Theoretical limits on the freestanding length of cantilevers produced by surface micromachining technology

Abstract

To determine the maximum possible length of freestanding micromachined cantilevers, in this paper we provide a theoretical analysis of three important forces on cantilevers, namely acceleration, Casimir and Coulomb forces. The analysis provides theoretical limits to cantilever lengths separate from the well-known effects of surface adhesion and capillary collapse. This analysis offers an insight into the problem of in-use stiction in microstructures, which is a major source of functional failure in dynamic micromechanical systems. In this paper we conclude with a table that lists the maximum free standing length of microstructures that would offer reliable operation without stick–slip motion, excluding the possible effects of surface adhesion.

Design Optimization of NEMS Switches for Suspended-Gate Single-Electron Transistor Applications

“…In particular and in contrast to micromechanical switches, the Casimir force is expected to be significant at the nanoscale [8] since it may overcome elastic restoring actions in the device and lead to the cantilever's sticking during the fabrication process, i.e., even without applying any voltage. The maximal length corresponding to the beam such that it does not stick to the substrate is called the detachment length and is an essential design parameter [9], [10]. Therefore, in this part, we purpose to determine a low-voltage (<1 V) actuation window for conventional cantilevers that accounts for this constraint in order to help with the systematic design of NEMS switches.…”

Nonlocal thin films in calculations of the Casimir force

“…Actuation and nonlinear behavior of a mechanical oscillator with the Casimir force were demonstrated 13 and the importance of the force in adhesion and stiction has also been discussed. [17][18][19] Due to technological reasons thin coating layers or multilayered structures are often in use in micromechanical devices. The main question to be addressed in this paper is how important are the nonlocal effects when the film thickness is smaller than the mean-free path of the electrons.…”

Mechanics of the dynamic release process for stiction failed microcantilever beams using structural vibrations

“…22 To understand this, two different simulations were carried out. In the first case Equation 4 and Equation 6 were simultaneously integrated, with the modal amplitude and its derivatives set to zero, such that lateral amplitude were completely ignored. The second case does not put any restrictions on the modal amplitude or its derivatives thus incorporating w m in the response.…”

“…These include the surface forces listed previously, as well as Casimir forces, and Coulomb forces. 1,6 Research efforts aimed at improving device reliability at the fabrication stages have taken various tacks. These include introducing novel materials, thin film coatings, smart design changes, and post-fabrication manipulation.…”

“…Designers have also proposed avoiding stiction by redesigns: by limiting the length of free standing cantilever beams stiction may be avoided during the operation of certain actuators. 6 Additional features, such as sidewall spacers and bumps, may be etched into the device and help reduce the contact area of the neighboring surfaces, thereby reducing the potential for stiction. 19 These design approaches have met with some success, though they limit design flexibility.…”