Adapt standard tests to non-standard devices: Automotive qualification of a MEMS-based sensor system

This feature shows how to adapt industry standard tests to a non-standard device, resulting in an assessment of the robustness of a MEMS-based sensor system.

Topics covered include:

Qualification challenge
The first natural step in designing the qualification plan for MEMS-based sensor and ASIC chip systems would be to review AEC-Q100 for the traditional automotive requirements. AEC-Q100 or "Stress Test Qualification for Integrated Circuits" is maintained by the Component Technical Committee of the Automotive Electronics Council (AEC). However, it's clear that AEC-Q100 does not have specific requirements for MEMS devices and does not address unencapsulated devices. This is where the engineer designing the test plan must get creative in seeking a solid physics of failure-based test regime.

Overview of circuit function
The ChipCap series humidity sensor by GE offers a new standard in the field of accurate relative humidity measurement. Based on a capacitive polymer sensing technology, this device offers signal conditioning and temperature compensation for a single system-on-chip (SoC) device. Its measurement capability is accurate to ±2% from 20 to 80% relative humidity (RH) and ±3% across the entire humidity range at 25C. The temperature accuracy is ±1C from 0 to 70C. ChipCap provides either analog or digital interfaces in a single, 5-VDC-powered chip. Dual outputs furnish humidity and temperature as linear (0 to 1V), ratiometric (10-90% of VDD), or with digital output (ZACwire one-wire interface).

ChipCap relative humidity sensors change capacitance in direct proportion to ambient relative humidity. An internal solid state band gap provides the temperature output measurement. The ChipCap 14-pin SOIC-packaged MEMS sensor and ASIC is shown below.

Device specifications