Jun 16, 2010
Moving beyond silicon CMOS: direct-write fabrication devised for digital logic circuits on individual nanowires
Researchers at the Institute of Bioengineering and Nanotechnology (IBN), Singapore, have successfully demonstrated a new way of fabricating digital logic gates on individual nanowires. While conventional silicon-complementary metal oxide semiconductor (Si-CMOS) fabrication is approaching its scalable limits, nanotubes and nanowires are emerging as potential alternative platforms. Nevertheless, low-throughput fabrication forms a major stumbling block for nanomaterial-based electronics. IBN's new "direct-write" technique resolves this drawback and has the potential to achieve rapid prototyping of nanoelectronic circuits.
IBN's approach towards the fabrication of transistors and logic devices on nanowires bypasses the inherent limitations of lithography. A high-energy beam is used to "write" metal interconnects and insulating layers directly onto predefined locations of a substrate with ultra-high precision. Dr Somenath Roy, IBN research scientist, explains: "We have integrated depletion-mode and enhancement-mode field-effect transistors (FET) on a single nanowire to realize a nanoscale logic inverter. By using a part of the nanowire as the 'load' and another part of it as the 'driver', we have harnessed these two different modes of operation in different sections of the nanowire to produce an inverter – the basic building block of a logic circuit. Our results show a higher level of precision and throughput with direct-write fabrication on the nanowire. We hope to further develop this breakthrough to produce functional integrated circuits on nanowires and nanotubes."
The IBN team succeeded in constructing an inverter using the direct-writing of platinum metal electrodes and a dielectric layer, with either a focused ion-beam or an electron-beam. In the presence of a precursor gas, the metals or insulators would then be deposited directly on the material with nanometer precision to fabricate the logic circuit. The logic inverter integrates the two modes of transistors on the nanowire and has a transition voltage of ~ 2.1 V for a supply voltage of + 5 V. Research estimations show that the voltage gain and noise immunity of this inverter on a nanowire are optimal for integrated circuit applications.
This advance helps to drive the development of novel nanoscale integrated circuit technologies in a fabrication industry that is moving beyond the boundaries of silicon.
The researchers presented their work in the journal Nanotechnology.