Accelerometers developed originally for the military, navigation and automotive applications are finding applications in consumer products. The applications include pointing devices and game pads which are mainly for motion sensing of users. The majority of accelerometers are made of silicon based materials. Since the cost of silicon accelerometers is high, consumer applications of accelerometers are restricted to high-end products. The proliferation of accelerometers in low-cost consumer products depends on the availability of low cost accelerometers....[ Read more ]

Accelerometers developed originally for the military, navigation and automotive applications are finding applications in consumer products. The applications include pointing devices and game pads which are mainly for motion sensing of users. The majority of accelerometers are made of silicon based materials. Since the cost of silicon accelerometers is high, consumer applications of accelerometers are restricted to high-end products. The proliferation of accelerometers in low-cost consumer products depends on the availability of low cost accelerometers.

To reduce the cost, one approach is to alter the fabrication method and material of accelerometer. PCB fabrication has similar fabrication characteristics with silicon fabrication but has a lower fabrication cost. Printed circuit board (PCB) fabrication is an alternative to replace silicon fabrication. In this study, a consumer-based capacitive PCB accelerometer is designed and fabricated. The prototypes were designed to have a dynamic range of ±5g and a bandwidth from 0 to 100Hz, which covered the range of acceleration for human limbs.

The issues for PCB accelerometer fabrication are the increase in sensor footprint and the thermal mis-matching of sensor materials. The PCB accelerometer was constructed by an aluminum sensing structure and a PCB substrate. Since the tolerance of aluminum etching is loose, a larger geometric variation of the PCB accelerometer is induced. The variation will lead to sensitivity deviation of the sensor. To minimize the effect, the feature size of the PCB accelerometer was increased. Minimum feature sizes (fabrication limits) related to the aluminum film thickness were defined in the study. Besides fabrication error, the thermal mis-matching of materials also affects the sensing capability of the PCB accelerometer. Compared with silicon accelerometers, the material set of the PCB accelerometer is complicated. Expansions of structures made by various materials are different, which deforms the sensing structure of the accelerometer. The deformation of sensing structures induced errors in sensor outputs. The thermal drift of the PCB accelerometer output was studied in the research.

The behavior of the PCB accelerometer prototype was characterized by its sensing capability and thermal stability. From the characterization results, the response of the PCB accelerometer was repeatable for the designed sensing range of ±5g, from 10Hz to 100Hz. The sensitivity of the prototype was 0.11pF. For the thermal stability of the prototype, the corresponding thermal drift was 29mg/ºC. The performance satisfied the requirement of consumer accelerometer applications. The prototypes sensing capabilities and stabilities are suitable for use in consumer applications.