Well ordered nanowire arrays will enhance the performance of nanowire field-effect transistors (NW-FETs) by increasing the switching speed, turn-on current and production yield of the devices. To prepare such an array, researchers at National Cheng Kung University (NCKU), Taiwan, have combined rolling and transfer printing. The low-cost method suits continuous and high-speed operation and is compatible with roll-to-roll processing.

The nanowires, which are grown on a donor substrate of any material (silicon, glass, polymer, etc), are first transferred to a polydimethylsiloxane (PDMS) sheet by placing the sheet on top of the donor substrate and sending the combination into a roller. Next, the donor substrate is peeled away to leave the PDMS sheet, which now contains nanowires that are orientated along the rolling direction. By repeating the roll-transfer process, ordered nanowires on the PDMS sheet can be transferred to the device substrate (silicon, glass, polymer, etc) to enable the fabrication of NW-FETs.

Although the group's roll-transfer technique can assemble nanowires effectively, further improvements are in progress. The NCKU team is now refining the method so that the density, position and alignment of nanowires can be precisely controlled to ensure uniform electrical characteristics over large areas.