旋塗式有機主動層薄膜電晶體的研究

Abstract

近年來，隨著有機半導體材料的開發，有機薄膜電晶體被廣泛地研究使用在各種低成本、低溫、可撓式的顯示元件。本論文中，我們選擇poly-3-hexylthiophene或簡稱P3HT的有機材料為主動層，以二氧化矽為閘極絕緣層，利用旋轉塗佈的方式成長有機薄膜，成功地製作出“bottom contact”結構的有機薄膜電晶體。 首先我們探討低溫製程的可行性。我們利用電漿增強式化學氣相沈積和液相沈積兩種方式成長二氧化矽作為閘極絕緣層。液相沈積製程具有低溫、大面積、低成本的優點。利用液相沈積所得的二氧化矽作為有機薄膜電晶體的閘極絕緣層除了閘極漏電流之外，其餘特性皆可與利用電漿增強式化學氣相沈積所得的二氧化矽相比。為了改善閘極漏電流，我們利用堆疊式結構，亦即在源極和汲極電極下面利用選擇性液相沈積成長二氧化矽作為隔絕層以降低閘極漏電流。透過堆疊式結構，我們成功地將閘極漏電流降低約十倍，但因額外的通道長度也造成導通電流下降約一倍。 再來我們探討在閘極絕緣層上不同的表面處理對電性的影響。我們試圖以O2、N2O、NH3三種不同電漿去除殘留在閘極絕緣層上的污染物，以期望改善元件的效能。經過不同的電漿處理時間，我們發現場效遷移率和臨界電壓呈現不規則的變化，並清楚地表現在導通電流上。在探討電漿處理的過程中，我們亦對電漿種類和電漿處理時間找出最佳化條件。和經過HMDS表面處理的元件相比，兩者均獲得一定程度的改善。

Recently, with the development of organic semiconductor materials, Organic Thin Film Transistors(OTFTs) have been widely investigated for low-cost, low-temperature and flexible display devices. In this thesis, we chose poly-3-hexylthiophene or P3HT as the active layer, SiO2 as the gate insulator, and deposited the organic thin film by spin coating process, organic thin film transistors have been successfully fabricated with “bottom contact”structure. First, we studied the possibility of low-temperature process. We deposited SiO2 as gate insulator by Plasma-Enhanced Chemical Vapor Deposition(PECVD) and Liquid-Phase Deposition(LPD). The advantages of LPD process include low-temperature, large coverage area, and low-cost. The performance of OTFT with LPD SiO2 as gate insulator is comparable with that with PECVD SiO2 except for the gate leakage current. To ameliorate the gate leakage current, we demonstrated a stacked structure which additional SiO2 was deposited by Selective LPD(S-LPD) as an isolation layer under source and drain electrodes. The gate leakage current was successfully reduced about one order, but the ON-current was reduced about half due to extra channel length. Next we studied how various plasma treatments on gate insulator affected device performance. We tried O2 plasma, N2O plasma, and NH3 plasma to remove residual contaminant on gate insulator, improving the performance of devices. With various plasma treatment time, we found that field-effect mobility and threshold voltage showed irregular variation with plasma exposure time, obviously shown with on current. In our experiment of plasma treatment, we also obtained the optimal condition according to various plasma sources and exposure time. Compared with devices with HMDS treatment, both mobility and threshold voltage of devices with plasma treatment have been improved.