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Author: Kaynak, Mehmet ×

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    Wide-angle scanning active transmit/receive reflectarray
    (London : IET, 2014) Chaloun, Tobias; Menzel, Wolfgang; Tabarani, Filipe; Purtova, Tatyana; Schumacher, Hermann; Kaynak, Mehmet; Luo, Qi; Gao, Steven; Starec, Rado; Ziegler, Volker
    A highly integrated phased array transmit/receive architecture is presented. Multilayer microstrip antennas with a scanning potential up to 60° are combined, on a common manifold, with SiGe MMICs including four RF channels each, together with the necessary digital control circuits. Power distribution and combining are realised by the concept of a folded planar reflectarray. This study also includes the necessary solutions for multilayer interconnects and efficient heat removal from the active circuits. To prove the concept, passive arrays with different fixed beam positions have been tested successfully; followed by a first active array demonstrating excellent scanning performance up to 60° both in E- and H-plane.
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    Non-isothermal phase-field simulations of laser-written in-plane SiGe heterostructures for photonic applications
    (London : Springer Nature, 2021) Aktas, Ozan; Yamamoto, Yuji; Kaynak, Mehmet; Peacock, Anna C.
    Advanced solid-state devices, including lasers and modulators, require semiconductor heterostructures for nanoscale engineering of the electronic bandgap and refractive index. However, existing epitaxial growth methods are limited to fabrication of vertical heterostructures grown layer by layer. Here, we report the use of finite-element-method-based phase-field modelling with thermocapillary convection to investigate laser inscription of in-plane heterostructures within silicon-germanium films. The modelling is supported by experimental work using epitaxially-grown Si0.5Ge0.5 layers. The phase-field simulations reveal that various in-plane heterostructures with single or periodic interfaces can be fabricated by controlling phase segregation through modulation of the scan speed, power, and beam position. Optical simulations are used to demonstrate the potential for two devices: graded-index waveguides with Ge-rich (>70%) cores, and waveguide Bragg gratings with nanoscale periods (100–500 nm). Periodic heterostructure formation via sub-millisecond modulation of the laser parameters opens a route for post-growth fabrication of in-plane quantum wells and superlattices in semiconductor alloy films.
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    Miniature switchable millimeter-wave BiCMOS low-noise amplifier at 120/140 GHz using an HBT switch
    (Basel : MDPI, 2019) Heredia, Julio; Ribó, Miquel; Pradell, Lluís; Wipf, Selin Tolunay; Göritz, Alexander; Wietstruck, Matthias; Wipf, Christian; Kaynak, Mehmet
    A 120-140 GHz frequency-switchable, very compact low-noise amplifier (LNA) fabricated in a 0.13 µm SiGe:C BiCMOS technology is proposed. A single radio-frequency (RF) switch composed of three parallel hetero junction bipolar transistors (HBTs) in a common-collector configuration and a multimodal three-line microstrip structure in the input matching network are used to obtain a LNA chip of miniaturized size. A systematic design procedure is applied to obtain a perfectly balanced gain and noise figure in both frequency states (120 GHz and 140 GHz). The measured gain and noise figure are 14.2/14.2 dB and 8.2/8.2 dB at 120/140 GHz respectively, in very good agreement with circuit/electromagnetic co-simulations. The LNA chip and core areas are 0.197 mm2 and 0.091 mm2, respectively, which supposes an area reduction of 23.4% and 15.2% compared to other LNAs reported in this frequency band. The experimental results validate the design procedure and its analysis. © 2019 by the authors.
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    Experiments on MEMS Integration in 0.25 μm CMOS Process
    (Basel : MDPI, 2018) Michalik, Piotr; Fernández, Daniel; Wietstruck, Matthias; Kaynak, Mehmet; Madrenas, Jordi
    In this paper, we share our practical experience gained during the development of CMOS-MEMS (Complementary Metal-Oxide Semiconductor Micro Electro Mechanical Systems) devices in IHP SG25 technology. The experimental prototyping process is illustrated with examples of three CMOS-MEMS chips and starts from rough process exploration and characterization, followed by the definition of the useful MEMS design space to finally reach CMOS-MEMS devices with inertial mass up to 4.3 μg and resonance frequency down to 4.35 kHz. Furthermore, the presented design techniques help to avoid several structural and reliability issues such as layer delamination, device stiction, passivation fracture or device cracking due to stress.
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    Advanced numerical investigation of the heat flux in an array of microbolometers
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Stocchi, Matteo; Mencarelli, Davide; Pierantoni, Luca; Göritz, Alexander; Kaynak, Canan Baristiran; Wietstruck, Matthias; Kaynak, Mehmet
    The investigation of the thermal properties of an array of microbolometers has been carried out by mean of two independent numerical analysis, respectively the Direct-Simulation Monte Carlo (DSMC) and the classic diffusive approach of the Fourier's equation. In particular, the thermal dissipation of a hot membrane placed in a low-pressure cavity has been studied for different values of the temperature of the hot body and for different values of the pressure of the environment. The results for the heat flux derived from the two approaches have then been compared and discussed.