LOW TEMPERATURE SPIN-TORQUE MRAM FOR INTEGRATION WITH SUPERCONDUCTING DIGITAL ELECTRONICS
Abstract
Low Temperature Spin-Torque MRAM for Integration with Superconducting Electronics Project Abstract The every increasing power requirements of ultra-high performance computing will soon result in an unacceptably high power cost for many if not all computationally intensive applications if there is not a major change in the underlying technology to substantially reduce the energy cost per digital operation. Cryogenic electronics based on high performance superconducting Josephson-junction digital circuitry operate on a much lower average energy budget per operation, even after adding in the cryogenic refrigeration costs, and offer an attractive pathway out of the impending dead-end for high performance computation. However cryogenic computation also requires high performance, low energy cost, memory cells and circuits that are compatible with integration with the superconducting circuitry. Magnetic random access memory (MRAM) cells that utilize electrical currents to reliably and quickly reverse the magnetic orientation of nanoscale thin film ferromagnets can provide a high performance solution to this requirement. Such devices operate on the fact that the electrons flowing in the device have their quantum-mechanical spin polarized in a particular direction and when these electrons impinge on the ferromagnet spin angular momentum is transferred from the flowing current to the ferromagnet. This “spin transfer” exerts a torque on the ferromagnet’s magnetic moment and, if the current is strong enough, will effect its reversal from one stable orientation to the other, whereby the magnetic moment reverses its orientation by 180o. Essential to the operation of the basic device is the strength of the spin polarization which is achieved by either passing the initially unpolarized current through a thin film ferromagnetic polarizer, or by utilizing the recently discovered spin Hall effect by which a current flowing through a normal metal layer, such as Pt or Ta, produces a spin current by a quantum mechanical spin scattering process. The focus of this project is on the study and further development of cryogenic spin torque (ST) phenomena for improved device performance in cryogenic ST-MRAM applications. Two efforts will be pursued. First, we will pursue a thin film materials development effort to utilize high-quality thin film layers of a class of ferromagnetic alloys, known as Heusler alloys, that have been shown to exhibit very high spin polarization as the magnetic free layer and as the in-plane polarizer/analyzer in a cryogenic spin torque (COST) device structure. The successful incorporation of such a material into a COST device will enhance both the readout signal of the MRAM cell, generally improve the reliability of the write process, and lower the write energy. Second we will study and further develop the spin Hall effect in Pt alloys and other spin Hall metallic systems with that have prospects for enhanced energy efficiency of the memory cell. The objective is to additionally enhance the effectiveness of the spin Hall generated torques for the reliable switching of ferromagnetic layers to enable second-generation cryogenic spin Hall effect devices that will better meet the performance metrics ultimately required for cryogenic ST-MRAM.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 08, 2016
- Source ID
- N000141512449
Entities
People
- Robert A. Buhrman
Organizations
- Cornell University
- Office of Naval Research
- United States Navy