IBM today announced it has created the highest performing nanotubes transistors to date and has proven that carbon nanotubes can outperform the leading silicon transistor prototypes available today.
By experimenting with different device structures, the researchers were able to achieve the highest transconductance (measure of the current carrying capability) of any carbon nanotube transistor to date. High transconductance implies that transistors can run faster, leading to more powerful integrated circuits.
According to IBM, the researchers also discovered that the carbon nanotube transistors produced more than twice the transconductance per unit width of top-performing silicon transistor prototypes.
‘Proving that carbon nanotubes outperform silicon transistors opens the door for more research related to the commercial viability of nanotubes,’ said Dr. Phaedon Avouris, manager of nanoscale science, IBM Research. ‘Carbon nanotubes are already the top candidate to replace silicon when current chip features just can’t be made any smaller, a physical barrier expected to occur in about 10 to 15 years.’
The IBM scientists made single-wall carbon nanotube field-effect transistors (CNFETs) in a structure resembling a conventional metal-oxide-semiconductor field-effect transistor (MOSFET) structure, with gate electrodes above the conduction channel separated from the channel by a thin dielectric.
They used these devices to study the performance improvements achieved by reducing the gate-to-channel separation.
The top gate devices are said to have exhibited excellent electrical characteristics, including steep sub-threshold slope and high transconductance at low voltages, a significant improvement to previously reported CNFETs which used the silicon wafer as a gate and a thick gate dielectric. The gate is an electrode that controls the flow of electricity through the device.
The IBM scientists were also able to fabricate both hole (p-type) and electron (n-type) transistors. The top-gate design is said to allow independent gating of each transistor, making it possible to generate CMOS (complementary metal-oxide-semiconductor) circuits that have a simpler design and consume less power.
By creating CNFETS that are similar in structure to that of conventional silicon MOSFETs, the team was able to compare CNTs with silicon transistors.
Usually transistor performance improves as the oxide thickness and channel length decrease. Although the nanotube devices were not optimised in this case, they still outperformed the prototype silicon transistor.
The IBM researchers concluded that as their gate length and gate oxide thickness decrease with further development, future CNFETs would likely outperform silicon transistors even more dramatically.