A physical model to predict stiction in MEMS

Abstract

One of the most important reliability problems in micro-electromechanical systems (MEMSs) is stiction, the adhesion of contacting surfaces due to surface forces. After reviewing the known physical theory, and the measurement method commonly used to investigate stiction, we present a model that can be used to investigate the sensitivity of MEMS to stiction. It quantitatively predicts the surface interaction energy of surfaces in contact. Included in the model is the roughness of the contacting surfaces and the environmental conditions (humidity and temperature). This is done by describing the surface interaction energy as a function of the distance between the surfaces. This distance is not a unique number, but rather a distribution of distances. It is shown that, if we know this distribution, we can calculate the surface interaction energy. The model is suitable for the prediction of forces due to capillary condensation and molecular interactions.

Stiction of Flexural MEMS Structures

“…Stiction is one of the most widespread hazards threatening the reliable operation of the microelectromechanical systems (MEMS) devices [1,2] . Stiction is often categorized as release-related stiction and in-use stiction [1,3] .…”

“…Stiction is often categorized as release-related stiction and in-use stiction [1,3] . The capillary force [1,2,4,[6][7][8][9] , electrostatic force [4,[9][10][11][12][13] , mechanical load [14] and inertial forces [8] during the MEMS release or in-use stage can all be the actuation mechanisms to bring the devices into contact with one another or with the substrate. The system free energy of the device in contact consists of two parts: the mechanical energy and surface energy.…”

“…The system free energy of the device in contact consists of two parts: the mechanical energy and surface energy. Adhesion energy is defined as the reduction of the surface energy per unit area when combining two surfaces into one interface [15] , which is also referred to as the surface interaction energy [1,2] . Once the external load is retracted, two things happen in terms of the system free energy: the increase of the mechanical energy due to the device deformation and the decrease of the surface energy due to adhesion.…”

“…(1) have been noticed [1] . Van Spengen et al [1] concluded that "the surface interaction energy measurement using stuck beams needs considerably more research before we can conclude anything definite about the precise magnitude of the measured surface interaction energy". Most of the previous studies, according to van Spengen et al [2] , have "never come further than a peel number".…”

“…Most of the previous studies, according to van Spengen et al [2] , have "never come further than a peel number". A more comprehensive way of studying the beam stiction should include the effect of surface roughness [1,2] , whose distribution determines how two surfaces contact each other. A more accurate description on the stuck beam deflection in essence only offers a better characterization of the nominal adhesion energy.…”