July 8, 1999 CHAMPAIGN, Ill. -- A computer simulation developed at the University of Illinois is helping scientists better understand the strange world of nanoelectronics -- where a single electron can control a device, but quantum mechanics is required to describe the behavior of that electron.
"We have simulated the operation of a silicon quantum-dot, floating-gate flash memory device," said Jean-Pierre Leburton, a U. of I. professor of electrical and computer engineering and a researcher at the university's Beckman Institute for Advanced Science and Technology. "The simulation can be used to explore and enhance the physical characteristics in future commercial devices."
Small, fast and rugged, flash memories can serve as temporary data storage in portable computers and cellular phones, and are key elements in digital imaging. They will eventually replace conventional magnetic storage media, Leburton said. "As fabrication technology continues to improve, the floating gates in flash memories may be reduced to nanometer-size structures that behave like quantum dots."
But as devices shrink to nanometer proportions, classical theory breaks down and quantum mechanics takes over. "You come to a point where things have become so small, you can identify the effects of a single electron charge with its wave-like behavior," Leburton said.
This "single-electron effect" reflects the granularity of matter in the nanoelectronic world. Not only must electrical current be understood as discrete particles governed by quantum mechanics (instead of millions of electrons flowing like a fluid); the physical composition of the device itself also must be taken into consideration.
"For example, the conductivity of a semiconductor is changed during manufacture by doping the material with impurities," Leburton said. "In the past, this doped material could be treated as a uniformly distributed background. Now, because of the incredibly small size, the characteristics of the device will change depending upon where atomic impurities are located."
To more thoroughly study the behavior of nanoelectronic devices, Leburton and graduate student Aaron Thean developed special simulation software. Their code consists of a three-dimensional,
self-consistent solver with the necessary quantum mechanics to capture both the granularity of matter and the wave nature of the electron.
"In our simulation, you can see the wave-particle duality of the electron," Leburton said. "On one hand you see the granularity of matter due to the presence of a single, charged particle. On the other hand you see the wave nature of the electron, manifested in the form of additional capacitances."
By taking both of these effects into consideration, the computer simulation can help scientists and engineers design and optimize the performance of the next generation of nanoscale electronic devices.
The researchers discuss their simulation in the June issue of IEEE Electron Device Letters.
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