Oliver Ambacher

Bio: Oliver Ambacher is an academic researcher from Fraunhofer Society. The author has contributed to research in topics: Amplifier & High-electron-mobility transistor. The author has an hindex of 64, co-authored 848 publications receiving 26256 citations. Previous affiliations of Oliver Ambacher include Osram & Siemens.

W-band direct detection radiometers using metamorphic HEMT technology

Abstract: At this paper we report on a W-band direct detection radiometer cascading a single-pole four-throw switch with integrated 50 Ω load as a reference noise source, a 3 x 20 dB low-noise amplifier chain, and a broadband Schottky-diode detector. All components are designed and fabricated in 100 nm metamorphic high electron mobility transistor (mHEMT) technology and use waveguide packaging. By using 2 channels of the switch module the Dicke-principle is implemented to drastically reduce the inherent amplifier noise. The multi-throw switch insertion loss is less than 3.5 dB on the chip level and 4.4 dB on the module level. The entire W-band direct detection radiometer chain is also integrated on a single chip and packaged into a waveguide module, which was successfully tested and is now ready for system integration.

Ion beam synthesis of 3C–(Si1–xC1–y)Gex+y solid solutions

Abstract: In the present study cubic 3C-(Si 1-x C 1-y )Ge x+y solid solutions were created by using ion beam synthesis. 3C-SiC thin layers grown on on-axis Si (111) substrates by Molecular Beam Epitaxy were implanted with Ge in order to incorporate Ge atoms in the Silicon Carbide lattice. Two series of experiments were carried out. The implantation energy was chosen to be 140 keV and 200 keV and the implantation dose 1 × 10 17 cm -2 and 4.7 × 10 16 cm -2 respectively. The samples were annealed under rapid thermal annealing conditions in the temperature range between 800 °C and 1300 °C. X-ray diffraction measurements indicate an enlargement of the lattice constant. The observed higher absorption in the implanted layers could be a sign of a band gap reduction as a consequence of Ge incorporation.

A broadband 175–245 GHz balanced medium power amplifier using 50-nm mHEMT technology

Abstract: In this paper, a balanced millimeter-wave monolithic integrated circuit (MMIC) medium power amplifier (MPA) is presented. This amplifier was developed by using an advanced 50 nm metamorphic high electron mobility transistor (mHEMT) process, where a grounded coplanar waveguide (GCPW) technology and a compact cascode configuration were adopted to achieve high gain and high output power at the WR-4 waveguide band (170–260 GHz). This two-stage MPA exhibits a 13.4 dB peak measured small-signal gain at 228 GHz and an excellent 3-dB bandwidth of 33.8% from 175 to 245 GHz. Good input and output return losses with higher values than 9.8 dB and 9.3 dB were measured. At 198 GHz a maximum output power of 9.5 dBm with 7.5 dB associated large signal gain is obtained, while at 235 GHz an output power-referred 2.3-dB compression point of 6.6 dBm is exhibited. A linear output power higher than 4 dBm (at 1-dB compression point) is realized from 198 GHz to 240 GHz (19% relative bandwidth, RBW).

Packaged AlGaN/GaN HEMT power bars with 900 W output power and high PAE at L-band

Abstract: This paper describes the performance of packaged power bars that are realized in a 0.5 μm gate length AlGaN/GaN HEMT technology on SiC substrates, assembled together with pre-matching circuitry in a ceramic package and designed for operation at 1030 MHz (L-Band). Two different package assemblies are compared: The first one uses a single power bar, and the second one uses four parallel power bars. Fundamental passive load-pull at 50 V DC drain supply voltage under pulsed excitation with 10% duty cycle shows output power levels of 260 W and 900 W at 3 dB compression with an associated PAE of 62% and 66%, respectively, for the first and second assembly. The first assembly is further characterized using an active harmonic load-pull system, which demonstrates an increased output power of about 325 W at 69% PAE when tuned for maximum power, or peak PAE values exceeding 75% at an output power of 260 W when tuned for maximum efficiency.

Internally-packaged-matched continuous inverse class-FI wideband GaN HPA

Abstract: This paper shows a wideband high power efficiency amplifier with internal package matching. The power amplifier has been designed and realized by using the Continuous Inverse Class-FI approach for wideband applications. In particular, the fundamental as well as the second and third harmonic output terminations have been matched inside the packaged transistor without the use of further external output matching conditions. The realized prototype shows drain efficiencies in the range of 59.5–71% while delivering 42.4–45.7 dBm of output power in the very wide frequency range of 1.8–2.7 GHz.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Principles of Neural Science

Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Phonons and related crystal properties from density-functional perturbation theory

Abstract: This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Conjugated polymer-based organic solar cells

Abstract: The need to develop inexpensive renewable energy sources stimulates scientific research for efficient, low-cost photovoltaic devices.1 The organic, polymer-based photovoltaic elements have introduced at least the potential of obtaining cheap and easy methods to produce energy from light.2 The possibility of chemically manipulating the material properties of polymers (plastics) combined with a variety of easy and cheap processing techniques has made polymer-based materials present in almost every aspect of modern society.3 Organic semiconductors have several advantages: (a) lowcost synthesis, and (b) easy manufacture of thin film devices by vacuum evaporation/sublimation or solution cast or printing technologies. Furthermore, organic semiconductor thin films may show high absorption coefficients4 exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The electronic band gap of organic semiconductors can be engineered by chemical synthesis for simple color changing of light emitting diodes (LEDs).5 Charge carrier mobilities as high as 10 cm2/V‚s6 made them competitive with amorphous silicon.7 This review is organized as follows. In the first part, we will give a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells. In the second part, we will focus on conjugated polymer/fullerene bulk heterojunction solar cells, mainly on polyphenylenevinylene (PPV) derivatives/(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61) (PCBM) fullerene derivatives and poly(3-hexylthiophene) (P3HT)/PCBM systems. In the third part, we will discuss the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells. In the fourth part, we will suggest possible routes for further improvements and finish with some conclusions. The different papers mentioned in the text have been chosen for didactical purposes and cannot reflect the chronology of the research field nor have a claim of completeness. The further interested reader is referred to the vast amount of quality papers published in this field during the past decade.