| Summary: | 碩士 === 國立交通大學 === 顯示科技研究所 === 94 === 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.
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