A Coplanar Crystalline InGaO Thin Film Transistor with SiO2 Gate Insulator on ZrO2 Ferroelectric Layer: A New Ferroelectric TFT Structure

Ferroelectric transistors with a large memory window (MW) and operational stability have been of increasing interest recently. In this study, a ferroelectric thin-film transistor (FE-TFT) with a novel metal-insulator-semiconductor-ferroelectric (MISF) structure is proposed. With the ferroelectric layer located under the semiconductor, the TFT process can be similar to a conventional coplanar structure with a SiO2 gate insulator (GI). In this work, both FE and active semiconductors are deposited by spray pyrolysis which is beneficial for large-area and low-cost manufacturing. The FE ZrO2 by spray pyrolysis has a nanocrystalline phase, and the semiconductor InGaO shows a polycrystalline structure. The TFT exhibits a MW of 5.6 V with an operating voltage range of -10-10 V. The device shows a low leakage current of 10(-12) A, and thus the on/off ratio is >10(7) at V-DS = 1.0 V. The device shows stable performance with increasing temperatures up to 80 degrees C. The endurance of the device is 5000 cycles at 0.1 Hz pulse with a negligible variation of MW less than 0.1 V, indicating excellent operational stability.