3-D Finite-Element Modeling of Multi-Finger High-Power Amplifiers With Compact Heat-Dissipation Packaging Structures

摘要

High-power amplifiers (HPAs) for wireless communication systems have shown significant progress in recent years and the interests for HPA-based dual-band systems are growing rapidly [1]. Miniaturizing HPAs is needed for future multi-band cellular phones. Due to the high-power density and high-linearity characteristics [2], the heterojunction bipolar transistor (HBT) is promising for HPA applications. The miniaturization of HPAs depends mainly on thermal management of HBTs. Conventional HPAs employing emitter-up HBTs suffer from large collector capacitance which limits RF performance. Besides, their thermal resistance is large because heat dissipates mostly through emitter wiring. Thus, special thermal designs, such as ballast resistors, thermal shunts, and wide finger pitches, have been required to improve thermal conduction. In the other respect, HPAs composed of collector-up HBTs, whose collector capacitance is much smaller than that of emitter-up HBTs, exhibit better RF performance [3]. Moreover, in the collector-up HBT with a heat-dissipation configuration, heat dissipates directly from the thermal via, so that collector finger pitches can be minimized. We develop a 3-D finite-element model (FEM) to analyze thermal performance in collector-up (C-up) HBTs and to conduct the miniaturization design of heat-dissipation packaging structures underneath collector fingers. It is shown that numerical methods are most appropriate for developing heat-dissipation structures in HBTs [4]. For this advanced packaging-technology analysis, the FEM methodology was used to calculate temperature distributions around the transistor by adjusting the thickness of plated heat sink (PHS) layer. Also the maximum operation temperature in the three-finger collector-up HBT with different finger pitches was examined. In this study, the results are demonstrated on the GaInP C-up HBT, which is a potential candidate for used in advanced HPAs owing to its low-power supply voltages and high-power handling capability [5].