SHF: Small: Collaborative Research: Energy Efficient Strain Assisted Spin Transfer Torque Memory

Non-volatile random access memory (NV-RAM) is often built with a device called spin transfer torque random access memory (STT-RAM), the main constituent of which is a circular nano-magnet. A bit is 'written' into the nano-magnet by passing a spin-polarized current whose polarity determines whether bit '1' or bit '0' is written. The energy barrier between these states prevents the magnetization from switching spontaneously due to thermal noise, making the device non-volatile. Unfortunately, the energy dissipated in the writing current is 100-1000 times more than the energy dissipated in today's CMOS devices, which is a large cost to pay for non-volatility. This project seeks to demonstrate that temporarily reducing the energy barrier between the 'up' and 'down' magnetization states with surface acoustic waves (SAW) can significantly lower the current needed to write a bit and reduce the energy dissipation by orders of magnitude. This would make the SAW-assisted STT-RAM ideal for embedded processors, internet of things, large data centers and cyber-physical systems requiring low energy memory. At least 3 PhD students would be trained on the techniques of complementary nano-fabrication, nano-characterization and computer modeling. The investigators will hold a nano-magnetism workshop for high school students and will host under-represented K-12 students in their labs for a summer month, as well as leverage the 'Nano-Days' program to reach out to high school students.

The key technical approach in this research project will involve the following complementary experimental and modeling research directions: (i) Modeling the combined effect of strain and spin transfer torque (STT) on the magnetization switching in the presence of thermal noise (ii) Experimental demonstration of strain induced reduction in STT write current in optimized devices (guided by the modeling effort) (iii) Proof-of-concept demonstration of acoustic wave induced reduction in STT write current. The knowledge generated by this research would lead to better understanding of the combined effect of strain and spin torque on switching nano-magnetic memory elements and the switching probability in the presence of thermal noise. If successful, it would demonstrate a low energy paradigm for writing information in non-volatile nano-magnetic memory devices.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.