Technology-design co-optimization of resistive cross-point array for accelerating learning algorithms on chip

Technology-design co-optimization methodologies of the resistive cross-point array are proposed for implementing the machine learning algorithms on a chip. A novel read and write scheme is designed to accelerate the training process, which realizes fully parallel operations of the weighted sum and the weight update. Furthermore, technology and design parameters of the resistive cross-point array are co-optimized to enhance the learning accuracy, latency and energy consumption, etc. In contrast to the conventional memory design, a set of reverse scaling rules is proposed on the resistive cross-point array to achieve high learning accuracy. These include 1) larger wire width to reduce the IR drop on interconnects thereby increasing the learning accuracy; 2) use of multiple cells for each weight element to alleviate the impact of the device variations, at an affordable expense of area, energy and latency. The optimized resistive cross-point array with peripheral circuitry is implemented at the 65 nm node. Its performance is benchmarked for handwritten digit recognition on the MNIST database using gradient-based sparse coding. Compared to state-of-the-art software approach running on CPU, it achieves >10³ speed-up and >10⁶ energy efficiency improvement, enabling real-time image feature extraction and learning.