This article describes the technical challenges related to automotive electronics qualification and verification of a MEMS-based sensor and ASIC system. The example device is a system-on-chip, fully calibrated, surface mount IC, which comes in one of three humidity outputs, digital, ratiometric, or linear (0-1V).
Testing results presented will focus on application of the following tests: Temperature-humidity bias life
High-temperature operating life
Early-life failure rate
ESD Human Body Model
ESD Charged Device Model
Wire bond pull testing (both encapsulated and unencapsulated).
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: Criteria for evaluating the quality and reliability of a MEMS-based temperature and humidity sensor to ensure reliable performance in automotive applications.
Assessment of electrical and environmental tests and requirements as they apply to dual silicon temperature and humidity devices.
Review of MEMS system qualification results, reliability assessments, and test results.
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.
RH Sensor: Planar Capacitive Polymer
RH Range: 0 to 100% RH
RH Accuracy @ 25C: ±2% from 20 to 80%; ±3% from 0 to 20% and 80 to 100%
RH Resolution: 0.4% RH
Temperature Sensor: Integral band gap PTAT
Temperature Scale: "55 to 150C
Temperature Accuracy: ±0.6C at 25C
Temperature Resolution: 0.2C
Storage Temperature: "55 to 150C
Operating Temperature: "40 to 85C
Operating RH Range: 0 to 100% RH, non-condensing