Direct demonstration of 1THz performance in InP HEMTs

Northrop Grumman Corp in the USA is claiming the first ever direct demonstration of gain at 1THz in indium phosphide (InP) high-electron-mobility transistors (HEMTs) [X. B. Mei et al, IEEE Electron Device Letters, published online 24 February 2015]. Usually, claims of 1THz+ frequency performance are made on the basis of extrapolations from lower-frequency measurements. The team has also developed a 10-stage amplifier circuit based on the technology.

Northrop Grumman Aerospace Systems (NGAS) has been developing high-frequency transistor performance over two decades (Table 1). Researchers at NGAS have also been developing terahertz monolithic integrated circuit (TMIC) processing techniques to enable wiring together the transistors into amplifier circuits with gain beyond 1THz.

Table 1: Summary of InP HEMT processes developed at NGAS.

Gate length	100nm	70nm	35nm	30nm	25nm (latest work)
Year	1998	2003	2007	2010	2013
InxGa1-xAs channel indium composition	60%	75%	100%	100%	100%
Source-drain spacing (μm)	2	2	1.5	1.0	0.5
Rc (Ω-mm)	0.12	0.1	0.04	0.04	0.04
gmp @ 1V (mS/mm)	1000	1400	2000	2500	3000
fMAX (THz)	0.4	0.6	1.1	1.3	1.5
Associated fT (THz)	0.2	0.25	0.4	0.5	0.61
Highest-frequency amplifier demonstrated (THz)	0.19	0.24	0.48	0.85	1.0
Associated amplifier device width (μm)	30	30	20	14	8

The researchers write of their achievement of 1THz-capable HEMTs and the associated amplifier circuit: "The transistor and next-generation circuits will find applicability in a variety of emerging applications at THz frequencies, including high-data-rate communication systems, atmospheric sensing, planetary exploration, and new classes of imagers."

The researchers see "transistor gate and layout scaling for parasitic reduction, epi material enhancement for improved electron transport properties, and process improvement associated with the aggressive scaling" as being key technologies for their achievement.

The transistor heterostructures were grown on semi-insulating InP by molecular beam epitaxy (MBE). The 95Å composite channel was indium arsenide (InAs) sandwiched between two lattice-matched indium gallium arsenide (In0.53Ga0.47As) layers. The channel carrier concentration was enhanced with silicon-doping planes above and below the channel. The Hall mobility was 13,000cm2/V-s with 4x1012/cm2 carrier density. The barrier layer was 20Å thick, measured between the bottom of the gate and the upper silicon-doped plane.

The HEMTs were fabricated with unalloyed titanium/platinum/gold ohmic contacts. The source-drain distance was reduced to 0.5μm to give low source resistance of 130mΩ-mm and contact resistance of 40mΩ-mm. The recessed T-shaped gate of titanium/platinum/gold had a 25nm footprint. The device was also passivated with silicon nitride grown by chemical vapor deposition (CVD). The aim of the passivation was to improve reliability and robustness.

The TMIC wiring process capability includes nickel-chromium thin-film resistors, metal-insulator-metal capacitors and two levels of metal interconnect. The second metal level can be air-bridged to give higher signal speed over dielectric insulated wiring. The back-end processing also includes wafer thinning to 18μm and full metalized back-side vias.

Frequency performance measurements were carried out over three bands: 10GHz-110GHz, 500GHz-700GHz, and 750GHz-1.0THz. The available gain at 1.0THz was ~3.5dB. Extrapolating the data to unity gain gave a maximum oscillation frequency (fMAX) of 1.5THz. The cut-off frequency (fT) was 650GHz.

Figure 1: Microphotograph of 1.0THz TMIC amplifier.

The TMIC process was used to create a 10-stage 1.03THz common-source amplifier, based on 8μm wide HEMTs (two 4μm fingers). The circuit (Figure 1) also included matching, DC-blocking and decoupling capacitors. The TMIC is described as a 'first iteration' scaling of a previous 850GHz design. The researchers expect improvement and optimization from future iterations.

The frequency performance was measured on equipment capable of 750GHz-1100GHz testing. The circuit achieved 9dB gain at 1.0THz - "the first demonstration of transistor amplifier gain at or above the 1.0THz mark", according to the researchers (Figure 2). At 1.05THz the gain reduced slightly to 7dB.

Figure 2: On-wafer measurement results showing 9dB on-wafer gain at 1.0THz.

The researchers comment: "This transistor and TMIC technology shows promise in enabling a new suite of components bridging microwave through THz frequencies." The 1THz shares "significant commonality" with NGAS' existing space-qualified 100nm InP HEMT technology, indicating a variety of space and airborne applications.

Tags: Northrop Grumman InP HEMTs InGaAs TMIC InP MBE

Visit: http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7047678

The author Mike Cooke is a freelance technology journalist who has worked in the semiconductor and advanced technology sectors since 1997.

Minuscule chips for NMR spectroscopy promise portability, parallelization

The small chips could be used in a portable spectrometer for on-demand applications in the field. Alternatively, they could be assembled in parallel to perform high-throughput NMR spectroscopy, dramatically accelerating molecular analysis in the laboratory. Credit: Dongwan Ha, Harvard SEAS

http://phys.org/news/2014-08-minuscule-chips-nmr-spectroscopy-portability.html

A team of engineers at the Harvard School of Engineering and Applied Sciences (SEAS), Schlumberger-Doll Research Center in Cambridge, Mass., and the University of Texas, Austin, have created a truly portable device for nuclear magnetic resonance (NMR) 
NMR spectroscopy is a technique that perturbs protons within a molecule to glean important clues about its structure. It can identify unknown substances, detect very slight variations in chemical composition, and measure how molecules interact, making it an essential tool in organic chemistry, structural biology, and drug discovery, as well as for quality control in many industries.

Led by Donhee Ham, Gordon McKay Professor of Electrical Engineering and Applied Physics at Harvard SEAS, and his student Dongwan Ha, Ph.D. '14, the team has dramatically shrunk the electronic spectrometer components, fitting them on a silicon chip smaller than a sesame seed. Combined with a compact permanent magnet, this minuscule spectrometer represents the smallest device that can presently perform multidimensional NMR spectroscopy—a process Ham calls "one of the most powerful analytical tools to determine molecular structures at atomic resolution."

Significantly reducing both the size and cost of the device—while also preserving the broad functionality of much larger spectroscopy setups—now enables the development of portable NMR spectrometers that could travel to remote sites for online, on-demand applications or simply to laboratories where massive, state-of-the-art systems would be prohibitively expensive. The chips can also operate accurately over a wide temperature range.

A paper demonstrating the use of this silicon-based chip with a compact permanent magnet will be published online this week in Proceedings of the National Academy of Sciences (PNAS).

"State-of-the-art NMR systems use very large superconducting magnets, and they are indeed necessary for probing the structure of complex molecules like proteins," says Ham. "But in many circumstances—for example, many experiments in biochemistry or organic chemistry, quality control in production lines, or chemical reaction monitoring—you're doing NMR on smaller molecules, and for those applications the big superconducting magnets may be avoided."

Permanent magnets, which have been made much smaller in recent years, are weaker than superconducting magnets but still adequate to resolve small-to-medium size hydrocarbons, drug compounds, and biomolecules such as metabolites and amino acids. The advent of these smaller magnets motivated Ham's team to try to miniaturize the electronic components of the spectrometer. Those components include the transmitter and receiver for radio-frequency signals that orchestrate complex proton motions and monitor the telltale responses that reveal the quantum-mechanical details of molecular structure.

In comparison to superconducting magnets, however, permanent magnets are far less stable. With slight changes in temperature, the magnetic field fluctuates and drifts—a severe challenge that accompanies the system miniaturization. Ha, who is the main architect of the silicon spectrometer chip and lead author of the paper in PNAS, overcame the thermal problem with a distinctly modern tactic.

"Not only did Dongwan design the chip, but he also came up with a way to use statistical distance minimization and entropy minimization to estimate the magnetic field drift and calibrate out its effect," explains Ham. "This signal-processing method obviates the need for physical thermal regulation for the permanent magnet, which would have added hardware and increased the power consumption. That would have defeated our aim of achieving portability."

While Ham and Ha demonstrated the tiny spectrometer chips for portable applications with the permanent magnet, they also see potential for a completely different application in conjunction with a larger superconducting magnet. The chips, they say, could one day be assembled into a massively parallel array in a superconducting magnet bore to tremendously accelerate analysis of complex molecules by performing many NMR spectroscopy experiments at once.

"An individual NMR spectroscopy experiment is inherently slow, taking several minutes to hours," says Ham. "Using a hundred of these cheap and small spectrometer chips in parallel within a superconducting magnet bore could counter the intrinsic slowness of NMR spectroscopy, enabling a high-throughput paradigm for pharmaceutical screening and structural biology. One year of testing could be completed in a few days. We have already started investigating this angle."

The research team has filed for a provisional patent on the miniature NMR spectrometer, and they are exploring avenues for commercialization with Harvard's Office of Technology Development (OTD).

"We see a strong opportunity to commercialize the IP that's emerged from this work," says Sam Liss, Director of Business Development in OTD. "The feedback has been very positive from pharmaceutical companies involved in drug discovery, as well as from companies poised to deliver next-generation instrumentation for spectroscopy applications."

 Explore further: Producing hyperpolarized xenon gas on a microfluidic chip

More information: Scalable NMR spectroscopy with semiconductor chips, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1402015111

Read more at: http://phys.org/news/2014-08-minuscule-chips-nmr-spectroscopy-portability.html#jCp

Precise control of optical frequency on a chip

http://phys.org/news/2014-04-precise-optical-frequency-chip.html#jCp

In the 1940s, researchers learned how to precisely control the frequency of microwaves, which enabled radio transmission to transition from relatively low-fidelity amplitude modulation (AM) to high-fidelity frequency modulation (FM). This accomplishment, called microwave frequency synthesis, brought about many advanced technologies now critical to the military, such as wireless communications, radar, electronic warfare, atomic sensors and precise timing. Today, optical communications employ techniques analogous to those of pre-1940 AM radio, due to the inability to control frequency precisely at optical frequencies, which are typically 1,000 times higher than microwaves. The higher frequency of light, however, offers potential for 1,000-fold increase in available bandwidth for communications and other applications.

As both government and commercial need for bandwidth continues to grow, DARPA's new Direct On-chip Digital Optical Synthesizer program seeks to do with light waves what researchers in the 1940s achieved with radio microwaves. Currently, optical frequency synthesis is only possible in laboratories with expensive racks of equipment. If successful, the program would miniaturize optical synthesizers to fit onto microchips, opening up terahertz frequencies for wide application across military electronics systems and beyond.

"The goal of this program is to make optical frequency synthesis as ubiquitous as microwave synthesis is today," said Robert Lutwak, DARPA program manager. "There are significant challenges, but thanks to related DARPA programs POEM, Quasar, ORCHID, PULSE and E-PHI and other advanced laboratory research, technology is at the tipping point where we're ready to attempt miniaturization of optical frequency synthesis on an inexpensive, small, low-power chip."

The basic concept is to create a "gearbox" on a chip that produces laser light with a frequency that is a precise multiple of a referenced radio frequency, such as is readily available within most existing DoD and consumer electronic systems. The ability to control optical frequency in a widely available microchip could enable a host of advanced applications at much lower cost, including:

• High-bandwidth (terabit per second) optical communications
• Enhanced chemical spectroscopy, toxin detection and facility identification
• Improved light detection and ranging (LiDAR)
• High-performance atomic clocks and inertial sensors for position, navigation and timing (PNT) applications
• High-performance optical spectrum analysis (OSA)

For example, digital optical synthesizers on a chip could increase accuracy for optical chemical sensing by six orders of magnitude while reducing cost, size and power requirements by many orders of magnitude over current capabilities. These improvements would make it possible to detect adversary chemical production facilities with high sensitivity from much farther away than is possible today.

The program envisions three phases, lasting a total of 42 months. Phase 1 would involve a demonstration of optical frequency synthesis in a laboratory, using low size, weight and power (SWaP) optical components. Phase 2 calls for a demonstration of an integrated electro-optical component. Phase 3 calls for successful demonstration of integrated optical frequency synthesizer and control electronics meeting all program performance and SWaP metrics.

"We're looking for multidisciplinary teams made up of experts in micro- and nano-fabrication, optics and photonics, and heterogeneous integration to bring the component technologies together," Lutwak said.

Read more at: http://phys.org/news/2014-04-precise-optical-frequency-chip.html#jCp

DARPA’s THz Electronics Program

DARPA’s THz Electronics Program

http://www.defenseindustrydaily.com/darpas-thz-electronics-program-05440/

Aug 15, 2013 14:11 UTC by Defense Industry Daily staff

THz flow

(click to view full)

In 2009, the US Defense Advanced Research Projects Agency (DARPA) began awarding contracts for innovative research proposals under its Terahertz (THz) Electronics Program. Readers will probably be asking the same question that crossed our mind: “when can I expect this in my laptop?”

Chip frequency has stalled out as a measure of computing power, but DARPA has a long history of helping to fund computing breakthroughs – from that minor nuisance we call the Internet to modern work on Gallium Nitride (GaN) semiconductors, non-thermionic transistors, research into graphene circuits, and more. Now, their Terahertz (THz) Electronics program is looking for technologies to enable revolutionary advances in electronic devices and integrated circuits, allowing them to reach THz frequencies of at least a trillion cycles per second…

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THz Electronics: Goals & Barriers

Commenting on the THz Electronics program, Dr. Mark Rosker, program manager of DARPA’s Microsystems Technology Office, said:

“The THz Electronics Program will develop a technology for integrated circuits operating at far higher frequencies than ever possible before. This will be crucially important for emerging applications like terahertz communications and radars. But of potentially even greater consequence, this program will drive the state of the art in high performance III-V electronics, with vast implication to RF circuits and systems operating at more conventional (microwave and millimeter-wave) frequencies.”

For many years, chip frequency was used as a substitute for speed and power. How fast is your computer? “1.3 GHz!” Unfortunately, current technologies are simply too hot to deal with beyond a certain level, and you can see the consequences. You’ve probably noticed that chip frequencies in your computers have stalled for the past few years, with increases in computing power largely driven by multi-core architectures instead. That development is here to stay, but multi-core architectures have their own scaling issues that involve both hardware and software.

So, how do we get to a state where both frequency and cores are making contributions? As DARPA’s own program brief explains:

“Until recently, active electronics using solid-state technologies were unable to access sub-MMW (millimeter wave) frequencies directly due to insufficient transistor performance. The compromise electronic option was to use frequency conversion to multiply circuit operating frequencies up from millimeter wave frequencies. Such an approach limited the output power level of the devices and the achievable signal-to-noise ratio. It also restricted the devices to relatively large sizes in terms of footprint and weight. These limitations and restrictions prevented widespread implementation and the subsequent exploitation of the sub-MMW frequency band. The enabling technology necessary to exploit the sub-MMW band is monolithic microwave integrated circuits (MMICs) that will operate up to THz frequencies. These THz MMICs or TMICs, require THz transistors with maximum oscillation frequencies (fmax) well above 1 THz.”

The program will work to develop a path to technologies such as THz transistor devices and integrated circuits, and THz high power amplifier modules for military application. The critical bridges to that future include micromachined vacuum electronics Terahertz High Power Amplifier Modules, and Terahertz Transistor Electronics (multi-THz InP HBT and InP HEMT transistor technologies, and THz low-loss inter-element interconnect and integration technologies).

Contracts and Key Events

All contracts are managed by the US Defense Advanced Research Projects Agency. Note that “metrology” is the science of measurement.

Aug 14/13: Northrop Grumman Space & Mission Systems in Redondo Beach, CA receives a $10.1 million cost-plus-fixed-fee contract modification under the Terahertz Electronics (THz) program. It continues their work on critical device and integration technologies for this phase’s high end of 1.03 THz compact, high-performance electronic circuits.

Work will be performed in Redondo Beach, CA (83.95%); Charlottesville, VA (6.17%), and Pasadena, CA (9.88%). The estimated completion date is Feb 15/15 (HR0011-09-C-0062).

1.03 THz integration, continued

July 31/12: Testing. Northrop Grumman announces  that they’ve demonstrated an 850 GHz integrated receiver, or 0.85 trillion cycles per second, under the $12.5 million contract for Phase 2 of DARPA’s Terahertz Electronics program.

Under Phase 1, they developed a Monolithic Integrated Circuit that operated at 670 GHz. The company also developed and tested low-noise amplifiers and power amplifiers.

July 10/12: Science. From the Lawrence Berkeley National Laboratory, some good news for the field :

“A multi-institutional team of researchers that included scientists with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has created the first artificial molecules whose chirality can be rapidly switched from a right-handed to a left-handed orientation with a beam of light. This holds potentially important possibilities for the application of terahertz technologies across a wide range of fields… Chirality is the distinct left/right orientation or “handedness” of some types of molecules, meaning the molecule can take one of two mirror image forms. The right-handed and left-handed forms of such molecules, called “enantiomers,” can exhibit strikingly different properties.

…Working with terahertz (THz) metamaterials engineered from nanometer-sized gold strips with air as the dielectric – Zhang and his colleagues fashioned a delicate artificial chiral molecule which they then incorporated with a photoactive silicon medium. Through photoexcitation of their metamolecules with an external beam of light, the researchers observed handedness flipping in the form of circularly polarized emitted THz light. Furthermore, the photoexcitation enabled this chirality flipping and the circular polarization of THz light to be dynamically controlled.”

April 20/11: Northrop Grumman Space & Mission Systems in Redondo Beach, CA receives a $12.5 million cost-plus-fixed-fee contract modification for the Terahertz (THz) Electronics Program. This contract focuses on critical device and integration technologies for this phase’s high end of 1.03 THz compact, high-performance electronic circuits.

Work will be performed in Redondo Beach, CA (82.58%); Charlottesville, VA (1.84%); Pasadena, CA (9.38%); Charlottesville, VA (3.51%); Tempe, AZ (1.73%); and University Park, PA (0.96%). Work is expected to be complete April 16/14 (HR0011-09-C-0062). See also April 3/09 entry.

1.03 THz integration

May 6/09: Teledyne Scientific & Imaging  in Thousand Oaks, CA receives an $18.8 million cost-plus-fixed-fee contract to develop transceiver arrays; specifically, receivers and exciters at carrier frequencies of 670 GHz, 850 GHz, and 1030 GHz (HR0011-09-C-0060).

April 3/09: Northrop Grumman Aerospace Systems (formerly, Space and Mission Systems) in Los Angeles, CA receives a $37 million contract for development of military and space satellites’ active receivers and transmitters operating at 670 gigahertz that ensure transmission of high-resolution images and other applications (HR0011-09-C-0062).

THz T/R

April 3/09: DARPA awards Northrop Grumman Electronic Systems an $8.9 million contract to develop and demonstrate technologies for high power amplification (HPA) of THz signals in compact HPA modules. These include demonstration of a power amplifier device capable of amplifying radiation at THz frequencies, the development of a compact THz HPA module (including an antenna and the ability to integrate with a solid-state exciter circuit), and THz metrology (HR0011-09-C-0061).

April 1/09: DARPA awards SAIC an $11.6 million contract to develop and demonstrate technologies for high power amplification (HPA) of THz signals in compact HPA modules. These include demonstration of a power amplifier device capable of amplifying radiation at THz frequencies, the development of a compact THz HPA module (including an antenna and the ability to integrate with a solid-state exciter circuit), and THz metrology (HR0011-09-C-0063).

Initial HPA contracts

Additional Readings

• DARPA – THz Electronics 
• UC Berkeley CS10 Fall 2010 – The Beauty and Joy of Computing: Concurrency  [YouTube]. Great introductory course for geeks and non-geeks alike; this lesson deals with the evolution of chips, and see esp. from 18:15 and 22:10. Is it pathetic or awesome that this is what we watch in our spare time? We vote for awesome.
• Lawrence Berkeley National Laboratory (July 10/12) – Metamolecules That Switch Handedness at Light-Speed 

Categories: Contracts - Awards, DARPA, Design Innovations, Electronics - General,Northrop-Grumman, Other Corporation, R&D - Contracted, Satellites & Sensors,Signals Radio & Wireless, T&C - SAIC, USA

Abstract- Nb5N6 microbolometer arrays for terahertz detection

Tu Xue-Cou (涂学凑), Kang Lin (康 琳), Liu Xin-Hua (刘新华), Mao Qing-Kai (毛庆凯), Wan Chao (万 超), Chen Jian (陈 健), Jin Biao-Bing (金飚兵), Ji Zheng-Ming (吉争鸣), Xu Wei-Wei (许伟伟) and Wu Pei-Heng (吴培亨)
http://iopscience.iop.org/1674-1056/22/4/040701

A novel room-temperature microbolometer array chip consisting of an Nb₅N₆ thin film microbridge and a dipole planar antenna, which is used as a terahertz (THz) detector, is described in this paper. Due to the high-temperature coefficient of the resistance of the Nb₅N₆ thin film, which is as high as −0.7% K⁻¹, such an antenna-coupled microbolometer is ideal for detecting signals in a frequency range from 0.22 THz to 0.33 THz. The dc responsivity, calculated from the measured I–V curve of the Nb₅N₆ microbolometer, is about −760 V/W at a bias current of 0.19 mA. A typical noise voltage as low as 10 nV/Hz^1/2 yields a low noise equivalent power (NEP) of 1.3 × 10⁻¹¹ W/Hz^1/2 at a modulation frequency above 4 kHz, and the best RF responsivity, characterized using an infrared device measuring method, is about 580 V/W, with the corresponding NEP being 1.7 × 10⁻¹¹ W/Hz^1/2. In order to further test the performance of the Nb₅N₆ microbolometer, we construct a quasi-optical type receiver by attaching it to a hyperhemispherical silicon lens, and the result is that the best responsivity of the receiver is up to 320 V/W. This work could offer another way to develop a large scale focal-plane array in silicon using simple techniques and at low cost.

Cream of the Crop: Sandwich Chips Combining the Best of Two Technologies

                          Wafer with "sandwich chips". (Credit: FBH/Immerz)
http://www.sciencedaily.com/releases/2012/12/121218081744.htm
Dec. 18, 2012 — Two Leibniz institutes broke new technological ground and successfully combined their -- up to now separate -- technology worlds. Due to their high performance the novel chips developed within the HiTeK project promises to open up new applications


Wolfgang Heinrich and Bernd Tillack are convinced of holding the key to faster and more powerful terahertz chips. The two scientists and their teams come from the Berlin-based Ferdinand-Braun-Institut (FBH) and from the IHP-Leibniz-Institut für innovative Mikroelektronik in Frankfurt/Oder -- and thus from two different technology worlds. FBH is one of the leading institutes in developing III-V semiconductors, while IHP is specialized in silicon-based systems and circuits. Both Leibniz institutes joined forces within the HiTeK project to combine the advantages of silicon-based CMOS (Complementary Metal Oxide Semiconductor) circuits from the IHP with those of indium-phosphide circuits from the FBH. The partners now accomplished an important step within the project by successfully integrating both circuits on a semiconductor wafer, with measurement results demonstrating their high performance. With the integration on one chip, new ambitious applications in the THz range are within reach such as high-resolution imaging systems for medical and security technology as well as ultra-broadband mobile communication applications.
For such applications high output powers along with faster computer processors are needed offering enhanced computer operation per second. In order to achieve this, circuits on the chips have to become smaller -- the key reason which boosts miniaturization in semiconductor industry. If the frequency range around 100 gigahertz and beyond is to be covered, however, the breakdown voltage in the CMOS switching circuits decreases significantly. Accordingly, the available output power of the chips declines, which implies that the capability to generate sufficiently strong signals to establish a radio link and to detect material defects becomes insufficient. To find a solution for this problem, IHP conducts research on bipolar CMOS based on silicon-germanium enhancing the breakdown voltages at high speed compared to pure CMOS. By combining a standard CMOS circuit with a second indium-phosphide circuit promises further improvement. Both circuits are realized "sandwich-like" on top of each other. Where the traditional silicon-based CMOS technology reaches its limits, this novel material combination delivers the desired properties: high output powers at high frequencies. The sandwich chips allow to keep benefiting from the high level of production routine and integration of CMOS circuits -- particularly regarding the fact that 95 % of all digital and analogue-digital circuits base on this technology.
"It was particularly challenging to make both technologies compatible at the interfaces," underlines Wolfgang Heinrich from the FBH. To achieve this, the whole development environment of both processes as, for example, the software for the circuit layout had to be merged in a first step. Subsequently, both layers had to be dimensioned so that they reach the essential good transmission properties for frequencies around 200 gigahertz. Precision work was also highly demanded to adjust the circuits precisely to each other with an accuracy of less than 10 micrometers. Heinrich is especially proud of the friction-less cooperation: "We managed to align both technology worlds so smoothly that the circuits deliver fully the specified high-frequency performance. This also demonstrates what added value can be created by bundling the competencies of two institutes like IHP and FBH."
The next steps are now to further stabilize the process and to optimize the circuits. A follow-up project has already been granted. This way, the potential of the hybrid chips shall be exploited fully to reach the borders of what is feasible -- thus setting the stage for the novel sandwich circuits to be integrated in sophisticated applications soon

Photonics: Graphene's Flexible Future

Plots showing that surface plasmons are more confined when propagating along on a monolayer of graphene (G) than they are along a thin film of gold (Au). (Credit: © 2012 A*STAR Institute of High Performance Computin

My Note: This is a follow-up to the article posted on December 5th, which is found here:
http://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=7516187338046434277

Dec. 10, 2012 — Theoretical calculations show graphene's potential for controlling nanoscale light propagation on a chip
http://www.sciencedaily.com/releases/2012/12/121210080425.htm
Semiconductors have revolutionized computing because of their efficient control over the flow of electrical currents on a single chip, which has led to devices such as the transistor. Working towards a similar tunable functionality for light, researchers from the A*STAR Institute of High Performance Computing (IHPC), Singapore, have shown how graphene could be used to control light at the nanometer scale, advancing the concept of photonic circuits on chips1.
Graphene, which is made from a single layer of carbon atoms, has excellent electronic properties; some of these are also useful in photonic applications. Usually, only metals are able to confine light to the order of a few nanometers, which is much smaller than the wavelength of the light. At the surface of metals, collective oscillations of electrons, so-called 'surface plasmons', act as powerful antennae that confine light to very small spaces. Graphene, with its high electrical conductivity, shows similar behavior to metals so can also be used for plasmon-based applications, explains Choon How Gan of IHPC, who led the research.
Gan and co-workers studied theoretically and computationally how surface plasmons travel along sheets of graphene. Even though graphene is a poorer conductor than a metal, so plasmon propagation losses are higher, it has several key advantages, says team member Hong Son Chu. "The key advantage that makes graphene an excellent platform for plasmonic devices is its large tunability that cannot be seen in the usual noble metals," he explains. "This tunability can be achieved in different ways, using electric or magnetic fields, optical triggers and temperature."
The team's calculations indicated that surface plasmons propagating along a sheet of graphene would be much more confined to a small space than they would traveling along a gold surface (see image). However, the team also showed that surface plasmons would travel far better between two sheets of graphene brought into close contact. Furthermore, by adjusting design parameters such as the separation between the sheets, as well as their electrical conductivity, much better control over surface plasmon properties is possible.
In the future, Gan and his co-workers plan to investigate these properties for applications. "We will explore the potential of graphene plasmonic devices also for the terahertz and mid-infrared regime," he explains. "In this spectral range, graphene plasmonic structures could be promising for applications such as molecular sensing, as photodetectors, or for optical devices that can switch and modulate light."
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing