The company is claiming the addition of 'Precessional Spin Current' (PSC) structure to pMTJ as a "breakthrough" that will allow MRAM to displace SRAM in embedded applications and DRAM elsewhere. Spin Transfer CEO Tom Sparkman commented: "While MRAM has long been considered an emerging memory solution, it had significant speed and endurance challenges — which our PSC structure has been proven to address. We believe our advances will propel MRAM to become a mainstream memory technology that will allow continued innovation across most cutting-edge and mainstream applications."
The structure adds 4nm to the height of the pMTJ and enables a Precessional Spin Current, which boosts performance by 40 to 70 percent, Spin Transfer claims. The improved efficiency is valuable for enabling MRAM to replace SRAM and DRAM in mobile equipment, datacentre storage and AI applications. It will also improve retention at high temperature in automotive applications.
The development was reported at Intermag 2018, held in Singapore. The structure is designed to be modular and can be added to any pMTJ, Spin Transfer said opening up the possibility of licensing the technology. The structure is compatible with standard MRAM manufacturing processes, materials and tools thus enabling a foundry to add the PSC structure into existing pMTJ stacks with minimal additional complexity and cost.
The PSC structure comprises a spacer/coupling and magnetic layers deposited on top of the free layer of the pMTJ, according to the abstract of the Intermag paper and measurements were performed on MTJ pillars of 60nm, 50nm and 40nm diameter. The effect is increased with reduced dimensions.
Previously lower writing current resulted in reduced retention and vice versa. The PSC structure effectively decouples the static energy barrier that determines retention from the dynamic switching processes that govern switching current. As a result the addition of a PSC structure to any pMTJ would produce two benefits:
1) A higher energy barrier when the pMTJ does not have current flowing