Carbon--the basis of all organic compounds--appears destined to supplant silicon as the material of choice for future semiconductors. According to researchers, various structures based on the element that sits just above silicon on the Periodic Table can surpass silicon's abilities in thermal performance, frequency range and perhaps even superconductivity.
"Of the carbon technologies, diamond is probably the closest [to commercialization§] at this time, as work in diamond has been taking place for 15 years or longer," said Dean Freeman, senior analyst at Gartner Inc. "Most of the others still have a ways to go."
Three-dimensional carbon--diamond--offers 10 times the heat dissipation of silicon, according to suppliers currently hawking 40-nanometer to 15-micron diamond films on silicon wafers. Two-dimensional carbon--3-angstrom-thick monolayers called graphene--could dismantle silicon's roadblock to terahertz performance by attaining 10 times the electron mobility of silicon.
|Cyclotron orbit of graphene electrons:|
NIST probe scans and maps the atomic contours of graphene by applying a magnetic field that causes its electrons to organize into cyclotron orbits.
Likewise, one-dimensional carbon--1-nm-diameter nanotubes--could solve digital silicon's speed woes. Nanotubes will appear first as printable "inks" that are 10 times faster than competing organic transistors.
Meanwhile, zero-dimensional carbon--60-atom, hollow spheres of carbon called fullerenes--could answer silicon's inability to attain high-temperature superconductivity. Tightly packed fullerenes intercalcated with alkali-metal atoms superconduct at 38 K.
Over the next few years, carbon process technologies will become available to replace nearly every circuit material in use today: conductors, for interconnecing devices; semiconductors; and insulators, for isolating devices. But how quickly the industry embraces the carbon-based materials, especially during uncertain economic times, remains to be seen.
Freeman related the experience of Nantero Inc. (Woburn, Mass.) and SVTC Technologies (Austin, Texas), which partnered to offer the first nanotube thin-film development foundry service for fabless silicon chip makers wishing to add carbon nanotube films as high-performance interconnects on commercial CMOS chips. "Nantero has developed several devices using carbon nanotubes, but it can't find any customers who want to commercialize the devices," he said.
"Carbon nanotubes are also being looked at closely for interconnect materials in CMOS devices below 22 nm, which would mean at least five years before commercialization," Freeman said.
Carbon nanotube films are being developed by mass- production experts such as DuPont and have appeared on electronics cast on flexible plastic substrates by industrial giants such as NEC.
Companies like Nanocomp Technologies Inc. (Concord, N.H.) are embedding nanotubes into carbon sheets that can sense cracks or other structural defects, as well as developing nanotube wires and cables that are comparable to copper in terms of electrical conductivity but are 80 percent lighter.
"There are already many applications being developed in flexible electronics, for both the military and civilian uses," said IBM fellow Phaedon Avouris, who manages the company's carbon transistor efforts, initially for nanotubes and more recently for graphene. "Of course, there are already many applications of nanotubes' being used to make materials more conductive, either electrically or thermally, but building thin-film transistors with micron-sized channels on flexible substrates will be the first commercial applications of nanotubes."
Carbon electronics developers are not aiming to go head-to-head with silicon semiconductors' mature process technology for perhaps a decade; instead, they are looking to create a whole new lineage of electronic capabilities, beginning with micron-sized devices reminiscent of the larger, early silicon transistors. Printable nanotube inks are being developed by suppliers such as Applied Nanotech Inc. (Austin, Texas) for inexpensive low-temperature deposition systems using noncontact aerosol jet printers, such as those offered by Optomec (Albuquerque, N.M.). The systems target cost-sensitive applications such as plastic solar cells and RFID tags on flexible polymer substrates.