Field Emission from Double-Gated, Isolated, Vertically Aligned Carbon Nanofiber Arrays

A collimated electron beam is often desired to achieve high performance for practical applications such as field emission display and ebeam lithography. We designed and fabricated a double-gated, isolated, vertically aligned carbon nanofiber field emission array (VACNF FEA) to produce a collimated electron beam. The first gate is used to extract electrons out of the tip and the second gate (focus gate) is biased at a lower voltage than the first gate to focus the emitted electrons.

In this work, we designed a device that maximizes the electric field generated at the tip and minimizes the shield effect from the neighbor while it is capable of handling a large breakdown voltage during the field emission operation. To accomplish this, an isolated VACNF with 4-µm-tall per emission site is needed with each site 10µm apart. The e-beam lithography and lift-off were used to define a 250-nm-diameter and 4-nm-thick Ni catalyst on an n-type Si substrate to guarantee nucleation of Ni dots and subsequent growth of CNFs. The 4-µm-tall VACNF was grown using plasma-enhanced chemical vapor deposition at 725ºC. Once the CNF was synthesized, the extraction gate and the out-of-plane focus gate were fabricated with a novel photoresist planarization technique. This technique offers a very fast, fairly uniform, and well-controlled planarization method of making the self-aligned gate, which can replace the CMP technique that has been reported and used. This abstract is perhaps the first report of double-gated, self-aligned, field emitter arrays with isolated VACNF.

With this fabrication process, two types of devices were fabricated: (1) with tip in-plane with the extraction gate and (2) CNF with tip 900nm below the extraction gate. They were characterized as three-terminal devices (focus and extraction gate at same bias) and as four-terminal devices (focus and extraction gates at different biases). A scanning electron microscope (SEM) picture of a complete device is studied. Using this device, a four-terminal current-voltage (I-V) measurement was performed. As the focus voltage increases, the anode current increases.