Room temperature fabricated thin film transistors with high-k BZN gate insulators

Abstract

Much of the attention of the room temperature fabricated TFT community has been focused on the search for high-mobility, stable semiconductor materials. But for the manufacture of high quality TFTs, it is also very important to incorporate a suitable gate insulator. The operating voltage can be reduced by increasing the gate capacitance. Some combination of higher gate dielectric constant and reduced film thickness leads to lower voltage operation. The use of a very thin gate insulator is not a suitable approach, given the relatively rough surfaces characteristics of polymer substrate. To ensure pinhole-free coverage, the film should be much thicker than the roughness of the substrate. The use of a high dielectric constant material is therefore the optimum approach for reducing the operation voltage of TFTs. Recently, there have been many efforts to use high-k oxides to reduce TFT operating voltage. This research composed largely 2 parts. At first, I tried to find out new candidate materials for a gate insulator in TFTs fabricated at room temperature in chapter 3 and 4. Three kinds of Bi-based pyrochlore, $Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7$ (BZN), $Bi_{1.5}Zn_{1.0}Sb_{1.5}O_7$ (BZS) and $Bi_{1.5}Zn_{1.0}Ta_{1.5}O_7$ (BZT), thin films were fabricated at room temperature using RF magnetron sputtering method in chapter 3. Their dielectric and electric properties were characterized to find out if there are any possibilities for application as gate insulator in room temperature fabricated TFTs. In chapter 4, MgO capping layer were introduced to improve the leakage current characteristics of BZN thin films. Thin MgO layer of ~30 nm were formed on BZN thin films by pulsed laser deposition (PLD) method and RF magnetron sputtering system. In later part, using those materials found in chapter 3 and 4 as a gate insulator, pentacene and ZnO based TFTs were fabricated and characterized in chapter 5 and 6, respectively. All fabrication processes were conducted at room temperat...