surface micromachining
TRANSCRIPT
![Page 1: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/1.jpg)
SURFACE MICROMACHINING
NIKITA JAVIA
GURUNATH APTE
![Page 2: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/2.jpg)
What is micromachining?
• Micromachining is used to fabricate three-dimensional
microstructures and it is the foundation of a technology called
Micro-Electro-Mechanical-Systems (MEMS).
• Micromachining is the basic technology for fabrication of micro-
components of size in the range of 1 to 500 micrometers.
• Their need arises from miniaturization of various devices in
science and engineering, calling for ultra-precision manufacturing
and micro-fabrication.
• Bulk micromachining and surface micromachining are two major
categories in this field.
![Page 3: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/3.jpg)
Surface micromachining
• Surface micromachining builds microstructures by deposition and
etching of different structural layers on top of the substrate.
• Generally polysilicon is commonly used as one of the layers and
silicon dioxide is used as a sacrificial layer which is removed or
etched out to create the necessary void in the thickness direction.
• Added layers are generally very thin with their size varying from 2-5
Micro metres.
• The size of the substrates can also be much larger than a silicon wafer,
and surface micromachining is used to produce TFTs on large area
glass substrates for flat panel displays.
![Page 4: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/4.jpg)
![Page 5: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/5.jpg)
Advantages• The main advantage of this machining process is the
possibility of realizing monolithic microsystems in which the
electronic and the mechanical components(functions) are built
in on the same substrate.
• The surface micromachined components are smaller in
thickness and mass.
• The expensive silicon wafers can be replaced by cheaper
substrates, such as glass or plastic.
• It is cost effective.
![Page 6: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/6.jpg)
Disadvantages
• Multiple deposition and etching required to build up
structures.
• Vertical dimensions are limited to the thickness of the
deposited layers leading to compliant suspended structures
with tendency to stick support
• Cleanliness is critical at end of process.
• Sawing, packing and testing is difficult.
![Page 7: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/7.jpg)
APPLICATIONS
• Used in manufacturing of flat panel television screen
• Used in production of thin solar cells
• Used in making bimetal cantilever used for monitoring
mercury vapour, moisture, protein conformational changes in
antigen antibody binding
![Page 8: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/8.jpg)
ExamplesSurface Micromachining can be seen in action in the following
MEMS products:
• Surface Micromachined Accelerometers.
• 3D Flexible Multichannel Neural Probe Array.
• Nanoelectromechanical relays
![Page 9: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/9.jpg)
Fabrication Process• Micromachining starts with a silicon wafer or other substrate
and grows layers on top.
• These layers are selectively etched by photolithography and
either a wet etch involving an acid or a dry etch involving an
ionized gas, or plasma.
• Dry etching can combine chemical etching with physical
etching, or ion bombardment of the material.
• Surface micromachining can involve as many layers as is
needed with a different mask on each layer.
• Surface micromachining uses developed technology which is
very repeatable for volume production.
![Page 10: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/10.jpg)
STUCTURAL LAYER• The layer of thin film material with which the microstructures are made of.
• Has physical and chemical properties that are suitable for the desired
application
• Mechanical properties such as high yield and fracture stresses, minimal
creep and fatigue, and good wear resistance
• Polysilicon is usually used as a structural material.
Disadvantages of poly Si (over single crystal Si)
• Lower yield strength
• Lower piezo resistivity
• Stiction.
![Page 11: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/11.jpg)
Sacrificial Layer
• The layer of material used during the fabrication process to
deposit microstructures.
• These are removed towards the end of the fabrication. So, the
layer has no role in the operation of the device.
• Good mechanical properties so that device does not fail while
fabrication
• Good adhesion
• Low residual stresses
![Page 12: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/12.jpg)
Basic Sacrificial Layer Processing
![Page 13: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/13.jpg)
Example: Scanning Probe
Microscopy
• Problems with existing processes
o Etching of positive pyramids
• Difficult tot control etch stop point
• uniformity difficult to obtain
o Bulk etching
• Long etching time involved to etch through
the wafer
![Page 14: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/14.jpg)
A hybrid method to fabricate SPM probes
![Page 15: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/15.jpg)
![Page 16: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/16.jpg)
![Page 17: Surface micromachining](https://reader038.vdocument.in/reader038/viewer/2022102614/55a6cac61a28ab581d8b489f/html5/thumbnails/17.jpg)
THANK YOU