Enhanced Performance of Spiral Co-planar Inter-Digital Capacitive Structures for Sensing Applications

In this work we consider a Spiral Inter-Digital Capacitive (SIDC) structure for its optimum design and performance analysis based on finite element simulation, for possible application as sensors. The effects of relevant geometrical parameters like sensor electrode width, inter-electrode gap, number of electrode pairs and electrode height on sensor output capacitance are evaluated and analyzed. In addition, influence of a test sample over the designed sensor for varying lift-off distances from the top of the sensor surface and for various material permittivity values are investigated. Results of the studies show that a spiral structure has about 25% higher sensitivity for its capacitance value compared to a corresponding Rectangular Inter-Digital Capacitive (RIDC) structure of comparable dimensions. The simulation results have been verified experimentally by fabricating and testing SIDC and RIDC structures for dielectric characterization of materials and proximity measurement applications. The results point to the possibility of designing and fabricating spiral inter-digital capacitive sensors with higher sensitivity for a multitude of applications.