Mechanics of rollable and foldable film-on-foil electronics
TL;DR: In this article, the mechanics of film-on-foil transistors on steel and plastic foils have been discussed in the context of thin-film transistors, where the transistors function well after the foils are rolled to small radii of curvature.
Abstract: The mechanics of film-on-foil devices is presented in the context of thin-film transistors on steel and plastic foils Provided the substrates are thin, such transistors function well after the foils are rolled to small radii of curvature When a substrate with a lower elastic modulus is used, smaller radii of curvature can be achieved Furthermore, when the transistors are placed in the neutral surface by sandwiching between a substrate and an encapsulation layer, even smaller radii of curvature can be attained Transistor failure clearly shows when externally forced and thermally induced strains add to, or subtract from, each other
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TL;DR: In this paper, the authors present a platform that makes electronics both virtually unbreakable and imperceptible on polyimide polysilicon elastomers, which can be operated at high temperatures and in aqueous environments.
Abstract: 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.
2,062 citations
TL;DR: In this article, the authors present stretchable and printable semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed, or otherwise deformed.
Abstract: 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.
1,673 citations
TL;DR: In this article, the authors present 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.
Abstract: 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.
1,305 citations
TL;DR: In this paper, a patterned layer of randomly oriented or partially aligned carbon nanotubes, such as one or more interconnected SWNT networks, is used to provide a semiconductor channel exhibiting improved electronic properties relative to conventional nanotube-based electronic systems.
Abstract: The present invention provides device components geometries and fabrication strategies for enhancing the electronic performance of electronic devices based on thin films of randomly oriented or partially aligned semiconducting nanotubes. In certain aspects, devices and methods of the present invention incorporate a patterned layer of randomly oriented or partially aligned carbon nanotubes, such as one or more interconnected SWNT networks, providing a semiconductor channel exhibiting improved electronic properties relative to conventional nanotubes-based electronic systems.
1,081 citations
01 Jun 2009
TL;DR: In this article, the authors presented the world largest flexible full color 6.5-inch active matrix organic light emitting diode (AMOLED) display with top emission mode on plastic film.
Abstract: The world largest flexible full color 6.5-inch active matrix organic light emitting diode (AMOLED) display with top emission mode on plastic film is demonstrated. The active matrix backplanes were fabricated using metal oxide thin film transistors (TFTs). The n-channel metal oxide TFTs on plastic film exhibited field-effect mobility of 17.8 cm2/Vs, threshold voltage of 0.4 V, on/off ratio of 1.1× 108, and subthreshold slope of 0.34 V/dec. These TFT performance characteristics made it possible to integrate scan driver circuit, demux switching and compensation circuit on the panel. Bending tests were performed with TFT backplane samples to determine critical curvature radius to which the panel can be bent without TFT performance degradation. The results were compared with the calculations that took into account thicknesses and mechanical constants of flexible substrate and of thin-film layers in AMOLED device.
997 citations
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TL;DR: In this paper, experimental and theoretical results are presented on the evolution of large elastic deformation, non-uniform curvature, shape changes and geometric instability in substrates of Si wafers with metal films.
Abstract: Experimental and theoretical results are presented on the evolution of large elastic deformation, non-uniform curvature, shape changes and geometric instability in substrates of Si wafers with metal films. The critical diameter and thickness of the Si wafer, for which large deformation and shape instability occur, are identified, as functions of the line tension in the film (which is the product of the biaxial stress in the film and the film thickness). Observations of the curvature and shape variations along the wafer diameter and geometry-dependence of the shape instability compare favorably with those predicted by detailed finite element analyses.
120 citations
TL;DR: In this paper, the relationship of the overall curvature of the film to the variation of properties and mismatch strain is reviewed, and it is shown that the mismatch strain distribution in the film can be expressed in terms of the dependence of curvature on film thickness.
Abstract: A thin film structure with through-the-thickness variation of properties and/or mismatch strain is considered. The relationship of the overall curvature of the film to the variation of properties and mismatch strain is reviewed. It is shown that, if the material properties are known, the mismatch strain distribution in the film can be expressed in terms of the dependence of curvature on film thickness. In addition, the case of film growth under conditions for which the mismatch strain of deposited material depends on the local strain conditions of the growth surface is considered. By means of an illustration, it is shown that the final state of strain within a free film following growth depends on the constraint conditions that were imposed on the film during its growth.
114 citations
TL;DR: In this paper, high performance amorphous silicon thin-film transistors (a-Si:H TFTs) were fabricated on 2 mil. (51 µm) thick polyimide foil substrates.
Abstract: We have fabricated high-performance amorphous silicon thin-film transistors (a-Si:H TFTs) on 2 mil. (51 µm) thick polyimide foil substrates. The TFT structure was deposited by r.f.-excited plasma enhanced chemical vapor deposition (PECVD). All TFT layers, including the gate silicon nitride, the undoped, and the n+ amorphous silicon were deposited at a substrate temperature of 150°C. The transistors have inverted-staggered back-channel etch structure. The TFT off-current is ∼ 10−12 A, the on-off current ratio is > 107, the threshold voltage is 3.5 V, the sub-threshold slope is ∼ 0.5V/decade, and the linear-regime mobility is ∼ 0.5 cm2V−1s−1. We compare the mechanical behavior of a thin film on a stiff and on a compliant substrate. The thin film stress can be reduced to one half by changing from a stiff to a compliant substrate. A new equation is developed for the radius of curvature of thin films on compliant substrates.
101 citations
TL;DR: In this article, the authors re-examine the Stoney's equation and point out that it was derived based on a neutral axis for zero bending moment which does not exist in the pure bending of a steel ruler on which his derivation was based.
Abstract: Since Stoney derived a simple relationship between the stress of a thin film and the curvature of its substrate for an electrolytically deposited metallic film on a thick substrate plate in 1909, the equation has been widely used by electrochemists to calculate stresses in electrolytically deposited films. Although the equation seems to work well for thin films with negligible thickness in comparison to the substrate, the underlying assumption in his derivation is found to be questionable. Various works have been published which calculate more precisely the stresses in the bending of a two-layer composite plate, where a thin layer on a thick substrate is an extreme case. However, there is some confusion in differentiating elastic bending due to internal stress from the externally applied moments (including our previous work). We re-examine the two bending conditions and point out that Stoney's equation was derived based on a neutral axis for zero bending moment which does not exist in the pure bending of a steel ruler on which his derivation was based. We also show that a single neutral axis for stresses does not exist in a two-layer system bent by internal stresses. Finally, we rederive the formula for the relationship between the wafer curvature and the lattice mismatch or differential thermal expansion for a binary composite plate using the proper bending moment calculation and examine the case of wafer bending of GaAs on Si substrate.
47 citations
TL;DR: In this article, the first amorphous silicon thin film transistors (TFTs) were fabricated on flexible, ultra-thin substrates of 25 µm thick stainless steel foil.
Abstract: We report the first amorphous silicon thin film transistors (TFTs) on flexible, ultra-thin substrates of 25 µm thick stainless steel foil. The transistors remain operational under convex or concave bending down to 2.5 mm radius of curvature. Taking advantage of the flexibility and resiliency of these devices, we have successfully fabricated TFTs using only xerographic toner masks printed directly on to the steel substrate and using mechanical alignment in the laser printer to obtain the necessary overlay accuracy. The goal of our work is to develop a foldable active-matrix transistor backplane, at low cost and high throughput, for use in highly rugged and portable applications such as foldable intelligent maps. Our results suggest that such foldable backplane circuits are feasible.
20 citations