Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field

Eklund, Anders, Bonetti, Stefano, Sani, Sohrab R., Majid Mohseni, S., Persson, Johan, Chung, Sunjae, Amir Hossein Banuazizi, S., Iacocca, Ezio, Östling, Mikael, Åkerman, Johan and Gunnar Malm, B. (2014) Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field. Applied Physics Letters, 104 (9). 092405. ISSN 0003-6951

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Abstract

The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150 MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18–25 GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films.

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