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Applications:
Actuated Systems
CSE 495/595: Intro to Micro- and Nano- Embedded Systems
Prof. Darrin Hanna
Ink Jet Printer Head
• Hewlett-Packard, Inc., Palo Alto, California
• Early inkjet heads used electroformed nickel nozzles
• More recent use nozzle plates drilled by laser ablation
• silicon micromachining more expensive
• High resolution printing – micromachined nozzles
• 1,200 dots per inch (dpi)
• spacing between adjacent nozzles is 21 µm
• cheaper using micromachining
Ink Jet Printer Head
• well contains a small volume of ink
• surface tension
• droplet propelled using thin-film resistor made of tantalumaluminum alloy
• locally heats water-based ink to over 250ºC
• within 5 µs, a bubble forms
• peak pressures reach 1.4 MPa
(200 psi)
• expels ink out of the hole
• after 15 µs, the ink droplet is ejected
from the nozzle
• volume on the order of 10-10 liters
Ink Jet Printer Head
• within 24 µs of the firing pulse, the tail of the ink droplet
separates
• bubble collapses inside the nozzle
• results in high cavitation pressure
• within less than 50 µs, the chamber refills
• ink meniscus at the hole settles
Ink Jet Printer Head
Sample Fabrication
• oxidize silicon wafer for thermal and electrical isolation
• sputter 0.1 µm of tantalum-aluminum alloy
• TaAl is resistive, near-zero thermal coefficient of
expansion
• sputter aluminum containing a small amount of copper
• aluminum and TaAl are patterned leaving an Al/TaAl
“sandwich” to form conductive traces.
Ink Jet Printer Head
Sample Fabrication
• remove aluminum from the resistor location leaving TaAl resistors
• resistors and conductive traces are protected by layers of PECVD
silicon nitride and silicon carbide
• SiN -- electrical insulator
• SiC -- electrically conductive at elevated temperatures but more
chemically inert than SiN
Ink Jet Printer Head
Sample Fabrication
• bilayer passivation with appropriate thermal properties and
needed chemical protection reduces pinholes
• SiC/SiN layers are patterned to make openings over the bond
pads
• tantalum sputtering is followed by gold sputtering
• Ta acts as an adhesion layer for the Au
• Au and Ta remain only on the contact pads and resistor
• Au etched off of the resistor
Ink Jet Printer Head
Sample Fabrication
• spin on polyimide and partially cure
• patterned to leave a channel through which ink flows
to the resistor
• fabricate nickel orifice plate separately using electroforming
or laser ablation
• aligned and bonded to silicon structure by the polyimide
Valves
• Applications
• difficult to compete with traditional valves (price and
performance) – more of a niche product
Micromachined Valve from Redwood
Microsystems
• Membrane is heated to either open or close the valve
• Fluorinert perfluorocarbon from 3M
Micromachined Valve from Redwood
Microsystems
• Membrane is heated to either open or close the valve
Micromachined Valve from Redwood
Microsystems
• boiling point ranges from 56° to 250ºC
• large temperature coefficients of expansion (~ 0.13% per degree
Celsius)
• electrically insulating
• control liquid choice determines:
• actuation temperature
• power consumption
• switching times
Micromachined Valve from Redwood
Microsystems
• NO-1500 Fluistor normally open gas valve
• control of the flow rate for noncorrosive gases
• flow rate ranges from 0.1 sccm up to 1,500 sccm
• maximum inlet supply pressure is 690 kPa (100 psig)
• switching time is typically 0.5s
• average power consumption is 500 mW
Micromachined Valve from Redwood
Microsystems
• The NC-1500 Fluistor normally closed gas valve
• similar pressure and flow ratings as NO-1500
• switching response is 1s and it consumes 1.5W
• measures approximately 6 mm × 6 mm × 2 mm
• Fluistor relies on the absolute temperature
• valve cannot operate at elevated ambient temperature
• rated for operation from 0° to 55ºC
Micromachined Valve from Redwood
Microsystems
• fluid flow through an ideal orifice depends on the differential
pressure across it
• volume flow rate
 CD A0 2P / 
ΔP is the difference in pressure
ρ is the density of the fluid
A0 is the orifice area
CD is the discharge coefficient
0.65 for a wide range of orifice
geometries
Micromachined Valve from Redwood
Microsystems
Fabrication
• intermediate silicon layer etched using KOH
• both sides of the wafer
• front-side etch forms the cavity to be filled with liquid
• bottom side forms the fulcrum as well as the valve plug
• timed etch rate of both etches form thin diaphragm
Micromachined Valve from TiNi Alloy
Company
• very different
• actuation mechanism is titanium-nickel (TiNi)
• a shape-memory alloy
• very efficient actuators
• can produce a large volumetric energy density
• approximately five to 10 times higher than other methods
• TiNi processing is not easily integrated in regular MEMS
processing
Micromachined Valve from TiNi Alloy
Company
• three silicon wafers
• one berylliumcopper spring
• maintain a closing force on the valve poppet (plug)
• one wafer incorporates an orifice
• second wafer is a spacer
• third wafer contains the poppet suspended from a spring structure
made of a thin-film titaniumnickel alloy
Micromachined Valve from TiNi Alloy
Company
• sapphire ball
• between a beryllium-copper spring and third wafer
• pushes the poppet out of the plane of the third wafer through the
spacer of the second wafer to close the orifice in the first wafer
• normally closed
Micromachined Valve from TiNi Alloy
Company
• current flow through the titanium-nickel alloy heats the spring above
its transition temperature (~ 100ºC)
• contracts and recover its original undeflected position
• pulls the poppet back from the orifice - opens
Micromachined Valve from TiNi Alloy
Company
Fabrication
• thin-film deposition and anisotropic etching
• form the silicon elements of the valve
• orifice and the spacer wafers is simple
Micromachined Valve from TiNi Alloy
Company
Fabrication
• third wafer containing the poppet and the titanium-nickel spring
• SiO2 is deposited on both sides of the wafer
• back side -- timed anisotropic etch using the SiO2 as a mask
defines a silicon membrane.
• TMAH because of its extreme selectivity to SiO2
Micromachined Valve from TiNi Alloy
Company
Fabrication
• sputter titanium-nickel film, a few micrometers thickness on front
• pattern
• this film determines the transition temperature
• double-sided lithography ensures that the TiNi pattern aligns with the
cavities on the back side
Micromachined Valve from TiNi Alloy
Company
Fabrication
• evaporation and pattern Au
• defines the bond pads and the metal contacts to the TiNi actuator
• wet or plasma etch from the back side to remove thin Si membrane
• frees the poppet
Micromachined Valve from TiNi Alloy
Company
Fabrication
• bond the three wafers together using glass thermo-compression
• Si fusion bonding not practical since TiNi rapidly oxidizes at
temperatures above 300ºC (that would be a bad thing)
• assembling valve elements is manual
• list price for one valve is about $200
Sliding Plate Microvalve
• many micromachined valves use a vertically movable diaphragm or
plug over an orifice
• diaphragm or plug sustains a pressure difference across it
• pressure difference x area = force that must be overcome for the
diaphragm to move
• high pressures and flow rates  large forces for a tiny device

Sliding Plate Microvalve
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low power consumption
fast switching speeds
consumes less than 200 mW
switches on in about 10 ms and off in about 15 ms
maximum gas flow rate & inlet pressure 1,000 sccm and 690 kPa
valve measures 8 mm × 5 mm × 2 mm
Sliding Plate Microvalve
• intended for use in such automotive applications
• braking and air conditioning
• require ability to control liquids or gases at high pressures
• ~2,000 psi (14 MPa)
• wide temperature range
• –40°C to +125°C
Sliding Plate Microvalve
• a plate, or slider, moves horizontally across the vertical flow
from an orifice
• forces due to pressure can be balanced to minimize the force
that must be supplied to the slider
Sliding Plate Microvalve
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once again, three layers of Si
inlet and outlets ports formed in the top and bottom layers
normally open valve
One of the two paths of fluid flow
• past the top orifice between the slider and the top wafer
• through the second layer of Si
• down out of the outlet port formed in the bottom wafer
Sliding Plate Microvalve
• A second path of the two paths of fluid flow
• through the slot in the slider
• under the slider
• through the lower controlling orifice
• out of the outlet port.
Sliding Plate Microvalve
• reduce or turn off the flow
• actuator moves the slider to the right
• reduces the area of the two controlling orifices
• pressure inside the slot = the inlet pressure pin
• horizontal pressure forces on internal surfaces of the
slot are equal and opposite (balanced)
• horizontal pressure forces on external surfaces of the
slot balance each other because the pressure outside the
slot is equal to the outlet pressure pout.
Sliding Plate Microvalve
• pressure forces also balanced vertically
• pressures on the top and bottom surfaces of the slider are
equal to the inlet pressure
• not perfect, but good
• operation is few MPa (hundreds of psi).
Sliding Plate Microvalve
Physical Desc
• actuator is entirely in the middle Si
layer
• a small gap above and below all
moving parts to allow motion
• approximately .5 to 1 µm
• thermal actuator - mechanically
flexible “ribs” suspended in middle and
anchored at edges
• electrically resistive
Sliding Plate Microvalve
Physical Desc
• current flow through ribs heats them
• expand
• centers of ribs push movable pushrod
to the left
• torque about the fixed hinge
• moves slider tip in the opposite
direction.
• after current stops ribs cool down
• mechanical restoring force of the
hinges and ribs returns the slider to its
initial position
Sliding Plate Microvalve
Physical Desc
• depending on the geometry of the
actuator ribs the actuation response
time can vary
• few to hundreds of ms
• depth of recesses above and below
ribs can be increased to lower the heatflow rate
• reduces power consumption
• slows the response when cooling
Sliding Plate Microvalve
Fabrication
• shallow recess cavities are etched in
top and bottom
• KOH etch creates the ports, deep
recess, and through hole for electrical
contacts
• actuator in the middle wafer is etched
using DRIE
• Si fusion bonding to stack wafers
• metal for electrical contacts in
middle wafer
• ports are protected with dicing tape
to keep them clean
Sliding Plate Microvalve
Fabrication
• typical design includes ten or more
rib pairs
• each rib is approximately 100 µm
wide, 2,000 µm long, and 400 µm
thick, and is inclined at an angle of a
few degrees
• water at pressures reaching 1.3 MPa
(190 psig) and flows of 300 ml/min
• does not match automotive
requirements yet 
Micropumps
• must compete with traditional small pumps
• Lee Company of Westbrook, Connecticut, manufactures a
family of pumps
• 51 mm × 12.7 mm × 19 mm (2 in × 0.5 in × 0.75 in)
• weigh only 50g (1.8 oz)
• dispense up to 6 ml/min with a power consumption of
2W from a 12-V dc supply
• micromachined pumps can be readily integrated along with
other fluidic components
• automated miniature system
Micropumps
• four wafers!
• bottom two wafers - two check valves at inlet and outlet
• top two wafers - the electrostatic actuation unit
• voltage applied between the top two wafers actuates the pump
diaphragm
• expands the volume of the inner chamber
• draws liquid through the inlet check valve to fill the
additional chamber volume
Micropumps
• when applied ac voltage goes through 0
• diaphragm relaxes
• pushes the liquid out through the outlet check valve
• flap can each move only in a single direction
• inlet valve flap moves only as liquid enters to fill the pump
inner chamber
• outlet valve is opposite
Micropumps
• So, is this bidirectional or will this only pump fluid in one
direction?
Micropumps
• So, is this bidirectional or will this only pump fluid in one
direction?
!
Micropumps
• as long as pump diaphragm displaces liquid at a frequency
lower than the natural frequencies of the two valve flaps
• at higher actuation frequencies—above the natural frequencies
of the flap—the response of the two flaps lags the actuation drive
Micropumps
• when pump diaphragm draws liquid into the chamber
• inlet flap can’t respond instantaneously
• remains closed for a moment longer
• outlet flap is still open from previous cycle and does not
respond quickly to closing
• the outlet flap is open and the inlet flap is closed
• draws liquid into the chamber through the outlet
• phase difference between the flaps and the actuation must
exceed 180º
Micropumps
• pump rate rises with frequency
• peak flow rate of 800 µl/min at 1 kHz
• at exactly the natural frequency of the flaps (1.6 kHz)
• pump rate rapidly drops to zero
• phase difference is precisely 180º
• both valves are simultaneously open— no flow
• after natural frequency the pump reverses direction
• further increase in frequency reaches a peak backwards flow
rate of –200 µl/min at 2.5 kHz
Micropumps
• at ~10 kHz actuation is much faster than the flaps’ response
• flow rate is zero
• peak actuation voltage is 200V
• power dissipation is less than 1 mW
Micropumps
Fabrication
Microfluidics
• rectangular trenches in a substrate with cap covers on top,
capillaries, and slabs of gel
• cross-sectional dimensions on the order of 10 to 100 µm
• lengths of tens of micrometers to several centimeters
• fluid drive or pumping methods
• applied pressure drop (common)
• capillary pressure (common)
• electrophoresis (common)
• electroosmosis (common)
• electrohydrodynamic force
• magnetohydrodynamic force
Microfluidics
• pressure drive
• apply positive pressure to one end of a flow channel
• negative pressure (vacuum) can be applied to the other end
Microfluidics
• Electrophoretic flow can be induced only in liquids or gels with
ionized particles
• apply voltage across the ends of the channel
• produces an electric field along the channel that drives positive
ions through the liquid toward the negative terminal and the
negative ions to the positive terminal
• velocity of the ions is proportional to the electric field and charge
and inversely related to their size
• in liquids
• velocity is also inversely related to the viscosity
• in gels
• velocity depends on porosity.
Microfluidics
• Electroosmotic flow occurs because channels in glasses and plastics
tend to have a fixed charge on their surfaces
• in glasses silanol (SiOH) groups at walls lose the hydrogen as a
positive ion, leaving the surface with a negative charge
• negative ions attract a layer of + ions forming a double layer
• layer of positive ions not tightly bound
• can move under an applied electric field
• moving ions drag the rest of the channel volume along creating
electroosmotic flow
• velocity at the center of the channel is about the same or slightly
less, giving the fluid a flat velocity profile