Terahertz emitter harnesses 45-nm CMOS

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The world's first phase-locked loop for a CMOS terahertz emitter harnesses 45-nm process with on-chip antenna.R. Colin Johnson

7/2/2012 10:12 AM EDT

http://www.eetimes.com/electronics-news/4376561/Terahertz-emitter-harnesses-45-nm-CMOS

DALLAS -- 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 Corp. (SRC, Research Triangle, N.C.) sponsored research demonstrating a CMOS detector operating in the terahertz range</A>. 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. 

SRC and UT Dallas Show Manufacturability of Affordable Terahertz Receiver, Opening New Industry Segment for Consumer Applications

  A one-pixel CMOS terahertz image chip (left) can see through solid objects, here showing the inner workings of an old-school floppy disk.

RESEARCH TRIANGLE PARK, N.C., Feb 21, 2012 (BUSINESS WIRE) -- Semiconductor Research Corporation (SRC), the world's leading university-research consortium for semiconductors and related technologies, and UT Dallas today announced research results that show circuits operating at the terahertz (THz) range can be affordably manufactured in complementary metal-oxide semiconductor (CMOS) silicon. The findings set the stage for new industry segments that create electronic applications not yet available for everyday use and that offer portability and cost effectiveness.

On the spectrum of wavelengths, THz waves occur at the far end of the infrared band, just above the millimeter waveband. Compared to other wavelengths, THz are considered to have numerous desirable properties. For instance, in contrast with x-ray, THz is intrinsically safe, non-destructive and non-invasive. However, THz was previously impractical for mainstream consumer uses due to cost.

With the breakthrough presented by SRC and UT Dallas, THz circuits can now be manufactured within economical CMOS technologies. As a result, the sensitive THz portion of the spectrum can become accessible for use in everyday products.

A key component of THz systems is a receiver that UT Dallas has shown can be manufactured affordably. Employing Schottky diodes in 130 nanometer (nm) CMOS with higher cut-off frequency than MOS transistors, the new detector's sensitivity allows reception of signals that are smaller than those previously achieved using MOS transistors in 65nm CMOS. The Schottky diodes can be fabricated without any process modifications.

"Our new technology can take the cost for producing THz systems down from hundreds of thousands of dollars to only a few hundred dollars," said Professor Ken O, lead researcher for SRC's program at UT Dallas. "The impact will be huge. The collective chip industry can literally light up a portion of the wavelength spectrum so all can benefit from the applications."

Multiple communities have expressed interest in leveraging these new THz capabilities, including defense, medical, industrial process control and public and industrial safety.

"The need for THz communications is great, and our progress holds tremendous potential for enhancing the lives of many -- both in a preventative and curative nature," said Betsy Weitzman, SRC executive vice president. "The results we have here will broadly enable many opportunities for consumers and the semiconductor industry."

THz can enable a wide range of uses such as monitoring for toxic molecules in the air, breath analyses for disease diagnostics, imaging cavities without use of the more harmful x-rays, imaging cancerous cells, controlling industrial processes and conducting remote high resolution imaging and high bandwidth communication. Until now, there has been no economical way to make the systems that can support these applications.

"SRC supports a comprehensive THz research effort through various programs, and advances from the projects will impact the electronics industry over the next decade," said Dale Edwards, a GLOBALFOUNDRIES assignee at SRC.

More information about the research is published in the paper titled, "280GHz and 860GHz Image Sensors Using Schottky-Barrier Diodes in 0.13um Digital CMOS," presented today at the annual International Solid-State Circuits Conference (ISSCC) in San Francisco. The research is funded through SRC and performed at the RF and THz laboratory of Texas Analog Center of Excellence at UT Dallas. The paper is co-authored by Ruonan Han, a former student of Professor O, and Yaming Zhang, Yongwan Kim, Dae-Yeon Kim and Sam Shichijo at UT Dallas.

About SRC

Celebrating 30 years of collaborative research for the semiconductor industry, SRC defines industry needs, invests in and manages the research that gives its members a competitive advantage in the dynamic global marketplace. Awarded the National Medal of Technology, America's highest recognition for contributions to technology, SRC expands the industry knowledge base and attracts premier students to help innovate and transfer semiconductor technology to the commercial industry. For more information, visit www.src.org .

SOURCE: Semiconductor Research Corporation