Optimization of Gate-Bias Stability and Gas-Sensing Properties of Triethylsilylethynyl Anthradithiophene Micro-Strip Field-Effect Transistors by Incorporating Insulating Polymer

Abstract

The control of the microstructure and patterning of 5,11-bis(triethylsilylethynyl)anthradithiophene (TES-ADT) film is essential for high-performance TES-ADT field-effect transistors (FETs) as a NO2 gas sensor. In this study, a binary blend film based on TES-ADT and insulating polymer was annealed by solvent vapor with patterned PDMS molds. The solvent-containing PDMS mold led to the TES-ADT crystallization under the phase-separation between TES-ADT and PMMA. This resulted in highly crystalline micro-strip films where TES-ADT and the insulating polymer were phase-separated on top and bottom, respectively. The micro-strip structures can have superior gas sensor performance because they have additional gas diffusion paths compared to non-patterned structures. Initial investigations to clarify morphology and microstructure of the films revealed that lateral phase separation got dominant with increasing the portion of the insulating polymer. The blended films were then used as the active layer in the FET-based gas sensors. The use of blended films instead of non-blended TES-ADT film in FETs is advantageous in reducing both the threshold voltage and subthreshold slope while compromising the field-effect mobility. The sensing response as the gas sensors is slightly lower in the blended TES-ADT FET than in the non-blended TES-ADT FET. However, the utilization of blended films significantly enhanced the bias-stress stability. Accordingly, a uniform baseline of the sensor performance was achieved in TES-ADT: insulating polymer blended FETs. This trend was in contrast to an abrupt decrease in the sensing signals of the non-blended TES-ADT FETs. The enhanced bias stability of the blended FETs was exhibited as a result of covering the silanol groups in SiO2 with a phase-separated insulating polymer. Our results provide a route for to the optimization of bias stability and response in TES-ADT micro-strip gas sensors through the application of a one-step blend technology.