Qing Wan

Freestanding Artificial Synapses Based on Laterally Proton-Coupled Transistors on Chitosan Membranes.

Freestanding synaptic transistors are fabricated on solution-processed chitosan membranes. A short-term memory to long-term memory transition is observed due to proton-related electrochemical doping under repeated pulse stimulus. Moreover, freestanding artificial synaptic devices with multiple presynaptic inputs are investigated, and spiking logic operation and logic modulation are realized.

Proton-Conducting Graphene Oxide-Coupled Neuron Transistors for Brain-Inspired Cognitive Systems.

Proton-conducting graphene oxide electrolyte films with very high electric-double-layer capacitance are used as the gate dielectrics for oxide-based neuron transistor fabrication. Paired-pulse facilitation, dendritic integration, and orientation tuning are successfully emulated. Additionally, neuronal gain controls (arithmetic) are also experimentally demonstrated. The results provide a new-concept approach for building brain-inspired cognitive systems.

Memory and learning behaviors mimicked in nanogranular SiO2-based proton conductor gated oxide-based synaptic transistors

In neuroscience, signal processing, memory and learning function are established in the brain by modifying ionic fluxes in neurons and synapses. Emulation of memory and learning behaviors of biological systems by nanoscale ionic/electronic devices is highly desirable for building neuromorphic systems or even artificial neural networks. Here, novel artificial synapses based on junctionless oxide-based protonic/electronic hybrid transistors gated by nanogranular phosphorus-doped SiO2-based proton-conducting films are fabricated on glass substrates by a room-temperature process. Short-term memory (STM) and long-term memory (LTM) are mimicked by tuning the pulse gate voltage amplitude. The LTM process in such an artificial synapse is due to the proton-related interfacial electrochemical reaction. Our results are highly desirable for building future neuromorphic systems or even artificial networks via electronic elements.

Synaptic Behaviors Mimicked in Flexible Oxide-Based Transistors on Plastic Substrates

In the human brain, synapses are the crucial connective parts between neurons, which endow neurons with significant computational abilities. Here, indium-zinc-oxide (IZO) based flexible synaptic transistors are fabricated on a plastic substrate by a simple self-assembly method. Proton conducting phosphorus-doped nanogranular SiO2 electrolyte is used as the gate dielectric. Excitatory postsynaptic current, paired-pulse facilitation, and long-term memory are mimicked in the flexible artificial synapses. Such IZO-based flexible electronic synapses are promising for building neuromorphic systems.

Energy-Efficient Artificial Synapses Based on Flexible IGZO Electric-Double-Layer Transistors

Flexible low-voltage indium-gallium-zincoxide (IGZO) electric-double-layer transistors are fabricated on polyethylene terephthalate substrates at room temperature and proposed for energy-efficient artificial synapse application. The IGZO channel conductance and the gate voltage pulse are regarded as synaptic weight and synaptic spike, respectively. The energy consumption of our IGZO synaptic transistor is estimated to be as low as ~0.23 pJ/spike. Short-term synaptic plasticity and high-pass filtering behaviors are also mimicked in an individual IGZO synaptic transistor.

Gas sensors based on semiconducting nanowire field-effect transistors.

One-dimensional semiconductor nanostructures are unique sensing materials for the fabrication of gas sensors. In this article, gas sensors based on semiconducting nanowire field-effect transistors (FETs) are comprehensively reviewed. Individual nanowires or nanowire network films are usually used as the active detecting channels. In these sensors, a third electrode, which serves as the gate, is used to tune the carrier concentration of the nanowires to realize better sensing performance, including sensitivity, selectivity and response time, etc. The FET parameters can be modulated by the presence of the target gases and their change relate closely to the type and concentration of the gas molecules. In addition, extra controls such as metal decoration, local heating and light irradiation can be combined with the gate electrode to tune the nanowire channel and realize more effective gas sensing. With the help of micro-fabrication techniques, these sensors can be integrated into smart systems. Finally, some challenges for the future investigation and application of nanowire field-effect gas sensors are discussed.

Flexible Metal Oxide/Graphene Oxide Hybrid Neuromorphic Transistors on Flexible Conducting Graphene Substrates

Flexible metal oxide/graphene oxide hybrid multi-gate neuromorphic transistors are fabricated on flexible conducting graphene substrates. Dendritic integrations in both spatial and temporal modes are emulated, and spatiotemporal correlated logics are obtained. A proof-of-principle visual system model for emulating Lobula Giant Motion Detector neuron is also investigated. The results are of great significance for flexible sensors and neuromorphic cognitive systems.

Flexible Transparent Junctionless TFTs With Oxygen-Tuned Indium-Zinc-Oxide Channels

Flexible low-voltage transparent junctionless thin-film transistors (TFTs) with oxygen-tuned indium-zinc-oxide (IZO) active layers are fabricated on polyethylene terephthalate plastic substrates at room temperature with only one shadow mask. IZO films deposited in gradient oxygen ambient are used as the channel and source/drain electrodes without any source/drain junction. High performance with a low subthreshold swing of 0.13 V/decade and a high drain current ON/OFF ratio 106 are obtained in both flat and curving states. A field-effect mobility with a upper limit value of ~60 cm2/V.s is obtained with a gate voltage sweep speed of 0.05 V/s. Such flexible IZO-based junctionless TFTs with lowcost are promising for portable flexible sensor and bioelectronics applications.

Short-Term Plasticity and Synaptic Filtering Emulated in Electrolyte-Gated IGZO Transistors

Artificial synaptic devices have attracted a broad interest for hardware implementation of brain-inspired neuromorphic systems. In this letter, a short-term plasticity simulation in an indium-gallium-zinc oxide (IGZO) electric-double-layer (EDL) transistor is investigated. For synaptic facilitation and depression function emulation, three-terminal EDL transistor is reduced to a two-terminal synaptic device with two modified connection schemes. Furthermore, high-pass and low-pass filtering characteristics are also successfully emulated not only for fixed-rate spike train but also for Poisson-like spike train. Our results suggest that IGZO-based EDL transistors operated in two terminal mode can be used as the building blocks for brain-like chips and neuromorphic systems.

Low-Cost pH Sensors Based on Low-Voltage Oxide-Based Electric-Double-Layer Thin Film Transistors

Indium-tin-oxide-based electric-double-layer (EDL) thin-film transistors (TFTs) are used as pH sensors. Such EDL devices show a low operation voltage of ~ 1.5 V and a high field-effect electron mobility (μFE) of ~ 20 cm²·V^-1·s^-1 when phosphorous-doped nanogranular SiO2-based electrolyte films are used as the gate dielectric. The pH sensor based on such EDL TFT exhibits a high sensitivity of 58.1 mV·pH^-1 and a good linearity in the pH range from 2 to 12. In addition, such pH sensors present a low threshold voltage drift rate of 2.2 mV·h^-1 and a hysteresis voltage of 8.3 mV after a pH loop of 7→ 4→ 7→ 10→7.