High‐Transconductance Stretchable Transistors Achieved by Controlled Gold Microcrack Morphology

Abstract

healthcare applications and robotics. [5][6][7] Organic electrochemical transistors (OECTs) are the building blocks of many of the most sensitive sensors. [8,9] Unlike conventional field effect transistors (FETs), OECTs consist of an active layer with mixed electronic and ionic transport, enabling remarkably high transconductance (g m ) for high amplification of signals. [10,11] For example, OECT-based devices for electrophysiological recording with high signal integrity, [8,9,12] highly sensitive biosensors, [13][14][15][16] neuromorphic applications, [17] display drivers, [18] and optical logic gates [19] have been reported. However, practical applications of OECTs critically rely on the development of devices with a high transconductance at high strain (≈100%) to accommodate for the dynamic range of motions and shapes of the human body. [20] The breakdown of high transconductance typically stems from the high resistance of the source/drain electrodes at high strain. Electrodes must be highly conductive at high strain, stable in the electrolyte, and soft enough to avoid stress concentration at the interface with the active layer. [21,22] While there have been reports of highly conductive stretchable conductors (Ag-based materials, carbon nanotubes, and liquid metals [3,[23][24][25][26][27] ), there has yet been a demonstration of a stretchable conductor which collectively satisfies the aforementioned requirements. Importantly, plain Au thin films are not stretchable while Au thin films with microcrack morphology are stretchable and electrolyte-stable. [28][29][30][31][32] However, the conductance at high strain (≈100%) was not ideal, with sheet resistance increasing over two orders of magnitude observed due to the large strain-induced microcrack propagation. This large microcrack propagation originates from the uncontrolled morphology of initial microcracks in as-deposited Au thin films. We propose that control over the initial microcrack morphology and propagation may lead to improved and stable conductance at high strains.Here, we report highly stretchable (≈140%) and hightransconductance (>0.1 mS) OECTs, enabled by microcracked Au conductors engineered by programming the initial microcrack formation (Figure 1a). Inspired by kirigami-structures, we hypothesized that highly stretchable Au can be obtained if the High-transconductance stretchable transistors are important for conformable and sensitive sensors for wearables and soft robotics. Remarkably high transconductance, which enables large amplification of signals, has been achieved through the use of organic electrochemical transistors (OECTs). However, the stretchability of such systems has been tempered by the lack of stretchable conductors with high stability in electrolytes, high conductance at high strain (100%), and process compatibility with active layers. Highly stretchable and strain-resistant Au conductors employed to fabricate intrinsically stretchable OECTs are demonstrated. Notably, the conductors exhibit a sheet resistance of 33.3 Ω Sq. −1 at...

Stretchable Electronics Based on PDMS Substrates

“…Here, the strain causes uniform microcracks in the metal thin film (Figure 1b‐II), forming a percolating network that serves as the pathway for electron transfer. [ 84–86 ] Two factors influence the stretchability of the metal film. The first factor corresponds to the local strain concentrating sites.…”

“…Because of the soft property of the PDMS substrate and weak metal film/PDMS interface adhesion, the PDMS substrate allows the percolating network structure to deform out of the plane by deflecting and twisting; thus, the strain in the film is further dissipated. [ 84,86 ] Inspired by this mechanism, carbon nanotubes (CNTs) have also been deposited on the surface of PDMS to fabricate stretchable electrodes or strain sensors. [ 87–89 ] The weak connecting points among the nanowires can serve as local strain concentrating sites.…”

“…b‐III) Reproduced with permission. [ 86 ] Copyright 2019, Wiley‐VCH. c‐II) SEM images of the silver nanowires burying PDMS.…”

Design of a Janus‐Faced Electrode for Highly Stretchable Zinc–Silver Rechargeable Batteries

“…This implies that the e-Ag NPs effectively preserve the electrical pathway under strain. [39,40] On the other hand, when the stress was released, the micro-fibril perfectly recovered to its initial state ( Figure 3F). Therefore, it can be concluded that the Janus-faced electrode effectively maintains the percolation network of e-Ag NPs even in the stretched state as well as its electrical performance after repeated deformations.…”

Recent Technological Advances in Fabrication and Application of Organic Electrochemical Transistors

“…Furthermore, neuro-inspired computational platforms made by OECTs interfaced with cellular systems, [205,206] integrated ionic-based logic gates including inverters and NAND gates [124,188] and stretchable synaptic OECTs [48] were also developed, which expand the functionality boundaries of the current neuromorphic devices. In general, the easily tailored features and continuously tunable conductance range reported in various organic materials and architectures for OECTs have demonstrated great perspective for neuromorphic computing applications.…”