Terahertz superchips can do it all

CORNELL (US) — Terahertz radiation—currently used in airport body scanners—could prove instrumental in a wide range of medical and science applications, from detecting cancer and tooth decay to inspecting food through packaging.

Terahertz’s range of wavelengths—between microwaves and infrared light—are able to penetrate cloth, paper, and leather and a very short distance into the skin—all without the damaging effects of X-rays and are also able to detect unique signatures of explosives.

Applications like these require a portable, low-power radiation source, but most terahertz sources are still bulky and expensive, usually involving lasers and vacuum tubes.

Researchers have generated signals in the lower end of the terahertz range on a microchip that is 10,000 times more powerful than previously possible, with the inexpensive CMOS chip technology used in everyday electronic devices.

“We broke the record, but it’s more important than that,” says Ehsan Afshari, assistant professor of electrical and computer engineering at Cornell University.

“Nobody can break our record because we have a method that can look at any given process and come up with a topology that can guarantee the maximum power and frequency.”

Solid-state terahertz devices could include hand-held medical scanners and portable weapons scanners for the military, Afshari says. A paper on the work is published in Journal of Solid-State Circuits.

The maximum frequency at which a chip can operate and the power it can put out are limited by the physical characteristics of the material, says Afshari, so oscillator circuits seldom reach the maximum possible frequency or power.

The best previous effort on a CMOS chip generated a signal at 410 GHz with an output power of 20 nanowatts (billionths of a watt). Using new techniques, Afshari built CMOS oscillators operating at up to 480 GHz with an output of 0.2 milliwatts (thousandths of a watt)—10,000 times higher power.

The systems are still very low-power signals, roughly comparable to Bluetooth devices, but enough for medical instruments that might be held close to the skin.

At radio frequencies, the length and shape of wires and other components are critical. Afshari and graduate student Omeed Momeni developed a mathematical analysis to calculate the characteristics of the components to achieve the highest possible frequency and power on a given chip material.

The next step, Afshari says, will be to work with researchers familiar with gallium nitride, a material capable of operating at much higher frequencies and with power levels up to 2,000 times more than can be handled by silicon.

Computer simulations indicate that a gallium nitride device could generate frequencies up to 1 terahertz with enough power to scan a 1-meter-square area 10 meters away, with resolution down to 1 square centimeter—more than adequate for a soldier or police officer to scan an approaching stranger for weapons.

The research was supported by the Semiconductor Research Corporation the National Science Foundation.

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