This paper presents a comprehensive study on radio frequency-microelectromechanical systems (RF-MEMS) switches, which are expected to be extensively integrated into 5G infrastructures. The specifications of the RF-MEMS switch in use case and scenario for 5G have been summarized in part 2 and followed by the study of the state-of-the-art RF-MEMS switches in part 3. Both metal-contact and capacitive RF-MEMS switches, which have been developed and fabricated within the last two decades, are studied and tabled. In order to meet with the specification requirements of 5G scenario, the performance and characteristics of the RF-MEMS switches should be enhanced, such as acceptable RF performance, low actuation voltage, good reliability, short switching time, multiband topology, and on-chip integration and packaging. Different techniques for the improvement of the RF-MEMS switches' properties, for instance low spring constant, large actuation area, diverse actuation methods, push-pull mechanism, modified driving voltage waveform, inductive compensation, and so on, have been thoroughly investigated, classified, and summarized in part 4, which serves as the main contribution of the review. The findings from this review can be beneficial for further RF-MEMS switches' design and improvement. The upgraded RF-MEMS switches are capable of satisfying the growing need of cutting edge performance for 5G or high-performance applications.

Printed electronics (PEs), as a fast-growing advanced manufacturing technology in recent years, plays an essential role in development of wearable electronic sensors, flexible displays, human-machine interaction, and thin electronics owing to its low cost, high throughput, and the possibility to be fabricated on diverse thin substrates with good flexibility and stretchability. Various PEs have been developed, such as physical sensing devices, electrochemical sensors, wearable supercapacitors and energy harvesters, stretchable electrodes, thin-film transistors (TFTs), and printed transceiving circuits. In this work, recent progress on physical sensing devices and their interface circuits developed by the printing process are reviewed in terms of their functions, printing methods, materials, and performance. The printed physical sensors used for monitoring the basic biometric parameters through physical sensing mechanisms, such as temperature sensors for skin temperature, pressure sensors for human pulse wave, strain sensors for human motions, biopotential electrodes for electrocardiogram signals, and multiple-function physical sensing platforms, have been studied and highlighted with their good designs and advanced materials. The state-of-the-art printed interface circuits for the wearable sensors such as interconnects, TFTs, digital circuits, amplifiers, oscillators, and antennas have been reviewed in terms of their structures and functions from basic to advanced levels. The challenge and suggestions of the printed wearable devices for future developments are discussed and end with a conclusion.

Diabetes mellitus is a worldwide leading disease that brings about fatal complications due to poor body glucose management which requires regular screening. With progressive evolution of healthcare monitoring system, high demand for wearable biosensors has efficiently bridged the gap between organic semiconductor devices and biological systems due to their flexibility and biocompatibility as enzyme-based transducing mechanism. In this work, significant features of existing glucose monitoring systems and integration components are evaluated to extend the fully integrated sensing platform with exciting potentials of organic thin-film transistor (OTFT) as electrochemical glucose sensor at low manufacturing process $< 200 ^{\circ }\text{C}$ . This review highlights the design strategies and challenges in developing printable OTFT devices with low voltage and high on/off-current ratio $> 10^{6}$ by considering material configuration including nanomaterials, advanced printing techniques and functionalization for highly sensitive performance based on amperometric or potentiometric measurements. For sample extraction, the role of microneedle is critically discussed with their prospects to provide real-time diagnosis of interstitial fluid through correlation with blood glucose for long wear period. It can be concluded that this paper accentuates the potentials of printable OTFT biosensors and ISF sampling system based on microneedle by adapting the key design requirements and characteristics presented here for novel breakthrough of cost-effective, minimally invasive and self-monitoring flexible integrated glucose sensor system that conform to skin.