Molecular Tailoring to Achieve Long‐Term Plasticity in Organic Synaptic Transistors for Neuromorphic Computing

Abstract

Organic synaptic transistors (OSTs) using intrinsic polymer semiconductors are demonstrated to be suitable for neuromorphic bioelectronics. However, diketopyrrolopyrrole (DPP)‐based copolymers are not applicable to neuromorphic computing systems because the DPP polymer film has demonstrated only short‐term plasticity with short retention (<50 ms) in synaptic devices because of their intrinsic difficulty of electrochemical doping. To expand their applications toward neuromorphic computing that requires long‐term plasticity, artificial synapses with extended retention time should be developed. Herein, molecular tailoring approach to extend the retention time in the ion‐gel‐gated OSTs that use DPP is suggested. The molecular structure is controlled by changing alkyl spacer lengths of side chains. As a result, the doping process is more favorable in DPP with long alkyl spacer, which is confirmed by high doping concentration and slow dedoping rate. Therefore, dedoping of ions is more suppressed in DPP with long alkyl side chain that exhibits extended retention time (≈800 s) of the OSTs. These optimized DPP‐based OSTs obtain high pattern recognition accuracy of ≈96.0% in simulations of an artificial neural network. Molecular tailoring strategies provide a guideline to overcome the intrinsic problem of short synaptic retention time of the OSTs for use in neuromorphic computing.

Tuning Gate Potential Profiles and Current–Voltage Characteristics of Polymer Electrolyte-Gated Transistors by Capacitance Engineering

“…Specific ion-semiconductor effects (e.g., ion-polymer binding) are not required to explain the I D –V G hysteresis when the gate electrode is undersized; device geometry alone can cause hysteresis in EGTs. In our view, this point is important for the community using EGTs for neuromorphic computing applications. ,,− …”

Modulating Neuromorphic Behavior of Organic Synaptic Electrolyte-Gated Transistors Through Microstructure Engineering and Potential Applications

“…The PSC decay curve after the second stimulation (Figure 4b) can be fitted by a triexponential function in the following to analyze the charge release mechanism: 31,32,52,53 i k j j j j j y { z z z z z i k j j j j j y { z z z z z i k j j j j j y…”

“…28−30 Functional organic semiconductor materials are synthesized to change the degree of ion doping in active layers and manipulate memory behavior of synaptic devices. 31,32 However, most works focus on features of dielectric layers correlated with neuromorphic electrical characteristics of organic synaptic transistors and their application in artificial neural networks. 10,18,[21][22][23][24][25][26]28 The significant impact of microstructural and interfacial properties on the electrical characteristics of organic thin-film transistors (TFTs) has been extensively studied and demonstrated, with an expected similar influence on the neuromorphic electrical properties of organic synaptic transistors.…”

Modulating short-term and long-term plasticity of polymer-based artificial synapses for neuromorphic computing and beyond

“…Removing the voltage spike induces the dedoping of ions from the semiconducting channel to their original positions and leads to decaying of the postsynaptic current. The device shows an LTP when it faces difficulty in diffusing out the doped ions in the channel, whereas it achieves an STP when it rapidly diffuses the doped ions from the channel layer [52][53][54]. In this regard, the dedoping process of ions can be modulated according to the interaction of ions with semiconducting layers.…”

“…In semiconducting layers, side chain engineering has been adopted to control the synaptic properties. First, a diketopyrrolopyrrole (DPP)/selenophene-vinylene-selenophene (SVS) copolymer was used as the semiconducting layer in IGPST to investigate how the length of the side chain affect synaptic plasticity [54]. Two types of DPP-SVS copolymers, which have different lengths of the alkyl spacers of the side chains, were fabricated.…”