Optimization of magnetoresistive sensor current for on-chip magnetic bead detection using the sensor self-field

Anders Dahl Henriksen, Giovanni Rizzi, Frederik Westergaard Østerberg, Mikkel Fougt Hansen

    Research output: Contribution to journalJournal articleResearchpeer-review


    We investigate the self-heating of magnetoresistive sensors used for measurements on magnetic beads in magnetic biosensors. The signal from magnetic beads magnetized by the field due to the sensor bias current is proportional to the bias current squared. Therefore, we aim to maximize the bias current while limiting the sensor self-heating. We systematically characterize and model the Joule heating of magnetoresistive sensors with different sensor geometries and stack compositions. The sensor heating is determined using the increase of the sensor resistance as function of the bias current. The measured temperature increase is in good agreement with a finite element model and a simple analytical thermal model. The heat conductance of our system is limited by the View the MathML source1μm thick electrically insulating silicon dioxide layer between the sensor stack and the underlying silicon wafer, thus the heat conductance is proportional to the sensor area and inversely proportional to the oxide thickness. This simple heat conductance determines the relationship between bias current and sensor temperature, and we show that View the MathML source25μm wide sensor on a View the MathML source1μm oxide can sustain a bias current of 30 mA for an allowed temperature increase of 5 °C. The method and models used are generally applicable for thin film sensor systems. Further, the consequences for biosensor applications of the present sensor designs and the impact on future sensor designs are discussed.
    Original languageEnglish
    JournalJournal of Magnetism and Magnetic Materials
    Pages (from-to)209-214
    Number of pages6
    Publication statusPublished - 2015


    • Joule heating
    • Magnetoresistive sensor
    • Magnetic biosensor
    • Thermal modeling
    • Planar Hall effect


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