Using Sol-gel method to fabricate Barium Strontium Titanate thin film for the MIS capacitor of high dielectric and the gate insulator of OTFTs

• Main Authors: Chien-Shian Wu, 吳建賢
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/33023998053164102701

碩士 === 國立雲林科技大學 === 電子與資訊工程研究所 === 95 === In this thesis divided into two gradation. First, using Sol-gel method to prepare the solution of Barium Strontium Titanate (BaXSr1-XTiO3，BST) and to deposite on n-type Silicon substrate to form high dielectric thin film by using spin coating technique. The MIS capacitor structure of Metal/Insulator/Semiconductor were fabricated. In this study, we fabricated four kinds of different Barium and Strontium mole ratio of the Barium Strontium Titanate solutions, where X is 1 , 0.8 , 0.7 and 0.5 respectively. The electrical properties of capacitance-voltage and current density-voltage measurements of thin film were performed by Keithley measurement system. The experiments were shown for the post-annealing 350℃ and 2 hours in oxygen ambient, where the accumulation capacitance (Cacc) are BaTiO3 (Cacc) =177.4 pF , Ba0.8Sr0.2TiO3 (Cacc) =150.6 pF , Ba0.7Sr0.3TiO3 (Cacc) =144.7 pF and Ba0.5Sr0.5TiO3 (Cacc) =143.3 pF, respectively, and the dielectric constants are BaTiO3 (k) = 78.1 , Ba0.8Sr0.2TiO3 (k) = 44.4 , Ba0.7Sr0.3TiO3 (k) = 54.5 and Ba0.5Sr0.5TiO3 (k) = 64.6, respectively. For the post-annealing 450℃ and 2 hours in oxygen ambient, the accumulation capacitance (Cacc) are BaTiO3 (Cacc) =228.3 pF , Ba0.8Sr0.2TiO3 (Cacc) =164.8 pF , Ba0.7Sr0.3TiO3 (Cacc) =150.1 pF and Ba0.5Sr0.5TiO3 (Cacc) =147.1 pF, respectively, and the dielectric constants are BaTiO3 (k) = 139 , Ba0.8Sr0.2TiO3 (k) = 89.5 , Ba0.7Sr0.3TiO3 (k) = 92.1 and Ba0.5Sr0.5TiO3 (k) = 95.5 respectively. Measured at an applied voltage of 2V, the current density is about 10-8 A/cm2. At the post-annealing 450℃ temperature 2 hours in oxygen ambient could be obtain the large potential barrier height. The second gradation of experiment is the fabrication of Organic Thin Film Transistors. There are four kinds of different Barium and Strontium mole ratio of the Barium Strontium Titanate solutions deposited on SiO2/Si substrate by spin coating technique, Moreover, a process of post-annealing at 450℃ and 2 hours in oxygen ambient is used to make the gate insulator of Organic Thin Film Transistors, where the channel layer is Pentacene, and the electrical properties of ID-VD , |ID|1/2-VG and Log|ID|-VG of devices are measured and the carrier mobility , threshold voltage , On/Off current ratio and sub-threshold slope are calculated. We obtained devices with excellent electrical characteristics, including carrier mobility as large as 0.37 cm2/V.s , threshold voltage as low as -1.5V , On/Off current ratio of 103 and sub-threshold slope as low as 2.73 V/decade. Experimental result showed the gate insulator of Organic Thin Film Transistors with a high dielectrics thin film could be effectively reduce operating voltage and threshold voltage.