Micro-spring is one of key elements for MEMS-devices. A good suspension spring not only provides stable support but also increases the performance of the sensors. In this study, a novel suspension spring, called the W-form spring, is proposed to provide a huge stiffness ratio in an out-of-plane direction, while retaining a large working range for a vertical comb electrodes capacitive sensor (VCECS). To realize the properties of the W-form spring, such as the spring constant and stiffness ratio, crab-leg and serpentine springs have also been designed, simulated and fabricated by MEMS techniques. The measured results show that the W-form spring has a very high stiffness ratio, over 39.2 times larger than the serpentine spring in an out-of-plane direction, which can resolve the mechanical decoupling for the VCECS.
To demonstrate the characteristics of the W-form spring, a capacitive force sensor using vertical comb electrodes is developed to detect normal loads. High sensitivity is achieved by the high aspect ratio comb electrodes with narrow comb gaps and large overlap areas. Furthermore, silicon nitride produced by plasma-enhanced chemical vapor deposition (PECVD) was deposited onto the comb electrodes of the sensor to increase the capacitance variation. Experimental results show that comb electrodes deposited with silicon nitride can enhance the sensitivity. The W-form springs used in this sensor also can increase the sensitivity as well as to stabilize the device by preventing collisions of the comb electrodes.
A three-dimensional (3-D) tactile sensor, based on differential capacitive sensing principle, has been fabricated by deep reactive-ion-etching (DRIE). Different from lower and upper electrodes of the conventional capacitive tactile sensor, normal and shear forces are differential detected by the vertical comb electrodes. Numerical analyses and measurement of the sensor is described. Experimental results show that the 3-D tactile sensor has a good linear response in the normal force.

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