Utkan Demirci: Orals Abstract for Tuesday 30th Nov.

Utkan Demirci utkan at stanford.edu
Mon Nov 29 17:26:51 PST 2004


Utkan Demirci, Department of Electrical Engineering

E.L. Ginzton Lab. AP#200
30th November 2004 at 3pm


There is growing demand in the fields of semiconductor manufacturing and
biotechnology to reliably generate repeatable, uniform, picoliter-size
fluid droplets. Such droplets can be generated using MEMS
(Micro-Electro-Mechanical Systems) technology. We propose 2-D micromachined
microdroplet ejector arrays for environmentally benign deposition of
photoresist and other spin-on materials, such as low-k and high-k
dielectrics used in integrated circuit (IC) manufacturing. Direct
deposition of these chemicals will reduce waste and production cost. These
ejectors are chemically compatible with the materials used in IC
manufacturing, and do not harm fluids that are heat or pressure sensitive.
Moreover, these ejectors are attractive to biomedicine and biotechnology
for droplet generation in applications such as printing of DNA or protein
assays and drug testing.

Two novel methods for generating millions of droplets per second using
acoustically actuated 2-D micromachined microdroplet ejector arrays will be
presented. First, membrane based 2-D micromachined ejector arrays will be
introduced. Each element of a membrane based 2-D ejector array consists of
a flexurally vibrating circular membrane on one face of a cylindrical fluid
reservoir. The membrane has an orifice at the center. A piezoelectric
transducer generating ultrasonic waves, located at the open face of the
reservoir, actuates the membrane and droplets are ejected through the
membrane orifice. The ejectors operated most efficiently at 1.2 MHz and
generated 3-7 µm diameter droplets. Second, acoustic focus based 2-D
micromachined ejector arrays will be demonstrated. The radiation pressure
associated with the acoustic beam overcomes the surface tension force, and
releases droplets into air in every actuation cycle. The ejectors operated
most efficiently at 34.7 MHz, and generated 28 µm diameter droplets in both
drop-on-demand and continuous modes of operation, as predicted by the finite
element analysis. Photoresist, water, isopropanol, ethyl alcohol, and
acetone were ejected from a 4x4 2-D micromachined ejector array. Silicon
wafer surfaces were covered by photoresist using these ejector arrays. The
theory of operation, fabrication and the experimental results obtained with
novel acoustically actuated 2-D micromachined microdroplet ejector arrays
will be presented.
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