Grain Boundary Induced Bias Instability in Soluble Acene-Based Thin-Film Transistors.

Ky V Nguyen,Kilwon Cho,Boseok Kang,John E Anthony,Wi Hyoung Lee,Eunjoo Song,Marcia M Payne,Jung Hun Lee

doi:10.1038/srep33224

Abstract

Since the grain boundaries (GBs) within the semiconductor layer of organic field-effect transistors (OFETs) have a strong influence on device performance, a substantial number of studies have been devoted to controlling the crystallization characteristics of organic semiconductors. We studied the intrinsic effects of GBs within 5,11-bis(triethylsilylethynyl) anthradithiophene (TES-ADT) thin films on the electrical properties of OFETs. The GB density was easily changed by controlling nulceation event in TES-ADT thin films. When the mixing time was increased, the number of aggregates in as-spun TES-ADT thin films were increased and subsequent exposure of the films to 1,2-dichloroethane vapor led to a significant increase in the number of nuleation sites, thereby increasing the GB density of TES-ADT spherulites. The density of GBs strongly influences the angular spread and crystallographic orientation of TES-ADT spherulites. Accordingly, the FETs with higher GB densities showed much poorer electrical characteristics than devices with lower GB density. Especially, GBs provide charge trapping sites which are responsible for bias-stress driven electrical instability. Dielectric surface treatment with a polystyrene brush layer clarified the GB-induced charge trapping by reducing charge trapping at the semiconductor-dielectric interface. Our study provides an understanding on GB induced bias instability for the development of high performance OFETs.

Highlights

Organic field-effect transistors (OFETs) have received much attention due to their potential applications in light-weight, low-cost, flexible electronics such as radio-frequency identification (RFID) tags, display drivers and sensors[1,2,3]
grain boundaries (GBs) between crystallites can create a number of traps which cause degradation of device characteristics such as threshold voltage shifts and on-current changes upon prolonged gate bias, which will disrupt the functioning of the display pixels connected to OFETs43
To understand spherulitic growth in TES-ADT thin films, the film morphology before and after solvent vapor annealing were first studied with an optical microscope

Summary

Introduction

Organic field-effect transistors (OFETs) have received much attention due to their potential applications in light-weight, low-cost, flexible electronics such as radio-frequency identification (RFID) tags, display drivers and sensors[1,2,3]. The TES-ADT spherulite is an interesting example with which to study GB effects in organic semiconductors as the in-plane packing motif of TES-ADT is much simpler than that of pentacene film[25] To this end, a small amount of F-TESADT added to a TES-ADT solution and heterogeneous nucleation in TES-ADT (host)/F-TESADT (guest) film leads to an increase in the number of GBs in TES-ADT spherulites during solvent vapor treatment[41,42]. As solution mixing time increased, self-aggregation of TES-ADT molecules occurred and a spin-cast film showed many aggregates This in turn resulted in a decrease in the grain size of TES-ADT spherulites (or an increase in the number of GBs) during solvent vapor annealing. A very thin organic layer was introduced as a surface modifier of the SiO2 dielectric for reducing charge trapping at the semiconductor-dielectric interface and thereby clarifying the GB-induced charge trapping

Methods

Results

Conclusion