Browsing by Author "Zaki, Tarek"

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    Short-channel organic thin-film transistors : fabrication, characterization, modeling and circuit demonstration
    (2014) Zaki, Tarek; Burghartz, Joachim N. (Prof. Dr.-Ing.)
    Plastic electronics based on organic thin-film transistors (OTFTs) pave the way for cheap, flexible and large-area products. Over the past few years, OTFTs have undergone remarkable progress in terms of reliability, Performance and scale of integration. This work takes advantage of high-Resolution Silicon stencil masks to build air-stable complementary OTFTs using a low-temperature fabrication process. Many factors contribute to the allure of this technology; the masks exhibit excellent stiffness and stability, thus allowing to pattern the OTFTs with submicrometer channel lengths and superb device uniformity. Furthermore, the OTFTs employ an ultra-thin gate dielectric that provides a sufficiently high capacitance of the order of 1 uF/cm^2 to enable the transistors to operate at voltages as low as 3 V. The critical challenges in this development are the subtle mechanisms that govern the properties of the aggressively-scaled OTFTs. These mechanisms, dictated by device physics, have to be described and implemented into circuit design tools to ensure adequate simulation accuracy. This is particularly beneficial to gain deeper insight into materials-related limitations. The primary objective of this work is to bridge the gap between device modeling and mixed-signal circuits by establishing an OTFT compact model, together with realizing the world-fastest organic digital-to-analog converter (DAC). A unified model that captures the essence in the static/dynamic behavior of the OTFTs is derived. Approaches to incorporate the implicit bias-dependent parasitic effects in the model are elucidated and accordingly a reliable fit to experimental data of OTFTs with different dimensions is obtained. It is demonstrated that the charge storage behavior in the intrinsic OTFTs agrees very well with Meyer's capacitance model. Moreover, the first comprehensive study of the frequency response of OTFTs using S-Parameter characterization is presented. In view of the low supply voltage and air stability, a record cutoff frequency of 3.7 MHz for a channel length of 0.6 um and a gate overlap of 5 um is accomplished. Finally, a 6-bit current-steering DAC, comprising as many as 129 OTFTs, is designed. The converter achieves a thousand-fold faster update rate (100 kS/s) than prior state of the art.