Conventional SRAM Cell Research Articles

Design of improved write and read performance 12T sram cell with leakage power control technique

Currently, memory occupies nearly eighty-five percent of the allocated chip area. Integrated electronics, such as workstations and mobile gadgets, need quick memory systems that use low power. Scaling issues make it impossible to obtain low-power and resilient SRAM cells, which are critical for Internet of Things (IoT) devices, using CMOS semiconductor technology. New nanoscale technologies, like FinFET, are being proposed as a substitute for CMOS in SRAM architecture. The study introduces a novel 12T SRAM cell design using FinFET technology, including differential writing and single-ended reading operation facilitated by write-read circuitry. The cell employs a write-assist-based approach to enhance the stability of reading and writing operations accordingly. In addition to differential writing architectures, single-ended reading decreases power use, while stacking transistors and minimizing read bit-line leakage minimizes leakage power utilization. The cell's performance has been evaluated utilizing a Cadence Spectre simulator featuring 18-nm FinFET technology and compared to current SRAM architectures at a supply voltage of 0.8 V. PVT variations are conducted to evaluate the efficiency of the suggested SRAM design. The reading and writing stability of the new SRAM cells has been enhanced by a minimum of 10 % when compared with the current counterparts. A 15 % decrease in power consumption has been seen in the suggested design compared to conventional SRAM cells of the same technology.

Performance investigation of stacked-channel junctionless Tri-Gate FinFET 8T-SRAM cell

Junctionless FinFET devices are a substitute for conventional FinFET devices due to their short channel effects and easy manufacturing at sub 22 nm technology node. The manuscript presents an 8T-SRAM cell based on tri-gate junctionless FinFET technology. The FinFET device is designed with source/drain of Si material and the channel as a stack of Si − Si 0.75 Ge 0.25 − Si. The proposed SRAM cell structure consists of a CMOS inverter with stacked p-FinFETs, improving its performance in terms of noise margin and leakage power consumption. The manuscript investigates the variation of Static Noise Margin (SNM), leakage power dissipation and delay with supply voltage to analyze the sub-threshold operation of SRAM cell. The results reveal that the cascaded p-FinFETs minimize the leakage current owing to the stack effect, resulting in improved noise margin and lower leakage power. The stacked p-FinFET devices based SRAM cell achieves 1.11x read noise margin, 1.11x hold noise margin, −1.08x write noise margin and 57.1% less leakage power compared to conventional SRAM cell at 1.0 V. However, it exhibits more delay due to increased resistance and capacitance of the cascaded transistors. The process variation analysis is also performed to investigate the SNM distribution using monte-carlo simulation by taking 10,000 samples. The results indicate that the SRAM cell structures provide higher than 6σ yield at range of supply voltages.

Comparison between Power Dissipation and Propagation Delay on 6T SRAM Cell Design Using GDI Logic with Transmission Gate VMSA and Voltage Divider

The rapid evolution of the semiconductor industry has witnessed shrinking portable and mobile devices alongside an increasing demand for extended battery life. Addressing the critical challenges of speed and battery life in digital devices, this paper investigated the effectiveness of innovative low-power design techniques. Focusing on the Gate Diffusion Input (GDI) approach, a recent advancement in the field, a comprehensive analysis revealed its significant potential for reducing power consumption in digital circuits. Additionally, a comparative analysis was conducted to evaluate the performance of conventional 6T GDI SRAM cells and their Modified 6T GDI SRAM with Voltage Divider, considering the influence of Sense Amplifiers. Simulation data demonstrated that Modified 6T SRAM designs, particularly the Voltage Divider and TGVMSA variants, achieved significantly lower power dissipation and delay despite having a larger cell area. Remarkably, the proposed design substantially improved power dissipation and propagation delay, achieving 1.3 ps, and 889.41mV at 1.8V shows that the suggested design enhances power dissipation and propagation delay. These findings suggest that the proposed design offers a promising strategy for enhancing power efficiency and performance in digital devices, thereby mitigating the limitations of battery life and speed in the modern technological landscape.

Performance analysis of OTFT-based SRAM topologies

In terms of mechanical flexibility, organic SRAM offers better designs and a commercially feasible option with the ability to deliver acceptable performance. This paper investigates the implementation of different SRAM topologies based on organic thin film transistors (OTFTs). In this work, a compact spice model is used to simulate pOTFT and nOTFT in LTSpice software. Time delays, power consumption, the power delay product (PDP), and static noise margin (SNM) for read and write operations are calculated, and a comparative analysis of OTFT based 6T, 7T, 8T, and 9T SRAM topologies is performed. Among different topologies, 9T OTFT SRAM cell achieves a 1.67× increase in SNM, compared to conventional 6T OTFT-based SRAM cell. The highest figure of merit value of 9T SRAM cell indicates its suitability for various applications.

Design of two-port SRAM cell with improved write operation

In this paper, a novel seven-transistor (7T) two-port SRAM cell incorporating an assist circuit is proposed. Wherein, the assist circuit is used to deal with the memory cell failures. During a write operation, this circuit is activated to connect a diode-connected transistor to the source of the drive transistor located near the write bit line. Accordingly, it can provide an efficient solution to the writing ‘1’ issue to improve write operations in this manner. Simulation results for the proposed cell design confirm that there is a conspicuous improvement over the conventional two-port SRAM cells and fast writing also can be achieved.

Soft-Error-Aware Radiation-Hardened Ge-DLTFET-Based SRAM Cell Design

In this paper, a soft-error-aware radiation-hardened 6T SRAM cell has been implemented using germanium-based dopingless tunnel FET (Ge DLTFET). In a circuit level simulation, the device-circuit co-design approach is used. Semiconductor devices are very prone to the radiation environment; hence, finding out the solution to the problem became a necessity for the designers. Single event upset (SEU), also known as soft error, is one of the most frequent issues to tackle in semiconductor devices. To mitigate the effect of soft error due to single-event upset, the radiation-hardening-by-design (RHBD) technique has been employed for Ge DLTFET-based SRAM cells. This technique uses RC feedback paths between the two cross-coupled inverters of an SRAM cell. The soft-error sensitivity is estimated for a conventional and RHBD-based SRAM cell design. It is found that the RHBD-based SRAM cell design is more efficient to mitigate the soft-error effect in comparison to the conventional design. The delay and stability parameters, obtained from the N-curve, of the Ge DLTFET-based SRAM cell performs better than the conventional Si TFET-based SRAM cell. There is an improvement of 305x & 850x in the static power noise margin and write trip power values of the Ge DLTFET SRAM cell with respect to the conventional Si TFET SRAM cell.

Performance and Stability Analysis of Built-In Self-Read and Write Assist 10T SRAM Cell

This work presents the performance and stability analysis of the proposed built-in self-read and write assist 10T SRAM (BSRWA 10T) for better performance in terms of thermal stability and fast write access, which is suitable for military and aerospace applications. The performance of the proposed SRAM cell dominates the previous SRAM cells, i.e., conventional, fully differential 10T-ST (FD 10T-ST), single stacked disturbance-free 9T-ST (SSDF 9T-ST). The proposed SRAM cell dominates the SSDF 9T-ST SRAM cell in terms of write ability. The built-in self-read and write assist structure of the memory cell also dominates the improved write ability of SSDF 9T-ST SRAM by assist circuits such as negative bit line, ultra-dynamic voltage scaling (UDVS), write assist combining negative BL, and VDD collapse. The impact of assist circuits on write performance of memory cells is observed using Monte Carlo simulation for write margin (WM) parameter. WM of SSDF 9T-ST SRAM is improved by 15% and 25% by adding UDVS assist circuit and write assist combining negative BL and VDD collapse circuit. But BSRWA SRAM cell itself can improve WM by 32% without any assist circuit. The impact of temperature variation on the performance of memory cells is observed using Monte Carlo simulation for the HSNM parameter. The deviation of HSNM for 15°C to 55°C is 14%, 5%, 4%, and 1% in conventional SRAM cell, FD 10T SRAM cell, SSDF 9T SRAM cell, and proposed BSRWA 10T SRAM cell, respectively. The proposed SRAM cell is designed at a 22 nm CMOS technology node and verified in the Synopsys Custom compiler. MC simulation results are monitored on Synopsys Cosmo-scope wave viewer.

6T and 8T SRAM Cell Simulation with Power Loss Analysis

Reducing the power consumption in a VLSI circuits is a prime concern now a days. Memory circuits play an important role in the design of electronic small power devices. Almost every digital systems is having memory as an important part in their design. The high speed circuits dissipate a considerable amount of power in a short time. In this paper conventional SRAM cell is modified little bit to reduce the dynamic power dissipation. The overall capacitance reduced by adding few extra transistors. Because of the fact that charging and the discharging of the bit lines consumes the most power , so 6T cell and 8T cell can be used to reduce the power by adding an extra number of transistors to the pull down path. In this paper 6T SRAM cell as well as 8T SRAM cell simulated and their performance compared in terms of power dissipation.

Soft-Error-Immune Read-Stability-Improved SRAM for Multi-Node Upset Tolerance in Space Applications

With aggressive scaling of transistor size and supply voltage, the critical charge of the sensitive nodes is reducing rapidly. As a result, when these deep submicron devices are used in memory cells in the space environment, single-event upsets (SEUs), also known as soft-errors, pose a great threat to the reliability of the cells. To mitigate the effects of SEUs, we propose a soft-error-immune read-stability-improved (SIRI) SRAM cell. To assess the performance of the proposed cell, it is compared with other soft-error-immune SRAM cells, namely, QUCCE12T, WE-QUATRO, RHPD12T, RHBD14T and RSP14T. Simulation results confirm that the detrimental effects of SEUs do not alter the state of SIRI as all the sensitive nodes can reattain their initial states after being impacted by an SEU. The cell can also recover from single-event multi-node upsets (SEMNUs) that occur at its storage node-pair. Moreover, the storage nodes of the proposed cell are isolated from the bitlines during read operation. Hence, it exhibits the highest read stability. The write ability and write delay of SIRI are also superior to those of the majority of the comparison cells, and it consumes much lower hold power than many of the conventional SRAM cells. All these improvements are brought about only at the expense of a slightly longer read delay.

Robust Low Power Transmission Gate (TG) based 9T SRAM cell with Isolated Read and Write Operation

Stability and performance of conventional SRAM cells operating at low voltages are severely affected due to enhanced process variations. This paper proposes a Transmission Gate (TG) based 9T SRAM cell with independent read/write operation and compares its performance with 6T, 8T, and 10T SRAM cells. The enhanced read and write ability of the cell is due to the selective use of positive feedback loop. To show the efficacy of the proposed technique, simulations are carried out using 130nm UMC technology files on Cadence Virtuoso and HSPICE. The transistor size with minimum length and width is used in each configuration using the UMC 130nm technology file for all the simulations. Various body biasing techniques (Reverse Body Bias and Forward Body Bias) are applied to reduce active and standby power. It has been observed that the proposed cell shows better results in terms of enhanced read, write and hold stability and for reduced power also. Further, the write access time is less for the proposed cell. The layout of the proposed architecture is also shown.

Darlington Based 8T CNTFET SRAM Cells with Low Power and Enhanced Write Stability

In this paper, a novel low power and high write margin Darlington based NCNTFET Darlington 8T SRAM cell is proposed. The power consumption of the proposed Darlington SRAM cell is compared with that of conventional 6T CNTFET and conventional 8T CNTFET SRAM cells. The power consumption of the proposed Darlington SRAM cells is very less as compared to that of conventional 6T and 8T CNTFET SRAM cells for all write, hold, and read operations. The write static noise margin (WSNM) of the proposed NCNTFET Darlington 8T cell is found to increase by 70.83% than that of both conventional 6T and 8T CNTFET SRAM cell. Effect of CNTFET parameters such as chiral vectors (m,n), gate oxide thickness (Hox), dielectric constant of gate oxide material (Kox), temperature, pitch value, number of carbon nano tubes (CNTs) and supply voltage (VDD), on the power performance, drain current (ID) and drain to source voltage (VDS) of the novel proposed Darlington SRAM cell are investigated. The write, hold, and read power consumption of proposed NCNTFET Darlington 8T SRAM cell is compared with that of some of the existing SRAM cells. The simulation is carried out using Stanford University 32 nm CNTFET model.

A read-disturb-free and write-ability enhanced 9T SRAM with data-aware write operation

ABSTRACT This paper presents a single-ended 9T SRAM cell with data-aware write-word-line structure to improve write ability, and a positive feedback sense amplifier (SA) to solve sensing challenge at an ultra-low voltage. The proposed 9T cell is well suited for bit-interleaving architecture in SRAM array. Simulation results indicate that at a 0.5 V supply voltage, the proposed SRAM cell achieves the same read static noise margin (RSNM) as that of conventional 8T SRAM cell, because the read-decoupled read buffer achieves read-disturb-free operation. While at the same supply voltage, its write margin (WM) is 2.68× compared with the 8T SRAM cell. As a result, a lower minimum operation voltage is achieved. Additionally, its leakage power consumption is reduced by 86.1% compared with the 8T SRAM cell in the 40-nm standard CMOS technology, TT corner, 25°C.

A novel ultra-low-power CNTFET and 45 nm CMOS based ternary SRAM

This paper presents a CNTFET based ultra-low-power ternary SRAM design which consumes merely 66 nW of power, achieving 84–98% reduction in power consumption as compared to the other CNTFET ternary SRAM designs reported in the literature. The 6-Transistor (6T) Standard Ternary Inverter (STI) cell or the 3T-STI cell form the basic building block of the conventional SRAM cells. These conventional STI designs have an undesirable direct path between VDD and ground during certain ternary input signals, resulting in higher power consumption. In this paper, a highly power-efficient 4T-STI based Ternary SRAM design is presented, which prevents a direct path between the power supply VDD and ground in all the possible ternary logic states.While CNTFET is preferred by many researchers around the world for low-power VLSI applications, CMOS technology is still widely used in the industry because of the availability of advanced CMOS manufacturing units. Therefore, the proposed ultra-low-power ternary SRAM design has been implemented with both 32 nm CNTFET and 45 nm CMOS devices. The performance of both the CNTFET and CMOS based ultra-low-power ternary SRAM circuits have been benchmarked with corresponding conventional SRAM circuits. The overall decrease in Power Delay Product (PDP) is 86–97% in the proposed ultra-low-power ternary 32 nm CNTFET SRAM circuit and 87–99% in the proposed 45 nm CMOS SRAM with respect to corresponding conventional ternary SRAM circuits.

A data‐independent 9T SRAM cell with enhanced ION/IOFF ratio and RBL voltage swing in near threshold and sub‐threshold region

SummaryThe conventional 8T SRAM cell with isolated read port is suggested as an alternative to overcome the read‐write conflicts associated with 6T SRAM cell. However, in near threshold and sub‐threshold regions, 8T cell performance is limited by reduced ION/IOFF ratio, deteriorated RBL voltage swing, data dependency, and higher read failures, although the existing SRAM cells address some of these issues but still suffer from degraded performance due to the trade‐off between leakage and read currents. In this paper, a 9T SRAM cell with novel read port is proposed that aims for low and data‐independent leakages, high ION/IOFF ratio, and large RBL voltage swing in near threshold and sub‐threshold regions. The performance of the proposed cell is compared with 7T, 8T, 9T, and 10T cells at 32 nm technology node by simulating a column of 128 cells to demonstrate its versatility over others. The proposed cell shows enhanced ION/IOFF ratio (71.2X), large RBL voltage swing and data‐independent leakages at VDD = 0.3 V in comparison to the conventional 8T SRAM cell. The results at different PVT corners are also captured to validate the impeccable performance of the proposed cell irrespective of operating conditions.

Design of 10T SRAM cell with improved read performance and expanded write margin

The need of genuine processors operation improvement cultivates the necessity for reliable, low power and fast memories. Several challenges follow this improvement at lower technology nodes. The impact of variability of process, temperature and voltage, on different performance parameters turns out to be most relevant issues in the nanometre SRAM design. The authors propose a 10T SRAM circuit that shows reduction in read power dissipation while maintaining fair performance and stability. Impression of process parameter variations on various design metrics such as read power, read current and data retention voltage of the proposed cell are presented and compared with already proposed SRAM cell. The projected topology offers differential read and single-ended write operation. The read margin and write margin are enhanced by 8.69% and 16.85% respectively in comparison to standard 6T SRAM cell even when single-ended write operation is performed. Furthermore, the read and write delay of projected topology improve by 1.78× and 2.326× in comparison with conventional 6T bit SRAM cell. In FF process corner, the proposed topology shows lowest data retention voltage (DRV) and minimum variation in DRV with temperature. Out of all considered topologies, the proposed circuit is optimized to minimum power delay product during read operation. Further, standby power and read power of proposed 10T cell is reduced by 34.65% and 2.03× in contrast to conventional 6T SRAM at 0.9 V supply voltage. Analysis of process variations tolerance read power and read current is also presented with 45 nm generic process design kit technology file using cadence virtuoso tool.

Low power SRAM using Adiabatic Logic

In this paper the design of low power SRAM has been presented. SRAM memory cell has been realized using adiabatic logic to achieve low power operation. Adiabatic SRAM has been realized using two methods such as i) gradual charging and discharging of bit-line during writing mode and ii) utilizing control transistor based adiabatic circuit i.e., Two Phase Adiabatic Dynamic Logic (2PADL) circuit for the design of memory cell. Furthermore, energy recovery of word line and bit line charge stored in the interconnect capacitances has been realized for the benefit of energy savings. Charge recovery circuits based on 2PADL has been employed in the proposed SRAM memory core to achieve energy recovery. SRAM memory array of (4×4) has been designed as a test circuit. All the circuits are implemented using 180nm CMOS technology and simulations are carried out using Cadence® Virtuoso tool. Simulation results prove that the proposed memory cell has significant amount of energy savings when compared to the conventional static CMOS SRAM cell.

Device and Circuit Level Design, Characterization and Implementation of Low Power 7T SRAM Cell using Heterojunction Tunneling Transistors with Oxide Overlap

The device scaling restricted due to the limitation of the subthreshold swing of the MOS transistor, which is not less than 60 mV/dec. The researchers are concentrating more on power efficient techniques for advanced, more featured, electronic systems. In place of MOS transistor, which is homojunction, if a heterojunction transistor with low bandgap materials used, the subthreshold swing of the transistor being reduce to below 60 mV/decade and low leakage current can obtain. Ge, GeSi, etc. materials are used in the design and implementation Heterojunction Tunneling Transistor (HETT) due to low band gap.In this work, both types of HETTs such as NHETT and PHETT designed and implemented using low bandgap materials with a technique of increasing tunneling area by overlapping. The performance of NHETT and PHETT described by the design and implementation of 7T MOSFET SRAM. The power and delay analysis of this SRAM cell using HETTs presented, and the results compared with MOSFET based standard 6T, conventional 7T SRAM cells.

Simulation of 6T and 8T SRAM Cell with Power Dissipation Analysis

Reducing the power consumption in a VLSI circuits is a prime concern now a days. Memory circuits plays an important role in the design of electronic small power devices. Almost every digital systems is having memory as an important part in their design. The high speed circuits dissipate a considerable amount of power in a short time. In this paper conventional SRAM cell is modified little bit to reduce the dynamic power dissipation. The overall capacitance reduced by adding few extra transistors. Because of the fact that charging and the discharging of the bit lines consumes the most power , so 6T cell and 8T cell can be used to reduce the power by adding an extra number of transistors to the pull down path. In this paper 6T SRAM cell as well as 8T SRAM cell simulated and their performance compared in terms of power dissipation.

NCFET-Based 6-T SRAM: Yield Estimation Based on Variation-Aware Sensitivity

The key feature of NCFET (negative capacitance field effect transistor) is its sub-threshold slope (SS) < 60 mV/decade at 300 K. In this work, the n-type NCFET (i.e., pull-down (PD) and passgate (PG) transistor in six-transistor (6T) SRAM bit-cell) has SS of 53.92 mV/decade, and the p-type NCFET (i.e., pull-up (PU) transistor in the 6T SRAM bit-cell) has SS of 58.96 mV/decade. In the NCFET-based SRAM cell (vs. conventional SRAM cell with conventional planar bulk MOSFETs), its read (hold)-stability and write-ability are evaluated by the metric of read static noise margin (SNM) and write-ability current (Iw), respectively. Then, under process-induced random variation, sensitivities of SNM and Iw are extracted. Finally, the yield of NCFET-based SRAM array (vs. conventional SRAM array) is quantitatively estimated using the cell-sigma.

Investigation of Radiation Hardened TFET SRAM Cell for Mitigation of Single Event Upset

This study analyzes the soft error sensitivity of SRAM cell which employs double-gate tunnel field effect transistor (DG TFET). The mitigation technique for the data recovery after the heavy ion strike is discussed. The conventional 6T TFET SRAM cell is designed using DG TFET of 30 nm. For the circuit simulation, the symbol of DG TFET is developed with the help of a look-up table based Verilog-A code. The radiation induced single event upset (SEU) causes a change in the stored data of SRAM cell. In order to improve the SEU sensitivity, the radiation hardening-by-design technique (RHBD) is introduced in 6T TFET SRAM cell by connecting the RC feedback loop between the two cross coupled inverters. The standby power of the TFET SRAM cell is calculated and compared before and after the radiation mitigation technique insertion.