Vacuum packaged single crystal silicon device

A method for forming a hermetically sealed vibrating micromechanical structure, the method comprising:

• micromachining one or more resonator structure anchors, a capacitive air gap, one or more isolation trenches, and one or more alignment marks in a single crystal silicon semiconductor material active layer of a first Silicon-On-Insulator wafer having a dielectric layer between a semiconductor material handle layer and the semiconductor material active layer;
• fusion bonding a single crystal silicon semiconductor material active layer of a second Silicon-On-Insulator wafer directly to the active layer of the first Silicon-On-Insulator wafer, the second Silicon-On-Insulator wafer having a dielectric oxide layer between a semiconductor material handle layer and the semiconductor material active layer;
• removing the handle and dielectric oxide layers of the second Silicon-On-Insulator wafer;
• etching one or more windows in the active layer of the second Silicon-On-Insulator wafer;
• silicon dry etch micromachining a single crystal silicon resonator structure in the single crystal silicon semiconductor material active layer of the second Silicon-On-Insulator wafer;
• forming one or more contact pads on the active layer of the second Silicon-On-Insulator wafer;
• forming a cover in a cover wafer having spaced apart top and bottom surfaces, forming the cover further comprising micromachining a plurality of access holes through the wafer between the spaced apart top and bottom surfaces with each of the access holes being positioned to align with a corresponding one of the contact pads formed on an outer surface of the active layer of the second Silicon-On-Insulator wafer;
• and
• in a controlled atmosphere, bonding a cover to the active layer of the second Silicon-On-Insulator wafer over the resonator structure with the access holes aligned with the respective corresponding contact pad.