Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1990-05-07
1992-02-18
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Diaphragm
73708, 338 4, G01L 708, G01L 906
Patent
active
050883291
ABSTRACT:
A piezoresistive pressure transducer employing a sapphire force collector diaphragm having piezoresistive films of silicon epitaxially formed on a major surface thereof, preferably in a Wheatstone bridge pattern. The piezoresistive elements of the Wheatstone bridge are oriented and located so that the pressure sensitivity is maximized, while the linearity errors of the output voltage of the Wheatstone bridge in relationship to the applied pressure are minimized. The silicon piezoresistive film is preferably of a thickness of from 1000 to 60,000 angstroms and is doped with boron in the range of from 5.times.10.sup.17 to 9.times.10.sup.20 atoms/cc. Electrical arms and contact pads are also formed on the major surface of the force collector diaphragm. The diaphragm is mounted on a ceramic body having a cavity in the upper surface thereof, the diaphragm enclosing the cavity so as to form a protective chamber with the piezoresistive silicon films within the chamber. The diaphragm is hermetically bonded by the ceramic glass to the body in a vacuum such that the chamber provides a low pressure of vacuum reference. The contact pads are positioned over a matching number of feed through tubes in the ceramic body and electrical connectors are fed through the tubes for carrying electrical signals from the piezoresistive film within the chamber. A protective assembly encloses the pressure transducer thereby insulating it from external shock or pressure. The ceramic body, the sapphire diaphragm and the isolation ring are all of approximately matching thermal expansion characteristics.
REFERENCES:
patent: 4127840 (1978-11-01), House
patent: 4600912 (1986-07-01), Marks et al.
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