FBH demos III-V electronics capability at Productronica, including InP and Si heterointegration

http://www.semiconductor-today.com/news_items/2017/oct/fbh_091017.shtml

Berlin-based Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH) – which researches compound semiconductor-based electronic and optical components, modules and systems – is presenting a selection of current developments and advances of its power amplifiers, circuits and heterointegrated chips in hall B2, booth 317 at Productronica 2017 in Munich (14-17 November). FBH is exhibiting jointly with partners from the Fraunhofer Group for Microelectronics and fellow Leibniz institute IHP-Innovations for High Performance Microelectronics of Frankfurt (Oder), Germany.

FBH’s heterointegrated chips for terahertz applications, for example, combine the advantages of two technologies at the chip level: the high output power of indium phosphide (InP) with the complexity of silicon technology.

Further exhibits target digitalization and the future mobile communications standard 5G, including digital power amplifiers that offer efficient performance management and the highest flexibility simultaneously in addition to broadband operation.

Pushing frequency boundaries and combining advantages with heterointegrated chips

Regarding high-performance communications, frequencies in the subterahertz range are gaining increasing attention. To overcome the exponentially growing volume of short-range data traffic, wireless transmission routes are needed in the 100-500GHz band. Other applications in this band include materials testing, security technology for passenger and baggage screening, and high-resolution radar technology for intricate robotics applications.

All these system applications require electronic circuits that can deliver high output power in the sub-terahertz range, and they cannot be built using conventional semiconductor technology. Instead, FBH uses the InP for its integrated circuits. InP heterojunction bipolar transistors (InP-HBTs) can currently achieve cut-off frequencies of more than 500GHz (fmax) at a collector current of 20mA. The breakdown voltage lies above 4V, enabling high output power.

An industry-compatible process line for InP circuit wafers is being built at FBH in the scope of the German government Federal Ministry of Education and Research (BMBF) initiative Research Fab Microelectronics Germany (FMD), launched in April. This process line also allows FBH - together with IHP - to integrate InP circuits onto silicon-germanium (SiGe) BiCMOS technology. The high output power of InP can hence be combined with the complexity of silicon technology. Millimeter-wave and sub-terahertz modules can therefore be created on a single chip, which is paramount for portable and cost-effective system applications. This process is also offered to external customers as a foundry service.

Components for 5G

In preparing the technical infrastructure for 5G, hardware components must be made more efficient and more flexible, says FBH. This can be aided by increasing the degree of digitalization. Currently, the focus is on power amplifiers because they dominate the efficiency, and thus the operating costs, of the entire system.

Up to now, multiple separate modules have always been required to accommodate different communication standards and frequencies. FBH has therefore been working for several years on developing new digital amplifier architectures offering efficient power management, maximum flexibility, and broadband operation. The long-term goal is a fully digital transmitter in which one chip serves all frequency bands.

Complementary to this, FBH is researching powerful modulation and encoding methods, which largely determine the properties of digital amplifiers. It has already developed a novel modulator that can be built using conventional digital components. It also allows signals to be generated by all kinds of modulation methods.

FBH’s digital power amplifiers have already achieved competitive overall efficiency and linearity compared with established analog amplifier concepts such as Doherty. One recent power amplifier offers overall efficiency of more than 40% at 10dB PAPR (peak-to-average power ratio) in the range of around 1GHz.

Another method for digitalizing power amplifiers is discrete envelope tracking (ET). Modulating the supply voltage of the amplifier output stage ensures high power efficiency despite the strongly fluctuating instantaneous power of modern broadband modulation methods. Modulation is performed by switching the voltage back and forth only between a number of specific (discrete) constant voltages. This digitalized version of ET yields highly efficient broadband solutions. New records were recently achieved at FBH, namely a modulation bandwidth of 120MHz in a 75W amplifier at 1.8GHz. This ET concept can also be converted relatively easily for millimeter-wavelength amplifiers, as is crucial for 5G base stations.

New Record for Quantum-cascade Laser Operation Temperature

Laser chip mounted on a heat sink. The chip with several terahertz quantum-cascade lasers is soldered in the middle of a U-shaped contact pad with attached electrical leads. Courtesy of PDI

By: Forschungsverbund Berlin e.V. (FVB)
http://www.scientificcomputing.com/news/2014/04/new-record-quantum-cascade-laser-operation-temperature

For the observation of cold matter in the interstellar medium, astronomers need instruments for the detection of terahertz radiation. Specific high-resolution instruments are based on terahertz quantum-cascade lasers, but operate only at cryogenic temperatures. Physicists have now developed a terahertz quantum-cascade laser, which operates at significantly higher temperatures than previously achieved. The new development allows for the use of more compact cooling systems — also reducing the obstacles for many other applications.

The wavelengths of terahertz radiation lie between the microwave and infrared range. It penetrates many materials such as plastics and clothes. At the same time, terahertz radiation is — due to its small energy — non-ionizing and not dangerous for people. Applications of terahertz radiation include non-destructive material testing and safety checks at airports.

For astronomers, terahertz radiation provides new insights in the investigation of so-called cold matter. This kind of matter does not emit visible light such as the stars, but electromagnetic radiation in the infrared to microwave range. The German Aerospace Center (DLR) measures such emission lines with high precision within the US-German SOFIA project. Due to the Doppler shift of the detected frequencies, the researchers can determine the velocity of the motion of cold matter through the galaxy. To reduce the absorption by water in the earth atmosphere, the measurements are carried out from an airplane. One key element of the detector system is a quantum-cascade laser developed at the PDI.

In a joint project funded by the Investitionsbank Berlin, researchers  at the Paul Drude Institute (PDI) in Berlin have developed a compact quantum-cascade laser system. The partners in this project were in addition to the PDI the Ferdinand Braun Institute in Berlin, the Humboldt University in Berlin, and the company Eagleyard Photonics located also in Berlin.

“One problem of the lasers are the low operating temperatures, which are typically even below the temperature of liquid nitrogen  of 77 Kelvin or -196 °C for continuous-wave  operation”, explains Martin Wienold from the PDI. “We achieved a new record: our lasers operate up to 129 Kelvin (-144 °C) improving the previous record by more than 10 degrees.” This is still rather cold, “but, in combination with a significantly reduced power dissipation of the new lasers, it allows for the use of much smaller mechanical coolers. Thereby, we will be able to reduce the size of systems based on terahertz quantum-cascade lasers in the future — an important point for flight missions such as SOFIA”, Wienold emphasizes.

The physicists at the PDI achieved the high operating temperatures by developing a semiconductor heterostructure, which requires only a very low driving power. The laser ridge is only about 10-15 microns high and 15 microns wide, while the emission wavelength is about 100 microns. The active region is confined by two metal layers, which are almost perfect mirrors in the terahertz range. This combination results in very low power dissipation and operation at low current densities and voltages.

“However, there has been an additional problem”, explains Martin Wienold: “We achieved relatively high operating temperatures, but the strong spatial confinement of the light in the laser resulted in an extremely divergent beam profile”. The physicists solved the problem by applying a concept from the early days of radio broadcasting. A grating on top of the laser ridge — a so-called third-order grating — acts as a directive antenna, which collimates the laser emission. “We are currently working on achieving even higher operating temperatures”, says Wienold. “However, room temperature operation will become difficult to achieve because of some physical limits.”

Quantum-cascade laser

Quantum-cascade lasers differ from common diode lasers by its structure and the involved physical processes. Typical diode lasers emit light, when electrons from the conduction band recombine with holes from the valence band. Upon recombination, a photon is emitted with the energy of approximately the semiconductors energy gap. Since the energy gap is determined by the used semiconductor material, the wavelength of a diode laser is basically determined by the material.

In a quantum-cascade laser, the electron remains in the conduction band, and the laser transitions takes place between two confined subband states within the conduction band. This performance is achieved by alternating extremely thin semiconductor layers, resulting in so-called potential wells in the conduction band. When an electric field is applied, the electrons move from an energetically higher lying potential well to an energetically lower lying potential well via the quantum mechanical tunneling effect. The electrons tumble down from one potential well to the next potential well in such a way, as falling down a staircase.

Citation: High-temperature, continuous-wave operation of terahertz quantum-cascade lasers with metal-metal waveguides and third-order distributed feedback. M. Wienold, B. Röben, L. Schrottke, R. Sharma, A. Tahraoui, K. Biermann, and H. T. Grahn.Optics Express, Vol. 22, Issue 3, pp. 3334-3348 (2014) http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-3-3334

Terahertz in Germany-A gentle look through

02 Oct 2013

Source: Berlin Adlershof

http://www.research-in-germany.de/dachportal/en/Infoservice/News/2013/10/2013-09-30-terahertz-rays-are-good-for-more-than-just-body-scans-at-airports.-fbh-is-one-of-the-world-leading-institutes.html

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Terahertz rays are good for more than just body scans at airports. FBH is one of the world leading institutes

The terahertz technology will soon be arousing interest for many applications in medicine, radar, communications, security, nondestructive materials testing, and quality assurance. The path that must be taken is being paved e.g. by researchers and their integrated componentry at the Ferdinand-Braun-Institut.
Whenever terahertz technology is mentioned, people think of the notorious “strip scanners” that can see through the clothing of air passengers. But this is a hasty reaction. Viktor Krozer, who holds an enclosed professorship of Terahertz Electronics at the Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH), puts it clearly: “That equipment has little to do with THz technology because it works with essentially lower frequencies.”
Many applications
A terahertz (THz) describes a frequency of one trillion vibrations a second. This can dramatically increase the resolution of conventional imaging systems. Yet this radiation can do more than penetrate packaging and clothes. “Imaging systems of this kind can also be used in industrial quality assurance, medical engineering, and broadband wireless communications,” explained Kozer. He continued that as early as the pilot applications THz was being used for nondestructive materials testing, e.g. for detecting fine hairline cracks in pipeline jackets – or damage in the connecting structures of wind turbine and aircraft rotor blades. “These applications are being pushed forward on a massive scale,” explained Krozer.
Pharmaceuticals companies are hoping that high frequency radiation can better control, for instance, the quality of capsule coatings. The food industry can analyse the quality of fresh goods like fish or meat by directing noncontracting THz technology through the walls of packaging.
Think the previously unthinkable
The crucial advantage of terahertz technology: it can penetrate many materials, but the low energy of its photons does not induce ionisation, making it suitable for many applications. Krozer expects initial marketable applications in three to five years. Until then, he and his team will be paving the way and meanwhile are regarded as one of the world leading institutes in this field. Here, they research and develop new integrated terahertz sources and detectors based on semiconductors. Among their achievements, the scientists have developed a unique semiconductor process that can realise complete system components with integrated circuitry. A complex field for absolute specialists with the courage to think the previously unthinkable. “We’re operating at the limits of the feasible,” commented Krozer casually.
By Chris Löwer for Adlershof Special
www.fbh-berlin.de