Micro and nano Flashcards
Name the different categories of Micro System Devices.
Microsensor
– Measures physical factors such as pressure, velocity and temperature
Microactuator
– Applies forces or creates positional changes
Microstructure/microcomponent
– Inactive part of system – needs to be used in combination with
actuator or sensor (e.g. gear, nozzle)
Microsystem/micro instrument
– Assembly of components into a system or instrument
MEMS – micro electromechanical machines
Outline how micro system devices are used in industry.
Automotive Industry:
- Air-bag Sensor
- Engine Management
- Anti-lock brake control
- Accelerometer position sensor
- Stereo
- Tyre Pressure Sensor
Medical Industry:
- Intelligent implants such as pacemakers and defibrillators
- Low invasive patient monitoring
Electronics:
-Integrated circuits with semiconductors
What are the four main micro-fabrication methods?
Machining
Lithography
LIGA Process
Film Deposition
Outline the different methods of micro-fabrication machining.
Silicone layer processing:
- Bulk micro-machining creates thin membranes by wet etching of silicone wafer.
- Surface micro-machining creates structures such as overhangs and cantilevers using a shallow layering process.
Photo-chemical machining:
- Electro-plating
- Electro-forming
- Electro-less Plating
Laser and electron beam machining:
-Produces small diameter holes in materials which are difficult to conventionally machine. (10-100um)
Ultrasonic machining:
-50um diameter holes in hard/brittle metals
Wire EDM:
-Wire electric discharge cutting
Outline Lithography. What are the different types of Lithography? Which are most commonly used?
It is a printing process where geometric patterns are transferred to a substrate surface.
Simple Lithography used in the printing industry whereas more advanced techniques are used for manufacturing processes.
X-ray and Photo are most commonly used
Photo/UV Lithography
X-Ray Lithography
Soft Lithography
- Micro-imprint
- Micro-contact
- micro-transfer
Outline the process for Photolithography.
Clean Materials
Coat with photo-resist: -Using a spin-coating method. -A photoresist consists of 3 parts: • Radiation sensitive polymer • Sensitizer to control polymer reaction • Solvent – delivers polymer in liquid form
Pre bake at 100 degrees Celsius:
-removes the solvent from the photoresist
and allows it to harden
-thickness of photoresist usually decreases during this
phase
Registration alignment of wafer with masks:
Uses a reticle (photomask/mask)
– Glass/quartz plate with chromium film deposited pattern
– Wafer must be perfectly aligned with reticle
Exposure and Development:
-Positive masking uses radiation to break chains in the
photoresist so that developer solution only dissolves
these regions
-Negative masking allows the photoresist to polymerise
and insoluble to the developer solution
Post baking:
-Used to harden and stabilise remaining photo-resist,
and drives off remaining solvent/developing solution
-Underlying film then either etched or implanted
Stripping:
-Final stage to remove processed photo-resist
-Wet stripping – photo-resist dissolved in solvents such as
acetone
-Dry stripping – plasma etching with oxygen
Which methods of lithography may be preferred to photo-lithography and why?
The resolution of UV or photolithography is limited
by the wavelength of the radiation source
X-ray, electron beam and ion-beam lithography are
all able to give higher resolution that UV lithography
– X-ray has shorter wavelength and able to have higher
aspect ratio compared with UV, but can be more costly
– e-beam and i-beam lithography use a process called
direct writing, and the resolution is limited by electron
scatter
Outline the different soft lithography processes
Microcontact printing
– Stamp coated with ‘ink’ to give one molecule thick layer on opposing surface, which acts as a mask for selective etching
Microtransfer moulding
– Recesses in the stamp are filled with polymer precursor and pushed against opposing surface. Once cured, stamp peeled off to leave pattern for further processing
Outline LIGA Microfabrication, including the process.
Combination of lithography, electrodeposition
and moulding
May have X-Ray, UV or Silicon- LIGA
• Thick resist layer (usually PMMA) deposited onto substrate
• Resist exposed to high energy X-ray radiation and
developed
• Electrodeposition of metal (often Nickel) onto primary substrate
• Remaining resist material (PMMA) removed to yield
3D metallic structure
• Metallic structure used for plastic injection moulding
What are the different film deposition methods?
Evaporation
Sputtering
Chemical-vapour deposition
Low pressure chemical-vapour deposition
Plasma-enhanced chemical-vapour deposition
What are the applications of Nanotechnology?
Medical Technology:
- Drug delivery
- Minimally invasive surgery
- Diagnosis
Electronics:
- Reducing the size of circuits
- Use of nano-wires to enable flexible display screens
Food Industry:
- Nano-films for food packaging
- Nano-sensors to detect contamination and bacteria
Energy Industry:
- Fuel Cells
- Solar Cells
- Battery technology
Space Travel
What are the different Nano-fabrication Processes?
Top-down Processing:
-Lithography methods
Bottom up Processing:
- Nano-tube production
- Scanning probe techniques
- Self assembly
Outline Top down Nano-fabrication
Starts with ‘big’ building blocks
Generally uses subtractive methods to create
geometry
Lithography is most common process
– Extreme UV lithography
– Nano-lithography
• Uses atomic force microscopy (AFM)
• Different probes/cantilevers used in contact with material to create grooves
• Tipped cantilevers ploughed through surface of material
– Dip Pen Nanolithography
•Uses AFM to deposit molecular ink onto a substrate
• Produces lines approx 10nm width
• As a ‘top-down application it delivers material to create masks for lithography process
What are the additive process methods for Nano-fabrication
•Deposition methods
– Physical vapour deposition
– Chemical vapour deposition
•Ion implantation
– Used in conjunction with lithography and associated with multi-level structures
Outline Bottom-up Nanofabrication
•Small starting materials (atoms, ions)
•Processed to bring together to form larger nanoscale structures
– Production of nanotubes
– Self-assembly
– DPN lithography – as a ‘direct-write’ method
