(Invited) Versatile Compact Model and Evolutionary Parameter Extraction Method for Organic Thin-Film Transistors

Abstract

Contact effects in thin-film transistors (TFTs), such as organic (OTFTs) and 2D field-effect transistors (2D-FETs), remain an important problem to be solved. The correct physio-chemical modeling of the contact regions in TFTs is necessary in order to incorporate these effects into transistor compact models [1,2]. Regarding OTFTs, much effort has been made to include contact effects into compact models, since the existence of a standard compact model, which effectively brings together the device- and system-level development, would place the OFET technology at a higher technological level [3].In this work, we present a versatile contact model, which is incorporated into a well-known generic analytical model for the current-voltage (I-V) characteristics of OTFTs, valid for all the operation regions of the transistor, including the subthreshold region [4,5]. The resulting model is complemented with an evolutionary procedure to extract the parameters that best fit experimental current-voltage characteristics [6]. Our motivation is that the combined compact model and parameter extraction method fulfils the conditions for this long expected standard compact model.The versatility of our proposal is based on the following pillars: (i) the contact model must reproduce linear, space-charge-limited and Schottky-barrier contacts [7]; and (ii) the contact model must be applied both, in transistors in which the source contact region is dominant (observed in many OTFTs), and in transistors in which drain and source contacts contribute in a similar way (mainly observed in some staggered OTFTs and 2D-FETs).In this work, we give details of how the compact model, including the contact effects, has been built from its origins [8] up to now. We also describe how the evolutionary procedure is adapted to extract the model parameters of different OTFTs, in which only the source contact, or both source and drain contact effects, limit the device performance [6, 7, 9].Finally, the compact model including contact effects and the extraction procedure mentioned above are tested successfully with coplanar and staggered OTFTs (with and without negligible drain contact effects). Our numerical calculations reproduce quite well the experimental electrical characteristics and the model parameters are extracted. The comparison of our results with other methods designed for specific TFTs confirms the validity of our standard compact model for TFTs with contact effects. Acknowledgments This work was partially financed by the Consejería de Economía y Conocimiento de la Junta de Andalucía, the Spanish “Ministerio de Ciencia, Innovación y Universidades”, and the European Regional Development Funds (ERDF), under projects A-TIC-117-UGR18 and PGC2018-098813-B-C31.