Miniature absolute pressure transducer assembly and method

• US 3,918,019 A
• Filed: 03/11/1974
• Issued: 11/04/1975
• Est. Priority Date: 03/11/1974
• Status: Expired due to Term

• Current Assignee: Timothy A. Nunn
• Original Assignee: Timothy A. Nunn
• Inventors: Nunn, Timothy A.
• Primary Examiner(s): Albritton, C. L.
• Application Number:
  US05/449,900
• Time in Patent Office: 603 Days
• Field of Search: 338/2-5,36,42 73/88.5SD,88.5R,398AR 29/626,628
• US Class Current: 338/42
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm

Abstract

A transducer assembly for measuring absolute pressure utilizing a glass substrate and a thin silicon diaphragm upon which is diffused a piezoresistive bridge circuit. Bridge circuit components are properly oriented and connected to bonding pads formed on the silicon. The glass substrate has a circular well formed therein having a diameter at least as large as the diameter of the diaphragm. Conducting leads are deposited on the glass substrate in a pattern matching that of the bonding pads on the silicon. The silicon is bonded to the glass substrate with the silicon diaphragm overlying the well in the glass and the bonding pads overlying the conducting leads deposited on the glass. The bond provides a hermetic seal around the well, trapping a prdetermined pressure therein which serves as a reference pressure. Ambient pressure variations cause stress variation in the diaphragm, resulting in unbalance of the bridge which can be sensed with associated circuits to give an indication of the ambient pressure.

Claims

1. An absolute pressure transducer comprising a semiconductor diaphragm, an integral reinforcing area surrounding and defining the boundaries of said diaphragm, means forming a bridge circuit on said diaphragm, said last named means having electrical characteristics related to stress in said diaphragm, conducting pads formed on said reinforcing area in a predetermined pattern, conducting paths connected between said means forming a bridge circuit and said conducting pads, an insulator substrate having a well formed therein with a diametral dimension at least as great as said diaphragm diametral dimension, and conducting leads formed on said insulator substrate spaced thereon to match said predetermined pattern of conducting pads, said substrate and reinforcing area being bonded together with the center of said diaphragm substantially overlying the center of said well for providing a hermetically sealed chamber therebetween, whereby said means forming a bridge circuit is enclosed in said hermetically sealed chamber for protection from ambient environments, said predetermined pattern of conducting pads substantially overlying and electrically conducting portions of said conducting leads, whereby pressure trapped in said sealed chamber provides a reference pressure and stress may be imposed in said diaphragm by ambient pressure.

2. An absolute pressure transducer as in claim 1 wherein said diaphragm is a thin silicon member, said means forming a bridge circuit is a piezoresistive integrated circuit bridge formed thereon, and said conducting paths are P+ diffusion areas.

3. An absolute pressure transducer as in claim 1 wherein said insulator substrate is glass and said conducting leads are electrically conductive strips deposited on the side of said glass in which said well is formed.

4. An absolute pressure transducer as in claim 1 wherein said insulator substrate has a larger area than said reinforcing area and said conducting leads extend beyond the area overlain by said reinforcing area, whereby saiD conducting paths are accessible for making connection to said means forming a bridge.

5. A transducer for absolute pressure measurement comprising a semiconductor integrated circuit pressure transducer having a diaphragm section with a piezoresistive bridge circuit formed thereon, an insulator substrate having a well formed therein, conducting leads deposited on said insulator substrate having externally accessible portions, said semiconductor integrated circuit pressure transducer being bonded to said insulator substrate with said diaphragm section overlying said well thereby forming a hermetically sealed chamber therebetween, said piezoresistive bridge circuit being enclosed in said sealed chamber for protection from ambient environment and being in electrical contact with said conductive leads on said insulating substrate, whereby said piezoresistive bridge circuit may be unbalanced by stress imposed in said diaphragm by pressure differential across said diaphragm.