Design and fabrication of capacitive interdigitated electrodes for smart gas sensors

In this paper, we study the design parameters of capacitive interdigitated electrodes (IDEs) and the effect of these parameters on the sensitivity of the IDEs when employed as a capacitive gas sensor. Finite element simulations using COMSOL Multiphysics were carried out to evaluate the sensitivity of the capacitive sensor. Simulations show that for permittivity-based sensing, the optimum thickness of the sensing film is slightly more than half the wavelength of the IDEs structure. On the other hand, sensing films that are thinner than half wavelength should be used if the required sensing mechanism is based on structural swelling. Increasing the IDEs metal thickness can increase the sensitivity by increasing the sidewall electric field, but this is only true if the sensing film is thick enough to completely fill the spacing between the electrodes. A simple and reliable IDEs structure and fabrication process are proposed. Physical dry etching provides good yield and fine resolution compared to liftoff technique. Fabricated and packaged prototype sensors are presented.