Experimental validation of a thermal modelling method dedicated to multichip power modules in operating conditions

In this paper, we present an implementation of a thermal modelling method applied to a multichip module used as a power converter. Analytical functions of thermal impedances, with original formulations for the mutuals are defined. They are derived from 3D thermal simulations and experimental validations with direct chips temperature measurements. Finally, simulations are performed in order to improve the capability of our model to assess, with fast computation, the thermal constraints applied on the multichip module in a real operating condition.     

Physical study of the dissipated power area in high electron mobility transistors for thermal modelling

The hot area in power transistors due to the power dissipation is determined from a 2D-hydrodynamic model. The power is calculated everywhere in the device from the knowledge of the physical quantities (current density, electric field). The hot area is determined accurately to be coupled to a thermal modelling giving the temperature everywhere in the device [J. Park, M.-W Shin, C.-C. Lee, Thermal modeling and measurement of GaN-based HFET devices, IEEE Electron Device Lett. 24(7) (2003) 424-426 [1]; J.-C Jacquet, R. Aubry, H. Gérard, E. Delos, N. Rolland, Y. Cordier, A. Bussutil, M. Rousseau, S.L. Delage, Analytical transport model of AlGaN/GaN HEMT based on electrical and thermal measurement, 12th GAAS Symposium, Amsterdam, 2004, pp. 235-238 [2].]. The method is applied to HEMTs (high electron mobility transistors) based on GaAs or GaN. It is shown that the hot area depends on the bias conditions and on the transistor gate recess topology.     

Thermal modelling of Ohmic heating microreactors

This paper describes the static and transient thermal modelling of an Ohmic heating microreactor for biological sample processing for the purpose of genetic analysis. Precise thermal management can be used for the effective preparation of analyte DNA molecules prior to detection. Due to the small dimensions of the microreactor, the direct measurement and monitoring of the temperature distribution presents a challenge. To overcome this, thermal modelling has been used to accurately predict the thermal behaviour of the microreactor and sample component. It is further possible to calculate the required input power levels and provide design criteria to optimise the design of the microreactor.     

Thermal analysis of layered electronic circuits with Green's functions

This paper presents a method for thermal simulation of electronic circuits using an analytical solution of the three-dimensional heat equation resulting from an appropriate circuit thermal model. The temperature fields in multilayered structures are computed analytically employing the Green's functions solution method. The entire solution methodology is illustrated in detail on the particular examples of electronic circuits containing multiple heat sources. Compared to the previous papers published by the authors, the method has been extended by including the possibility of simulating imperfect layer contacts. The simulation results are validated with infra-red measurements and results obtained using other methods. Additionally, the discussion of simulation errors caused mainly by different non-linear phenomena is included.     

Dynamic electrothermal simulation of integrated resistors at device level

This paper presents the dynamic electrothermal simulation of a rectangular resistor integrated on a semi-conductor substrate. Due to the temperature dependence of the electrical conductivity of the resistive sheet, self-heating provokes a coupling between the electrical and thermal problem and gives rise to nonlinear phenomena. We introduce a time stepping iterative method to perform the calculations. The electrical and thermal solvers are based on FEM and Green's functions techniques, respectively. An extensive dynamic analysis of the device will be presented. The results include heating and cooling curves, Nyquist plot (complex locus) of the thermal impedance, time constant spectrum and structure function. Comparisons with the linear case, i.e. a temperature independent resistor, are made and accompanied by analytical approximations if possible. One key observation is that the nonlinearity may easily be overlooked: its detection is only possible in particular characteristics.     

Generalization of the thermal model of infrared radiation sensors

In many theories and applications, generalized models can give a good head start for further research where the implementation of new elements and/or boundary conditions could become quite complex. In this paper the development of a compact thermal model of an infrared sensor will be presented. This thermal model includes not only the thermal resistances and capacitances of the sensor structure itself but the radiative and convective thermal resistances to the ambience and between the sensor plate and the heat source (thermal transfer impedance) which is important when the heat source and the sensor are in close proximity. Limitations and the applicability of the proposed model are also discussed. We also aim to present how the proposed model can be used for other IR sensor structures as well.     

慢波组件散热性能研究的发展现状

综合叙述了目前人们为提高螺旋线行波管慢波组件的散热性能而在装配方法、组件材料以及夹持杆的结构这三方面所进行的研究。     

Monitoring the operation of a graphene transistor in an integrated circuit by XPS

One of the transistors in an integrated circuit fabricated with graphene as the current controlling element, is investigated during its operation, using a chemical tool, XPS. Shifts in the binding energy of C1s are used to map out electrical potential variations, and compute sheet resistance of the graphene layer, as well as the contact resistances between the metal electrodes. Measured shifts depend on lateral positions probed, as well as on polarity and magnitude of the gate-voltage. This non-contact and chemically specific characterization can be pivotal in diagnoses.     

Modelling and IR measurement of the electronic substrate thermal conductivity

The temperature distribution on a ceramic substrate with a small heating element in the middle has been measured by infrared thermography. By comparing the experimental data with a theoretical analysis, the thermal conductivity could be easily obtained.     

Thermal simulation of joints with high thermal conductivities for power electronic devices

The thermal properties of new power modules joined by materials with high thermal conductivities, such as Ag or Cu nanoparticle joints, can differ from those of current modules joined by ordinary solders with low thermal conductivities. However, these properties have not been thoroughly investigated thus far. The overall thermal resistance of a simple simulation module was calculated by the 3-dimensional finite element method to study the correlation between the thermal conductivity of the joint layer and the thermal properties. The calculation results identified an optimal thickness to achieve the minimum thermal resistance when the thermal conductivity of the joint layer is much higher than that of the heatsink. This is presumed to occur because the thermal resistance decreases in the heatsink much more than it increases in the joint layer, owing to the increased uniformity of thermal spreading as the joint-layer thickness increases to the optimal value. This effect of thermal resistance reduction with thickening of the joint layer is seen when the thermal conductivity of the joint layer is sufficiently higher than that of the heatsink and the area of the joint layer is sufficiently smaller than that of the heatsink. The same effect is also expected in an actual module with a joint between a silicon carbide chip and a direct bonded copper substrate. This study reveals that the design concept for power modules should change to preliminarily estimate the optimal thickness to achieve the minimum thermal resistance when the thermal conductivity of the joint layer is much higher than that of the heatsink.     

New possibilities in the thermal evaluation, offered by transient testing

After giving an introductory overview of a method for the evaluation the thermal transient measurement results with the help of the structure functions, the use of the method of transient testing is presented by application examples. The first example shows how to control the quality of the die attachment or soldering with fast transient measurements and subsequent evaluation. The second example presents how transient testing can be used to determine thermal material parameters; e.g. the effective thermal conductivity of printed circuit boards.     

具有自动增益控制的射频振荡器稳定性分析

设计了一个具有自动增益控制(AGC)的电路来稳定射频功率振荡器的输出幅度,然而在加入AGC负反馈环路之后,该环路可能会产生自激振荡,使得振荡器输出的幅度更加不稳定。通过对整个电路系统传递函数的分析,采用调节反馈电路中三极管发射极电阻阻值的方法,使该电路工作在稳定的状态,进而达到稳定振荡器输出幅度的目的。     

Investigation of the thermal performance of micro-whisker structured silicon heat spreaders for power devices

The driving forces of developments in power electronics are the continuing miniaturization and enhancement of power densities. New packaging concepts are required allowing the dissipation of a power loss density of up to several hundred W/cm² at operation temperatures as low as possible. A promising attempt to decrease the thermal resistance to the ambient is the development of silicon substrates structured with microwhiskers perpendicular to its surface. An industrial application of this new heat spreader technology in power electronic modules makes necessary the specification of the substrate properties. In this work, a new method for determination of thermal qualities based on laser heating of the heat spreader, surface temperature measurement by thermovision, and dynamic reverse modeling is described. For numerical determination of the thermal characteristics, the measured data are evaluated with the help of a thermal model of the heat spreaders under various boundary conditions. The respective temperature distributions are calculated with a new simulation tool using an alternating-direction implicit algorithm (ADI-method). Results obtained from heat spreaders with microwhisker treatment are compared with those from reference samples with a polished surface. Based on these results a view on future applications for power electronics assemblies are derived.     

The effect of thermal constriction on heat management in a microelectronic application

Thermal contact constriction between a chip and a heat sink assembly of a microelectronic application is investigated in order to access the thermal performance. The finite element model (FEM) of the electronic device developed using ANSYS software was analysed while the micro-contact and micro-gap thermal resistances were numerically analysed by the use of MATLAB. In addition, the effects of four major factors (contact pressure, micro-hardness, root-mean-squared (RMS) surface roughness, and mean absolute surface slope) on thermal contact resistance were investigated. Two lead-free solders (SAC305 and SAC405) were used as thermal interface materials in this study to bridge the interface created between a chip and a heat sink. The results from this research showed that an increase in three of the factors reduces thermal contact resistance while the reverse is the case for RMS surface roughness. In addition, the use of SAC305 and SAC405 resulted in a temperature drop across the microelectronic device. These results might aid engineers to produce products with less RMS surface roughness thereby improving thermal efficiency of the microelectronic application.     

Thermal analysis of high power LED package with heat pipe heat sink

The goal of this study is to improve the thermal characteristics of high power LED (light-emitting diode) package using a flat heat pipe (FHP). The heat-release characteristics of high power LED package are analyzed and a novel flat heat pipe (FHP) cooling device for high power LED is developed. The thermal capabilities, including startup performance, temperature uniformity and thermal resistance of high power LED package with flat heat pipe heat sink have been investigated experimentally. The obtained results indicate that the junction temperature of LED is about 52 °C for the input power of 3 W, and correspondingly the total thermal resistance of LED system is 8.8 K/W. The impact of the different filling rates and inclination angles of the heat pipe to the heat transfer performance of the heat pipe should be evaluated before such a structure of heat pipe cooling system is used to cool high power LED system.     

Estimation of thermal parameters of the enclosed electronic package system by using dynamic thermal response

A methodology for modeling and simulating the electro-thermal behavior of an enclosed electronic package is presented and validated. The electro-thermal model is constructed using system dynamics. The system model, in which the electrical and the thermal domain are combined, is presented. The developed model describes the dynamic thermal behavior system that was an electronic device in the test enclosure. An effective way to identify the thermal parameters of the system, especially the thermal contact resistance, is suggested. In detail, the new method for thermal resistance identification is based on the temperature difference behavior between the component and the air temperature inside the enclosure. Based on the proposed model, either the variation of the heat source or the ambient temperature can be estimated. Simulated results were in good agreement with the measured temperature in the transient state accompanying with the variation of the environment.     

Investigation of the thermal properties of thin solid materials at different temperature levels using a set of microresistors

The measurement of thermal properties of solid materials at different temperatures above ambient is investigated using a set of microresistors. Samples consisted of suspended films with sets of long, parallel resistive wires deposited on their surfaces. One resistive wire was heated by an alternating current. Surface temperature changes in DC and AC regimes were then detected by measuring the change in electrical resistance of the other wires deposited on the surface. The length of wires was chosen so that they may be assumed isothermal and such that heat diffusion acts perpendicularly to their axes. By measuring the dependence of the surface alternating temperature oscillation on the modulation frequency f and on the separation between the heating wire and the probing wires, the thermal diffusivity of the sample was determined. Through adjustment of the alternating current amplitude in the source wire, the temperature at which the thermal diffusivity of the sample was evaluated was finely controlled. For the validation of the method, pure silicon samples were first studied. An experimental bench was set up and resistive source and probes were experimentally characterized. Results obtained from ambient temperature to 500 K for pure silicon are in accordance with reference data found in the scientific literature.     

Three-dimensional modeling of the heat flow into a GaAs substrate. Influence of thermal phenomena on the RF behavior of power HBTs and technological optimization

Using three-dimensional modeling of the heat flow into the substrate, and taking into account the variation of thermal conductivity with temperature, we study the sensitivity of the thermal resistance R_TH to parameters such as the substrate thickness, its nature (GaAs, Si, AlN or diamond), the topology of the power source (length and width) or even the power density. Thus, we show that the transfer of active GaAs layers onto a host substrate with a higher thermal conductivity such as Si, AlN or diamond is of greater interest than the thinning of the substrate.We developed an accurate electrothermal model for the AlGaAs/GaAs heterojunction bipolar transistor (HBT) allowing prediction of the static and mainly dynamic (RF) behavior at a high signal operating mode. We show that if the HBT layers are transferred onto a diamond substrate, a 50% gain in RF power can be expected at 10 GHz.Finally, we present the technological solutions investigated for the transfer and the heteroassembly of HBT active layers on substrates better suited for thermal dissipation.     

多发光区大功率激光器的热特性分析

通过电学温敏参数法测得多发光区大功率激光器瞬态加热响应曲线,利用结构函数法给出了多发光区激光器热阻构成,分析了多发光区激光器热特性。通过串并联热阻网络模型刻画了单发光区、两发光区、四发光区激光器的热阻构成,给出了激光器芯片热阻与发光区个数之间的定量关系。实验结果表明,不同发光区激光器的芯片级热阻随着发光区数量的增加成比例减小,而封装级热阻不变,这对激光器热设计提供了重要的参考准则。     

Comparison of transient and static test methods for chip-to-sink thermal interface characterization

Accurate thermal interface characterization is essential for high flux microelectronic package design. However, it is increasingly difficult as interfacial bond lines are thinned and thermal interface materials (TIM) evolve to more complex formulations with better performance. This paper compares a static versus transient characterization method targeted at the chip-to-package interface in a test fixture that closely resembles a packaged chip. The static method requires measurements over multiple bond line thicknesses while the transient method yields additional information about the package at the cost of greater numerical complexity, hardware requirements, sensitivity to noise and experimental uncertainty. Both are compared with existing techniques. We conclude that the static method is more generally-applicable while transient is well-suited to rapid characterization of the interface when the rest of the package is well-defined. While both methods are sensitive to the accuracy and resolution of temperature and bondline thickness measurements, the transient technique is additionally sensitive to the relative contribution of the TIM in the full junction-to-ambient thermal path. These points are illustrated through experimental results and compact numerical modeling.