Date of Graduation

Summer 2020

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Kartik Ghosh

Keywords

thin film transistor (TFT), TFT channel, transfer characteristics, output characteristics, bottom gated TFT, co-planar TFT, pulsed laser deposition, photo-luminescence

Subject Categories

Electrical and Computer Engineering | Electronic Devices and Semiconductor Manufacturing | Engineering Science and Materials | Physics | Semiconductor and Optical Materials

Abstract

The performance of ZnO thin film (grown in different parameters) as a thin film transistor (TFT) is the focus of this study. ZnO is renowned for being n-type semiconductor naturally which was utilized in fabricating a thin film transistor here. This thesis is compared the performance of ZnO thin film transistor by growing the thin film using pulsed laser deposition (PLD) on two slightly different substrates at different temperatures in an optimal 0.1 milli bar oxygen pressure which was later analyzed using other material characterization methods. The substrates were both Si (100) but had different resistivity due to different amount of doping. The naturally oxidized silicon layer acted as the insulating di-electric layer between the substrate and the ZnO layer. The films were grown using the PLD with 20,000 laser pulses for each sample and one of them was annealed in the same oxygen environment to see the change in behavior as a device. The TFT’s were fabricated as a bottom gated co-planar design and the samples were tested for output and transfer characteristics using a microprobe station in two different light exposure. The ZnO films were tested for structural and optical properties using X-ray diffraction and photoluminescence which gave important clues for explaining the device characteristics found in electrical characterization. The Raman and scanning electron microscopy were also performed for the samples which produced similar results for the samples. The best two samples were found where the ZnO was grown at 700 C and 500 C without annealing. They have the optimal oxygen vacancies for better transistor performance. On the other hand, the sample primarily grown at 350 C after initial 500 C base growth was inferior compared to the above-mentioned samples. The annealing was found to be detrimental to the TFT performance. Moreover, the substrate with minimal doping in silicon was found to be photosensitive giving a significant rise in channel current when exposed to the stronger light. The mobility of the two good samples of TFT was found in relevant range compared to the existing literature. The study would be more comprehensive with an inclusion of variation of oxygen pressure and different insulation layer with varying dielectric constant, which can be the future scope of this thesis.

Copyright

© Shahidul Asif

Available for download on Friday, December 31, 2021

Open Access

Share

COinS