Printing sensors and electronics over flexible substrates are 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, the 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/noncontact 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 production lines for system level integration.

https://cris.fbk.eu/bitstream/11582/300858/1/Technologies%20for%20Printing%20Sensors%20and%20Electronics%20Over%20Large%20Flexible%20Substrates-A%20Review.pdf

Technologies for Printing Sensors and Electronics Over Large Flexible Substrates: A Review

The mechanical and electronic properties of two-dimensional materials make them promising for use in flexible electronics1–3. Their atomic thickness and large-scale synthesis capability could enable the development of ‘smart skin’1,3–5, which could transform ordinary objects into an intelligent distributed sensor network6. However, although many important components of such a distributed electronic system have already been demonstrated (for example, transistors, sensors and memory devices based on two-dimensional materials1,2,4,7), an efficient, flexible and always-on energy-harvesting solution, which is indispensable for self-powered systems, is still missing. Electromagnetic radiation from Wi-Fi systems operating at 2.4 and 5.9 gigahertz8 is becoming increasingly ubiquitous and would be ideal to harvest for powering future distributed electronics. However, the high frequencies used for Wi-Fi communications have remained elusive to radiofrequency harvesters (that is, rectennas) made of flexible semiconductors owing to their limited transport properties9–12. Here we demonstrate an atomically thin and flexible rectenna based on a MoS2 semiconducting–metallic-phase heterojunction with a cutoff frequency of 10 gigahertz, which represents an improvement in speed of roughly one order of magnitude compared with current state-of-the-art flexible rectifiers9–12. This flexible MoS2-based rectifier operates up to the X-band8 (8 to 12 gigahertz) and covers most of the unlicensed industrial, scientific and medical radio band, including the Wi-Fi channels. By integrating the ultrafast MoS2 rectifier with a flexible Wi-Fi-band antenna, we fabricate a fully flexible and integrated rectenna that achieves wireless energy harvesting of electromagnetic radiation in the Wi-Fi band with zero external bias (battery-free). Moreover, our MoS2 rectifier acts as a flexible mixer, realizing frequency conversion beyond 10 gigahertz. This work provides a universal energy-harvesting building block that can be integrated with various flexible electronic systems. Integration of an ultrafast flexible rectifier made from a two-dimensional material with a flexible antenna achieves wireless energy harvesting of Wi-Fi radiation, which could power future flexible electronic systems.

Two-dimensional MoS2-enabled flexible rectenna for Wi-Fi-band wireless energy harvesting.

Flexible electronics has significantly advanced over the last few years, as devices and circuits from nanoscale structures to printed thin films have started to appear. Simultaneously, the demand for high-performance electronics has also increased because flexible and compact integrated circuits are needed to obtain fully flexible electronic systems. It is challenging to obtain flexible and compact integrated circuits as the silicon based CMOS electronics, which is currently the industry standard for high-performance, is planar and the brittle nature of silicon makes bendability difficult. For this reason, the ultra-thin chips from silicon is gaining interest. This review provides an in-depth analysis of various approaches for obtaining ultra-thin chips from rigid silicon wafer. The comprehensive study presented here includes analysis of ultra-thin chips properties such as the electrical, thermal, optical and mechanical properties, stress modelling, and packaging techniques. The underpinning advances in areas such as sensing, computing, data storage, and energy have been discussed along with several emerging applications (e.g., wearable systems, m-Health, smart cities and Internet of Things etc.) they will enable. This paper is targeted to the readers working in the field of integrated circuits on thin and bendable silicon; but it can be of broad interest to everyone working in the field of flexible electronics.

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Ultra-thin chips for high-performance flexible electronics

This expanded and thoroughly revised edition of Thomas H. Lee's acclaimed guide to the design of gigahertz RF integrated circuits features a completely new chapter on the principles of wireless systems. The chapters on low-noise amplifiers, oscillators and phase noise have been significantly expanded as well. The chapter on architectures now contains several examples of complete chip designs that bring together all the various theoretical and practical elements involved in producing a prototype chip. First Edition Hb (1998): 0-521-63061-4 First Edition Pb (1998); 0-521-63922-0

The Design of CMOS Radio-Frequency Integrated Circuits: RF CIRCUITS THROUGH THE AGES

Flexible and stretchable electronics can dramatically enhance the application of electronics for the emerging Internet of Everything applications where people, processes, data and devices will be integrated and connected, to augment quality of life. Using naturally flexible and stretchable polymeric substrates in combination with emerging organic and molecular materials, nanowires, nanoribbons, nanotubes, and 2D atomic crystal structured materials, significant progress has been made in the general area of such electronics. However, high volume manufacturing, reliability and performance per cost remain elusive goals for wide commercialization of these electronics. On the other hand, highly sophisticated but extremely reliable, batch-fabrication-capable and mature complementary metal oxide semiconductor (CMOS)-based technology has facilitated tremendous growth of today's digital world using thin-film-based electronics; in particular, bulk monocrystalline silicon (100) which is used in most of the electronics existing today. However, one fundamental challenge is that state-of-the-art CMOS electronics are physically rigid and brittle. Therefore, in this work, how CMOS-technology-enabled flexible and stretchable electronics can be developed is discussed, with particular focus on bulk monocrystalline silicon (100). A comprehensive information base to realistically devise an integration strategy by rational design of materials, devices and processes for Internet of Everything electronics is offered.

CMOS-Technology-Enabled Flexible and Stretchable Electronics for Internet of Everything Applications.

This letter presents fabrication of a flexible 1.5-μm -channel-length silicon thin-film transistor (TFT) on a plastic substrate with a cutoff frequency fT of ~ 3.7 GHz and a maximum oscillation frequency fmax of ~ 12 GHz. Radio-frequency (RF) characterization is conducted for the flexible TFT under uniaxial mechanical bending conditions, indicating slight but notable monotonic performance enhancement with larger bending strains. Equivalent circuit model and theoretical analysis are employed to understand the underlying mechanism. Flexible gigahertz TFTs are shown to be naturally suitable for high-performance RF/microwave applications under mechanical bending (deformation) environment. This letter provides insight on designing and employing flexible gigahertz active devices.

RF Characterization of Gigahertz Flexible Silicon Thin-Film Transistor on Plastic Substrates Under Bending Conditions

This letter presents the fabrication and characterization of flexible microwave p-intrinsic-n diodes on a plastic substrate employing single-crystal germanium (Ge) nanomembranes. The fabricated flexible device displays high frequency response (e.g., insertion loss smaller than 1.5 dB and isolation larger than 10 dB at frequencies up to 10 GHz). Flexible Ge diodes with various diode structures are modeled and reveal radio frequency (RF) performance tradeoff with device parameters. Furthermore, the flexible Ge diodes show better RF/microwave properties than the flexible Si diodes. The study demonstrates great potential of using flexible active/passive components based on single-crystal Ge nanomembrane for high-performance RF/microwave applications.

Fabrication and Characterization of Flexible Microwave Single-Crystal Germanium Nanomembrane Diodes on a Plastic Substrate

The flexible photodetector is the essential device for many of the optoelectronic applications and its performance can be influenced by a number of factors, including semiconductor materials, illumination conditions, device structures, etc. Therefore, in order to better design and use the flexible photodetectors, it is necessary to understand how these factors affect their performance. In this study, we fabricated flexible lateral p-intrinsic-n photodetectors formed with single-crystalline silicon and germanium nanomembranes on polyethylene terephthalate substrates. The performance of the flexible photodetectors with various dimensions is presented under different illumination conditions. The influences of different semiconductor materials, illumination conditions (wavelength and power of the incident light), and dimensions of the intrinsic region (length and width) on the photocurrent and efficiency are investigated, and the underlying mechanisms are studied based on experimental, simulation, and theoret...

The fabrication and characterization of flexible single-crystalline silicon and germanium p-intrinsic-n photodetectors on plastic substrates

Investigation of various mechanical bending strains on characteristics of flexible monocrystalline silicon nanomembrane diodes on a plastic substrate

The invention discloses a monolithic integrated radio frequency high-gain low-noise amplifier which comprises an input match circuit, a first level amplifying circuit, a second level amplifying circuit and an output match circuit. A typical cascode structure with source electrode inductance negative feedback is adopted by the first level amplifying circuit. The second level amplifying circuit is of a common source electrode structure with resistance feedback. Due to the fact that the Chart 0.18-micrometer radio frequency complementary metal oxide semiconductor (RFCMOS) technology is adopted by the second level amplifying circuit, the circuit design of complete integration of all active devices and passive devices on a monolithic is finished. The monolithic integrated radio frequency high-gain low-noise amplifier achieves optimal noise matching and input impedance matching at the same time, not only enables a circuit to have optimal noise performance, but also enables the circuit to achieve power transfer better. Besides, the monolithic integrated radio frequency high-gain low-noise amplifier is high in gain, good in stability and capable of enabling the circuit structure to be high in practical value. Through validating, input and output matching of the circuit is good, and the circuit has gain of more than 27dbs and noise of 2dbs.

Qin Guoxuan

Papers

RF Characterization of Gigahertz Flexible Silicon Thin-Film Transistor on Plastic Substrates Under Bending Conditions

Fabrication and Characterization of Flexible Microwave Single-Crystal Germanium Nanomembrane Diodes on a Plastic Substrate

The fabrication and characterization of flexible single-crystalline silicon and germanium p-intrinsic-n photodetectors on plastic substrates

Investigation of various mechanical bending strains on characteristics of flexible monocrystalline silicon nanomembrane diodes on a plastic substrate

Monolithic integrated radio frequency high-gain low-noise amplifier