Packaging boosts terahertz sensor
Researchers at MIT in the US have developed a higher power terahertz amplifier-multiplier system with specialist transistors from Intel without the need for silicon lenses.
The team fixed a thin, patterned sheet of material to the back of the chip and used Intel’s higher-power Intel transistors for a scalable, chip-based terahertz wave generator.
This could be used to make terahertz arrays for applications like improved security scanners for detecting hidden objects or environmental monitors for pinpointing airborne pollutants.
“To take full advantage of a terahertz wave source, we need it to be scalable. A terahertz array might have hundreds of chips, and there is no place to put silicon lenses because the chips are combined with such high density. We need a different package, and here we’ve demonstrated a promising approach that can be used for scalable, low-cost terahertz arrays,” says Jinchen Wang, a graduate student in the Department of Electrical Engineering and Computer Science (EECS) and lead author of a paper on the terahertz radiator.
The MIT researchers used matching to equal out the dielectric constants of silicon and air to minimize the amount of signal that is reflected at the boundary. That is where the thin sheet of dielectric on the rear of the chip comes in, so that most waves will be transmitted out the back rather than being reflected.
A laser cutter punched tiny holes in the sheet until the dielectric constant was exactly right. “Since the dielectric constant of air is 1, if you just cut some subwavelength holes in the sheet, it is equivalent to injecting some air, which lowers the overall dielectric constant of the matching sheet,” said Wang.
The Intel THz transistors, first shown in 2001 at the IEDM conference, use silicon in insulator and specialist materials to provide a higher maximum frequency and breakdown voltage than traditional CMOS transistors.
“These two things taken together, the more powerful transistors and the dielectric sheet, plus a few other small innovations, enabled us to outperform several other devices,” said Wang.
Their chip generated terahertz signals with a peak radiation power of 11.1 dBmW, and can be integrated into real-world electronic devices.
The next step is to build a phased array of terahertz sources, enabling them to steer and focus a powerful terahertz beam with a low-cost, compact device.
The research is supported, in part, by NASA’s Jet Propulsion Laboratory and Strategic University Research Partnerships Programme, as well as the MIT Centre for Integrated Circuits and Systems. The chip was fabricated through the Intel University Shuttle Programme.
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