有機薄膜電晶體之研究

Abstract

在此論文中，我們首先針對不同厚度的五環素(pentacene)做材料方面的分析，以原子力顯微鏡(AFM)探究表面的輪廓，以及X射線繞射(XRD)量測，來分析材料品質，並且與製作成元件的電特性相比較。在此製程當中，五環素厚度為1000Å時，可以得到最佳的特性。在變更量測溫度方面，我們發現隨著溫度升高，電流增加，載子的遷移率(mobility)也隨之上升，然而到了臨界的溫度之後，汲極(drain)電流在飽和區的時候會有降低的現象發生，我們將此現象歸因於自我致熱(self-heating)現象所致。這也是由於溫度升高，晶格之間擾動造成的散射效應所導致。在不同溫度的量測之間，我們亦萃取了活化能(activation energy)並找出其和閘極偏壓之間的關係，同時和常見的邊界位障降低的模型(grain boundary barrier lowering model)做比較。 在有機薄膜電晶體當中，接面電阻的效應是格外嚴重的。我們利用電流和電壓以及通道長度L之間的相關性，來萃取出和通道長度L不相關的接面電阻部份，並且也找出接面電阻和閘極偏壓之相關性。除此之外，不同溫度量測得到的接面電阻可以釐清在溫度改變時，特性變化產生的原因。 在提升有機薄膜電晶體特性的方法之中，表面處理是一種相當有效且直接的方式。在本實驗中，我們利用HMDS(Hexamethyldisilazane) 來做為表面處理的材料，實驗結果也可驗證表面處理對於元件的特性是有助益的。

In this thesis, we first discuss the material characteristics of the pentacene-based OTFTs with different pentacene film thicknesses. The grain size and film quality can be analyzed by AFM and XRD measurements, respectively. The performances are the best for the 1000Å-thick device. By changing the measurement temperatures, we find the drain current and mobility get larger as the temperature increases. After the critical temperature, the lattice vibration is more severe and the drain current decreases in the saturation region due to scattering which is the so-called self-heating effect. We also extract the activation energy from the measurements of different temperatures and find its gate voltage dependence, which corresponds to the generally-used grain boundary barrier lowering model. The effect of contact resistance is especially serious in OTFTs. We extract the contact resistance by using the relationship between the drain current and drain voltage and channel length L. The dependence of the gate bias on the contact resistance is also investigated. Among the methods for improving the characteristics of the OTFTs, surface treatment is an effective one. We use HMDS (Hexamethyldisilazane) for surface treatment and the performances of devices after surface treatment are much improved.