Low-Threshold-Voltage AC Thin-Film Electroluminescent Device

Abstract

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.

Synthesis of Tetragonal BaTiO3by Microwave Heating and Conventional Heating

“…The Ti−O−Ti bonds were broken and are believed to lead to interaction of Ba and Ti via Ti(OH) 6 2- groups. A metastable cubic phase crystallized from this solution. ,, This dissolution process is an endothermic process.…”

“…Barium titanate is of interest due to its high dielectric constant and ferroelectric properties at temperatures below 130 °C where it assumes a tetragonal phase. , BaTiO 3 finds a wide range of applications in electronic and electrooptic devices. , The ferroelectric and dielectric properties of BaTiO 3 strongly depend on the grain size and the density of the particles. − Traditionally, this material is prepared by heating mixtures of BaCO 3 and TiO 2 at a temperature between 1000 and 1200 °C accompanied by the introduction of impurities. , This procedure leads to powders that are coarse and inhomogeneous in size. Another problem concerned with this synthesis is the high cost required by high-temperature sintering.…”

Sensors and Actuators Using Ferroelectric Thin Films

“…The EL device using PbTiO 3 films instead of Y 2 O 3 films, as shown in Figure 5.7 B, has a very low operating voltage, and has a low voltage shift after aging [18]. The threshold voltage of the EL device is reduced from about 210 to 50 V.…”