Electric field and Charged Molecules Mediated Self-Assembly for Electronic Devices
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C11.17.1
Electric field and Charged Molecules Mediated Self-Assembly for Electronic Devices Sang Woo Lee1, Helen A. McNally1, and Rashid Bashir1,2,♣ School of Electrical and Computer Engineering, 2 Department of Biomedical Engineering, Purdue University, West Lafayette, IN. 47907. 1
Abstract In this paper we present techniques, utilizing dielectrophoresis and electrohydrodynamics, which can possibly be used for assembling devices suspended in a solution onto a binding site on a substrate. We explored the concepts using micro-scale negatively charged polystyrene beads and rectangular silicon blocks. Dielectrophoretic forces on devices in buffer solutions were examined as a function of frequency of the applied AC signal. The observed results can be explained by taking in account electro-thermal and AC electroosmotic effects. The study described in the paper can be used for placing and assembling micro and nano-electronic devices and objects at specific sites on various substrates, in combination with bio-inspired biological binding techniques such as DNA hybridization, antigen-antibody interactions, and ligand-receptor (avidin-biotin) interactions. Introduction A suspended device in a solution under non-uniform electric field is polarized, resulting in a dipole moment of the device. Due to the interaction between the dipole moment and electric field, the device is moved in the solution. This phenomenon is termed dielectrophoresis (DEP), as described earlier [1]. In recent years, through the use of micro-fabrication techniques, the behavior of micro and nano-scale objects on microelectrode structures has been studied by many researchers. For example, dielectrophoretic separation and manipulation of cells has been demonstrated [2, 3]. Dielectrophoretic separation of nano-particles with different sizes has also been reported [4, 5]. Metallic nano-wires have been aligned on a micro-interdigitated electrodes using dielectrophoretic forces [6]. It is also important to note that when a high electric field is applied to these micro-structures, power is generated, which causes the generation of heat in a medium, resulting in local temperature gradients. Due to the local temperature gradients, the spatial variations of electrical conductivity and permittivity occur, leading to an electrothermal force [7, 8]. This electro-thermal force can play an equally important role in the motion of the suspended and polarized devices, when compared to the role of the DEP forces. Moreover, in the low frequency range, AC electroosmotic force is also introduced while an AC signal is applied to the electrode [7]. Thus, DEP and electrohydrodynamic effects such as electrothermal and AC electroosmotic effects should be considered when describing the movement of devices on a microelectrode structure under AC signal. There are several reports, explaining the movement of the devices on microelectrodes using both the above-mentioned effects [3,5,7-9]. Our goal is to be able to explore the precise positioning and placement of the devices at specific
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