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A record maximum frequency of operation for a transistor of more than 1000GHz (1THz) has been reported by Northrop Grumman Space Technology (NGST) of Redondo Beach, CA, USA at this week’s 53rd annual IEEE International Electron Devices Meeting (IEDM 2007) in Washington D C, USA.

By fabricating a sub-50nm InGaAs/InAlAs/InP high-electron-mobility transistor device structure on an indium phosphide substrate (an InP HEMT), researchers led by Richard Lai were able to extrapolate a maximum frequency of oscillation of above 1THz with unilateral gain to 1.2THz and maximum stable gain (MSG) to 1.1THz. “This represents, to the best of our knowledge, the state of the art in high-frequency transistor capability,” says Dwight Streit, NGST’s VP of Technical Development and Microelectronics Technology.

To demonstrate the capabilities of the devices, in tests conducted by NASA’s Jet Propulsion Laboratory in Pasadena, CA the InP HEMTs were installed in a three-stage common-source low-noise monolithic-microwave integrated circuit (MMIC) amplifier. The amplifier achieved 6dB gain per stage at 300GHz and 5dB gain per stage at 340GHz.

To improve performance further, device modifications of the baseline NGST InP HEMT process were applied, including reducing the transistor’s gate length from 70nm to less than 50nm using electron-beam lithography.
Following the refinements, on-wafer measurements were made on the low-noise MMIC amplifiers. They yielded 21dB total amplifier gain at 285GHz, with 18dB total amplifier gain at 300GHz and 15dB amplifier gain at 340GHz. The results closely match computer simulated values and are consistent with extrapolations based on measured S-parameter data through 110GHz, say the researchers.

The transistors should provide much higher frequency and bandwidth capabilities for future military communications, radar and intelligence applications. Development of the terahertz-speed InP HEMT was supported by the Defense Advanced Research Projects Agency’s Sub-millimeter Wave Imaging Focal-plane Technology program, the US Army Research Laboratory, and internal company funds. “These advancements will enable a new generation of military and commercial applications that operate at higher frequencies with improved performance,” Streit adds.

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