Fabrication and characterization of a capacitive micromachined shunt switch

Abstract

The design and fabrication of a capacitive shunt switch are described. The switch is based on a bridge structure that can be modulated using electrostatic actuation. The switch has two states: when the bridge is up the signal passes through with less than 0.1 dB insertion loss. When the bridge is down the signal is attenuated by 15–20 dB at 20 GHz. The residual stress of the bridge material is critical to operation of these switches. This stress was tightly controlled by varying the temperature of the plating bath. Different bridge widths and shapes are compared. “Bowtie” shaped bridges are demonstrated to have increased insertion loss and similar isolation compared to straight bridges. These devices were observed to be sensitive to packaging stress, resulting in more than doubling the actuation voltage. This work also describes the development of a test fixture that facilitates standard microwave connections for testing the devices without a probe station. The test fixture was observed to have an insertion loss of less than 3 dB up to 20 GHz.