Stiction, or adhesion of components to one another, is a major failure mechanism in surface micromachined MEMS. In this paper we discuss roughening of the surface of polysilicon, which forms the structural layer in surface micromachining, by the formation of porous silicon and its effect on stiction. The adhesivity of the surface is investigated by measurements of contact angle and the roughness is measured by a surface profiler. Measurements to estimate stiction on surface micromachined cantilevers and accelerometers are reported. © 2005 WELEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enakshi Bhattacharya

Department of Electrical Engineering

U. Venu Babu

P. R.S. Rao

MEMS

SURFACE MICROMACHINING

SURFACE PROFILERS

Accelerometers

Microelectromechanical devices

Micromachining

Polysilicon

Stiction

Surface roughness

Porous silicon

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

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IIT Madras

Physica Status Solidi (A) Applications and Materials Science

In this paper, we estimate the stiction force from electrical (current-voltage) measurements on surface micromachined polysilicon cantilever beams. A bias voltage was applied between the beam and the substrate. At the pull-in voltage, the beam collapsed to the substrate and the current rose rapidly from zero. Similarly, at the pull-out voltage during bias sweep back, the current dropped rapidly to zero when the contact between the beam and the substrate was broken. An analytic model for the stiction force was developed in terms of the pull-in and pull-out voltages and was used to estimate a stiction force of about 70 nN from the measured electrical characteristics. This method of characterization is suitable for use in packaged devices. An analytic model was developed to estimate stiction force from optical surface-profile measurements of the curvature of long collapsed cantilever beams in a cantilever-beam array, in the absence of any electrostatic actuation. The force per unit length of about 14 nN/m thus obtained was used to compare the effects of surface roughness on stiction. © 2007 IEEE.

Journal of Microelectromechanical Systems

Estimation of stiction force from electrical and optical measurements on cantilever beams

An estimate of stiction force, rather than the more commonly reported surface energy, helps design reliable structures. Stiction is a major cause of failure in surface micromachined structures. We report on the modeling and estimation of the stiction force from simple I-V curves on cantilever beams which can be measured even on packaged devices. We have fabricated oxide anchored cantilever beams of polysilicon by surface micromachining. Current is measured for an applied bias between the beam and the substrate. Pull-in and pull-out voltages are determined as the points of maximum slope calculated by differentiating a cubic spline fit to the measured I-V data. The commercial package CoventorWare was used to develop an empirical model for estimating the pull-out voltage for the cases when there is no stiction and in the presence of stiction. A model is developed for finding the stiction force from the simulated and the experimental pull-out voltages. The method uses only measured values of pull-in and pull-out voltages and the beam length and does not require the value of Young's modulus. We also discuss an independent visual method to estimate the process stiction force from the cantilever beam array that is normally used to estimate the surface adhesive energy. An analytical model is developed to calculate the stiction force from the attachment length of long stuck cantilever beams that are released in the same process.

Proceedings of SPIE - The International Society for Optical Engineering

Stiction force estimation from attachment length and electrostatic measurements on cantilever beams

Smart Materials, Structures, and Systems

Contact angle measurements on polysilicon for surface micromachining applications

Device and Process Technologies for MEMS and Microelectronics II

Intelligent star tracker

Journal of Applied Physics

Accurate method for determining adhesion of cantilever beams

Sensors and Actuators A: Physical

Novel prevention method of stiction using silicon anodization for SOI structure

World Patent Information

How a US Patent Protects You, and Does Your Project Qualify for a US Patent?

Effect of porous silicon formation on stiction in surface micromachined MEMS structures

Journal	Physica Status Solidi (A) Applications and Materials Science
ISSN	18626300
Open Access	No