COMPARISON OF THE LOW-TEMPERATURE (LESS-THAN-OR-EQUAL-TO-600-DEGREES-C) POLYSILICON THIN-FILM TRANSISTORS (TFTS) WITH 2 KINDS OF GATE DIELECTRICS

Low-temperature (less than or equal to 600 degrees C) polysilicon thin film transistors (TFTs) were processed with two types of gate insulat or: wet oxide/LPCVD Si3N4 double layer and APCVD SiO2 thin film. Elect rical performances were analyzed and compared for the two types of TFT . The thermal oxide with LPCVD Si3N4 thin film provides a better gate insulator/poly-Si interface than the gate APCVD SiO2 insulator in term s of effective interface state density, which is approximately ten tim es lower (N-T=9-10x10(11) cm(-2) eV(-1) versus 8-9X10(12) cm(-2) eV(-1 )), and in terms of field effect mobility, which is much higher (mu=58 cm(2) V-1 s(-1) versus 6 cm(2) V-1 s(-1)). However, the threshold vol tage is higher (V-T=6.5 V versus 5 V) because of a hot carrier trappin g effect at the SiO2/Si3N4 interface. In addition, gate insulation wit h oxide/nitride is not as good as with APCVD SiO2.