Effect of Charge Injection Due to ESD on the Operation of MEMS

The relative effect of charge injection due to human-body model electrostatic discharge (ESD) on the operation of capacitive microelectromechanical systems (MEMS) structures is studied. The influence on the operating characteristics as a function of feature size is analyzed; for small gaps (< 5 mum), the modified Paschen´s law applies. A force factor is introduced to compare forces due to the control voltage and trapped charge due to ESD or triboelectrification and assess possible failure due to stiction. The results show that the relative effect of injected charge due to ESD increases inversely as the square of the gap separation for floating targets and inversely as the square of the plate area for grounded targets. For comparison purposes, the relative effect of charge injection due to triboelectrification is shown to be independent of device scaling. An electric-field model for the air gap and dielectric layer is introduced to assess the reliability of MEMS due to trapped charge in the dielectric.