Fabrication and Electrical Characterization of Dot Capacitors for Cold Field Emission Applications

The aim of this work was to study the dielectric properties of dot capacitors composed of a microtip coated with a thin layer of epoxy resin bonded to a steel plate. Two microtips with radii ranging from 3 to 5 μm were fabricated via electrochemical etching and coated with an epoxy layer 27-35 μm in thickness. The microtips were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). This study showed that composite cold-field emission emitters behave as dot capacitors. The real and imaginary parts of the impedance and permittivity, along with the direct and alternating conductivities, activation energies, and hopping energies, were examined. These evaluations were conducted at temperatures of 30, 45, 60, 75, and 90 °C, with a frequency range of 1 to 10⁶ Hz using impedance spectroscopy. The results indicated that both the impedance and electrical permittivity decreased slightly with increasing temperature, whereas the AC conductivity was independent of temperature. Additionally, a decrease in the activation and jump energies was observed as the thickness of the epoxy layer increased. The low values of the activation and hopping energies facilitated electron transport through the epoxy layer. The modified hopping model also provides an explanation for the conduction mechanism through the epoxy layer. The Nyquist plot shows that the capacitance decreased with increasing temperature. A slight increase in relaxation time was also observed, indicating the onset of conductive pathway formation. These findings contribute to a better understanding of the capacitance of the composite emitters and the formation of conductive pathways.