Novel tapered-width micro-cantilevers are introduced to give more design parameters in design space for controlling and synthesizing their pull-in (actuation) voltages. For a given fabrication process, the pull-in voltage of a micro-cantilever is generally a function of the taper function of width along the length, its initial width, and its length. By controlling these design parameters, a specific pull-in voltage for a micro-cantilever can be obtained. Three types of taper functions, linear, parabolic, and exponential, were selected as the width taper functions of micro-cantilevers in this study. Pull-in voltage as low as 1V is achieved with a fast growing taper function for a micro-cantilever. From the simulation and measurement results it shows that a micro-cantilever with a fast growing width along the length has a smaller pull-in voltage but occupies more area and has a smaller bandwidth.