Electricity: electrical systems and devices – Electrostatic capacitors – Variable
Patent
1993-04-05
1994-11-29
Reynolds, Bruce A.
Electricity: electrical systems and devices
Electrostatic capacitors
Variable
73718, H01G 700
Patent
active
053695445
ABSTRACT:
A method and structure for forming a capacitive transducer having a deformable single crystal diaphragm. A first well region is formed within a semiconductor substrate in an SOI wafer having a sacrificial layer of known thickness and a top single-crystal silicon layer thereon. Next, a silicon epitaxial layer is deposited on the top silicon layer for forming a flexible single crystal membrane. The epitaxial layer and the sacrificial layer are masked and etched to define the flexible diaphragm. An electrical insulating conformal support layer is deposited on the substrate and attached to the diaphragm so as to seal the sacrificial layer therebetween. An access opening is etched through the diaphragm, and then a wet etchant is inserted through the access opening for removing the sacrificial layer, thereby defining a diaphragm cavity between the remaining epitaxial layer and the substrate. The thickness of the diaphragm cavity is substantially equal to the thickness of the sacrificial layer removed from the SOI wafer. Conductive ions are diffused into facing sections of the diaphragm and the first well of the substrate so as to define fixed and deformable electrodes of the sensing capacitor. Next, a plug is selectively deposited within and for sealing the access opening without substantially reducing the volume of the diaphragm cavity. In this manner, a deflection of the flexible diaphragm in response to variations between the ambient pressure and the pressure sealed within the diaphragm cavity causes a o corresponding change in the capacitance between the first well region and the conductive region in the diaphragm. A reference capacitive sensor of similar construction is also provided for ratiometric pressure measurements. A pressure transducer manufactured in accordance with this process is also described.
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Dixon Richard D.
Ford Motor Company
May Roger L.
Mills Gregory L.
Reynolds Bruce A.
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