有機薄膜電晶體特性探討

Abstract

有機薄膜電晶體雖然其發展歷史較短，載子遷移率相對於低溫複晶矽薄膜電晶體仍較低，尚未有市場應用出現，但是其製程容易，成本低，可製作於可撓性基板上及可低溫製程等優勢，被視為一可用於電子紙張、射頻識別標籤及可撓式顯示等應用之關鍵技術，使得有機薄膜電晶體在近年來備受矚目。雖然目前已有許多針對材料及元件之改善，然而尚未有一完整之元件模型可描述及預測該類元件之電化學特性。而且，有機材料在穩定性上仍有許多待解決的問題存在，尚且需要一個完整的直流電與交流電應力測試研究。 本論文先從直流電化學特性出發，先從基本之半導體金氧半元件基礎公式出發，建立解析解直流電元件模型，並進一步粹取關鍵參數。再從電路模擬著手，利用解析解元件模型所獲得的參數，發展更為精確的微電路模型。在比較其他材料的電流電壓特性，我們可發現有機薄膜電晶體之元件特性與一般半導體金氧半元件大不相同，我們發展出了五苯晶粒大小模型，以解釋所獲得的實驗現象。根據我們所得到直流電元件模型與晶粒大小模型，我們實作直流電應力測試，以尋求有機薄膜半導體穩定性的可能。 接著，我們更進一步探討交流電化學特性。我們先從交流電元件模型建立著手，以深入瞭解有機薄膜電晶體對於交流電流所產生的巨觀反應機制，並根據其反應機制，我們模擬出有機薄膜電晶體的交流電元件模型。再者，我們並進一步實作交流電應力測試，以探求交流電應力對於元件所造成的影響，以及交流電應力破壞有機半導體材料的關鍵點為何，研究有機材料其可改善之電化學特性。最後，我們對元件作了Quasi-Stable CV測試。不同於交流電元件模型所量測電容的方式，Quasi-Stable CV乃是用極為低頻的方式，量測電容與閘極電壓的變化關係。為了瞭解有機半導體的晶格邊界陷阱補捉電荷之機制，以探求有機薄膜電晶體微觀的電荷傳導現象。

Organic thin film transistors (OTFTs) have attracted much attention because of the advantages of low-cost, large-area and flexible-substrate capability which can be widely used in the applications such as radio frequency identification tags, electronic papers, and flexible display. Although a lot of research groups focus on organic material synthesis, a self sustained electrical model for such devices is far from perfect right now. To understand the electrochemistry of organic materials and find the solution of stabilities of organic materials, a complete modeling and research on DC and AC is needed. In this paper, we started our simulations from the basic current-voltage equations of a semiconductor metal-oxide-semiconductor (MOS) device to build the DC modeling and extract the parameters. Comparing the differences between the organic and semiconductor devices, we found that, in an OTFT, the current-voltage characteristics are quite different from that in a semiconductor-MOS, and we developed the petacene grain size model to explain the experiment. And we perform DC stress to investigate the stability of organic material. And we try to investigate the variations of physical and modeling parameters that respond to AC current changes. Therefore, starting from small signal and large signal AC models, we built up the macroscopic AC response models from carrier point of view, which is essential to AC modeling since the polystalline property of OTFTs hasn't been considered in AC model previously. Furthermore, we perform AC stress test to study the device failure mechanism. The results will be helpful to identify better material and device structures. Finally, we carry out the quasi-stable C-V test in a pentacene OTFT. The quais-stable C-V is a low frequency test to realize carrier transport behaviors under different applied voltages, swing durations and gate channel sizes. Our results indicate that carrier trap and de-trap process will affect the C-V profiles under different stress.