Nanotechnology, micro and nano fabrication - Hickman
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Who was the first one to describe the possibilities of nanotechnology?
Physicist Richard Feynman - December 29, 1959.
What is nanoscience?
An emerging area of science which studies materials that have very small dimensions.
Scientists of chemistry, biology and physics are studying very small things in order to better understand our world. Nanoscience is the study of objects which are anywhere from hundreds to tens of nanometers in size.
As objects shrink, the ratio of surface area to volume (increases/decreases), rendering surface forces (more/less) important.
Increases making surface forces more important.
If a system is reduced _______ in size, the change in length, area and volume ratios alter the reative influence of all various physical effects that determine the overall operation.
Scalled down with all dimenions of the system decreased uniformly.
In scaling, equal reduction of ______ and volume is not normally achievable.
What are some volume related physical quantities?
Mass, heat capacity
What are some surface related physical quantities?
Pressure, buoyand force, heat flux
The surface to volume ratio (S/V) is (larger/smaller) for an elephant compared to a bug.
The surface to volume ratio of an elephant is smaller than a bug.
(T/F) Heat loss is surface dependent.
True. Think flux (J/m^2)
What happens as the surface to volume ratio increases?
As objects shrink isomorphically, surface to volume ratio increases.
Surface forces have larger importance/role such as heat loss. Time constants for actions decrease.
(T/F) As the size of the object of interest decreases, the time constant for actions also decreases.
What are macro-nano equivalents of structural elements?
Metals, plastic polymers
What are macro-nano equivalents of power systems?
Eletric motors, pneumatic actuators, smart materials, batteries
ATPase, VPL Motor, DNA
What are macro-nano equivalents of compliance devices (elastic/absorption)?
- Beta-pleated sheets
What are macro-nano equivalents of transmission elements?
Gears, Belts, Chains etc
VPL Platforms, DNA double crossover molecules
(T/F) Some types of viruses employ molecular motors to inject their DNA into target cells.
True. It spins to line up and funnel DNA.
What does MEMS stand for?
Micro-electro-mechanical-systems. Does not have to be electrical and/or mechanical in broad terms.
What is made in MEMS?
microfabricated micron-sized sensors and actuators.
Miniaturized sensors, actuators, and subsystems fabricated by the use of lithography and/or other precision techniques.
This would include MOEMS, BioMEMS, RF-MEMS, m-TAS, Lab-on-a-chip
What is MEMS?
- A portfolio of techniques and processes to design and create miniature systems.
- A physical product dedicated for a certain final application
- A way of making things: Functions of sensing and actuation with computation and communication to locally control physical paramters at the microscale, yet cause effects at much larger scales.
What are four examples of MEMS and their applications?
Accelerometer, gyroscope, blood pressure sensors, digital mirror displays
What is Moore's law?
The number of transisors on a microprocessor would double approximately every 18 months.
What are some examples of materials for MEMS substrates?
- Semiconductor: Si, Ge, GaAs, GaP
- Insulator: glass, quartz, polymers
What are some examples of materials for MEMS additive materials?
- Structural: Polysilicon
- Electrical: Conductors and insulators
- Functional: Active materials
What is the most common material used for electronics and for MEMS?
- 1) Slicing
- 2) Lapping and etching
- 3) thickness sorting and flatness measurement
- 4) Chemical mechanical polishing
- 5) Quality inspection (electrical, dimensional)
What are four MEMS basic processes?
- Deposition processes (physical deposition; chemical deposition)
- Patterning (Lithography, Diamond Patterning)
- Etching processes (Wet Etching, Dry Etching)
- Micromachining (Bulk micromachining, surface micromachining)
What are two deposition processes for MEMS?
Physical and chemical deposition result in growth in the z-direction.
Chemical deposition includes Chemical Vapor Deposition (CVD) and chemical reactions exploit the chemical reactions for creation of solid materials.
Physical deposition includes Physical Vapor Deposition (PVD) which includes materials physically being deposited onto the structure such as vaporized materials.
What are two patterning methods for MEMS?
Lithography and Diamond Patterning. Restrictions in x-y plane.
Lithography in MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs.
What are two etching process for etching?
Wet and Dry etching.
- Wet etching the material is dissolved when immersed in a chemical solution.
- Dry etching the material is sputtered or dissolved using reactive ions or a vapor phase etchant
What are two fabrication methods in MEMS?
Bulk machining - Structures are made of single crystal silicon, typically by wet or dry etching (subtractive process)
Surface micromachining - Structures are made of deposited or grown layers on top of the substrate, by thin-film deposition. (Additive process)
What is lithography?
- Photolithyography = "light" + "stone" + "writing"
- Pattern definition process in micromachining
- Generation and transfer of patterns by the use of exposing radiation through a mask or without a mask
- Visible light, UV, x-ray, E-beam, ion beam
- Optical lithography; photolithography - formation of image with visible or ultraviolet radiation in a photoresist using contact, proximity, or projection printing.
What is the resolution of Uv light?
What is the resolution of EUV (extreme ultraviolet)
What is the resolution of x-ray?
What is the resolution of E-beam?
What is X-ray lithography?
- Small wavelength, diffraction effects may be eliminated. 1nm
- Opaque areas on the mask cast shadows onto the wafter below
- Electron impact source, plasma heated source and synchrotron used
- Mask is dfficult to make and expensive: SiC, Si3N4, Al2O3 and Si with Gold are commonly used
- Good contrast but poor sensitivity of PR
- Limited PR: PMMA
What does LIGA stand for?
- Lithographie (lithography)
- Galvanik (electroplating)
- Abformung (molding)
Used for lithography, usually x-ray from synchrotron is used
- Create 3D structure as thick as bulk
- micromachined devices while retaining the same degree of design freedom as surface micromachining
What items have been made via LIGA in the past?
- Gear wheels for a dentist's drill bit or Swiss watches
- Lenses and mirrors for micro-sprectrometers
What is EBL?
Electron beam lithography.
- Higher resolution than optical lithography because of small wavelength of 10-50 keV electrons
- Resolution not limited by diffraction but by electron scattering
- Throughput is much less than optical lithography because of serial pattern generation
- Widely used for mask making - not actual device fabrication.
What method is typically used for mask making but not actual device fabrication?
EBL - electron beam lithography because of the lower throughput
What is ion-beam lithography?
- Ions are used as the beam rather than electrons in EBL.
- Higher resolution because of less scattering - electrons can scatter within material upon impact
- Need high energy
- Electrostatic lens has higher aberrations; small aperture and small scan field used
- low throughput
What is SPL?
Scanning Probe Lithography
- Atomic scale writing process based on scanning tunneling microscope (STM)
- A typical STM has sub-angstrom vertical resolution and sub-nano lateral resolution
- + use of low electron energy (<100eV) compared to EBL (10-100keV)
- - Low throughput
What is DPN?
Dip pen nanolithography
- Use of AFM tip as a "nib", a solid-state substrate (au) as "paper" and molecules with a chemical affinity for the solid-state substrate as "ink"
- Molecules are transported via capillary action (water meniscus) from the AFM tip to the solid substrate then self-assembled.
"ink"s include thiol groups
What lithography does not use a radiation source?
What is soft lithography?
- Transfer of ink from a relief structure to a target surface.
- Fabricate chemical patterns with micronscale resolution on surfaces
- demonstrated with molecular monolayer of the thiol molecules on gold surface
- Versatile technology showing high potential for MEMS
- Deformation and distortion of master mold
What is 2-d replication - printing?
- Relief printing
- Movable type metal printing press
- Gutenberg metal pytopgraphy
- Intaglie printing
- lithographic and xerographic printing
- screen or stencil printing
- ink jet printing
What is NIL?
Nano imprint lithography
A technique to generate nano-structures in hard polymers by pressing a rigid master into a thin thermoplastic polymer film that is heated to the glass transition temperature.
What is the glass transition temperature?
The temperature which hard/brittle materials such as polymers transition to a rubber like material for deformation.
NIL uses this for the imprints
What are the steps for NIL?
- 1) Press in mold.
- 2) Heat up mold and substrate
- 3) Mold separation after cooling
- 4) O2 RIE
What is the Affymetrix GeneChip Probe?
- 1) Hydroxylated quartz substrate
- 2) Silane treatment -> convalent link terminated with photoactive molecules
- 3) Photolithography generates deprotected link
- 4) Nucleotide coupling
What is the cantilever process flow for manufacturing?
- 1) thin film deposition
- 500 nm of low stres nitride
- 1 um of oxide
- 2) patterning and RIE of nitride
- Contact photolith + 15 min RIE
- 3) HF undercut of nitride
- (49% for 20 min)
- 4) KOH (25% for 20 min)
- Immediately following the HF H2O rinse
5) crital point drying
What is isotropic vs directional vs vertical etching?
- Isotropic - no preference
- Directional - crystal planes
- Vertical - anisotropic
(T/F) Nanoparticles can detect E. coli in food.
Silica particles (60 nm) with a fluorescent dye are coated with a enzyme specific to O157:H7 E. coli strain
A single bacterium can be detected in 20 minutes
(T/F) Nanotubes, depending on their structure can be metals or semiconductors.
What properties of nanotubes make them attractive?
- Extremely strong materials
- Good thermal conductivity
- Metals or semiconductors
Possible use for nano-electronic and nano-mechanical devices (ie nano-wires of field-effect transistors)
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