Experimental analysis and modeling of micromachined high-Q integrated inductors

Abstract

Integrated inductors for RF ICs have been intensively investigated since the performance of the integrated inductor can determine that of the RF ICs. Recently, the integrated inductor using micromachining technologies have developed and the performance of the integrated inductor has been much enhanced compared to that of inductors using conventional IC process. In this thesis, the micromachined high-Q integrated inductors have been experimentally analyzed and the model for the integrated inductor has been proposed. In this thesis, the effect of two important factors, metal thickness and insulating layer thickness, to the performance of integrated inductors has been investigated with the experimental results. The inductors for the analyses have been fabricated by thick metal surface micromachining technology to fabricate the thick metal line and high separation gap. From the experimental analysis of the effect of metal thicknesses, it was reported that the enhancement of Q-factor as increasing metal thickness is mainly determined by the proximity effect to induce eddy current and the Q-factor can be enhanced by thicker metal line if the proximity effect in the inductor is negligible. Through the study into the effect of insulating layer thickness, we have shown that the Q-factor of the air-suspended inductor strongly depends on not only the thick air-gap but the oxide thickness below the under-pass line. Especially, we have firstly shown that the under-pass line in the integrated inductor plays an important role to determine the Q-peak frequency when the insulating layer between the inductor line and substrate is fairly thick. In this thesis, we have tested feasibility of the PDMS encapsulation of the air-suspended inductors by investigating structural deformation and RF performance variation after encapsulation with PDMS. From this study, we have shown that encapsulation with PDMS can be a good and practical solution for addressing the mechanical stability and ...