Sensitivity of spin-torque diodes for frequency-tunable resonant microwave detection

TL;DR

This paper evaluates the efficiency of magnetic tunnel junctions as resonant microwave detectors via the spin-torque diode effect, deriving expressions and measuring sensitivities in different device configurations.

Contribution

It provides a theoretical expression for detection efficiency and compares it with experimental measurements, highlighting the impact of device structure on sensitivity.

Findings

Measured sensitivities agree with theory for unpatterned devices.

Sensitivity is reduced in patterned SAF devices due to magnetic coupling.

Optimized junctions could exceed 10,000 mV/mW sensitivity.

Abstract

We calculate the efficiency with which magnetic tunnel junctions can be used as resonant detectors of incident microwave radiation via the spin-torque diode effect. The expression we derive is in good agreement with the sensitivities we measure for MgO-based magnetic tunnel junctions with an extended (unpatterned) magnetic pinned layer. However, the measured sensitivities are reduced below our estimate for a second set of devices in which the pinned layer is a patterned synthetic antiferromagnet (SAF). We suggest that this reduction may be due to an undesirable coupling between the magnetic free layer and one of the magnetic layers within the etched SAF. Our calculations suggest that optimized tunnel junctions should achieve sensitivities for resonant detection exceeding 10,000 mV/mW.