Mark A. Crowder

Orientation- and position-controlled alignment of asymmetric silicon microrod on a substrate with asymmetric electrodes

In this paper, we demonstrate the orientation-controlled alignment of asymmetric Si microrods on a glass substrate with an asymmetric pair of electrodes. The Si microrods have the shape of a paddle with a blade and a shaft part, and the pair of electrodes consists of a narrow electrode and a wide electrode. By applying AC bias to the electrodes, the Si microrods suspended in a fluid align in such a way to settle across the electrode pair, and over 80% of the aligned Si microrods have an orientation with the blade and the shaft of the paddle on the wide and the narrow electrodes, respectively. When Si microrods have a shell of dielectric film and its thickness on the top face is thicker than that on the bottom face, 97.8% of the Si microrods are aligned with the top face facing upwards. This technique is useful for orientation-controlled alignment of nano- and microsized devices that have polarity or a distinction between the top and bottom faces.

Asymmetric AC electrophoresis with insulated electrodes: Toward positional control of microand nanoscale devices

This paper demonstrates electrophoresis of silicon micro-rods by applying asymmetric AC bias to two electrodes capped with a thin dielectric film. The silicon micro-rods migrate bi-directionally when asymmetric AC bias is applied to the electrodes. The insulated electrodes significantly contribute to elimination of bubbling and contamination originating from electrochemical reactions, which makes adoption of the technique to mass production processes realistic. This technique is widely applicable to positional control of small objects including micro- and nanoscale devices.

Low-temperature processing of SiO2 thin films by HD-PECVD technique for gate dielectric applications

We report on the fabrication and characterization of SiO2 thin films by high-density plasma enhanced chemical vapor deposition (HD-PECVD) technique at a processing temperature lower than 400°C for gate dielectric applications in thin film transistor (TFT) devices. An inductively coupled plasma source was used to couple the rf power to the top electrode. The SiO2 thin films were fabricated on p-Si wafers using nitrogen, nitrous oxide, and silane precursors. The deposition process was optimized in terms of the effects of rf power, gas flow rates, and system pressure on deposition rate, chemical etch rate, optical properties, and electrical characteristics. The effects of the processing variables on the refractive index, Si-O bond formation, and impurity related bonds were analyzed. The electrical properties of the films were evaluated from the I-V and C-V characteristics of the MOS capacitors. The effects of the SiO2 film thickness on the electrical characteristics of MOS capacitors were also investigated in the range of 30-100 nm. The influence of the low temperature processed gate dielectric on the performance of 500 Å poly-Si TFTs was evaluated in terms of the transfer and gate leakage characteristics. The microstructural and electrical characteristics of the HD-PECVD deposited SiO2 thin films suggest their suitability for the low temperature integration of TFTs on glass or other low temperature substrates.

Orientation-controlled dielectrophoretic alignment of silicon microrod on a substrate with high positional accuracy

We demonstrate the orientation-controlled dielectrophoretic alignment of asymmetric Si microrods on a glass substrate with an asymmetric pair of electrodes. By applying AC bias to the electrodes, over 80% of the Si microrods align on the electrode pair so that a particular end of the microrod relates to a certain part of the electrode; the thick and thin ends overlap the thick and thin electrodes, respectively. Furthermore, the orientation of the top and bottom face of the Si microrod is also controllable when the thicknesses of the dielectric film on the top and bottom faces are different.

Bidirectional migration of Au colloids and silicon microrods in liquid using asymmetrical alternating current electric field with insulated electrodes

In this study, we demonstrate the migration of Au colloids and silicon microrods in deionized (DI) water and isopropyl alcohol (IPA) by applying asymmetrical AC bias to two electrodes capped with a thin dielectric film. Both Au colloids and silicon microrods successfully migrate from one electrode to the other when asymmetrical AC bias is applied to the electrodes. Furthermore, the direction of the migration can be easily reversed by inverting the wave form. The insulated electrodes have the potential to prevent contamination and bubbling originating from electrochemical reactions, which makes the adoption of the technique for mass production processes easy and realistic. The bidirectional migration acts similarly to electrophoresis and is effective even in DI water and IPA in which conventional DC electrophoresis with insulated electrodes is ineffective. This technique is widely applicable to the positional control of small objects including nano- and micro-sized devices.