有機薄膜電晶體後退火之影響研究

Abstract

在有機材料中，載子的傳遞主要是以載子躍遷的方式進行，遷移率受限於元件製程中有機薄膜品質的好壞。較差的成膜品質會使得有機薄膜電晶體之載子移動率無法有效提升，因此如何在元件製程中提升薄膜品質一直是非常重要的議題。本研究之主要目的在於探討元件熱退火處理對有機薄膜電晶體之元件特性的影響和元件效能改善的機制，並探討熱退火處理如何影響有機半導體層-pentacene-之成膜品質。

實驗結果顯示，有機薄膜電晶體經由元件熱退火處理後，元件的遷移率由原先的0.42 cm^2/V-s提升至0.8 cm^2/V-s，其中的原因部分來自於熱退火處理使得元件的通道電阻大幅下降。另外，透過原子力顯微鏡我們證明pentacene通道部分的晶界，在熱退火處理後有減少的趨勢，我們推測這是造成通道電阻下降的主因。然而，熱退火處理卻使得元件的接觸電阻和半導體層中垂直於通道部分的電阻上升了。其內部機制，我們也進一步由原子力顯微鏡和X光繞射儀的分析結果來探討。另外，我們也發現當我們結合poly-a-methylstyrene表面修飾及元件後退火效應，可以使得元件的interface traps大幅下降，而且pentacene和基板表面的附著變的更好，進而使得元件遷移率由0.11 cm^2/V-s提升到0.8 cm^2/V-s。

Charge transport in organic semiconductor is typically described by hopping of charges between localized states. For this type of transport, the charge carriers are easily trapped at the grain boundary or by the disorder and impurities around the grains, resulting in the limitation of organic thin-film transistors (OTFTs) device mobility. Therefore, how to improve organic thin film quality becomes a very important issue. Based on the principle of controlling the growth of pentacene film, the effect of post-annealing treatment on pentacene-based TFTs is investigated in this study. Aims of our researches are to examine the effect of post-annealing treatment on device performance, pentacene crystal structures, and their correlations. It is found that the device mobility is increased from 0.42 to 0.80 cm^2/V-s, which results from the reduced channel resistance. Images of atomic force microscopy (AFM) show that it is because the pentacene grain boundaries are reduced after thermal annealing. However, both contact and bulk resistances are slightly raised after post-annealing treatment. The mechanisms are further discussed by the investigation of the X-ray diffraction spectra and AFM patterns. In addition, the device mobility can be improved from 0.11 to 0.8 cm^2/V-s by combining PaMS modification and the post-annealing treatment. It is because that traps in pentacene/insulator interface are significantly moved and the adhesion between pentacene and insulator are improved.