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.
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.
- 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.
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