EETimes – Downsizing big bulky terahertz (THz) detectors for integration on CMOS image chips has been accomplished by the University of Texas (Dallas) with funding from the Semiconductor Research Corp. (SRC). Accomplished under SRC’s Focus Research Program, the demonstration of terahertz speeds on standard CMOS opens a door for a new slew of consumer devices that can see through solid objects.
We can now build a CMOS image chip for a cell-phone-sized camera module that sees in the terahertz range,” said Ken O, a professor and lead researcher for SRC’s program at UT Dallas and a key investigator in the Center for Circuit and System Solutions, a part of SRC’s Focus Center Research Program.
Today terahertz cameras are used, for instance, in the airport to see inside luggage and under clothing to detect hidden weapons, but the devices require expensive discrete components. By downsizing terahertz sensors for standard CMOS chips, the terahertz camera can be both size and cost reduced in the extreme.
A one-pixel CMOS terahertz image chip (left) can see through solid objects, here showing the inner workings of an old-school floppy disk.
“Inexpensive handheld terahertz cameras could be used to detect counterfeit money or documents, to see inside envelopes or packages, or to find where the studs, wires and pipes are in walls,” said O.
The key to SRC’s successful integration of terahertz imager on-a-chip is the discovery that high-speed Schottky diodes can be easily fabricated in CMOS. Even at the relaxed design rules of130 nanometer used for the demonstration chip, the high-speed Schottky diodes were able to achieve THz-range performance without changing the standard CMOS processing steps.
“We have figured out how to create high-speed Schottky diodes in CMOS without changing the process, just the layout,” said O. “We just take an active region where a transistor would normally go, and don’t draw the source-drain implantation mask layer, resulting in a Schottky diode.”
All the details on how to make terahertz image arrays using Schottky diodes is presented in a paper entitled “280GHz and 860GHz Image Sensors Using Schottky-Barrier Diodes in 0.13µm Digital CMOS,” at the International Solid-State Circuits Conference this week in San Francisco.
Many other application areas should be able to profit from terahertz CMOS, which works as well as x-rays, but which are safe, non-destructive and non-invasive. Besides terahertz cameras, the new high-speed Schottky diode process should also enable cheaper safer medical scanners, cost-reduced security systems, and high-speed telecommunications applications.
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