Takashi Chuman

High Efficiency Electron-Emission in Pt/SiOx/Si/Al Structure

A high efficiency electro-emission device (HEED) has been developed with a structure of Pt/SiOx /Si/Al on a thermally-oxidized Si substrate. The thicknesses of the SiOx and Si films were 400 nm and 5 µ m, respectively. Electron emission characteristics of the HEED are reported. It was found that the HEED has an electron-emission efficiency as high as 28% and a high brightness of 80 kcd/m2 using phosphor ZnS:Cu,Al. This high electron-emission efficiency was obtained in a range of applied voltage in which negative resistance occurred.

5.1: Active Matrix Organic Light Emitting Diode Panel using Organic Thin-Film Transistors

By using organic thin-film transistors with pentacene as the active organic layer, active matrix organic light emitting diode panel has been developed. The number of pixels in the panel is 8 × 8, and each pixel is driven by switching and driving transistors. We confirmed 16 gray scales representation by means of an analog driving method.

Active Matrix Driving Organic Light-Emitting Diode Panel Using Organic Thin-Film Transistors

We developed an active matrix driving organic light-emitting diode (OLED) panel on a glass substrate using two organic thin-film transistors (OTFTs) per pixel, a switching OTFT and a driving OTFT. The OTFTs are bottom contact structures with the high-dielectric constant gate insulator tantalum oxide (Ta2O5, relative dielectric constant of 23) produced by anodization in ammonium adipate solution and with pentacene as the active layer. The W/L (where W and L are the OTFTs channel width and length, respectively) was 400 µm/10 µm for the switching OTFTs and 680 µm/10 µm for the driving OTFTs. The characteristics of the OTFTs were improved by treating the Ta2O5 surface with hexamethyldisilazane (HMDS), so that the field-effect mobility was 2.0×10-1 cm2 V-1 s-1 and the current on/off ratio was 105. A green phosphorescent dopant, tris(2-phenylpyridine)iridium [Ir(ppy)3], was used for the OLED layer. The panel had 8×8 pixels and the aperture ratio was 27%. We confirmed a 16-gray-scale representation and a luminance of 400 cd/m2.

Improved cold electron emission characteristics of electroluminescent porous silicon diodes

The property of electroluminescent porous silicon (PS) diodes as surface-emitting cold cathodes were investigated. The experimental PS diodes consist of thin Au films, PS, n+-type Si substrates, and ohmic back contacts. When a positive bias voltage VPS is applied to the Au electrode with respect to the substrate, electrons are uniformly emitted through the Au contact as well as photons. The cold electron emission characteristics are presented here in terms of the PS layer thickness dependence, effects of rapid thermal oxidation (RTO), and electroluminescence (EL) characteristics. It was demonstrated that both the decrease in the PS layer thickness (dPS) and the introduction of RTO treatment are useful for a significant improvement in the emission characteristics, and that the emission current and efficiency for a RTO-treated diode with dPS=3 μm reach 450 μA/cm2 and 0.2%, respectively, at VPS=27 V. It is also shown that in every case, the Fowler–Nordheim scheme holds in the bias voltage dependence of the e...

Solution-Processed Organic Thin-Film Transistor Array for Active-Matrix Organic Light-Emitting Diode

We developed a 3-in. organic thin-film transistor (OTFT) array with an ink-jetted organic semiconductor. All layers except electrodes were fabricated by solution processes. The OTFT performed well without hysteresis, and the field-effect mobility in the saturation region was 0.45 cm2 V-1 s-1, the threshold voltage was 3.3 V, and the on/off current ratio was more than 106. We demonstrated a 3-in. active-matrix organic light-emitting diode (AMOLED) display driven by the OTFT array. The display could provide clear moving images. The peak luminance of the display was 170 cd/m2.