To a terahertz and beyond

This month, two researchers working at the Micro and Nanotechnology Laboratory at the University of Illinois Urbana-Champaign announced that they have pushed transistor operating frequency more than halfway towards a terahertz. Developed by physicists Walid Hafez and Milton Feng, the pseudomorphic HBT (heterojunction bipolar transistor) has a maximum operating frequency of 604GHz. It’s fabricated from indium phosphide and indium gallium arsenide.

The researchers have been developing increasingly fast transistors; Two years ago, they broke the 500GHz barrier. Before this latest development, the team’s fastest transtor operated at 550GHz and operated at 176 degrees C. As always, heat is a big issue with high-frequency transistor operation. According to Hafez, "Projections from our earlier high-frequency devices indicated that in order to create a transistor with a cutoff frequency of 1 terahertz, the devices would have to operate above 10,000 degrees C. By introducing grading into the layer structure of the device, we have been able to lower the potential operating temperature for a terahertz transistor to within an acceptable range."

The 604GHz transistor surpasses what was previously the world’s fastest transistor, a 562GHz HEMT (high electron mobility transistor) FET developed in 2002 by Akira Endoh at Fujitsu Laboratories. Endoh and his colleagues are also shooting for a terahertz and beyond.