Pressure Sensor Devices Featuring a Chemical Passivation Made of a Locally Synthesized Diamond Layer

The rear side of a pressure sensor diaphragm is prepared with an additional diamond layer as protective coating against harsh media. The preparation sequence for the diamond coating is developed as a simple backend process, combining only two additional steps in the standard process. These are the local seeding of nanodiamond layer and the low-temperature diamond growth at <300 degrees C in a linear antenna microwave plasma-enhanced chemical vapor deposition reactor, where only at the nanodiamond seeded sites, a high-quality diamond film was synthesized. The seeding resolution in the setup used was limited to approximate to 80 mu m, but can be further reduced. In an industry-typical assembly sequence the diamond coated pressure sensor devices are further equipped with a support wafer and mounted to a TO-8 socket. Tests of such sensor systems indicate that the diamond layer does not hamper the stability of the device. This proofed method of postprocessing an only-local and low-temperature synthesis of a diamond layer on the wafer-level opens- up possibilities for many other applications, since this approach is scalable and in general cost effective.