Drop-on-demand inkjet printing is one of the most attractive techniques from a manufacturing perspective due to the possibility of fabrication from a digital layout at ambient conditions, thus leading to great opportunities for the realization of low-cost and flexible thin-film devices. Over the past decades, a variety of inkjet-printed applications including thin-film transistors (TFTs), radio-frequency identification devices, sensors, and displays have been explored. In particular, many research groups have made great efforts to realize high-performance TFTs, for application as potential driving components of ubiquitous wearable electronics. Although there are still challenges to enable the commercialization of printed TFTs beyond laboratory-scale applications, the field of printed TFTs still attracts significant attention, with remarkable developments in soluble materials and printing methodology. Here, recent progress in printing-based TFTs is presented from materials to applications. Significant efforts to improve the electrical performance and device-yield of printed TFTs to match those of counterparts fabricated using conventional deposition or photolithography methods are highlighted. Moreover, emerging low-dimension printable semiconductors, including carbon nanotubes and transition metal dichalcogenides as well as mature semiconductors, and new-concept printed switching devices, are also discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201801445

Recent Progress in Inkjet‐Printed Thin‐Film Transistors

Design and demonstration of integrated micro-electro-mechanical relay circuits for VLSI applications

Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined.

/pdf/a-review-of-micro-contact-physics-for-microelectromechanical-4z1vzxhmv2.pdf

A review of micro-contact physics for microelectromechanical systems (MEMS) metal contact switches

3D Printing of Multilayered and Multimaterial Electronics: A Review

The need for more energy-efficient solid-state switches beyond complementary metal-oxide-semiconductor (CMOS) transistors has become a major concern as the power consumption of electronic integrated circuits (ICs) steadily increases with technology scaling. Nano-Electro-Mechanical (NEM) relays control current flow by nanometer-scale motion to make or break physical contact between electrodes, and offer advantages over transistors for low-power digital logic applications: virtually zero leakage current for negligible static power consumption; the ability to operate with very small voltage signals for low dynamic power consumption; and robustness against harsh environments such as extreme temperatures. Therefore, NEM logic switches (relays) have been investigated by several research groups during the past decade. Circuit simulations calibrated to experimental data indicate that scaled relay technology can overcome the energy-efficiency limit of CMOS technology. This paper reviews recent progress toward this goal, providing an overview of the different relay designs and experimental results achieved by various research groups, as well as of relay-based IC design principles. Remaining challenges for realizing the promise of nano-mechanical computing, and ongoing efforts to address these, are discussed.

https://www.mdpi.com/2072-666X/6/8/1046/pdf

Nanoelectromechanical Switches for Low-Power Digital Computing

The impact of device operating parameters on the ON-state resistance (RON) of microelectromechanical relays with tungsten (W) electrodes is reported. Due to the susceptibility of W to oxidation, RON increases undesirably over the device operating cycles. This issue is aggravated by Joule heating when the relay is in the on state. The experimental results confirm that shorter ON time, as well as shorter off time, provides for more stable RON with respect to the number of ON/OFF switching cycles.

Characterization of Contact Resistance Stability in MEM Relays With Tungsten Electrodes

Three-dimensional (3-D) nano-electro-mechanical (NEM) switches (relays) are proposed to reduce the die area and power consumption of digital logic and memory circuits.

Hybrid CMOS/BEOL-NEMS technology for ultra-low-power IC applications

Printed electronics employing solution-processed materials is considered to be the key to realizing low-cost large-area electronic systems, but the performance of printed transistors is generally inadequate for most of the intended applications due to limited performance of printable semiconductor materials. We propose an alternative approach for a printed switch, where the use of semiconductors can be avoided by building mechanical switches with printed metal nanoparticle-based inks. In this work, we detail the first demonstration of inkjet-printed microelectromechanical (MEM) switches with abrupt switching characteristics, very low on-state resistance (∼10 Ω), and very low off-state leakage. The devices are fabricated using a novel process scheme to build three-dimensional cantilever structures from solution-processed metallic nanoparticles and sacrificial polymer layers. These printed MEM switches thus represent a uniquely attractive path for realizing printed electronics.

A new switching device for printed electronics: inkjet-printed microelectromechanical relay.

Micro-electro-mechanical relays are of interest for low-power digital integrated circuits, due to their ideally zero OFF-state leakage current. The first relay-based integrated circuits utilized tungsten (W) as the contacting material because of its excellent resistance to physical wear. However, W oxidizes easily so that the contact resistance increases to an unacceptably high level over the device operating lifetime. Ruthenium (Ru) is a promising alternative contacting electrode material because it forms an electrically conductive native oxide. In this work, challenges and solutions for integrating Ru into a relay fabrication process are described. Ru-contact relays with good switching behavior and more stable ON-state resistance than W-contact relays are demonstrated.

Stable ruthenium-contact relay technology for low-power logic

The effect of the body bias voltage on logic relay performance is investigated. The switching hysteresis voltage, which sets a lower limit for the relay operating voltage, is experimentally found to decrease with increasing body bias voltage, due to reduced surface adhesive force. It is demonstrated that the switching energy of a relay can be reduced by body biasing, at a tradeoff of increased mechanical turn-ON delay. Simulations of nanoscale relay designs indicate that body biasing can be used to mitigate relay manufacturing challenges, while enabling ultralow-voltage (sub-100 mV) operation with relatively fast switching speed.

Yenhao Chen

Papers

Characterization of Contact Resistance Stability in MEM Relays With Tungsten Electrodes

Hybrid CMOS/BEOL-NEMS technology for ultra-low-power IC applications

A new switching device for printed electronics: inkjet-printed microelectromechanical relay.

Stable ruthenium-contact relay technology for low-power logic

Effect of Body Biasing on the Energy-Delay Performance of Logic Relays