PORTLAND, Ore. Characterizing the electron flow and the resulting causes of heat dissipation in low-dimensional nanoscale electronics could lead to cool-running single-electron "quantum dot" transistors, according to a researcher here at the University of Wisconsin-Madison.
Better understanding of heat dissipation in semiconductor materials should enable chip makers to cool down even massive heat-generating chips like central processing units (CPUs).
"So much heat is being dissipated by CPUs today that may people's laptops get uncomfortably warm. Our technique for studying low-dimensional electron systems should help future chips avoid generating so much heat," said Robert Blick, electrical and computer engineering associate professor. He collaborated on the work with his
graduate student, Eva Hhberger, as well as with professor Werner Wegscheider at the University of Regensburg, Germany, and researcher Tomas Krmer of Ludwig Maximilians University in Munich.
In particular, the researchers describe how they embedded a gated suspended low-dimensional electron gas inside a free-standing beam processed from a GaAs/AlGaAs heterostructure. By varying the number of gating electrodes on the suspended membrane, the dimensionality of the electronic system was changed from a conventional two-dimensional "Hall
effect" area, to a one dimensional quantum wire, down to
zero-dimensional quantum dot.
The embedded quantum devices were "observed" by virtue of the built-in ultrasensitive bolometer, an instrument that measures heat by correlating a radiation-induced change in frequency with the amount of radiation absorbed. The correlation between heat absorbed and the frequency of vibration of the suspended membrane, Blick said, could help future chip designers avoid generating excess heat.
"Our technique advances the fundamental understanding of how
individual electrons generate heat, and at the speed that chips are shrinking, in just two or three years semiconductor manufacturers are going to need the understanding that we are building up today," said Blick.
The device, measuring just 100 nanometers, vibrates in the gigahertz range whenever heat is dissipated inside the embedded transistor-like quantum devices, causing a measurable voltage change relative to a nearby gate.
With Blick's system tuned to the zero-dimensional quantum dot, the researchers plan on characterizing the thermal behavior of individual electrons as they approach the "qubit" state where they can encode many values simultaneously on their wave function.
"When an electron spreads out as a wave, it has a scale of only about five nanometers, which is just the size scale we can address with our device." Blick said.