Impact of Gate Offset in Gate Recess on DC and RF Performance of InAlAs/InGaAs InP-based HEMTs

In this work, a set of 100-nm gate-length InP-based HEMTs were designed and fabricated with different gate offsets in gate recess. A novel technology was proposed for independent definition of gate recess and T-shaped gate by electron beam lithography. DC and RF measurement was conducted. With the gate offset varying from drain side to source side, the maximum drain current (Ids,max) and transconductance (gm,max) increased. In the meantime, f T decreased while f max increased, and the highest f max of 1096 GHz was obtained. It can be explained by the increase of gate-source capacitance and the decrease of gate-drain capacitance and source resistance. Output conductance was also suppressed by gate offset toward source side. This provides simple and flexible device parameter selection for HEMTs of different usage.

Frequency and mode measurement techniques for megawatt-class gyrotrons

State-of-the-art vacuum electron tubes such as gyrotrons, deliver RF output powers up to more than 2 MW at frequencies up to 170 GHz. In terms of the very high power levels, a proper verification of the gyrotron components itself and measurements during gyrotron operation are vital to prevent possible fatal errors. Several basic RF measurement setups, which are used at IHM/KIT, are discussed. Currently, their upper frequency limit is 175 GHz. In terms of future gyrotron operation above 200 GHz, upgrades of the measurement setups for operation up to 260–330 GHz are prepared. The experimental devices discussed herein are a quasi-optical mode generator for the verification of the quasi-optical gyrotron output system, the window measurement test stand to verify the ceramic gyrotron output window and the frequency diagnostic system to measure the operating frequency and thereby the excited mode.

Performance Analysis and Validation of Precision Multisatellite RF Measurement Scheme for Microsatellite Formations

Almost all existing studies on inter-satellite radio frequency (RF) measurement have focused on two-satellite formations. Although some frequency division multiple access and code division multiple access multisatellite RF measurement schemes have been proposed, their poor scalability does not satisfy the inter-satellite measurement requirements of multisatellite formations, especially large-scale formations. Two-way ranging (TWR), which is based on a time division mechanism, is an effective solution that has been used for inter-satellite links in the global positioning system and Beidou navigation constellations. However, the high measurement accuracy achieved with TWR in these navigation constellations is heavily reliant on high-performance atomic clocks and the assistance of navigation ephemeris, which are not available on microsatellite platforms. This work focuses on a scalable multisatellite measurement scheme that adopts a distributed broadcast-based time division multiple access mechanism as the media access control layer and uses an asymmetric double-side TWR method as the physical layer. The measurement performance of the proposed scheme is evaluated through in-depth theoretical modeling, simulation verification, and experimental validation, along with a comprehensive comparison with the conventional TWR method. The experimental results show that centimeter-level measurement accuracy can be achieved with the proposed scheme when only a common miniaturized frequency source is used. This accuracy level is two orders of magnitude better than that of the TWR method, and thus satisfies the application requirements of general large-scale microsatellite formations.

Realization of Accurate Load Impedance Characterization for On-Wafer TRM Calibration

In this paper, the uncertainty and the impact of imperfect load calibration standard for on-wafer Through-Reflect-Match calibration method are analyzed with the help of 3D electromagnetic simulations. Based on the finding that load impedance can lead to significant errors in calibration, an automatic algorithm to determine the complex impedance of the load standard is proposed. This method evaluates the resistance as well as the parasitic inductance introduced by the misalignment of the probe tip to the substrate pad at mm-wave frequencies or the non-precize load standard. The proposed algorithm was verified by practical measurement, and the results show that by incorporating actual load impedance into the calibration algorithm, the deviations of RF measurement results are greatly suppressed.

Resonance Frequency Assessment: The Challenge of Standardizing Heart Rate Variability Biofeedback Research

The resonance frequency (RF) is the rate at which a system, like the cardiovascular system, can be activated or stimulated for maximal variability. Precise RF measurement is needed to standardize training protocols to help researchers determine the importance of RF breathing in achieving clinical and optimal performance outcomes. Lehrer and colleagues have developed and standardized a psychometrically reliable RF measurement protocol that can facilitate training and replication. This article provides a detailed description of their protocol and explains the nuanced decision-making process involved in identifying the RF. The validity and reproducibility of results using this protocol depend on quality control in (a) confirming that individuals successfully follow a breathing pacer, and (b) manually removing artifacts from data records. While this protocol requires an electrocardiogram or photoplethysmograph sensor and a respirometer, professionals should consider the addition of autonomic, musculoskeletal, and respiratory measures to better understand the patterns of physiological activity produced by different breathing rates.

Thermal and efficiency droop in InGaN/GaN light-emitting diodes: decoupling multiphysics effects using temperature-dependent RF measurements

Multiphysics processes such as recombination dynamics in the active region, carrier injection and transport, and internal heating may contribute to thermal and efficiency droop in InGaN/GaN light-emitting diodes (LEDs). However, an unambiguous methodology and characterization technique to decouple these processes under electrical injection and determine their individual roles in droop phenomena is lacking. In this work, we investigate thermal and efficiency droop in electrically injected single-quantum-well InGaN/GaN LEDs by decoupling the inherent radiative efficiency, injection efficiency, carrier transport, and thermal effects using a comprehensive rate equation approach and a temperature-dependent pulsed-RF measurement technique. Determination of the inherent recombination rates in the quantum well confirms efficiency droop at high current densities is caused by a combination of strong non-radiative recombination (with temperature dependence consistent with indirect Auger) and saturation of the radiative rate. The overall reduction of efficiency at elevated temperatures (thermal droop) results from carriers shifting from the radiative process to the non-radiative processes. The rate equation approach and temperature-dependent pulsed-RF measurement technique unambiguously gives access to the true recombination dynamics in the QW and is a useful methodology to study efficiency issues in III-nitride LEDs.