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Electrowetting simulation for micro device assembly

Electrowetting provides a means of moving and manipulating small amounts of fluids without any mechanical components. We are simulating an optimizing the electrowetting process for transporting and assembling micro devices.

Transporting micro devices

Figure 1 and video 1 shows a droplet carrying a device on top where movement is induced by electro capillarity effects. The fluid is modeled with MDPD (many-body DPD), the device with different types of hook forces and different particle-pair forces represent fluid-structure interactions.

Figure 2 indicates the discretization with particles. Electric forces result of a finite-element-discretization (FEM) of the Laplace equation which is coupled then into the Korteweg-Helmholtz body force acting on particle side. Figure 3 shows schematically a FEM domain with the potential field coming from the fixed electrodes' potentials. Potential gradients and  different dielectricity numbers of the involved materials nearby the three-phase boundary line substrate-liquid-vapor mainly determine the actuation force on the droplet.

Electrode optimization

For EWOD - electrowetting on dielectrics - electrode geometry and building capacitance correspond to acting forces on droplets. Figure 4 indicates the numerical folding of droplet and electrode surface to determine the capacitors.

The exact form of the electrodes are significant for reliability and efficiency of  electrowetting devices.  Figure 5 shows different electrode designs and possible maximum forces along the movement line of a droplet. The simple electrode structure in a) leads partially to vanishing actuating forces while finger structures ensure functionality over the whole range. Figure 6 shows the influence of the droplet diameter on the force.

Relevant publications:

  • Jan Lienemann, Andreas Greiner, Jan G. Korvink, Xiaorong Xiong, Yael Hanein, and Karl F. Böhringer. Modelling, simulation and experimentation of a promising new packaging technology – parallel fluidic self-assembly of micro devices. Sensors Update, 13:3–43, March 2004.
  • Jan Lienemann, Andreas Greiner, and Jan G. Korvink. Modeling, simulation and optimization of electrowetting. IEEE T Comput Aid D, Special Issue on Design Automation Methods and Tools for Microfluidics-Based Biochips, 25(2):234–247, February 2006.
  • Jan Lienemann, Andreas Greiner, and Jan G. Korvink. Surface tension defects in micro-fluidic self-alignment. In Proc. DTIP, pages 55–63, Cannes-Mandelieu, France, May 5–8 2002.
  • Jan Lienemann, Andreas Greiner, and Jan G. Korvink. Electrode shapes for electrowetting arrays. In Proc. nanotech, volume 1, pages 94–97, San Francisco, CA, USA, February 23–27 2003.
  • Andreas Greiner, Jan Lienemann, Jan G. Korvink, Xiaorong Xiong, Yael Hanein, and Karl F. Böhringer. Capillary forces in micro-fluidic self-assembly. In International Conference on Modeling and Simulation of Microsystems, Tech. Proc. MSM, 2002.
  • Jan Lienemann, Andreas Greiner, and Jan G. Korvink. Volume shrinking in micro-fluidic selfassembly. In Proc. ASDAM, pages 369–372, Smolenice Castle, Slovakia, October 14–16 2002.

Contact persons:

Jan Lienemann, Dennis Weiß
Files
Video 1   584.9 kB  
Electrowetting droplet movement
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