Abstract-Active Terahertz Imaging Using Schottky Diodes in CMOS: Array and 860-GHz Pixel

Ruonan Han, Yaming Zhang, Youngwan Kim, Dae Yeon Kim,  Shichijo, H,  Afshari, E. ; Kenneth, K.O.

http://ieeexplore.ieee.org/xpl/abstractAuthors.jsp?tp=&arnumber=6557453&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6557453
Schottky-barrier diodes (SBD's) fabricated in CMOS without process modification are shown to be suitable for active THz imaging applications. Using a compact passive-pixel array architecture, a fully-integrated 280-GHz 4 × 4 imager is demonstrated. At 1-MHz input modulation frequency, the measured peak responsivity is 5.1 kV/W with ±20% variation among the pixels. The measured minimum NEP is 29 pW/Hz1/2. Additionally, an 860-GHz SBD detector is implemented by reducing the number of unit cells in the diode, and by exploiting the efficiency improvement of patch antenna with frequency. The measured NEP is 42 pW/Hz1/2 at 1-MHz modulation frequency. This is competitive to the best reported performance of MOSFET-based pixel measured without attaching an external silicon lens (66 pW/Hz1/2at 1 THz and 40 pW/Hz1/2 at 650 GHz). Given that incorporating the 280-GHz detector into an array increased the NEP by ~ 20%, the 860-GHz imager array should also have the similar NEP as that for an individual detector. The circuits were utilized in a setup that requires neither mirrors nor lenses to form THz images. These suggest that an affordable and portable fully-integrated CMOS THz imager is possible.

New Research Could Mean Cellphones That Can See Through Walls

Team Finds New Possibilities in Untapped Terahertz Range With Implications For a Host of Devices

http://www.utdallas.edu/news/2012/4/18-17231_New-Research-Could-Mean-Cellphones-That-Can-See-Th_article-wide.htmlApr. 18, 2012

Dr. Kenneth O, director of the Texas Analog Center of Excellence and a professor of electrical engineering, left, worked with a team including Dae Yeon Kim, who was among the authors of the research report.

Comic book hero superpowers may be one step closer to reality after the latest technological feats made by researchers at UT Dallas. They have designed an imager chip that could turn mobile phones into devices that can see through walls, wood, plastics, paper and other objects.

The team’s research linked two scientific advances. One involves tapping into an unused range in the electromagnetic spectrum. The other is a new microchip technology.

The electromagnetic spectrum characterizes wavelengths of energy. For example, radio waves for AM and FM signals, or microwaves used for cell phones or the infrared wavelength that makes night vision devices possible.

But the terahertz band of the electromagnetic spectrum, one of the wavelength ranges that falls between microwave and infrared, has not been accessible for most consumer devices.

“We’ve created approaches that open a previously untapped portion of the electromagnetic spectrum for consumer use and life-saving medical applications,” said Dr. Kenneth O, professor of electrical engineering at UT Dallas and director of the Texas Analog Center of Excellence(TxACE).  “The terahertz range is full of unlimited potential that could benefit us all.”

Tapping the Terahertz Gap

Shown is the electromagnet spectrum, from radio waves used for FM and AM signals, to infrared waves used for remote controls, to gamma rays that kill cancer cells.  A team at UT Dallas is focusing on the "terahertz band," which has not been accessible for most consumer devices.

Using the new approach, images can be created with signals operating in the terahertz (THz) range without having to use several lenses inside a device. This could reduce overall size and cost.

The second advance that makes the findings applicable for consumer devices is the technology used to create the microchip. Chips manufactured using CMOS (Complementary Metal-Oxide Semiconductor) technology form the basis of many consumer electronic devices used in daily life such as personal computers, smart phones, high definition TV and game consoles.

“CMOS is affordable and can be used to make lots of chips,” Dr. O said. “The combination of CMOS and terahertz means you could put this chip and receiver on the back of a cellphone, turning it into a device carried in your pocket that can see through objects.”  Due to privacy concerns, Dr. O and his team are focused on uses in the distance range of less than four inches.

Consumer applications of such technology could range from finding studs in walls to authentication of important documents. Businesses could use it to detect counterfeit money. Manufacturing companies could apply it to process control.  There are also more communication channels available in terahertz than the range currently used for wireless communication, so information could be more rapidly shared at this frequency.

“The combination of CMOS and terahertz means you could put this chip and receiver on the back of a cellphone, turning it into a device carried in your pocket that can see through objects.”

Dr. Kenneth O,
Texas Instruments Distinguished Chair, TxACE director

Terahertz can also be used for imaging to detect cancer tumors, diagnosing disease through breath analysis, and monitoring air toxicity. 

“There are all kinds of things you could be able to do that we just haven’t yet thought about,” said Dr.  O, holder of the Texas Instruments Distinguished Chair.

The research was presented at the most recent International Solid-State Circuits Conference (ISSCC). The team will work next to build an entire working imaging system based on the CMOS terahertz system.

Other authors of the paper include Ruonan Han and Yaming Zhang, former students of Professor O, Yongwan Kim and Dae Yeon Kim, TxACE members,  and Hisashi Sam Shichijio, research professor at TxACE.

The work was supported by the Center for Circuit & System Solutions (C2S2 Center) and conducted in the TxACE laboratory at UT Dallas, which is funded by the Semiconductor Research Corporation (SRC), the state through its Texas Emerging Technology Fund, Texas Instruments Inc., The UT System and UT Dallas.

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Media Contact: LaKisha Ladson, UT Dallas, (972) 883-4183, lnl120030@utdallas.edu
or the Office of Media Relations, UT Dallas, (972) 883-2155, newscenter@utdallas.edu.

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