Low loss conductors for CMOS and through glass/silicon via (TGV/TSV) structures using eddy current cancelling superlattice structure

Abstract

Superlattice structuresconsisting of nonferromagnetic/ferromagnetic metals have been used to create high performance conductors for radio frequency (RF) transmission lines and low loss vias in CMOS and through silicon/glass via (TSV/TGV) structures, whose ohmic resistance and RC delays have been greatly reduced. Two permalloys of Ni80Fe20 and FeCo are studied as the ferromagnetic materials with low and high magnetization saturation that can be used for designing superlattice structures with low and high GHz frequency ranges, respectively. The effects of design parameters including the number of layers and thickness ratio of the superlattice structures have been studied. Full wave simulations have been used to verify them. Finally, a radial superlattice structure consisting of Cu/NiFe layers has been implemented and its resistance has been compared with the control solid-core devices made of copper; proving the effectiveness of the proposed radial superlattice structure for reducing the RF loss. IntroductionThe operation frequency of monolithic integrated circuits has been growing up and reaching the GHz range in modern communication and consumer electronic applications and the clock frequency of today's microprocessors has reached 3 GHz and tends to move to higher frequencies [1]. One of the limiting factors of the high frequency operation is the radio frequency (RF) loss including the dielectric and conductor loss which are associated with devices and circuits operating in the RF range. The mentioned losses together with the inherent parasitic capacitance in those circuits result in the so called RC time delay, preventing the operating frequencies from going higher. The dielectric loss would be reduced by locally removing the dielectric materials forming air-lifted architectures ([2-3]) or using very low loss dielectric materials [4]. Meantime, most electrodes or interconnectors are adopting copper as a conducting material because of its low electrical resistivity, ease of deposition and moderate cost. However, in higher frequencies, its higher conductivity is not as effective and beneficial as it is in the low frequency and DC operation because of the skin effect, where most current is confined in the outermost surface of the conductor and therefore the volume of the conductor is underutilized. As a result, the effective cross section is reduced in RF frequencies and the resistance and conductor loss are increased. Therefore, the high frequency interconnects, transmission lines and vias in a standard CMOS process and in through silicon/glass via (TSV/TGV) structures suffer from large conductor loss. The larger conductor loss will also be significant in high speed digital circuits including analog-to-digital/digital-to-analog converters and processors

Low Ohmic Loss Cylindrical Radial Superlattice Conductors Using Alternatingly Electroplated Magnetic/Nonmagnetic Thin Films for Microwave Applications

“…The fabrication method is fully compatible with the standard MEMS and CMOS processes and therefore can be integrated with the current manufacturing processes for reducing the RF loss. In this work, NiFe with fAR=28GHz has been used which limits the maximum frequency of operation to be smaller than fAR; however, other ferromagnetic materials with higher fAR could be used to design low loss passive devices in higher frequency ranges [8][9].…”

Eco‐friendly glass wet etching for MEMS application: A review

“…One significant advantage of alkaline etching is its high selectivity, owing to its anisotropic characteristics 73–76 . This makes it a crucial technique for fabricating delicate patterns and structures 72,77–81 . However, several obstacles exist in applying alkaline etching in industrial settings.…”

“…[73][74][75][76] This makes it a crucial technique for fabricating delicate patterns and structures. 72,[77][78][79][80][81] However, several obstacles exist in applying alkaline etching in industrial settings. One major drawback is the hightemperature process, with etching typically occurring at temperatures above 70 • C. Additionally, alkaline etching tends to be time-consuming.…”