Investigations of Indium-Tin-Zinc-Oxide Thin-Film Transistors with High-k Dielectrics on Flexible Substrate

Abstract

In this thesis we fabricated ITZO thin-film transistors (TFTs) with high-k dielectrics on flexible substrate by Ultrasonic Spray Pyrolysis Deposition (USPD) Electrical characteristic of ITZO TFTs with the aluminum oxide and yttrium oxide as gate dielectrics on flexible substrate before and after bending We deposited the ITZO channel layer and the Al2O3 dielectric layer by USPD USPD has the advantages of non-vacuum low cost high deposition rates and it also can deposit thin films with good uniformity and good quality In this work ITZO has higher mobility and stability than IGZO Grazing Incident X-ray Diffraction spectroscopy measurements were carried out and indicated that the ITZO thin film of C-axis-aligned crystalline (CAAC) structure This structure compared with polycrystalline there is no clear grain boundary which indicated CAAC-ITZO has lower density of defect states in the gap than polycrystalline Therefore TFTs with the CAAC-ITZO as an active layer have good electrical characteristics and reliability In the dielectric layer we choose high dielectric constant materials which can enhance the control ability of devices Aluminum oxide and yttrium oxide also have the advantages of low fabrication cost and high deposition rates Therefore aluminum oxide and yttrium oxide are used as the gate dielectric layer In this work the characteristics of TFTs with different oxide layer were investigated Furthermore we did research into the difference of electrical characteristics between the flexible PI substrate and traditional glass substrate First the ITZO/Al2O3 TFT and ITZO/Y2O3 TFTs are fabricated with the same thickness on the glass substrate The Y2O3 gate dielectric material has higher dielectric constant than Al2O3 so ITZO/Y2O3 TFT has higher capacitance at the same thickness Therefore ITZO/Y2O3 TFT is easier to accumulate electrons and it has higher on-current and steeper subthreshold swing values than ITZO/Al2O3 TFT In the linear region the device exhibited higher on-current 4 51×10-4 A higher μFE of 28 4 cm2/V-s Ion/Ioff of >107 S S of 109 3 mV/dec and Vth of -0 1V Then alumina oxide and yttrium oxide were used to fabricate TFTs on the PI substrate The electrical performance of TFT on the flexible substrate is similar to the TFT on the glass substrate In the linear region the flexible ITZO/Y2O3 TFT has higher on-current 4 45×10-4 A higher μFE of 27 2 cm2/V-s Ion/Ioff of >107 S S of 110 7mV/dec and Vth of -0 45V and it still has more stable electrical performance after bending In this study the ITZO TFTs were successfully fabricated by USPD The USPD method has considerable advantages of high deposited rate and low cost The ITZO TFTs using Al2O3 or Y2O3 as oxide layer have good interface quality In the electrical performance flexible ITZO/Y2O3 TFT has the advantages of higher electron mobility and good stability Therefore ITZO TFTs become as an alternative choice for IGZO TFTs in the next-generation of the flat panel display industry which requires light-weight soft and flexible applications The flexible ITZO TFT by USPD can exhibit great potential for bendable electronic/display equipment

Date of Award	2020
Original language	English
Supervisor	Wei-Chou Hsu (Supervisor)