Stiction in microeiectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when so...Stiction in microeiectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films,the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part.展开更多
The pull-in instability of a cantilever nano-actuator model incorporating the effects of the surface, the fringing field, and the Casimir attraction force is investigated. A new quartic polynomial is proposed as the s...The pull-in instability of a cantilever nano-actuator model incorporating the effects of the surface, the fringing field, and the Casimir attraction force is investigated. A new quartic polynomial is proposed as the shape function of the beam during the deflection, satisfying all of the four boundary values. The Gaussian quadrature rule is used to treat the involved integrations, and the design parameters are preserved in the evaluated formulas. The analytic expressions are derived for the tip deflection and pull-in parameters of the cantilever beam. The micro-electromechanical system （MEMS） cantilever actuators and freestanding nano-actuators are considered as two special cases. It is proved that the proposed method is convenient for the analyses of the effects of the surface, the Casimir force, and the fringing field on the pull-in parameters.展开更多
Three flavonoids have been isolated from the leaves of Glycyrrhiza uralensis Fisch(licorice,Leguminosae).The structures have been identified as 5,7,3',4'-tetrahydroxy-3-methoxy-5'-isoprenyl flavone(I,urale...Three flavonoids have been isolated from the leaves of Glycyrrhiza uralensis Fisch(licorice,Leguminosae).The structures have been identified as 5,7,3',4'-tetrahydroxy-3-methoxy-5'-isoprenyl flavone(I,uralenol-3-methylether),5,6,3',4'-tetrahydroxy-3-methoxy-6'-isoprenyl flavone (Ⅱ, unalene) and quercetin(Ⅲ).Ⅰ and Ⅱ are new compound.展开更多
文摘Stiction in microeiectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films,the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part.
基金supported by the National Natural Science Foundation of China(No.11201308)the Natural Science Foundation of Shanghai(No.14ZR1440800)the Innovation Program of the Shanghai Municipal Education Commission(No.14ZZ161)
文摘The pull-in instability of a cantilever nano-actuator model incorporating the effects of the surface, the fringing field, and the Casimir attraction force is investigated. A new quartic polynomial is proposed as the shape function of the beam during the deflection, satisfying all of the four boundary values. The Gaussian quadrature rule is used to treat the involved integrations, and the design parameters are preserved in the evaluated formulas. The analytic expressions are derived for the tip deflection and pull-in parameters of the cantilever beam. The micro-electromechanical system （MEMS） cantilever actuators and freestanding nano-actuators are considered as two special cases. It is proved that the proposed method is convenient for the analyses of the effects of the surface, the Casimir force, and the fringing field on the pull-in parameters.
文摘Three flavonoids have been isolated from the leaves of Glycyrrhiza uralensis Fisch(licorice,Leguminosae).The structures have been identified as 5,7,3',4'-tetrahydroxy-3-methoxy-5'-isoprenyl flavone(I,uralenol-3-methylether),5,6,3',4'-tetrahydroxy-3-methoxy-6'-isoprenyl flavone (Ⅱ, unalene) and quercetin(Ⅲ).Ⅰ and Ⅱ are new compound.
