Electronic devices have advanced from their heavy, bulky origins to become smart, mobile appliances. Nevertheless, they remain rigid, which precludes their intimate integration into everyday life. Flexible, textile and stretchable electronics are emerging research areas and may yield mainstream technologies. Rollable and unbreakable backplanes with amorphous silicon field-effect transistors on steel substrates only 3 μm thick have been demonstrated. On polymer substrates, bending radii of 0.1 mm have been achieved in flexible electronic devices. Concurrently, the need for compliant electronics that can not only be flexed but also conform to three-dimensional shapes has emerged. Approaches include the transfer of ultrathin polyimide layers encapsulating silicon CMOS circuits onto pre-stretched elastomers, the use of conductive elastomers integrated with organic field-effect transistors (OFETs) on polyimide islands, and fabrication of OFETs and gold interconnects on elastic substrates to realize pressure, temperature and optical sensors. Here we present a platform that makes electronics both virtually unbreakable and imperceptible. Fabricated directly on ultrathin (1 μm) polymer foils, our electronic circuits are light (3 g m(-2)) and ultraflexible and conform to their ambient, dynamic environment. Organic transistors with an ultra-dense oxide gate dielectric a few nanometres thick formed at room temperature enable sophisticated large-area electronic foils with unprecedented mechanical and environmental stability: they withstand repeated bending to radii of 5 μm and less, can be crumpled like paper, accommodate stretching up to 230% on prestrained elastomers, and can be operated at high temperatures and in aqueous environments. Because manufacturing costs of organic electronics are potentially low, imperceptible electronic foils may be as common in the future as plastic wrap is today. Applications include matrix-addressed tactile sensor foils for health care and monitoring, thin-film heaters, temperature and infrared sensors, displays, and organic solar cells.

An ultra-lightweight design for imperceptible plastic electronics

It is now widely accepted that skin sensitivity will be very important for future robots used by humans in daily life for housekeeping and entertainment purposes Despite this fact, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition, mainly because good artificial “electronic skin” with a large area and mechanical flexibility is not yet available The fabrication of a sensitive skin consisting of thousands of pressure sensors would require a flexible switching matrix that cannot be realized with present silicon-based electronics Organic field-effect transistors can substitute for such conventional electronics because organic circuits are inherently flexible and potentially ultralow in cost even for a large area Thus, integration of organic transistors and rubber pressure sensors, both of which can be produced by low-cost processing technology such as large-area printing technology, will provide an ideal solution to realize a practical artificial skin, whose feasibility has been demonstrated in this paper Pressure images have been taken by flexible active matrix drivers with organic transistors whose mobility reaches as high as 14 cm2/V·s The device is electrically functional even when it is wrapped around a cylindrical bar with a 2-mm radius

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A large-area, flexible pressure sensor matrix with organic field-effect transistors for artificial skin applications

The present invention provides stretchable, and optionally printable, semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed or otherwise deformed. Stretchable semiconductors and electronic circuits of the present invention preferred for some applications are flexible, in addition to being stretchable, and thus are capable of significant elongation, flexing, bending or other deformation along one or more axes. Further, stretchable semiconductors and electronic circuits of the present invention may be adapted to a wide range of device configurations to provide fully flexible electronic and optoelectronic devices.

http://science.sciencemag.org/content/sci/311/5758/208.full.pdf

Stretchable form of single crystal silicon for high performance electronics on rubber substrates

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

The present invention provides methods, systems and system components for transferring, assembling and integrating features and arrays of features having selected nanosized and/or microsized physical dimensions, shapes and spatial orientations. Methods of the present invention utilize principles of ‘soft adhesion’ to guide the transfer, assembly and/or integration of features, such as printable semiconductor elements or other components of electronic devices. Methods of the present invention are useful for transferring features from a donor substrate to the transfer surface of an elastomeric transfer device and, optionally, from the transfer surface of an elastomeric transfer device to the receiving surface of a receiving substrate. The present methods and systems provide highly efficient, registered transfer of features and arrays of features, such as printable semiconductor element, in a concerted manner that maintains the relative spatial orientations of transferred features.

Pattern Transfer Printing by Kinetic Control of Adhesion to an Elastomeric Stamp

A process temperature of ~300°C produces amorphous-silicon (a-Si) thin-film transistors (TFTs) with the best performance and long-term stability. Clear organic polymers (plastics) are the most versatile substrate materials for flexible displays. However, clear plastics with a glass-transition temperature (Tg) in excess of 300°C can have coefficients of thermal expansion (CTE) much larger than that of the silicon nitride (SiNx) and a-Si in TFTs deposited by plasma-enhanced chemical vapor deposition (PECVD). The difference in the CTE that may lead to cracking of the device films can limit the process temperature to well below that of the Tg of the plastic. A model of the mechanical interaction of the TFT stack and the plastic substrate, which provides design guidelines for avoid cracking during TFT fabrication, is presented. The fracture point is determined by a critical interfacial stress. The model was used to successfully fabricate a-Si TFTs on novel clear-plastic substrates with a maximum process temperature of up to 280°C. The TFTs made at high temperatures have higher mobility, lower leakage current, and higher stability than TFTs made on conventional low-Tg clear-plastic substrates.

Amorphous-silicon thin-film transistors made at 280°C on clear-plastic substrates by interfacial stress engineering

This chapter looks toward a practical model of a-Si:H defects in intensity-time-temperature space

Toward a practical model of a-Si:H defects in intensity-time-temperature space

Six flexible force sensors, two on the backrest and four on the seat, were embedded in the upholstery of an off-the-shelf office chair to enable non-intrusive monitoring of sitting postures. Besides the sensors, the monitoring platform comprises an Arduino Nano microcontroller with Wi-Fi transmitter, embedded on the chair, a Wi-Fi receiver communicating with a remote server and a Graphical User Interface (GUI) showing real-time readings. Approximately 26,000 observations corresponding to 9 different postures were collected, labelled and classified using supervised machine learning. The results show that only a subset of the 6 sensors is needed for predicting these 9 sitting postures with high accuracy. This opens up the possibility for intelligent, real-time monitoring systems that can improve safety and wellbeing of today’s office workers.

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Flexible Force Sensors Embedded in Office Chair for Monitoring of Sitting Postures

We adapted a new technique for depositing copper lines, at a maximum process temperature of 200°C. The technique is based on the decomposition of copper hexanoate by UV light, followed by annealing in H2[1]. A copper film resistivity of 8 µΩcm is obtained. We patterned this copper metallization on Corning 7059 glass substrates by three different techniques, including exposure through a shadow mask, lift-off of xerographic toner, and direct writing.

Helena Gleskova

Papers

Amorphous-silicon thin-film transistors made at 280°C on clear-plastic substrates by interfacial stress engineering

Toward a practical model of a-Si:H defects in intensity-time-temperature space

Flexible Force Sensors Embedded in Office Chair for Monitoring of Sitting Postures

Direct Writing and Lift-Off Patterning of Copper Lines at 200°C Maximum Process Temperature

Effect of substrate temperature on vapor-phase self-assembly of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors