MRAM process development and production briefing

An article written by Dr. Meng Zhu, Dr. Roman Sappey, and Jeff Barnum from KLA, for SEMICONDUCTOR ENGINEERING – What is MRAM and why is it becoming more attractive to the industry?

MRAM (Magnetoresistive Random-Access Memory) is a type of non-volatile memory (NVM) that utilizes magnetic states to store information. The basic structure of MRAM is a magnetic-tunnel junction (MTJ), which consists of two ferromagnetic (FM) layers separated by an insulating tunnel barrier (Fig.1). When the magnetizations of the two magnetic layers are parallel, the electrons tunnel easily across the barrier from one magnetic layer to the other, giving a low resistance state (RP). However, when the two magnetic layers are anti-parallel, the electron tunneling becomes difficult causing a higher resistance state (RAP). One of the most important parameters of an MTJ is tunneling magnetoresistance (TMR), which quantifies how well we can differentiate high and low resistance states. By manipulating the magnetization of one of the layers, information can be stored as “1” (high-R state) and “0” (low-R state) in the junction and then the information can be read by measuring the junction resistance. Changing the layer’s magnetization direction can be achieved by applying an external field, or by pulsing an electric current through the junction. The latter uses an effect called “spin-transfer-torque (STT)” to change the magnetization by polarized electrons.

STT-MRAM offers excellent scaling capability and friendly integration into current chip fabrication processes. Unlike DRAM, which needs to be continuously refreshed, STT-MRAM stores information without drawing power. Replacing DRAM with MRAM could prevent data loss and enable computers to start instantly without waiting for software to boot up. STT-MRAM has higher density than SRAM, and superior read/write speed over flash, with much higher endurance. All these merits make STT-RAM an attractive candidate to replace existing memories in certain applications, and perhaps eventually to become a universal memory solution… Full article