Semiconductor p-n junctions formed in a cylindrical geometry as concentric cladding layers surrounding a wire or fiber ‘substrate’ could have significant advantages for optoelectronic devices such as LEDs and solar cells, especially with regard to optical coupling efficiency and high-throughput manufacturing. Fiber-based semiconductor device components may also prove useful in conformable electronics or electrotextiles, and for giant -area flexible circuits. We describe techniques and results for chemical vapor deposition and melt coating to form 2- to 50-micron thick cladding layers of silicon or germanium on various types of fibers and refractory metals. These Ge or Si cladding layers can be recrystallized to achieve large (several millimeters or greater) grains oriented along the axis of the fiber. Additional GaAs cladding layers are grown on the recrystallized Ge or Si by vapor-phase epitaxy or metallic solution growth. p-n junctions are formed by diffusion or epitaxy. Light-sensitive diodes have been fabricated in these structures.

The ability to integrate electrical functionality into textile garments is becoming increasingly desired for consumer devices, military applications and for companies with large distributed workforces. This technology has the potential to facilitate the transfer of information and increase efficiency in many arenas. One of the major hurdles that has hindered the wedding of electronics and clothing has been the need to wash the resulting garment. This paper describes a study of the long term effects of washing and dry-cleaning electrotextile elements.

In order for electronic textiles to truly qualify as textiles, they must maintain one of the intrinsic qualities of textiles, flexibility, or the ability to resist permanent deformation under bending, lateral stress and strain. Flexibility will allow electric textiles to be intimate, soft, wearable, conformable and durable. Unfortunately, flexibility is poorly understood by many researchers who come from a traditional electronics background. This paper presents some common terminology of textiles, and different approaches to understanding flexibility in fibers and yarns. Because one of the most mechanically stressful textile manufacturing process is machine sewing and embroidery, this paper defines the necessary properties of machine sewable yarns and demonstrates a formal Curl Test for judging the sewability and flexibility of stainless steel yarns. This paper also examines flexibility in yarns and fibers, historically and based on a mathematical model and more qualitative properties.

Weaving, knitting or placing electronic circuits within a textile matrix offer exciting possibilities for large-scale conformal circuits where the circuit dimensions can be measured on the scale of yards instead of inches. However, compared with conventional printed circuit board circuits, the textile manufacturing process and the electrical/mechanical properties of the fibers used in making the textile place unusual constraints on the electrical performance of textile circuits. In the case of distributed sensors connected via an electronic fabric, signal attenuation and the ability to form reliable interconnections are major challenges. To explore these challenges we have woven and knitted a variety of electrical transmission lines and optical fibers in fabrics to analyze their performance. The formation of interconnects and disconnects between conductors woven in textiles is also discussed, and a passive acoustic array is described as a possible electronic textile application.

Organic electronic systems offer the advantage of low weight and flexibility at potentially lower cost. Although the fabrication of functioning plastic transistors using approaches such as ink jet, lithography and stamping has been described i1–3, chemically compatible materials that allow for the sequential application of liquid layers is a technical barrier. Material issues maybe the Achilles heel of ultimately printing organic electronic devices as newspapers today, at high speeds and in a reel to reel process. We introduce a novel process–thermal transfer–a non-lithographic technique that enables printing multiple, successive layers via a dry additive process. This method is capable of patterning a range of organic materials at high speed over large areas with micron size resolution and excellent electrical performance. Such a dry, potentially reel-to-reel printing method may provide a practical route to realizing the expected benefits of plastics for electronics. We illustrate the viability of thermal transfer and the ability to develop suitable printable organics conductors by fabricating a functioning 4000 cm2 transistor array.

This paper describes the development of woven electrical circuits, which are formed by interlacing conducting and non-conducting threads into a woven fabric. Conductive threads in these electrical networks are arranged and woven such that they follow desired electrical circuit designs. Electronic devices can be attached to these electrical networks, which can serve as flexible circuit boards. In these woven circuits, an efficient transfer of current from one conductive yarn to an orthogonal one is achieved by the formation of an effective electrical interconnect at the point of intersection of these yarns. Formation of woven conductive networks also involves disconnect formation or cutting of conductive yarns at certain specified points. Different methods and processes were identified and applied in order to form interconnects and disconnects at specified points of these fabrics. Efficacy of these interconnects was evaluated by DC resistance and AC Signal measurements. The results of these evaluations are reported. The conductive threads woven into these fabric-based circuits were also evaluated for signal integrity issues.

In this paper, we present design considerations pertinent to amorphous silicon pixel circuits for mechanically flexible active matrix display applications. We describe both circuit topologies and pixel architectures that are amenable to surface emissive pixels in a-Si:H technology. Metastable shifts in the a-Si:H material characteristics after prolonged gate bias or mechanical stress are manifested in the form of increasing TFT threshold voltages and varying mobilities. As a result, the TFT drive current and consequently the OLED brightness decrease, and the pixel eventually turns off. The circuits presented here compensate for this decrease in current through the use of current programming and feedback, and allow for stable OLED brightness over longer time periods. They also enable the implementation of high aperture ratio (close to 100%), low leakage current, surface emissive OLED pixels. Results show that the circuits provide higher linearity and dynamic range than currently available pixel circuits while minimizing the pixel area. Charge injection effects at the gate of the drive TFT have been reduced by using smaller switching TFTs, along with circuit topologies that provide in-pixel current gain. All circuits meet the speed requirements of a QVGA 60 Hz refresh rate display, and occupy less than 300um x 300um area.

Electrotextiles have attracted increasing attention in recent years. The combinations of textile structures that are lightweight, flexible, conformable, and strong, with electronics have aroused keen interest from many disciplines. With technological innovations appearing in both textile and electronics, integration of these has started giving benefits. Innovations like the sensate liner, soft switches and smart composites have found many applications in sports, healthcare, military, aerospace engineering, civil engineering and many other fields. The purpose of this paper is to provide an overview of various electrotextile products available and explain their functionality. Additionally, the paper provides a review of future electrotextile products, which are in the developmental phase, and the challenges that need to be addressed by researchers and industry.

Electronic textiles offer possibilities for producing large-area sensors circuits on conformal substrates. To demonstrate this concept, a 5×4 element acoustic array was produced on a 3m × 1m fabric substrate. In the course of fabricating the acoustic array a variety of production issues were identified that impacted the performance of the prototype when experimental tests were carried out with this prototype acoustic array. Fabric-based acoustic array design and production, along with design issues related to scaling an acoustic array to handle larger numbers of microphones on large-area fabrics, are the focus of this paper.

We present a novel microfabrication process for realizing a new type of flexible sensory “smart skin”. In this work, we focus on demonstration of a skin containing a two dimensional array of tactile sensors using polyimide and metal strain gauges. A novel polymer microfabrication approach coupled with surface release methods is demonstrated. The process yields flexible sensory skins in a low cost, efficient manner. Experimental characterization of the devices is also presented. The demonstrated sensors use metal-film strain gauges in a multiplexed two-dimensional array of tactile pixels (taxels) embedded in a polyimide thin film membrane to detect force distribution on the flexible skin. The arrays have been used to image force distributions and could be used with slip-detection friction measurement for robotic gripping application.

Numerous applications of electrotextiles and flexible circuits have been identified that can advance systems performance for many commercial, military, and aerospace devices. Several novel uses of electrotextiles have been developed for lab testing, while others have been utilized in products on the commercial market, as well as items that have flown in space. ILC Dover, Inc. has utilized conductive fibers in various inflatable and tensile structures for signal transmission and electrostatic charge protection. Conductive and pressure sensitive textiles have been incorporated in the advanced development space suit (I-Suit) as switch controls for lights and rovers, and as signal transmission cables. Conductive fibers have been used in several stitched applications for electrostatic charge dissipation. These applications include large pharmaceutical containment enclosures where fine potent powders are being captured for transfer between manufacturing facilities, as well as impact attenuation airbags used in landing spacecraft on the surface of Mars. In both cases, conductive threads are uniquely located in seams and panel locations to gather and direct charge through surface fibers and panel interconnects. Conductive fibers have also been utilized in a conformal Sensate Liner garment for the identification of wound locations and medical sensor signal transmission for soldier health monitoring while on the battlefield. The performance challenges of these structures require a careful, systematic application of electrotextiles because of the flexing, straining, and exposure of the materials to harsh environments. ILC has also been developing “gossamer” spacecraft components utilizing unique materials and multi-functional structures to achieve extremely low mass and low launch volumes. Examples of large deployable structures featuring very thin, large flexible circuits for use in space include synthetic aperture radar (SAR) antennas, communications antenna reflectarrays, and active variable reflectance solar sails. Design and materials challenges of electrotextile and large-area flexible circuit membrane structures as demonstrated in engineered applications will be discussed in this paper.

The goal of the project was to determine whether PDAC (poly (diallyldimethylammonium chloride), also abbreviated PDADMAC) could be printed reproducibly to create patterns with a sub-micron resolution. PDAC was stamped onto bare silicon using PDMS stamps having features only about 150 nm wide. A variety of aqueous PDAC inks were tried, to study the effect of concentration and ionic strength on the pattern produced. In order to get good prints, new stamping techniques were also required. A rigid stamping apparatus was built to ensure steady placement, and the stamps were spin coated with a different ink solution to produce thin, even coats of ink. [1] Using these methods, the pattern transferred.

We have synthesized Pb(Zr0.54Ti0.48)O3 fibers with diameter ranging from 500 nm to several microns using electrospinning and metallo-organics decomposition (MOD) techniques. By a refinement of our electrospinning technique, i.e. by increasing the viscosity of the precursor solution, and by adding a filter to the tip of the syringe, the diameter of synthesized PZT fibers has been reduced to the neighborhood of a hundred nanometers. The complex thermal decomposition was characterized using Fourier-transform infrared (FTIR) spectroscopy and x-ray diffraction (XRD). It was found that alcohol evaporated during electrospinning and that the organic groups had pyrolized before the intermediate pyrochlore phase was formed. There is a good correspondence between XRD and FTIR spectra. It was also found that a thin film of platinum coated on silicon substrate surface not only seems to have catalyzed the phase transformation to PZT but also favored the formation of 110 texture in the synthesized PZT fibers.

Polyallylamine films, deposited on Si wafers by radio frequency (RF) pulsed plasma polymerization (PPP), were employed as insulating layers of metal-insulator-semiconductor (MIS) capacitors. The insulating polymer films were deposited at substrate temperatures of 25°C and 100°C. Multiple frequency capacitance-voltage (C-V) measurements indicated that an in-situ heat treatment during film deposition increased the insulator dielectric constant. The dielectric constant, calculated from the C-V data, rose from 3.03 for samples with no heat treatment to 3.55 for samples with an in-situ heat treatment. For both sample sets, the I-V data demonstrate a low leakage current value (<20fA) up to 100V with an area of 0.0307 mm2, resulting in a current density of <0.65 pA/mm2. Hysteresis in the C-V curves with differing sweep directions was more pronounced for in-situ heat-treated samples indicative of positive mobile ions.

The research objective of this project was the spray deposition of CdSe films using a nanoparticle CdSe suspension as the precursor ink. This ink consisted of CdSe nanoparticles (nano-CdSe) mixed with a “reactive dispersant” in a non-aqueous solvent. The reactive dispersant, a metal-organic molecule, served two purposes; (1) to form a dispersed CdSe suspension at room temperature, and (2) to thermally “unzip” giving CdSe and a byproduct. The CdSe thereby formed could be deposited at the grain boundaries and serve to physically and electrically connect the CdSe nanoparticles at moderate, plastic-compatible temperatures. If electronics-grade CdSe layers could be produced at low deposition temperatures, this approach may be applicable to printed CdSe-based thin film field-effect transistors (TFTs) on flexible substrates.

A structure for organic TFTs suitable for being transferred on unusual substrates is described in each technological step. The proposed device consists in a “bottom-structure” assembled on a flexible and transparent insulating layer, without any substrate, with source and drain contacts on one side and the gate on the opposite side. The main advantage is to avoid the substrate because the insulator itself is able to support the whole structure. For this reason, application to any kind of substrates after the built-in process is possible.

Power generation from lead zirconate titanate (PZT) piezoelectric fibers in the form of 1–3 composites under application of an external force was investigated. Green fibers consisting of PZT powder dispersed in a cellulose binder were made by the Viscous Suspension Spinning Process (VSSP). The composites were made by firing sheets of parallel green PZT fibers at 1270 °C, and then laminating the sintered sheets in epoxy. Composites of several PZT fiber diameters (15, 45, 120, and 250 μm), with the fiber volume fraction fixed at ∼0.4, were investigated. Transducers comprised of electrode and poled plates of the composites, in which the plate thickness direction was in the fiber axis direction, were made. Power generation experiments were conducted by dropping a 33 g stainless steel ball onto the electroded face of each transducer from a height of 10 cm and recording the output voltage on an oscilloscope. A peak voltage of 350 V corresponding to 120 mW of peak power was obtained. The output voltage and power was the highest for the transducers made with the smallest diameter fibers (15μm) and increased with increasing of transducer thickness. The average piezoelectric coefficient, d33, of the transducers was about 300 pC/N and decreased with decreasing transducer thickness. In this paper, the power generation capability and dielectric properties of the laminated 1–3 fiber composites are discussed.

Konarka Technologies has developed efficient electrolyte compositions based on nonvolatile ionic liquids. The electrolyte compositions were subsequently gelled using a metal ion complexation technique, without compromising the photovoltaic performance of the dye sensitized solar cells (DSSCs). The photovoltaic performance of the gel electrolyte incorporated DSSCs is quite stable for extended period of time even in the absence of sealing. Detailed results on performance and stability of the gel electrolyte incorporated DSSCs are presented.

ElectroTextiles is a technology area that is in its formative stages of development. Over the past three years, several government and industrial workshops as well as international conferences have discussed and presented fundamental technical approaches and a few small companies are starting to offer commercial products. The combination electronics and textiles offer a new and unique way to fabricate novel large-area, flexible and conformable military and commercial systems. This paper will discuss the some of the challenges that need to be addressed for this technology to mature in the future.

The electro-mechanical response of thin gold layers evaporated onto silicone substrates is reported. Gold layers are prepared either thin and flat or thin and wavy on the compliant substrate. The electrical resistance of gold/silicone stripes is measured and analyzed during tensile deformation. For a 100-nm thick gold layer evaporated on a 1-mm thick silicone membrane, we have observed electrical continuity up to ∼ 22 % strain. This maximum strain decreases when the gold layer thickness is raised.