#### Sponsor

Portland State University. Department of Electrical and Computer Engineering

#### Advisor

Marek A. Perkowski

#### Date of Award

6-6-2018

#### Document Type

Dissertation

#### Degree Name

Doctor of Philosophy (Ph.D.) in Electrical and Computer Engineering

#### Department

Electrical and Computer Engineering

#### Physical Description

1 online resource (xvii, 186 pages)

#### DOI

10.15760/etd.6256

#### Abstract

Over the past five decades, exponential advances in device integration in microelectronics for memory and computation applications have been observed. These advances are closely related to miniaturization in integrated circuit technologies. However, this miniaturization is reaching the physical limit (i.e., the end of Moore's Law). This miniaturization is also causing a dramatic problem of heat dissipation in integrated circuits. Additionally, approaching the physical limit of semiconductor devices in fabrication process increases the delay of moving data between computing and memory units hence decreasing the performance. The market requirements for faster computers with lower power consumption can be addressed by new emerging technologies such as memristors.

Memristors are non-volatile and nanoscale devices and can be used for building memory arrays with very high density (extending Moore's law). Memristors can also be used to perform stateful logic operations where the same devices are used for logic and memory, enabling in-memory logic. In other words, memristor-based stateful logic enables a new computing paradigm of combining calculation and memory units (versus von Neumann architecture of separating calculation and memory units). This reduces the delays between processor and memory by eliminating redundant reloading of reusable values. In addition, memristors consume low power hence can decrease the large amounts of power dissipation in silicon chips hitting their size limit.

The primary focus of this research is to develop the circuit implementations for logic computations based on memristors. These implementations significantly improve the performance and decrease the power of digital circuits. This dissertation demonstrates in-memory computing using novel memristive logic gates, which we call volistors (voltage-resistor gates). Volistors capitalize on rectifying memristors, i.e., a type of memristors with diode-like behavior, and use voltage at input and resistance at output. In addition, programmable diode gates, i.e., another type of logic gates implemented with rectifying memristors are proposed. In programmable diode gates, memristors are used only as switches (unlike volistor gates which utilize both memory and switching characteristics of the memristors). The programmable diode gates can be used with CMOS gates to increase the logic density. As an example, a circuit implementation for calculating logic functions in generalized ESOP (Exclusive-OR-Sum-of-Products) form and multilevel XOR network are described. As opposed to the stateful logic gates, a combination of both proposed logic styles decreases the power and improves the performance of digital circuits realizing two-level logic functions Sum-of-Products or Product-of-Sums.

This dissertation also proposes a general 3-dimentional circuit architecture for in-memory computing. This circuit consists of a number of stacked crossbar arrays which all can simultaneously be used for logic computing. These arrays communicate through CMOS peripheral circuits.

#### Persistent Identifier

https://archives.pdx.edu/ds/psu/25568

#### Recommended Citation

Aljafar, Muayad Jaafar, "New Approaches for Memristive Logic Computations" (2018). *Dissertations and Theses.* Paper 4372.

https://pdxscholar.library.pdx.edu/open_access_etds/4372

10.15760/etd.6256