Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
2000-02-15
2001-05-22
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S417000, C257S418000
Reexamination Certificate
active
06236095
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to semiconductor transducers and, more particularly, to such transducer assemblies that employ a single block semiconductor carrier structure for supporting semiconductor piezoresistive elements (e.g., strain gages).
Semiconductive transducers are widely used in automotive, biomedical and a variety of other applications because of their relatively small dimensions, reliability and high signal output relative to other devices. In performing the transducer function, one or more piezoresistive semiconductor elements are utilized, in which the resistance thereof varies according to the intensity or magnitude of an applied force upon an associated diaphragm to which the elements are mechanically coupled (bonded). The diaphragm to which the force is applied is typically a metal or semiconductor membrane-like substrate upon which the piezoresistive elements are dielectrically mounted. A force applied to the diaphragm deflects the diaphragm and hence causes the associated piezoresistive element to vary resistance in accordance with the deflection. The force being measured is transferred to the piezoresistive element, which is strain responsive, causing the element to expand or compress, thereby producing a change in the electrical resistance of the element. The piezoresistive elements are typically arranged in a Wheatstone bridge circuit with one to four of the bridge legs being active. Other circuit configurations are also possible.
A desire is to continue improving the characteristics of transducers of the foregoing type so that devices may be manufactured that are relatively small, sensitive and which produce a relatively large resistance in a relatively small area. The devices should also exhibit a linear operation and small deviations in sensitivity and null offset over a wide range of temperatures, as well as having a relatively low manufacturing cost.
A problem in achieving these improved characteristics and cost efficiencies, however, relates to the manner in which prior art transducers are manufactured and assembled. Prior art transducer assemblies require multiple piezoelectric elements, i.e., “gages,” to be manufactured as discrete elements. Manufacturing process and material variations contribute to a lack of uniformity of these elements. The gages must subsequently be electrically normalized based upon their mechanical deviation and their deviation from optimum bonding position on the diaphragm, and it is therefore difficult to achieve consistent results from one transducer assembly to the next.
SUMMARY OF THE INVENTION
The present invention, accordingly, describes a cost effective transducer assembly having a semiconductor carrier structure that integrally supports multiple piezoelectric elements for mounting as a single unit to a diaphragm or other force-impacted substrate.
The integrally formed piezoelectric elements, i.e., gages, are separated from the carrier structure in a space defined by the structure while maintaining their electrical contact and their precise position relative to the structure by using electrically conductive, metallic bonding wires and thin film metalized traces attached to both the structure and the elements. The carrier structure maintains the precise, relative position of the elements throughout the manufacturing process. The transducer assembly is thus well suited for precise registration and mounting to a substrate by an automated process.
In one embodiment, a carrier structure for semiconductor transducers mounts as a single unit to a force-impacted substrate and includes multiple piezoelectric elements integrally formed with the carrier structure, such that the elements are located on the same elevation level as the carrier structure while maintaining their electrical contacts and their precise positions relative to the structure by using electrically conductive wires attached to both the structure and the elements.
In another embodiment, a carrier structure for semiconductor transducers mounts as a single unit to a force-impacted substrate and includes multiple piezoelectric elements integrally formed with the carrier structure, such that the elements are located on the same elevation level as the carrier structure, and the elements are connected into a bridge circuit form by metalized traces, and connected to the carrier structure through bonding wires. Therefore, in the assembly process, it is not necessary to handle and mount individual elements separately, since they are already in the bridge circuit form. Accordingly, automated handling and assembly machines can be used for better quality control and reduced manufacturing cost.
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Dresser Equipment Goup, Inc.
Hayes and Boone LLP
Ngo Ngan V.
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