Measuring and testing – Dynamometers – Responsive to force
Patent
1994-05-10
1997-02-04
Chilcot, Richard
Measuring and testing
Dynamometers
Responsive to force
73DIG4, 257419, G01L 110
Patent
active
056000740
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is related to a silicon chip for use in a force sensor used, for example, to measure pressure in the combustible chamber of internal engines. The force sensor has at least one piezoresistive element producing signals and circuits for evaluating the signals of the piezoresistive elements. Silicon chips for use in force sensors, and in particular for detecting pressure in the combustion chamber of internal combustion engines, in which the force is applied to the silicon chip by way of a stamp have been described in German Patent Application No. 41 061 020. The silicon chip contains piezoresistive elements having a resistance which changes when subjected to a force. The signals produced by these piezoresistive elements are preprocessed by circuits, also present on the chip, and forwarded, via leads, to other circuits external to the chip. Unfortunately, such known silicon chips provide no means of protecting the circuits from the disruptive influence of mechanical strains. Therefore, it is an object of the present invention to provide a silicon chip including components which are protected from mechanical strains.
SUMMARY OF THE INVENTION
The present invention achieves the above object by advantageously arranging piezoresistive elements in an area of the silicon chip which will experience high mechanical tension, and arranging the circuits in an area of the silicon chip which will experience low mechanical tension. This arrangement maximizes the signal produced by the piezoresistive elements and minimizes the interference of the circuits.
By arranging four piezoresistive elements around the force application area of the silicon chip, two having their longitudinal direction oriented parallel to the force application area and two having their longitudinal direction oriented perpendicular to the force application area, the evaluation of the signals produced by the piezoresistive elements using, for example, a bridge circuit, is greatly simplified. The use of two piezoresistive elements of the same orientation in the force application area is particularly space-saving.
For non-symmetrical configurations of the silicon chip, arranging four piezoresistive elements on a measurement line, two having their longitudinal direction oriented parallel to the line and two having their longitudinal direction oriented perpendicular to the line is particularly advantageous. Once again, a bridge circuit having four piezoresistive elements simultaneously arranged in the area of greatest mechanical tension is possible.
In a simplified configuration of the silicon chip according to the present invention, a solid piece of silicon has a force application area in its center and the circuits are provided on a peripheral area of the silicon chip. The circuits can be effectively decoupled from the mechanical tensions of the force application area by introducing grooves on the top surface of the silicon chip arranged between the force application area and the circuits.
If the bottom surface of the silicon chip is structured with grooves, the circuits on the top surface of the silicon chip are less severely strained by the etching processes used to introduce the grooves. If, in this case, only an area opposite the force application area lies on a support attached to the bottom surface of the chip, the circuits will be effectively decoupled from the force application area. If the force application area is surrounded by a groove on the bottom surface of the chip, the circuits will be mechanically decoupled from the force application area. Further, since the circuits are still above an area of the bottom surface which still contacts the support, the heat generated by the circuits is effectively dissipated via the support. To increase the concentration of tension in the area of the piezoresistive elements, the above structure can also be given a recess in the bottom surface at a center of the area surrounded by the groove.
Mechanical tensions between the silicon chip and the support can al
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Bantien Frank
Herden Werner
Kuesell Matthias
Marek Jiri
Schmidt Steffen
Chilcot Richard
Dougherty Elizabeth L.
Robert & Bosch GmbH
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