Capacitive RF MEMS switch dielectric charging and reliability: a critical review with recommendations

Abstract

This paper presents a comprehensive review of the reliability issues hampering capacitive RF MEMS switches in their development toward commercialization. Dielectric charging and its effects on device behavior are extensively addressed, as well as the application of different dielectric materials, improvements in the mechanical design and the use of advanced actuation waveforms. It is concluded that viable capacitive RF MEMS switches with a great chance of market acceptance preferably have no actuation voltage across a dielectric at all, contrary to the ‘standard’ geometry. This is substantiated by the reliability data of a number of dielectric-less MEMS switch designs. However, a dielectric can be used for the signal itself, resulting in a higher Con/Coff ratio than that one would be able to achieve in a switch without any dielectric. The other reliability issues of these devices are also covered, such as creep, RF-power-related failures and packaging reliability. This paper concludes with a recipe for a conceptual ‘ideal’ switch from a reliability point of view, based on the lessons learned.

A Second-Order Delta-Sigma Control of Dielectric Charge for Contactless Capacitive MEMS

“…Dielectric charging is a serious reliability problem that slows down the use of electrostatic MEMS in many applications [1]. The horizontal voltage shift of the C(V ) curve, V sh , is related to the net amount of charge trapped in the dielectric, Q d .…”

“…Several actuation strategies, based on the opposite effects of bipolar voltages on the charge dynamics, have been proposed to mitigate the effects of dielectric charging [1]- [4]. However, only closed-loop control strategies based on periodical sensing of dielectric charge or its effects can ensure long-term stability of the device features.…”

Charge induced by ionizing radiation understood as a disturbance in a sliding mode control of dielectric charge

“…Usually a complex combination of processes may contribute to the injection of charge into the dielectric, such as trap-assisted tunnelling (TAT) and Schottky emission from the conductors directly into the dielectrics [6]- [10]. This reliability problem has slowed down the introduction of MEMS devices in some applications [11]. Accordingly to its importance, MEMS dielectric charging has received considerable research attention over the past years.…”

“…Accordingly to its importance, MEMS dielectric charging has received considerable research attention over the past years. In order to mitigate the effects of actuation-induced charging, several open-loop strategies using bipolar actuations have been proposed [11], [12]. The main drawback of these strategies is that they cannot guarantee long-term stability since they cannot adapt to drifts of the charging characteristics of the dielectric layers.…”

Simultaneous Control of Dielectric Charge and Device Capacitance in Electrostatic MEMS

“…Dielectric charging is an important reliability issue for the use of electrostatic MEMS devices in many applications [1]. This phenomenon, caused by the actuation of the device, produces effects such as shifting of the C-V curve and even device failure due to stiction.…”