Terahertz emitter leverages 45-nm CMOS

July 04, 2012 // By R. Colin Johnson
Millimeter wavelength alternatives to traditional X-rays are already using terahertz-range frequencies to safely scan passengers, luggage and cargo at airports, albeit using bulky discrete devices. Silicon-based terahertz range emitters and detectors could downsize millimeter wave devices for a wide variety of applications beyond airport security, including safer medical imaging along with industrial and environmental applications aimed at detecting hazardous substances.

Earlier this year, Semiconductor Research Corporation (SRC, Research Triangle, N.C.) sponsored research demonstrating a CMOS detector operating in the terahertz range. Now, Texas Instrument's has demonstrated a companion terahertz-range emitter created in cooperation with the SRC-sponsored Texas Analog Center of Excellence at the University of Texas at Dallas. TI's terahertz-range emitter uses a phase-locked loop (PLL) to stabilize its frequency, a necessity for making millimeter wavelength systems in CMOS commercially feasible.

"This is the highest frequency ever demonstrated for a phase-locked loop," claimed Brian Ginsburg, a design engineer at TI's Kilby Labs. "Stabilizing these ultra-high frequencies is [the] key to the future commercial success of millimeter wavelength CMOS applications [and] PLLs are fundamental to all high-performance electronics."

TI’s demonstration used an on-chip antenna that emits 390-GHz frequencies, but the researchers believe that improvements will enable the CMOS emitter to reach 600 GHz or higher using TI's 45-nm process technology.

"The [Federal Communications Commission] defines the terahertz range to be from 300 GHz to 3 THz," said Eunyoung Seok, a design engineer at TI's Kilby Labs. "For the future, we want to use TI's 45-nanometer process to cover more of this wider frequency range, as well as to increase our output power."

The current demonstration chip operates at 390 GHz using a multiplying PLL architecture with two frequency dividers in the feedback loop. The power emanating from the on-chip antenna was 2.2 microWatts.

In some applications, the ultra-high-frequency output from the on-chip antenna can be propagated and reflected by lenses and other optical components since the terahertz-range wavelengths are between the far infrared and microwave frequencies used for communications.