L1 - Overview and Scaling Flashcards
(42 cards)
What does MEMS stand for?
Micro Electro Mechanical Systems
What is the differnce between Micromechanics and MEMS?
Micromechanics are purely mechanical components. In MEMS they are implimented with some form of control electronics or electrical connection.
Define Microsystem
Silicon chips with non-conventional, non-mechanical functions and multichip systems
Define Nanosystems
Systems where nanoscale devices are intergrated (biological or molecular functionality)
What does NEMS stand for?
Nano Electro Mechanical Systems
How can Micromechanical sensors improve a devices redundancy?
Building 100 sensors on a chip might take the same fabrication as building just 1. So a lot of ‘spare’ or redundant devices can be made at little to no extra cost.
Why is Silicon such a common MEMS material?
- Silicon semiconductor fabrication techniques and equipment can be utilised
- Semiconductor technology is optimised for mass production
- Allows for transducers on the same substrate as electrical circuitry. Saving space,reducing contacts and reducing noise.
- Silicon is mechanically robust
- Silicon is cheaply and readily available (because of its use in semiconductors)
Outline the steps involved in Bulk Micromachining
- Lay a photoresist over a silicon substrate
- Lay a mask over the photoresist
- Develop the photoresist
- Dissolve the undeveloped areas *
- so the areas covered by the mask will be etched
The sides of the etched area (usually) will not be vertical
outline the steps involved in Surface Micromachining
- Lay a sacrificial PSG layer over the silicon substrate
- Etch the PSG layer (in the Bulk Micromachining fashion)
- Lay a Polysilicon layer using vapor deposition
- Completely desolve the remaining PSG layer
the more common method today
Consider elements with a linear dimension L
As L varies state the scale with which the surface area will vary.
Surface Area scales at L^2
Consider elements with a linear dimension L
As L varies state the scale with which the volume will vary.
Volume scales at L^3
Consider elements with a linear dimension L
As L varies state the scale with which the mass will vary.
Mass scales at L^3
As density remains constant Mass will scale with Volume
Consider elements with a linear dimension L
As L varies state the scale with which the earths gravitation force will vary.
Force due to gravity scales at L^3
Fg = mg gravity is constant, F scales with mass which scales with volume
Consider elements with a linear dimension L
As L varies state the scale with which the pressure exerted by the element on the ground will vary.
Pressure due to gravity scales at L
Pressure = Force(Gravity) / SurfaceArea
L^3 / L^2
Consider elements with a linear dimension L
As L varies state the scale with which the earths gravitation force will vary.
Force due to gravity scales at L^3
Fg = mg gravity is constant, F scales with mass which scales with volume
Often in the Macro and Nano world gravitation is negligable.
Consider elements with a linear dimension L
As L varies state the scale with which the Van der Waal’s force will vary.
Force due to Van der Waal’s will scale at L^2
van der Walls is proportional to surface area
How does the relation between van der Wall’s force and gravity change due to scaling?
What effect will this cause?
Fg scales at L^3
Fvdw scales at L^2
Therefore their relation scales at L^-1
Fg will reduce faster at small scale, Fvdw willl dominate.
This can cause adheision between parts.
Consider elements with a linear dimension L
As L varies state the scale with which Friction force will vary.
Friction force will scale at L^3
Ffr = u.Fgr = u.mg The friction and gravitation coefficients wont change so F is proportional to mass
Consider elements with a linear dimension L
As L varies state the scale with which the spring Force will vary.
Fspring will scale at L
Fspring = -k.dL k is constant and dL (spring elongation) will scale with L
Consider elements with a linear dimension L
As L varies state the scale with which the Spring Oscillation frequency will vary.
Spring oscillation frequency will scale at L^-3/2
Consider elements with a linear dimension L
As L varies state the scale with which Reynolds Number will vary
Re varies with L²
Re = velosity∘length / viscosity
velocity ∝ L
length ∝ L
Consider elements with a linear dimension L
As L varies state the scale with which Diffusion Time will vary
τ ∼ L²
Diffusion time = Length²/αD
α is a geometrical constant
D is the diffusion constant
Consider elements with a linear dimension L
As L varies state the scale with which Thermal Conductance will vary.
Pdiss ~ ∝ L²
Power dissipation due to conductance is proportional to area.
Consider elements with a linear dimension L
As L varies state the scale with which Time to cool will vary.
τ ∝ L²
Time to homogonise temperature
