Handbook of Silicon Based MEMS Materials and Technologies

38.3. Technologies and Methods

All methods described for thin-film encapsulation begin with definition of the MEMS device on top of a sacrificial layer followed by covering of the device with another sacrificial layer (e.g., silicon dioxide, photoresist, other polymers). The maximum gap width that can be etched into the device is often determined by the relative thickness of this top sacrificial layer to the underlying device layer (Figures 38.1 and 38.2).

Fig 38.1. For the case where the device layer, t^device, is thicker than the sacrificial sealing layer (t^covering), t^covering must be at least half of w^gap for an effective seal. This typically sets w^gap to a few μm or less.

Fig 38.2. For the case where the sacrificial sealing layer, t