Applications des technologies mémoires MRAM appliquées aux processeurs embarqués (2013)

The Semiconductors Industry with the advent of submicronic manufacturing flows below 45 nm began to face new challenges to keep evolving according with the Moore's Law. Regarding the widespread adoption of embedded systems one major constraint became power consumption of IC. Also, memory technologies like the current standard of integrated memory technology for memory hierarchy, the SRAM, or the FLASH for non-volatile storage have extreme intricate constraints to be able to yield memory arrays at technological nodes below 45nm. One important is up until now Non-Volatile Memory weren't adopted into the memory hierarchy, due to its density and like flash the necessity of multi-voltage operation. These theses has by objective work into these constraints and provide some answers. Into the thesis will be presented methods and results extracted from this methods to corroborate our goal of delineate a roadmap to adopt a new memory technology, non-volatile, low-power, low-leakage, SEU/MEU-resistant, scalable and with similar performance as the current SRAM, physically equivalent to SRAM, or even better with a area density between 4 to 8 times the area of a SRAM cell, without the necessity of multi-voltage domain like FLASH. This memory is the MRAM (Magnetic Memory), according with the ITRS one candidate to replace SRAM in the near future. MRAM instead of storing charge, they store the magnetic orientation provided by the spin-torque orientation of the free-layer alloy in the MTJ (Magnetic Tunnel Junction). Spin is a quantical state of matter, that in some metallic materials can have it orientation or its torque switched applying a polarized current in the sense of the field orientation desired. Once the magnetic field orientation is set, using a sense amplifier, and a current flow through the MTJ, the memory cell element of MRAM, it is possible to measure the orientation given the resistance variation, higher the resistance lower the passing current, the sense will identify a logic zero, lower the resistance the SA will sense a one logic. So the information is not a charge stored, instead it is a magnetic field orientation, reason why it is not affected by SEU or MEU caused due to high energy particles. Also it is not due to voltages variations to change the memory cell content, trapping charges in a floating gate. Regarding the MRAM, this thesis has by objective address the following aspects: MRAM applied to memory Hierarchy: -By describing the current state of the art in MRAM design and use into memory hierarchy; -by providing an overview of a mechanism to mitigate the latency of writing into MRAM at the cache level (Principle to composite memory bank); -By analyzing power characteristics of a system based on MRAM on CACHE L1 and L2, using a dedicated evaluation flow-by proposing a methodology to infer a system power consumption, and performances.-and for last based into the memory banks analysing a Composite Memory Bank, a simple description on how to generate a memory bank, with some compromise in power, but equivalent latency to the SRAM, that keeps similar performance.