Marina Vroubel

Integrated tunable magnetic RF inductor

We demonstrate, for the first time to our knowledge, a passive, electrically tunable integrated radio frequency (RF) inductor based on a planar solenoid with a thin-film ferromagnetic(FM) (NiFe) core. Variation of inductance is achieved by leading an additional dc current through the same device, thereby changing the effective permeability of the FM core. Tuning ranges (relative variations in inductance) of 85%, 35%, and 20% are achieved at 0.1, 1, and 2 GHz, respectively, for inductances in the range of 1 to 150 nH.

Integrated solenoid inductors with patterned, sputter-deposited Cr/Fe/sub 10/Co/sub 90//Cr ferromagnetic cores

Ferromagnetic (FM) films suitable for implementation in between interconnect layers of a standard CMOS fabrication process are demonstrated to yield considerable size reduction of monolithic radio frequency (RF) inductors, leading to lower cost. The deposition of a FM Cr(5 nm)/Fe/sub 10/Co/sub 90/(500 nm)/Cr(15 nm) stack is performed by magnetron sputtering at room temperature under a dc magnetic field of /spl sim/ 10 mT along the magnetic easy-axis. A lift-off technique, using a four-layer shadow mask, is used for pattern transfer to the magnetic stack to circumvent apparent difficulties in the patterning of FM films. A series of solenoid-type inductors with FM cores are demonstrated and compared to control devices with air cores. A more than eight-fold enhancement of the inductance and a seven-fold improvement of the quality factor are achieved.

Ferromagnetic RF inductors and transformers for standard CMOS/BiCMOS

Integrated solenoidal radio-frequency (RF) inductors and transformers with a ferromagnetic core are demonstrated by using a fully IC-compatible fabrication process. For a 500-nm-thick Ni/sub 80/Fe/sub 20/ film, a cut-off frequency of over 7.5 GHz for a 2.5-nH inductor is realized. Optimum inductor design based on tailored inductance, quality factor, and cut-off frequency is discussed. RF transformers realized have a coupling factor of /spl sim/70% up to 200 MHz.

Suppression of skin effect in metal∕ferromagnet superlattice conductors

We propose and theoretically investigate a superlattice consisting of alternating normal-metal and ferromagnetic layers as a low-loss conductor for realization of planar-integrated radio-frequency devices. At sufficiently high frequencies, the negative permeability of the ferromagnetic films effectively compensates the positive permeability of the nonmagnetic metal layers, leading to an overall suppression of the skin effect. Simulations based on realistic material parameters demonstrate the effectiveness of this approach regardless of intrinsic relaxation losses in the magnetic films.

Nonreciprocal spin wave spectroscopy of thin Ni–Fe stripes

The authors report on the observation of nonreciprocal spin wave propagation in a thin ( ? 200?nm) patterned Ni–Fe stripe. The spin wave transmission spectrum is measured using a pair of microstrip lines as antennas. The nonreciprocity of surface wave dispersion brought about by an adjacent aluminum ground leads to a nonreciprocal coupling of the antennas. The effects of Ni–Fe film conductivity, thickness, and reflections caused by the lateral confinement of the magnetic stripe are discussed. The nonreciprocity observed in this structure can potentially be used to realize nonreciprocal microwave devices on silicon.

Magnetic properties of electroplated nano/microgranular NiFe thin films for rf application

A granular NiFe thin film with large in-plane magnetic anisotropy and high ferromagnetic-resonance frequency developed for radio-frequency integrated circuit (IC) applications is presented. During the deposition, three-dimensional (3D) growth occurs, yielding NiFe grains (? ? 1.0??m). Nanonuclei (? ? 30–50?nm) are observed in single NiFe grains by atomic-force microscopy (AFM). The in-plane magnetic anisotropy is estimated to be ? 50?mT. The frequency-dependent complex permeability is extracted. By taking the NiFe film as a magnetic core, solenoid-type inductors are fabricated and demonstrated and show a high operating frequency ( ? 5.5?GHz) with a maximum quality factor ( ? 3).

Calculation of shape anisotropy for micropatterned thin Fe-Ni films for on-chip RF applications

We present a self-consistent calculation of the effective anisotropy of patterned, integrated ferromagnetic films. For comparison, experimental data were obtained from electroplated thin (0.5 /spl mu/m) Ni-Fe films with different patterns. The effective anisotropy of patterned samples was increased by shape demagnetizing effects from just 10 Oe up to 100 Oe. The samples with suitable characteristics were subsequently used as cores for on-chip inductors and microstrips.

Shape-induced ultrahigh magnetic anisotropy and ferromagnetic resonance frequency of micropatterned thin permalloy films

Magnetic anisotropy Hk>200?Oe was observed from bar-shaped Permalloy strips. The film was deposited on sputtered Cr seed layer by electroplating under ? 800?Oe external magnetic field. Tiny degradation of Hk was observed after 30 min postannealing at 400?°C in the absence of external magnetic field. The Permalloy strip with in-plane aspect ratio of 40:1 showed the ferromagnetic resonance at ? 5.3?GHz. The ferromagnetic resonance frequency and magnetic anisotropy decreased to ? 1?GHz and ? 50?Oe, respectively, as the in-plane aspect ratio reduced from 40:1 to 10:1. In comparison, Permalloy strips plated on combined Ti/TiN seed layers did not show clear anisotropy features.

Assessment of ferromagnetic integrated inductors for Si-technology

Recent experimental results for integrated magnetic inductors for radio frequency (RF) applications are reviewed. The effects of eddy-current loss in the conductive ferromagnetic film, permeability anisotropy, and inductor geometry on the inductance of magnetic inductors are discussed using several examples.

Magnetic-Multilayered Interconnects Featuring Skin Effect Suppression

A novel concept for a high-frequency, low-loss interconnect with significant skin effect suppression over a wide frequency band is presented. The concept is based on a multilayer comprising thin magnetic (Ni80Fe20) and metal (Cu) layers. The negative permeability of the magnetic layers leads to a near-cancellation of the overall permeability of the multilayer stack. This results in a significant increase of skin depth and thus, a more uniform distribution of the current density and a dramatic reduction of loss within a certain frequency range. Coplanar waveguides built using the multilayer technology show more than 50% loss reduction at 14 GHz compared to their thick Cu-based counterparts.