Field-write mode MRAMs

Abstract

Introduction Magnetic ferrite core memory was invented and produced in the 1960s, prior to semiconductor memory. Ferrite cores are made from a paste of ferrite powers, which are sintered at high temperature. The process of forming a discrete core is not as scalable as the integrated circuit process on a silicon wafer. The product life of a magnetic core was short, and in the 1970s this technique was replaced by semiconductor memory. A similar fate happened to magnetic bubble memory, another type of magnetic memory, which was built on a magnetic garnet material substrate (gadolinium gallium garnet, Gd 3 Ga 2 (GaO 4 ) 3 ). The bit density of bubble memory technology is scalable since it is made with a planar process, similar to the silicon integration circuits. However, because it is on garnet, it is passive and cannot perform logic functions (such as address decoding), and it requires a companion silicon chip to provide the logic function to complete the memory access function. Even with better memory performance, magnetic bubble memory could not compete against magnetic hard disk and semiconductor memory, which continue to show a clear path of scaling for a lower cost. By the mid 1980s, commercial magnetic bubble production had ended. Subsequent efforts in the development of magnetic memory have been focused on the integration of magnetic thin-film memory devices into silicon wafer processes. Magnetic memory devices exist in the form of thin-film stacks, which can easily be integrated into the back-end metal wiring metallurgy process.