Handbook of Silicon Based MEMS Materials and Technologies

Chapter Thirty. Introduction to Encapsulation of MEMS

30.1. Early Work on Bulk-MEMS Devices

When early micromachined devices (later called bulk-MEMS devices) were created from a silicon wafer by etching, it was soon found that a single silicon wafer was not sufficient for creating practical functional devices. Even for a simple pressure sensor, it was necessary to join two wafers together. Many early pressure sensors consisted of a silicon wafer anodically bonded to a glass wafer [1, 2].

Besides pressure sensors other early devices were made out of several wafers for a number of reasons. An early accelerometer [3] consisted of three wafers, one silicon wafer and two glass ones, to achieve mechanical rigidity and to provide protection from environmental ...