Associative learning, a critical learning principle to improve an individual’s adaptability, has been emulated by few organic electrochemical devices. However, complicated bias schemes, high write voltages, as well as process irreversibility hinder the further development of associative learning circuits. Here, by adopting a poly(3,4-ethylenedioxythiophene):tosylate/Polytetrahydrofuran composite as the active channel, we present a non-volatile organic electrochemical transistor that shows a write bias less than 0.8 V and retention time longer than 200 min without decoupling the write and read operations. By incorporating a pressure sensor and a photoresistor, a neuromorphic circuit is demonstrated with the ability to associate two physical inputs (light and pressure) instead of normally demonstrated electrical inputs in other associative learning circuits. To unravel the non-volatility of this material, ultraviolet-visible-near-infrared spectroscopy, X-ray photoelectron spectroscopy and grazing-incidence wide-angle X-ray scattering are used to characterize the oxidation level variation, compositional change, and the structural modulation of the poly(3,4-ethylenedioxythiophene):tosylate/Polytetrahydrofuran films in various conductance states. The implementation of the associative learning circuit as well as the understanding of the non-volatile material represent critical advances for organic electrochemical devices in neuromorphic applications.

With fast recovery time and effective in situ tumor tissue killing ability, thermal ablation has become a popular treatment for tumors compared with chemotherapy and radiation. The thermal dose measurement of current technology is usually accompanied by monitoring a large area impedance across two ablation catheters and the localized impedance measurement is difficult to achieve.In this work, thermal-resistive sensor and impedance sensor are fabricated on the curved surface of a capillary tube with 1 mm outer diameter. The device is applied for real-time in situ tissue impedance monitoring during thermal ablation. The calibrated thermal-resistive sensors have an average temperature coefficient of resistance (TCR) of 0.00161 ± 5.9% • C -1 with an accuracy of ±0.7 • C. By adding electro-polymerized PEDOT:PSS (poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)) on the 300 µm diameter gold electrodes, the interface impedance reduces two orders from 408 to 3.7 kΩ at 100 Hz. The Randles equivalent circuit model fittings show a two-order improvement in the electrode capacitance from 7.29 to 753 nF. In the ex vivo porcine liver laser ablation test, the temperature of the porcine liver tissue can reach 70 • C and the impedance would drop by 50% in less than 5 minutes. The integration of laser ablation fiber with the impedance and temperature sensors can further expand the laser ablation technique to smaller scale and for precise therapeutics.

Thermal ablation has been adopted as one of the most common cancer treatment approaches in medical surgery. By increasing the temperature (>50 °C) on the cells, the cells are destroyed because of denaturation. Herein, an ultrathin Archimedean spiral pattern heater/sensor technology is introduced which can perform ablation by attaching conformally onto the organs for precise heating and temperature sensing. In the heater mode, the heater temperature is linearly proportional to the input joule heating power up to 400 mW. In the sensor mode, the temperature of the conformal metal wire is also linearly related to the resistance by the temperature coefficient of resistance (TCR). The conformal heater to perform ex vivo ablation on the porcine liver is utilized. By further integrating the devices with robotic palm and perform heat‐and‐sense interactions, a human–machine interface (HMI) apparatus is demonstrated which can be potentially applied in surgical robots or other tactile stimulation systems.

Solution-processed organic semiconductors (OSCs) promote the development of the next generation of large-area, low-cost flexible electronics. To date, the properties of the flexible substrates such as chemical compatibility, roughness, and surface energy are still big challenges for the solution process, especially for high-performance ultrathin monolayer OSCs. Herein, van der Waals assembled organic field-effect transistors (OFETs) with layerby-layer lamination processes are reported. The active layer is an ultrathin single molecular layer 2,9-Didecyldinaphtho[2,3-b:2′,3′-f ]thieno[3,2-b] thiophene (C 10 -DNTT) which maintains decent electrical fidelity with mobility of 10.4 cm 2 V -1 s -1 after transfer. With the active layer transfer technique, the bias stability of OFETs can be significantly improved by tuning diverse hydrophobic self-assembly monolayers (SAMs) onto the dielectric which is a challenging task before the solution processing organic monolayer. A small subthreshold swing (SS) of 63 mV decade −1 is achieved by low surface energy phosphonic acid SAMs on high-κ AlO x dielectric. We further demonstrate a high-gain organic inverter amplifier that can be powered up by a coin cell on the 1.5 µm conformal parylene substrate and apply it for high-resolution electrocardiograph (ECG) sensing. The ECG sensors can provide a signal-tonoise ratio as high as 34 dB. It is believed that our device demonstrates the prospect of continuous monitoring for human health management.

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Miniaturization and minimization of mechanical mismatch in neural probes have been two well‐proven directions in suppressing immune response and improving spatial resolution for neuronal stimulations and recordings. While the high impedance brought by the miniaturization of electrodes has been addressed by using conductive polymers coatings in multiple reports, the stiffness of such coatings remains orders of magnitude higher than that of the brain tissue. Here, a flat neural probe based on a highly flexible microelectrode array with electrodeposited hydrogel coatings poly(2‐hydroxyethyl methacrylate) (pHEMA) and conductive polymer poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS), with a cross‐section area at only 300 µm × 2.5 µm is presented. The PEDOT/PSS coating provides a low interfacial impedance, and the pHEMA deposition bridges the mechanical mismatch between the probe and the brain tissues. The two layers of polymers modification enhance the signal‐to‐noise ratio and allow the microelectrodes array to be engineered for both recording and stimulation purposes. Besides, in vivo testing of microelectrode arrays implanted in rat hippocampus confirms a high senstivity in neural signal recording and excellent charge injection capacity which can induce long‐term potentiation in neural activities in the hippocampus. The probes provide a robust and low‐cost solution to the brain interfaces problem.

sophisticated circuits such as ring oscillators [13][14][15] and logic gates. [16][17][18] However, the number and density of the transistors must be increased to enhance their performance and application, thus necessitating the downsizing of the OFETs. To date, various lithographic technologies such as multilayer photolithography, [19] deep X-ray lithography, [20] electron beam lithography, [21] and extreme ultraviolet lithography (EUV), [22,23] have been developed and used to fabricate transistors at the microto nanoscale. However, these approaches usually require expensive equipment or relatively complicated processing steps and, more importantly, may have compatibility issues with respect to the organic semiconductors, which are sensitive to chemicals and processing temperatures.Recently, Soleymani and Moran-Mirabal et al. [25] demonstrated the use of a shrinkable substrate that supports the standard fabrication process while enabling size reduction by application of an external stimulus. The shrink films consisted of prestressed polymers such as polystyrene (PS) that release the biaxial internal stress and relax the polymer chain after heating. [24] Previously, microfluidic channels [26,27] have been fabricated by using shrink films, as they can reduce the channel dimensions and form thick channel walls. [24] Biosensors with wrinkled electrodes have also used shrink film substrates to achieve small-scale electrodes with large surface areas, [25,26] thus potentially reducing the sheet resistance and solving the measurement bottleneck. As the film allows homogeneous shrinking, the shapes of the microfluidic channels and metal electrodes would remain unchanged after the size reduction. This homogeneous size reduction is particularly important in microelectronic fabrication to avoid shorting. [25,26] Moreover, studies have shown that the homogenous size reduction can be well controlled according to the material properties (e.g., the elastic modulus) and thickness of the deposition film, along with the wavelength and amplitude of the wrinkles that are formed during shrinkage as summarized in Figure S1 (Supporting Information).In the present study, both the size reduction and the potential use of the wrinkle structures to improve the electrical performance of the OFET is explored. The polystyrene shrinkable film substrate is shown to provide a 65-70% reduction in the effective area of the OFETs, along with reductions in the threshold voltage (from −1.44 to −0.18 V), the subthreshold In the development of flexible organic field-effect transistors (OFET), downsizing and reduction of the operating voltage are essential for achieving a high current density with a low operating power. Although the bias voltage of the OFETs can be reduced by a high-k dielectric, achieving a threshold voltage close to zero remains a challenge. Moreover, the scaling down of OFETs demands the use of photolithography, and may lead to compatibility issues in organic semiconductors. Herein, a new strategy based on the ductile properties of or...