die attach film daf or room temperature vulcanizing rtv silicone elastomer which is commonly used for a pressure sensor the packaging substrate may be a multi layer packaging substrate such as a land grid array lga in an embodiment a bonded device substrate would comprise a cmos substrate with a conductive layer such as an aluminum or copper top metallization layer eutectically bonded to first and second mems substrates on either side of the cmos substrate an additional conductive layer on the back side of the cmos substrate allows for electrical connections between the cmos substrate and the second mems substrate at least one of the mems substrate may comprise a handle substrate with etched cavities coated by a thin silicon oxide layer and fusion bonded to a silicon device layer the device layer may be patterned so as to define the desired moveable or stationary structure in an embodiment the conductive layer may comprise any electrically conductive metal or semiconductor an opening is etched in the back of the cmos substrate stopping on one of the cmos metallization layers the cmos metallization layer may be any one of the existing cmos metallization layers the sidewalls of the opening are then electrically passivated by depositing an insulating film ex silicon oxide silicon nitride polymer typically the insulating film will also be deposited on the bottom surface of the opening covering the previously exposed cmos metallization layer the cmos metallization layer is then once again exposed by an etching or saw.