CuO nanowires have found promising applications in batteries, magnetic storage media, superconductors, field emission, gas sensors, energetic materials, nano initiator and field effect transistors. Controlling the placement of nanowires at well defined positions on a surface (localization) is a key issue. Nevertheless, very little study on the localization of CuO nanowires is found in the literature.

Researchers at City University of Hong Kong have achieved CMOS-compatible local synthesis of CuO nanowires on a MEMS-based microheater fabricated on a silicon substrate. The localization of CuO nanowires is obtained by locally heating an e-beam evaporated copper thin film in ambient air using micro resistive heaters. The heaters are fabricated by a standard polySi based surface micromachining process, and provide an alternative to global furnace heating.

The above figure shows an SEM image of two suspended micro-tip heaters used in the nanowire synthesis. In this case, there is heating at tip-heater-1 and no heating at tip-heater-2 (a higher magnification SEM image of tip-heater-1 is shown on the right hand side). It can be seen that well aligned long nanowires have grown from the copper film after local heating.

Since the synthesis is performed globally at room temperature, the process is compatible with standard CMOS. The localization of CuO nanowires can be controlled by the shape of the microheaters. Furthermore, most of the nanowires grow vertically along the film surface (self-alignment), which is supposed to be beneficial for future CuO nanowire based device fabrication.

This approach provides a significant step towards the process integration of CuO nanowires with MEMS to realize functional devices. The group anticipates that this method could be employed to locally grow other nanowires on a silicon substrate. This will probably open the door to integrate the nanowires into MEMS, thus leading to nanowire based functional devices.

A full description of this work can be found in the journal Nanotechnology.