Impact of Hydrogen Bonds Limited Dipolar Disorder in High-k Polymer Gate Dielectric on Charge Carrier Transport in OFET.

Bartosz Paruzel,Miroslav Menšík,Udit Acharya,Jiří Pfleger,Jiří Brus,Francesco Piana

doi:10.3390/polym12040826

Abstract

The paper contributes to the characterization and understanding the mutual interactions of the polar polymer gate dielectric and organic semiconductor in organic field effect transistors (OFETs). It has been shown on the example of cyanoethylated polyvinylalcohol (CEPVA), the high-k dielectric containing strong polar side groups, that the conditions during dielectric layer solidification can significantly affect the charge transport in the semiconductor layer. In contrast to the previous literature we attributed the reduced mobility to the broader distribution of the semiconductor density of states (DOS) due to a significant dipolar disorder in the dielectric layer. The combination of infrared (IR), solid-state nuclear magnetic resonance (NMR) and broadband dielectric (BDS) spectroscopy confirmed the presence of a rigid hydrogen bonds network in the CEPVA polymer. The formation of such network limits the dipolar disorder in the dielectric layer and leads to a significantly narrowed distribution of the density of states (DOS) and, hence, to the higher charge carrier mobility in the OFET active channel made of 6,13-bis(triisopropylsilylethynyl)pentacene. The low temperature drying process of CEPVA dielectric results in the decreased energy disorder of transport states in the adjacent semiconductor layer, which is then similar as in OFETs equipped with the much less polar poly(4-vinylphenol) (PVP). Breaking hydrogen bonds at temperatures around 50 °C results in the gradual disintegration of the stabilizing network and deterioration of the charge transport due to a broader distribution of DOS.

Highlights

The idea of “organic electronics” is supported by the actual need of the production of low-end electronic devices using large area printing technology
Inspired by the above mentioned literature, in our work we investigated organic field effect transistors (OFETs) with another high-k gate dielectric, namely cyanoethylated polyvinyl alcohol (CEPVA)
Poly(4-vinylphenol) (PVP, Mw = 25,000),benzoguanamine (HMBG—crosslinking agent), propylene glycol monomethyl ether acetate (PGMEA) 99.5%, purity grade, N, N-dimethylformamide (DMF) anhydrous 99.8% purity grade and toluene CHROMASOLV HPLC 99.9%, purity grade, all obtained from Sigma Aldrich, were used as received. 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-P), and the ultra-flat glass substrates coated with a 20 nm layer of synthetic quartz were purchased from Ossila Ltd (Sheffield, UK)

Summary

Introduction

The idea of “organic electronics” is supported by the actual need of the production of low-end electronic devices using large area printing technology. Most of the OFETs available today, still suffer from low charge carrier mobility and not sufficient stability and reproducibility of their electrical parameters. For this reason, significant attention is put on the development of new organic semiconducting materials. Regardless of the organic materials used, OFETs often exhibit deviations from ideal electrical characteristics, which make their application in electronic circuitry difficult. Such deviations even complicate a reliable extraction of basic transistor parameters such as charge carrier mobility or threshold voltage. It is widely accepted that the hysteresis with a back sweep current higher compared to the forward direction, often observed in OFETs with polymeric gate dielectrics such as poly(4-vinylphenol)

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Conclusion