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9-32 MEMS: Design and Fabrication

Outlet
Valve
Parylene
diaphragm Nickel
Gap

(a) Paraffin Channel Inlet
Photodefinable glass substrate Heater

Circular Heater Reservoir Inlet
reservoir
hole

(b)
200 µm
Channel
Paraffin Channel
actuator
500 µm

FIGURE 9.30 (See color insert following page 9-22.) (a) Cross-section of paraffin active blocking valve actuator and
(b) optical micrograph of a nickel-plated microvalve from the backside (after Carlen and Mastrangelo (2002)).

Kapton
Metal
Adhesive
Dielectric
Electric
field

Load still applied; V>VPl;
unit cell collapsed
1/2 Cell
Force

V=0; Load applied;
Unit cell fully extended

No applied load or 3-D actuator
voltage

FIGURE 9.31 Biomimetic MEMS actuator (after Horning and Johnson (2002)).

aluminum or gold. The expansion of the paraffin vertically displaces the flexible parylene diaphragm.
Circular microactuators were fabricated with a 200-µmradius and a 9-mm-thick paraffin film. The result-
ing vertical displacement was 2.6mm for a 5-volt, 100-mW heater input. This actuator was fabricated into
an active blocking microvalve by forming a channel and valve seat above the piston using photoresist and
3
electroplated nickel, as shown in Figure 9.30(a) and Figure 9.30(b). Flow rates of 10 10 1 sccm were
obtained, with an 800-Torr pressure differential (from inlet to outlet) for paraffin actuators from 200 to
800µm in diameter, and power consumption levels in the range of 50–150mW. Leak rates as low as
5 10 4 sccm were obtained for the smallest devices. Additional structures such as a mass flow control
valve, an inline microvalve, microfluidic pumps, and a polymerase chain reactor device were also fabri-
cated, showing that paraffin microactuators can be quite readily fabricated into a variety of structures.

© 2006 by Taylor & Francis Group, LLC