Electrolyte-gated transistors (EGTs) have been extensively studied as a next-generation neuromorphic device mimicking the biological ionic flux in synapses. However, its long-term plasticity characteristic lasts only for few seconds because of the rapid self-discharge of electrical double layer. Here, ultraviolet ozone (UVO) treated water-in-bisalt (WiBS)/polymer electrolytegated synaptic transistor (WEST) which excellently implements multiple synaptic functions is proposed. Ultraviolet (UV) light and reactive oxygen radicals generated during UVO treatment form trap sites on the surface of active layer, causing lithium cations in the WiBS/polymer electrolyte to be captured at the electrolyte/active layer interface. The UVO treated WEST shows enhanced nonvolatile memory performance for 10 000 s, up to 1186 times longer than that of the untreated WEST. Also, near-ideal weight update over 10 000 cycle tests with 0.32 and −0.55 nonlinearities of long-term potentiation and depression is acquired with a ten times improved symmetricity. These results confirm that the surface engineering is a key technique for sophisticated ion transport, and demonstrate various applicability of EGTs as a neuromorphic device.

Li + electrolyte-gated transistors (EGTs) have received much attention as artificial synapses for neuromorphic computing. EGTs, however, have been still challenging to achieve long-term synaptic plasticity, which should be linearly and symmetrically controlled with the magnitude of electrical potential at the gate electrode. Herein, a fluoroalkylsilane (FAS) self-assembled monolayer (SAM) is introduced as a channel-electrolyte interlayer with the function of sequential ion-trapping in Li + EGTs. It is demonstrated that the retention of Li + ions can be enhanced, resulting in stable non-volatile channel conductance update with high fidelity, linearity, and symmetry in EGTs treated with FAS with 5 fluoroalkyl chains. Through investigating electrical analysis and chemical analysis, it is verified that fluoroalkyl chains enable the sequential ion-trapping at the channel-electrolyte interface by coulombic attraction between Li + ions and fluorocarbons. Simulations of artificial neural networks using 20 × 20 digits show FAS-treated EGTs are suitable as artificial synapses with an accuracy of 89.71% by identical gate pulses and 91.97% by non-identical gate pulses. A methodological approach is newly introduced for developing synaptic devices based on EGTs for neuromorphic computing with high fidelity.

Li+ electrolyte-gated transistors (EGTs) have attracted significant attention as artificial synapses because of the fast response of Li+ ion, low operating voltage, and applicability to flexible electronics. Due to the inherent nature of Li+ ion, Li+ EGTs show, however, limitations, such as poor long-term synaptic plasticity and nonlinear/nonsymmetric conductance update, which hinder the practical applications of artificial synapses. Herein, Li+ EGTs integrated with poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) ferroelectric polymer as a channel–electrolyte interlayer are presented. Owing to the polarized domains of PVDF-TrFE, the transport of Li+ ions at the channel–electrolyte interface is accelerated, and Li+ ions effectively penetrate the channel. Moreover, the self-diffusion of Li+ ions from the channel to the electrolyte is suppressed by the downward polarized domains. Li+ EGTs, therefore, successfully demonstrate synaptic characteristics, including excitatory postsynaptic current, short-/long-term synaptic plasticity, and paired-pulse facilitation. Also, conductance update in Li+ EGTs shows a dynamic range ( Gmax/ Gmin) of 92.42, high linearity, and distinct stability over 100 cycles. Based on their synaptic characteristics, inference simulations using a convolution neural network for the CIFAR-10 dataset imply that Li+ EGTs are suitable as artificial synapses with an inference accuracy of 89.13%. The new methodological approach addressing modulation of ion dynamics at the interface is introduced for developing practical synaptic devices.

Cuprous oxide (Cu2O) p-type thin-film transistors (TFTs) can be practically applied for complementary metal oxide semiconductor (CMOS) logic circuits, but the electrical performances are still insufficient due to high off-current and low field-effect mobility. Here, we have demonstrated Cu2O TFTs with improved field-effect mobility and low off-current through reduction of cupric oxide (CuO) impurities and dissociative Cu defects with the combination of deposition and annealing conditions. Copper oxide was deposited by radio frequency sputtering in mixed gases of argon and oxygen. After that, the deposited copper oxide was annealed at 800 °C in the tube furnace under a N2 atmosphere instead of a high vacuum condition. The fabricated Cu2O thin film had a high crystalline quality, the ratio of dissociative Cu defects decreased from 11.3 to 3.1%, and the electrical performances of the TFT including the fabricated Cu2O thin film exhibited the field-effect mobility of 1.11 ± 0.05 cm2/V·s, the on/off current ratio of 4.68 ± 0.8 × 104, and the subthreshold swing value of 3.91 ± 0.21 V dec–1. The fabricated Cu2O TFT showed a Vth shift of 3.31 V in the transfer curve under negative bias stress. Nitrogen plays a role in promoting Cu2O phase formation while it prevents CuO phase formation during the annealing process. In addition, oxygen added during sputtering increases the ratio of CuO in the copper oxide thin film and works effectively to reduce dissociative Cu defects in the annealing process. To determine the feasibility of the CMOS logic circuit, we also demonstrated the inverter with n-type indium–gallium–zinc oxide (IGZO) TFT and p-type Cu2O TFT, which showed a voltage gain of 14 at V DD = 20 V.

Novel solvent-assisted vacancy engineering (SAVE) is proposed for S vacancy generation in MoS2, considering the solubility and polarity of the solvent. The SAVE-treated MoS2 synaptic memristor shows non-volatile memory characteristics and synaptic behavior.