Silicon nitride, chip protection

Figure 3.48 Exploded schematic view of a flow-cell FPW liquid sensor. The silicon chip containing die thin silicon-nitride membrane, piezoelectric film and transducers is sandwiched between two etched silicon chips. The upper chip is a cap with fluid inlet and outlet fittings, b also provides vias for contact to a temperature-sensing polysilicon resistor deposited on the FPW chip below it. The lower chip introduces transducer contact leads and protects the underside of the membrane fitm contact with the fluid. (Hgwc courtesy of Beo Costello, Bokeley Microliulratitents, Inc.)...

Although the surface of most IC chips has been passivated with a layer of inorganic dielectric material such as silicon dioxide or silicon nitride (polyimides have also been used as final passivating layers), the protection provided by such layers is not sufficient to ensure reliable operation throughout the lifetime of the device. The three basic methods of protection are... 

The sensor chip was bonded to a socket with inlet and outlet flow channels. The aqueous solution to be measured was pumped through the inlet tubes into the silicon chip cavity coated with a 220 nm thick PECVD silicon nitride film to provide chemical protection. In the present work, three sensor designs have been used ... 

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