An on-chip magnetic probe based on MOSFET technology

Abstract

An original application for a magnetic field-sensitive Split-Drain MOSFET (MAGFET) used to monitor both the integrity of the electrical signal on-chip, as well as the magnetic flux density radiation on-chip is presented in this work. We introduce experimental and simulation results of a test chip that prove static and low-frequency on-chip generated magnetic fields that can be detected on-chip leading to a fluctuation in the drain current ($\Delta $I$_{DS}$) of a MAGFET device. The design of this first version of the test chip is intended for DC characterization as the pads, package and wiring do not allow going above a frequency of 300 MHz. In this particular case of a 0.5 $\mu $m CMOS technology and the used dimensions, the cutoff frequency of the test MAGFET is in the range of 500 MHz to 1 GHz depending on the bias conditions. For the static and low-frequency case used in this experimental work the capacitive coupling between the interconnect line and the gate electrode is negligible. The current in the interconnected line, that varies from 500 $\mu $A to 35 mA, generates a magnetic flux density at a rate of 100~$\mu $T/mA. When these magnetic lines cross through the channel of the MOS transistor, an electromagnetic coupling rate ($\Delta $I$_{DS}$/B) as far as 1.5 $\mu $A/mT is induced. We observed that from the 0.7, 0.5, and 0.35 $\mu $m characterized MOS technologies data, the ($\Delta $I$_{DS}$/B) rate increases with the miniaturization process of fabrication technology. This electromagnetic rate reduces as the temperature is increased from 20 to 120$^{\circ}$C. From numerical simulations we conclude that this phenomenon is attributed to the way carrier mobility and inversion channel charge interplay with the on-chip tangential and perpendicular components of the (B) field. Having an array of MAGFETs distributed on the surface of the chip would serve to monitor the EM radiation, which in turn may be used for estimation and mitigation of RF interference. These results allow establishing the basis for a future development for on-chip magnetic probe for nanometer MOS technologies.