Spin-torque Sensors for Energy Efficient and High Speed Global Interconnects

Zubair Al Azim, Purdue University

Abstract

Reduction of power dissipation in global interconnect lines while maintaining fast performance is an ongoing challenge in scaled CMOS technology. In order to address this issue, we propose low-voltage, low-current interconnect architectures using spin-torque (ST) sensors that can optimize the overall delay and energy consumption. Conventional techniques for reducing power dissipation on long interconnects involve low voltage swing on the interconnect lines. However, such techniques require power consuming voltage converters or trans-impedance amplifiers at the receivers. We propose ST sensor based signal conversion at the receiver that offers an efficient signal conversion process. The proposed ST sensor devices consist of a nanomagnetic strip with tunable magnetization. The magnetization of the nanomagnet can be modified by using input data dependent low-current or low-voltage signals. The nanomagnet is used as the free layer of a magnetic tunnel junction (MTJ). The resistance of the MTJ changes with the magnetization of the nanomagnet and this resistance change can be easily sensed using a reference MTJ. Such a receiver configuration acts as a built-in latch and hence, expensive voltage converters or trans-impedance amplifiers can be avoided. We explore several spintronic device structures that can be used as the driving mechanism for achieving data dependent tunable magnetization. We first use a domain wall magnet adjacent to a spin-Hall metal (SHM) layer. The magnetization can be controlled by passing a low current through the SHM layer that can displace the domain wall. Next, we replace the domain wall magnet with a skyrmion nanotrack. Again, the SHM layer current can move the skyrmion and thereby control the magnetization of the nanotrack. We finally use magnetoelectric effect induced magnetization reversal to use a voltage signal instead of a current signal to modify the magnetization. We evaluate the different pros and cons of using these different spintronic device structures to design an ST sensor based global interconnect. The performance metrics are thoroughly investigated and are compared with existing CMOS techniques. Our simulation results indicate the possibility of significant performance improvement using the proposed ST sensor based global interconnect. Finally, we extend our concept to optical interconnect design. Optical interconnect can greatly increase the interconnect density and bandwidth since light signals can travel long distances with minimal attenuation. However, the conversion from optical-to-electrical signal at the receiving end is the performance bottleneck. We propose the use of both light helicity dependent and independent magnetization reversal to design efficient optical receivers. The proposed optical receivers do not require photodiodes or power hungry trans-impedance amplifiers that limit the performance of existing optical receivers. Our simulation results show tremendous energy efficiency by using light induced magnetization reversal based optical receivers for optical interconnects.

Degree

Ph.D.

Advisors

Roy, Purdue University.

Subject Area

Electrical engineering

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