Leveraging Contact Effects for Field-Effect Transistor Technologies with Reduced Complexity and Superior Current Uniform
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Leveraging Contact Effects for Field-Effect Transistor Technologies with Reduced Complexity and Superior Current Uniformity
R. A. Sporea1, S. Georgakopoulos1, X. Xu2, X. Guo2, M. Shkunov1, J. M. Shannon1 and S. R. P. Silva1 1
Advanced Technology Institute, University of Surrey, Guildford GU2 7XH, U.K. Department of Electronic Engineering, Shanghai Jiao Tong University, 800 Dongchuan Rd, Shanghai 200240, P. R. China 2
ABSTRACT In order to achieve high performance, the design of devices for large-area electronics needs to be optimized despite material or fabrication shortcomings. In numerous emerging technologies thin-film transistor (TFT) performance is hindered by contact effects. Here, we show that contact effects can be used constructively to create devices with performance characteristics unachievable by conventional transistor designs. Source-gated transistors (SGTs) are not designed with increasing transistor speed, mobility or sub-threshold slope in mind, but rather with improving certain aspects critical for real-world large area electronics such as stability, uniformity, power efficiency and gain. SGTs can achieve considerably lower saturation voltage and power dissipation compared to conventional devices driven at the same current; higher output impedance for over two orders of magnitude higher intrinsic gain; improved bias stress stability in amorphous materials; higher resilience to processing variations; current virtually independent of source-drain gap, source-gate overlap and semiconductor thickness variations. Applications such as amplifiers and drivers for sensors and actuators, low cost large area analog or digital circuits could greatly benefit from incorporating the SGT architecture.
INTRODUCTION Contact effects in thin-film transistors are currently being investigated theoretically [1] as well as experimentally [1-5]. In general these effects are responsible for a degradation in device performance mainly through a reduction in current and switching speed. Here we show that contact effects can be used to engineer devices which have substantially better performance in some respects than the conventional TFT device architecture. The source-gated transistor (SGT) is a variation of the standard TFT transistor with what has been previously described [6] as an “extreme example” of a contact effect. SGTs are not designed with increasing transistor speed, mobility or sub-threshold slope in mind, but rather with improving certain aspects critical for real-world large area electronics such as stability, uniformity, power efficiency and gain.
Despite the fact that the SGT architecture differs only subtly from conventional TFT, its operation is governed by a source potential barrier, which is the dominant means of controlling the current, and SGT operation is altogether different. For a transistor to be an SGT: its source needs to comprise a potential barrier; the electrode structure has to be staggered (source and gate on opposite sides of the semiconductor); and we have to be able to deplete the semic
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