Characterization of low voltage operating $InGaZnO_4$ based thin film transistor with high-k insulator

Abstract

Mechanically flexible, optically transparent, light, and low cost thin film transistors (TFTs) on polymer substrate are intensively interested for flexible and transparent display at future ubiquitous era. Until now organic thin film transistors (OTFTs) satisfied the requirements and they were studied for applications like active matrix OLED or LCD display, sensor devices, and radio frequency identification (RFID) tags. However, the operation voltage of OTFTs is large because of low capacitance of organic dielectrics. For low voltage operation devices suitable at portable and battery-powered electronic devices, high capacitance gate dielectrics are necessary. They can be obtained by using very thin film or using high-k dielectrics. Very thin gate dielectrics can lead to significant manufacturing problems such as poor leakage characteristics and pinholes come from rough surface of polymer thin film. I had an effort to use high-k oxides $Ba_{0.6}Sr_{0.4}TiO_3$ (BST) to reduce the operation voltage of TFTs. However, because BST films had poor leakage characteristics despite high dielectric constant, I added excess MgO having good leakage characteristics. In Chap. 3, four kinds of dielectrics BST, $MgO_{0.1}BST_{0.9}$, $MgO_{0.2}BST_{0.8}$, and $MgO_{0.3} BST_{0.7}$ thin films were fabricated at room temperature using pulsed laser deposition (PLD) at room temperature for feasibility test. As increasing MgO contents the leakage characteristics got better while the dielectric constants were decreased. After confirmed the possibility of MgO-BST to gate insulator of TFTs, I used sputtering method for large area application. I demonstrated the reason of reducing dielectric constant of the MgO-mixed BST thin film can be explained as the sum of each individual thin film (MgO and BST) using a series connection capacitance model, and the MgO plays a significant role in reducing the leakage current density of the thin film forming potential barrier. Another problem of OTF...