Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-08-30
2003-07-08
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C257S094000, C257S096000
Reexamination Certificate
active
06590336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to light emitting devices and more particularly to light emitting devices having luminescent layers comprising piezoelectric material.
2. Description of the Related Art
Piezoelectric thin-films have been widely used in vibrators, such as piezoelectric resonators and piezoelectric actuators, and driving devices. In recent years, piezoelectric thin-films also have attracted attention as optical devices. For example, Japanese Unexamined Patent Application Publication No. 7-262801 discloses a light emitting device which has a ZnO film formed on a sapphire substrate and emits ultraviolet light by the effects of excitons. Moreover, Japanese Unexamined Patent Application Publication No. 10-256673 discloses a light emitting device which emits ultraviolet light by laser oscillation.
Properties of piezoelectric films, however, have not been sufficiently known. In particular, properties of piezoelectric films suitable for light emitting devices and methods for making the piezoelectric films have not yet been sufficiently studied. Thus, piezoelectric films used in conventional light emitting devices do not have high luminous efficiency.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a light emitting device having high luminous efficiency and high luminous intensity. The light emitting device comprises: a substrate; and a first piezoelectric film held on the substrate and having one of a positive plane and a negative plane, the first piezoelectric film functioning as a light emitting layer.
According to another aspect of the present invention, a method for making a light emitting device comprises the steps of: preparing a substrate; and forming a first piezoelectric film having one of a positive (+) upper plane and negative (−) upper plane on the substrate, according to properties of the substrate.
When the first piezoelectric film has the positive plane, it is preferable that the substrate is selected from the group consisting of a c-plane sapphire substrate, an R-plane sapphire substrate, an m-plane sapphire substrate, an X-plane sapphire substrate, an a-plane sapphire substrate, a rotated Y-cut plate sapphire substrate, a double rotated sapphire substrate, a rotated Y-cut plate quartz substrate, a Z-plane quartz substrate, a LiTaO
3
substrate having a negative Z plane of a rotated Y-cut plate, and a LiNbO
3
substrate having a negative Z plane of a rotated Y-cut plate.
When the first piezoelectric film has the negative plane, it is preferable that the substrate is selected from the group consisting of a LiNbO
3
substrate having a positive Z plane of a rotated Y-cut plate LiNbO
3
substrate, a LiTaO
3
substrate having a positive Z plane of a rotated Y-cut plate LiTaO
3
substrate, a LiTaO
3
substrate having a positive Z plane, a LiNbO
3
substrate having a positive Z plane, a glass substrate, A Si substrate, a metal substrate, and a substrate having a metal film thereon.
The first piezoelectric film preferably comprises a material selected from ZnO, AlN, and CdS.
The light emitting device may further comprises a second piezoelectric film, the first piezoelectric film and the second piezoelectric film having different conductivity types.
In the light emitting device, the substrate may have a plurality of metal film stripes thereon, the first piezoelectric film covers the metal film stripes, and the first piezoelectric film has the negative plane.
According to the present invention, a piezoelectric film having a positive plane or a negative plane is selectively provided depending on the type of the substrate, and the piezoelectric film has high crystallinity. Thus, the resulting light emitting device has high brightness and high luminescent efficiency.
REFERENCES:
patent: 5432397 (1995-07-01), Koike et al.
patent: 5604763 (1997-02-01), Kato et al.
patent: 6057561 (2000-05-01), Kawasaki et al.
patent: 6437363 (2002-08-01), Kadota et al.
patent: 6448585 (2002-09-01), Kadota
patent: 0383215 (1990-08-01), None
patent: 0383215 (1990-08-01), None
patent: 0905799 (1999-03-01), None
patent: 0905799 (1999-03-01), None
patent: 7-262801 (1995-10-01), None
patent: 10-256673 (1998-09-01), None
German Office Action dated Apr. 29, 2002, with English translation.
T. Ohnishi, et al.: Determination of surface polarity of c-axis oriented ZnO films by coaxial impact-collision ion scattering spectroscopy. In: Applied Physics Letters, ISSN 0003-6951, vol. 72, No. 8, 1998, pp. 824-826.
P. Kung, et al.: Laterial epitaxial overgrwoth of GaN films on sapphire and silicon substrate. In: Applied Physics Letters, ISSN 0003-6951, vol. 74, No. 4, 1999, pp. 570-572.
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
Patel Vip
Williams Joseph
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