Abstract
This work has been focused on the deposition of perpendicular-anisotropy CoFeB/MgO free layer, measurement of thermal stability in different size devices, and the experimental setup of measuring thermal stability. Moreover, develop a new double CoFeB structure with higher thermal stability. Then, evaluate the effective field when a current passed and the threshold switching current density. In the single CoFeB layer, I have tuned the thickness of CoFeB and the condition of annealing to get the better perpendicular anisotropy. After that, I have tuned the thickness of bottom CoFeB and sputter condition to get a double CoFeB structure with higher MS*t and a constant HK value. In order to fabricate different size devices, I have used photolithography and E-beam lithography to pattern the Hall cross structure. I would like to use the Hall voltage which had been measured by AHE to investigate the properties of small-sized devices. I mainly used pulse magnetic switching probability and dynamic coercivity method to measure the thermal stability of micro-sized and nano-sized devices. In the last part, I would like to compare the effective field and threshold switching current density between single CoFeB and double CoFeB structure.