Non-volatile memory (NVM) is a form of computer memory in which the logical value (1 or 0) of a bit is retained when the computer is in its’ powered off state. Flash memory is a major form of NVM found in many computer-based technologies today, from portable solid state drives to numerous types of electronic devices. The popularity of flash memory is due in part to the successful development and commercialization of the floating gate transistor. However, as the floating gate transistor reaches its’ limits of performance and scalability, viable alternatives are being aggressively researched and developed. One such alternative is a memristor-based memory application often referred to as ReRAM or RRAM (Resistive Random Access Memory). A memristor (memory resistor) is a passive circuit element that exhibits programmable resistance when subjected to appropriate current levels. A high resistance state in the memristor corresponds to a logical ‘0’, while the low resistance state corresponds to a logical ‘1’. One memristive system currently being actively investigated is the metal/metal oxide/metal material stack in which the metal layers serve as contact electrodes for the memristor with the metal oxide providing the variable resistance functionality. Application of an appropriate potential difference across the electrodes creates oxygen vacancies throughout the thickness of the metal oxide layer, resulting in the formation of filaments of metal ions which span the metal oxide, allowing for electronic conduction through the stack. Creation and disruption of the filaments correspond to low and high resistance states in the memristor, respectively. For some time now, HfO2 has been researched and developed to serve as a high-k material for use in high performance CMOS MOSFETs. As it happens, HfO2-based RRAM devices have proven themselves as viable candidates for NVM as well, demonstrating high switching speed (< 10 ns), large OFF/ON ratio (> 100), good endurance (> 106 cycles), long lifetime, and multi-bit storage capabilities. HfO2-based RRAM is also highly scalable, having been fabricated in cells as small as 10 x 10 nm2 while still maintaining good performance. Previous work examining switching properties of micron scale HfO2-based RRAM has been performed by the Vogel group. However, a viable process for fabrication of nano-scale RRAM is required in order to continue these studies. In this work, a fabrication process for nano-scale cross-point TiN/ HfO2/TiN RRAM devices will be developed and described. Materials processing challenges will be addressed. The switching performance of devices fabricated by this process will be compared to the performance of similar devices from the literature in order to confirm process viability.

No description available.

The objective of the research is to design an electro-optic control for the Active Vertical Coupler-based Optical Cross-point Switch (OXS). The electronic control should be implemented on Printed Circuit Board (PCB) and therefore the design will include the PCB design as well. The aim of the electronic control board is to process the headers of the packets prior to entering the OXS to be switched and from the information in the headers, determine the state that the OXS should be configured in. It should then configure the optical cross-point accordingly. The electronic control board should show flexibility in the sense that it can handle different types of traffic and resolve possible contention that may occur. The research seeks to understand the problems associated with Photonic Packet Switching (PPS) networks. Two of the main problems identified in a PPS network are contention resolution and the lack of variable delays for storing optical packets. The OXS was analyzed and found to meet the requirements for future ultra-high speed PPS network technology with its high extinction ratio, wide optical bandwidth, ultra-fast switching speed and low crosstalk levels. Photonic packets were generated with 4-bit, 8-bit or 16-bit headers at a bit rate of 155 Mbit/s followed by a PRBS (Pseudo Random Bit Sequence) payload at 10 Gbit/s. Different scenarios were created with these types of packets and the electro-optic control and OXS were subjected to these scenarios with the aim of testing the flexibility of the electro-optic control to control the OXS. These scenarios include: <ul><li>Fixed length packets arriving synchronously at one input of the OXS. Some packets are destined for output 1, some are destined for output 2 and some are destined for output 3, therefore realizing a 1-to-3 optical switch.</li> <li>Eight variable length packets arriving synchronously at the OXS at one input, all of them destined for one output. The electro-optic control should open the switch cell for the correct amount of time.</li> <li>Three variable length packets arriving synchronously and asynchronously at one input of the OXS. Some packets are destined for output 1 while other packets are destined for output 2. The electro-optic control should open the correct switch cell for the correct amount of time.</li> <li>Two fixed length packets arriving at the OXS synchronously on different input ports at the same time, both destined for the same output port. The electro-optic control should detect the contention and switch the packets in such a way as to resolve the contention.</li> The electro-optic control and OXS managed to switch all these types of data traffic (scenarios) successfully and resolve the contention with an optical delay buffer. The success of the results was measured in two ways. Firstly it was deemed successful if the expected output sequence was measured at the corresponding output ports. Secondly it was successful if the degradation in quality of the packet was not drastic, meaning the output packets should have an BER (Bit Error Rate) of less than 10-9. The quality of the packets was measured in the form of eye diagrams before and after the switching and then compared. The research resulted in the design and implementation of a flexible electro-optic control for the OXS. The problem of contention was resolved for fixed length synchronous packets and a proposal is discussed to store packets for variable lengths of time by using the OXS. This electro-optic control has the potential to control the OXS for traffic with higher complexities and make the OXS compatible with future developments. / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / MEng / unrestricted

<div> <div> <p>Phase transition materials (PTM) have garnered immense interest in concurrent post-CMOS electronics, due to their unique properties such as - electrically driven abrupt resistance switching, hysteresis, and high selectivity. The phase transitions can be attributed to diverse material-specific phenomena, including- correlated electrons, filamentary ion diffusion, and dimerization. In this research, we explore the application space for these materials through extensive device-circuit co-design and propose new ideas harnessing their unique electrical properties. The abrupt transitions and high selectivity of PTMs enable steep (< 60 mV/decade) switching characteristics in Hyper-FET, a promising post-CMOS transistor. We explore device-circuit co-design methodology for Hyper-FET and identify the criterion for material down-selection. We evaluate the achievable voltage swing, energy-delay trade-off, and noise response for this novel device. In addition to the application in low power logic device, PTMs can actively facilitate non-volatile memory design. We propose a PTM augmented Spin Transfer Torque (STT) MRAM that utilizes selective phase transitions to boost the sense margin and stability of stored data, simultaneously. We show that such selective transitions can also be used to improve other MRAM designs with separate read/write paths, avoiding the possibility of read-write conflicts. Further, we analyze the application of PTMs as selectors in cross-point memories. We establish a general simulation framework for cross-point memory array with PTM based <i>selector</i>. We explore the biasing constraints, develop detailed design methodology, and deduce figures of merit for PTM selectors. We also develop a computationally efficient compact model to estimate the leakage through the sneak paths in a cross-point array. Subsequently, we present a new sense amplifier design utilizing PTM, which offers built-in tunable reference with low power and area demand. Finally, we show that the hysteretic characteristics of unipolar PTMs can be utilized to achieve highly efficient rectification. We validate the idea by demonstrating significant design improvements in a <i>Cockcroft-Walton Multiplier, </i>implemented with TS based rectifiers. We emphasize the need to explore other PTMs with high endurance, thermal stability, and faster switching to enable many more innovative applications in the future.</p></div></div>