Dynamic, self consistent electro-thermal simulation of power microwave devices including the effect of surface metallizations

We present an efficient simulation technique to account for the thermal spreading effects of surface metallizations in the self-consistent dynamic electro-thermal analysis of power microwave devices. Electro-thermal self-consistency is achieved by solving the coupled nonlinear system made of a temperature dependent device electrical model, and of an approximate description of the device thermal behavior through a thermal impedance matrix. The numerical solution is pursued in the frequency domain by the Harmonic Balance technique. The approach is applied to the thermal stability analysis of power AlGaAs/GaAs HBTs and the results show that metallizations have a significant impact on the occurrence of the device thermal collapse

Linking X Parameters to Physical Simulations for Design-Oriented Large-Signal Device Variability Modeling

We propose various techniques extending X parameters to include the effect of active microwave device variability by exploiting TCAD simulations. We discuss two possible implementations into Agilent ADS. Both approaches are validated against full microwave amplifier TCAD simulations

Cyclostationary noise modeling of radio frequency devices

We present a review of the current status of research in the modeling and simulation of cyclostationary (nonlinear) noise properties of semiconductor active devices operated in forced large-signal conditions, a typical operating regime for high-frequency applications. We discuss both the case of physics-based device simulations, where numerical burden is the most important issue, and the derivation of compact cyclostationary noise models. In the latter case, both phenomenological amplitude modulation approaches and the derivation of consistent analytical device descriptions are discussed. We show examples of both physics-based simulations of the noise properties of a realistic high-electron mobility transistor resistive mixer and show for the first time the application of a novel, fully analytical cyclostationary noise bipolar transistor model

Global Assessment of PA variability through concurrent Physics-based X-parameter and Electro-Magnetic simulations

The novel technique introduced in [1] is exploited to address a full variability analysis of a GaAs MMIC X-band power amplifier, including the statistical variations of several technological parameters, both in the active and passive components. The active device is modelled by means of X-parameters, directly extracted from physics-based analysis. A non-50 O X-Par model is used to take into account the input port mismatch with respect to the conventional 50 O reference. The scattering parameters of the passive structures are extracted from accurate electromagnetic simulations and then imported into the circuit simulator through data intercharge files (e.g. MDIF or CITIfile) as a function of the most important MMIC fabrication parameters, e.g. the thickness of the MIM capacitor dielectric layer. The analysis shows that more than 10% of output power variations can be ascribed to the concurrent MIM and doping variations in conventional GaAs MMIC technology

PA design and statistical analysis through X-par driven load-pull and EM simulations

Modeling the active device is a key step for the successful statistical analysis of power amplifiers: the nonlinear model must not only depend on the most relevant device fabrication parameters, but should also work accurately in source/load-pull analysis, since variations of the passive embedding network effectively act as a load-pull at the active device ports. We demonstrate that the X-parameter model extracted from physics-based nonlinear TCAD simulations is extremely accurate for load-pull analysis. The X-parameter model is coupled to electromagnetic simulations to assist the variability-aware design of a GaAs MMIC X-band power amplifier (PA): concurrent variations of the active device doping and of the capacitor dielectric layer thickness are considered as the main contributions to PA variability. Two possible output matching networks, with distributed or semi-lumped design, are compared: already for moderate doping variations the PA output power spread is dominated by the active device variability, while passive network variations are always the relevant contribution to PA efficiency

Evaluating the Impedance Field through several transport models: a comparison

J. APPL. PHYS

Physics-based modeling of FinFET RF variability

This paper presents the physics-based variability analysis of multi-fin double-gate (DG) MOSFETs, representing the core structure of FinFETs for RF applications. The variability of the AC parameters as a function of relevant geometrical and physical parameters, such as the fin width, the fin separation, the source (drain)-gate distance and the doping level is investigated. The analysis exploits a numerically efficient Green’s Function technique [1]-[2], extending to the RF case the linearized approach well known from DC variability analysis. The variability of a single fin DG-MOS transistor is compared to a more realistic structure with two fins and raised source/drain contacts, i.e. including both the active part of the FinFET and a significant amount of passive (parasitic) components at the device level. Although presently implemented in a 2D in-house software, the technique can be easily exported to standard 3D TCAD tools, e.g. for tri-gate FinFETs analysis

Anomalous AMS radiocarbon ages for foraminifera from high-deposition-rate ocean sediments

Radiocarbon ages on handpicked foraminifera from deep-sea cores are revealing that areas of rapid sediment accumulation are in some cases subject to hiatuses, reworking and perhaps secondary calcite deposition. We present here an extreme example of the impacts of such disturbances. The message is that if precise chronologies or meaningful benthic planktic age differences are to be obtained, then it is essential to document the reliability of radiocarbon ages by making both comparisons between coexisting species of planktomc foraminifera and detailed down-core sequences of measurements