High aspect ratio lead zirconate titanate tube structures: II. Directed assembly via dielectrophoresis

This paper reports on the controlled manipulation of high aspect ratio ferroelectric microtubes on pre-patterned templates by dielectrophoresis. Microtubes of ferroelectric lead zirconate titanate (PZT, a chemical formula of Pb(Zr0.52Ti0.48 )O3) with an outer diameter of 2 ?m, a length of about 30 ?m and a wall thickness of 400 nm were prepared by vacuum infiltration method using macroporous silicon templates. To position and align tubes at designed places, an alternating electric field was applied to a colloidal suspension of PZT tubes through lithographically defined microelectrodes. This would enable creation of a stable electrical connection to individual tubes for making a testing structure for rapid electrical characterization. Electric-field assisted assembly experiments demonstrated that the frequency and magnitude of the applied electric field control dielectrophoretic long-range forces, and hence spatial movement of the tubes in a non-uniform electric field. The most efficient biasing for the assembly of tubes across the electrode gap of 12 ?m was a square wave signal of 5 Vrms and 10 Hz. By varying the applied frequency in between 1 and 10 Hz, an enhancement in tube alignment was observed due to possible changes in dielectrophoretic torque. The results indicate a great potential for utilizing dielectrophoresis in construction of more complex, hierarchical 3-D device structures using the PZT 1-D like tubes as the building units.