MEMS overviewMicron level mechanical parts
Made from transistor materials and metals
Van Der Waals forces Intermolecular bonding Plays an important part in design
Fabrication TechniquesMask Lithography Injection moldingMicrostereolithographySilicon Surface MicromachiningSilicon Bulk Micromachining
Mask LithographyUse of photo resist
Positive Dissolves under light
Negative Hardens under light
Both get covered with desired material, then photo resist is dissolved by a solvent
Multiple layers – Multiple steps
Injection Molding
Starts with mask lithographyMetal poured over resistResist gets dissolvedMetal form is left for plastic injection
molding
Microstereolithography
Similar principal to mask lithography, but for 3D pieces Uses an “active mask”
Not a physical mask Utilizes a photo-reactive acrylic resin Each layer image projected through a DMD(digital mirror
device) Projected into the resin
Uses lenses Resin that is illuminated, Cross-links and hardens Piece is then covered in a hardened layer
Microstereolithography
Dimensional capabilitiesLateral and Vertical resolution: 10μm Maximum field size: 10.24mm x
7.68mm Structural height: up to 5mm
Silicon Surface Micromachining Uses the same process as IC fabrication Needs multiple layers to create structures Cheapest form of Micromachining Similar to lithography
Sacrificial material Structural material
When sacrificial material is removed, only whole structures are left
Silicon Bulk Micromachining
Done with Crystalline silicon Constructed using etch stop planes Chemical process Anisotropic Etching
Speed dependent – Directional etch in different crystallographic directions at
different rates Slower directions create and etch stop plane
References http://home.earthlink.net/~trimmerw/mems/tour.html http://home.earthlink.net/~trimmerw/mems/BM_bulk.h
tml http://www.samcointl.com/apps/mems.html http://www.cmf.rl.ac.uk/latest/msl.html http://www.chemguide.co.uk/atoms/bonding/vdw.html “Micromachining for Optical and Optoelectronic
Systems”. MING C. WU