Probing the Magnetodynamics of Magnetic Tunnel Junctions with the Aid of SiGe HBTs

TL;DR

This paper demonstrates how SiGe HBTs as cryogenic preamplifiers significantly enhance the bandwidth and signal quality of high-impedance magnetic tunnel junction measurements, enabling better time-resolved magnetodynamics studies.

Contribution

The study introduces the use of SiGe HBTs as cryogenic preamplifiers to improve measurement bandwidth and noise performance in high-impedance MTJ experiments.

Findings

Bandwidth increased by a factor of 3.89

Signal-to-noise ratio improved by a factor of 6.62

TMR signal gain of 7.75 achieved

Abstract

High impedance (about 1 Megaohm) magnetic tunnel junctions (MTJs) are used to observe and record the magnetodynamics of the nanomagnets that form the junctions themselves. To counteract the bandwidth limitations caused by the high impedance of the junction and the parasitic capacitance intrinsic to any cryogenic system, silicon-germanium heterojunction bipolar transistors (SiGe HBTs) are used as cryogenic preamplifiers for the MTJs. The resulting measurement improvements include an increase in bandwidth by a factor of 3.89, an increase in signal-to-noise ratio by a factor of 6.62, and a gain of 7.75 of the TMR signal produced by the MTJ. The limitation to the measurement system was found to be from the external, room temperature electronics. Despite this limitation, these improvements allow for better time-resolved magnetodynamics measurements of the MTJs. These experiments pave the way for future cryogenic, magnetodynamics measurement improvements, and could even be useful in cryogenic memory applications.