United Business Media EE Times


Search

HOMEMARKET INTELLIGENCE UNITFORUMSDESIGNNEW PRODUCTSCAREERSBLOGSCONTACTEVENTSSIGN UP!RSSMost Popular contentTrusted Sources

 

Graphene circuit combines Si, GaAs functions
Print this article Email this article Reprints RSS Digital Edition

EE Times


PORTLAND, Ore. — Graphene transistors could enable complex new circuits using relatively simple architectures, according to Massachusetts Institute of Technology researchers who recently demonstrated a single transistor frequency multiplier.

Graphene transistors can transport both electrons like a silicon transistor, and holes like a GaAs transistor, enabling graphene field-effect transistors that outperform both silicon and gallium arsenide.

"Our new device is based on a property of graphene called 'ambipolar transport'," said MIT professor Tomas Palacios. "In conventional semiconductors, you normally have to choose between one of two different carriers: electrons [negative particles] and holes [positive particles].

"In graphene, because of the ambipolar transport, you don't need to choose, and you can have both of them in the same material by just changing the voltage applied to the graphene layer," Palacios added. "Our device uses this property to double the frequency of the input signal."

The new circuit consists of one graphene transistor and a resistor. "It is therefore a lot simpler than conventional circuitry where you need a filter to select the desire output signal," said Palacios. "It is also expected to work at much higher frequencies than conventional devices."

A single transistor frequency multiplier demonstrated by MIT combines the functions of both silicon and GaAs transistors.

The basic diagram for the MIT circuit is a single transistor in common source configuration with a pull-up resistor. The main difference is how the graphene transistor is biased. Unlike silicon, which only transports electrons, and GaAs, which only transports holes, the gate of a graphene transistor induces the transport of electrons or holes depending on whether the input signal is positive or negative.

"Independently of the nature of the carriers, the current always flows through the resistor in the same direction, which allows for the frequency multiplication effect," said Palacios.

For frequency multiplication, whenever the alternating current (AC) input signal passes through zero and becomes positive, it induces an'electron current through the drain. When the input goes negative, it induces a'hole current. In both cases, the output voltage'starts at zero, then ramps up with peaks and valleys in the AC input voltage, thus doubling its frequency.

The proof-of-concept demonstration has yet to be optimized for high-frequency applications, but the researchers claim that the high electron mobility of graphene transistors--100-times greater than silicon--should allow the frequency multiplier to be cascaded to repeatedly double output, perhaps into the terahertz range.

Graphene is composed of a single-crystalline lattice of carbon atoms whose electron mobility is higher than both silicon and GaAs, but which are more difficult to fabricate. The MIT researchers are growing their own graphene sheets, which so far have only been demonstrated in small flakes. Their goal is to fabricate entire wafers of the graphene material.

"For commercialization, it is important to fabricate these devices in large area graphene sheets or wafers," said Palacios. "We have recently achieved progress in this direction by growing large graphene flakes on silicon substrates using chemical vapor deposition."

Palacios estimated that it will take as long as two years to demonstrate wafer-scale fabrication of the graphene circuitry.






  Free Subscription to EE Times
First Name Last Name
Company Name Title
Email address
  Click here for your Free Subscription to EETimes Europe
 
CAREER CENTER
Looking for a new job?
SEARCH JOBS
SPONSOR

RECENT JOB POSTINGS
CAREER NEWS
DoD Recognizes University Scientists For Basic Research
Annual awards to university faculty to conduct next-generation research projects were announced this week by the Defense Department.

For more great jobs, career related news, features and services, please visit EETimes' Career Center.



All White Papers »   

  Around Silicon Strategies

10 emerging technologies to watch: EE Times has compiled a list of emerging technologies that we think will be worth watching out for in 2010. Biofeedback or thought-control of electronics are among the contenders. More...

Hot applications in 2010: We've compiled a list of 10 technology applications you should watch for in 2010, ranging from e-book readers to 3-D TVs. We examine the features that make these apps so compelling as well unresolved issues. More...

Top 25 predictions for semis in 2010: 2010 is just beginning to unfold in the electronics industry. Looking into our crystal ball, we have released our own chip forecasts--and other predictions--for 2010. More...

Seven things to fix in 2010: The editors of EE Times came up with their own informal list of things we hope engineers fix in 2010, spanning everything from nano-lithography to space travel. What do you want to see get done this year? More...

'09 moves that are shaping the future: This was a brutal year, but the industry gets a nod for showing grace under fire. Here's our Top 10 guide to the coming year, illustrating what to expect in 2010. More...

10 CEOs out in 2009: It's been a tough year for the global electronics industry and CEOs. We survey the dismissal of 10 industry CEOs during the first three quarters of 2009 and what's ahead for the rest of the year. More...

Notable women in microelectronics: There is no better time than a global economic recession to examine the keys to successful corporate governance. So, EE Times has compiled an international list that celebrates women who are business and technology leaders in semis. More...

EE Times updates Silicon 60: Seventeen companies have been added to the lastest version of our Silicon 60 list of emerging startups. Forty-three companies survived as emerging companies that are still worth watching. More...

 
Education and
Learning


Learn Now:












Home | About | Editorial Calendar | Feedback | Subscriptions | Newsletter | Media Kit | Contact | Reprints|  RSS|   Digital|  Mobile
Network Websites
International
Network Features




All materials on this site Copyright © 2010 TechInsights, a Division of United Business Media LLC All rights reserved.
Privacy Statement | Terms of Service | About