Magnesium and Magnesium Oxide:
Use in Creating Magnetic Tunnel Junctions
Magnetic tunnel junctions (MTJs) have gained wide attention throughout the semiconductor and data storage community for use in magnetic random access memory (MRAM), magnetic sensor and thin film head applications. The ability of MTJs to operate at room temperature and at extremely low power has made them attractive for a variety of applications.
Advantages of Mg and MgO
MTJs generally consist of an insulating layer - the tunnel junction - sandwiched between two ferromagnetic layers that are typically made of deposited cobalt-iron-boron (CoFeB). The most popular insulating layer for the MTJ is made from crystalline magnesium-oxide (MgO) because of its excellent tunneling magnetoresistance effect (TMR). In the presence of an external magnetic field, a TMR thin film can be “switched” between a high and low electrical resistive states allowing electrons to tunnel through the MgO layer. In its deposited form, MgO is amorphous, requiring an annealing process to undergo crystalline transformation. MgO allows for a very high TMR ratio to be achieved, largely due to its excellent coherent tunneling properties when compared to that of aluminum oxide (AlOx).
The MgO layer in MTJs is usually no more than 1-3 nm in thickness. It can be deposited via pulsed laser or molecular beam epitaxy but the most common method is by physical vapor deposition (PVD). In the case of PVD, target choices include deposition from either an MgO target or from pure magnesium metal. Non-volatile memory devices, like STT-RAM, are formed directly onto a complementary metal-oxide semiconductor (CMOS) wafer. A major concern is yield loss related to particle generation from the target and shielding. However, particle generation can be reduced through the use of high quality raw materials and tight process controls during the target manufacturing process.
Increase Product Yield
Materion uses technologies designed to reduce internal stresses and surface imperfections that lead to particle generation in MgO and Mg targets. Impurities known to cause issues are reduced or eliminated and key attributes like target density, strength, and surface finish have been maximized to increase product yield. For more information about Materion high purity targets, contact John Kuphal, Product Marketing Manager, John.Kuphal@Materion.com.
Image: Magnesium Oxide Structure