Architecture-Specific Contributions to Short Channel Effects in Organic Transistors
A. F. Fernandez
Institute of Solid State Physics, Graz University of Technology
15:00 - 17:00 Monday 28 September 2015 Foyer Alte Technik Organic thin film transistors still suffer from an insufficient stability and cannot compete with the performance of their inorganic counterparts. Nevertheless, highly promising advances in switching speeds were achieved upon aggressive scaling of device dimensions such as the channel length and the gate dielectric thickness [1, 2]. The benefits of reducing the channel length, i.e., the separation of source and drain are, however, counteracted by non-desired short channel effects and increasingly dominant contact resistances. Moreover, theoretical work indicates that, in general, the contact resistance is strongly related to the efficiency of injection at the contacts and depends not only on the carrier mobilities and injection barriers, but also on the device dimensions, the device architecture, and the point of operation. [3, 4]
We, therefore, investigate the dependence of the contact resistance on the abovementioned properties for channel lengths varying by 4 order of magnitudes, i.e., from several micrometers to 100 nanometers and below. We utilize two-dimensional drift-diffusion-based simulations including the self-consistent consideration of thermionic and tunneling injection, interface recombination, and back drift, to determine the contact resistance and short channel effects directly from the simulation of the device at a given point of operation. We particularly focus on how the onset and the extent of short channel effects for given material properties depend on the actual device architecture, i.e., the staggered (top-contact bottom gate) or the coplanar (bottom-contact bottom-gate) device configuration.
We demonstrate that conventional methods to extract the contact resistance, i.e., the transfer line method, fail for both architectures due to a profound dependence of the contact resistance on the channel length.[5] Based on our analysis of the relationships between material and geometric parameters, we suggest architecture-specific routes to suppress short channel effects.
[1] F. Ante, D. Kälblein et.al., Contact Doping and Ultrathin Gate Dielectrics for Nanoscale Organic Thin-Film Transistors, SMALL 7-9, 1186-1191 (2011)
[2] H. Kleemann, A. A. Günther et.al., High-Performance Vertical Organic Transistors, SMALL 9-21, 3670-3677 (2013)
[3] M. Gruber, E. Zojer et. al., Impact of Materials versus Geometric Parameters on the Contact Resistance in Organic Thin-Film Transistors, Adv. Func. Mater. 23-23, 2941-2952 (2013)
[4] F. Maddalena, M. Spijkman et. al., Device characteristics of polymer dual-gate field-effect transistors, Org. Electron. 9-5, 839-846 (2009)
[5] M. Gruber, F.Schürrer et. al., Relation between injection barrier and contact resistance in top-contact organic thin film transistors, Org. Electron. 13, 1887-1899 (2012)
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Institute of Solid State Physics
