The key parameters of vertical A1N Schottky barrier diodes (SBDs) with variable drift layer thickness (DLT) and drift layer concentration (DLC) are investigated.The specific on-resistance (Ron,sp) decreased to 0.5 mΩ· cm2 and the breakdown voltage (VBR) decreased from 3.4 kV to 1.1 kV by changing the DLC from 1015 cm-3 to 3 × 1016 cm-3.The VBR increases from 1.5 kV to 3.4 kV and the Ron,sp also increases to 12.64 mΩ· cm2 by increasing DLT from 4-μm to 11-μm.The VBR enhancement results from the increase of depletion region extension.The Baliga's figure of merit (BFOM) of 3.8 GW/cm2 was obtained in the structure of 11-μm DLT and 1016 cm-3 DLC without FP.When DLT or DLC is variable,the consideration of the value of BFOM is essential.In this paper,we also present the vertical A1N SBD with a field plate(FP),which decreases the crowding of electric field in electrode edge.All the key parameters were optimized by simulating based on Silvaco-ATLAS.