Yasuhiro Nasu

Low-Threshold-Voltage AC Thin-Film Electroluminescent Device

Thin-film electroluminescent (EL) devices having low-threshold-voltages less than 50 volts have been developed utilizing ferroelectric insulating layers. Ferroelectric PbTiO3 and PLT layers having a dielectric constant of 100–200 and a breakdown strength of 0.5–1.5×106 V/cm have been employed as insulating layers. Typical threshold voltages of 60 volts for the PbTiO3 film and 45 volts for the PLT film obtained are approximately four times smaller than that of the conventional EL devices. Typical brightness and power conversion efficiency are measured to be 300 fL at 60 volts and 3×10-3 W/W, respectively. The very slight change in the threshold voltage during an initial ageing process is found to be less than 10 volts, which is about one order of magnitude smaller than that of the conventional EL devices. Technical data on the relation between the device performances and the device structure are presented and discussed.