A complementary metal-oxide semiconductor (CMOS)-compatible, capacitive, shunt-type radio frequency MEMS switch design is demonstrated. The switch is actuated by an electrothermal actuator and an electrostatic actuator at the same time, and the switching status is latched by electrostatic force only. Since thermal actuators require a lower voltage than electrostatic actuators, and since an electrostatic force can maintain switching status with virtually no power, the benefits of the mechanism are a very low actuation voltage and low power consumption. The switch is fabricated by a standard 0.35-µm 2P4M CMOS process. The movable membrane can be released by either wet or dry postprocessing etching technologies. The design's CMOS-process compatibility is important because radio frequency (RF) characteristics are determined not just by the device itself. The design can minimize parasitic capacitance when a packaged RF switch and a packaged IC are wired together. The switch contains a set of coplanar waveguide transmission lines and a suspended membrane. The CPW lines and the membrane are contained in the metal layers of the CMOS process. The electrothermal actuators are contained in the polysilicon layer. Only standard CMOS process layers are needed for both the electrothermal and electrostatic actuations in the RF switch. The measurement results show that the electrothermal or electrostatic actuation requires less than 7 V.
This paper demonstrates a capacitive shunt type RF MEMS switch, which is actuated by electro-thermal actuator and
electrostatic actuator at the same time, and than latching the switching status by electrostatic force only. Since thermal
actuators need relative low voltage compare to electrostatic actuators, and electrostatic force needs almost no power to
maintain the switching status, the benefits of the mechanism are very low actuation voltage and low power consumption.
Moreover, the RF MEMS switch has considered issues for integrated circuit compatible in design phase. So the switch is
fabricated by a standard 0.35um 2P4M CMOS process and uses wet etching and dry etching technologies for postprocess.
This compatible ability is important because the RF characteristics are not only related to the device itself. If a
packaged RF switch and a packaged IC wired together, the parasitic capacitance will cause the problem for optimization.
The structure of the switch consists of a set of CPW transmission lines and a suspended membrane. The CPW lines and
the membrane are in metal layers of CMOS process. Besides, the electro-thermal actuators are designed by polysilicon
layer of the CMOS process. So the RF switch is only CMOS process layers needed for both electro-thermal and
electrostatic actuations in switch. The thermal actuator is composed of a three-dimensional membrane and two heaters.
The membrane is a stacked step structure including two metal layers in CMOS process, and heat is generated by poly
silicon resistors near the anchors of membrane. Measured results show that the actuation voltage of the switch is under
7V for electro-thermal added electrostatic actuation.