Abstract
Flexible pressure sensors based on organic field‐effect transistors (OFETs) have emerged as promising candidates for electronic‐skin applications. However, it remains a challenge to achieve low operating voltages of hysteresis‐free flexible pressure sensors. Interface engineering of polymer dielectrics is a feasible strategy toward sensitive pressure sensors based on low‐voltage OFETs. Here, a novel type of solution‐processed bilayer dielectrics is developed by combining a thick polyelectrolyte layer of polyacrylic acid (PAA) with a thin poly(methyl methacrylate) (PMMA) layer. This bilayer dielectric can provide a vertical phase separation structure from hydrophilic interface to hydrophobic interface which adjoins well to organic semiconductors, leading to improved stability and remarkably reduced leakage currents. Consequently, OFETs using the PMMA/PAA dielectrics reveal greatly suppressed hysteresis and improved mobility compared to those with a pure PAA dielectric. Using the optimized PMMA/PAA dielectric, flexible OFET‐based pressure sensors that show a record high sensitivity of 56.15 kPa−1 at a low operating voltage of −5 V, a fast response time of less than 20 ms, and good flexibility are further demonstrated. The salient features of high capacitance, good dielectric performance, and excellent reliability of the bilayer dielectrics promise a bright future of flexible sensors based on low‐voltage OFETs for wearable electronic applications.
Highlights
The good interfacial compatibility of poly(methyl methacrylate) (PMMA) with organic semiconductor (OSC) promotes the formation of a good contact at the semiconductor/dielectric interface, which is significant for the organic field-effect transistors (OFETs) performance in terms of suppressed hysteresis and improved stability
If a thinner substrate with better flexibility and stability is used for the highly flexible devices,[8] the performance of these low-voltage OFET-based pressure sensor could be further improved. All these results demonstrate that the flexible OFETs and pressure sensors using the novel bilayer PMMA/polyacrylic acid (PAA) dielectric provide a feasible approach to realize high-performance flexible electronic devices
We have demonstrated a novel type of bilayer polymer dielectrics for achieving high-performance low-voltage OFETs and flexible pressure sensors
Summary
To achieve high-performance flexible OFETs, interface engineering of dielectric materials on organic semiconductors for suppressing leakage currents and forming good interfacial contacts is critical to enhance the charge carrier transportation.[32,33] We chose a top-gate/bottom-contact device configuration to fabricate efficient and stable flexible OFETs. Flexible PMMA is well known for its easy solution processability, good film formation, excellent dielectric properties, and outstanding stability.[36] More importantly, the good interfacial compatibility of PMMA with OSC promotes the formation of a good contact at the semiconductor/dielectric interface, which is significant for the OFET performance in terms of suppressed hysteresis and improved stability. These attributes make the PMMA/PAA composite a promising multifunctional dielectric material for regulating and enhancing device performance of flexible lowvoltage OFETs and the resulting pressure sensors. To complete the fabrication of final OFETs, Au was thermally evaporated as the gate electrode on the top of the dielectric
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