Active device under bond pad to save I/O layout for high-pin-count SOC

Abstract

To save layout area for electrostatic discharge (ESD) protection design in the SOC era, test chip with large size NMOS devices placed under bond pads has been fabricated in 0.35-mum one-poly-four-metal (1P4M) 3.3V CMOS process for verification. The bond pads had been drawn with different layout patterns on the inter-layer metals to investigate the effect of bonding stress on the active devices under the pads. Threshold voltage, off-state drain current, and gate leakage current of these devices under bond pads have been measured. After assembled in wire bond package, the measurement results show that there are only little variations between devices under bond pads and devices beside bond pads. This result can be applied on saving layout area for on-chip ESD protection devices or I/O devices of IC products, especially for the high-pin-count system-on-a-chip (SOC).