Charge writing in silicon-silicon dioxide for nano-assembly

Interest in using electrostatics for active nano-assembly has grown significantly over the last five years. One common electret structure for such electrostatic constructs is the silicon-silicon dioxide interface. In this paper, an experimental and mathematical analysis of the process of writing negative charge spots in Si-SiO₂ is presented. It is demonstrated that controlling the spread of the charge can reduce the spot size and the drop in written potential. Simulation results of a one-dimensional charging model that assumes tunnelling of electrons through the oxide and trapping within SiO₂ are presented and compared with the experimental data. The model assumes charge trapping at the Si-SiO₂ interface and none at the oxide-air interface or within the oxide bulk. Conducted experiments also show that although the lateral spread of charge places a lower limit on the minimum spot size in silicon-silicon dioxide structures, the use of a hydrophobic hexamethyldisilazane layer can be effective in improving the size stability of the written electrical spots.