Red Emitting Electroluminescent Devices Using Ga 2 O 3 Phosphor Thin Films Prepared by Sol-Gel Process
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Red Emitting Electroluminescent Devices Using Ga2O3 Phosphor Thin Films Prepared by Sol-Gel Process Tadatsugu Minami, Tetsuya Shirai and Toshihiro Miyata Optoelectronic Device System R&D Center, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa, 921-8501, JAPAN ABSTRACT High-luminance red-emitting thin-film electroluminescent (TFEL) devices have been developed using Ga2O3 phosphor thin films prepared by a sol-gel deposition method. Single-insulating-layer-type TFEL devices were fabricated by depositing a Cr- or a Eu-activated Ga2O3 phosphor thin film onto a thick BaTiO3 ceramic sheet insulator. The Ga2O3:Cr or Ga2O3:Eu thin-film emitting layer was prepared by a sol-gel process using gallium acethylacetonate (Ga(C5H7O2)3) as the Ga source with Cr(C5H7O2)3 or EuC13 as the dopant source, respectively. A high red luminance of 622 cd/m2 was obtained for a Ga2O3:Cr TFEL device driven by a sinusoidal wave voltage at 1 kHz. INTRODUCTION Oxide phosphors feature a higher chemical stability than the sulfide phosphors which are widely used as the screen of cathode ray tubes (CRT) and the emitting layer of conventional thin-film electroluminescent (TFEL) devices [1]. As a result, oxide phosphors have become widely used in various emissive flat panel displays such as plasma display panels (PDP) and field emission displays (FED) [2-4]. Recently, we have reported that high-luminance TFEL devices are realizable using various oxide phosphors [5,6]. In addition, we reported that a stable long term operation in the atmosphere could be achieved in TFEL devices using oxide phosphors such as ZnGa2O4:Mn and Ga2O3:Mn [7,8]. In particular, TFEL devices with an oxide phosphor thin-film emitting layer can be fabricated in the presence of water. Recently, we demonstrated that high luminance oxide phosphor TFEL devices could be fabricated by chemical deposition using either a solution coating technique [9-11] or a sol-gel process [12-15], both eliminating the need for vacuum processes. TFEL devices using Ga2O3, SnO2 and SnO2-Ga2O3 phosphor thin films prepared by a sol-gel process produced higher luminances than devices prepared by r.f. magnetron sputtering using these thin films [16-20]. Since the sol-gel process eliminates the need for a heat treatment with a rapid temperature rise as well as the need for vacuum processes, it can be suited for large area thin-film deposition and inexpensive device fabrication. In this paper, we describe newly developed high-luminance red-emitting TFEL devices using either Cr- or Eu-activated Ga2O3 phosphor thin films prepared by the sol-gel deposition method. Single-insulating-layer-type TFEL devices were fabricated by depositing the Ga2O3 phosphor thin-film emitting layer onto a thick BaTiO3 ceramic sheet insulating layer. EXPERIMENTAL DETAILS The TFEL devices were fabricated by depositing Ga2O3 phosphor thin films onto thick sintered BaTiO3 insulating ceramic sheets (thickness, about 0.2 mm), as shown in Fig.1 [21]. The Ga2O3:Cr or Ga2O3:Eu thin-film emitting layer was prepared by a sol-gel
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