Thin film electroluminescent device

• US 4,727,004 A
• Filed: 11/18/1986
• Issued: 02/23/1988
• Est. Priority Date: 11/21/1985
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Tanaka, Koichi, Ogura, Takashi, Mikami, Akiyoshi, Yoshida, Masaru, Taniguchi, Koji
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/932,034
• Time in Patent Office: 462 Days
• Field of Search: 428/690, 428/691, 428/917, 428/698, 428/699, 313/503, 313/502, 313/506, 313/509
• US Class Current: 428/690
• CPC Class Codes: C09K 11/7731 with alkaline earth metals
• CPC Class Codes: H05B 33/14 characterised by the chemical or physical composition or the arrangement of the electroluminescent material , or by the simultaneous addition of the electroluminescent material in or onto the light source
• CPC Class Codes: H05B 33/20 characterised by the chemical or physical composition or the arrangement of the material in which the electroluminescent material is embedded

Abstract

A thin film EL device having a double-insulated structure and comprising an emitting layer made of an alkaline-earth sulfide as its host material and doped with Eu²⁺ for providing luminescent centers. The emitting layer has a Eu concentration of 0.15 to 0.75 atm. % and a controlled thickness of at least 1.3 μm to impart hysteresis to the brightness vs. applied voltage characteristics of the device.

Claims

1. A thin film EL device which exhibits a memory effect comprising an emitting layer made of an alkaline-sulfide as a host material, doped with 0.15 to 0.75 atm. % of Eu for providing luminescent centers and having a controlled thickness of at least 1.3 μ

m, insulating layers sandwiching the emitting layer, and a pair of electrodes provided on the outer surfaces of the insulating layers, at least one of the electrodes being transparent.

2. A device as defined in claim 1 wherein the sulfide of alkaline earth metal is CaS, SrS or BaS.

3. A device as defined in claim 1 wherein the amount of Eu is 0.3 to 0.5 atm. %.

4. A device as defined in claim 1 wherein the emitting layer is 1.3 to 5 μ

m in thickness.

5. A device as defined in claim 1 wherein each of the insulating layers is a film of a oxide or nitride selected from among Al₂ O₃, SiO₂, Y₂ O₃, TiO₂, HfO₂, Ta₂ O₅, Si₃ N₄ and AlN, a film of a highly dielectric material selected from among BaTiO₃, PbTiO₃, SrTiO₃, PZT and PLZT, or a composite film comprising these films.

6. A device as defined in claim 1 wherein the transparent electrode comprises a film of ITO or SnO₂.

7. A device as defined in claim 1, wherein the emitting layer further comprises ZnS:

Mn dopant to provide a multi-color display.