(Invited) Organic Permeable-Base Transistors: Physically Motivated Simplification of Device Structure for Modeling and Simulation
Authors: Darbandy Ghader , Rastegar Pashaki Elahe , Iniguez Benjamin , Kleemann Hans , Kloes Alexander 
Published: August 2024

Vertical organic transistors are an attractive alternative to conventional lateral organic transistors due to their high DC and AC performance [1]. Among them, organic permeable-base transistors (OPBTs) are considered to be promising candidates for low-voltage flexible electronics due to their unique properties. However, their complex structures necessitate a deeper understanding of their operational mechanisms and the underlying physics [2, 3]. Compact models are essential for designing and optimizing integrated circuits (ICs). They are also used to develop and improve new transistor technologies. Analytical modeling of OPBTs based on geometrical parameterization has been reported [4]. A Gaussian DOS charge-based model has also been developed for organic transistors and adapted to OPBTs [5]. Their AC performance have been analyzed quantitatively, paving the way to reach GHz high frequency in organic transistors [6].

In this work, we report on the simplification of the complex structure of OPBTs in terms of their DC performance and characteristics. This simplification makes it easier to simulate, analyze, understand, and explain the working principle, optimize, and model OPBTs. We calibrate the TCAD simulation to the fabricated device structure and its characteristics to ensure that the simulation represents the OPBT to validate this simplification. Based on the calibrated TCAD simulation, we demonstrate that the characteristics of fabricated OPBTs with n pinholes (number of pinholes is determined by the density of pinholes) are equivalent to those of n single pinhole OPBTs connected in parallel. This is proved by physical models and arises from the fact that the pinholes are shielded by the base electrode, resulting in no electrostatic interaction known as screening effects between them. Therefore, it appears as multiple pinholes (transistors) have been fabricated in a single device (OPBT). Thus, one needs to analyze, optimize, and model a single pinhole (where the pinhole density determines the performance and specific structural dimension of the single pinhole) from the fabricated OPBTs and multiply its DC characteristics by the number of pinholes. The new simplification and formulation show good agreement with the experimental data of fabricated OPBTs, as well as the results obtained from TCAD simulations and a Gaussian DOS charge-based model.

Acknowledgements: This project is funded by the German Research Foundation (DFG) under the grants "DA 2578/2-1" and "KL 2961/10-1", the Spanish Ministry of Science (PRX21/00726), and the EU EIC-PATHFINDER (BAYFLEX, no 101099555).

References

[1] H. Kleemann et. al., “A review of vertical organic transistors,” Adv. Funct. Mater., 1907113, 2020.

[2] F. Dollinger et. al., “Vertical organic thin-film transistors with an anodized permeable base for very low leakage current,” Advanced Materials, vol. 31, no. 19, 2019.

[3] H. Lee et. al., “Vertical organic transistors with a permeable base: from fundamentals to performance prediction,” J. Mater. Chem. C, vol. 11, 2023.

[4] S. S. Joshi et. al., “Analytical modeling of organic permeable-base transistors based on geometrical parameterization,” Journal of the Korean Physical Society, 2023.

[5] E. Rastegar Pashaki et. al., “Gaussian DOS charge-based DC compact modelling of organic transistors,” IEEE TED, vol. x, no. x, under review, 2023.

[6] G. Darbandy et. al., “Towards high-frequency fT and fmax in organic transistors: performance and perspective,” Adv. Electron. Mater. Under review, 2023.