Autonomous Systems for Characterization of Spin Torque Oscillators : Design, Production, Optimization and Measurement

• Main Author: Banuazizi, Seyed Amir Hossein
• Format: Others
• Language: English
• Published: KTH, Material- och nanofysik 2013
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140531

The Spin Torque Oscillator (STO) is a nano-scale electrical device, with a wide current and field tunability, highly promising for applications in next generation wide band microwave frequency generators, multifunction microwave components, ultra-fast microwave sensors, etc. For a better fundamental understanding of the functional properties of STOs it is important to develop flexible and easy-to-use characterization tools, in particular for routine test and characterization in preparation for a successful commercial applications. Most present measurement systems do not fulfill these qualities and have very low through-put. Therefore, an automated system including all capabilities for characterization of STO is indeed necessary in laboratories. In this work, two different setups for characterization of STO are proposed, designed and built. To increase measurement performance a high frequency (up to 60 GHz) measurement setup was designed and built based on the rotation of a large field electromagnet (up to 2 T), instead of rotating the sample as in older system. A second high frequency measurement setup utilizes a total of 5 degrees of freedom to rotate and position a permanent magnet with a magnetic field of 1 T. Moreover, as preliminary experimental investigation of STOs, the resistance of nanocantact (NC) STOs with different NC size and variation of the thickness of the Cu seed layer, was studied to find the real NC size based on Sharvin-Maxwell methods. The study resolves how the real resistance value of the NC and the resistance of the mesa varies. This will help to understand the microwave power delivery issues between the mesa and the NC and has direct applicability to the problem of impedance matching between these two sub-elements. This study will be finally useful to find a criteria for seed layer thickness and necessary NC size in order to get a high output power from STOs and will assist to design novel geometries of high power STO for commercial applications.