Use of ferroelectric gate insulator for thin film transistors with ITO channel

Typical n-channel transistor characteristics with nonvolatile memory operation of ferroelectric-gate thin film transistors (TFTs) using indium-tin-oxide (ITO) channel have been demonstrated. It is shown that relatively large “on” current can be obtained in ITO/(Bi,La)4Ti3O12(BLT) TFTs. Since the calculated field-effect mobility is as small as 4 cm2/Vs, the large “on” current is due to the large charge density induced by the ferroelectric gate insulator. It is also shown that the thin conductive ITO channel can be depleted completely by the ferroelectric polarization and “off” current of the device is as low as 10−7 A. Drain current - gate voltage characteristics exhibit counterclockwise hysteresis due to the ferroelectric nature of the gate insulator, which demonstrates nonvolatile memory operation. The memory window is approximately 4 V, which agrees with the theoretical calculation. In addition, no change in both “on” and “off” currents has been observed up to 103 s.