Yuqin Sun

Dartmouth College, Hanover, NH, United States

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Publications (8)5.05 Total impact

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    ABSTRACT: We have studied obliquely sputtered Co-Zr-O films. We found that oblique deposition gives rise to the formation of columnar morphology and thus higher perpendicular magnetic anisotropy in the films, which finally results in the occurrence of stripe domains and degradation of soft magnetic properties. Applying substrate bias during Co-Zr-O film deposition gave some improvement in magnetic softness with small slope angles, but did not provide any improvement for large angles. Using a multilayer structure Co-Zr-O/ZrO<sub>2</sub> effectively eliminates the columnar structure and helps the films regain favorable soft magnetic properties.
    IEEE Transactions on Magnetics 01/2008; · 1.42 Impact Factor
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    ABSTRACT: Nano-granular metal-nonmetal soft magnetic materials offer low losses at frequencies up to 100 MHz, with higher flux density and temperature capability than ferrites. We present the design, fabrication, and testing of a high- Q 30 MHz toroidal inductor using Co-Zr-O nano-granular magnetic materials.
    Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007
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    ABSTRACT: Co-Zr-O granular films were prepared by reactive sputtering. The films show strong uniaxial in-plane anisotropy as well as good soft magnetic properties and high dc resistivity. In order to confirm their electrical characteristics at high frequency, the frequency and current density dependences of resistivity were investigated. Resistivity was found to be constant over the range measured (up to 18 MHz and 100 MA/m<sup>2</sup>). Furthermore, the films exhibit virtually no hysteresis along the hard-axis direction and have very little anisotropy dispersion. The frequency dependence of the initial permeability was measured and used to predict the power loss expected when granular films are used as high-frequency core materials for film inductors. The power loss is predicted to be lower than that of commercial NiZn ferrite for high-frequency applications.
    IEEE Transactions on Magnetics 11/2005; · 1.42 Impact Factor
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    ABSTRACT: Microfabricated thin-film inductors for high-frequency DC-DC power conversion at high currents and low voltages with fast transient response have been fabricated and tested. Inductors with a Co-Zr-O thin-film core and a copper conductor have been fabricated in a silicon substrate. Prototype inductors have been characterized and applied in a 3.3-V-to-1.1-V, 8-A, 5-MHz DC-DC converter and have been shown to exhibit efficiency of up to 89% and power density up to 96 W/cm<sup>2 </sup> of substrate area. The inductors discussed in this paper emerge as strong candidates for high-efficiency, high-power-density DC-DC converters for advanced digital systems such as microprocessors wherein the fast transient response of the microfabricated inductors can result in significant reduction in the converter's output capacitance
    Power Electronics Specialists Conference, 2005. PESC '05. IEEE 36th; 07/2005
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    ABSTRACT: Soft granular Co–M–O films have promise for application in high-frequency thin-film inductors. But granular Co-based films are often found with perpendicular anisotropy, which can result in stripe domains and poor hysteresis behavior. Film microstructure was analyzed for Co-rich Co–Zr–O granular films with and without stripe-domain behavior. It is suggested that perpendicular anisotropy originates from columnar structure with Co columns perpendicular to film plane. The appearance of columnar structure is determined by sputter pressure and oxygen content.
    Journal of Applied Physics 05/2005; 97(10):10N301-10N301-3. · 2.21 Impact Factor
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    C.R. Sullivan, Yuqin Sun
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    ABSTRACT: Measurements show that lumped RLC models for multilayer ceramic capacitors are inadequate. A new transmission-line model offers advantages over previous transmission-line models: a closer fit to measured data, and a physical basis for the model.
    Electrical Performance of Electronic Packaging, 2003; 11/2003
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    From Transactions of the Magnetics Society of Japan. 01/2003; 3:126-8.
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    C.R. Sullivan, Yuqin Sun, A.M. Kern
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    ABSTRACT: Time-domain and frequency-domain measurements show that a simple lumped RLC model for a multilayer ceramic capacitor is inadequate, overestimating high-frequency impedance by a factor of five. A lossy transmission-line model works better, and is improved by placing incremental resistance in series with the incremental capacitance. Refinements of this model are developed based on time-domain step-response measurements and on frequency-domain impedance measurements. Better packaging to reduce series inductance is discussed.
    Industry Applications Conference, 2002. 37th IAS Annual Meeting. Conference Record of the; 02/2002