Date of Award
Doctor of Philosophy
Materials Science and Engineering
Philip D. Rack
Michael L. Simpson, Thomas T. Meek, Syed K. Islam
The characterization and fabrication of active matrix thin film transistors (TFTs) has been studied for an addressable microfluidic electrowetting channel device as application. A new transparent semiconductor material, Amorphous Indium Gallium Zinc Oxide (a-IGZO), is used for TFT, which shows high electrical performance rather than amorphous silicon based TFT; higher mobility and even higher transparency. The purpose of this dissertation is to optimize each TFT process including the optimization of a-IGZO properties to achieve robust device for application. To minimize hysteresis of TFT curves, the gate dielectric is discussed extensively in this dissertation. By optimizing gas ratio of NH3SiH4, it is found that the TFT with NH3 rich SiNx gate dielectric deposited with NH3/SiH4 =5.1 and stoichiometric SiO2 demonstrates best condition to reduce hysteresis. a-IGZO films is investigated as a function of power and substrate bias effect which affects to electrical performance; the higher power and substrate bias increase the carrier density in the film and mainly cause threshold voltage(VT) to shift in the negative gate voltage direction and mobility to increase, respectively. In addition, the powerful method to estimate the electrical properties of a-IGZO is proposed by calculating O2 and IGZO flux during sputtering in which the incorporation ratio with O2/IGZO ≈1 demonstrates the optimized a-IGZO film for TFT. It is confirmed that both physical and chemical adsorption affects the electrical property of a-IGZO channel by studying TFT-IV characteristics with different pressure and analyzing X-ray photoelectron spectroscopy (XPS), which mainly affects the VT instability. The sputtered SiO2 passivation shows better electrical performance. To achieve electrically compatible (lower back channel current) a-IGZO film to SiO2 sputter passivated device, a-IGZO TFTs require oxygen rich a-IGZO back channel by employing two step a-IGZO deposition process (2nd 10nm a-IGZO with PO2 = 1.5mTorr on 1st 40nm a-IGZO with PO2=1mTor). Electrowetting microfluidic channel device as application using a-IGZO TFTs is studied by doing preliminary test. The electrowetting channel test using polymer post device platform is candidate for addressable electrowetting microfluidic channel device driven by active matrix type a-IGZO TFT.
Kwon, Seyeoul, "Characterization and Fabrication of Active Matrix Thin Film Transistors for an Addressable Microfluidic Electrowetting Channel Device. " PhD diss., University of Tennessee, 2010.