Development of parallel-plate-based MEMS tunable capacitors with linearized capacitance–voltage response and extended tuning range

Abstract

This paper presents a design technique that can be used to linearize the capacitance-voltage (C-V) response and extend the tuning range of parallel-plate-based MEMS tunable capacitors beyond that of conventional designs. The proposed technique exploits the curvature of the capacitor's moving electrode which could be induced by either manipulating the stress gradients in the plate's material or using bi-layer structures. The change in curvature generates a nonlinear structural stiffness as the moving electrode undergoes out-of-plane deformation due to the actuation voltage. If the moving plate curvature is tailored such that the capacitance increment is proportional to the voltage increment, then a linear C-V response is obtained. The larger structural resistive force at higher bias voltage also delays the pull-in and increases the maximum tunability of the capacitor. Moreover, for capacitors containing an insulation layer between the two electrodes, the proposed technique completely eliminates the pull-in effect. The experimental data obtained from different capacitors fabricated using PolyMUMPs demonstrate the advantages of this design approach where highly linear C-V responses and tunabilities as high as 1050% were recorded. The design methodology introduced in this paper could be easily extended to for example, capacitive pressure and temperature sensors or infrared detectors to enhance their response characteristics.

Multi input versus single input sliding mode for closed-loop control of capacitive micro structures

“…The Fig. 1 Movable electrode of parallel plates micro capacitor from top view [34] structure of the common microcapacitors is mostly similar to the one shown Fig. 2a.…”

“…As it was shown, using closed loop control, we were able to reduce the relative electrodes distance to 0.85 of initial distance, without any instability occurring. But according to the references [31][32][33][34][35][36][37][38][39] using open loop control, this distance can only be reduced to about 0.33 times of the initial gap of the two electrodes. This condition also occurs for nanostructures that have been stimulated by electrostatic force [38,43].…”

Linearization and tunability improvement of MEMS capacitors using flexible electrodes and nonlinear structural stiffness

“…Gary [11] and Bakri-Kassem and Mansour [15] introduced designs that incorporate nonlinear springs to increase the tuning range. We previously introduced parallel-plate tunable capacitors utilizing modified geometries and nonlinear structural stiffness, with a so-called linear tunability ranging from 30% to 300% [12,16,17], and reported tunability higher than 1000% for a design with an initially curved moving electrode [18]. Bakri-Kassem and Mansour used a similar technique to develop a capacitor with 400% linear tunability [19].…”

“…Bakri-Kassem and Mansour used a similar technique to develop a capacitor with 400% linear tunability [19]. The designs introduced in [18] and [19] have flexible moving electrodes and the main part of their tunability is achieved by the deformations of the moving plate in the contact mode, where a thin dielectric layer insulates them. Even though this technique drastically increases the tuning range, due to large interfacial adhesion force between the two contacting surfaces [20], the C-V response may exhibit a noticeable hysteresis loop, thus altering the reversibility of the response which is not desired in tunable elements.…”

Electrostatic repulsive out-of-plane actuator using conductive substrate

“…Micro out-of-plane electrostatic actuators are among the most important microelectromechanical systems (MEMS) devices, and have been widely applied in radio frequency (RF) MEMS 1 2 3 4 and optical MEMS 5 6 7 . Compared with thermal and piezoelectric actuators, electrostatic actuators have the advantages of fast response, low power consumption, and hysteresis-free characteristics 8 9 .…”