Optimization of Capacitive Membrane Sensors for Surface-Stress-Based Measurements

Surface stress-based measurement is a relatively new mechanism in biological and chemical sensing. The viability of this mechanism depends on the maximum sensitivity, accuracy, and precision that can be achieved with these sensors. In this paper, an analytical approximate solution and a finite-element model are employed to describe the electromechanical behavior of a surface stress-based sensor with capacitive measurements. In the proposed model, a circular membrane is assumed as the sensing component, while only a smaller concentric circular area of its surface is subjected to a change in surface stress. The presented approximate analytical solution has a good correspondence with the finite-element model and is computationally fast and accurate enough to be an effective design tool. Based on this modeling study, we can determine the optimum design of the sensor to obtain the maximum capacitive sensitivity. Moreover, we study the effect of this optimization on the precision of the system in surface stress sensing. This paper shows that the ratio of sensing area to the whole membrane plays a key role in the overall performance of such a sensor.