Six-transistor Static Random Access Memory Cell Research Articles

Variation tolerant and stability simulation of low power SRAM cell analysis using FGMOS

With technology scaling, stability, power dissipation, and device variability, the impact of process, voltage and temperature (PVT) variations has become dominant for static random access memory (SRAM) analysis for productivity and failure. In this paper, ten-transistors (10T) and low power eight-transistors SRAM cells are redesigned using floating-gate MOS transistors (FGMOS). Power centric parameters viz. read power, write power, hold power and delay are the performance analysis metrics. Further, the stochastic parameter variation to study the variability tolerance of the redesigned cell, PVT variations and Monte Carlo simulations have been carried out for 10T FGMOS SRAM cell. Stability has been illustrated with the conventional butterfly method giving read static noise margin (RSNM) and write static noise margin (WSNM) metrics for read stability and write ability, respectively. A comparative analysis with standard six-transistor SRAM cell is carried out. HSPICE simulative analysis has been carried out for 32[Formula: see text]nm technology node. The redesigned FGMOS SRAM cells provide improved performance. Also, these are robust and reliability efficient with comparable stability.

A 7T Security Oriented SRAM Bitcell

Power analysis (PA) attacks have become a serious threat to security systems by enabling secret data extraction through the analysis of the current consumed by the power supply of the system. Embedded memories, often implemented with six-transistor static random access memory (SRAM) cells, serve as a key component in many of these systems. However, conventional SRAM cells are prone to side-channel PA attacks due to the correlation between their current characteristics and written data. To provide resiliency to these types of attacks, we propose a security-oriented 7T SRAM cell, which incorporates an additional transistor to the original 6T SRAM implementation and a two-phase write operation, which significantly reduces the correlation between the stored data and the power consumption during write operations. The proposed 7T SRAM cell was implemented in a 28 nm technology and demonstrates over $1000 {\times }$ lower write energy standard deviation between write “1” and “0” operations compared to a conventional 6T SRAM. In addition, the proposed cell has a 39%–53% write energy reduction and a 19%–38% reduced write delay compared to other PA resistant SRAM cells.

Low-Power Near-Threshold 10T SRAM Bit Cells With Enhanced Data-Independent Read Port Leakage for Array Augmentation in 32-nm CMOS

The conventional six-transistor static random access memory (SRAM) cell allows high density and fast differential sensing but suffers from half-select and read-disturb issues. Although the conventional eight-transistor SRAM cell solves the read-disturb issue, it still suffers from low array efficiency due to deterioration of read bit-line (RBL) swing and $\text{I}_{\mathbf {on}}/\text{I}_{\mathbf {off}}$ ratio with increase in the number of cells per column. Previous approaches to solve these issues have been afflicted by low performance, data-dependent leakage, large area, and high energy per access. Therefore, in this paper, we present three iterations of SRAM bit cells with nMOS-only based read ports aimed to greatly reduce data-dependent read port leakage to enable 1k cells/RBL, improve read performance, and reduce area and power over conventional and 10T cell-based works. We compare the proposed work with other works by recording metrics from the simulation of a 128-kb SRAM constructed with divided-wordline-decoding architecture and a 32-bit word size. Apart from large improvements observed over conventional cells, up to 100-mV improvement in read-access performance, up to 19.8% saving in energy per access, and up to 19.5% saving in the area are also observed over other 10T cells, thereby enlarging the design and application gamut for memory designers in low-power sensors and battery-enabled devices.

Lowering data retention voltage in static random access memory array by post fabrication self-improvement of cell stability by multiple stress application

We propose a new version of the post fabrication static random access memory (SRAM) self-improvement technique, which utilizes multiple stress application. It is demonstrated that, using a device matrix array (DMA) test element group (TEG) with intrinsic channel fully depleted (FD) silicon-on-thin-buried-oxide (SOTB) six-transistor (6T) SRAM cells fabricated by the 65 nm technology, the lowering of data retention voltage (DRV) is more effectively achieved than using the previously proposed single stress technique.

Impact of Channel Hot Carrier Effect in Junction-and Doping-Free Devices and Circuits

In this brief, we have investigated the time-dependent performance degradation of digital benchmark circuits due to channel hot carrier (CHC) stress in junction-and doping-free devices. For device–circuit interaction, we have developed the lookup table-based Verilog-A models of both devices for circuit simulations. At device level, the drain current of conventional n-type junctionless FET (JLFET) is degraded by 20%–25%; however, dopingless JLFET experiences 10%–15% degradation in drain current due to CHC stress of different time spans. The circuit-level simulations of digital benchmark circuits, such as standard six-transistor static random access memory (SRAM) cell and ring oscillator (RO), have large impact of CHC stress. For example, operating frequency of RO designed with conventional JLFET is degraded by 3.3 to 5 times due to CHC stress of 2000 and 6000 s. Similarly, read and write delays of SRAM cell are also degraded by CHC stress conditions.

Low standby leakage 12T SRAM cell characterisation

ABSTRACTIn this work, a low power and variability-aware static random access memory (SRAM) architecture based on a twelve-transistor (12T) cell is proposed. This cell obtains low static power dissipation due to a parallel global latch (G-latch) and storage latch (S-latch), along with a global wordline (GWL), which offer a high cell ratio and pull-up ratio for reliable read and write operations and a low cell ratio and pull-up ratio during idle mode to reduce the standby power dissipation. In the idle state, only the S-latch stores bits, while the G-latch is isolated from the S-latch and the GWL is deactivated. The leakage power consumption of the proposed SRAM cell is thereby reduced by 38.7% compared to that of the conventional six-transistor (6T) SRAM cell. This paper evaluates the impact of the chip supply voltage and surrounding temperature variations on the standby leakage power and observes considerable improvement in the power dissipation. The read/write access delay, read static noise margin (SNM) and write SNM were evaluated, and the results were compared with those of the standard 6T SRAM cell. The proposed cell, when compared with the existing cell using the Monte Carlo method, shows an appreciable improvement in the standby power dissipation and layout area.

Low power and robust memory circuits with asymmetrical ground gating

Multi-threshold CMOS (MTCMOS) technique is commonly used for suppressing leakage currents in idle circuits. The application of MTCMOS technique to static random access memory (SRAM) circuits is investigated in this paper. Two asymmetrically ground-gated MTCMOS SRAM circuits are presented for providing a low-leakage SLEEP mode with data retention capability. The read and hold static noise margins are increased by up to 7.24× and 2.39×, respectively, with the new asymmetrical SRAM cells as compared to conventional six-transistor (6T) SRAM cells in a 65nm CMOS technology. The overall electrical quality of a memory array is enhanced by up to 103.52× and 57.75% with the proposed asymmetrically ground-gated memory cells as compared to the conventional ground-gated 6T and eight-transistor (8T) SRAM cells, respectively. The new asymmetrical SRAM cells also exhibit enhanced tolerance to process parameter variations and lower minimum applicable power supply voltages as compared with the conventional 6T and 8T SRAM cells.

Variability-aware 7T SRAM circuit with low leakage high data stability SLEEP mode

The design of nanoscale static random access memory (SRAM) circuits becomes increasingly challenging due to the degraded data stability, weaker write ability, increased leakage power consumption, and exacerbated process parameter variations in each new CMOS technology generation. A new asymmetrically ground-gated seven-transistor (7T) SRAM circuit is proposed for providing a low leakage high data stability SLEEP mode in this paper. With the proposed asymmetrical 7T SRAM cell, the data stability is enhanced by up to 7.03x and 2.32x during read operations and idle status, respectively, as compared to the conventional six-transistor (6T) SRAM cells in a 65nm CMOS technology. A specialized write assist circuitry is proposed to facilitate the data transfer into the new 7T SRAM cells. The overall electrical quality of a 128-bit×64-bit memory array is enhanced by up to 74.44x and 13.72% with the proposed asymmetrical 7T SRAM cells as compared to conventional 6T and 8T SRAM cells, respectively. Furthermore, the new 7T SRAM cell displays higher data stability as compared to the conventional 6T SRAM cells and wider write voltage margin as compared to the conventional 8T SRAM cells under the influence of both die-to-die and within-die process parameter fluctuations.

A Novel Robust and Low-Leakage SRAM Cell With Nine Carbon Nanotube Transistors

A novel static random-access memory (SRAM) cell with nine carbon nanotube MOSFETs (9-CN-MOSFETs) is proposed in this paper. With the new 9-CN-MOSFET SRAM cell, the read data stability is enhanced by 99.09%, while providing similar read speed as compared with the conventional six-transistor (6T) SRAM cell in a 16-nm carbon nanotube transistor technology. The worst-case write voltage margin is increased by $4.57\times $ and $3.90\times $ with the proposed 9-CN-MOSFET SRAM cell as compared with the conventional 6T SRAM cell and a previously published eight-transistor (8T) SRAM cell, respectively. A 1 Kibit SRAM array with the new memory cells consumes 34.18% and 12.27% lower leakage power as compared with the memory arrays with 6T and 8T SRAM cells, respectively, in idle mode. The overall electrical quality is enhanced by up to $13.63\times $ with the proposed 9-CN-MOSFET memory circuit as compared with the other memory cells that are evaluated in this paper.

High density and low leakage current based SRAM cell using 45 nm technology

This article is based on the observation of a Complementary Metal-Oxide Semiconductor (CMOS) five-transistor Static Random Access Memory (SRAM) cell (5T SRAM cell) for very high density and low power applications. This cell retains its data with leakage current and positive feedback without refresh cycle. This 5T SRAM cell uses one word-line and one bit-line and extra read-line control. The new cell size is 21.66% smaller than a conventional six-transistor SRAM cell using the same design rules with no performance degradation. Simulation and analytical results show purposed cell has correct operation during read/write and also the delay of new cell is 70.15% smaller than a six-transistor SRAM cell. The new 5T SRAM cell contains 72.10% less leakage current with respect to the 6T SRAM memory cell using cadence 45 nm technology.

Design and analysis of 45 nm low power 32 kb embedded static random access memory (SRAM) cell

In sub-100 nm generation, gate-tunneling leakage current increases and dominates the total standby leakage current of LSIs based on decreasing gate-oxide thickness. Showing that the gate leakage current is effectively reduced by lowering the gate voltage, we propose a local DC level control (LDLC) for static random access memory (SRAM) cell arrays and an automatic gate leakage suppression driver (AGLSD) for peripheral circuits. We designed and analyzed a 32 kb 1-port SRAM using 45 nm CMOS technology. The six-transistor SRAM cell size is 1.25 µm2. Evaluation shows that the standby current of 32 kb SRAM is 1.2 µA at 1.2 V and room temperature. It was reduced to 7.5% of the conventional SRAM. Key words: Embedded static random access memory (SRAM), gate leakage, low power, standby current, random access memory (RAM).

A Novel Nanoinjection Lithography (NInL) Technology and Its Application for 16-nm Node Device Fabrication

For more than 45 years, photon- and electron-sensitive materials have been used to produce pattern-transfer masks in the lithographic manufacturing of integrated circuits. With the semiconductor technology feature size continuing to shrink and the requirements of low-variability and low-cost manufacturing, optical lithography is driven to its limits. In this paper, we report a novel nanoinjection lithography (NInL) technique that employs electron-beam-assisted deposition to form pattern-transfer hard mask in a direct-write deposit approach. By scanning the 4.6-nm-diameter electron beam while injecting a suitable organometallic precursor gas around the location of e-beam and just above the substrate, we form a high-density (pitch: 40 nm) high-uniformity (3-sigma linewidth roughness: 2 nm) hard mask for subsequent etching without using proximity-effect correction techniques. Furthermore, this technique can also directly deposit a metal pattern for interconnect or a dielectric pattern without the need for separate metal or dielectric deposition, photoresist etch-mask, and etching processes. The NInL approach simplifies the hard-mask creation or even metal or dielectric pattern creation process modules from five or tens of steps to only a single step. Therefore, it saves both photomask making and wafer processing costs. In addition, room-temperature NInL deposition of conductor/dielectric materials enables the fabrication of small versatile devices and circuits. For demonstration, we fabricated a functional 16-nm six-transistor static random access memory (SRAM) cell (area: occupying only 0.039 μm2), 43% the size of the smallest previously reported SRAM cell, using the FinFET structure and a dynamic Vdd regulator approach. The NInL technique offers a new way of exploring low-volume high-value 16-nm complementary metal-oxide-semiconductor (CMOS) devices and circuit designs with minimal additional investment and obtains early access to extreme CMOS scaling.