Over the last years, CoFeB has developed into one of the most used magnetic materials for tunneling magnetoresistance (TMR) applications. In combination with MgO, the CoFeB crystallizes during a so-called solid-state epitaxy process and developes highly spin-polarized bands. To exploit the TMR effect in a CoFeB-MgO-CoFeB stack, the relative orientation of magnetization in the two CoFeB electrodes needs to change in external magnetic fields. In practice, often one of the magnetic layers is pinned in an exchange-bias structure. Recently, we showed that oblique-incidence deposition (OID) is an easy and flexible technique to tailor the magnetic properties of ultra-thin films by inducing additional shape anisotropy . By using the two angular degrees of freedom during sputter deposition, the orientation of magnetization as well as the coercive field can freely be tuned in every single magnetic layer of a multilayer stack.
In this contribution, we present the interdependencies of film thickness, layer structure, polar deposition angle and resulting magnetic properties in single CoFeB layers. Beyond that, we will show how OID can be used to custom-design TMR-stacks for the first time in a simple and convenient fashion: There are three easy accessible parameters to adjust TMR properties in CoFeB-MgO-CoFeB stacks. The polar deposition angles and layer thicknesses of the magnetic electrodes define the different coercive fields that result in a tailored double-switching behavior. The thickness of the tunnel barrier additionally influences the interactions between the two magnetic electrodes which can also be seen in a shift of the switching field as well as the TMR effect strength. By altering the azimuthal deposition angle, completely new functionalities with crossed remanent magnetization axes can be realized.
A thorough understanding of the OID parameters’ influence on magnetic and magneto-resistive properties of CoFeB itself and embedded in a TMR stack could pave the way to custom-designed TMR sensors in the future.