Ultrafast and Energy-efficient Anti-ferromagnetic Electric-field-controlled Memory Devices

Northwestern University, Evanston IL

Investigators

Abstract

There is a fast-growing demand for new on-chip memory and data storage solutions in computing systems, fueled by the growth of data-intensive computing tasks for artificial intelligence and autonomous systems. Increasingly, the performance of computing systems is determined by the speed and energy efficiency of reading data from or writing it into the memory components of the system, rather than the speed with which logic operations can be performed. This trend is driving a paradigm shift of the semiconductor industry from logic-centric to memory-centric computing architectures, where storage and processing of data are closely integrated to increase computational efficiency. This memory-centric computing paradigm puts new requirements on the memory devices in terms of speed, switching energy, endurance, and manufacturing processes. However, present memory solutions do not scale adequately to address all of these demands and suffer from standby power dissipation due to leakage and/or refresh requirements. This project is focused on the development of a new type of two-terminal magnetic memory device, referred to as antiferromagnetic voltage-controlled memory, to address the requirements of memory-centric computing applications. In addition to its technical and scientific impact, the project will impact the education of students at undergraduate and graduate levels, including women and underrepresented minorities at Northwestern. The students will study, develop, and implement state-of-the-art nano-fabrication and high-speed measurements for emerging memory devices, working at the intersection of physics, material science, and electrical engineering. Due to the interdisciplinary nature of the project, they will also take part in collaborations with industry and other departments at Northwestern and other universities. The project also leverages and contributes to on-going outreach efforts at Northwestern, engaging the general public in the advancement of science. The proposed project incorporates two innovative elements in the device structure of magnetic random-access memory: (i) It uses metallic antiferromagnetic layers with uniaxial magnetic anisotropy for data storage. This is different from the conventionally used ferromagnetic free layers in existing magnetic memory, and provides a number of advantages: First, due to the zero overall magnetic moment of the antiferromagnet, the resulting device is robust against external magnetic fields, without any requirements for magnetic shielding. Second, it eliminates bit-to-bit dipole interactions, which may result in scaling challenges and increased error rates in ferromagnetic memory arrays with tight pitch. Third, much faster switching can be achieved using antiferromagnetic resonance, which can have frequencies up to the Terahertz range due to the large built-in exchange field of the antiferromagnetic material. (ii) Voltage-Controlled Magnetic Anisotropy will be used for energy-efficient writing of data. Specifically, a very short voltage pulse will be used to initiate the resonant dynamics and will be timed to result in a voltage-induced complete switching of the N?el vector. The switching occurs without the need for electric current, thus reducing write energy to reach the atto-Joule per bit range. The voltage-controlled magnetic anisotropy effect has previously only been demonstrated in the case of ferromagnetic devices. Hence, its demonstration and utilization in the case of antiferromagnets is one of the key intellectual merits of the present proposal. 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.