A new non-capacitive method of determining surface charge densities using floating field ring devices

A new method has been developed for determining surface charge densities that is based on the dependence with surface charge of the potential of floating field rings in reversed biased planar structures. This method is most attractive for determining charge densities on semiconductor surfaces that are passivated with materials for which it is difficult or impossible to make the standard capacitive measurements. These include the passivants commonly used on power devices, such as glasses and silicon rubber. A feature of the technique is that the surface charge is determined over the depletion region in actual devices after all processing is completed. The experimental technique used is first to measure the floating field ring potential as a function of the applied reverse bias between the anode and cathode. The value of surface charges is obtained by calculating the dependence of the field ring potential on the applied voltage and then varying the surface charge until good agreement between the theoretical and experimental results is obtained.