B a c kg r o u n d
MEMS
Salland Engineering ready to accelerate MEMS testing The world doesn’t seem to be able to get enough of micromechanical sensors. However, the chip industry currently lacks the test technology when it comes to high-volume production of MEMS. Salland Engineering wants to change this by 2020. René Raaijmakers
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icroelectromechanical systems (MEMS) have experienced a real triumph in recent decades. Invisibly, but steadily, they’ve penetrated almost every application that requires information from its environment. For highly specialized applications, discrete, customized MEMS sensors are already being utilized. But in some cases, the technology can also be integrated on CMOS chips. This allows MEMS to meet the high demands of the largest market, ie consumer electronics: compact dimensions, low costs and increased functionality. Navigation, height measurement and the current trend in movement tracking during sports – it’s all done utilizing information provided by MEMS sensors. The technology is no longer limited to the automotive industry. In the 90s, MEMS were a big hit in acceleration sensors for airbags. Nowadays, they’re much more widely used. Movement, pressure, light, moisture, sound and ultrasound – it can all be measured with micromechanical technology. The market for MEMS sensors is expected to continue to grow by more than 10 percent a year, based on trends such as the Internet of Things and people’s insatiable hunger to gather information about their environment and health. Research agency Yole predicts that the MEMS market will reach 100 billion dollars in 2023. In 2018, this was 62 billion dollars.
Limitations
The fact that traditional MEMS testing is currently reaching its limits became clear 32
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at the Salland MEMS Seminar. The test specialist from Zwolle recently received international MEMS experts to discuss trends, challenges and solutions for future product generations. “With the growth of portable applications and systems that monitor people’s health at home, it’s now about technical challenges that ultimately decide on life and death,” said Nigel Beddoe of Cohu from Poway, California, maker of specialized MEMS testing equipment. “That means that designers of ICs, packag-
MEMS trends
ing, final testing and end applications need to work more closely together.” Beddoe made it clear that Cohu is increasingly facing technical limitations in terms of test quality and productivity. He explained that for the most advanced microphones with a signal-to-noise ratio of 70 dB, there are actually no good tests – while 75 dB is already coming. Cohu supplies machines that test 0.8 mm by 0.8 mm MEMS parts with 256 pieces at a time. “This really puts us at the limit of what we can do,”
Accelerometers are one of the most common MEMS applications. In their traditional form, they consist of a mass suspended from springs. If this mass is moved by a physical stimulus, the resulting movement or vibration can be picked up in many ways: capacitive, piezoelectric, piezoresistive, thermal, optical or with tunneling. The toolkit of the MEMS designer seems infinite. MEMS-based accelerometers were already used in airbag systems over thirty years ago, but nowadays, these sensors can also be found in drones, game consoles, mobile phones, sports watches, GPS devices, medical applications and much more. MEMS have evolved from stand-alone components to integrated six-axis and even nine-axis sensors. The progress in MEMS technology is astonishing. While the first MEMS-based rotation sensors were able to detect a 1.5-degree rotation, now 0.1 degree is common, and 0.05 degrees is coming. Gyroscopes and e-compasses make grateful use of this accuracy. MEMS barometers had an accuracy of meters when they first came on the market, now 25 centimeters is normal. For MEMS microphones, a signal-to-noise ratio of 55 dB is the current standard and 70 dB is the absolute top, but for mobile phones, 75 dB is already in the works. Two trends stand out. Due to the requirements for compactness and price, MEMS technology is increasingly being integrated into chips but also in advanced packaging. For example, Bosch is supplying a system-in-package with a three-axis 14-bit accelerometer, a three-axis 16-bit gyroscope and a three-axis geomagnetic sensor. All of this is packaged with a 32-bit microcontroller in a module measuring just 5.2 by 3.8 by 1.1 millimeters.
