Accurate and efficient analysis of the upward heat flow in InGaP/GaAs HBTs through an automated FEM‐based tool and Design of Experiments

Abstract

This paper presents an extensive analysis aimed at quantifying the impact of all the key technology parameters on the upward heat flow in state-of-the-art InGaP/GaAs heterojunction bipolar transistors (HBTs) for various emitter areas and shapes. Extremely accurate thermal simulations are conducted in a relatively short time with a tool relying on a commercial 3-D finite-element method (FEM) solver and an in-house routine for automated geometry construction, optimized mesh generation, sequential solution, and data storing/processing. Design of Experiments is used to define a thermal resistance model as a function of the aforementioned parameters on the basis of a few FEM data. also studied the beneficial effect of a thermally-conductive and/or shorter path from the heat dissipation region to the sink, which can be obtained with flip-chip packaging 13,14,19,20,22,30 or alternative strategies based on thermal vias. 17,32 Unfortunately, almost all the thermal analyses presented in the above papers are (sometimes unacceptably) inaccurate: the real-and complex-device structures are always represented with simplified (or even oversimplified) domains to allow (1) the development of analytical models for the temperature distribution or (2) an easy construction/meshing of the 3-D geometry for numerical simulations; still now, in spite of the continuous improvement in PC performances, task (2) is not trivial if performed manually, especially when all technological details must be taken into account.Recently, the upward heat flow has been given attention in some works from the authors. [37][38][39][40] In particular, besides the metallization, the often overlooked role played by the emitter stack (previously investigated only in a study by Anholt 22 ) has been analyzed in a state-of-the-art InGaP/GaAs HBTs in previous papers [38][39][40] ; the relevance of these studies is driven by the low thermal conductivities of the ternary InGaAs and InGaP emitter layers (even lower than GaAs), which make thermal shunt solutions less effective. For this purpose, the authors have used a simulation/modeling strategy based on combining (1) a tool that relies on a 3-D finite-element method (FEM) software package aided by an in-house routine, and (2) Design of Experiments (DOE) to analytically derive a predictive thermal resistance model starting from a minimized number of FEM results. Contrary to prior work, the proposed tool ensures very high simulation accuracy: starting from the actual masks used for device fabrication, it allows an automated and extremely detailed construction/meshing of the 3-D transistor structure in the environment of the FEM solver. Thanks to this feature, it can be easily integrated into a standard design process, and can in principle be used for any device technology.This work aims at extending the analysis presented in Catalano et al 38 where the impact of emitter stack and metallization layers on the thermal behavior was evaluated for various emitter areas and shapes in single-finger InGaP/GaAs HBTs. Compared wi...

Compact Modeling of a 3.3 kV SiC MOSFET Power Module for Detailed Circuit-Level Electrothermal Simulations Including Parasitics

“…The linear equivalent network extraction procedure is briefly explained in the following. First, an exceptionally detailed 3-D geometry is created from PM structural data in the finite-element method (FEM) environment of COMSOL Multiphysics [40], as shown in Figure 4; the building process is entirely automated by the in-house routine presented in [41], which relies on the livelink between COMSOL and MATLAB. Then, the domain is discretized into a tetrahedral grid; a smart meshing approach was conceived in order to make the grid finer in the surroundings of the dies (Figure 4).…”

Analysis of Electrothermal Effects in Devices and Arrays in InGaP/GaAs HBT Technology

“…The 3-D geometry/mesh of each domain was constructed in the environment of the COMSOL software package [16] by making use of an in-house routine that relies on the MATLAB-COMSOL Livelink and the Toolbox for files in GDSII format provided by U. Griesmann [17]. The procedure is described as follows: first, the GDS layout file (i.e., the masks used for the technological process) is input to the routine along with the thicknesses of the layers, mask biases, and material parameters; then, the routine automatically draws the 3-D geometry, and finally generates and optimizes the mesh in the COMSOL environment.…”

“…A single heat source (geometrically coinciding with the base-collector SCR [17]) and a single subcircuit were assigned to each unit cell (Figure 1); as mentioned earlier (Section 3.1), this intrinsically assumes that the fingers within the cell are tightly thermally coupled, and thus not prone to thermal hogging. Figure 4 depicts the geometry of the 1-cell test device, while Figure 5 shows the mesh of the 2-cell one.…”

“…In that case, a simple ETN based on the N×N thermal resistance (R TH ) matrix, N being the number of individual HBTs (each associated to one heat source), was adopted in the macrocircuits. The R TH s were determined through pre-processing 3-D linear FEM simulations performed with COMSOL [16] aided by an in-house routine [17] for an exceptionally accurate and automated construction of the geometry/mesh of the structures. Nonlinear thermal effects dictated by high temperatures were taken into account through the Kirchhoff's transformation [18,19].…”

Influence of Selected Factors on Thermal Parameters of the Components of Forced Cooling Systems of Electronic Devices

“…Compact thermal models allow much faster computations, but they do not allow the computation of temperature distribution in the modelled device. In [41][42][43][44], a method of formulating compact models of semiconductor devices based on the result obtained by solving the heat transfer equation is proposed. In the cited papers, a multipath heat transfer in power modules or LED lamps is taken into account.…”