Triple-mode transistors show potential: Researchers introduce graphene-based amplifiers

Oct 13, 2010

(PhysOrg.com) -- Rice University research that capitalizes on the wide-ranging capabilities of graphene could lead to circuit applications that are far more compact and versatile than what is now feasible with silicon-based technologies.

Triple-mode, single-transistor amplifiers based on -- the one-atom-thick form of carbon that recently won its discoverers a -- could become key components in future . The discovery by Rice researchers was reported this week in the online journal ACS Nano.

Graphene is very strong, nearly transparent and conducts electricity very well. But another key property is ambipolarity, graphene's ability to switch between using positive and negative carriers on the fly depending on the input signal. Traditional usually use one or the other type of carrier, which is determined during fabrication.

A three-terminal single-transistor made of graphene can be changed during operation to any of three modes at any time using carriers that are positive, negative or both, providing opportunities that are not possible with traditional single-transistor architectures, said Kartik Mohanram, an assistant professor of electrical and computer engineering at Rice. He collaborated on the research with Alexander Balandin, a professor of electrical engineering at the University of California, Riverside, and their students Xuebei Yang (at Rice) and Guanxiong Liu (at Riverside).

Mohanram likened the new transistor's abilities to that of a water tap. "Turn it on and the water flows," he said. "Turn it off and the water stops. That's what a traditional transistor does. It's a unipolar device -- it only opens and closes in one direction."

"But if you close a tap too much, it opens again and water flows. That's what ambipolarity is -- current can flow when you open the transistor in either direction about a point of minimum conduction."

That alone means a graphene transistor can be "n-type" (negative) or "p-type" (positive), depending on whether the carrier originates from the source or drain terminals (which are effectively interchangeable). A third function appears when the input from each carrier is equal: The transistor becomes a frequency multiplier. By combining the three modes, the Rice-Riverside team demonstrated such common signaling schemes as phase and frequency shift keying for wireless and audio applications.

"Our work, and that of others, that focuses on the applications of ambipolarity complements efforts to make a better transistor with graphene," Mohanram said. "It promises more functionality." The research demonstrated that a single graphene transistor could potentially replace many in a typical integrated circuit, he said. Graphene's superior material properties and relative compatibility with silicon-based manufacturing should allow for integration of such circuits in the future, he added.

Technological roadblocks need to be overcome, Mohanram said. Such fabrication steps as dielectric deposition and making contacts "wind up disturbing the lattice, scratching it and introducing defects. That immediately degrades its performance (limiting signal gain), so we have to exercise a lot of care in fabrication.

"But the technology will mature, since so many research groups are working hard to address these challenges," he said.

Explore further: Study reveals new characteristics of complex oxide surfaces

More information: Read the abstract at pubs.acs.org/doi/abs/10.1021/nn1021583

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marraco
not rated yet Oct 13, 2010
Great! Polinary transistors are the way to go. The next big thing.

We are near of the end of Moore Law because of approaching atom size, and quantum effects, but we can extend it if we achieve poly-states transistors (instead of binary state).

For example, a 4 state transistor can replace 2 binary transistor, and a 8 state can replace 3 binary ones.
PPihkala
1 / 5 (1) Oct 13, 2010
For example, a 4 state transistor can replace 2 binary transistor, and a 8 state can replace 3 binary ones.


That is called analog computing and it's currently used in some form of flash memories to hold more than one bit in each memory location. But the other side of the coin is speed loss. Analog computers need more time to settle to the correct logic state, which means that binary logic is faster.
Parsec
not rated yet Oct 14, 2010
For example, a 4 state transistor can replace 2 binary transistor, and a 8 state can replace 3 binary ones.


That is called analog computing and it's currently used in some form of flash memories to hold more than one bit in each memory location. But the other side of the coin is speed loss. Analog computers need more time to settle to the correct logic state, which means that binary logic is faster.

Unless of course the charge carriers move 100x faster than the corresponding binary circuits. There is no law dictating that the slowdown will always overwhelm the speedup.
marraco
not rated yet Oct 14, 2010
For example, a 4 state transistor can replace 2 binary transistor, and a 8 state can replace 3 binary ones.


That is called analog computing and it's currently used in some form of flash memories to hold more than one bit in each memory location. But the other side of the coin is speed loss. Analog computers need more time to settle to the correct logic state, which means that binary logic is faster.

Analog is the opposite to discrete.
Polinary transistors are not necesarly analog, they can be discrete.

And there are no physics law that dictate that they should be slow.

Because a polinary transistor can emulate many binary ones, they share a similar advantage of Quantum computing: they potentially can do many tasks in paralell. But it is not the only advantage, they can reduce latency because they are -potentially- able to do common complex tasks (like floating point calculations) in less stages than binary transistors.
marraco
not rated yet Oct 14, 2010
For example, a 4 state transistor can replace 2 binary transistor, and a 8 state can replace 3 binary ones.


That is called analog computing and it's currently used in some form of flash memories to hold more than one bit in each memory location. But the other side of the coin is speed loss. Analog computers need more time to settle to the correct logic state, which means that binary logic is faster.

Also, replacing many binary transistors with polinary ones, may lead to power savings, and unlock faster frequencies than the 4 Ghz practical limit we are facing today for mainstream CPUs.