Tiny, inexpensive silicon microchips that generate and radiate terahertz waves could be incorporated into handheld devices, such as smartphones, to suss out explosives in solid objects. Developed by a pair of engineers at California Institute of Technology (Caltech), the imager generates and radiates high-frequency electromagnetic waves that can penetrate a host of materials without the ionizing damage of x-rays. The chips could be used in applications ranging from homeland security to wireless communications — even touchless gaming. The technology could even lead to noninvasive cancer diagnosis, the researchers say. Caltech electrical engineers have developed tiny silicon microchips that can generate and radiate terahertz waves. Courtesy of Kaushik Sengupta/Caltech. “Using the same low-cost, integrated-circuit technology that’s used to make the microchips found in our cell phones and notepads today, we have made a silicon chip that can operate at nearly 300 times their speed,” said Ali Hajimiri, the Thomas G. Myers professor of electrical engineering at Caltech. “These chips will enable a new generation of extremely versatile sensors.” Terahertz imaging and scanning is not new; it can render high-resolution image details and detect the chemical fingerprints of pharmaceutical drugs, biological weapons or illegal drugs and explosives. However, most existing systems involve bulky and expensive laser setups that sometimes require exceptionally low temperatures. But with help from IBM, the Caltech team used standard CMOS technology to design silicon chips that operate at terahertz frequencies, while fitting on a fingertip. The chips boast signals more than 1000 times stronger than existing approaches and can be dynamically programmed to point in a specific direction. A metal key tucked inside an envelope. Inset: The terahertz image obtained with the silicon chip. Courtesy of Kaushik Sengupta/Caltech. The researchers used the scanner to reveal a razor blade hidden within a piece of plastic and to determine the fat content of chicken tissue. “We are not just talking about a potential. We have actually demonstrated that this works,” Hajimiri said. “The first time we saw the actual images, it took our breath away.” Translating the CMOS technology into a workable terahertz chip was no easy feat because silicon chips are not designed to operate at such frequencies. In fact, every transistor has a frequency, known as the cutoff, above which it fails to amplify a signal — and no standard transistors can amplify terahertz signals. To work around the cutoff-frequency hurdle, Hajimiri and postdoctoral scholar Kaushik Sengupta harnessed the collective strength of many transistors operating in unison. If operated at the right times and at the right frequencies, the combined power of multiple elements can boost the strength of the collective signal. Caltech electrical engineers Kaushik Sengupta and Ali Hajimiri demonstrate the capabilities of their terahertz chips for imaging. Courtesy of Caltech. “We are about 40 or 50 percent above the cutoff frequencies, and yet we are able to generate a lot of power and detect it because of our novel methodologies,” Sengupta said. The team also determined how to transmit the terahertz signal once it was produced by turning the whole silicon chip into an antenna. They achieved this by incorporating onto the chip many small metal segments that can all be operated at a certain time and strength to radiate the signal en masse. “Our chips are an example of the kind of innovations that can be unearthed if we blur the partitions between traditional ways of thinking about integrated circuits, electromagnetics, antennae and the applied sciences,” Sengupta said. “It is a holistic solution.” The work was described in IEEE Journal of Solid-State Circuits. For more information, visit: www.caltech.edu