MEMS variable capacitance devices utilizing the substrate: I. Novel devices with a customizable tuning range

Abstract

This paper, the first in a series of two, presents a paradigm shift in the design of MEMS parallel plate PolyMUMPS variable capacitance devices by proposing two structures that utilize the substrate and are able to provide predetermined, customizable, tuning ranges and/or ratios. The proposed structures can provide theoretical tuning ranges anywhere from 4.9 to 35 and from 3.4 to 26 respectively with a simple, yet effective, layout modification as opposed to the previously reported devices where the tuning range is fixed and cannot be varied. Theoretical analysis is carried out and verified with measurements of fabricated devices. The first proposed device possessed initially a tuning range of 4.4. Two variations of the structure having tuning ranges of 3 and 3.4, all at 1 GHz, were also successfully developed and tested. The second proposed variable capacitance device behaved as a switch.

Low-voltage puzzle-like fractal microelectromechanial system variable capacitor suppressing pull-in

“…♥ This work belongs to one of the authors of this letter. Although the SRF was not reported in the paper, it was measured to be 8 GHz in [7] and 6 GHz in [9].…”

“…The source of the electrostatic forces is two-fold: the fringing capacitance that is present between the top plate and the bottom plate, and the capacitance that is present between the top plate and the semiconducting substrate. The effects of substrate coupling in PolyMUMPS are significant and cannot be ignored as clearly demonstrated in [7,9]. By using both the concept of fractals and substrate coupling, a variable capacitor with a high tuning range was attainable as will be shown.…”

“…At a first glance, one may be tempted to ignore the effect of F S . However, it was clearly demonstrated experimentally that the substrate effects in PolyMUMPS on actuation are significant in [7,9], and as such, ignoring F S is not a reasonable assumption.…”

“…If the latter were to happen, then the varactor would resemble the one that was previously introduced in [7,9]. However, the presence of the bottom plates provides two important advantages.…”

Differential RF MEMS interwoven capacitor immune to residual stress warping

“…Secondly, and once the weave is created, the complete structure can be suspended a considerable distance above the substrate (i.e. 2.6µm), which reduces parasitic coupling [8]. The resonant frequency, f R , of a capacitor is generally given by:…”