This article reviews the properties, fabrication and assembly of inorganic semiconductor materials that can be used as active building blocks to form high‐performance transistors and circuits for ...flexible and bendable large‐area electronics. Obtaining high performance on low temperature polymeric substrates represents a technical challenge for macroelectronics. Therefore, the fabrication of high quality inorganic materials in the form of wires, ribbons, membranes, sheets, and bars formed by bottom‐up and top‐down approaches, and the assembly strategies used to deposit these thin films onto plastic substrates will be emphasized. Substantial progress has been made in creating inorganic semiconducting materials that are stretchable and bendable, and the description of the mechanics of these form factors will be presented, including circuits in three‐dimensional layouts. Finally, future directions and promising areas of research will be described.
Large‐area electronics that offer mechanical flexibility or stretchability are promising for many emerging areas of application. Micro‐ to nanoscale semiconductor elements, in the form of wires, ribbons, membranes, and related structures, can serve as building blocks for these systems. A silicon‐based flexible electrical circuit is shown as an example.
A convenient process for generating large‐scale, horizontally aligned arrays of pristine, single‐walled carbon nanotubes (SWNTs) is described. The approach uses guided growth, by chemical vapor ...deposition (CVD), of SWNTs on miscut single‐crystal quartz substrates. Studies of the growth reveal important relationships between the density and alignment of the tubes, the CVD conditions, and the morphology of the quartz. Electrodes and dielectrics patterned on top of these arrays yield thin‐film transistors that use the SWNTs as effective thin‐film semiconductors. The ability to build high‐performance devices of this type suggests significant promise for large‐scale aligned arrays of SWNTs in electronics, sensors, and other applications.
All lined up: Aligned arrays of single‐walled carbon nanotubes (SWNTs) can be formed over large areas by guided growth through chemical vapor deposition on commercially available, single‐crystal quartz substrates (as depicted in the picture). Electrodes and dielectrics patterned on top of these arrays yield high‐performance thin‐film transistors that use the SWNTs as effective thin‐film semiconductors.
An increasing number of technologies require large-scale integration of disparate classes of separately fabricated objects into spatially organized, functional systems. Here we introduce an approach ...for heterogeneous integration based on kinetically controlled switching between adhesion and release of solid objects to and from an elastomeric stamp. We describe the physics of soft adhesion that govern this process and demonstrate the method by printing objects with a wide range of sizes and shapes, made of single-crystal silicon and GaN, mica, highly ordered pyrolytic graphite, silica and pollen, onto a variety of substrates without specially designed surface chemistries or separate adhesive layers. Printed p-n junctions and photodiodes fixed directly on highly curved surfaces illustrate some unique device-level capabilities of this approach.
The hard-drive and electronic industries can benefit by using the properties of light for power transfer and signalling. However, the integration of silicon electronics with lasers remains a ...challenge, because practical monolithic silicon lasers are not currently available. Here, we demonstrate a strategy for this integration, using an elastomeric stamp to selectively release and transfer epitaxial coupons of GaAs to realize III-V lasers on a silicon substrate by means of a wafer-scale printing process. Low-threshold continuous-wave lasing at a wavelength of 824 nm is achieved from Fabry-Pérot ridge waveguide lasers operating at temperatures up to 100 °C. Single and multi-transverse mode devices emit total optical powers of >60 mW and support modulation bandwidths of >3 GHz. This fabrication strategy opens a route to the low-cost integration of III-V photonic devices and circuits on silicon and other substrates.
Transfer printing is a materials assembly technique that uses elastomeric stamps for heterogeneous integration of various classes of micro‐ and nanostructured materials into two‐ and ...three‐dimensionally organized layouts on virtually any type of substrate. Work over the past decade demonstrates that the capabilities of this approach create opportunities for a wide range of device platforms, including component‐ and system‐level embodiments in unusual optoelectronic technologies with characteristics that cannot be replicated easily using conventional manufacturing or growth techniques. This review presents recent progress in functional materials and advanced transfer printing methods, with a focus on active components that emit, absorb, and/or transport light, ranging from solar cells to light‐emitting diodes, lasers, photodetectors, and integrated collections of these in functional systems, where the key ideas provide unique solutions that address limitations in performance and/or functionality associated with traditional technologies. High‐concentration photovoltaic modules based on multijunction, micro‐ and millimeter‐scale solar cells and high‐resolution emissive displays based on microscale inorganic light‐emitting diodes provide examples of some of the most sophisticated systems, geared toward commercialization.
Micro‐transfer printing is a materials assembly technique that enables heterogeneous integration of various classes of micro‐ and nanostructured materials. This article presents recent progress in functional materials and advanced transfer printing methods for active components that emit, absorb, and/or transport light, ranging from solar cells to light‐emitting diodes, lasers, photodetectors, and integrated functional systems, where the key ideas provide unique solutions to address limitations with traditional technologies.
Compound semiconductors like gallium arsenide (GaAs) provide advantages over silicon for many applications, owing to their direct bandgaps and high electron mobilities. Examples range from efficient ...photovoltaic devices to radio-frequency electronics and most forms of optoelectronics. However, growing large, high quality wafers of these materials, and intimately integrating them on silicon or amorphous substrates (such as glass or plastic) is expensive, which restricts their use. Here we describe materials and fabrication concepts that address many of these challenges, through the use of films of GaAs or AlGaAs grown in thick, multilayer epitaxial assemblies, then separated from each other and distributed on foreign substrates by printing. This method yields large quantities of high quality semiconductor material capable of device integration in large area formats, in a manner that also allows the wafer to be reused for additional growths. We demonstrate some capabilities of this approach with three different applications: GaAs-based metal semiconductor field effect transistors and logic gates on plates of glass, near-infrared imaging devices on wafers of silicon, and photovoltaic modules on sheets of plastic. These results illustrate the implementation of compound semiconductors such as GaAs in applications whose cost structures, formats, area coverages or modes of use are incompatible with conventional growth or integration strategies.
Transfer printing by kinetically switchable adhesion to an elastomeric stamp shows promise as a powerful micromanufacturing method to pickup microstructures and microdevices from the donor substrate ...and to print them to the receiving substrate. This can be viewed as the competing fracture of two interfaces. This paper examines the mechanics of competing fracture in a model transfer printing system composed of three laminates: an elastic substrate, an elastic thin film, and a viscoelastic member (stamp). As the system is peeled apart, either the interface between the substrate and thin film fails or the interface between the thin film and the stamp fails. The speed-dependent nature of the film/stamp interface leads to the prediction of a critical separation velocity above which separation occurs between the film and the substrate (i.e., pickup) and below which separation occurs between the film and the stamp (i.e., printing). Experiments verify this prediction using films of gold adhered to glass, and the theoretical treatment extends to consider the competing fracture as it applies to discrete micro-objects. Temperature plays an important role in kinetically controlled transfer printing with its influences, making it advantageous to pickup printable objects at the reduced temperatures and to print them at the elevated ones.
The fabrication of organic electron and optoelectronic systems using micro- and nanopatterning methods is discussed. The molding and embossing in the manufacturing of CDs and DVDs using these methods ...are evaluated.
This paper presents methods for solution casting and transfer printing collections of individual single-walled carbon nanotubes (SWNTs) onto a wide range of substrates, including plastic sheets. The ...deposition involves introduction of a solvent that removes surfactant from a suspension of SWNTs as it is applied to a substrate. The subsequent controlled flocculation (cF) produces films of SWNTs with densities that can be varied between a few tubes per square micron to thick multilayers in a single deposition step and with orientation determined by the direction of solution flow. High-resolution rubber stamps inked in this manner can be used to print patterns of tubes with geometries defined by the relief structure on the surface of the stamp. Thin film transistors fabricated with these techniques demonstrate their potential use in flexible “macroelectronic” systems.
We have developed methods for creating microscale inorganic light-emitting diodes (LEDs) and for assembling and interconnecting them into unusual display and lighting systems. The LEDs use ...specialized epitaxial semiconductor layers that allow delineation and release of large collections of ultrathin devices. Diverse shapes are possible, with dimensions from micrometers to millimeters, in either flat or "wavy" configurations. Printing-based assembly methods can deposit these devices on substrates of glass, plastic, or rubber, in arbitrary spatial layouts and over areas that can be much larger than those of the growth wafer. The thin geometries of these LEDs enable them to be interconnected by conventional planar processing techniques. Displays, lighting elements, and related systems formed in this manner can offer interesting mechanical and optical properties.
