Microwave Oscillators and Detectors Based …
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Fig. 20 a RF detection voltage (V detect ) as a function of the RF input frequency under various dc bias
currents (I dc ). The radio frequency detection sensitivity of 12,000 mV/mW is achievable at room
temperature. Adapted by permission from Macmillan Publishers Ltd: (Nature Materials) Miwa et
al. [35], copyright (2013). b, c shows the rectified voltage observed for the core expulsion and
spin-torque diode measurements taken at 6 and 0 mA, respectively, for I rf = 0.2 mA. The maximum
effective sensitivity observed is as large as 80,000 mV/mW [143]. Adapted by permission from
Macmillan Publishers Ltd: (Nature Nanotechnology) Jekins et al. [144], copyright (2016)
9.1.2 Enhancement of Sensitivity Using Nonlinear FMR
Miwa et al. [35] showed a much greater microwave detection sensitivity of 12,000
mV/mW at room temperature, which exceeds that of the commercial semiconductor diode detectors (3800 mV/mW). The results of Miwa et al. [35] are shown in
Fig. 20a. They showed that sensitivity increases significantly when dc bias currents
are applied to an MTJ. This high sensitivity has been explained on the basis of
nonlinear FMR [142]. In the nonlinear FMR process, the center of the precession
orbit is energy-dependent because of the higher-order nonlinear terms. This causes
a change in the relative angle between the free-layer magnetization and the pinnedlayer magnetization and, consequently, a change in the dc resistance, leading to
higher sensitivity. However, the frequency of operation was limited to 1–2 GHz.
9.1.3 Enhancement of Sensitivity Using Vortex Expulsion
Jenkins et al. [144] reported a significant enhancement in the sensitivity of a vortexbased MTJ-based STNOs using the phenomenon of resonant expulsion of the vortex
core. This method is shown in Fig. 20b; it produces a large, sharp change in the
resistance, associated with the difference in magnetoresistance between the vortex
ground state and the final C-state magnetization configuration. Sensitivities as high
as 40,000 mV/mW were reported by Tsunegi et al. [143], which were later improved
to 80,000 mV/mW (Fig. 20c). A proof of concept for simultaneous detection of
33
Fig. 20 a RF detection voltage (V detect ) as a function of the RF input frequency under various dc bias
currents (I dc ). The radio frequency detection sensitivity of 12,000 mV/mW is achievable at room
temperature. Adapted by permission from Macmillan Publishers Ltd: (Nature Materials) Miwa et
al. [35], copyright (2013). b, c shows the rectified voltage observed for the core expulsion and
spin-torque diode measurements taken at 6 and 0 mA, respectively, for I rf = 0.2 mA. The maximum
effective sensitivity observed is as large as 80,000 mV/mW [143]. Adapted by permission from
Macmillan Publishers Ltd: (Nature Nanotechnology) Jekins et al. [144], copyright (2016)
9.1.2 Enhancement of Sensitivity Using Nonlinear FMR
Miwa et al. [35] showed a much greater microwave detection sensitivity of 12,000
mV/mW at room temperature, which exceeds that of the commercial semiconductor diode detectors (3800 mV/mW). The results of Miwa et al. [35] are shown in
Fig. 20a. They showed that sensitivity increases significantly when dc bias currents
are applied to an MTJ. This high sensitivity has been explained on the basis of
nonlinear FMR [142]. In the nonlinear FMR process, the center of the precession
orbit is energy-dependent because of the higher-order nonlinear terms. This causes
a change in the relative angle between the free-layer magnetization and the pinnedlayer magnetization and, consequently, a change in the dc resistance, leading to
higher sensitivity. However, the frequency of operation was limited to 1–2 GHz.
9.1.3 Enhancement of Sensitivity Using Vortex Expulsion
Jenkins et al. [144] reported a significant enhancement in the sensitivity of a vortexbased MTJ-based STNOs using the phenomenon of resonant expulsion of the vortex
core. This method is shown in Fig. 20b; it produces a large, sharp change in the
resistance, associated with the difference in magnetoresistance between the vortex
ground state and the final C-state magnetization configuration. Sensitivities as high
as 40,000 mV/mW were reported by Tsunegi et al. [143], which were later improved
to 80,000 mV/mW (Fig. 20c). A proof of concept for simultaneous detection of