"SPECIAL SEMINAR: Challenges and strategies for using spin torque oscillators for practical microwave applications"

 

 

 

Spin torque oscillator (STO) is an emerging device that can generate a microwave signal simply by injecting a DC current. It is expected to serve as a microwave signal source in radio frequency (RF) integrated circuits due to many beneficial features such as its simple structure, tiny dimension, compatibility with CMOS processes and so on.

 

However, various performance indicators have to satisfy industry specifications in order for a STO to be used for such applications. One of the most serious performance problems is its poor frequency stability, i.e. large phase noise. The phase noise levels of STOs are far larger than required for most microwave applications, thus need to be largely reduced.  For this purpose, we recently developed a phase locked loop (PLL) circuit custom designed to stabilize a STO, and successfully demonstrated stable phase locked oscillation, characterized by an extremely sharp peak at the target frequency [1]. While we believe this accomplishment is a major milestone for the productization of STOs, its residual phase noise is still significantly larger than commercial PLL circuits consisting of a transistor based amplifier and external resonator, thus further improvement is crucial [2].

 

In this talk, I will present the performance of the STO stabilized by PLL, sources of residual phase noise, and future strategies for further improving the phase noise performance to compete with commercial PLL circuits.

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