MEMS Environmental Sensors Testing: Maximizing Performances and Consistency

How to achieve peak performance and consistency in production testing for MEMS Environmental Sensors

Microelectromechanical systems (MEMS) environmental sensors are ubiquitous, silently underpinning the functionality of numerous devices in our daily lives. From smartphones and wearables to smart homes and industrial automation, these miniature marvels measure temperature, pressure, humidity, and a plethora of other environmental parameters.

Their role is becoming pivotal in several industry applications, fueled by the rising need for environmental monitoring and the implementation of strict regulations regarding air quality. Whether the application is in consumer, automotive or medical electronics, these sensors are required to provide accurate and real-time data about a combination of parameters, which include temperature, humidity, pressure, and gas presence.

Testing is a crucial step for MEMS environmental sensors, as their accuracy is of paramount importance.

Inaccurate testing can harm performance and safety

Consider a fitness tracker with a temperature sensor consistently reading five degrees Celsius higher than reality, jeopardizing calorie burn calculations. Alternatively, a weather station with a faulty humidity gauge could lead to inaccurate forecasts. Inaccurate data from MEMS sensors can have significant ramifications, impacting not only user experience but potentially safety-critical applications.

Production testing serves as a crucial quality control checkpoint, ensuring that only sensors meeting predefined performance criteria make it into the final product.

From manufacturers’ perspective, fewer faulty sensors reaching consumers translates to lower warranty costs and improved customer satisfaction. Enhanced product reliability is at the basis of the brand reputation, fostering customer loyalty and trust.

Testing MEMS environmental sensors is a complex task

Production testing of MEMS environmental sensors presents several hurdles compared to traditional electronic components.

As these devices – like all other MEMS sensors – work as interfaces into the physical world, traditional electrical testing is not enough to capture their mechanical aspects. The key thing about their testing is giving physical stimulus into the devices, in order to activate the transducer inside them: The input is run through a transducer to convert into an electrical signal, which can then be processed. What differentiates the test of environmental sensors is that they respond to various stimuli like pressure, temperature, or humidity. Creating a test setup able to perfectly match all the real-world environmental variations that influence the sensor functionality can be a complex task.

The sensor-type specificities represent a further challenge: each sensor type might require unique testing setups and parameters, according to its functionalities and intended applications.

This intricate scenario makes it difficult to develop generic testing methods: a “one size fits all” approach – as the one used for mixed signal devices testing – won’t work. On the other hand, answering customized testing needs for the wide variety of sensor designs through customized testing procedures and equipment can be excessively time-consuming and add to the overall development cost.

In addition to these specific technical requirements, a highly competitive market pushes the manufacturers to an effort to reduce the cost for test equipment and the test time.

These challenges collectively make production testing for MEMS environmental sensors a complex undertaking. However, ongoing research and development in MEMS testing methodologies are continuously improving efficiency and accuracy.

Multi-stimulus testing ensures performance compliance

As environmental sensors are sensitive to multiple environmental factors and respond to various stimuli (pressure, temperature, humidity, gas, …), the key thing about their testing resides in the need to develop testing setups able to capture all the electrical and mechanical aspects of the sensor, simulating and controlling a multiplicity of environmental factors.

Testing these devices requires the application of multiple stimuli into the same sensor chip, forcing us to go beyond traditional single-parameter testing. Sensors must be exposed to a combination of factors simultaneously, to mimic the real-world conditions that can influence their performance. These may include frigid temperatures far below freezing, scorching heat exceeding typical operating ranges, pressure variations simulating altitude changes, and humidity levels encompassing arid deserts to tropical rainforests.

As various combinations of “pressure + x” sensors have emerged to provide multi-parameter measurements, several elements of the environment have to come into the “pressure + x” sensor chips for their testing: pressure, gas, temperature, humidity. Simulating and controlling these various environmental factors during testing can be complex and expensive.

Furthermore, not only the sensors must be subject to several physical inputs, but these must often be applied simultaneously, to take into account the interplay between the different sensor units and the interaction mechanisms of multiple parameters.

Balancing cost, throughput, and accuracy is essential

Advanced test equipment for MEMS environmental sensors can be expensive, and achieving high-volume production often necessitates balancing test accuracy with cost. Very precise testing equipment and procedures might be too expensive for mass production lines. At the same time, however, many applications are requiring more accurate and sensitive devices, that means, inevitably, very accurate test equipment is required for their verifications. The trick to achieve the required test cost efficiency and avoid any bottlenecks due to testing operations lies in maximizing the test throughput, therefore lowering the cost of test per device.

Specialized equipment to address testing challenges

A main approach to address the testing challenges for MEMS environmental sensors consists in the adoption of test equipment able to perform the high-volume, single-insertion test and calibration of integrated environmental sensors measuring pressure, temperature, humidity, and gas. Combined, multi-stimulus equipment can provide the perfect match to mimic real-world conditions, while multi-site capabilities and modular setups help meet tailored test requirements and throughput, reducing costs and setup time. Latest-generation test handlers incorporate universal test chambers in which multiple physical stimuli can be applied at the same time, to replicate realistic working conditions. Fast switching between various pressure and/or temperature levels makes a comprehensive test and calibration process as efficient as possible.

The test setup is composed by three main elements:

MEMS Test Handlers to precisely position and move the sensors during testing. They must provide high-speed motion and high multi-site capability for high-volume manufacturing.
MEMS Test Stimuli to create the combination of temperature, pressure, humidity and gas required to activate the sensors and measure their response.
Automated Test Equipment (ATE) to analyze the sensor’s electrical output in response to the stimuli and compare it to pre-defined specifications.

This type of test setup allows test processes and hardware in use to remain largely unchanged when switching from an application to another, as the test unit can be easily reconfigured inside the same base handler. The base handler itself should be designed to support the reliable and robust handling of compact MEMS packages, which are typical for environmental sensors, especially in consumer applications.

Looking forward

As MEMS technology continues to mature and play an ever-increasing role in our lives, from self-driving cars to connected homes, the importance of robust production testing will only become more critical. By employing a combination of established and cutting-edge test equipment and techniques, manufacturers can ensure that these tiny powerhouses deliver accurate data, ultimately contributing to the success of the countless devices they are integrated into. The future of MEMS environmental sensors is undoubtedly bright, and the latest advancements in testing will play a key role in unlocking their full potential.

By adopting high-throughput, multi-stimulus test solutions, semiconductor companies can ensure the quality and reliability of MEMS environmental sensors before they reach their final application.

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