In this paper we discuss the potential of emerging spintorque devices for computing applications. Recent proposals for spinbased computing schemes may be differentiated as 'all-spin' vs. hybrid, programmable vs. fixed, and, Boolean vs. non-Boolean. Allspin logic-styles may offer high area-density due to small form-factor of nano-magnetic devices. However, circuit and system-level design techniques need to be explored that leaverage the specific spin-device characterisitcs to achieve energy-efficiency, performance and reliability comparable to those of CMOS. The non-volatility of nanomagnets can be exploited in the design of energy and area-efficient programmable logic. In such logic-styles, spin-devices may play the dual-role of computing as well as memory-elements that provide field-programmability. Spin-based threshold logic design is presented as an example (dynamic resisitve threshold logic and magnetic threshold logic). Emerging spintronic phenomena may lead to ultralow-voltage, current-mode, spin-torque switches that can offer attractive computing capabilities, beyond digital switches. Such devices may be suitable for non-Boolean data-processing applications which involve analog processing. Integration of such spin-torque devices with charge-based devices like CMOS and resistive memory can lead to highly energy-efficient information processing hardware for applicatons like pattern-matching, neuromorphic-computing, image-processing and data-conversion. Towards the end, we discuss the possibility of applying emerging spin-torque switches in the design of energy-efficient global interconnects, for future chip multiprocessors.
Keywords: spin, logic, low power, threshold logic, analog, neural networks, non-Boolean, programmable logic array , interconnect
Boolean Logic with Spin-Torque Devices:Recent experiments on spin-torque in device structures like lateral spin valve (LSV) [1], ( fig. 1a), domain wall magnets (DWM) [2], and magnetic tunnel junctions; have opened new avenues for spin based computation. Several digital logic schemes have been proposed based on such devices. Such proposals may be classified as programmable or fixed logic styles.
Fixed Logic Styles using Spin-Torque SwitchesAll Spin Logic (ASL) proposed in [3], employs cascaded LSV's interacting through spin-torque, to realize logic gates and larger blocks like compact full adders [4], based on spin majority evaluation ( fig. 1). The key feature of ASL is its compactness; however, energy inefficiency resulting from relatively larger magnet-switching delay can be identified as the down-side of it. In a standard ASL design, achieving 500MHz operation for an 8x8 multiplier would require ~60ps switching-speed for individual magnets (of size 30x15x1.5nm 3 ), leading to untenably high current-levels. This results in large static power in the ASL device ( fig. 2). Non-volatility of nano-magnets can be exploited by introducing 2-phase pipelining, which would result in high-throughput for a given switching current, thereby mitigating the requirement of hi...