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0965-S06-01

Fabrication of Organic Thin Film Transistors Using Low Temperature, Soluble Silicon Oxide as the Gate Dielectrics Jeng-Hua Wei, HorngJiunn Lin, and Ying-Ren Chen Electronic Engineering, Ching Yun University, 229, Chien Hsin Rd., Jung-Li, Taiwan, 320, Taiwan Abstract In this paper, a unique water-based, liquid phase deposited silicon oxide (LPD SiO2) is adapted to the fabrication process of the organic thin film transistor (OTFT). Through the use of this process, an OTFT with a silicon oxide gate insulator is successfully fabricated at 100oC or less. At this low process temperature, the SiO2 functions efficiently as a gate dielectric with the breakdown field being larger than 5 MV/cm, the leakage current being near 1 pA/um2 with a gate bias of 20 V and the surface roughness being less than 1nm. Due to the high quality silicon oxide, the oxide-gated OTFT shows the low threshold voltage (-1 ~ -2V) and medium on/off current ratio (~1000). Because this oxide is a water-based process, it is highly resistant to the following soluble semiconductor material and its solvent.

Organic thin film transistors (OTFTs) have received increased attention in the last several years as a suitable material for low cost devices in flexible electronics [1-3] including radio-frequency identification (RFID), OLED display, smart cards and smart sensors. For the low manufacturing cost, the solution process is believed to have the highest chance of achieving this goal. The technologies for these soluble materials and processes for the OTFTs have developed progressively [4,5]. In this paper, a low-temperature water-based liquid phase depositing silicon oxide (LPD SiO2) [6,7] is used as the OTFT’s gate insulator and the bottom-gate OTFT is fabricated. Using this LPD process, a good-quality silicon oxide is deposited by the solution process and the process temperature, including deposition and annealing, can be lower than 100oC. The oxide-gated OTFT shows a low leakage current (0.56 pA/um) & medium on/off current ration (>103) . The fabrication process for the LPD SiO2 and oxide-gated OTFTs are listed as follows: For the LPD SiO2, the deposited procedures are illustrated in Fig. 1. First, 1000 ml of the 3.09M hydrofluorosilicic (H2SiF6) and 65 gm of silicic acid (SiO2:xH2O) were mixed at 30oC for 3 hours. Then, the solution was filtered to remove the undissolved acid and post-diluted with water. Next, the Si wafer was immersed in this solution to grow silicon oxide of 60 nm thickness at 50oC. For testing the oxide’s quality, the MOS structure is completed by evaporating 30nm Au film on LPD SiO2 as the top electrode. The device structure is shown in Fig. 2A and the area of the top electrode is 0.02 cm2. For the oxide-gated OTFT, the device was formed in the top contact structure and is shown to have a lower contact resistance[5] by shadow masks, as shown schematically in Fig. 2B. First, we used the Si wafer as the planar bottom gate and a 60 nm silicon oxide film was grown by LPD SiO2. Then, pentacene film of 30 nm thickness was evapor