Microprotein 30Month meeting Brno Partner TUV

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Microprotein 30Month meeting BrnoPartner TUV

• TUV - Team
• S. Kvasnica (PECVD technology, characterization)
• J. Schalko (Technology infrastructure)
• M. Rakohl (Technician)
• F. Kohl (Characterization)
• A. Jachimowicz (Thin-film technology)

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Outline

• Introduction
• Experimental results
• Conclusions
• Future Work

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Electrowetting basics
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Film properties

• extremely thin insulating films top of metal pads
  (V2 ? d)
• extremely high dielectric strength (E2 ? 1/d)
• high permittivity (V2 ? 1/?r)
• hydrophobic surface (only enhancement of wetting
  is possible)
• sustainable actuation demands for
• tight structure (no ion migration/trapping)
• adressable microspotting on an array needs
• reproducible cycling behaviour (stable surfaces)
• potential for miniaturization

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Electrowetting transport experiments
Technology Silicon, Metal electrodes (Au/Ti) 2
µm Teflon AF (6)
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User interface for host controlled operation
Zero mean potential of wafer droplet
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Electrowetting transport Gap size dependence
Sawtooth pattern 40µm pitch, 72 µm height
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Electrowetting transport Dependence on
excitation voltage
Excitation pattern shifted along the electrode
chain according to the actual droplet movement.
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Observations

• At low actuation potentials (40V)
• Very slow, creeping motion
• Droplet overcomes only gaps lt18µm

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Observations

• At 60V actuation potential
• More agile movement
• Speed decreases with gap width
• Up to 28µm gaps passed
• Droplet shape develops a tail

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Observations

• At 80V actuation potential
• Gaps of 58 µm are easily passed by
• Droplet tail turns out to be caused by a dust
  particle
• Adsorption of particles is promoted by the
  excitation voltage
• Adsorbed particles effectively hinder the droplet
  transport

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Conclusions

• High actuation potentials are needed to enable
  droplet transport by electrowetting
• High actuation potentials promote (dust)
  adsorption at the electrodes
• Adsorbed particles resemble a severe obstacle for
  droplet transport
• Any additional solid surface in contact with the
  droplet will hinder the droplet transport if not
  actuated.

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Discontinuous surfaces may prevent low actuation
voltages especially within closed arrangements
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Future work
Possible solutions

• New low surface energy FC coating materials
• Cytop,
• OPTOOL-DSX,
• Fluorothane
• enabling thinner coatings, lower actuation
  potentials, ....
• Droplet transport
• driven by external pressure difference
• controlled through capillary pressure modulation
• (by the electrowetting effect)

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Future Work

• Microfluidic fine spotting Adaptation of the
  Proposed concept

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Modified spotting arrangement
Pressure
Electrowetting Actuation

Capillary
-
Biomolecule
Solution
FC Layer
Si-Wafer
Substrate
Passivation
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Technology concept

• Si-wafer used for EW actuation
• Micromachining of the nozzle cone
• Surface passivation by Oxide/Nitride (HT)
• FC coating on top side by plasma assisted process
• Orifice (spot size) definition by dry etch
  (bottom side)
• Assembly, electrical connection

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Operation

• Apply sub-threshold static pressure
• Capillary pressure prevents spitting
• Position substrate
• Switch capillary pressure by application of a
  short electrical pulse
• Move to the next spot site