Lecture 22 Mechanical Microsystems

Lecture 22 Mechanical Microsystems - Mechanical Actuators...

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Mechanical MEMS Dr. Bruce K. Gale Fundamentals of Micromachining Mechanical Actuators Actuation mechanisms: electrostatic = electrostatic attraction of charged plates thermal = expansion of solids or fluids shape memory alloy = considerable change in length pneumatic/hydraulic = fluid pressure piezoelectric = electrically induced strain – magnetic – chemical – biological Electrostatic Actuators Based on attraction of two oppositely charged plates Typically low power Simple to fabricate Coulomb’s law: 2 2 1 4 1 x q q F o r elec ε πε = Electrostatic Actuation Cantilever Actuators electrostatic force tip deflection 2 ) ( 2 ) ( = x d d V x q o ε dx x wq x L EI x d T ) ( ) 3 ( 6 ) ( 2 = δ + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ _
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Electrostatic Actuation Fabrication polysilicon with sacrificial oxide electroplated metal with sacrificial organic layer sputtered metal with sacrificial organic layer Torsional Actuators dual deflection electrodes small deflection Torsional spring for mirror application Electrostatic Actuation Comb Drives use large number of electrostatically actuated fine “fingers” attractive force is mainly due to fringing fields generate large movements Electrostatic Actuation Rotary Micromotors use freely moving central rotor with surrounding capacitive plates up to 300,000 rpm up to 300 V – Fabrication: • polysilicon/oxide • metal/resist Electrostatic Actuation
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