Patent FR-2947628-A1 (FR)
Title: Microelectromechanical system for measuring mechanical deformation on a surface of a structure, comprises a support mounted with a substrate made of monocrystalline silicon, where the substrate is provided with an active zone sensitive
Inventor: BUISSON RAYMOND
IPC: B81B3/00
Filed: 2009-07-01
Abstract: The microelectromechanical system comprises a support mounted with a substrate made of monocrystalline silicon. The substrate is provided with an active zone (11) sensitive to mechanical deformations, and arranged at the center of the substrate in a well (12) formed in the mass of the substrate. The active zone is constituted of four beams (1, 2, 3, 4) made of monocrystalline silicon, and laid parallel to each other, where the length determined along a longitudinal direction to undergo longitudinal mechanical deformations by elongation or contraction. The microelectromechanical system comprises a support mounted with a substrate made of monocrystalline silicon. The substrate is provided with an active zone (11) sensitive to mechanical deformations, and arranged at the center of the substrate in a well (12) formed in the mass of the substrate. The active zone is constituted of four beams (1, 2, 3, 4) made of monocrystalline silicon, and laid parallel to each other, where the length determined along a longitudinal direction to undergo longitudinal mechanical deformations by elongation or contraction. The beams are built in by each of their respective ends using an anchoring unit (13, 14) for protruding into the pit and mechanically decoupled into the edges of the well so that the inner face of each silicon beam is mechanically detached from the support. The first and second beams are provided to exhibit coefficients of longitudinal sensitivity equal to positive sign, and third and fourth beams are provided to exhibit longitudinal sensitivity coefficients equal to negative sign. The first and second beams are constituted by the pair of external beams of the four beams arranged parallel to each other, and the third and fourth beams are constituted by the pair of interior beams of the four beams arranged parallel to each other. The absolute value of longitudinal sensitivity coefficients of the respective first and second beams and third and fourth beams are same or different, and have coefficients of drift temperature of same sign or different sign. A ratio between the absolute values of temperature drift coefficients of the first and second beams and the third and fourth beams is equal to the inverse relationship between the absolute values of longitudinal sensitivity coefficients of the first and second beams and third and fourth beams. A unit is arranged for adjusting the coefficients of drift temperature of beams, and is formed by resistors for adjusting coefficient of temperature drift associated with each beam. A packaging electronic circuit is integrated in areas of the substrate adjacent to the active zone. A conditioning circuit (5) is adapted to interconnect the electrical resistors of four beams and the resistors for adjusting the coefficient of temperature drift associated respectively with each beam to form a Wheatstone bridge. The resistors of the first and second beams are arranged in two opposite branches of the Wheatstone bridge in series respectively with the resistance for adjusting drift temperature coefficient associated with the beam, and the resistors of third and fourth beams are arranged in the two other opposite arms of the bridge in series with resistance for adjusting temperature drift coefficient associated with the beam. The packaging electronic circuit comprises a unit for analog-digital conversion for transforming measurement signals obtained from Wheatstone bridge into digital signals, a unit for digital signal transmission through a current loop, and a calculation unit to correct the digital signals according to information for temperature measurement and coefficient of linear expansion of the material constituting the structure for eliminating the effect of purely heat deformations. The support is constituted of an insulating layer to be pasted on the surface of the structure. The active zone further comprises three zones to carry out measurements in three directions at angles of 45[deg] , 60[deg] or 120[deg] . An independent claim is included for a process for fabricating a microelectromechanical system.