Conventional Static Random Access Memory Cell Research Articles

Design of Static Random-Access Memory Cell for Fault Tolerant Digital System

This paper comparatively analyzes the static random-access memory (SRAM) cell designs for fault tolerance. Since SRAM cells are sensitive to radiation-induced single event upsets, various circuit-level approaches have been applied. Compared to the conventional SRAM cell circuits, one possibility is adding redundant storage nodes by means of additional transistors. The strength and weakness of the SRAM cells in terms of various performance aspects—speed, area, power, stability, fault tolerance, etc.—according to the design approaches are compared analytically and discussed. The discussion concludes that, in the future, it is paramount to develop an SRAM cell design with a mitigated trade-off between read/write performance and SEU tolerance.

A 7T SECURITY ORIENTED SRAM BITCELL USING VLSI

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 (6T) 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 power analysis 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× 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 power analysis resistant SRAM cells. Key Words: Power Analysis, SRAM Design, 6T SRAM, 7T SRAM, Power Dissipation Software Tools:  Tanner eda Tool

A Low-Power and High-Stability 8T SRAM Cell with Diode-Connected Transistors

This research paper proposes a low-power, high-stability 8T static random access memory (SRAM) cell. The proposed SRAM cell is a modified structure of the conventional 6T SRAM cell. The introduction of two diode-connected transistors in the pull-down network of the conventional 6T SRAM cell gives the proposed 8T SRAM cell structure. The presence of diode-connected transistors improves the power and noise performances of the proposed cell as compared to those of the conventional bit cells. The power consumption and static noise margin (SNM) of the suggested SRAM cell are calculated for write, hold and read operations. Also, the write and read delays of the proposed and conventional bit cells are observed. The power, speed, noise margin and area of the proposed 8T SRAM cell are compared with those of some of the existing SRAM cells. In comparison to conventional SRAM cells, the proposed cell consumes less power and has higher stability, according to the study. A novel dual-supply ([Formula: see text][Formula: see text]V and [Formula: see text][Formula: see text]V or 200[Formula: see text]mV) concept is applied for the existing and proposed SRAM cells. The noise and power performances of SRAM cells are well improved under the condition of dual supply as compared to the conventional supply voltage ([Formula: see text][Formula: see text]V and [Formula: see text][Formula: see text]V). A [Formula: see text] memory array of the proposed 8T SRAM cell is formed and the performance of the array structure is compared with that of [Formula: see text] array of the conventional 6T SRAM cell. The layouts of existing and proposed SRAM cells are illustrated. The simulation is carried out using the Cadence Virtuoso simulation EDA tool in 90-nm CMOS technology.

Low Power PPN inverter based 10T SRAM Cell

Objectives: In the present power-hungry world, the objective of this paper is to design a system that helps in the reduction of power consumption of systems. A memory cell, more specifically an SRAM cell being the major contributor to the increased power becomes an important unit to be considered in such systems for reducing power. This paper presents an improved single-ended PPN inverter based 10T SRAM cell. Methods: The proposed cell makes use of PPN-inverters. The CMOS inverter is replaced by the PPN-inverter in the conventional 8T SRAM cell giving an improved single-ended PPN-based 10T SRAM cell. Findings: The proposed work is compared with other SRAM cells based on delay, power dissipation, and power delay product (PDP). The proposed cell is designed and simulated on Cadence Virtuoso EDA tool version IC6.1.7 at a standard CMOS 45nm technology. The simulation results show that the proposed SRAM cell consumes lesser power and hence lower PDP compared to conventional 8T SRAM cell as well as other SRAM cells and with the use of high threshold voltage transistors in the read circuit a further decrease in the power consumption is observed. So, by use of PPN inverter in 8T SRAM cell a new design for low power consuming SRAM cell is achieved. Novelty: The proposed cell is optimized in terms of power dissipation making it more efficient for use in portable battery-operated devices. Keywords 10T SRAM cell, Low power, PPN inverter, Static Random­Access Memory (SRAM)

High Stable and Low Power 10T CNTFET SRAM Cell

The ultimate aim of a memory designer is to design a memory cell which could consume low power with high data stability in the deep nanoscale range. The implementation of Very Large-Scale Integration (VLSI) circuits using MOSFETs in nanoscale range faces many issues such as increasing of leakage power and second-order effects that are easily affected by the PVT variation. Hence, it is essential to find the best alternative of MOSFET for deep submicron design. The Carbon Nanotube Field Effect Transistor (CNTFET) can eradicate all the demerits of MOSFET and be the best replacement of MOSFET for nanoscale range design. In this paper, a 10T CNTFET Static Random Access Memory (SRAM) cell is proposed. The power consumption and Static Noise Margin (SNM) are analyzed. The power consumption and stable performance of the proposed 10T CNTFET SRAM cell are compared with that of conventional 10T CNTFET SRAM cell. The power and stability analyses of the proposed 10T and conventional 10T CNTFET SRAM cells are carried out for the CNTFET parameters such as pitch and chiral vector ([Formula: see text]). The power and SNM analyses are carried out for [Formula: see text]20% variation of oxide thickness (Hox), different dielectric constant (Kox). The supply voltage varies from 0.9[Formula: see text]V to 0.6[Formula: see text]V and temperature varies from 27∘C to 125∘C. The simulation results show that the proposed 10T CNTFET SRAM cell consumes lesser power than conventional 10T CNTFET SRAM cell during the write, hold and read modes. The write, hold and read stability of the proposed 10T CNTFET SRAM cell are higher as compared with that of conventional 10T CNTFET SRAM. The conventional and proposed 10T SRAM cells are also implemented using MOSFET. The stability and power performance of proposed 10T SRAM cell is also as good as conventional 10T SRAM for MOSFET implementation. The proposed 10T SRAM cell consumes lesser power and gives higher stability than conventional 10T SRAM cell in both CNTFET and MOSFET implementation. The simulation is carried out using Stanford University 32[Formula: see text]nm CNTFET model in HSPICE simulation tool.

A Secure Data-Toggling SRAM for Confidential Data Protection

We study the security feature of static random access memory (SRAM) against the data imprinting attack and provide a solution to protect the SRAM from this attack. There are four main contributions in this paper. First, the negative-bias temperature-instability (NBTI) degradation of PMOS transistors in the conventional SRAM cell that causes the data imprinting effect is explained. Second, the data imprinting effect that leaks the stored information in the conventional SRAM cell is investigated. Third, a novel low transistor-count transmission-gate-based master–slave SRAM cell is proposed to periodically toggle the stored data for reducing the data imprinting effect. Fourth, an efficient imprinting analysis flow is proposed to evaluate the proposed data-toggling SRAM for quantifying the data imprinting effect. Based on a 65-nm CMOS process, we implement and prototype the proposed 1k-byte data-toggling SRAM design. We perform our imprinting analysis flow on various SRAM ICs and benchmark our proposed data-toggling SRAM IC against the non-toggling SRAM IC and a commercial Lyontek SRAM IC. From the measurement results, the non-toggling SRAM and Lyontek SRAM suffer from 60% and 81% data imprinting effects, respectively, whereas our data-toggling SRAM has only 11% data imprinting effect (at 160-kHz toggling frequency). The data-toggling SRAM could switch between high security (< 5% data imprinting effect) high power mode for hardware security applications and low power (< 0.1mW) low security mode for power-saving applications. Particularly, our data-toggling SRAM could feature as low as ~1% data imprinting effect when increasing the toggling frequency to 1.6 MHz by compromising the power dissipation. Using the image analysis flow, the stored information is revealed in both the non-toggling and Lyontek SRAM ICs but is well protected in the proposed data-toggling SRAM IC.

Design of Novel SRAM Cell Using Hybrid VLSI Techniques for Low Leakage and High Speed in Embedded Memories

Static or leakage power is the dominating component of total power dissipation in deep nanometer technologies below 90 nm, which has resulted in increase from 18% at 130 nm to 54% at 65 nm technology due to continued device and voltage scaling. Static random access memory (SRAM) is a type of RAM in which data is not written permanently and it does not need to be refreshed periodically. Different techniques have been applied to SRAM cell to reduce leakage power without affecting its performance. A novel 10T SRAM architecture is proposed in this paper which operates in three modes (active, park, standby or hold). The main objective of the proposed architecture is to provide better stability and reduced delay in active mode, reduced leakage current in standby mode and retaining the logic state in park mode. Design metrics such as static and dynamic power, delay, power delay product, energy, energy delay product, rise and fall time, slew rate and static noise margin are taken into account. All the circuits were designed using SYNOPSYS EDA tool and simulated in 30 nm technology. Simulation results shows that the proposed SRAM is much better than conventional and other SRAM cells designed using hybrid techniques.

Single Bit-Line 7T SRAM Cell for Near-Threshold Voltage Operation With Enhanced Performance and Energy in 14 nm FinFET Technology

Although near-threshold voltage (NTV) operation is an attractive means of achieving high energy efficiency, it can degrade the circuit stability of static random access memory (SRAM) cells. This paper proposes an NTV 7T SRAM cell in a 14 nm FinFET technology to eliminate read disturbance by disconnecting the path from the bit-line to the cross-coupled inverter pair using the transmission gate. In the proposed 7T SRAM cell, the half-select issue is resolved, meaning that no write-back operation is required. A folded-column structure is applied to the proposed 7T SRAM cell to reduce the read access time and energy consumption. To reduce the standby power, the proposed 7T SRAM cell uses only a single bit-line for both read and write operations. To achieve proper “1” writing operation with a single bit-line, a two-phase approach is proposed. Compared to the conventional 8T SRAM cell, the proposed 7T SRAM cell improves the read access time, energy, and standby power by 13%, 42%, and 23%, respectively, with a 3% smaller cell area.

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.

Ratioless full-complementary 12-transistor static random access memory for ultra low supply voltage operation

In this study, a ratioless full-complementary 12-transistor static random access memory (SRAM) was developed and measured to evaluate its operation under an ultra low supply voltage range. The ratioless SRAM design concept enables a memory cell design that is free from the consideration of the static noise margin (SNM). Furthermore, it enables a SRAM function without the restriction of transistor parameter (W/L) settings and the dependence on the variability of device characteristics. The test chips that include both conventional 6-transistor SRAM cells and the ratioless full-complementary 12-transistor SRAM cells were developed by a 180 nm CMOS process to compare their stable operations under an ultralow supply voltage condition. The measured results show that the ratioless full-complementary 12-transistor SRAM has superior immunity to device variability, and its inherent operating ability at the supply voltage of 0.22 V was experimentally confirmed.

Comparison and distribution of minimum operation voltage in fully depleted silicon-on-thin-buried-oxide and bulk static random access memory cells

The minimum operation voltage (Vmin) of intrinsic channel fully depleted (FD) silicon-on-thin-buried-oxide (SOTB) static random access memory (SRAM) cells are measured and compared with those of conventional bulk SRAM cells in order to directly compare the worst cells. It is confirmed that the worst Vmin of 1 kbit SOTB SRAM cells is half that of 1 kbit bulk cells. The distribution of Vmin of 48 kbit SOTB and bulk SRAM cells are also measured and compared. The results show a great advantage of SOTB SRAM cells for lower power and lower voltage operation upon introducing SOTB, because of reduced VTH variability.

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.

A Compact Half Select Disturb Free Static Random Access Memory Cell with Stacked Vertical Metal–Oxide–Semiconductor Field-Effect Transistor

In this paper, a half select disturb free compact static random access memory (SRAM) cell with the stacked vertical metal–oxide–semiconductor field-effect transistor (MOSFET) is proposed, and the impacts on its cell size, stability and speed performance are evaluated. The proposed SRAM cell has a small cell size, which is 67% of the conventional eight-transistor (8T) SRAM cell, because of its stacked vertical MOSFET structure. It realizes a half select disturb free SRAM operation; therefore, a larger static noise margin of 5.9 times is achieved in comparison with the conventional 8T SRAM cell. It suppresses the degradation of the write margin, thus its write margin is 84.2% of the conventional 8T SRAM cell. Furthermore, it suppresses the degradation of the write time by 39% (0.249 ns). The proposed compact SRAM cell with the stacked vertical MOSFET is a suitable SRAM cell with a small cell size, immunity to the half select disturb, wide write margin and fast write time.

A Compact Half Select Disturb Free Static Random Access Memory Cell with Stacked Vertical Metal–Oxide–Semiconductor Field-Effect Transistor

In this paper, a half select disturb free compact static random access memory (SRAM) cell with the stacked vertical metal–oxide–semiconductor field-effect transistor (MOSFET) is proposed, and the impacts on its cell size, stability and speed performance are evaluated. The proposed SRAM cell has a small cell size, which is 67% of the conventional eight-transistor (8T) SRAM cell, because of its stacked vertical MOSFET structure. It realizes a half select disturb free SRAM operation; therefore, a larger static noise margin of 5.9 times is achieved in comparison with the conventional 8T SRAM cell. It suppresses the degradation of the write margin, thus its write margin is 84.2% of the conventional 8T SRAM cell. Furthermore, it suppresses the degradation of the write time by 39% (0.249 ns). The proposed compact SRAM cell with the stacked vertical MOSFET is a suitable SRAM cell with a small cell size, immunity to the half select disturb, wide write margin and fast write time.

Design and Analysis of Two Low-Power SRAM Cell Structures

In this paper, two static random access memory (SRAM) cells that reduce the static power dissipation due to gate and subthreshold leakage currents are presented. The first cell structure results in reduced gate voltages for the NMOS pass transistors, and thus lowers the gate leakage current. It reduces the subthreshold leakage current by increasing the ground level during the idle (inactive) mode. The second cell structure makes use of PMOS pass transistors to lower the gate leakage current. In addition, dual threshold voltage technology with forward body biasing is utilized with this structure to reduce the subthreshold leakage while maintaining performance. Compared to a conventional SRAM cell, the first cell structure decreases the total gate leakage current by 66% and the idle power by 58% and increases the access time by approximately 2% while the second cell structure reduces the total gate leakage current by 27% and the idle power by 37% with no access time degradation.