Perpendicular magnetic tunnel junctions with TbFeCo-based pinned layer and CoFeB-MgO free layer

다국어 초록 (Multilingual Abstract)

We have fabricated perpendicular magnetic tunnel junctions (pMTJs) with a CoFeB/ TbFeCo pinned layer and Ta/ CoFeB/ MgO free layer using in-situ annealing process. The TbFeCo-based hybrid pinned layer is a useful approach to obtain a high perpendicular magnetic anisotropy (PMA). However, a high temperature annealing, often required for MgO-based MTJs to obtain a high tunneling magnetoresistance (TMR), may deteriorate the PMA of TbFeCo films. Our experimental results show a possibility to obtain a reasonable TMR and high PMA simultaneously by conducting an annealing process to achieve a grain-to-grain epitaxy in CoFeB/MgO/CoFeB layers before depositing the TbFeCo layer. The pMTJs prepared by this process show a tunneling magnetoresistance (TMR) ratio of 15% to 19 % at room temperature.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• Chapter 2. Theoretical Background 6
• 2.1 Tunneling magnetoresistance (TMR) 6
• 2.2 Magnetic tunnel junction (MTJ) 9
• Chapter 3. Experimental Details 23
• 3.1 Film preparation 23
• 3.2 Magnetic characterization and TMR measurements 26
• Chapter 4. Results and discussion 27
• 4.1 Magnetic properties of pinned layer materials 27
• 4.2 The effect of annealing on the magnetic properties of pinned layers 30
• 4.3 CoFeB thickness dependence of the TMR of pMTJs 34
• Chapter 5. Conclusions 39
• References 40