Low-threshold-voltage thin-film electroluminescent devices

ZnS: Mn thin-film electroluminescent (EL) devices having a low-threshold voltage of about 50 V have been developed by utilizing ferroelectric PbTiO3a and PLT thin films as insulating layers. The ferroelectric PbTiO3and PLT thin film have a considerably high dielectric constant of 190, above 80-percent transparency, and breakdown strength of more than 500 kV/cm. The threshold voltages of 45 and 60 V have been achieved by the device using PLT and PbTiO3thin films, respectively. These values are approximately four times lower than those of reported thin-film EL devices. The developed EL device provides the practical available level of brightness, typically 300 fL at 60 V with the maximum level of more than 800 fL. A typical luminous efficiency is measured as 2.7 lm/W. The very slight change in the threshold voltage during an initial aging treatment is found to be less than 10 V, which is about one order of magnitude smaller than that observed in the conventional EL device using an Y2O3thin film as the insulating layer. A series of technical data on the fabrication processes of the PbTiO3and PLT thin films and performances of the developed EL device have been presented and discussed.