This paper reports on the successive improvements introduced in the shunt switches fabricated with the RF MEMS multiuser technology platform available at FBK-irst. In the course of a multiyear development several technological features and design methods have been made available to enhance the operation of capacitive switches. This work analyzes their effects by reviewing the behaviour of the FBK-irst capacitive switches at three different stages of this optimization process. Improvements have been assessed by means of DC electromechanical characterizations, which use a simple quasistatic C-V measurement to extract the switch actuation voltage and the capacitance in the on and off states (Con and Coff) and RF measurements. The addition of a floating metal layer into the process flow has allowed a great increase of the switch on state capacitances, getting Con/Coff ratios of 200, up to 50 times greater than the ones obtained for the same structures without this feature.