一种全nMOS SOI晶体管4管静态存储器单元

提出了一种新颖的无负载4管全部由nMOS管组成的随机静态存储器(SRAM)单元.该SRAM单元基于32nm绝缘体上硅(SOI)工艺结点,它包含有两个存取管和两个下拉管. 存取管的沟道长度小于下拉管的沟道长度. 由于小尺寸MOS管的短沟道效应,在关闭状态时存取管具有远大于下拉管的漏电流,从而使SRAM单元在保持状态下可以维持逻辑“1" . 存储节点的电压还被反馈到存取管的背栅上,使SRAM单元具有稳定的“读”操作. 背栅反馈同时增强了SRAM单元的静态噪声容限(SNM). 该单元比传统的6管SRAM单元和4管SRAM单元具有更小的面积. 对SRAM单元的读写速度和功耗做了仿真和讨论. 该SRAM单元可以工作在0.5V电源电压下.     

一种全nMoS SOI晶体管4管静态存储器单元

提出了一种新颖的无负载4管全部由nMOS管组成的随机静态存储器(SRAM)单元.该SRAM单元基于32nm绝缘体上硅(SOI)工艺结点,它包含有两个存取管和两个下拉管.存取管的沟道长度小于下拉管的沟道长度.由于小尺寸MOS管的短沟道效应,在关闭状态时存取管具有远大于下拉管的漏电流,从而使SRAM单元在保持状态下可以维持逻辑"1".存储节点的电压还被反馈到存取管的背栅上,使SRAM单元具有稳定的"读"操作.背栅反馈同时增强了SRAM单元的静态噪声容限(SNM).该单元比传统的6管SRAM单元和4管SRAM单元具有更小的面积.对SRAM单元的读写速度和功耗做了仿真和讨论.该SRAM单元可以工作在0.5V电源电压下.     

Analysis of leakage reduction technique on FinFET based 7T and 8T SRAM cells

We propose a FinFET based 7T and 8T Static Random Access Memory (SRAM) cells. FinFETs also promise to improve challenging performance versus power tradeoffs. Designers can run the transistors more rapidly and use the similar amount of power, compared to the planar CMOS, or run them at the similar performance using less power. The aim of this paper is to reduce the leakage current and leakage power of FinFET based SRAM cells using Self-controllable Voltage Level (SVL) circuit Techniques in 45nm Technology. SVL circuit allows supply voltage for a maximum DC voltage to be applied on active load or can reduce the supplied DC voltage to a load in standby mode. This SVL circuit can reduce standby leakage power of SRAM cell with minimum problem in terms of chip area and speed. High leakage currents in submicron regimes are primary contributors to total power dissipation of bulk CMOS circuits as the threshold voltage V _th, channel length L and gate oxide thickness t _ox are scaled down. The leakage current in the SRAM cell increases due to reduction in channel length of the MOSFET. Two methods are used; one method in which the supply voltage is reduced and other method in which the ground potential is increased. The Proposed FinFET based 7T and 8T SRAM cells have been designed using Cadence Virtuoso Tool, all the simulation results has been generated by Cadence SPECTRE simulator at 45nm technology.     

Stability and leakage characteristics of novel conducting PMOS based 8T SRAM cell

The stability and leakage power of SRAMs have become an important issue with scaling of CMOS technology. This article reports a novel 8-transistor (8T) SRAM cell improving the read and write stability of data storage elements and reducing the leakage current in idle mode. In read operation, the bit-cell keeps the noise-vulnerable data ‘low’ node voltage close to the ground level and thus producing near-ideal voltage transfer characteristics essential for robust read functionality. In write operation, a negative bias on the cell facilitates to change contents of the bit. Unlike the conventional 6T cell, there is no conflicting read and write requirement on sizing the transistors. In standby mode, the built-in stacked device in the 8T cell reduces the leakage current significantly. The 8T SRAM cell implemented in a 130 nm CMOS technology demonstrates 2× higher read stability while bearing 20% better write-ability at 1.2 V typical condition and a reduction by 45% in leakage power consumption compared to the standard 6T cell. Results of the bit-cell architecture were also compared to the dual-port 8T SRAM cell. The stability enhancement and leakage power reduction provided with the proposed cell are confirmed under process, voltage and temperature variations.     

A robust and low-power near-threshold SRAM in 10-nm FinFET technology

This paper presents a robust and low-power single-ended robust 11T near-threshold SRAM cell in 10-nm FinFET technology. The proposed cell eliminates write disturbance and enhances write performance by disconnecting the path between cross-coupled inverters during the write operation. FinFETs suffer from width quantization, and SRAM performance is highly dependent to transistors sizing. The proposed structure with minimum sized tri-gate FinFETs operates without failure under major process variations. In addition, read disturbance is reduced by isolating the storage nodes during the read operations. To reduce power consumption this cell uses only one bit-line for both read and write operations. The proposed SRAM cell reduces write delay, average power and PDP by 20, 78 and 62%, respectively as compared to the 9T single-ended SRAM cell. Moreover, the proposed cell enhances write static noise margin by 33% under process variation.     

Design and analysis of noise margin,write ability and read stability of organic and hybrid 6-T SRAM cell

This paper analyzes SRAM cell designs based on organic and inorganic thin film transistors (TFTs). The performance in terms of static noise margin (SNM), read stability and write ability for all-p organic (Pentacene–Pentacene), organic complementary (Pentacene–C₆₀) and hybrid complementary (Pentacene–ZnO) configurations of SRAM cell is evaluated using benchmarked industry standard Atlas 2-D numerical device simulator. Moreover, the cell behaviour is analyzed at different cell and pull-up ratios. The electrical characteristics and performance parameters of individual TFT used in SRAM cell is verified with reported experimental results. Furthermore, the analytical result for SNM of all-p organic SRAM cell is validated with respect to the simulated result. Besides this, the cell and pull-up ratios of the hybrid and organic SRAM cells are optimized for achieving best performance of read and write operations and thereafter, the results are verified analytically also. The SNM of hybrid cell is almost two times higher than the all-p SRAM, whereas this improvement is just 18% in comparison to the organic memory cell. On the other hand, the organic complementary SRAM cell shows an improvement of 26% and 22% for the read stability in comparison to the all-p organic and hybrid SRAM cells, respectively. Contrastingly, this organic cell demonstrates a reduction of 16% in the SNM and an increment of 76% in write access time in comparison to the hybrid cell. To achieve an overall improved performance, the organic complementary SRAM cell is designed such that the access transistors are pentacene based p-type instead of often used n-type transistor. Favorably, this organic SRAM design shows reasonably lower write access time in comparison to the cell with n-type access OTFTs. Moreover, this cell shows adequate SNM and read stability that too at substantially lower width of p-type access OTFTs.     

A read disturbance free differential read SRAM cell for low power and reliable cache in embedded processor

Energy consumption and data stability are vital requirement of cache in embedded processor. SRAM is a natural choice for cache memory owing to their speed and energy efficiency. Noise insertion to the SRAM cell during read is a serious problem which reduces its stability. A read disturbance free differential SRAM cell consisting of seven transistors is proposed here which increases cell stability along with maintaining the most desirable differential read technique for faster read. The read SNM of the proposed cell is 154%, 31% and 58% large than that of the conventional 6T-SRAM cell and 2 other 7T-SRAM cells [5,6] compared here. Various factors such as short circuit current reduction, use of single write access transistor, partial bit line swing etc. reduces the overall energy consumption of the proposed cell by 41% compared to 6T-SRAM cell. The proposed cell is also compared with an eight transistor based read disturbance free SRAM cell. The cell delay of the proposed cell is around 55% lesser than that of the 8T-SRAM cell. Besides CMOS the performance achievement of the proposed 7T-SRAM cell is also validated at miniaturized dimension of 20 nm using FinFET based predictive technology model library.     

Single-Ended Boost-Less (SE-BL) 7T Process Tolerant SRAM Design in Sub-threshold Regime for Ultra-Low-Power Applications

A novel single-ended boost-less 7T static random access memory cell with high write-ability and reduced read failure is proposed. Proposed 7T cell utilizes dynamic feedback cutting during write/read operation. The 7T also uses dynamic read decoupling during read operation to reduce the read disturb. Proposed 7T writes “1” through one NMOS and writes “0” using two NMOS pass transistors. The 7T has mean \((\mu )\) of 222.3 mV (74.1 % of supply voltage) for write trip point where 5T fails to write “1” at 300 mV. It gives mean \((\mu )\) of 276 mV (92 % of supply voltage) for read margin, while 5T fails due to read disturb at 300 mV. The hold static noise margin of 7T is maintained close to that of 5T. The read operation of 7T is 22.5 % faster than 5T and saves 10.8 % read power consumption. It saves 36.9 % read and 50 % write power consumption as compared to conventional 6T. The novel design of proposed 7T consumes least read power and achieves the lowest standard deviation as compared to other reported SRAM cells. The power consumption of 1 kb 7T SRAM array during read and write operations is 0.70\(\times \) and 0.65\(\times \), respectively, of 1 kb 6T array. The techniques used by the proposed 7T SRAM cell allow it to operate at ultra-low-voltage supply without any write assist in UMC 90 nm technology node. Future applications of the proposed 7T cell can potentially be in low-voltage, ultra-low-voltage and medium-frequency operations like neural signal processor, sub-threshold processor, wide-operating-range IA-32 processor, FFT core and low-voltage cache operation.     

Device-Optimization Technique for Robust and Low-Power FinFET SRAM Design in NanoScale Era

In this paper, we propose a methodology to model and optimize FinFET devices for robust and low-power SRAMs. We propose to optimize the gate sidewall offset spacer thickness to simultaneously minimize leakage current and drain capacitance to on-current ratio in FinFET. With the source/drain extension doping controlled at the outer edges of the spacer, the thickness of the spacer determines the channel length. Optimization reduces the sensitivity of the device threshold voltage to the fluctuations in silicon thickness (by 32%) and gate length (by 73%). Our analysis shows that optimization of spacer thickness results in 65% reduction in SRAM cell leakage and improves cell read-failure probability (by 200 X) compared to conventional FinFET SRAM. Access time of an SRAM cell designed with optimized devices is comparable to conventional SRAM. We also compared the optimized-spacer-thickness SRAM cell with one designed using longer gate length and minimum-spacer-thickness transistors. The long-channel-device-based SRAM cell is marginally robust than optimized SRAM; however, increased gate-edge direct-tunneling leakage and parasitic capacitances degrade the power consumption and access time.     

An Experimental 0.8 V 256‐kbit SRAM Macro with Boosted Cell Array Scheme

This work presents a low‐voltage static random access memory (SRAM) technique based on a dual‐boosted cell array. For each read/write cycle, the wordline and cell power node of selected SRAM cells are boosted into two different voltage levels. This technique enhances the read static noise margin to a sufficient level without an increase in cell size. It also improves the SRAM circuit speed due to an increase in the cell read‐out current. A 0.18 µm CMOS 256‐kbit SRAM macro is fabricated with the proposed technique, which demonstrates 0.8 V operation with 50 MHz while consuming 65 µW/MHz. It also demonstrates an 87% bit error rate reduction while operating with a 43% higher clock frequency compared with that of conventional SRAM.     

Full-VDD and near-threshold performance of 8T FinFET SRAM cells

We evaluate full-V_DD and near-threshold operation of nine novel eight-transistor (8T) FinFET SRAM cell schemes using shorted gate (SG) and low power FinFET configurations for 32-bit by 1024-word SRAMs. 8T SRAM schemes outperform six-transistor schemes since SG-configured read FinFETs minimize delay and reverse-biased inverter FinFETs’ back gates reduce leakage current by up to 97%. At near-threshold, 8T FinFET cell delay increases by 56%, but leakage current and energy-delay product (EDP) decrease by up to 16% and 77%, respectively. 8T Low-Power Inverters scheme uses these configurations and reduces EDP by 60% (79% at near-threshold) versus the conventional SG 8T FinFET SRAM.     

A proposed DG-FinFET based SRAM cell design with RadHard capabilities

The radiation induced soft errors have become one of the most important and challenging failure mechanisms in modern electronic devices. This paper proposes a new circuit level hardening technique for reduction of soft error failure rate in DG-FinFET (double gate FinFET) based static random access memory (SRAM). Analysis for 32 nm and 45 nm technology nodes is carried out. It is inferred from the paper that the proposed SRAM cell outperforms over DICE latch in terms of fault tolerance of external data and control lines, power dissipation and fast recovery when exposed to radiation for both the technology nodes. This is primarily due to the addition of extra transistors used to neutralize the effect of single event upset without affecting normal operations. Transistor count increase the area and write delay by 7% and 20% respectively over that of DICE latch. While read delay decreases by 14% for the proposed SRAM cell.     

Novel low-power and stable SRAM cells for sub-threshold operation at 45 nm

In scaled technologies with lower supply voltage, conventional Static Random Access Memory (SRAM) cell suffers from unsuccessful read & write operation due to high off state current in sub-threshold region at nanometre technologies. This work proposes new functional low-power designs of SRAM cells with 7, 8, 9 and 12 transistors which operate at only 0.4V power supply in sub-threshold operation at 45 nm technology. Stability analysis is carried out using static noise margins as well as N-curve cell stability metrics. For performance measurement, read/write access time and leakage power consumption in hold mode are analysed. The comparison with published designs shows that two new proposed designs namely M8T, MPT8T have 30% less leakage power consumption along with 2× read stability, 2× write ability, more than 60% faster read & write operation.     

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.     

Impact of Fin-Height on SRAM Soft Error Sensitivity and Cell Stability

FinFET technology has become the most promising alternative to continue CMOS scaling due to its improved short channel effects. Design flexibility reduces on FinFET based circuits such as SRAM cells due to the effective channel width is determined by an integer number of fins. In this work, the impact of fin height size of FinFET transistors on the simultaneous behavior of soft error sensitivity and SRAM cell static noise margin is investigated. 3-D TCAD Sentarus environment is used to quantify the amount of collected and critical charges of an SRAM cell due to a heavy ion strike while Mix-Mode Hspice-TCAD simulation is used for stability analysis. Even more, the influence of process variations on sensitivity to soft errors and cell stability is considered. A 10 nm-SOI Tri-Gate FinFET technology is used. Results show that increasing the fin height of FinFET transistors considerably increases SRAM cell sensitivity to soft errors but improves its stability. This suggests that the optimum fin height value of FinFET transistors of an SRAM cell depends on the best tradeoff between soft error robustness and stability.     

Variation resilient subthreshold SRAM cell design technique

This article presents a circuit technique for designing a variability resilient subthreshold static random access memory (SRAM) cell. The architecture of the proposed cell is similar to the conventional 10T SRAM cell with the exception that dynamic threshold MOS is used for the read/write access FETs and cell content body bias scheme is used for bitline droppers (FETs used to drop bitlines). Moreover, the proposed bitcell utilises single differential port unlike conventional 10T bitcell which utilises dual differential ports. The proposed design offers 2.1× improvement in T _RA (read access time) and 3.2× improvement in T _WA (write access time) compared to CON10T at iso-device-area and 200?mV. It exhibits three roots in its read voltage transfer characteristic (VTC) even at 150?mV showing its ability to function as a bistable circuit. The combination of write and read VTCs for write static noise margin of the proposed design also shows single root signifying its write-ability even at 150?mV. It proves its robustness against process variations by featuring narrower spread in T _RA distribution (by 1.3×) and in T _WA distribution (by 1.2×) at 200?mV.     

High Performance Process Variations Aware Technique for Sub-threshold 8T-SRAM Cell

The demand of low power high density integrated circuits is increasing in modern battery operated portable systems. Sub-threshold region of MOS transistors is the most desirable region for energy efficient circuit design. The operating ultra-low power supply voltage is the key design constraint with accurate output performance in sub-threshold region. Degrading of the performance metrics in Static random access memory (SRAM) cell with process variation effects are of major concern in sub-threshold region. In this paper, a bootstrapped driver circuit and a bootstrapped driver dynamic body biasing technique is proposed to assist write operation which improves the write-ability of sub-threshold 8T-SRAM cell under process variations. The bootstrapped driver circuit minimizes the write delay of SRAM cell. The bootstrapped driver dynamic body bias increases the output voltage levels by boosting factor therefore increasing in switching threshold voltage of MOS devices during hold and read operation of SRAM latch. The increment in threshold voltage improves the static noise margin and minimizing the process variation effects. Monte-Carlo simulation results with 3 \(\sigma \) Gaussian distributions show the improvements in write delay by 11.25 %, read SNM by 12.20 % and write SNM by 12.57 % in 8T-SRAM cell under process variations at 32 nm bulk CMOS process technology node.     

Robust FinFET SRAM design based on dynamic back-gate voltage adjustment

In this paper, we propose a robust SRAM design which is based on FinFETs. The design is performed by dynamically adjusting the back-gate voltages of pull-up transistors. For the write operation, we use an extra write driver which sets the desired back-gate voltages during this operation. This approach considerably increases the write margin. During the hold state, the back-gates are precharged to the supply voltage using an extra precharge circuit. This decreases the static power. Finally, we use nMOS switches to provide the optimum back-gate voltages during the read state. To minimize the area and power overheads, an instance of the circuitry is used for each column. The performance of the proposed technique is assessed using mixed mode device/circuit simulations for a physical gate length of 22 nm. The results show that the minimum operating voltage for six-sigma read and write yield is about 0.15 V lower than that of the recently proposed structures. In addition, the suggested SRAM shows significantly higher write margin and lower static power compared to the recently proposed structures. The minimum operating voltage of our proposed structure can be lowered down to 0.5 V through some work function tuning to balance the read and write stability. This minimum voltage is 0.1 V lower than the minimum operating voltage of the other structures with similar work function tunings.     

A Near-Threshold Soft Error Resilient 7T SRAM Cell with Low Read Time for 20 nm FinFET Technology

Shrinking of technology node in advanced VLSI devices and scaling of supply voltage degrade the performance characteristics and reduce the soft error resilience of modern downscaled digital circuits. In this paper, we propose a reliable near-threshold 7T SRAM cell with single ended read and differential write operations based on a previous proposed 5T cell. Our new cell improves read speed without degrading of write speed compared to the recently reported 7T cell. Furthermore, our proposed cell provides high soft error reliability amongst all the SRAM cells mentioned in this paper. We compared the performance and reliability characteristics of 5T, 6T, 8T and previous 7T cells with our new 7T SRAM cell to show its efficacy. The simulations are performed using HSPICE in 20 nm FinFET technology at V_DD = 0.5 V. The results show that the new 7T cell has high write speed, read and write margins with improved read speed and low leakage power in the hold “0” state compared to 5T cell. In addition, the study of performance parameters under process and environmental variations considering ageing effect in near-threshold region shows the robustness of the proposed 7T SRAM cell against these variations.     

Read Stability and Write-Ability Analysis of SRAM Cells for Nanometer Technologies

SRAM cell read stability and write-ability are major concerns in nanometer CMOS technologies, due to the progressive increase in intra-die variability and V_dd scaling. This paper analyzes the read stability N-curve metrics and compares them with the commonly used static noise margin (SNM) metric defined by Seevinck. Additionally, new write-ability metrics derived from the same N-curve are introduced and compared with the traditional write-trip point definition. Analytical models of all these metrics are developed. It is demonstrated that the new metrics provide additional information in terms of current, which allows designing a more robust and stable cell. By taking into account this current information, V_dd scaling is no longer a limiting factor for the read stability of the cell. Finally, these metrics are used to investigate the impact of the intra-die variability on the stability of the cell by using a statistically-aware circuit optimization approach and the results are compared with the worst-case or corner-based design