Low Frequency Noise Measurements And Analysis Of Capacitive Micro-Accelerometers
Capacitive-sensing micro-accelerometers are being used by the hundreds of millions in the automobile safety systems, health care and consumer electronics products. Their performance is limited by the combined effects of the thermally-dependant electrical and mechanical noise sources. They limit the...
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| Format: | Thesis |
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2014
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| Summary: | Capacitive-sensing micro-accelerometers are being used by the hundreds of millions in the automobile safety systems, health care and consumer electronics products. Their performance is limited by the combined effects of the thermally-dependant electrical and mechanical noise sources. They limit the detectable levels of the devices for low acceleration and their precision in high accuracy applications. A thorough review of noise in MEMS, including micro-accelerometers, was published as part of the background studies for this research. Two research groups from Tohoku and Michigan investigated both noise sources of their prototypes at room temperature. Their results showed the existence of 1/f noise at low frequencies, and white noise at higher frequencies. The 1/f noise is thought to be electrical in origin. However, both groups reported mismatches between simulated and measured data. Concurrently, another group from TU-Delft characterized directly the mechanical-thermal noise spectrum from their custom micro-sensors without the electronics system. They demonstrated the existence of ambient pressure-independent 1/f noise, and noted the likelihood of its having mechanical origin. These results demonstrate the need to perform further noise studies on capacitive micro-accelerometers. The data could be useful when these devices are used for critical applications, such as rate responsive heart pacemakers and defibrillators. This thesis describes custom apparatus and measurement techniques to study the low frequency noise characteristics of commercial capacitive micro-accelerometers. They were used to demonstrate the dependence of noise on temperature and acceleration, the two most dynamic parameters that affect the output accuracies. |
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