Memory and Logic Electronics Based on Nanoscale Resistive Switching Devices

Wei Lu
Electrical Engineering and Computer Science
University of Michigan, Ann Arbor, MI 48109, USA
Abstract
Resistive switching memory (RRAM), along with STT-MRAM, has been widely regarded as a promising candidate for future non-volatile memory and logic applications. In this talk, I will discuss our recent progress based on these two-terminal, nanoscale resistive switching devices. Two types of devices – one with abrupt resistance change (digital) and one with incremental resistance change (analog) have been developed by choosing the proper combinations of electrode and switching materials, film stack and programming conditions. The digital RRAM devices show excellent memory performance metrics in terms of scalability, speed, ON/OFF ratio, endurance and retention. Detailed TEM studies have been carried out to verify the switching mechanism. Functional high-density crossbar arrays have been integrated directly on top of CMOS circuits using a back-end-of-line (BEOL) process, enabling hybrid non-volatile memory and reconfigurable circuit applications. The analog devices (sometimes referred as memristors) exhibit activity-dependent, incremental conductance changes and are well suited for hardware-based, bio-inspired neuromorphic logic systems. Besides the ability to emulate synaptic behaviors phenomenologically, the internal ionic dynamics of these devices allow them to implement a number of important synaptic functions realistically. Device and circuit models based on properly chosen internal state variables have been developed that highlight the dynamic behaviors of the devices and enable efficient simulation of these devices at the system level. Prototype neuromorphic circuits based on memristor arrays have been shown to be able to perform tasks such as pattern recognition in an unsupervised fashion.

Bio Sketch
Wei Lu is an associate professor at the Electrical Engineering and Computer Science Department at the University of Michigan – Ann Arbor. He received B.S. degree in physics from Tsinghua University, Beijing, China, in 1996, and Ph.D. in physics from Rice University, Houston, TX in 2003. From 2003 to 2005, he was a postdoctoral research fellow at Harvard University, Cambridge, Massachusetts. In 2005, he joined the faculty of the Electrical Engineering and Computer Science Department at the University of Michigan as an Assistant Professor and is currently an Associate Professor. His research interest includes high-density memory based on two-terminal resistive switches (RRAM), memristor-based neuromorphic circuits, aggressively scaled nanowire transistors, and electrical transport in low-dimensional systems. To date Prof. Lu has published over 80 journal papers that have received over 9000 citations.  Prof. Lu is a co-Editor -in-Chief for Nanoscale, a member of the International Technology Roadmap for Semiconductors (ITRS), and member of two IEEE technical committees and several program committees. He is also co-founder of Crossbar Inc, a startup company based in Silicon Valley with more than $50M VC funding to date aiming to commercialize RRAM technologies. He received the NSF CAREER Award in 2009.