Multi-port Memory Design for Advanced Computer Architectures

In this thesis, we describe and evaluate novel memory designs for multi-port on-chip and off-chip use in advanced computer architectures. We focus on combining multi-porting and evaluating the performance over a range of design parameters. Multi-porting is essential for caches and shared-data systems, especially multi-core System-on-chips (SOC). It can significantly increase the memory access throughput. We evaluate FinFET voltage-mode multi-port SRAM cells using different metrics including leakage current, static noise margin and read/write performance. Simulation results show that single-ended multi-port FinFET SRAMs with isolated read ports offer improved read stability and flexibility over classical double-ended structures at the expense of write performance. By increasing the size of the access transistors, we show that the single-ended multi-port structures can achieve equivalent write performance to the classical double-ended multi-port structure for 9% area overhead. Moreover, compared with CMOS SRAM, FinFET SRAM has better stability and standby power. We also describe new methods for the design of FinFET current-mode multi-port SRAM cells. Current-mode SRAMs avoid the full-swing of the bitline, reducing dynamic power and access time. However, that comes at the cost of voltage drop, which compromises stability. The design proposed in this thesis utilizes the feature of Independent Gate (IG) mode FinFET, which can leverage threshold voltage by controlling the back gate voltage, to merge two transistors into one through high-Vt and low-Vt transistors. This design not only reduces the voltage drop, but it also reduces the area in multi-port current-mode SRAM design. For off-chip memory, we propose a novel two-port 1-read, 1-write (1R1W) phasechange memory (PCM) cell, which significantly reduces the probability of blocking at the bank levels. Different from the traditional PCM cell, the access transistors are at the top and connected to the bitline. We use Verilog-A to model the behavior of Ge2Sb2Te5 (GST: the storage component). We evaluate the performance of the two-port cell by transistor sizing and voltage pumping. Simulation results show that pMOS transistor is more practical than nMOS transistor as the access device when both area and power are considered. The estimated area overhead is 1.7�, compared to single-port PCM cell. In brief, the contribution we make in this thesis is that we propose and evaluate three different kinds of multi-port memories that are favorable for advanced computer architectures

Design and Simulation of Single Electron Transistor based SRAM and its Memory Controller at Room Temperature

Heterogeneous 3D integration of single electron transistor (SET) circuits with CMOS based circuits is achieved by stacking a SET layer above CMOS IC. Low power and delay efficient circuits can be designed using SET. In this paper, we have designed and simulated 6T SRAM array operating at room temperature and at CMOS comparable voltage. Peripheral circuit like sense amplifier, decoder, write circuit and pre-charge circuit using SET have been designed for optimum performance. The stability of 6T SRAM cell is verified using N-curve method. The designed SET based 8 x 8 bit SRAM is 99.54 % power efficient, 92.19 % faster in write access time and 78.58 % faster in read access time compared to 16 nm CMOS based SRAM. The SRAM is designed to work at CMOS comparable voltage of 800 mV, which can be scaled up to 20 mV with better efficiency. The designed SRAM is tested and verified for variation in process, voltage and temperature. The maximum frequency of operation for the designed SET based SRAM with memory controller is 4 GHz

Review on suitable eDRAM configurations for next nano-metric electronics era

We summarize most of our studies focused on the main reliability issues that can threat the gain-cells eDRAM behavior when it is simulated at the nano-metric device range has been collected in this review. So, to outperform their memory cell counterparts, we explored different technological proposals and operational regimes where it can be located. The best memory cell performance is observed for the 3T1D-eDRAM cell when it is based on FinFET devices. Both device variability and SEU appear as key reliability issues for memory cells at sub-22nm technology node.Peer ReviewedPostprint (author's final draft

Performance Analysis of FinFET Based Inverter circuit, NAND and NOR Gate at 22nm and 14nm Node technologies.

The size of integrated devices such as PC, mobiles etc are reducing day by day with multiple operations, all of these is happening because of the scaling down the size of MOSFETs which is the main component in memory, processors and so on. As we scale down the MOSFETs to the nanometer regime the short channel effects arises which degrades the system performance and reliability. Here in this paper we describe the alternative MOSFET called FinFET which reduces the short channel effects and its performance analysis of digital applications such as inverter circuit, nand and nor gates at 22nm and 14nm node technologies. DOI: 10.17762/ijritcc2321-8169.15050

Analysis of SoftError Rates for future technologies

La fiabilitat s'ha convertit en un aspecte important del disseny de sistemes informàtics a causa de la miniaturització de la tecnologia. En aquest projecte s'analitza la fiabilitat de les tecnologies actuals i futures simulant els components bàsics d'un processador

Design of Negative Bias Temperature Instability (NBTI) Tolerant Register File

Degradation of transistor parameter values due to Negative Bias Temperature Instability (NBTI) has emerged as a major reliability problem in current and future technology generations. NBTI Aging of a Static Random Access Memory (SRAM) cell leads to a lower noise margin, thereby increasing the failure rate. The register file, which consists of an array of SRAM cells, can suffer from data loss, leading to a system failure. In this work, we study the source of NBTI stress in an architecture and physical register file. Based on our study, we modified the register file structure to reduce the NBTI degradation and improve the overall system reliability. Having evaluated new register file structures, we find that our techniques substantially improve reliability of the register files. The new register files have small overhead, while in some cases they provide saving in area and power

A novel optimization framework for controlling stabilization issue in design principle of FinFET based SRAM

The conventional design principle of the finFET offers various constraints that act as an impediment towards improving ther performance of finFET SRAM. After reviewing existing approaches, it has been found that there are not enough work found to be emphasizing on cost-effective optimization by addressing the stability problems in finFET design.Therefore, the proposed system introduces a novel optimization mechanism considering some essential design attributes e.g. area, thickness of fin, and number of components. The contribution of the proposed technique is to determine the better form of thickness of fin and its related aspect that can act as a solution to minimize various other asscoiated problems in finFET SRAM. Implemented using soft-computational approach, the proposed system exhibits that it offers better energy retention, lower delay, and potential capability to offer higher throughput irrespective of presence of uncertain amount of noise within the component

Performance analysis of 22NM FinFET-based 8T SRAM cell

As CMOS devices are approaching nanometer regime, there are a lot of consequences found in scaling down CMOS devices such as short channel effects and process variations which affect the reliability and performance of the devices. Researchers have found that FinFET is one of the outstanding nominee to overcome this issue since FinFET has better control over the channel and the lower overall capacitance which will increase the performance of the 6T Static Random Access Memory (SRAM) circuit design. It will help in reducing bitline loading and hence improve SRAM performance. The conventional 6T SRAM cell suffers serious stability degradation issue due to access disturbance at low power mode. The major problem in 6T SRAM is that, when the output voltage reduced below the threshold voltage of the transistor, it will destroy the read operation of the 6T SRAM cell. The noises are easy to destruct the stored-data in the nodes of the 6T SRAM cell due to the direct path between storage nodes and bit lines. To overcome this issue, an 8T SRAM cell has been proposed where the read stability is expected to improve. The purpose of this study is to simulate and evaluate the performance of FinFET-based 6T SRAM and 8T SRAM cell and compare their results. In 8T SRAM, the two additional access transistors eliminate the discharging path from RBL to ground in 6T SRAM cell which in turn help in improving the stability of read operation in 8T SRAM. The stability of SRAM cell is determined by the butterfly curve which is obtained by combining the voltage transfer curve (VTC) of the two cross-coupled inverters of the SRAM cell. GTS Framework TCAD tool is used to design and simulate the FinFET device structure, the schematic and the layout of SRAM cell. From the findings, the FinFET gives better Vth, DIBL, SS and ION than MOSFET. In addition, 6T and 8T FinFET-based SRAM cell have shown a better stability than 6T and 8T MOSFET-based SRAM cell in retention mode, read mode and write mode. Compared to FinFET-based 6T SRAM cell, FinFET-based 8T SRAM cell improved the read stability by 68.5% and not causing any degradation on the write and retention noise margin

Accurate statistical circuit simulation in the presence of statistical variability

Semiconductor device performance variation due to the granular nature of charge and matter has become a key problem in the semiconductor industry. The main sources of this ‘statistical’ variability include random discrete dopants (RDD), line edge roughness (LER) and metal gate granularity (MGG). These variability sources have been studied extensively, however a methodology has not been developed to accurately represent this variability at a circuit and system level. In order to accurately represent statistical variability in real devices the GSS simulation toolchain was utilised to simulate 10,000 20/22nm n- and p-channel transistors including RDD, LER and MGG variability sources. A statistical compact modelling methodology was developed which accurately captured the behaviour of the simulated transistors, and produced compact model parameter distributions suitable for advanced compact model generation strategies like PCA and NPM. The resultant compact model libraries were then utilised to evaluate the impact of statistical variability on SRAM design, and to quantitatively evaluate the difference between accurate compact model generation using NPM with the Gaussian VT methodology. Over 5 million dynamic write simulations were performed, and showed that at advanced technology nodes, statistical variability cannot be accurately represented using Gaussian VT . The results also show that accurate modelling techniques can help reduced design margins by elimiating some of the pessimism of standard variability modelling approaches