基于DICE结构的抗辐射SRAM设计

空间应用的SRAM必须具备抗辐射加固能力.介绍了SRAM工作原理与双互锁存储单元(DICE)技术,给出了基于DICE结构的SRAM存储单元的电路设计、版图设计及其功能仿真.在SMIC 0.13μm工艺下,应用HSPICE进行单粒子效应模拟,与传统6T CMOS SRAM相比,基于DICE结构的SRAM在相同工艺条件下抗辐照能力有显著的提高.     

钟控传输门绝热逻辑电路和SRAM的设计

本文利用NMOS管的自举效应设计了一种新的采用二相无交叠功率时钟的绝热逻辑电路——钟控传输门绝热逻辑电路,实现对输出负载全绝热方式充放电.依此进一步设计了一种新型绝热SRAM,从而可以以全绝热方式有效恢复在字线、写位线、敏感放大线及地址译码器上的大开关电容的电荷.最后,在采用TSMC 0.25 μ m CMOS工艺器件参数情况下,对所设计的绝热SRAM进行HSPCIE模拟,结果表明,此SRAM逻辑功能正确,低功耗特性明显.     

基于分离位线DICE结构的SRAM存储单元版图抗辐射设计

在SRAM加固设计中,存储单元的版图抗辐射设计起着重要的作用。基于分离位线的双互锁存储单元（DICE）结构,采用0.18μm体硅工艺,根据电路功能、结构和抗辐射性能,设计了一种新的NMOS隔离管的SRAM存储单元版图结构。根据分析结果,SRAM存储单元在确保存储单元功能的前提下,具备抗总剂量效应、抗单粒子翻转和抗单粒子闩锁效应,同时可实现单元面积的最优化。     

PDSOI CMOS SRAM单元临界电荷的确定

PDSOI CMOS SRAM单元的临界电荷(Critical Charge)是判断SRAM单元发生单粒子翻转效应的依据.利用针对1.2μm抗辐照工艺提取的PDSOI MOSFET模型参数,通过HSPICE对SRAM 6T存储单元的临界电荷进行了模拟,指出了电源电压及SOI MOEFET寄生三极管静态增益β对存储单元临界电荷的影响,并提出了在对PDSOI CMOS SRAM进行单粒子辐照实验中,电源电压的最恶劣偏置状态应为电路的最高工作电压.     

三值钟控绝热静态随机存储器设计

通过对多值逻辑、绝热电路和三值SRAM结构的研究,提出一种新颖的三值钟控绝热静态随机存储器(SRAM)的设计方案。该方案利用NMOS管的自举效应,以绝热方式对SRAM的行列地址译码器、存储单元、敏感放大器等进行充放电,有效恢复储存在字线、位线、行列地址译码器等大开关电容上的电荷,实现三值信号的读出写入和能量回收。PSPICE模拟结果表明,所设计的三值钟控绝热SRAM具有正确的逻辑功能和低功耗特性,在相同的参数和输入信号情况下,与三值常规SRAM相比,节约功耗达68%。     

驱动能力对SOI SRAM单元单粒子效应的影响仿真

采用silvaco软件对抗辐射不同沟道宽度的PD SOI NMOS器件单元进行了三维SEU仿真,将瞬态电流代入电路模拟软件HSPICE中进行SRAM存储单元单粒子翻转效应的电路模拟。通过这种电路模拟的方法,可以得到SRAM存储单元的LET阈值。通过对比LET阈值的实际测量值,验证了这种方法的实用性,并对不同驱动能力的SRAM单元进行了翻转效应的对比。在NMOS和PMOS驱动比相同的情况下,沟道宽度越大,SRAM的翻转LET阈值反而越高。     

基于DICE结构的SRAM抗辐照加固设计

存储单元的加固是SRAM加固设计中的一个重要环节。经典DICE单元可以在静态情况下有效地抗单粒子翻转,但是动态情况下抗单粒子翻转能力较差。提出了分离位线的DICE结构,使存储单元在读写状态下具有一定的抗单粒子效应能力。同时,对外围电路中的锁存器采用双模冗余的方法,解决锁存器发生SEU的问题。该设计对SRAM进行了多方位的加固,具有很强的抗单粒子翻转能力。     

阈值电压对超深亚微米SRAM存储单元SNM的影响

采用基于物理模型的 α指数 MOSFET模型 ,对超深亚微米 (VDSM:Very Deep Submicron) SRAM存储单元的静态噪声容限 (SNM:Static Noise Margin)进行了解析分析 ,分析中考虑了随机工艺涨落造成的VDSM SRAM存储单元阈值失配对 SNM的影响 ,结果与 HSPICE仿真相符 ;文中同时分析了栅宽与 SNM的关系 ,其结论与实验结果一致 ,并给出了 VDSM SRAM存储单元设计中应注意的问题     

高可靠性的读写分离14T存储单元设计

为了提高航空航天设备的可靠性和运行速度,提出了一种新型读写分离的14T静态随机存储器(SRAM)单元。基于65 nm体硅CMOS工艺,对读写分离14T存储单元的性能进行仿真,并通过在关键节点注入相应的电流源模拟高能粒子轰击,分析了该单元抗单粒子翻转(Single Event Upset,SEU)的能力。与传统6T相比,该单元写速度、读静态噪声容限和位线写裕度分别提升了约5.1%、20.7%和36.1%。写速度优于其他存储单元,读噪声容限优于6T单元和双联锁存储单元(DICE),在具有较好的抗SEU能力的同时,提高了读写速度和读静态噪声容限。     

SOI CMOS SRAM单元单粒子翻转效应的模拟

为简单快速模拟静态随机存储器(SRAM)的单粒子效应,在二维器件数值模拟的基础上,以经典的双指数模型为原型,通过数值拟合得到了单粒子效应瞬态电流脉冲的表达式,考虑晶体管偏压对瞬态电流的影响,得到修正的瞬态电流表达式,将其带入电路模拟软件HSPICE中进行SRAM存储单元单粒子翻转效应的电路模拟,通过与实际单粒子实验结果的对比,验证了这种模拟方法的实用性。     

X-Calibration: A Technique for Combating Excessive Bitline Leakage Current in Nanometer SRAM Designs

In an SRAM circuit, the leakage currents on the bit lines are getting increasingly prominent with the dwindling of transistors' threshold voltages as the technology scales down to 90 nm and beyond. Excessive bit-line leakage current results in slower read operations or even functional failure. In this paper, we present a new technique, called X-calibration, to combat this phenomenon. Unlike the previous method that attempts to compensate the leakage current directly, this scheme first transforms the bit-line leakage current into an equilibrium offset voltage across the bit-line pair, and then simple circuitry is utilized to cancel this offset accurately at the input of the sense amplifier so that the sensing is not affected by the bit-line leakage. SPICE simulation of a 1 Kbit SRAM macro shows that this X-calibration scheme can handle 83% higher bit-line leakage current than the previous bit-line leakage compensation scheme. Measurement results of the test chip show that the SRAM macro adopting X-calibration scheme can cope with up to 320 $mu{hbox{A}}$ bit-line leakage current.      

A Novel Hot-Electron Programming Method in a Buried Diffusion Bit-Line SONOS Memory by Utilizing Nonequilibrium Charge Transport

We propose a new hot-electron programming method with a low drain-to-source voltage in a buried-diffusion (BD) bit-line SONOS memory array. In this method, channel electrons are preaccelerated in a cell preceding a program cell. For a small bit-line width, some energetic electrons will traverse an $ hbox{n}^{+}$ BD region and enter a program cell with residual energy due to nonequilibrium transport. Our measurement result shows that this residual energy can significantly enhance hot-electron programming efficiency even at a $V_{rm ds}$ of 2.5 V. The concept of this method is verified by means of a Monte Carlo analysis. Our study shows that this method is more effective as a bit-line width reduces.      

A variable precharge voltage sensing

A new DRAM sensing approach that uses variable precharge voltage has been developed and analyzed in simulations. It uses a voltage swing only on the bit-line connected to the accessed cell. The bit-line precharge voltage varies from one RAS cycle to the next, depending on the level of the data in the accessed cell. The reference voltage for bit-line sensing is given by a new reference-cell control circuit without using a reference-voltage generator. The current required for sensing decreases as the precharge voltage increases, resulting in reduced power without any reduction of the sensing signal. Detailed analysis shows that the sensing current is only 2/3 of that in 1/2 T_DD sensing, even in the worst case     

Analysis of coupling noise between adjacent bit lines in megabitDRAMs

Different bit-line structures, bit-line materials, widths, spacings, and passivation materials were fabricated to analyze the effect of the coupling noise between adjacent bit lines in megabit DRAMs. Each component of total bit-line capacitance was measured to obtain the bit-line-to-bit-line capacitance and the other contributions to the total bit-line capacitance. Accelerated soft error tests were performed on each sample. The results suggest the existence of two types of noise effects. One is the READ-signal degradation just after the work-line rises. The other is the disturbance in sensing operation. The larger the ratio of the bit-line coupling capacitance to the other bit-line capacitance contributions the more serious both the noise effects are. These noise mechanisms can be explained by the charge conservation model and the simulation of sensing operation. A polycide bit-line structure is less susceptible to these noises than an Al bit line because its thickness and layer position     

Twisted bit-line technique for multi-gigabit DRAMs

A new twisted bit-line (TBL) technique is presented to reduce bit-line coupling noise for multi-gigabit DRAMs. Sufficient noise reduction effects have been monitored through soft-error rate measurement on test chips using the proposed TBL technique. Also, the problem of excessive chip area penalty in the conventional TBL techniques can be solved in the proposed TBL technique     

A high-speed clamped bit-line current-mode sense amplifier

A clamped bit-line current-mode sense amplifier that maintains a low-impedance fixed potential on the bit lines is introduced. Using a general model for active-drive memory cells that include the two-transistor (2T) and three-transistor (3T) dynamic cells and the four-transistor/two-resistor (4T-2R) and six-transistor (6T) static cells, the new sense amplifier is shown to have a response speed that is insensitive to bit-line capacitance. This is achieved by relocating the large bit-line capacitance to a node within the sense amplifier that has only a minimal effect on the speed of the circuit. Bit-line clamping also minimizes inter-bit-line voltage noise coupling     

3D NAND flash memory with laterally-recessed channel (LRC) and connection gate architecture

A three-dimensional (3D) stacked bit-line NAND flash memory is investigated. The fabrication process flow for the formation of a laterally-recessed bit-line stack is described. Program operation is simulated using a stacked bit-line structure. Inter-layer interference (ILI) is addressed and the minimum isolation oxide thickness between stacked bit-lines is extracted. Simple device and array with the laterally-recessed bit-line stack are fabricated and electrical characteristics are measured. A new array architecture having a connection gate is designed for the 3D stacked bit-line NAND flash memory application.     

Scaling of digital BiCMOS circuits

A generalized first-order scaling theory for BiCMOS digital circuit structures is presented. The effect of horizontal, vertical, and voltage scaling on the speed performance of various BiCMOS circuits is presented. The generalized scaling theory is used for the MOSFET, and the constant collector current (CIC) scaling scheme is used for the bipolar junction transistor (BJT). In scaling the bipolar transistor, polysilicon emitter contact and bandgap narrowing are taken into account. A case study for scaling BiCMOS circuits operating at 5- and 3.3-V power supplies shows that scaling improved BiCMOS buffers more significantly than CMOS buffers. Moreover, the low delay-to-load sensitivity of BiCMOS is preserved with scaling     

A 12-ns ECL I/O 256 K×1-bit SRAM using a 1-μm BiCMOStechnology

An ECL (emitter-coupled-logic) I/O 256K×1-bit SRAM (static random-access memory) has been developed using a 1-μm BiCMOS technology. The double-level-poly, double-level-metal process produces 0.8-μm CMOS effective gate lengths and polysilicon emitter bipolar transistors. A zero-DC-power ECL-to-CMOS translation scheme has been implemented to interface the ECL periphery circuits to the CMOS decode and NMOS matrix. Low-impedance bit-line loads were used to minimize read access time. Minimization of bit-line recovery time after a write cycle is achieved through the use of a bipolar/CMOS write recovery method. Full-die simulations were performed using HSPICE on a CRAY-1     

A divided/shared bit-line sensing scheme for ULSI DRAM cores

A new dynamic RAM (DRAM) signal sensing principle, a divided/shared bit-line (DSB) sensing scheme, is proposed. This sensing scheme provides folded bit-line sensing operation in a crosspoint-type memory cell array. The DSB scheme offers a high-density DRAM memory core with the common-mode array noise eliminated. A bit-line architecture based on this new sensing principle and its operation are demonstrated. A divided/pausing bit-line sensing (DIPS) scheme, which is an application of this DSB principle to the conventional folded bit-line type of memory cell arrangement, is also proposed. The DIPS architecture achieves complete pausing states for alternate bit lines throughout the active period. These alternate pausing bit lines shield the inter-bit-line coupling noise between active bit lines. Here the inter-bit-line coupling noise is eliminated by a slight architectural change to the conventional folded bit-line memory cell array. These new memory core design alternatives provide high-density DRAM memory cores suitable for the 64-Mb level and beyond. with the memory array noise reduced significantly