Thermal-assisted switching
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Thermal-assisted switching, or TAS, is one of the new second-generation approaches to magnetoresistive random-access memory (MRAM) currently being developed. A few different designs have been proposed, but all rely on the idea of reducing the required switching fields by heating.[1] The first design's cell, which was proposed by James M. Daughton and co-workers, had a heating element, an MRAM bit, an orthogonal digit line,[1] and used a low-Curie point ferromagnetic material as the storage layer.[2] In a second and more-promising design, which was developed by the Spintec Laboratory (France) and subsequently licensed to Crocus Technology, the storage layer is made of a ferromagnetic and an antiferromagnetic layer. When the cell is heated by flowing a heating current through the junction and the temperature exceeds the "blocking temperature" (Tb), the ferromagnetic layer is freed, and the data is written by application of a magnetic field while cooling down.[1] When idle, the cell's temperature is below the blocking temperature and much more stable.[3]
This approach offers multiple advantages over previous MRAM technologies:[2]
- Because the write selection is temperature-driven, it eliminates write-selectivity problems;
- It is a low-power approach as only one magnetic field is required to write, and because the cell stability and magnetic susceptibility are decoupled as a result of the introduction of the blocking temperature; and
- It is thermally stable due to the exchange bias of the storage layer.
