Analysis of a Disc-Loaded Circular Waveguide for Interaction Impedance of a Gyrotron Amplifier

A rigorous electromagnetic analysis of a circular waveguide loaded with axially periodic annular discs was developed in the fast-wave regime, considering finite axial disc thickness and taking into account the effect of higher order space harmonics in the disc-free region and higher order modal harmonics in the disc-occupied region of the structure. The quality of the disc-loaded circular waveguide was evaluated with respect to its azimuthal interaction impedance that has relevance to the gain of a gyrotron millimeter-wave amplifier (gyro-traveling-wave tube) in which such a loaded waveguide finds application as a wideband interaction structure. The results of electromagnetic analysis of the structure with respect to both the dispersion and azimuthal interaction impedance characteristics were validated against the commercially available code: high frequency structure simulator (HFSS). The analysis predicts that the value of the interaction impedance at a given frequency decreases with the increase of the disc hole radius and disc periodicity. The change of the axial disc thickness does not significantly change the value of the interaction impedance though it shifts the frequency range over which appreciable interaction impedance is obtained. Out of the three disc parameters, namely the disc hole radius, thickness and periodicity, the lattermost is most effective in controlling the value of the azimuthal interaction impedance. However, the passband of frequencies and the center frequency of the passband both decrease with the increase of the disc periodicity. Moreover, the disc periodicity that provides large azimuthal interaction impedance would in general be different from that giving the desired dispersion shape for wideband interaction in a gyro-TWT, suggesting a trade-off in the value of the disc periodicity to be chosen.     

Novel Quantum Dot Gate FETs and Nonvolatile Memories Using Lattice-Matched II–VI Gate Insulators

This paper presents the successful use of ZnS/ZnMgS and other II–VI layers (lattice-matched or pseudomorphic) as high-k gate dielectrics in the fabrication of quantum dot (QD) gate Si field-effect transistors (FETs) and nonvolatile memory structures. Quantum dot gate FETs and nonvolatile memories have been fabricated in two basic configurations: (1) monodispersed cladded Ge nanocrystals (e.g., GeO _x -cladded-Ge quantum dots) site-specifically self-assembled over the lattice-matched ZnMgS gate insulator in the channel region, and (2) ZnTe-ZnMgTe quantum dots formed by self-organization, using metalorganic chemical vapor-phase deposition (MOCVD), on ZnS-ZnMgS gate insulator layers grown epitaxially on Si substrates. Self-assembled GeO _x -cladded Ge QD gate FETs, exhibiting three-state behavior, are also described. Preliminary results on InGaAs-on-InP FETs, using ZnMgSeTe/ZnSe gate insulator layers, are presented.     

Optical backbone and control of attocell network

Photonic Network Communications - For serving futuristic applications like distributed robotic systems with robots equipped with humanoid intelligence, wireless access to high-performance computing...     

A source degenerated LC quadrature VCO (SD-QVCO) using 0.18-μm SiGe BiCMOS

This letter presents a fully integrated BiCMOS quadrature voltage-controlled oscillator (QVCO). The QVCO consists of two nMOSFET cross-coupled oscillator stacked in series with source degenerated HBT transistors. SiGe HBT introduces low flicker noise compared to CMOS devices. To generate quadrature phase signals with strong coupling strength, the proposed design uses two MOS-coupled LC-tank cores instead of passive device-coupled cores. This source degeneration topology can improve the phase noise performance of the QVCO as compared to the sub-VCO. The proposed QVCO has been implemented with the TSMC 0.18 μm SiGe 3P6M BiCMOS process, can generate quadrature signals in the frequency range of 4.52–5.05 GHz with core power consumption of 5.76 mW at the dc bias of 1.8 V. At 4.53 GHz, phase noise at 1 MHz offset is ?124.52 dBc/Hz. The die area of the fabricated prototype is 0.453 × 0.898 mm².     

A single-stage zero-voltage zero-current-switched full-bridge DCpower supply with extended load power range

A single-stage power-factor-corrected pulsewidth modulation power converter with extended load power range is presented. The topology is based on a zero-voltage zero-current-switched full-bridge (ZVZCS-FB) inverter. Steady-state analysis of the topology shows that by operating the LC load filter in discontinuous mode, the DC-link voltage remains bounded and independent of the load level. Therefore, the load power range can be further expanded, including the no-load operating condition. The analysis also shows that the extension of the load power range is achieved without any penalty in: (1) the input power factor (due to the input current waveshaping feature); (2) the power converter efficiency (due to ZVZCS and the single-stage features); and (3) the load voltage quality (due to the high bandwidth of the phase control loop). Simulated and experimental results are included to show the feasibility of the proposed scheme     

Temperature-controlled and constant-power radio-frequency ablation: what affects lesion growth?

Radio-frequency (RF) catheter ablation is the primary interventional therapy for the treatment of many cardiac tachyarrhythmias. Three-dimensional finite element analysis of constant-power (CPRFA) and temperature-controlled RF ablation (TCRFA) of the endocardium is performed. The objectives are to study: 1) the lesion growth with time and 2) the effect of ground electrode location on lesion dimensions and ablation efficiency. The results indicate that: a) for TCRFA: i) lesion growth was fastest during the first 20 s, subsequently the lesion growth slowed reaching a steady state after 100 s, ii) positioning the ground electrode directly opposite the catheter tip (optimal) produced a larger lesion, and iii) a constant tip temperature maintained a constant maximum tissue temperature; b) for CPRFA: i) the lesion growth was fastest during the first 20 s and then the lesion growth slowed; however, the lesion size did not reach steady state even after 600 s suggesting that longer durations of energy delivery may result in wider and deeper lesions, ii) the temperature-dependent electrical conductivity of the tissue is responsible for this continuous lesion growth, and iii) an optimal ground electrode location resulted in a slightly larger lesion and higher ablation efficiency.     

The effect of deterministic spatial variations in retrograde wellimplants on shallow trench isolation for sub-0.18 μm CMOS technology

The high energy retrograde well implants for sub-0.18 microns CMOS are done at a normal or near normal incidence to minimize the shadowing due to the thick photoresist edges. The endstation geometry in a high energy implanter results in an incident angle variation across the wafer, which causes strong spatial variations in the well profile and can negatively impact device performance. We show that the spatial variations can have significant impact on shallow trench isolation (STI), by causing in a deterministic pattern the failure of STI devices on a wafer. These spatial variations are important and need to be taken into consideration for STI design     

Nonlinear Eulerian Analysis of Harmonic Generation in Traveling-Wave Tubes

A third-order nonlinear Eulerian hydrodynamic formulation was developed for the analysis of harmonic generation in helix traveling-wave tubes. The analysis was simple and computationally fast compared to Lagrangian analysis, and contrary to the existing belief, the theory could as well demonstrate the saturation behavior of the device. The performance of the theory was also found to be in close agreement with that of the Lagrangian analysis. The theory is expected to be useful as a first-hand design and simulation tool for microwave and millimetric wave traveling-wave tubes.     

Plastic Flow and Dislocation Compensation in ZnS y Se1?y /GaAs (001) Heterostructures

An important goal of lattice-mismatched semiconductor device design is control of threading dislocation densities, which are of particular importance for optoelectronic devices such as photodetectors and light-emitting diodes. The basis for this field of research is an understanding of the dislocation dynamics in mismatched heteroepitaxial structures. We have developed a dislocation dynamics model including dislocation multiplication, misfit–threading dislocation interactions, annihilation and coalescence, and thermal strain, which can be used to understand the strain relaxation and threading dislocation densities in arbitrarily graded ZnS _y Se_1?y /GaAs (001) structures. On the basis of this model, we demonstrate that the dislocation compensation mechanism, whereby mobile threading dislocations can be removed by insertion of a mismatched interface in a graded structure, can be explained by the bending over of threading dislocations associated with misfit segments of one sense by misfit dislocations having the opposite sense. Dislocation compensation, if utilized in device structures, can provide a pathway for the attainment of devices with low threading dislocation densities (D?<?10⁶?cm^?2) while using the minimum total thickness of epitaxial material, with a reduction in deposition time and source chemicals.