An RF MEMS switch with a differential gap between electrodes for high isolation and low voltage operation

Abstract

A double-actuation RF microelectromechanical system (MEMS) switch with high isolation and low voltage operation for RF and microwave applications is presented. The operation voltage of the suggested double-actuation vertical RF MEMS switch structure was reduced without decreasing the actuation gap. Theoretically, the operation voltage of the suggested structure is about 29% lower than that of a single-actuation vertical RF MEMS switch with the same fabrication method, electrode area and equal contact gap. The proposed RF MEMS switch was fabricated by surface micromachining with seven photo-masks on a quartz wafer. To achieve planarization and the stair-like structure, a polyimide sacrificial layer was spin-coated, cured and etched in two steps and patterned by a dry etching step which defines the double-actuation mechanism. The measured results of the fabricated RF MEMS switch demonstrate that the insertion loss was lower than 0.11 dB for the 20 V ON state, the isolation was higher than 39.1 dB for the OFF state and the return loss was better than 32.1 dB for the 20 V ON state from dc to 6 GHz. The minimum pull-in voltage of the fabricated RF MEMS switch was 10 V.

A square wave is the most efficient and reliable waveform for resonant actuation of micro switches

“…Compared with a classic single micro beam design, they demonstrated a reduction of about 32% for static pull-in voltage. Jang et al [2] proposed a design for doubly-clamped microswitches using a stepped (reduced) electrostatic gap which resulted in a 29% reduction in pull-in voltage and better switch metrics. However, reduction of the electrostatic gap to reduce the pull-in voltage sacrifices also the RF performances of the MEMS switch [21].…”

“…MEMS switches gained the attention of researchers owing to their attractive RF characteristics compared to solid state micro switches: almost zero power consumption, high isolation and low insertion loss [1]. Electrostatic actuation is predominant over electromagnetic, piezoelectric and thermoelectric actuation, because of its simplicity, speed and low power requirements [2]. These switches obtain their ON/OFF states via an actuation voltage designed to exceed a 'pull-in voltage' in order to overcome the elastic rigidity of the micro switch structural elements.…”

The Design of Micro Electrostatic Structure with Low Driving Voltage

“…The main advantages of the electrostatic actuator include a simple structure, a rapid response, low power consumption, and compatibility with the IC process. Nevertheless, the electrostatic driver has a high pull-in voltage which is generally more than 40V, even up to 90V [2] . As a result, the supply voltage is not compatible with the IC voltage and the lifetime is short.…”

“…This structure can reduce the driving voltage of the device effectively while the plate gap is kept the same. Generally, the new structure can reduce the actuate voltage about 30% [2] .…”