W. Batty

Electrothermal CAD of power devices and circuits with fully physical time-dependent compact thermal modeling of complex nonlinear 3-d systems

An original, fully analytical, spectral domain decomposition approach is presented for the time-dependent thermal modeling of complex nonlinear (3-D) electronic systems, from metallized power FETs and MMICs, through MCMs, up to circuit board level. This solution method offers a powerful alternative to conventional numerical thermal simulation techniques, and is constructed to be compatible with explicitly coupled electrothermal device and circuit simulation on CAD timescales. In contrast to semianalytical, frequency space, Fourier solutions involving DFT-FFT, the method presented here is based on explicit, fully analytical, double Fourier series expressions for thermal subsystem solutions in Laplace transform s-space (complex frequency space). It is presented in the form of analytically exact thermal impedance matrix expressions for thermal subsystems. These include double Fourier series solutions for rectangular multilayers, which are an order of magnitude faster to evaluate than existing semi-analytical Fourier solutions based on DFT-FFT. They also include double Fourier series solutions for the case of arbitrarily distributed volume heat sources and sinks, constructed without the use of Greens function techniques, and for rectangular volumes with prescribed fluxes on all faces, removing the adiabatic sidewall boundary condition. This combination allows treatment of arbitrarily inhomogeneous complex geometries, and provides a description of thermal material nonlinearities as well as inclusion of position varying and non linear surface fluxes. It provides a fully physical, and near exact, generalized multiport network parameter description of nonlinear, distributed thermal subsystems, in both the time and frequency domains. In contrast to existing circuit level approaches, it requires no explicit lumped element, RC-network approximation or nodal reduction, for fully coupled, electrothermal CAD. This thermal impedance matrix approach immediately gives rise to minimal boundary condition independent compact models for thermal systems. Implementation of the time-dependent thermal model as N-port netlist elements within a microwave circuit simulation engine, Transim (NCSU), is described. Electrothermal transient, single-tone, two-tone, and multitone harmonic balance simulations are presented for a MESFET amplifier. This thermal model is validated experimentally by thermal imaging of a passive grid array representative of one form of spatial power combining architecture.

Electrothermal modeling and measurement for spatial power combining at millimeter wavelengths

In this paper, the first completely physical coupled electrothermal model, suitable for large-signal simulation of MESFET- and HEMT-based MMICs and MMIC arrays, on a timescale suitable for computer-aided design, is presented. The model is validated experimentally by high-resolution thermal imaging of a MMIC 38-GHz three-stage balanced amplifier, mounted on a Cu/FR-4 substrate and cooled entirely by natural convection and radiation into free space.

Global coupled EM-electrical-thermal simulation and experimental validation for a spatial power combining MMIC array

The first fully coupled electromagnetic-electro-thermal global simulation of a large microwave subsystem, here a whole spatial power combining MMIC array, is described. The modeling effort is supported by parallel developments in electro-optic and thermal measurement. The CAD tools and experimental characterisation described, provide a unique capability for the design of quasi-optical systems and for the exploration of the fundamental physics of spatial power combining devices.

Thermal transients in microwave active devices and their influence on intermodulation distortion

A fully physical transient thermal model is used to investigate the effects of temperature on the intermodulation distortion performance of microwave devices. A 24 mm, 60 finger PHEMT is used to compare measurements with predictions from the model. Results are in very good agreement and are a strong indication of thermally induced intermodulation distortion.

Electro-Thermal Modelling of Monolithic and Hybrid Microwave and Millimeter Wave IC's

The first completely physical electro-thermal model is presented that is capable of describing the large signal performance of MESFET- and HEMT-based, high power microwave and millimeter wave monolithic and hybrid ICs, on timescales suitable for CAD. The model includes the effects of self-heating and mutual thermal interaction on active device performance with full treatment of all thermal non linearities. The electrical description is provided by the rapid quasi-2D Leeds Physical Model and the steady-state global thermal description is provided by a highly accurate and computationally inexpensive analytical thermal resistance matrix approach. The order of the global thermal resistance matrix describing 3-dimensional heat flow in complex systems, is shown to be determined purely by the number of active device elements, not the level of internal device structure. Thermal updates in the necessarily iterative, fully coupled electro-thermal solution, therefore reduce to small matrix multiplications implying orders of magnitude speed-up compared to the use of full numerical thermal solutions capable of comparable levels of detail and accuracy.

Fully physical coupled electro-thermal simulations and measurements of power FETs

A fully physical coupled electro-thermal model is presented. It is fast, efficient, suitable for CAD applications and capable of describing power FETs, MMICs and MMIC arrays. Results are presented which show the model gives good agreement with measurements for large power devices.

Compact Electrothermal Modeling of an X-band MMIC

Compact electrothermal modeling of lumped electrical devices and compact thermal modeling of volumetric materials enables efficient electrothermal modeling of microwave circuits. The compact thermal model of the body of an X-band MMIC is based on analytical solutions of the heat diffusion equation in thermal sub-volumes. The model is accurate and captures thermal nonlinearities. The model considers complex MMIC features such as surface metallization and vias, as well as the mounting configurations including lead-frame, carrier, and printed circuit board. This is coupled with electrothermal models of transistors and of resistors. The models are incorporated in a multi-physics simulator that uses the same model in both transient and harmonic analysis of an X-band LNA MMIC. Simulations are validated with steady-state thermal measurements

Fully physical time-dependent compact thermal modelling of complex non linear 3-dimensional systems for device and circuit level electro-thermal CAD

An fully analytical spectral domain decomposition approach to solution of the nonlinear time-dependent heat diffusion equation in complex volumes is introduced. Its application to device/circuit level electro-thermal simulation on CAD timescales is illustrated. The full treatment in coupled electro-thermal CAD of thermal nonlinearity due to temperature dependent diffusivity is described. Thermal solutions are presented in the form of thermal impedance matrix expressions for thermal subsystems. These include double Fourier series solutions for rectangular multilayers, which are an order of magnitude faster to evaluate than existing semi-analytical Fourier solutions based on DFT-FFT. They also include double Fourier series solutions for arbitrarily distributed volume heat sources and sinks, constructed without use of Greens function techniques, and for rectangular volumes with prescribed fluxes on all faces. These analytical solutions allow treatment of arbitrary device structures without invoking conventional numerical methods. They provide minimal boundary condition independent compact thermal models, allowing CAD timescale coupled electro-thermal solution for complex systems, without requiring lumped element RC network extraction or node reduction. The time-independent thermal resistance matrix description of device structure is illustrated by a fully physical, coupled electro-thermal study of the interaction of substrate thickness and surface convection in power HEMTs. The thermal time-dependent implementation is illustrated by circuit level harmonic balance simulation of a 3/spl times/3 MMIC amplifier array.

Electro-thermal modelling of microwave transistors and MMICs for optimised transient and steady-state performance

The influence of the physical layout of MESFET-based MMICs, on active device temperature and I-V characteristics, is investigated. These transient and steady state simulations represent the first reported, fully physical, coupled electro-thermal studies on CAD timescales. Calculated temperature rises are compared against experimental results obtained by thermal imaging.

Global electrothermal CAD of complex nonlinear 3-D systems based on a fully physical time-dependent compact thermal model

An original spectral domain decomposition approach is presented for the time-dependent thermal modelling of complex, nonlinear, 3-dimensional systems. This fully analytical approach immediately gives rise to compact models of nonlinear distributed thermal subsystems, without requiring approximation by a lumped element RC network, or nodal reduction. In combination with any thermally self-consistent models of analogue, digital, RF and microwave, microelectromechanical or photonic devices, it supplies a CAD timescale description of mutual thermal interaction between power dissipating and temperature sensitive elements. It therefore has the potential for thermal description of the whole system-in-package. In combination with microwave circuit simulator, Transim (NCSU), the thermal model is applied to the self-consistent global electrothermal harmonic balance simulation of a spatial power combining power FET array. The model is validated by comparison of electrothermal simulation of a power HEMT against experimentally obtained thermal images.