Design And Properties Research Of The Capacitive RF MEMS Switch

As one of the most important MEMS devices, capacitive RF MEMS switch has many benefits compared to the traditional switch devices. Capacitive RF MEMS switch is increasingly under focus. However, there are some disadvantages such as high-actuated voltage and low resonant frequency for capacitive RF MEMS switches. In this paper, three kinds of capacitive RF MEMS switches are designed and researched for optimizing the structure parameter and improving the actuated voltage and resonant frequency. The performance and failure are also researched and analyzed by testing the I-V and C-V behavior of the capacitive RF MEMS switch.Straight beam, cable-stayed beam and bending beam capacitive RF MEMS switches are designed in this paper. The simulation results show that the height and thickness of the bridge film are the most important structure parameters for the actuated voltage of straight beam capacitive RF MEMS switches. The actuated voltage is lower with smaller height and thickness of the bridge film. The lowest actuated voltage is 5V. For the natural frequency,it is higher with thicker and longer bridge film. The highest natural frequency is 6.0×10⁵ Hz. The diagonal length and actuated area are the most important structure parameters for cable-stayed beam capacitive RF MEMS switches. The actuated voltage can be reduced to 3V by increasing the diagonal length and actuated area. The natural frequency can be improved to 3.0×10⁵Hz by reducing the diagonal length and increasing the actuated area. The features of the bending beam capacitive RF MEMS switches are that the bridge film has a lower spring constant because of the hinge structure. Its actuated voltage is from 3V to 9V, and natural frequency is from 1.0×10⁵ Hz to 1.5×10⁵Hz. I-V testing results show that the actuated voltage is about 20V for straight beam switch, 10V for cable-stayed beam switch and 5V for bending beam switch. By C-V testing, the up-state capacitance is about 6.0×10^-12F, and the off-state capacitance is about 1.5×10^-11F. The performance is not good and the switch has some failure phenomenon. Three kinds of failures are found by observing the morphology of the switch, which is insulation failure, adhesion failure and performance deterioration failure. There are two main reasons for the failures. One is residual stress, which can make the insulation fracture and shedding. It also can make the cantilever fracture and deformation. The solution of this problem is choosing coefficient of thermal expansion matched materials and improving the manufacturing process. Another reason is surface force including capillary force, Vander Waals force and electrostatic force. The solution is increasing surface roughness,reducing surface electrostatic charge and not using hydrophilic materials.