IGZO TFT versus the MOSFET

Abstract

Indium gallium zinc oxide thin film transistor (IGZO TFT) characteristics are investigated, improved and then compared with the standard metal-oxide semiconductor field effect transistor (MOSFET). The device tends to operate with a negative threshold voltage which is undesirable as it means the device is ‘ON’ at 0.0 V. For the device to be an effective CPU switch, it needs to operate with voltage values between 0.0 V and 5.0 V where the lower value means it is completely ‘OFF’ with no leakage currents. Negative fixed charge was introduced to help turn the device ‘OFF’ whereas the MOSFET had negligible values. The TFT was driven at a drain voltage of 1.0 V whereas the MOSFET was at 0.1 V. This made the two devices comparable with similar threshold voltage of 0.6 V and an ideal subthreshold swing of 60 mV/decade. The experiment shows that the subthreshold voltage for the IGZO TFT is excellent at lower drain currents but degrades at higher currents. The quick degradation observed on the subthreshold region can also be attributed to short channel effects (SCEs).