抗辐照SRAM单元的老化研究与防护

发布时间：2018-05-30 22:01

本文选题：抗辐照静态随机存储器 + 偏置温度不稳定性　；参考：《合肥工业大学》2017年硕士论文

【摘要】：抗辐照加固的SRAM由于其特殊的应用场景,需要高可靠性和长寿命的支持;而在纳米工艺水平下,偏置温度不稳定性(Bias Temperature Instability,BTI)效应引起的电路老化成为威胁存储器电路寿命和可靠性的主要元素。BTI效应会使受压晶体管阈值电压发生漂移,导致SRAM单元变得不对称,进而导致噪声容限发生退化,甚至读写功能失效。通常SRAM的抗老化方法主要集中在系统级以及存储策略上的调整,使SRAM单元受压平衡,延缓老化;或者采用冗余存储单元的设计,为SRAM的寿命提供余量。这些策略从本质上只能延缓老化的发生。而抗辐射加固SRAM单元由于其冗余存储节点的特性,为结构级SRAM抗老化提供了新的思路。因此,本文针对抗辐照SRAM单元的老化特性和结构级抗老化进行研究。本文针对抗辐照静态随机存储器DICE (dual interlocked cell, DICE)单元进行了研究。为得到BTI老化效应对其性能的具体影响,并针对其性能退化特性提出抗老化设计方案,延长电路使用时限,通过SPICE仿真实验分析了 DICE单元在受BTI效应影响下的老化特性,发现因老化加重的读干扰和半选择干扰是影响DICE结构的SRAM单元稳定性和寿命的主要原因。并针对DICE单元抗辐照的特性,通过在组成读写端口的4个晶体管之间加入额外的控制晶体管,阻断了 DICE单元存储节点相连的路径,消除了读干扰和半选择干扰的影响,避免了单元的读故障和半选择故障的出现;并通过仿真实验验证了改进后DICE单元的功能有效性和抗老化有效性。同时通过在读写端口加入控制管,提升了 DICE单元在读状态和半选择状态时的抗辐照能力。实验结果表明,新结构避免了 108s老化后22.6%的读失效率,大大提升了 DICE单元的可靠性。针对抗辐照静态随机存储器 QUATRO(quad-node ten transistor cell, QUATRO)单元,本文也通过实验分析了其老化特性,发现单元的读稳定性和写稳定性均在BTI的影响下均有较大的退化,但是由于QUATRO本身的写噪声容限余量大大高于读噪声容限,因此针对读失效的防止仍然是抗老化的首要目标。本文利用QUATRO单元节点冗余的特性,通过转移读写端口避免了因老化造成越来越大的读干扰对QUATRO单元的影响;通过调整QUATRO单元中各晶体管的相对驱动能力保证了正确的读写功能。试验结果表明。新结构避免了 108s老化后4.1%的读失效率,提升了其可靠性和寿命。
[Abstract]:SRAM strengthened by irradiation requires high reliability and long life support due to its special application scenarios; and at the nanotechnology level, The bias temperature instability and the circuit aging caused by the Bias Temperature stability Temperature effect become the main element threatening the life and reliability of the memory circuit. The BTI effect will drift the threshold voltage of the transistor and cause the SRAM cell to become asymmetrical. This will lead to the degradation of noise tolerance and even the failure of reading and writing functions. In general, the anti-aging methods of SRAM mainly focus on the adjustment of system level and storage strategy to balance the pressure of SRAM cells and delay the aging, or adopt the design of redundant memory cells to provide allowance for the life of SRAM. In essence, these strategies can only delay the occurrence of aging. Because of the characteristics of the redundant storage node, the radiation resistant SRAM cell provides a new idea for the structural level SRAM to resist aging. Therefore, the aging characteristics and structural grade aging resistance of irradiated SRAM units are studied in this paper. In this paper, we study the DICE dual interlocked cell, DICE) cell of the radiation resistant static random access memory (RRAM). In order to obtain the specific effect of BTI aging effect on its performance, and to put forward an anti-aging design scheme for its property degradation characteristics and prolong the circuit time, the aging characteristics of DICE cell under the influence of BTI effect are analyzed by SPICE simulation experiment. It is found that the reading interference and semi-selective interference due to aging are the main factors affecting the stability and lifetime of SRAM elements in DICE structure. In view of the anti-irradiation characteristics of DICE cells, by adding extra control transistors between the four transistors that make up the read and write ports, the path connected to the storage nodes of the DICE cells is blocked, and the effects of read interference and semi-selective interference are eliminated. The failure of reading and semi-selection is avoided, and the function and anti-aging effectiveness of the improved DICE unit are verified by simulation experiments. At the same time, the control tube is added to the read / write port to improve the radiation resistance of the DICE cell in the read and half selected states. The experimental results show that the new structure avoids the reading failure rate of 22.6% after 108s aging and greatly improves the reliability of DICE units. In this paper, the aging characteristics of QUATRO(quad-node ten transistor cell, QUATRO) cells are also analyzed by experiments. It is found that both the read stability and write stability of the cells are degraded greatly under the influence of BTI. However, because the tolerance of writing noise of QUATRO is much higher than that of reading noise, the prevention of reading failure is still the primary goal of anti-aging. In this paper, by transferring the read and write ports of QUATRO cell node redundancy, we avoid the influence of increasing read interference caused by aging on QUATRO cells, and ensure the correct reading and writing function by adjusting the relative driving ability of each transistor in QUATRO cell. The experimental results show that. The new structure avoids the reading failure rate of 4.1% after 108 s aging and improves its reliability and life.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP333

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