Manufacturing Bits: Jan. 21

New high-frequency transistors; exotic 5G materials.


New high-frequency transistors
The Fraunhofer Institute for Applied Solid State Physics IAF has developed a novel high-frequency transistor type—the metal oxide semiconductor HEMT or MOSHEMT.

Still in R&D, Fraunhofer’s MOSHEMT has reached record frequencies of 640GHz. MOSHEMTs are designed for the 100GHz frequency ranges and above. Applications include communications, radar and sensors.

A high-electron-mobility transistor (HEMT) is a field-effect transistor that operates at higher frequencies. HEMTs are used in satellite receivers, voltage converters, radar and other equipment.

HEMTs have become faster by scaling the gate length to 20nm, but there are some challenges. The barrier material, based on indium aluminum arsenide (InAlAs), is prone to leakage as the materials become thinner.

The current HEMT has also reached its scaling limits. To solve the problem, researchers have combined the advantages of III-V semiconductors and silicon MOSFETs.

They also replaced the Schottky barrier of a HEMT with an isolating oxide layer. Specifically, they replaced the barrier material with a combination of isolating layers, which consists of aluminum oxide and hafnium oxide.

This in turn results in the MOSHEMT. Fraunhofer IAF has realized the world’s first amplifier MMIC based on indium-gallium arsenide (INGaAs) MOSHEMTs. The frequencies range between 200GHz and 300GHz.

“We have developed a new device which has the potential to exceed the efficiency of current HEMTs by far. The MOSHEMT allows us to downscale it even further, thus making it faster and more efficient,” said Arnulf Leuther, researcher at Fraunhofer IAF. “This surpasses the global state of the art for any MOSFET technology, including silicon MOSFETs.”

Exotic 5G materials
Tomsk State University is developing a database of new and exotic composite materials for use in developing devices in the terahertz range.

Targeted for 5G and space communications, these composite materials include ABS plastics, nanotubes and others. In addition, researchers are also measuring their properties in a frequency range from 10MHz to 1THz.

So far, researchers have studied the properties of 50 samples. In one example, researchers have made passive elements in the terahertz range, such as absorbers and polarizers.

In another example, researchers are taking polymers and filling them with carbon nanotubes. “By adding nanotubes of different concentrations, we change the electrophysical properties of the material, for example, we can increase the dielectric constant. Then, using 3D technology, a printed circuit board with elements (conductors, resistors, and others) can be created,” said Alexander Badyin, associate professor at Tomsk State University. “From the material obtained on a 3D printer, we print a control sample – plates or rings, depending on the standard of the measuring installation, and examine the properties of the composite in the terahertz range.”

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