Electrical properties of functional Y2O3 films applied to thin film transistors

Abstract:
In this study, the electrical performance of atomic layer deposited (ALD) Y2O3 films using yttrium tris(di-isopropyl-formamidinate) [Y(DPfAMD)3] and yttrium tris(di-tertbutyl-formamidinate) [Y(DBfAMD)3] as precursors are characterised to verify the suitability of Y2O3 as high-k dielectric as well as surface passivation layer in thin-film devices. The films derived from the optimized ALD processes are uniform and smooth with a root-mean-square (RMS) roughness of Rq, [Y(DBfAMD)3] = 0.28 nm and Rq, [Y(DPfAMD)3] = 0.48 nm, respectively. The permittivity, interface trap density and breakdown voltages were determined using a metal-insulator semiconductor (MIS) capacitor. A permittivity of 13.9 (12.3), breakdown voltages of 5 MV cm-1 (4 MVcm-1) and low leakage current densities ~10^-7 A cm^-1 at 2 MV cm^-1 were determined for films using the optimized ALD process with [Y(DPfAMD)3] ([Y(DBfAMD)3]). Finally, solution processed metal-oxide thin-film transistors (MOTFTs) were passivated by a 4 nm thick Y2O3 film in order to study the impact of the surface passivation on the electrical performance of the TFTs under ambient conditions. The Y2O3 encapsulation improved the performance by substantially reducing the hysteresis of the transistor characteristic, compared to a nonpassivated reference sample. While the integration of the [Y(DPfAMD)3] based ALD process initiates a significant negative onset voltage shift (Von = -30 V), the integration of the [Y(DBfAMD)3] based ALD process results in an onset voltage close to zero.