Integrated On-chip Planar Solenoid Inductors with Patterned Permalloy Cores for High Frequency Applications
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Integrated On-chip Planar Solenoid Inductors with Patterned Permalloy Cores for High Frequency Applications Jinsook Kim, Weiping Ni and Edwin C. Kan, School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853. ABSTRACT The on-chip magnetic inductors with patterned permalloy (Ni80Fe20) cores are fabricated on Si-substrates with different resistivities and thicknesses as well as on thin membranes. With the patterned permalloy cores, the on-chip magnetic inductors achieve high self-resonant frequencies over 25GHz in thin membranes. To distinguish the influence from the permalloy core patterns and substrate losses on the inductance and quality factor, multiple solenoids in series and parallel are designed to investigate the resistive, capacitive, and magnetic coupling losses. INTRODUCTION The on-chip passive inductor for high frequency applications is a key microwave IC element. There have been numerous efforts to incorporate ferromagnetic (FM) materials to improve the performances and reduce the size of the integrated inductors in the RF and microwave frequencies [1-4]. An ideal ferromagnetic material should have high saturation magnetization, small coercive force, and process compatibility with the standard IC technology. With these material considerations, metallic ferromagnetic materials have been successfully employed to build on-chip inductors to enhance the inductance and quality (Q) factor [1-4]. However, the inductors with ferromagnetic materials have relatively poor performance at high frequency due to the eddy-current loss and ferromagnetic resonance (FMR), and the air-core inductors have been a common practice in high-frequency applications [5-6]. In this work, we have designed and characterized planar solenoid inductors (PSIs) and solenoid arrays (PSAs) with various permalloy core patterns, including pie, vertical bars, multiring, and unpatterned core, while the air-core solenoid inductor serves as the control sample. To control the substrate loss, silicon substrates with different resistivities and thicknesses as well as released thin membranes are designed as process splits. Not only the capacitive and magnetic losses but also magnetic coupling and damping were investigated using multiple solenoids in series and parallel. Careful design considerations of capacitive loss, eddy-current loss, magnetization orientation of permalloy, and patterning of FM cores result in enhanced inductance and Q factor as well as extending the self-resonant frequency to over 25GHz. STRUCTURE AND DESIGN FMR, eddy-current, capacitive, and resistive losses are the main loss mechanisms for onchip integrated magnetic inductors. Without any external dc magnetic field and nearly zero anisotropy magnetic fields, the FMR loss in permalloy generally limits the useful frequency range to the lower gigahertz [5]. The Eddy current induced inside permalloy will generate the demagnetization field, and hence dissipates and transfers the magnetic energy into the form of heat. One of the effective ways to resolv
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