31 respectively. The model consists of i = 1,2,��,m linear beam elements located in a single layer and j = 1,2,��,k motion limiters or supports (0 < k < 2 m) that are located in i = 1,2,��,m nodes. Each beam element has two nodes with three degrees of freedom (DOF) at each one (displacement in x- and y-axis directions and rotation in x0y plane). The model was meshed manually with number of finite elements m equal to 50, thereby resulting in 150 total DOFs. The sufficiency of this particular mesh density was confirmed by comparative simulations presented in Section 2 and summarized in Figures 4�C5. Impac
Microelectromechanical system (MEMS) technology has become popular for the miniaturization of sensors.
The advantages of micro sensors fabricated by MEMS technology include small size, easy mass-production and low cost.
Many micro capacitive pressure sensors have recently been manufactured by using MEMS technology. For instance, Habibi et al. [1] utilized a surface micromachining process to fabricate a capacitive pressure sensor array on a glass substrate. The array consisted of electrically parallel individual sensors with composite SiO2-Cr-SiO2 diaphragms and vacuum-sealed cavities underneath, and the cavities were formed by etching an aluminum sacrificial layer. Sippola and Ann [2] presented a ceramic capacitive pressure sensor fabricated by using thick film screen-printing technique, which the sensor consisted of a bottom electrode deposited on an alumina substrate and a top electrode deposited on a ceramic diaphragm.
The cavity and diaphragm were created using a thick film sacrificial layer, and the pressure sensor had a sensitivity of 9.2 fF/psi. Wang and Ko [3] employed the silicon fusion bonding technique to develop a touch mode capacitive Cilengitide pressure sensor, and the sensor had a good linearity in the operating range and had a overload protection. A capacitive pressure sensor with a sandwich structure, Batimastat proposed by Zhou et al. [4], was fabricated using a three-mask process and an anodic bonding, which the sensitivity of the sensor was 0.2 pF/kPa. These pressure sensors [1-4] did not have integrated circuits on a chip, so they needed to be coupled with circuits by packaging, leading to an increase in parasitic capacitance.
Because the parasitic capacitance increased, the noise of capacitive sensors raised, resulting in lowering the performance of sensors. Integrating capacitive sensors with circuits on a chip helps to reduce the parasitic capacitance and packaging cost, so that the sensors have the benefits of low noise, high performance and small area. Thereby, in this work we developed a capacitive pressure sensor integrated with a sensing circuit on chip.