Appeal No. 1998-0091
Application No. 08/404,054
A. The invention
The invention relates to a capacitive pressure sensor
including a ceramic substrate and a ceramic diaphragm having
respective electrodes which are spaced apart to form a cavity
therebetween. Appellants' specification explains (at 2, lines
23-32) that in prior art pressure sensors of this type, short
circuiting of the two electrodes may result from any of three
different causes: (a) material particles coming between the
electrodes during manufacture; (b) excessive pressure causing
the electrodes to move into contact; and (c) part of an
electrode becoming detached from the diaphragm or substrate
and contacting the other electrode. Referring to Figure 2,
appellants solve the short-circuiting problem by coating the
substrate electrode 13 with a glass layer 14, which in turn is
coated with an insulating layer 20. Spacers 17 separate the
insulating layer from diaphragm electrode 15 to form a cavity
therebetween. Figure 4 shows the same technique applied to a
both halves of a capacitive differential pressure sensor.2
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