Nanowires show great promise for application in the next generation of electronic devices, biosensors and solar energy technology. Batteries and lighting are also sectors that nanowires are likely to witness growth in over the next decade. Over the past decade, significant research effort has been directed towards the synthesis and characterization of silicon nanowires. They are promising materials in printable electronics due to their well-developed synthesis processes and the ability to tailor material properties through shape, size, and atomic-composition control.
The main target for nanowires is the transparent conductors market, which is valued at over $6 billion in 2012 and likely to more than double in the next few years. LED lighting based on nanowires is also expected to enter the market in 2014. There have also been several research breakthroughs over the last 12 months in nanowire transistors used as switches or memory components.
NANOWIRES
A nanowire is a filament typically measuring 2 to 100 nm in diameter. Nanowires of a variety of materials (Carbon nanotubes, graphene, carbon fiber; Nanoforms of wide band gap materials such as SiC, GaN, AlN, BN, ZnO; other semiconductors such as Si, CdTe, CdS; and nanostructures and nanowires of established electron emitters such as LaB6) have gained importance in the past decade owing to their potential for reliable integration into electronic devices.
These devices benefit from nanowires large surface to volume ratios, small active volumes, quantum confinement effects and integration in complex architectures on the nanoscale including sensors, optoelectronics, nanoelectronic and energy harvesting applications. Basic electronic devices like junction diodes, transistors, FETs and logic gates can be fabricated by using semiconductor and superlattice nanowires. Controlled and uniform assembly of nanowires with high scalability is still one of the major bottleneck challenges towards the materials and device integration for electronics.
LIGHT-EMITTING DIODES (LED)
GaN-Nanowire-based LEDs are under development by a number of companies. Advantages include higher lumens, increased efficiency and lower power consumption than traditional lighting modules. Their waveguiding properties and the ability to grow nonpolar GaN nanowire-based heterostructures, leads to increased light extraction and improved internal quantum efficiency.
ITO REPLACEMENT
The performance, cost, and durability of current touch sensors are limited by the shortfalls of the current industry standard material, indium tin oxide (ITO). Silver nanowires are one of the leading candidates for ITO replacement for capacitance touch screens, along with graphene, carbon nanotubes and PEDOT. Films utilizing silver nanowires offer several advantages over ITO including lower cost, flexibility, and durability. Companies involved in product development in this market include Blue Nano, Cambrios, Agfa, Blue Nano, Carestream Advanced Materials, Cima Nanotech, Dow Chemical, PolyIC, Ferro, Saint-Gobain, Sigma Technologies, Suzhou NanoGrid Technology and Sumitomo Metals and Mining. Cambrios and Cima NanoTech have developed conductive coatings by suspending silver nanowires in a solution. The ability to deposit the films using low-temperature processing such as roll-to-roll coating and printing makes the technology cost-effective and easily scalable, as opposed to high-temperature sputtering for ITO. Silver nanowires are also superior to ITO in transmission and conductivity. These cathodes can also be flexed (unlike ITO), making them more viable candidates for flexible electronics.
TRANSISTORS
Silicon nanowire transistors are of interest for future generation integrated circuits. Current devices are formed laterally on a single crystal silicon substrate by lithography and etching – processes which are rapidly reaching their limits in terms of device feature size. Nanowire growth provides an alterative route to the fabrication of very small diameter (<20 nm) high density vertical transistor arrays with a wrap-around gate structure that offers improved performance.
COMPANIES
Blue Nano, www.bluenanoinc.com, USA
The company is a manufacturer of silver nanowires for use in transparent conductors and flexible electronics. Price of their nanowires is $495/g.
Cambrios Technologies Corporation, www.cambrios.com, USA
The leading silver nanowires company. The company’s ClearOhm™ coating material produces a transparent, conductive film by wet processing. ClearOhm™ films have improved properties by comparison to ITO and other transparent conductive oxides.
Carestream Advanced Materials, www.carestream.com/specials/adv-materials, USA
Carestream FLEXX Transparent Conductive Films use silver nanowire technology and roll-to-roll process to provide a more flexible, durable and affordable alternative to ITO films. Products such as the Cypress TrueTouch® capacitive touchscreen controllers (http://www.cypress.com/touch/?source=CY-ENG-HEADER) incorporate the company’s technology.
Cima Nanotech, www.cimananotech.com, USA
The company has developed conductive coatings by suspending silver nanowires in a solution. SANTE™ is a custom formulated silver nanoparticle emulsion that is applied via a low-cost and clean wet coating process. SANTE™ self-assembles into a transparent conductive network with very high electrical conductivity, high transparency and flexibility. The resulting mesh has a similar transparency to ITO retaining the required screen brightness and is 4 to 10 times more conductive than ITO which allows for a faster response to touch. The company’s technology has been incorporated into products for Renias, Getac, NEC and LG.
Crayonano, http://crayonano.com, Norway
The company was spun-off from the Norwegian University of Science and Technology (NTNU) to commercialize a new technology to grow gallium arsenide (GaAs) nanowires on graphene using molecular beam epitaxy. The new hybrid electrode material offers excellent optoelectronic properties. The responsivity of the company’s GaAs nanowire device is estimated to be around 30 mA/W which is 3 orders of magnitude larger than previously reported for a single GaAs nanowire. Their nanowires demonstrate no degradation in the optoelectronic material quality, as compared to GaAs nanowires grown on GaAs substrates.
Glo AB, www.glo.se, Sweden
The company is focused on nanowire light-emitting diodes (nLED) based on its proprietary heterostructured semiconductor nanowire epitaxial growth and process technologies. glō produces LED chips based on highly dense III‐V nanowire arrays on silicon applicable to next generation LEDs.
Seashell Technology LLC, www.seashelltech.com, USA
Seashell produces silver nanowires using HiFlex eFilmTM technology. The company’s manufacturing processes can be used to create silver nanorods and nanowires with diameters as thin as 50 nanometers and lengths as great as several hundred microns.
Sinovia Technologies, www.sinoviatech.com, USA
The company is a recent start-up producing silver nanowire-based transparent conductive films for capacitive and resistive touch sensors for flexible displays
