Electrical Distortion
Stress-induced changes in the resistivity of silicon resistors create an unwanted differential voltage in balanced analog circuits. This piezoresistive offset arises when mechanical force from the surrounding package is unevenly distributed across the matched resistor networks of an amplifier or digital-to-analog converter.
Gradient Mapping
The magnitude of this offset is directly proportional to the stress gradients existing across the die surface. Because resistor values shift in response to both tension and compression, any mismatch in the local stress field produces a corresponding error in the output voltage. This is particularly problematic in bridge circuits where high-precision matching is essential.
Package Cushioning
To prevent this mismatch, manufacturers employ compliant die-attach films and soft gel coatings that isolate the sensitive silicon from the rigid plastic package. Specialized leadframe designs also incorporate stress-relief slots that redirect the mechanical forces away from the active sensor regions. Selecting resistors with low piezoresistive coefficients, such as thin-film metal alloys instead of diffused silicon resistors, further reduces the offset drift.
This choice of materials is critical for devices operating in harsh environments.
Offset Verification
Testing involves measuring the output offset before and after the circuit is subjected to thermal cycling and solder reflow. High-precision sensors are calibrated after assembly to cancel the residual offset. These values are stored in nonvolatile memory.
