[paper] Compact Modeling of Hysteresis in OTFTs

Compact modeling of hysteresis in organic thin-film transistors

A. Romero^a, J.A. Jiménez-Tejada^a, R. Picos^b, D. Lara^a, J.B. Roldán^a, M.J. Deen^c

Organic Electronics 129 (2024) 107048

DOI : 10.1016/j.orgel.2024.107048

a Departamento de Electrónica y Tecnología de Computadores, CITIC-UGR, Uni Granada, Spain
b Department of Industrial Engineering and Construction, Universitat de les Illes Balears, Spain
c Department of Electrical and Computer Engineering, McMaster University, Canada

Abstract: In this work, we propose a model that describes the temporal evolution of the threshold voltage and trapped charge density in Thin-Film Transistors (TFTs) under dynamic conditions, paving the way for the characterization and modeling of memory transistors. The model is expressed as a first-order differential equation for the trapped charge density, which is controlled by a time constant and an independent term proportional to the drain current. The time-dependent threshold voltage is introduced in a previously developed compact model for TFTs with special consideration to the contact effects. The combination of both models and the use of an evolutionary parameter extraction procedure allow for reproducing the experimental dynamic behavior of TFTs. The results of the model and the evolutionary procedure have been validated with published experimental data of pentacene-based transistors. The procedure is able to simultaneously reproduce three kinds of experiments with different initialization routines and constraints in each of them: output and transfer characteristics with hysteresis and current transients characteristics

FIG: a.) Modeling the contact regions and intrinsic channel of an OTFT structure (a bottom contact configuration); b.)  Comparison of experimental transfer characteristics

Acknowledgements : The authors acknowledge support from the project PID2022 139586NB-44 funded by MCIN/AEI/10.13039/501100011033 and FEDER, EU. Funding for open access charge: Universidad de Granada / CBUA.

Appendix: Supplementary material related to this article can be found online.

[paper] Organic semiconductor (OSC) OFETs

Boyu Peng, Ke Cao* Albert Ho Yuen Lau, Ming Chen, Yang Lu* and Paddy K. L. Chan

Crystallized Monolayer Semiconductor for Ohmic Contact Resistance, High Intrinsic Gain, and High Current Density

Adv. Mater. 2020, 32, 2002281 

DOI:10.1002/adma.202002281

Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road (HK)

*Department of Mechanical Engineering, City University of Hong Kong, Kowloon (HK)

Abstract: The contact resistance limits the downscaling and operating range of organic field-effect transistors (OFETs). Access resistance through multilayers of molecules and the nonideal metal/semiconductor interface are two major bottlenecks preventing the lowering of the contact resistance. In this work, monolayer (1L) organic crystals and nondestructive electrodes are utilized to overcome the abovementioned challenges. High intrinsic mobility of 12.5 cm2 V−1 s−1 and Ohmic contact resistance of 40 Ω cm are achieved. Unlike the thermionic emission in common Schottky contacts, the carriers are pre- dominantly injected by field emission. The 1L-OFETs can operate linearly from VDS = −1 V to VDS as small as −0.1 mV. Thanks to the good pinch-off behavior brought by the monolayer semiconductor, the 1L-OFETs show high intrinsic gain at the saturation regime. At a high bias load, a maximum current density of 4.2 µA µm−1 is achieved by the only molecular layer as the active channel, with a current saturation effect being observed. In addition to the low contact resistance and high-resolution lithography, it is suggested that the thermal management of high-mobility OFETs will be the next major challenge in achieving high-speed densely integrated flexible electronics.

Fig: a) Schematic charge accumulation and b) output curves of short-channel OFETs. c) Schematic charge accumulation and d) output curves of source-gated transistors. e) Schematic charge accumulation and f) output curves of 1L-OFETs. 

Acknowledgements: The authors gratefully acknowledge the support from the General Research Fund (GRF) under Grant Nos. HKU 17264016 and HKU 17204517, University of Hong Kong Seed Funding Grant Nos. 201711159068 and 201611159208. The authors appreciate Prof. Xin Cheng and Xin Zhuang from Southern University of Science and Technology for their support on e-beam lithography. The authors also thank Dr. Hagen Klauk and James W. Borchert for the fruitful discussions and suggestions.

[paper] Model for Organic Thin-Film Transistor

Physically Based Compact Mobility Model for Organic Thin-Film Transistor

T. K. Maiti, L. Chen, H. Zenitani, H. Miyamoto, M. Miura-Mattausch and H. J. Mattausch

in IEEE Transactions on Electron Devices, vol. 63, no. 5, pp. 2057-2065, May 2016.

doi: 10.1109/TED.2016.2540653

Abstract: A physically based compact mobility model for organic thin-film transistors (OTFTs) with an analysis of bias-dependent Fermi-energy (EF) movement in the bandgap (Eg) is presented. Mobility in the localized and extended energy states predicts the drain-current behavior in the weak and strong accumulation operations of OTFTs, respectively. A hopping mobility model as a function of the surface potential is developed to describe the carrier transport through localized energy states located inside Eg. The Poole-Frenkel parallel-field-effect mobility and vertical-field-effect mobility are considered to interpret the bandlike carrier transport in the extended energy states. The parallel field effect on mobility is more pronounced for shorter channel length OTFTs and is considered by developing a channel-length-dependent mobility model. The vertical field effect on mobility is included to account for the effect of mobility on carrier transport at high gate-voltage-induced fields. We also compared the model results with 2-D device simulations and measurements to verify the developed mobility model [read more...]