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Published byDerrick Carroll Modified over 8 years ago
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Micro Electro Mechanical Systems (MEMS) Device Fabrication
What is a MEM? How are they used? How are they made? What are the challenges encountered during fabrication? EE4611 04/13/2016 David Niska
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Preview MEM applications Fabrication Techniques MEM design challenges
Lithography Sacrificial layers Micromachining Surface Bulk HAR Material deposition MEM design challenges MEM industry challenges
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What is a MEM? Applications Sensors Actuators Sensor Animation
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What’s so special about that??
Grain of pollen
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Device Fabrication Basics
Substrate (Si Wafer) Photoresist applied Photoresist masked and exposed Photoresist removal Further processing Materials etched/dissolved And/or Material deposition Rinse/Repeat
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Keystone Bridge Sacrificial Layers
Sacrificial Layers
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Material Removal (Micromachining)
Surface micromachining Bulk micromachining High Aspect Ratio (HAR) Micromachining
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Material Deposition Spin-on deposition Thermal oxidation
No chemical reactions occur Similar to frost on a window Poly Silicon, Silicon Nitride, Silicon Dioxide, metals Photoresist, glass Spin-on deposition Thermal oxidation Chemical vapor deposition Physical vapor deposition Electroplating
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Surface micromachining - planar - 2.5-d
Advantages: Use existing MOS equipment Batch Fabrication Integration with logic components Silicon has good mechanical properties Photoresist Selective etching SiO2 Sacrificial layers Insulators Poly crystalline Si Structural Layers
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Bulk micromachining Isotropic etching Anisotropic etching
Long etching processes Silicon Nitride used to mask Wet etching Isotropic Anisotropic Isotropic etching Anisotropic etching
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HAR (high aspect ratio) Micromachining
LIGA Deep Reactive Ion Etching (DRIE) “Bosch” process High etching rate Alternate between etching cycles and passivation cycles Ions “bombard” the bottom, and not the sides Both processes use electroplating to build up the final component
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Other Types of Micromachining
Xenon Difluoride dry phase etching Electro-Discharge micromachining Laser micromachining Focused Ion Beam micromachining
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Design Issues/mitigation Examples
Stiction Planarization Imaging Interference parts
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Current Industry Challenges
Cost Standardization between manufacturers to ensure compatibility Also important for packaging Integration with electronics “system on a chip”
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WORKS CITED Alexandre Reis, Raj Bhattacharya Deep Reactive Ion Etching (DRIE): “A (not so) short Introduction to Micro Electromechanical Systems”, F. Chollet, HB. Liu, version 5.2, 2015: “MEMS devices for biomedical applications”, Dr. Ramesh Ramadoss, 2013: PQE06AbWd&nohtml5=False
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5 Key Points Two main applications for mems are sensors and actuators.
Isotropic etching attacks a material in all directions, anisotropic etching attacks at different rates in different directions depending on the material’s properties. The three main fabrication techniques are surface micromachining, bulk micromachining, and HAR micromachining. In bulk micromachining, the etching process attacks along the crystalline planes, making orientation of the Si substrate very important. MEMs fabrication differs from MOSFET fabrication mainly by the use of sacrificial layers.
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