Investigation of indium zinc oxide thin film transistors fabricated by sputtered system and their optoelectronic application

Abstract

In this thesis we use RF sputtering system to fabricate a-IZO thin film and vary the oxygen flow to obtain IZO thin films of different electrical characteristics In terms of electrical device we first fabricate the TFT applying the a-IZO thin film as active layer and SiO2 as gate dielectric layer We obtain the optimized TFT having the mobility of 8 71 cm2/Vs threshold voltage of 0V subthreshold swing of 0 25 V/decade and Ion/Ioff ratio of 6 8×104 In addition we find that the devices have different electrical characteristic with different oxygen ratio And we obtain the optimized IZO thin film under 10% oxygen ratio In the first part of the experiment we fabricate the a-IZO thin film transistor using SiO2 as gate dielectric In second part we make an improvement on the SiO2 dielectric with SiN buffer layer The TFT using SiN/SiO2 gate dielectric has the mobility of 13 67 cm2/Vs threshold voltage of 1 27 V subthreshold swing of 0 216 V/decade and Ion/Ioff ratio of 1 57E6 Compared with normal SiO2 dielectric layer we obtain higher Ion/Ioff ratio after impact SiN improvement In addition we also replace SiO2 with high κ material Al2O3 as gate dielectric The Al2O3 TFT has the mobility of 34 15 cm2/Vs threshold voltage of 2 51V subthreshold swing of 0 2 V/decade and Ion/Ioff ratio of 7 36E6 At last we also investigate the reliability of these dielectric In the part of a-IZO thin film photoelectrical application we fabricate the IZO MSM photodetector and IZO thin film phototransistor with IZO thin film of 10% oxygen ratio The photodetector has Ion/Ioff ratio of 7 21E2 and rejection ratio of 325 under 5V bias The phototransistor has the Ion/Ioff ratio of 2 54E4 rejection ratio of 1 2E6 under -5V bias The result indicates that the phototransistor has the better photoelectrical characteristic than photodetector As we know IZO is easy to form oxygen vacancy which could yield a leakage current path for IZO device Therefore a simple surface treatment process is reported for improving its surface defects We deposit 3-aminopropyltrimethoxysilane (APTMS) onto the IZO MSM photodetector to passivate its surface After APTMS modification the dark current of IZO phtodetector has decrease nearly an order and the rejection ratio increase from 325 to 728

Date of Award	2014 Aug 9
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)