- The newly developed accelerometer is 100 times more sensitive and 10 times less noisy than conventional ones.
- It was able to achieve 1 µG level resolution.
- It can be used in various motion sensing applications, and medical and healthcare technology.
The global consumer electronics market is expected to cross $1.8 trillion by 2024. Thus, analysts are expecting significant growth in the demand of accelerometers, an electromechanical instrument used to measure acceleration forces.
These mass-producible, miniaturized instruments are usually developed by Micro-Electro-Mechanical Systems (MEMS) technology where the method of fabrication is well established.
Now, researchers at Tokyo Institute of Technology and NTT Advanced Technology Corporation have developed a new method to reduce the size of MEMS accelerometers to less than 1/10th while increasing its sensitivity over 100 times as compared to conventional accelerometers.
In order to design an effective accelerometer, there is a trade-off between noise reduction and size reduction. This happens because mechanical noise is inversely proportional to the proof mass (mass of the moving electrode).
In capacitive accelerometers, the sensitivity is directly proportional to the size of the accelerometer. Therefore, there is also a trade-off between the sensitivity increase and size reduction.
The existing silicon-based MEMS accelerometers cannot detect minor (on the scale of microgravity) level of input acceleration.
New Design
To develop high-resolution accelerometers, researchers used gold material: they added multi-layer metal structures to the proof mass and spring modules. The resulting instrument was able to achieve 1 µG level resolution.
Reference: Sensors and Materials | DOI:10.18494/SAM.2018.1840 | Tokyo Tech
Researchers employed multiple layers of gold to the proof mass structure, which helped them reduce the mechanical noise while increasing the mass per area. They also reduced the warpage of the proof mass to utilize the entire area of the 4-millimeter square chip, which made capacitive accelerometer over 100 times more sensitive.
Chip and scanning electron microscope picture of the new accelerometer | Courtesy of researchers
The measured characteristics of this gold proof-mass MEMS accelerometer were consistent with the designed values, demonstrating the practicality of the new approach.
More specifically, the mechanical noise (dominated by the Brownian noise) of the new instrument was found to be 22 nG/√Hz, which is more than one order magnitude lower than those of traditional accelerometers with the same capacitance sensitivity.
Since they used semiconductor microfabrication process and electroplating to manufacture new accelerometers, these structures can be implemented on an integrated circuit chip, allowing manufacturers to improve the resolution of miniaturized accelerometers for everyday use.
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For instance, these accelerometers can be used in various motion sensing applications, infrastructure monitoring, mobile vehicle control, lightweight robots, and medical and healthcare technology. They can also be applied to space environment measurements that require extremely low acceleration sensing and to navigation systems where GPS cannot be used.
