The vertical comb electrodes capacitive sensor (VCECS) has been widely used in inertia sensors, resonant sensors, and pressure sensors, etc. In this paper, we present an improved microspring, called a W-form spring, that provides a large stiffness ratio in an out-of-plane direction while retaining a long sensing range for a VCECS. The stiffness ratio, defined as the ratio of the stiffness in the lateral direction to the out-of-plane direction, is an important parameter for determining the stability of the VCECS. To realize the properties of the W-form spring, such as the spring constant and stiffness ratio, theoretical analysis and numerical simulations are performed. In addition, VCECSs with W-form and other springs have been fabricated using microelectromechanical systems (MEMS) micromachining technology. The spring constants of the sensor have been calculated from simulations and measured results. The characteristics among different suspension springs are compared. According to the numerical simulations and experiment results, the working range and stability of the device are both improved for the VCECS by using the W-form suspension spring.
Proc. SPIE. 5836, Smart Sensors, Actuators, and MEMS II
KEYWORDS: Sensors, Electrodes, Deep reactive ion etching, Photomasks, Capacitance, Micromachining, Silicon, High aspect ratio silicon micromachining, Finite element methods, Microelectromechanical systems
This paper presents a three dimensional micro capacitive tactile sensor that can detect normal and shear forces which is fabricated using deep reactive ion etching (DRIE) bulk silicon micromachining. The tactile sensor consists of a force transmission plate, a symmetric suspension system, and comb electrodes. The sensing character is based on the changes of capacitance between coplanar sense electrodes. High sensitivity is achieved by using the high aspect ratio interdigital electrodes with narrow comb gaps and large overlap areas. The symmetric suspension mechanism of this sensor can easily solve the coupling problem of measurement and increase the stability of the structure. In this paper, the sensor structure is designed, the capacitance variation of the proposed device is theoretically analyzed, and the finite element analysis of mechanical behavior of the structures is performed.