Fabrication of Indium Gallium Zinc Oxide Doping Nitrogen Thin film Transistors by Sputtering

Abstract

In this thesis the indium gallium zinc oxide (InGaZnO) is deposited by RF magnetron sputtering and the film properties are discussed with or without nitrogen doping Because of the InGaZnO is a material easy to produce oxygen vacancies and zinc interstitial defects so the nitrogen was doped in InGaZnO films to reduce the vacancies which have caused the problem of exceed carrier concentration and instability Next we will use InGaZnO on the thin film transistor fabrication In the part of the experimental results and features discussion first of all we fabricated InGaZnO TFT doping oxygen and nitrogen with silicon oxide as gate dielectric layer And changing different nitrogen flow rate to find out the best transfer characteristics The optimized parameters of InGaZnO TFT is doped 2% N2 Vth is 1V field effect mobility is 5 27cm2V-1S-1 On/off current ratio is 5 order and SS is 0 98V/decade Then we deposited two different films with oxygen or nitrogen to analyze thin films properties for three aspects which are structure optical and element The structure shows the InGaZnO doping nitrogen is amorphous as same as without nitrogen Roughness of thin film is lower with nitrogen doped In elementary analysis with content of nitrogen increasing the amount of oxygen vacancies are decrease And the nitrogen content in doping nitrogen films is higher than doping oxygen Finally in the optical aspect the bandgap is become large with nitrogen doped And the transmittance in the visible light region is around 80% In the second part of experiment we capped InGaZnO doping nitrogen layer on the InGaZnO channel making a double layer structure The purpose of double layer is to prevent back channel absorb or desorb oxygen with atmosphere which is a promotion to threshold voltage and field effect mobility As result the field effect mobility is high as 14 34 cm2V-1S-1 threshold voltage is 0 5V at room temperature The positive gate bias stress stability of InGaZnO doping nitrogen are apparently improved comparing with doping oxygen Also we extend the application to the phototransistors In the third part we use a high dielectric constant of hafnium oxide and silicon nitride replace silicon oxide as gate dielectric to reduce the leakage current and subthreshold swing Moreover we added a silicon oxide as buffer layer to decrease interface defects between gate dielectric and channel The transfer characteristics of hafnium oxide as gate dielectric with silicon oxide buffer layer shows on/off current switch ratio up to seven orders And subthreshold improved to 0 32 V/decade Keyword：InGaZnO; Thin Film Transistor; Nitrogen doped

Date of Award	2016 Aug 11
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)