1. Applications: Actuated Systems
CSE 495/595: Intro to Micro- and Nano- Embedded Systems
Prof. Darrin Hanna

2. 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

3. Ink Jet Printer Head
well contains a small volume of ink
surface tension
droplet propelled using thin-film resistor made of tantalum-aluminum 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 liters

4. 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

5. 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.

6. 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

7. 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

8. 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

9. Valves
Applications
difficult to compete with traditional valves (price and performance) – more of a niche product

10. Micromachined Valve from Redwood Microsystems
Membrane is heated to either open or close the valve
Fluorinert perfluorocarbon from 3M

11. Micromachined Valve from Redwood Microsystems
Membrane is heated to either open or close the valve

12. 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

13. 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

14. 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

15. Micromachined Valve from Redwood Microsystems
fluid flow through an ideal orifice depends on the differential pressure across it
volume flow rate
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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26.  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 

27. Sliding Plate Microvalve
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

28. 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

29. 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

30. Sliding Plate Microvalve
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

31. 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.

32. 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.

33. 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).

34. 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

35. 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

36. 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 heat-flow rate
reduces power consumption
slows the response when cooling

37. 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

38. 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 

39. 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

40. 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

41. 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

42. Micropumps
So, is this bidirectional or will this only pump fluid in one direction?

43. Micropumps
So, is this bidirectional or will this only pump fluid in one direction? !

44. 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

45. 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

46. 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

47. 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

48. Micropumps
Fabrication

49. 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

50. Microfluidics
pressure drive
apply positive pressure to one end of a flow channel
negative pressure (vacuum) can be applied to the other end

51. 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.

52. 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