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Operation Frequency (operation + frequency)
Selected AbstractsStrain-engineered novel III,N electronic devices with high quality dielectric/semiconductor interfacesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003M. Asif Khan Abstract Since the early demonstration of 2D-electron gas [M. A. Khan et al., Appl. Phys. Lett. 60, 3027 (1992)] and a heterojunction field effect transistor (HFET) [M. Asif Khan et al., Appl. Phys. Lett. 63, 1214 (1993)] in III,N materials, rapid progress has been made to improve the DC and RF performance of GaN,AlGaN based HFETs. Stable and impressive microwave powers as high as 4,8 W/mm have been reported for device operation frequencies from 10 to 35 GHz. The key reason for these high performance numbers is an extremely large sheet carrier densities (>1 × 1013 cm,2) that can be induced at the interfaces in III,N hetereojunction [A. Bykhovsk et al., J. Appl. Phys. 74, 6734 (1993); M. Asif Khan et al., Appl. Phys. Lett. 75, 2806 (1999)]. These are instrumental in screening the channel dislocations thereby retaining large room temperature carrier mobilities (>1500 cm2/Vs) and sheet resistance as low as 300 ,/sq. These numbers and the high breakdown voltages of the large bandgap III,N material system thus enable rf-power approximately 5,10 times of that possible with GaAs and other competitor's technologies. We have recently introduced a unique pulsed atomic layer epitaxy approach to deposit AlN buffer layers and AlN/AlGaN superlattices [J. Zhang et al., Appl. Phys. Lett. 79, 925 (2001); J. P. Zhang et al., Appl. Phys. Lett. 80, 3542 (2002)] to manage strain and decrease the dislocation densities in high Al-content III,N layers. This has enabled us to significantly improve GaN/AlGaN hetereojunctions and the device isolation. The resulting low defect layers are not only key to improving the electronic but also deep ultraviolet light-emitting diode devices. For deep UV LED's they enabled us to obtain peak optical powers as high as 10 mW and 3 mW for wavelengths as short as 320 nm and 278 nm. Building on our past work [M. Asif Khan et al., Appl. Phys. Lett. 77, 1339 (2000); X. Hu et al., Appl. Phys. Lett. 79, 2832 (2001)] we have now deposited high quality SiO2/Si3N4 films over AlGaN with low interface state densities. They have then been used to demonstrate III,N insulating gate transistors (MOSHFET (SiO2) and MISHFET (Si3N4) with gate leakage currents 4,6 order less than those for conventional GaN,AlGaN HFETs. The introduction of the thin insulator layers (less then 100 Å) under the gate increases the threshold voltage by 2,3 V. In addition, it reduces the peak transconductance gm. However the unity cut-off frequency, the gain and the rf-powers remain unaffected as the gm/Cgs (gate-source capacitance) ratio remains unchanged. In addition to managing the defects and gate leakage currents we have also employed InGaN channel double heterojunction structures (AlInGaN,InGaN,GaN) to confine the carriers thereby reducing the spillover into trappings states. These InGaN based MOS-DHFETs exhibited no current-collapse, extremely low gate leakage currents (<10,10 A/mm) and 10,26 GHz rf-powers in excess of 6 W/mm. We have also demonstrated the scalability and stable operation of our new and innovative InGaN based insulating gate heterojunction field effect transistor approach. In this paper we will review the III,N heterojunction field-effect transistors progress and pioneering innovations including the excellent work from several research groups around the world. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Contactless passive diagnosis for brain intracranial applications: A study using dielectric matching materialsBIOELECTROMAGNETICS, Issue 5 2010Ioannis A. Gouzouasis Abstract A prototype system for passive intracranial monitoring using microwave radiometry is proposed. It comprises an ellipsoidal conductive wall cavity to achieve beamforming and focusing, in conjunction with sensitive multiband receivers for detection. The system has already shown the capability to provide temperature and/or conductivity variations in phantoms and biological tissue. In this article, a variant of the initially constructed modality is theoretically and experimentally investigated. Specifically, dielectric matching materials are used in an effort to improve the system's focusing attributes. The theoretical study investigates the effect of dielectric matching materials on the system's detection depth, whereas measurements with phantoms focus on the investigation of the system's detection level and spatial resolution. The combined results suggest that the dielectric matching layers lead to the improvement of the system's detection depth and temperature detection level. Also, the system's spatial resolution is explored at various experimental setups. Theoretical and experimental results conclude that with the appropriate combination of operation frequencies and dielectric layers, it is possible to monitor areas of interest inside human head models with a variety of detection depths and spatial resolutions. Bioelectromagnetics 31:335,349, 2010. © 2010 Wiley-Liss, Inc. [source] Gain,bandwidth limitations of microwave transistorINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 6 2002Filiz Güne Abstract This work enables one to obtain the potential gain (GT) characteristics with the associated source (ZS) and load (ZL) termination functions, depending upon the input mismatching (Vi), noise (F), and the device operation parameters, which are the configuration type (CT), bias conditions (VDS, IDS), and operation frequency (f). All these functions can straightforwardly provide the following main properties of the device for use in the design of microwave amplifiers with optimum performance: the extremum gain functions (GT max, GT min) and their associated ZS, ZL terminations for the Vi and F couple and the CT, VDS, IDS, and f operation parameters of the device point by point; all the compatible performance (F, voltage,standing wave ratio Vi, GT) triplets within the physical limits of the device, which are F , Fmin, Vi , 1, GT min , GT , GT max, together with their ZS, ZL termination functions; and the potential operation frequency bandwidth for a selected performance (F, Vi, GT) triplet. The selected performance triplet and termination functions can be realized together with their potential operation bandwidth using the novel amplifier design techniques. Many examples are presented for the potential gain characteristics of the chosen low-noise or ordinary types of transistor. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12, 483,495, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce.10049 [source] A 57-GHz CMOS VCO with 185.3% tuning-range enhancement using tunable LC source-degenerationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2009Chuan-Wei Tsou Abstract A 57-GHz CMOS voltage-controlled oscillator (VCO) using tunable LC source-degeneration for operation frequency and tuning-range enhancement is demonstrated. The tunable LC source-degeneration is made by adding two tunable LC tanks, where varactors are used as the needed capacitors, to the source terminals of the cross-coupled transistor pair of the VCO. Compared with the traditional cross-coupled transistor pair, the proposed one significantly decreases the equivalent parallel capacitance (CEQ). This in turn results in the increase of both the operation frequency and the tuning range of the VCO. The measurement result shows the tunable LC source-degeneration achieved a 185.3% enhancement [from 1.36 GHz (53.36,54.72 GHz) to 3.88 GHz (53.36,57.24 GHz)] in tuning range by tuning the varactors of the proposed cross-coupled transistor pair. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2682,2685, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24706 [source] Microwave characteristics of substrate integrated waveguide photodetectorMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2009Ebrahim Mortazy Abstract In this article, using a novel structure, simulated and measured microwave characteristics from substrate integrated waveguide photodetector (SIWPD) are obtained and compared with the conventional microstrip waveguide photodetector. A Ka-band microstrip to rectangular waveguide multilayer transition for OC-768/STM-256 optical systems is designed and fabricated. Attenuation constant results shows that by replacing substrate integrated waveguide (SIW) instead of conventional microstrip in waveguide photodetectors, operation frequency can be increased. Microwave fields in the proposed structure show a good transition from quasi-TEM mode to TE10 mode in multilayer structure. The multilayer structure is considered to separate SIW and DC bias of the photodetector. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2204,2207, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24528 [source] | ||||||||||