whose composition is expressed as La
1−x
Ca
x
MnO
3+&dgr;
and which is a fourth aspect of the present invention, is characterized in that the film has Ca component ratio x of 0.1 to 0.5 and the oxygen-component ratio (3+&dgr;) is controlled to cause metal-to-insulator phase transition to occur in a range of thermoelectrically obtainable temperatures.
A thin film of perovskite type manganese oxide whose composition is expressed as La
1−y
Sr
y
MnO
3+&dgr;
and which is a fifth aspect of the present invention, is characterized in that Sr-component ratio y exists within a range of 0.05-0.185 and the metal-to-insulator transition can occur therein at temperatures obtainable by a thermoelectric cooling method.
A thin film o
Nakanishi Kenji
Nojima Hideo
Ogimoto Yasushi
Takahashi Yoshihiro
Alexander John B.
Conlin David G.
Edwards & Angell LLP
Jones Deborah
Sharp Kabushiki Kaisha
LandOfFree
Thin film of perovskite type manganese oxide process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thin film of perovskite type manganese oxide process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thin film of perovskite type manganese oxide process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2972668