Mass Manufacture For Nanowire Devices Possible Fabrication & Assembly

Researchers have devised a method that could be used for the mass manufacture of nanowire photonic and electronic devices. Semi conducting nanowires are attracting great attention for next generation devices but it has proven difficult to assemble them into functional devices in a highly parallel, reliable, and controlled fashion.

To overcome this challenge, the researchers combine spin-on glass technology – a mainstay of the semi conducting industry – with photolithographic definition of electrical contacts to the top and bottom of nanowires. “These processes will provide the necessary control to enable integrated nanowire photonic circuits in a standard manufacturing setting,”.

What allows the researchers to follow this approach is the geometry of their devices. Instead of contacting axially nanowires at each end, the researchers employ a sandwich geometry where the nanowires are placed horizontally between a highly conductive substrate, which acts as one contact, and a top metallic layer, which acts as the other. What prevents the device from shorting is a spin-on glass spacer layer. The spinning process results in uneven coverage of the film – which is thinner on top of the nanowires. After controlled etching, the nanowires can be exposed without revealing the underlying substrate. Photolithography can then be used to define a pattern of metallic contacts.

Sandwich geometry nanowire devices. An n-type ZnO nanowire is placed between a heavily doped p-type Si substrate and a top metallic contact, using spin-on glass as a spacer (a,b). (c) A finished wafer, and (d) a typical device

“One can make electrical contacts to a large number of nanowires… simultaneously using mainstream integrated circuit processing methods,” Heterojunction diodes comprising n-type ZnO nanowires on a ρ-type Si substrate showed good rectification properties and can also function as ultraviolet light emitters. “Such an advance could lead to the development of a completely new class of integrated circuits, such as large arrays of ultrasmall nanoscale lasers that could be designed as high-density optical interconnects or used for on-chip sensing,” .