Fabrication of cantilever type microswitches using surface micromachining technology

Abstract

Cantilever type microswitches have advantages of low electrostatic actuation voltage and high isolation in RF applications. Of particularly importance, it can be integrated with microstrip line in series or shunt connection mode for building the RF circuit or system directly. Figure 1(a) is an idea switch with single pole, single throw configuration (SPST). As shown in figure 1(b). the microswitch in our study is similar in structure to an ideal switch. Suspended aluminum membrane with perforation holes is used as a movable electrode that will form the resistive contact with the bottom electrode underneath at the free end through electrostatic actuation process. The fabrication processes will be described as shown in figure 2 for constructing the 4 um gap structure of microswitches. Figure 3 shows the structure of microswitch using field emission scanning electron microscope (FESEM). The bending of the membrane was resulted from the thermal histogram of lithography and dry release process in reactive ion etching system, which can be controlled by process parameters optimization. Hysteresis measurement on HP-4156 as shown in figure 4 has demonstrated the operation of microswitch. The actuation voltage shows higher value than expected from simulation due to the existence of residual stress. However, the small curvature of this cantilever type membrane indicates the feasibility of building the application circuit from this low stress membrane microswitches.