Author
Oliver Ambacher
Other affiliations: Osram, Siemens, Cornell University ...read more
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.
Papers published on a yearly basis
Papers
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01 Sep 2015TL;DR: In this paper, two high-efficiency power amplifier MMICs utilizing a 100 nm AlGaN/GaN HEMT MMIC technology at Ka-band frequencies are reported in order to ensure high output power and high gain.
Abstract: Two high-efficiency power amplifier MMICs utilizing a 100 nm AlGaN/GaN HEMT MMIC technology at Ka-band frequencies are reported in this paper. They have also been designed in order to ensure high output power and high gain. In continuous-wave (CW) operation, the first three stage power amplifier provides 4.5 W of output power and 33% of power-added-efficiency (PAE) at 30 GHz. The first power amplifier has been mirrored and combined in order to reach higher output power levels. This second MMIC power amplifier provides 8.1 W of output power and 30% of PAE at 30 GHz.
16 citations
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26 Jul 2016-Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
TL;DR: In this article, the influence of process pressure and N2 concentration has been evaluated by means of spectroscopic ellipsometry, residual stress measurements, xray diffraction, atomic and piezoresponse force microscopy, along with analysis of the piezoelectric charge coefficient d33,f.
Abstract: Aluminum nitride (AlN) thin films deposited by reactive radio frequency magnetron sputtering in an Ar/N2 discharge on Si(001) substrates were studied with respect to structure, stress, and piezoelectric properties. In order to optimize the AlN layers for flexural plate wave (FPW) devices, the influence of process pressure and N2 concentration has been evaluated by means of spectroscopic ellipsometry, residual stress measurements, x-ray diffraction, atomic and piezoresponse force microscopy, along with analysis of the piezoelectric charge coefficient d33,f. FPW devices with low compressively stressed (−200 to −300 MPa) AlN layers were prepared and characterized by white light interferometry and Raman measurements. With increasing pressure from 3×10−3 to 8×10−3 mbar, a transition from −840 MPa compressive stress to +300 MPa tensile stress was measured. Increasing the nitrogen concentration from 3.3% to 50% resulted in a change in stress from +150 to −1170 MPa. All films exhibited a high degree of c-axis ori...
16 citations
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19 Apr 2006
TL;DR: In this article, a novel semiconductor material, called InN, was used as THz surface emitter and the material was irradiated with fs-laser pulses at 1060 nm and 800 nm and the emitted ultrashort THz pulses were measured by phase sensitive detection.
Abstract: InN, a novel semiconductor material, is used as THz surface emitter. The material is irradiated with fs-laser pulses at 1060 nm and 800 nm and the emitted ultrashort THz pulses are measured by phase sensitive detection. Pulsforms, amplitudes and spectra are compared to the THz emission of p-doped InAs, the standard material for THz surface emission.
16 citations
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TL;DR: In this paper, the fabrication and performance of common-source (CS) and common-gate transistors for operation at millimeter-wave frequencies are presented, and the advantages of the dual-gate (DG) devices in power gain over the CS high electron mobility transistors are discussed.
Abstract: In this paper, the fabrication and performance of common-source (CS) and common-gate transistors for operation at millimeter-wave frequencies are presented. The AlGaN/GaN devices have a gate length of 100 nm and yield a high maximum transconductance of above 550 mS/mm with a very low contact resistance of less than 0.12 Ω·mm. The baseline technology with its optimized epitaxial structures and their transition frequency of more than 80 GHz allows reproducible designs for monolithic microwave integrated circuits up to the W-band frequency range (75-110 GHz). In addition, GaN dual-gate (DG) devices were developed for substantial improvement of the bandwidth of the devices and of the gain per stage on circuit level. This paper discusses the advantages of the DG devices in power gain over the CS high electron mobility transistors for millimeter-wave applications.
16 citations
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TL;DR: A multilayered stacked patch antenna on quartz with a dielectric lens, functioning in tandem with a GaAs-based multiplier chain, for applications operating in the frequency region around 300 GHz.
Abstract: This paper presents a novel transmitter system for applications operating in the frequency region around 300 GHz. A relatively simple packaging approach is taken, allowing for a variety of integrated or embedded applications. This paper presents a multilayered stacked patch antenna on quartz with a dielectric lens, functioning in tandem with a GaAs-based multiplier chain. When operating, an input signal between 7.8 and 8.6 GHz is multiplied 36 times to a frequency range between 280 and 310 GHz, via two in-house fabricated GaAs-based monolithic microwave integrated circuits (MMICs). The antenna is fabricated on quartz wafers via an in-house process. Both, the MMICs and the antenna, are placed on a printed circuit board. A high-density polyethylene lens encloses the system-in-package (SiP), with a footprint of 1 cm $^{2}$ . The SiP has a center frequency of 300 GHz and an absolute pattern bandwidth of 21 GHz. The measured antenna gain along the broadside is 23 dBi, which corresponds to an equivalent isotropic radiated power of 20 dBm. This is achieved with 0.3 W power consumption. The design, simulation, and the analysis are performed via an electromagnetic simulation and modeling tool (Computer Simulation Technology Microwave Studio). Both, separate measurement data for the individual parts of the SiP and complete system experimental characterization are included in this paper.
16 citations
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TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
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 …
33,785 citations
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TL;DR: 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 her own research.
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
7,563 citations
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TL;DR: In this paper, the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method, is reviewed.
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.
6,917 citations
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TL;DR: In this article, the authors present a comprehensive, up-to-date compilation of band parameters for the technologically important III-V zinc blende and wurtzite compound semiconductors.
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.
6,349 citations
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TL;DR: This review gives a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells, and discusses the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid 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.
6,059 citations