Anodic tantalum: Fabrication, breakdown characteristics of capacitor and integration with a WSe₂ field effect transistor

The anodization of metals is a simple and low cost method of producing metal-oxides. This article discusses the procedure for anodizing tantalum (Ta) and details the characterization of capacitors formed by tantalum pentoxide (Ta₂O₅) dielectric. The breakdown field for the un-annealed, 200 °C and 400 °C annealed samples are 5.4, 5.1 and 3.3 MV/cm respectively. A number of factors affect the electrical properties of dielectrics and from our experiments, we observe that at an annealing temperature of 200 °C and pressure of 7.5 Torr, the dominant conduction mechanism of the capacitor changed from Schottky Emission to Poole-Frenkel Emission. In addition, we report the deposition of exfoliated WSe₂ on anodic tantalum using the scotch tape method. Good adhesion has been observed between the WSe₂ flakes and the anodic tantalum with obvious colour variation in relation to the thickness of the WSe₂. Subsequently, a WSe₂ Field Effect Transistor (FET) has been designed and fabricated using a mask-less lithographic technique. The anodic tantalum has been used as the gate dielectric while the bulk Ta as the back gate electrode. The transfer characteristics of the integrated device have been discussed, showing promise for low power operation.