(Invited) Analysis of Hysteresis in OTFTs Using a Physically-Based Compact Model
Authors: Zaibi Ameur , Mounir Ahmed , Golec Patryk , Cerdeira Antonio , Estrada Magali , Kadura Lina , Calvet Laurie , Iniguez Benjamin 
Published: August 2024

Organic TFTs (OTFs) have the potential to become essential devices for flexible, wearable and printed electronics. However, several issues related to their behavior still needs to be studied in detail and completely understood. One of these issues is hysteresis. In this abstract we analyze the hysteresis behavior in OTFT by applying a previously developed physically-based model to the direct (forward) and reverse (backward) dc sweeps of the transfer characteristics at different drain voltages. The identification of the model parameters which change provides more information about the hysteresis mechanism.

The so-called UMEM (unified model and extraction method) model [1,2] developed for OTFT has been demonstrated to accurately reproduce the I-V characteristics for a wide range of geometries, bias and temperature conditions [3], as well as to extract physical values of most parameters. In this work we will show that it can reproduce the post-hysteresis I-V-characteristics of OTFT and that only a few parameters need to be changed.

In the above threshold regime, where Variable Range Hopping dominates, the current is proportional to a field-effect mobility μFET= μ0(VGS-VT)γ/VAA
γ , being VT the threshold voltage. The γ parameter depends on the DOS characteristic temperature T0 as = 2(T0/T-1).

In the subthreshold regime diffusion dominates and the current is exponentially dependent on VGS:

IDS=IDS0 exp (2.3(VGS-VT)/S) (1-exp(-VDS/Vth))

where S is the subthreshold swing and Vth the thermal voltage.

Aunified model of the drain current, valid and continuous from subthreshold to the above threshold regime, is finally obtained by means of a hyperbolic tangent function [1,2].

In order to analyze the hysteresis behavior, this model was applied to both direct and reverse dc sweeps of the I-V characteristics of OTFT samples fabricated at CEA-Liten (Grenoble). Figs. 1 and 2 shows very good agreement from subthreshold toabove threshold. The parameter values extracted for the direct and reverse dc sweeps are shown in Table I. It is observed that the threshold voltage is shifted. The increase of γ indicates a higher degree of disorder in the reverse dc sweep characteristics. However, we can see that although IDS0 is higher, the extracted subthreshold swing value, S, does not change. The saturation parameter α is lower in the reverse sweep, but the rest of model parameters are not affected. Only γ and α show a variation with VDS, although rather small.

[1] B. Iñiguez, et al., "New Compact Modeling Solutions for Organic and Amorphous Oxide TFTs," IEEE Journal of the Electron Devices Society, vol. 9, pp. 911-932, September 2021

[2] C. H. Kim, et al., , “A Compact Model for Organic Field-Effect Transistors With Improved Output Asymptotic Behaviors,”IEEE Trans. on Electron Devices, vol. 60, no. 3, pp. 1136-1141, March 2013.

[3] H. Cortés-Ordóñez, et al., “Parameter extraction and compact modeling of OTFT from 150 to 350K,”, Trans. on Electron Devices, vol. 67, no. 12, pp.5695-5692, Dec 2020.

Acknowledgements:

This work was funded by the Spanish Ministry of Science (PRX21/00726), and the EU EIC-PATHFINDER (BAYFLEX, no 101099555

Figure 1