Special cells
Tap cells●Tap cells are used to provide substrate connection.●They are used to avoid latch-up.●They connect n-well to VDD and p-sub to VSS.●They are inserted in layout at regular intervals based on tap rules (tap to gate distance) defined in the technology DRC file.Filler cells●Filler cells are used to provide rail continuity, thereby reducing the DRC violations created by the base.●Filler cells are designed in such a way that they contain n-well and p substrate.Metal eco-able cells● The filler cells which are converted to attain any functionality are called metal eco-able cells.●The base layers of both filler cells and metal eco-able cells are same. Some extra metal connections will be added in metal eco-able cells to attain the functionality.●Sizes of these cells are more when compared to normal cells of same functionality.●For example, consider a design having hold violation after the fabrication. One way to overcome the violation is to delay the data-path. In this case we can convert metal eco-able cells to buffer for the delay. (generally done during re-spin of chip).Antenna diode●During fabrication stray charges get accumulated in metal layers. The gate gets ruptured when the amount of these charges are more than threshold. This effect is called antenna effect. The threshold is decided by metal layer area to gate area ratio.●To overcome the antenna effect we use antenna diodes.●Zener diodes will be connected to the metal layers to remove the excess charges.原文链接:https://mp.weixin.qq.com/s/91uIeOu6Q1MuJuJiZ5OFjg
感谢阅读,别走!点赞、关注、转发后再走吧
转载:全栈芯片工程师