Spin Torque Oscillators - An Emerging Technology for Microwave Signal Generation
Michielsen, W.; Garcia, J.; Persson, J.; Zhou, Y.
NanOsc AB

State-of-the-art oscillators in wireless devices, such as e.g. bluetooth chips, use inductive coils in order to generate microwave power. These coils consume large chip area and it has been estimated that more than 75% of the silicon could be saved using a Spin Torque Oscillator (STO). The working principle of this device lies in the interaction between a spin polarized dc current and the magnetization of the various magnetic layers in the STO, resulting in an angular precession of the magnetization itself. As the resistance of the device is proportional to the magnetization angle, the device is an ac resistor, and the dc current causes an ac voltage output. Experiments have demonstrated oscillations from 1 GHz to 40 GHz with high Q-values (up to 18,000).

We will review the state-of-the-art of the STO technology, present its potential and possible limitations, and discuss its applicability to microwave signal generation over a wide frequency range. Magnetodynamic simulations of STO operation will be presented as well as basic circuits to further improve the signal quality and the frequency control.