三维单片集成SRAM重离子单粒子效应研究

Monolithic 3D integration is currently in the spotlight as a solution to full use of the third dimension at transistor level due to its high alignment precision and small contact size. It improves the integration and decreases the delay in interconnections and process variations. The monolithic 3D integrated circuits feature small areas, high speed and low power, showing great potential for aerospace applications. However, when the cosmic rays strike the 3D chips, the charge will be generated and collected in the sensitive nodes for different layers, leading to complicated single-event effects. This project concerns the single-event effects induced by heavy ions for monolithic 3D integrated SRAM in 180 nm SOI CMOS technology. The single-event effects of 2-layer 6T SRAM cell interconnected by monolithic inter-layer via will be simulated using Monte Carlo method. The physical mechanism of energy transport will be revealed for different heavy ions. Based on this, TCAD is employed to simulate the single-event effects for monolithic 3D 6T SRAM cell with different transistor placements and layouts. Based on a Daisy chain and an inverter chain, the parasitic resistance and capacitor of monolithic inter-layer via will be measured and a model considering the effect of micro voids and misalignments will be developed. Finally, the single-event effects of monolithic 3D 6T SRAM cell in circuit-level can be performed. This work in this project can provide the guidelines for the estimation and radiation-hardened design of single-event effects in monolithic 3D SRAM.

三维单片集成技术具有高对准精度和小接触孔尺寸，成为实现晶体管级垂直互连的热门选择，可大幅提高集成度、降低互连延迟和工艺波动。采用三维单片集成的芯片体积小、速度快、功耗低，在航天电子器件中展现了广阔应用前景。然而，宇宙射线穿过三维器件时，会在多层晶体管敏感节点产生电离电荷，进而引起复杂的单粒子效应。本项目旨在研究180纳米SOI CMOS工艺下三维单片集成SRAM重离子单粒子效应。利用蒙特卡洛方法研究了重离子在2层三维单片集成6管SRAM单元中的能量沉积规律。为了实现抗重离子单粒子效应加固，TCAD仿真了不同晶体管布局和版图对三维单片集成SRAM单元重离子单粒子效应的影响。通过Daisy链和反相器链，本项目测量并建模了层间孔寄生电阻和电容。最终，利用查找表的方法实现了三维单片集成SRAM单元的电路级仿真，为三维单片集成SRAM的单粒子效应评估及加固设计提供了理论指导。

三维单片（M3D）集成电路体积小、速度快、容量大，在新一代航天电子设备上具有广阔应用前景，如高精度传感卫星、微小卫星、卫星互联网等。然而，空间重离子导致的单粒子翻转（SEU）效应影响着航天电子器件的可靠性，特别是SRAM（Static Radom Access Memory，SRAM）存储器，如发生SEU，必将导致数据错误。本项目针对M3D集成电路堆叠结构和重离子轰击各层能量沉积差异，提出了双粒子注入模型，建立了单片三维集成电路的重离子单粒子效应仿真方法。基于此方法，分析了6管SRAM单元的SEU机理，提出了层间电荷共享可用于SRAM存储单元SEU加固设计。其次，系统研究了晶体管级和门级M3D布局对6管SRAM单元SEU的影响，发现门级SRAM布局中两个存储节点同类型晶体管垂直对齐可完全抑制SEU的发生，这是因为电荷共享效应破坏了SRAM翻转机理中的反馈机制。再次，从M3D电路特有的层间串扰效应以及层间孔寄生效应讨论了对单粒子效应的影响，发现层间串扰效应可通过简单的方法有效抑制，而层间孔的寄生效应对SET的影响本身较小；并根据M3D电路串扰的特征，提出了单粒子诱导串扰的加固方案：一方面采用门级布局，并避免将不同反相器链的敏感晶体管垂直对齐布局；另一方面，增加层间距至1 μm，可在不增加芯片面积的前提上有效抑制串扰效应。最后，通过双指数电流源模型和查找表建立了与版图相关的电路级M3D集成电路单粒子效应仿真方法，完成了M3D集成非门、或非门、SRAM电路和D触发器的单粒子效应仿真，并验证了该方法的准确性。本项目的研究成果可用于M3D集成电路单粒子软错误EDA工具开发和抗单粒子电路加固设计，最终支撑新一代航天器发展。