GaN-based high-voltage switching transistors enable particularly efficient power converters. At FBH, normally-off 300 V GaN transistors with only 80 mW on-state resistance for the opened transistor biased at +5 V gate voltage have been developed. The maximum pulse current is above 50 A.
Research News 2011
Monolithic micro resonators are characterized by a very low size and extremely high optical performance. These properties make them attractive for applications in optical signal processing and sensor technology. FBH and Humboldt-University of Berlin have recently started a common research project for the development of a novel technology platform. Aim is to develop the technological preconditions for the application of the technology and its commercialization.
Red broad area laser diodes (100 µm x 1,5 mm) show an output power of 2.5 W and a conversion efficiency of 35% at 15°C. Reliability tests were carried out at an output power of up to 1.2 W for in total 20 000 h revealing a degradation rate of at most 3x10-6 h-1. Based on this measurements, a lower limit of the mean time to failure of 87.000 h at 1.2 W can be extrapolated.
Within the framework of a research project, FBH systematically compared devices fabricated on epitaxial wafers from different vendors. After having demonstrated its stable and reproducible GaN-HEMT process, FBH was offered the opportunity to provide devices for a payload experiment on board of the Alphasat communication satellite taking off in May 2012. This experiment tests GaN devices under real-space conditions, in particular, their sensitivity to cosmic radiation und sends the respective data to earth. These data are of particular importance for further optimization of GaN electronics for highly reliable space applications.
At FBH, a novel ps light source has been developed consisting of a mode-locked diode laser with hybrid-integrated pulse picker and amplifier. The compact module provides ultra-short light pulses <10 ps with a selectable repetition rate from the Hz up to the GHz range. Applications for the capable and highly flexible laser source are especially in materials analytics and materials processing.
Jointly with partners from research and industry, FBH develops focusable LEDs with an emission near 360 nm for applications in the analysis of bodily fluids. In a first step, top-emitting LEDs have been fabricated emitting through a small area on the chip front side.
Network analyzer measurements are the most important means for the characterization of RF circuits in the upper GHz range. As the raw measurement data do not only reflect the behavior of the structure under investigation but also show undesired influences, these effects must be deducted from the measured data of thedevice under test in order to describe it correctly. Thus, several dedicated CPW structures are measured and special algorithms are applied to the results to correct for the undesired effects.
Only recently, FBH has successfully demonstrated a new generation of direct-converting line detectors. Within the system, GaAs sensors directly convert X-ray photons into charge carriers with a lateral resolution of 100 µm per pixel. Key benefits are very low crosstalk between adjoining pixels, simple construction and expanded lifetime of the detector chips.
For interferometric measurement and atomic spectroscopy, a micro-integrated, tunable external cavity diode laser (ECDL) with a reflection Bragg grating has been developed at FBH. The single-mode, tunable light source emits around 633 nm and features a narrow linewidth. The concept can additionally be transferred to other wavelengths.
With a thin n-doped AlGaN layer under the channel FBH scientists significantly improved the trade-off between on-state resistance and breakdown voltage of GaN HFETs for power switching applications.
FBH managed to reduce the dislocation density of AlN by more than one order of magnitude by the epitaxial lateral overgrowth of patterned AlN layers. Thus, the dislocation density of AlN layers can be reduced down to an average value of 109 cm-2. These layers are now used for further development of efficient UV LEDs.
FBH acquired a new semi-automatic on-wafer characterization system enabling 500 GHz measurements. This system is ideally suited for on-wafer characterization in the frequency range beyond 100 GHz, which is currently subject of world-wide research.
Highly efficient electrical power converters are indispensible for ecology-minded future electronic systems. Thus, Schottky diodes with lateral device topology have been developed at FBH which fully utilize the high channel conductivity provided by the 2-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction interface.
Vertical integration plays a key role with regard to the increasing integration density of electronic devices. Vertical interconnect accesses (VIAs) from the device’s front through the substrate down to the backside allow simple and space-saving contacting of the devices in packages. FBH recently optimized its patented, laser-assisted manufacturing process for VIAs for power electronics applications.
FBH systematically examines frequency doubling of diode lasers in bulk crystals, planar and channel waveguides. Comparison reveals that frequency doubling of diode lasers in planar waveguides is currently the solution of choice to realize compact visible diode laser modules with output powers of several Watt and an electro-optical conversion efficiency of more than 10%.
Due to their blindness in the visible region (solar blind) and the radiation resistance, GaN-based UV photodetectors are highly demanded for many application. FBH developed such detectors directly from AlGaN-GaN heterostructures of transistors (MSM type) which are specifically interesting for applications with high photocurrent.
So far, the works on UV LEDs focussed on the optimization of the epitaxial structures. By means of UV LEDs (wavelength approx. 320 nm) a technology has now been developed which allows to fabricate LEDs as single chips and mount them on heat spreaders and into standard housings. The feasibility of the mounting technology was proven.
Microwave power amplifiers in modern telecommunication systems have to work over large bandwidth with high peak-to-average-power-ratio signals. Dedicated source- and load-pull measurement setups allow for analyzing and improving the trade-off between linearity and efficiency. The findings are reflected in improved circuit design and advances in device technology.
The normally-off p-GaN gate technology developed at FBH combines low leakage currents for the unbiased gate (0 V) in the off-state with high currents and low resistances in the on-state. For high-voltage GaN transistors blocking up to the kV range a special carbon-doped GaN buffer has been introduced in parallel to keep the electrons well confined in the transistor channel made of undoped GaN. Both technologies have now been successfully combined in one device.
FBH uses frequency-selective Bragg gratings for its diode lasers in order to achieve a low temperature dependence and a very narrow line width of the emitted laser light. With its newly developed dry-chemical etch process the tilt angle of the lattice structure can be controlled and the profile of the grid near the active layer thus be precisely adjusted.
The FBH succeeded to realize a compact and rugged micro-integrated master oscillator power amplifier (MOPA) that features a narrow linewidth with high-power output. It is thus suitable for a variety of fields like coherent optical communication, precision measurements, spectroscopy, and laser cooling and could replace solid state or fiber lasers which have been used so far.
Disk lasers as optically pumped surface emitters combine the high beam quality of a vertically emitting laser with a high output power. FBH succeeded in fabricating InGaN disk lasers with a peak pulse output power of more than 300 W and an emission wavelength of 393 nm. First semiconductor disk lasers with an emission wavelength of 420 nm have additionally been realized.
Leistungsstarke Breitstreifenlaser mit internen, epitaktisch überwachsenen distributed feedback (DFB) Gittern für die Stabilisierung auf eine geringe spektrale Breite, zeigen signifikante Verbesserungen: Zum ersten Mal konnte eine elektro-optische Konversionseffizienz hc > 60% und eine …
Efficient blue-violet laser diodes with high reliability and long device lifetimes require GaN substrates with high material quality at affordable prices. As an alternative approach to growth on foreign substrates, FBH is developing a technology for the growth of thick GaN boules of which a number of high-quality substrates is then sliced out.
Radar systems in the 77 GHz range have become an essential part of the comfort and safety features in high-end cars. One of the dominant cost factors for such systems is packaging. LTCC (Low-Temperature Cofired Ceramics) offers interesting possibilities as carrier substrate in the package, since it combines multi-level routing capabilities with an acceptable price tag.
The linearity of AlGaN/GaN heterojunction field-effect transistors (HFETs) is one of the key parameters in modern telecom systems. The FBH works on optimizing this feature to design GaN-based RF circuits fulfilling modern system requirements.
With Sentech Instruments' SI500D the FBH has a new capable tool for plasma deposition of silicon nitride at hand that significantly expands the institute’s possibilities in this field.