Thermal and electro-thermal modeling of electronic devices and systems for high-power and high-frequency applications

Questo lavoro è incentrato sulla modellazione termica ed elettro-termica di dispositivi elettronici per applicazioni ad alta potenza ed alta frequenza. Quattro argomenti principali vengono affrontati: 1) il metodo agli Elementi Finiti (FEM) viene impiegato per studiare gli aspetti termici e fluido-termo-dinamici in alimentatori di potenza progettati per funzionare, con vincoli termici stringenti, in esperimenti di Fisica delle Alte Energie. 2) Un’ampia analisi è stata effettuata riguardo alla modellazione auto-consistente, elettro-termica a grande segnale di dispositivi elettronici, con la creazione di modelli termici dinamici, non-lineari, a parametri concentrati (costruiti con resistenze e capacità termiche), che si possono utilizzare con simulatori circuitali in maniera tale da poter essere accoppiati in modo auto-consistente con modelli (tipo SPICE) elettro-termici, a grande segnale dei dispositivi elettronici (HEMTs, MOSFETs). Questi modelli termici a parametri concentrati sono costruiti basandosi sulla struttura fisica del dispositivo, senza parametri di fitting, e sono stati confrontati con modelli FEM equivalenti (che invece non possono essere usati in simulatori circuitali assieme a modelli elettrotermici dei componenti), con eccellente accordo tra i due modelli. Quando l’approccio fisico non si può utilizzare, un metodo empirico per ricavare una rete dinamica compatta tipo Foster viene illustrato. 3) Il progetto di un banco di misura della temperatura su componenti integrati mediante tecnica di termo-riflettanza (ad alta risoluzione spaziale) viene illustrato. 4) Il progetto di un banco elettronico per la generazione di impulsi ad alta tensione (kV), con durata dell’ordine dei nanosecondi, da utilizzarsi in applicazioni biomedicali, assieme alla costruzione ed al collaudo di alcune sue parti, vengono illustrati.This work is focused on the thermal and electro-thermal modeling of electronic devices for high-power and high-frequency applications. This work covers four main topics: 1) the Finite Element Method (FEM) is used to study thermal and fluid-thermal aspects in power supplies, designed to meet stringent thermal constraints, to be used in High-Energy Physics Experiments. 2) An extensive analysis has been carried out about the self-consistent, electro-thermal large-signal modeling of electron devices, with the creation of non-linear, dynamic lumped-element (LE) thermal models (made of thermal resistances and thermal capacitances) suitable to insertion into circuit CAD tools, to be self-consistently coupled with large-signal, electro-thermal SPICE-like models of electron devices (HEMTs, MOSFETs). These LE thermal models are built in a physics-based way, and they were found to be in excellent agreement with Finite Element models (which, conversely, do not lend themselves to insertion into circuit-CAD tools), without using fitting parameters. When the physics-based approach is not suitable, an empirical approach to the creation of compact Foster dynamic LE models is shown. 3) The design of a bench for carrying out high-spatial resolution temperature measurements (on integrated components), using the thermo-reflectance technique, is illustrated. 4) The design of an electronic bench capable of generating high-voltage (kV), nano-second time duration pulses for biomedical applications is described, as well as the manufacturing and the assembly of some parts

Strain rate influence on the thermo-mechanical deformation behavior of Aluminum thin films

Thin metal films used as top metallization in power semiconductor applications may repetitively undergo rapid temperature changes with heating rates reaching 106 K/s. It is well known that the mismatch of the coefficients of thermal expansion between metal and substrate causes stresses in the films, and this effect may lead to their thermo-mechanical fatigue. The stress vs. temperature behavior of such film-on-substrate combinations is mostly analyzed using X-ray diffraction or wafer-curvature-based methods. Both classes of methods can generally only be applied for analyzing materials undergoing slow temperature changes, either due to experimental constraints, e.g. measurement times in the XRD, or due to problems with stress calculation, e.g. Stoney formula being only valid for homogeneously heated specimens. It is questionable if the material response at low and high heating rates is comparable; hence, the development of methods to monitor the material behavior in a situation close to the application conditions is needed. A novel setup which allows measuring wafer curvature during rapid temperature changes has recently been developed 1, allowing the rapid heating of the tested metallizations using Joule heating and the simultaneous measurement of specimen curvature using either a high speed camera or laser scanning Doppler vibrometer. Using this setup, heating rates between 102 and 105 K/s can be utilized, to study the effect of cyclic heating with various temperature amplitudes and repetition rates on the metallization behavior. The stress-temperature behavior measured in such films is compared to the results obtained by standard wafer curvature experiments conducted at heating rates of less than 1 K/s. When comparing films cycled at 10² K/s and 10-1 K/s, the measurement results show that below 85 °C the coatings deform elastically and an identical deformation behavior is observed. The good comparability of the material behavior in the elastic regime proves that the novel setup is able to correctly measure curvature at high heating rates. At temperatures above 85 °C, where plastic deformation sets in, significant differences are seen in the specimens, which are caused by the influence of the different time-dependent relaxation mechanisms active at such temperatures. Microstructural changes in the films undergoing cycling at various heating rates are monitored using scanning electron microscopy and confocal laser scanning microscopy. Finally, the advantages and disadvantages of the application of fast temperature cycling to measure the stress-temperature behavior are discussed. 1 T. Islam, J. Zechner, M. Bernardoni, M. Nelhiebel, and R. Pippan, Rev. Sci. Instrum. 88, 24709 (2017)

Non-linear thermal simulation at system level: Compact modelling and experimental validation

In this work, a general methodology to extract compact, non-linear transient thermal models of complex thermal systems is presented and validated. The focus of the work is to show a robust method to develop compact and accurate non-linear thermal models in the general case of systems with multiple heat sources. A real example of such a system is manufactured and its thermal behaviour is analyzed by means of Infra-Red thermography measurements. A transient, non-linear Finite-Element-Method based model is therefore built and tuned on the measured thermal responses. From this model, the transient thermal responses of the system are calculated in the locations of interest. From these transient responses, non-linear compact transient thermal models are derived. These models are based on Foster network topology and they can capture the effect of thermal non-linearities present in any real thermal system, accounting for mutual interaction between different power sources. The followed methodology is described, verification of the model against measurements is performed and limitations of the approach are therefore discussed. The developed methodology shows that it is possible to capture strongly non-linear effects in multiple-heat source systems with very good accuracy, enabling fast and accurate thermal simulations in electrical solvers

Ultra-thin oxide breakdown for OTP development in power technologies

AbstractOTP (One Time Programmable) memory in power technology enables electrical performance optimization together with area occupation reduction. In this paper, the aspects relative to the oxide breakdown (which is the key mechanism for memory programmability) are studied and applied to the development of an antifuse OTP cell in a 350 nm-CMOS power technology. The physical analysis of the degradation phases of an oxide layer is presented together with the physical models, exploited to foresee the device time-to-breakdown depending on applied voltage, oxide thickness etc. The achieved results are used in the development and reliable implementation of OTP cells in the target 350 nm-CMOS node

Deformation and fatigue behavior measurement of thin films undergoing thermomechanical loading at high strain rates – A novel test setup

The deformation and fatigue behavior of thin films on substrates undergoing either single or repetitive thermo-mechanical loading has been investigated extensively in the last years due to the high relevance for industrial applications, ranging from cutting tools to microelectronic devices. A popular method to evaluate the stresses occurring in the thin film during temperature cycling is to measure the change in the curvature of the thin film on the substrate during heating and cooling. From the change in curvature, knowing the elastic constants of the substrate and the film and substrate thickness, the stresses in the film can be calculated using Stoney’s formula. Such wafer-curvature measurements are generally conducted at slow heating rates lower than several 10 K/s. This is mainly due to experimental constraints, but also originates in the fact that Stoney’s formula is only valid if substrate and thin film have a homogeneous temperature, which will not be the case for high heating rates. In power semiconductors, short high power pulses cause material heating with rates in the range of 10e5 - 10e6 K/s. It is questionable if the material response at low and high heating rates is comparable, which necessitates the development of methods to monitor the material behavior at heating rates comparable to the ones occurring during usage. Therefore, a new wafer curvature measurement setup has been developed, where the curvature is measured from the reflection of incident parallel laser beams using a high speed camera, allowing much faster data acquisition rates than with conventional cameras. Thin metallization films deposited onto polysilicon and single crystalline Si are heated by Joule heating using a pulse generator allowing to vary pulse shape, length, repetition rate and power. This can be used to vary the heating rate between 10e2 and 10e5 K/s and can be utilized to study the effect of cyclic heating with various temperature amplitudes and frequencies on the metallization behavior. Besides the description of the test setup, an overview on the stress evaluation procedure, necessitating the use of finite element modeling is presented. Changes in material response are deduced from changes in the stress-temperature behavior of the thin films after either one temperature cycle, or after thermo-mechanical fatiguing. Microstructural and morphological changes in the coatings are investigated using SEM, FIB cross-sections and surface roughness measurements

Empirical and physical modeling of self-heating in power AlGaN/GaN HEMTs

This work shows results of dynamic lumped-element (LE) thermal modeling of power AlGaN/GaN HEMTs. A realistic 3D structure including top-side metals, GaN-Si thermal boundary resistance, die-attach, and source via hole is modeled using a finite-element (FE) tool, and the results are used to develop simplified LE dynamic thermal models. We show that the LE models can match the FE data with excellent accuracy

Feedback Control Simulation of PowerElectronic Converters for Renewable Energies

doi: 10.1109/ICCEP.2009.521202