Simultaneously Defined Semiconducting Channel Layer Using Electrohydrodynamic Jet Printing of a Passivation Layer for Oxide Thin-Film Transistors

Advancements in Flexible Electronics Fabrication: Film Formation, Patterning, and Interface Optimization for Cutting-Edge Healthcare Monitoring Devices

Flexible electronics can seamlessly adhere to human skin or internal tissues, enabling the collection of physiological data and real-time vital sign monitoring in home settings, which give it the potential to revolutionize chronic disease management and mitigate mortality rates associated with sudden illnesses, thereby transforming current medical practices. However, the development of flexible electronic devices still faces several challenges, including issues pertaining to material selection, limited functionality, and performance instability. Among these challenges, the choice of appropriate materials, as well as their methods for film formation and patterning, lays the groundwork for versatile device development. Establishing stable interfaces, both internally within the device and in human-machine interactions, is essential for ensuring efficient, accurate, and long-term monitoring in health electronics. This review aims to provide an overview of critical fabrication steps and interface optimization strategies in the realm of flexible health electronics. Specifically, we discuss common thin film processing methods, patterning techniques for functional layers, interface challenges, and potential adjustment strategies. The objective is to synthesize recent advancements and serve as a reference for the development of innovative flexible health monitoring devices.

Strain-Sensor-In-Pixel Technology for Resolution-Sustainable Stretchable Displays

One of the limitations of stretchable displays is the severe degradation of resolution or the decrease in the number of pixels per unit area when stretched. Hence, we suggest a strain-sensor-in-pixel (S-SIP) system through the adoption of hidden pixels that are activated only during the stretch mode for maintaining the density of on-state pixels. For the S-SIP system, the gate and source electrodes of InGaZnO thin-film transistors (TFTs) in an existing pixel are connected to a resistive strain sensor through the facile and selective deposition of silver nanowires (AgNWs) via electrohydrodynamic-jet-printing. With this approach, the strain sensor integrated TFT functions as a strain-triggered switch, which responds only to stretching along the designated axes by finely tuning the orientation and cycles of AgNW printing. The strain sensor-integrated TFT remains in an off-state when unstretched and switches to an on-state when stretched, exhibiting a large negative gauge factor of -1.1 × 1010 and a superior mechanical stability enduring 6000 cycles, which enables the efficient structure to operate hidden pixels without requiring additional signal processing. Furthermore, the stable operation of the S-SIP in a 5 × 5-pixel array is demonstrated via circuit simulation, implying the outstanding applicability and process compatibility to the conventional active-matrix display backplanes.

Tungsten-Doped Indium Tin Oxide Thin-Film Transistors for Dual-mode Proximity Sensing Application

Technologies for human-machine interactions are booming now. In order to achieve multifunctional sensing abilities of electronic skins, further developments of various sensors are in urgent demand. Herein, a dual-mode proximity sensor based on an oxide thin-film transistor (TFT) is reported. Although InSnO (ITO) is featured with high mobility, the inherent high carrier concentration limits its use as a channel material for thin-film transistors. Herein, the tungsten element was introduced as a carrier suppressor to develop ITO-based semiconducting materials and devices. TFTs with amorphous tungsten-doped ITO (ITWO) channel layers were fabricated. As for a flat panel display application, the TFT device from 250 °C-annealed ITWO layer with an atomic ratio of In/Sn/W = 86:9:5 presented the optimal device performance with carrier mobility of 11.53 cm2 V-1 s-1, swing subthreshold of 0.66 V dec-1, threshold voltage of -2.18 V, and Ion/Ioff ratio of 3.33 × 107 and much small hysteresis of transfer characteristic. ITWO TFT devices were further developed as dual-mode proximity sensors that could work with both extended-gate and compact configurations, where the drain current was directly related to the surface potential of a charged object and the distance between the sensing end and the object, enabling the proximity sensing of charged stimuli. For extended-gate-configured proximity sensing, a charged object modulated the formation of a conductive channel at the semiconductor/SiO2 interface, while this conductive channel occurred at the semiconductor/air interface for compact-configured sensing. Formation of the conductive channel of the compact transistor was modulated by the electric field component in the direction perpendicular to the interface, and the drain current was sensitive to the orientation of the approaching object, which implied the capacity of angle sensing to the approach of a charged object. This work further emphasizes that the basic device performance should be optimized according to its specific application scenarios rather than only considering the requirements of the panel display.

Prediction of Both E-Jet Printing Ejection Cycle Time and Droplet Diameter Based on Random Forest Regression

Electrohydrodynamic jet (E-jet) printing has broad application prospects in the preparation of flexible electronics and optical devices. Ejection cycle time and droplet size are two key factors affecting E-jet-printing quality, but due to the complex process of E-jet printing, it remains a challenge to establish accurate relationships among ejection cycle time and droplet diameter and printing parameters. This paper develops a model based on random forest regression (RFR) for E-jet-printing prediction. Trained with 72 groups of experimental data obtained under four printing parameters (voltage, nozzle-to-substrate distance, liquid viscosity, and liquid conductivity), the RFR model achieved a MAPE (mean absolute percent error) of 4.35% and an RMSE (root mean square error) of 0.04 ms for eject cycle prediction, as well as a MAPE of 2.89% and an RMSE of 0.96 μm for droplet diameter prediction. With limited training data, the RFR model achieved the best prediction accuracy among several machine-learning models (RFR, CART, SVR, and ANN). The proposed prediction model provides an efficient and effective way to simultaneously predict the ejection cycle time and droplet diameter, advancing E-jet printing toward the goal of accurate, drop-on-demand printing.

Fabrication and electrical properties of printed three-dimensional integrated carbon nanotube PMOS inverters on flexible substrates

The low resolution of current printing technology (usually 10-100 μm) limits the number of printed thin film transistors (TFTs) per processable area, resulting in the low integration of printed circuits. In this work, we developed a three-dimensional (3D) integration technology to increase the integration of printed TFTs and firstly achieved printed 3D single-walled carbon nanotube (SWCNT) PMOS inverter arrays on the flexible substrates. The flexible 3D PMOS inverter consists of a bottom-gate SWCNT TFT (i.e., a driving TFT) and a top-gate SWCNT TFT (i.e., a load TFT). Printed SWCNT TFTs exhibited good electrical properties with high carrier mobility (up to 9.53 cm² V^-1 s^-1), high I_on/I_off ratio (10⁵-10⁶), low hysteresis, and small subthreshold swing (SS) (70-80 mV dec^-1). As-prepared 3D PMOS inverters exhibited rail-to-rail voltage output characteristics, high voltage gain (10) at a low operating voltage (V_DD < 1 V), and good mechanical flexibility. Furthermore, the printed 3D PMOS inverters could be utilized to detect ammonia gases, exhibiting satisfactory stability and recovery rate. It is crucial for realizing high-density, multi-functional printed carbon-based electronic devices and circuits for wearable electronics and the Internet of Things (IoT).

High-Resolution 3D Printing for Electronics

The ability to form arbitrary 3D structures provides the next level of complexity and a greater degree of freedom in the design of electronic devices. Since recent progress in electronics has expanded their applicability in various fields in which structural conformability and dynamic configuration are required, high-resolution 3D printing technologies can offer significant potential for freeform electronics. Here, the recent progress in novel 3D printing methods for freeform electronics is reviewed, with providing a comprehensive study on 3D-printable functional materials and processes for various device components. The latest advances in 3D-printed electronics are also reviewed to explain representative device components, including interconnects, batteries, antennas, and sensors. Furthermore, the key challenges and prospects for next-generation printed electronics are considered, and the future directions are explored based on research that has emerged recently.