Study on the Reliability of Pentacene-Based Organic Thin Film Transistor
Dr. Po-Tsun Liu
|關鍵字:||五環素;有機;薄膜電晶體;Organic;Pentacene;Thin Film Transistor|
在有機薄膜電晶體的技術演進中，其載子遷移率表現出來的電性已經迎頭趕上複晶矽薄膜電晶體的電性了。而其中的五環素為電洞導通的有機半導體，載子遷移率最高已高過 1cm2/V s，可說已到了單晶有機的傳輸極限了。不過儘管電性已有大幅改善，但是在接面電阻，導通機制和電性上的不穩定這三個方面還未作有系統的探討。
接著我們作變溫量測，此可在遷移率與溫度有關的半導薄膜上作量測。在與溫度相關的遷移率中，蘊育著半導體和傳導機制有關或和缺限分布有關的資訊。有一些模型已提出來解釋這些半導晶體中熱活化的載子遷移率現象，然而“Multiple trapping and release model(MTR)”是最為被大家所廣泛接受的。因此我們再利用橫向電導，可同時來觀測Meyer-Neldel relationship的電性傳輸行為。而我們也適當的利用Multiple trapping and release model(MTR)來解釋變溫量測中過程的熱活化現象。
Abstract Recent progress in organic thin film transistor (OTFT) technology has led to charge carrier mobility comparable to amorphous silicon. Pentacene, a hole conductor, has shown the highest OTFT mobility(>1 cm2/V s) to date, and has nearly reached the intrinsic transport limit of organic single crystals. Despite the progress in realizing OTFTs with good properties, three important aspects of OTFTs have not been systematically studied: contact resistance, conduction mechanism, and electrical instability. In this thesis, at first, we use an improved four-probe method for ascertaining contact resistance. The four-probe method is based on the standard OTFT source and drain geometry, but with two additional mid-channel voltage sensing probes. Thus, we use two electrodes to inject and receive current, and two to sense voltage in the OTFT channel. The technique we employ is similar to other recently reported four-probe transistor devices. The major advantage of the four-probe method over conventional RvsL plots is that it allows the film and each contact resistance to be measured independently in a single device, which facilitates assessment of device-to-device variation in these resistances. Hence, we use it to further analyze the phenomenon. Variable temperature TFT measurements are adapted later. It can be used to determine the temperature dependence of the mobility in a semiconductor thin film. The temperature dependence of the mobility can yield information about the conduction mechanism and trap states in the semiconductor. Several models have been proposed to explain thermally activated mobility in crystalline organic semiconductor films, but the multiple trapping and release (MTR) model is the most widely accepted.. Thus, A Meyer–Neldel relationship was simultaneously observed for electrical transport ,using a transconductance. we properly use the multiple trapping and release model to explain the thermally activated phenomenon from the variable temperature measure.. Finally, we understand the instability of electrical characteristics in a continued series measurements and investigated the characteristics of bottom-contact pentacene-based OTFTs under drain current stress conditions. Here, we find that polarization phenomenon plays an important role during stress, and thus we provide the rough energy band figure to depict these special properties of OTFTs. The effect of these charge trapping instability on the measured threshold voltage and mobility of the transport studies would be discussed.