A Compact SPICE Model for Organic TFTs and Applications to Logic Circuit Design

Abstract

This work introduces a compact DC model developed for Organic Thin Film Transistors (OTFTs) and its SPICE implementation. The model relies on a modified version of the Gradual Channel Approximation (GCA) that takes into account the contact effects, occurring at non-ohmic metal/organic semiconductor junctions, modeling them as reverse biased Schottky diodes. The model also comprises channel length modulation and scalability of drain current with respect to channel length. To show the suitability of the model, we used it to design an inverter and a ring oscillator circuit. Furthermore, an experimental validation of the OTFTs has been done at the level of the single device as well as with a discrete-component setup based on two OTFTs connected into an inverter configuration. The experimental tests were based on OTFTs that use small molecules in binder matrix as an active layer. The experimental data on the fabricated devices have been found in good agreement with SPICE simulation results, paving the way to the use of the model and the device for the design of OTFT-based integrated circuits.

A Brief Review on Flexible Electronics for IoT: Solutions for Sustainability and New Perspectives for Designers

“…Since many researchers and designers in the field of electronics usually work with SPICE-like simulators, studies aimed at importing device models implemented with new materials into SPICE are of particular importance. In [248] a compact DC model of organic thin film transistors (OTFTs) and its SPICE implementation is presented and the experimental data on the fabricated devices resulted in good agreement with SPICE simulation results; in [249] a SPICE compatible compact modeling of IGZO (Indium gallium zinc oxide) transistors and inverters having an atomic layer deposition (ALD) Al2O3 gate insulator on a flexible polyethylene terephthalate (PET) substrate is proposed, that enables a reliabilityaware circuit simulation so that the operation of the flexible transistor and circuit can be predicted with high accuracy; in [250] an in-depth study of three-dimensional inkjet-printed flexible organic field-effect transistors (FETs) and integrated circuits (ICs) is reported, highlighting the necessity of modelling-driven design and analysis. With respect to such a consideration, compact modelling of the flexible printed organic FETs has been performed together with SPICE simulations of both static and dynamic behaviors of flexible printed organic circuits.…”

Recent progress in organic field‐effect transistor‐based integrated circuits

“…Valletta et al developed a compact spice model for OFETs in which non-ohmic contact effects were included and modeled as Schottky diodes. 108 The Schottky diodes exist in both source and drain ends, but only one of them is reverse biased at the same time and will be considered in the model. The potential drop on the diode connecting in series to the transistor will affect the transistor operation.…”

Compact modelling and SPICE simulation for three-dimensional, inkjet-printed organic transistors, inverters and ring oscillators

“…Considering the other parasitic capacitances C oth of 246 pF and for NFET and 49.2 pF for the PFET (ignoring the Miller effect), the simulated oscillation frequency became 3.16 Hz, which matches well with the measured oscillation frequency of 3.14 Hz (at V DD = 30 V). Analysis on the contribution of parasitic capacitances have been reported mostly on organic ring oscillators that have been fabricated by evaporation [37][38][39]: reports on flexible inkjet-printed organic ring oscillators are rare. We observed that the contribution of other parasitic capacitances is greater than that of channel capacitance (figures 6(a), (c) and table 2).…”