Chuan Qian

Flexible organic field-effect transistors on biodegradable cellulose paper with efficient reusable ion gel dielectrics

Reusable and renewable electronics is an emerging field aimed at the development of environmentally safe, disposable and biocompatible devices. Here, we demonstrate the fabrication of flexible poly(3-hexylthiophene) (P3HT) field-effect transistors (FETs) on cellulose paper with biopolymer chitosan smoothing layers and efficient reusable ion gel gate dielectrics. The high specific capacitance of ion gels led to the formation of an electric-double-layer (EDL) at the channel/dielectric interface that plays a critical role in modulating the currents of the devices. Reasonable electrical characteristics and mechanical flexibility were observed. Transistors with an operating voltage as low as 2 V, a source drain current of up to ∼1 mA, a current on/off ratio of 3–4 orders of magnitude and a large field-effect mobility of ∼0.97 cm2 V−1 s−1 have been obtained. Especially, the laminated ion gels can be in situ peeled off and reused in other FETs and the device performance is not degenerated obviously with repeated use. The unique flexibility of the FETs on paper with reusable ion gel dielectrics manifests their applications as the next generation of throwaway electronics.

Multi-gate organic neuron transistors for spatiotemporal information processing

Due to similar transmission characteristics of biological synaptic activities, neuromorphic behaviors simulated by organic electrochemical transistors (OECTs) is of great interest. In this letter, the fabrication and performance of multi-gate poly(3-hexylthiophene) (P3HT) OECTs with ion-gel gating are reported. The neuromorphic behaviors, such as dendrite correlated excitatory postsynaptic current (EPSC), paired pulse facilitation, and modulation, were simulated in the OECTs. These behaviors were observed to depend on the degree of temporal correlation and distance between the in-plane-gate and the channel. More importantly, by using dendritic integration from two different gates, spatiotemporally correlated outputs were also emulated. The spatial orientations of the input pulse are defined, and changing the orientation will result in a change in the EPSC amplitude. Our results provide a way to construct spatiotemporally neural network based on multi-gate OECTs.

Artificial synapses based on biopolymer electrolyte-coupled SnO2 nanowire transistors

The fabrication of biologically inspired solid-state devices has attracted tremendous attention for decades, and the hardware implementation of artificial synapses using individual ionic/electronic hybrid devices is very important for neuromorphic applications. Herein, electric double-layer (EDL) synaptic transistors coupled by proton neurotransmitters with a multiple in-plane gate structure were successfully fabricated using SnO2 nanowires. Not only the important synaptic functions were mimicked in these devices, but also the synaptic behaviors can be modulated over a dynamic range via the multi-terminal regulation of synaptic inputs. Furthermore, a light source was used to illuminate the SnO2 nanowire synaptic transistors, which were used as the light-modulating terminals. The observed neuromorphic functions were also dynamically modulated via the light density. These excellent nanoscale synaptic transistors may find significant applications in synaptic electronics.

Low contact resistance in solid electrolyte-gated ZnO field-effect transistors with ferromagnetic contacts

Understanding the role of contacts and interfaces between ferromagnetic metals and semiconductors is a critical step for spin injection and transport. Here, high performance solid electrolyte gated ZnO field-effect-transistors (FETs) with ferromagnetic Co contacts as the source and drain electrodes were demonstrated. Solid electrolyte gating provides a large electric field in the FETs that leads to an ohmic contact between the Co electrode and the ZnO film. The contact resistance can be tuned by the gate voltage and reduced to 66 Ω cm. Compared with FETs using a traditional SiO2 dielectric, an improved transistor performance is achieved with a current on/off ratio of 106 and a field-effect mobility of 5.24 cm2 V−1 s−1. The magnetoresistance calculation based on a spin diffusion model indicates that the on-state contact resistance of the solid electrolyte gated FETs falls in the optimal range for the injection and detection of spin-polarized charge carriers. These results reveal that the electrolyte gating allows for engineering the contacts for nanoelectronic and spintronic devices.

Ion-dependent gate dielectric characteristics of ion-conducting SiO2 solid-electrolytes in oxide field-effect transistors

The effect of ions on the gate dielectric behavior of oxide field-effect transistors (FETs) was studied using lithium ion-incorporated porous SiO2. The frequency dependence of the impedance was observed to vary with the ion concentrations in the ion-conducting SiO2 solid-electrolyte. The microstructure of the porous SiO2 was tailored by changing the depositions and porous SiO2 with an ordered columnar microstructure was realized, which provides an unobstructed pathway for the transportation of electrolyte ions. An enhanced electric-double-layer (EDL) capacitance of 11.9 μF cm(-2) and an improved EDL formation upper-limit-frequency of ∼10(5) Hz were obtained. Due to the enhanced EDL capacitance, oxide FETs gated by these solid-electrolytes showed a very low operating voltage of 0.6 V. A current on/off ratio of ∼10(6), a subthreshold swing of ∼82 mV per decade, a near-zero threshold voltage of ∼-0.01 V, and an electron field-effect mobility of ∼27.1 cm(2) V(-1) s(-1) were obtained. These ultra low-voltage FETs have potential applications in portable devices and biochemical sensors.

Flexible Neuromorphic Architectures Based on Self-Supported Multiterminal Organic Transistors

Because of the fast expansion of artificial intelligence, development and applications of neuromorphic systems attract extensive interest. In this paper, a highly interconnected neuromorphic architecture (HINA) based on flexible self-supported multiterminal organic transistors is proposed. Au electrodes, poly(3-hexylthiophene) active channels, and ion-conducting membranes were combined to fabricate organic neuromorphic devices. Especially, freestanding ion-conducting membranes were used as gate dielectrics as well as support substrates. Basic neuromorphic behavior and four forms of spike-timing-dependent plasticity were emulated. The fabricated neuromorphic device showed excellent electrical stability and mechanical flexibility after 1000 bends. Most importantly, the device structure is interconnected in a way similar to the neural architecture of the human brain and realizes not only the structure of the multigate but also characteristics of the global gate. Dynamic processes of memorizing and forgetting were incorporated into the global gate matrix simulation. Pavlovs learning rule was also simulated by taking advantage of the multigate array. Realization of HINAs would open a new path for flexible and sophisticated neural networks.