标题：高鲁棒性高压Esd工程用多指SCR维持电压下降的研究

Investigation and Suppression of Holding Voltage Deterioration in Multifinger SCR for Robust High-Voltage ESD Engineering

摘要：

For robust high-voltage (HV) electrostatic discharge (ESD) protection engineering, such as 8-KV or 15-KV ESD target, the silicon-controlled rectifiers (SCRs) with high holding voltage are needed to mitigate latch-up risk. However, when implemented in the multifinger layout configuration for satisfying high robust ESD requirement, these devices may encounter holding voltage deterioration problems. In this article, such holding voltage deterioration has been explored by theoretical analysis and experimental verification. The transmission line pulsing (TLP) results indicate that the sharing of adjacent WELL pickup and removing of inner guard ring in the typical multifinger layout (TMF) are the root causes for holding voltage deterioration. Through the appropriate test-key design, both of these culprits have been identified independently. Finally, by keeping the average WELL pickup length and average number of parasitic paths of each SCR finger in the multifinger layout constant, such holding voltage deterioration can be restrained effectively, achieving a stable holding voltage regardless of the number of fingers. Therefore, this article offers very useful work for HV ESD engineering.

**作者：**Du Feibo,Jiang Guijun,Huang Meichen,Zou Kepeng,Hou Fei,Song Wenqiang,Liu Jizhi,Xiong Xuanlin,Hou Lingli,Liu Zhiwei,Liou Juin J.

**出版年份：**2021

**期刊/影响因子：**IEEE Transactions on Electron Devices/2

**数字对象唯一标识符DOI：**10.1109/TED.2021.3122390

研究内容：

研究了SCR结构多指布局时，会出现维持电压下降的原因。

影响要素：

共用WELL-Pickups
由外部隔离环引入的BJT晶体管的变化导致的

所用工艺：

0.18um的BCD工艺

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从Fig. 3中可以看出随着指数的增加器件的Vh出现了明显的下滑，这便引出了这篇文章需要研究的主要问题：是什么导致多指布局的维持电压出现了下降？

实验组（器件剖面和TLP测试数据）：

Fig. 4和Fig. 10分别展示了两种增加NWELL pickup和PWELL pickup宽度的方法。同时从Fig. 5 和Fig. 6可以看出两者确实可以提升器件的维持电压。但是维持电压任然低于单指结构的维持电压，说明还有其他因素导致器件维持电压的下降。作者进一步研究了保护环的影响，设置了Fig. 15的对比实验。

可以看到综合WELL pickup和保护环的影响已经能够将器件的保持电压恢复到单指的保持电压了。这也说明了影响保持电压的两个因素，作者是理论先行，然后根据理论分析设计实验，本笔记为了记录的快速性和整体的简略性，将作者的理论分析放入了后面，此处只谈作者设计的对比实验和所得到的实验结果。

应用范围：

高压领域，且要求高鲁棒性和高维持电压的领域。比如：汽车通信用的CAN收发器芯片，RS485芯片，一些高压驱动芯片等等。

结论：

普通交叉多指结构之所以出现维持电压下降的原因有两个：

一. 由于WELL pickup共用导致。
二. 外侧保护环因素（普通交叉多指结构显然减少了由外侧保护环引入的分流路径对整体的分流能力）

创新点：

研究清楚了传统多叉指结构导致SCR结构维持电压下降的原因。

理论解释：

原文解释：“This phenomenon is mainly related to the change of WELL contact resistance. When the SCR enters the holding state, the strong conductivity modulation in WELLs reduces RNW and RPW sharply, thus facilitating RNW_CO and RPW_CO to account for much larger proportions of total WELL resistances (i.e., RNW_CO + RNW for N-WELL, and RPW_CO + RPW for P-WELL) and affecting Vh more effectively. In TMF layout configuration, as depicted in Fig. 7, the inner pickup lengths belonging to each SCR finger decrease as the number of fingers increases, resulting in larger WELL contact resistances. According to Fig. 8, this can prompt more current to flow through the SCR path (red dashed line in Fig. 1) rather than the DIODE path (blue dashed line in Fig. 1)inESDevents, thus strengthening the current regeneration loop in SCR path and generating a lower Vh.”  (Du 等, 2021, p. 3)

“Here, another explanation is also feasible. With the increase in number of fingers, the emitter junction area and thus the emitter injection efficiency increase. This will flood the base region with lots of carriers which cannot be collected effectively by the single (shared) base contact region. Due to this flooding of carriers in the base region, the efficiency of the BJTs in SCR is improved so that they can be maintained at lower holding voltages.” (Du 等, 2021, p. 4)
此处的another explanation 我认为更加接近本质一些，关键还是在于：多指结构注入到基区的载流子翻倍增加，然而由于多指共用WELL pickup区域导致对WELL内部这些注入的非平衡载流子的收集能力却没有翻倍增加导致基区内由发射结注入的载流子浓度相比于单指结构更大一些，从而使得寄生三极管工作效率好，β更大，从而导致维持电压下降。

当然导致基区（也就是NWELL和PWELL）内由发射区注入的载流子浓度提高的原因，除了WELL pickup共用导致，还有就是外面由于保护环引入的分流路径的效果由于指数的增加也逐渐减小了。

可以看到的是，SCR的维持电压与其为完全开启后内部基区“载流子”浓度有很大的关系。减小其维持点（完全开启时）基区载流子的浓度便能有效提升器件的维持电压。（基区载流子浓度越高其寄生的BJT器件便能越高效的工作“也就是意味着更大的β”导致SCR路径的正反馈更强从而导致维持电压下降。）