Large Area Electronic Skin

Technological advances have enabled various approaches for developing artificial organs such as bionic eyes, artificial ears, and lungs etc. Recently electronics (e-skin) or tactile skin has attracted increasing attention for its potential to detect subtle pressure changes, which may open up applications including real-time health monitoring, minimally invasive surgery, and prosthetics. The development of e-skin is challenging as, unlike other artificial organs, tactile skin has large number of different types of sensors, which are distributed over large areas and generate large amount of data. On top of this, the attributes such as softness, stretchability, and bendability etc., are difficult to be achieved as today's electronics technology is meant for electronics on planar and stiff substrates such as silicon wafers. This said, many advances, pursued through “More than Moore” technology, have recently raised hope as some of these relate to flexible electronics and have been targeted towards developing e-skin. Depending on the technology and application, the scale of e-skin could vary from small patch (e.g. for health monitoring) to large area skin (e.g. for robotics). This invited paper presents some of the advances in large area e-skin and flexible electronics, particularly related to robotics

Towards flexible asymmetric MSM structures using Si microwires through contact printing

This paper presents development of flexible metal-semiconductor-metal devices using silicon (Si) microwires. Monocrystalline Si in the shape of microwires are used which are developed through standard photolithography and etching. These microwires are assembled on secondary flexible substrates through a dry transfer printing by using a polydimethylsiloxane stamp. The conductive patterns on Si microwires are printed using a colloidal silver nanoparticles based solution and an organic conductor i.e. poly (3,4-ethylene dioxthiophene) doped with poly (styrene sulfonate). A custom developed spray coating technique is used for conductive patterns on Si microwires. A comparative study of the current–voltage (I–V) responses is carried out in flat and bent orientations as well as the response to the light illumination of the wires is explored. Current variations as high as 17.1 μA are recorded going from flat to bend conditions, while the highest I on/I off ratio i.e. 43.8 is achieved with light illuminations. The abrupt changes in the current response due to light-on/off conditions validates these devices for fast flexible photodetector switches. These devices are also evaluated based on transfer procedure i.e. flip-over and stamp-assisted transfer printing for manipulating Si microwires and their subsequent post-processing. These new developments were made to study the most feasible approach for transfer printing of Si microwires and to harvest their capabilities such as photodetection and several other applications in the shape of metal-semiconductor-metal structures

Flexible FETs using ultrathin Si microwires embedded in solution processed dielectric and metal layers

This work presents a novel manufacturing route for obtaining high performance bendable field effect transistors (FET) by embedding silicon (Si) microwires (2.5 μm thick) in layers of solution-processed dielectric and metallic layers. The objective of this study is to explore heterogeneous integration of Si with polymers and to exploit the benefits of both microelectronics and printing technologies. Arrays of Si microwires are developed on silicon on insulator (SOI) wafers and transfer printed to polyimide (PI) substrate through a polydimethylsiloxane (PDMS) carrier stamp. Following the transfer printing of Si microwires, two different processing steps were developed to obtain top gate top contact and back gate top contact FETs. Electrical characterizations indicate devices having mobility as high as 117.5 cm2 V−1 s−1. The fabricated devices were also modeled using SILVACO Atlas. Simulation results show a trend in the electrical response similar to that of experimental results. In addition, a cyclic test was performed to demonstrate the reliability and mechanical robustness of the Si μ-wires on flexible substrates

Optimisation of Wearable Thermoelectric Generators

This meta-study explores some factors that can potentially affect the efficiency of a wearable thermoelectric generator. These include, but are not limited to; doping percentage, manufacturing technology, thermocouple length, area, use of heat spreaders, material, airflow and specific position on the human body. These specific designs and materials have been reviewed in this paper and specific variables have been proposed to ensure greater efficiency. In this meta- study, Bi0.5Sb1.5Te3 and Ag2Se are found to be the most effective materials, with PVD as the most effective manufacturing method. A broad temperature differential generates greater power output. Practically, a condition where there is a difference in temperature of more than 40K between the body and its environment in the application of wearable thermoelectric devices is unlikely. Despite this, a temperature difference below 40K, although small, is extremely feasible and would be able to enough power to keep intended wearable thermoelectric devices running at a constant. Keywords: Thermoelectric; Seebeck Effect; Peltier; TEG; ZT; Wearabl

Device Modelling of Silicon Based High-Performance Flexible Electronics

The area of flexible electronics is rapidly expanding and evolving. With applications requiring high speed and performance, ultra-thin silicon-based electronics has shown its prominence. However, the change in device response upon bending is a major concern. In absence of suitable analytical and design tool friendly model, the behavior under bent condition is hard to predict. This poses challenges to circuit designer working in the bendable electronics field, in laying out a design that can give a precise response in a stressed condition. This paper presents advances in this direction and investigates the effect of compressive and tensile stress on the performance of NMOS and PMOS transistor and a touch sensor comprising a transistor and piezoelectric capacitor

E-skin: from humanoids to humans

With robots starting to enter our lives in a number of ways (e.g., social, assistive, and surgery), the electronic skin (e-skin) is becoming increasingly important. The capability of detecting subtle pressure or temperature changes makes the e-skin an essential component of a robot's body or an artificial limb [1], [2]. This is because the tactile feedback enabled by e-skin plays a fundamental role in providing action-related information such as slip during manipulation/control tasks such as grasping, and estimation of contact parameters (e.g., force, soft contact, hardness, texture, and temperature during exploration [3]). It is critical for the safe robotic interaction - albeit as a coworker in the futuristic industry 4.0 setting or to assist the elderly at home

High-performance printed electronics based on inorganic semiconducting nano to chip scale structures

The Printed Electronics (PE) is expected to revolutionise the way electronics will be manufactured in the future. Building on the achievements of the traditional printing industry, and the recent advances in flexible electronics and digital technologies, PE may even substitute the conventional silicon-based electronics if the performance of printed devices and circuits can be at par with silicon-based devices. In this regard, the inorganic semiconducting materials-based approaches have opened new avenues as printed nano (e.g. nanowires (NWs), nanoribbons (NRs) etc.), micro (e.g. microwires (MWs)) and chip (e.g. ultra-thin chips (UTCs)) scale structures from these materials have been shown to have performances at par with silicon-based electronics. This paper reviews the developments related to inorganic semiconducting materials based high-performance large area PE, particularly using the two routes i.e. Contact Printing (CP) and Transfer Printing (TP). The detailed survey of these technologies for large area PE onto various unconventional substrates (e.g. plastic, paper etc.) is presented along with some examples of electronic devices and circuit developed with printed NWs, NRs and UTCs. Finally, we discuss the opportunities offered by PE, and the technical challenges and viable solutions for the integration of inorganic functional materials into large areas, 3D layouts for high throughput, and industrial-scale manufacturing using printing technologies

Inorganic semiconducting nanowires for green energy solutions

Single-crystalline inorganic semiconducting nanowires (NWs) of technologically important materials such as Si, Ge, GaAs, ZnO and so on. have attracted significant attention in providing sustainable energy solutions (generation/storage) due to their attractive physical and chemical properties. Currently, the production processes of these devices is unavoidably wasteful and requires urgent attention. There is need to establish resource efficient and eco-friendly manufacturing for energy devices using inorganic NWs. The present work is dedicated to identifying such a route and materials, through critical analysis of various device development stages, namely (i) NW’s synthesis methods, (ii) NW-based electronic layer fabrication, and (iii) metals, interconnects, and packaging forming techniques. We have also presented the current state-of-the-art of NW-based green energy solutions for next-generation of energy autonomous systems on flexible substrates

Novel Magnetic Properties in Curved Geometries

This reprint focuses on fundamentals and applied research on magnetic structures with curved geometries. The influence of curvature in the magnetic structures is an appealing topic of research opening novel perspectives to engineer the magnetic textures and the magnetisation reversal processes. Special attention is given to the fabrication and optimisation of magnetic structures, their characterisation and possible use in technological applications

Technologies for printing sensors and electronics over large flexible substrates: a review

Printing sensors and electronics over flexible substrates is an area of significant interest due to low-cost fabrication and possibility of obtaining multifunctional electronics over large areas. Over the years, a number of printing technologies have been developed to pattern a wide range of electronic materials on diverse substrates. As further expansion of printed technologies is expected in future for sensors and electronics, it is opportune to review the common features, complementarities and the challenges associated with various printing technologies. This paper presents a comprehensive review of various printing technologies, commonly used substrates and electronic materials. Various solution/dry printing and contact/non-contact printing technologies have been assessed on the basis of technological, materials and process related developments in the field. Critical challenges in various printing techniques and potential research directions have been highlighted. Possibilities of merging various printing methodologies have been explored to extend the lab developed standalone systems to high-speed roll-to-roll (R2R) production lines for system level integration