Effect of Passivation Layers Permittivity on DC and RF Parameters of GaN MESFETs

Surface passivation impact on DC and RF characteristics of GaN MESFETs was studied using ATLAS simulator from Silvaco. It has been shown that when the relative permittivity, ε_r, of the inter-electrode passivation layers increases, the breakdown voltage as well as the maximum output power density increases thus improving the applications of the MESFET device in high voltage and high power. However, the high values of relative permittivity lead to an increase in the gate-source C_GS and gate-drain C_GD capacitances on which the radio frequency performance of GaN MESFET transistors depends strongly. In effect, this increase leads to a limitation of the performances, RF of the GaN MESFET transistors. Finally, the variations of the parameters studied as a function of ε_r have been quantified and mathematical expressions are established. These formulas can be very useful for the judicious choice of the passivation layer in GaN MESFETs.