Evaluation of computation-in-memory using traditional (SRAM) and emerging non-volatile devices (memristors)

Abstract

Modern computer application require large amounts of data processing. Traditional computing models involve constant data transfer between memory and processor. This data transfer is a major contributor to high energy consumption. As these applications scale, the energy demand increases. This poses challenges in terms of sustainability and operational costs. Computation In Memory (CIM) integrates processing within the memory. This reduces the need for data transfer between memory and processor. Potential for drastically lowering energy consumption.

CIM macros are often implemented using modified SRAM cells, though recent literature explores memristor-based CIM designs due to the memristor’s low-energy, non-volatile characteristics. However, no comprehensive comparisons between SRAM-based and memristor-based CIM designs exist. While memristor-based designs are hypothesized to be more energy-efficient, this has not yet been proven.

This thesis compares SRAM-based and memristor-based CIM designs to determine which is better suited for CIM applications. This has been achieved by exploring the state of the art of memristive devices, memristor based CIM macros and SRAM based CIM macros. A selection of designs were chosen to compare, including the 1T1R and 8T SRAM design, which are the most popular memristor based and SRAM based CIM designs. The schematics of all the designs were recreated and simulated using as much of the same parameters as possible in all of the designs. A simulation of performing the logic AND and the MAC operation was made. Additionally a layout of the designs was made to extract the area. The designs were compared based on area, energy consumption and delay.

From the results could be concluded that the best device for CIM depends on the application. The memristor design had the smallest area and consumed the least amount of energy for reading, logic and MAC operations. The memristor design also consumed the most amount of energy during writing and the delay for all operations is longer than with the SRAM based designs. If area, energy consumption and delay are equally important for an application, then memristor based CIM would be the better choice only if there are much more logic/read operations than write operations. It could be the better choice for MAC operations if a more energy efficient ADC was used than the one used in this thesis.