Self-Assembling Nanosphere Lithography Process for Gated Carbon Nanotube Field Emission Arrays
Society of Photo-Optical Instrumentation Engineers (SPIE)
Proceedings of SPIE 7637, Alternative Lithographic Technologies II,
Carbon nanotubes (CNTs) have many unique properties ideal for field emission such as narrow diameters, high aspect ratios, high temperature stability, good conductivity, and structural strength. A gated array is preferable to a diode type array due to the lower extraction voltages and reduced screening effects. An inexpensive fabrication process has been developed using self-assembling nanosphere lithography for sub-micron gate dimensions of a CNT field emission array. The array fabrication process consists of a silicon wafer with a 20 nm titanium diffusion barrier followed by 10 nm nickel catalyst layer covered with 1-2 μm of silicon dioxide. Self-assembling polystyrene spheres are deposited in a monolayer across the substrate to create the gate mask. The diameter of the spheres is reduced to the desired gate dimensions using an oxygen plasma ash. The gate metal is then deposited via evaporation. The gate openings are created through lift-off facilitated by dissolving the polystyrene spheres in an ultrasonic acetone bath. Reactive ion etching is used to remove the silicon dioxide and expose the nickel catalyst layer for CNT synthesis within the gate openings. The process is demonstrated for both 1 μm and 500 nm diameter polystyrene spheres for gate dimensions and gate pitch of 500 nm and 250 nm respectively. The resulting array is analyzed using a scanning electron microscope. Further development of the polystyrene monolayer deposition method is necessary to decrease defects in the monolayer structure. Future work will investigate the reduction of gate dimensions to 20 - 50 nm to facilitate a single CNT per gate array.