Assembly of mesoscopic to macroscopic particles with optoelectronic tweezers (OET)

In this paper we will look at the relative merits of assembling particles in the mesoscopic to macroscopic size range with Optical Tweezers and Optoelectronically enhanced Tweezers. Optical tweezers provide an elegant method for controlling the position of microscopic particles in three dimensions, allowing their assembly into desired patterns. The technique works well when moving particle similar in size to the diffraction limited spots of the laser tweezers. In comparison to this Optoelectronic Tweezers (OET) use a light patterned photoconductive device to move particles in two dimensions through light patterned electrical fields. At light/dark boundaries on the biased photoconductor of an OET device high electrical gradients are created which move particles by dielectrophoresis forces in a similar manner to how the optical gradients move particles in a standard optical tweezers system. Xerox recently reported the manipulation of 150 and 300 micron silicon chips with optoelectronic tweezers, with coarse assembly of 1000 objects per second with the goal of creating a printer system for electronics assembly. We have demonstrated the alignment of commercial 250 micron InP stripe laser dies, 50 micron diameter solder beads for the creation of conductive paths and SMT components up to 600x300x300 microns in dimension. In this paper we will discuss the remaining challenges including different strategies for fixing the assembled components into place. Finally, we will look at the assembly of particles at the small end of the size range and discuss the potential uses for the large area patterning of mesoscopic particles.