Capacitor construction for use in pressure transducers

• US 4,831,492 A
• Filed: 05/04/1988
• Issued: 05/16/1989
• Est. Priority Date: 05/08/1987
• Status: Expired due to Term

• Current Assignee: Vaisala OY
• Original Assignee: Vaisala OY
• Inventors: Kuisma, Heikki
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US07/190,113
• Time in Patent Office: 377 Days
• Field of Search: 361/283, 73/718, 73/721, 73/724
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm

Abstract

This publication discloses a capacitor construction for use in pressure transducers, including a substrate plate having of a silicon wafer and a thinner glass wafer. A first fixed capacitor plate is provided for overlying the substrate plate plate. A silicon plate is adapted to encircle the substrate plate with its thinned center area acting as a moving capacitor plate by virtue of its diaphragm behavior and a top plate overlying the silicon plate includes a silicon wafer and a glass wafer bonded to the silicon wafer and having a thickness essentially smaller than that of the silicon wafer. According to the invention, over the supporting substrate plate and between the first capacitor plate and its encircling silicon plate, is provided another overlying capacitor overlying plate, which essentially encloses the first capacitor plate. With this design, a reduced temperature sensitivity is accomplished in the capacitor construction.

Claims

1. A capacitor construction for use in pressure transducers, comprising:

a supporting substrate plate consisting of a silicon wafer and a glass wafer attached onto said silicon wafer by an electrostatic bonding method, said glass wafer being essentially thinner than the silicon wafer;

a first fixed capacitor plate overlying the substrate plate;

a silicon plate overlying the substrate plate to encircle the fixed capacitor plate, said silicon plate having a center part thinned to perform as a diaphragm acting as the moving capacitor plate so that well-shaped cavities are formed above and under the diaphragm structure for introduction of the measured pressure medium;

a top plate overlying the silicon plate, said top plate consisting of a silicon wafer and of a glass wafer attached onto said silicon wafer and placed against the silicon plate, said glass wafer being essentially thinner than the silicon wafer; and

a second capacitor plate overlying the supporting substrate plate between the first capacitor plate and the silicon plate which encircles the first capacitor plate in such a manner so as to essentially enclose the first capactor plate;

whereby the second capacitor plate together with the center part of the silicon plate forms a compensating capacitor, whose capacitance (Ct) is essentially less dependent on displacement of the center part of the silicon plate than the capacitance (Cp) formed by the first capacitor plate and the center part of the silicon plate.

2. A capacitor construction in accordance with claim 1, wherein the shape of the second capacitor plate is essentially that of the circumference of a rectangle.

3. A capacitor construction in accordance with claim 1, wherein the top plate is provided with a channel penetrating the silicon wafer and the glass wafer so that the measured pressure medium can be introduced through the channel into an upper cavity formed above the diaphragm in order to permit the measurement of pressure difference.