Preloaded linear beam vibration sensor and its manufacturing method

• US 5,629,243 A
• Filed: 09/14/1995
• Issued: 05/13/1997
• Est. Priority Date: 11/23/1994
• Status: Expired due to Fees

• Current Assignee: Tokyo Gas Company Limited
• Original Assignee: Tokyo Gas Company Limited
• Inventors: Shoeys, Walter, Nakamura, Kenichi, Cahill, Sean S.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/528,043
• Time in Patent Office: 607 Days
• Field of Search: 73/654, 73/514.32, 73/514.36, 73/514.37, 73/514.02, 73/514.22, 437/228, 437/919, 156/657.1
• US Class Current: 438/50
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

A method is described for manufacturing a miniaturized accelerometer having a narrow bandwidth and behaving as a switch sensitive only to low frequencies such as are contained in earthquakes. The method includes provision of an unbalanced see-saw beam assembly composed of beams 2 and masses 3 at opposite ends of the beams 2. The beams 2 have their suspension at a location with slightly different distances from the masses 3 along a line parallel to and vertically offset from the line connecting centers of gravity of the masses 3.

Claims

1. A method for manufacturing a preloaded linear beam vibration sensor including an unbalanced see-saw type see-saw beam having its suspension at an intermediate portion thereof and a mass at each end thereof, comprising the steps of:

providing a substrate;

depositing on said substrate an oxide film;

integrally making on said substrate, via a polysilcon film deposited on said oxide film, a see-saw beam comprising two parallel beams, two masses connecting said beams at respective ends and hinge posts extending from said beams at a location spaced different distances from said masses;

depositing an oxide film on said see-saw beam;

forming on said oxide film covering said hinge posts, via a polysilcon film, hinges which cover said hinge posts;

etching part of said substrate underlying said see-saw beam to form a space permitting pivotal movement of said see-saw beam; and

removing said oxide film covering said see-saw beam and said hinge posts to allow said beam to move freely within said hinges.

2. A method for manufacturing a preloaded linear beam vibration sensor including an unbalanced see-saw type see-saw beam having its suspension at an intermediate portion thereof and a mass at each end thereof, comprising the steps of:

providing a substrate;

depositing on said substrate an oxide film;

integrally making on said substrate, via a polysilicon film deposited on said oxide film, a see-saw beam comprising, two parallel beams, two masses connecting said beams at respective ends and hinge posts extending from said beams at a location spaced different distances from said masses;

depositing an oxide film on said see-saw beam;

forming on said oxide film, via a polysilicon film, hinges which cover said hinge posts;

providing a lubricant layer of silicon nitride (SiN_x) between said hinge posts and said hinges;

etching part of said substrate underlying said see-saw beam to form a space permitting pivotal movement of said see-saw beam; and

removing said oxide film covering said see-saw beam and said hinge posts to allow said beam to move freely within said hinges.