Low k-dielectric benzocyclobutane encapsulated AlGaN/GaN HEMTs with Improved off-state breakdown voltage

The impact of low-k dielectric benzocyclobutane (BCB) encapsulation on the electrical performance and structural stability of AlGaN/GaN HEMTs on Si were investigated. After BCB encapsulation, devices exhibited no degradation in their drain current density, extrinsic transconductance and small signal microwave performances. The curing temperature (280 °C) of BCB layer had no influence on the device electrical performances. Compared to devices without BCB encapsulation, the BCB encapsulated devices achieved ~2 orders of magnitude lower gate- and drain-leakage current. An order of magnitude lower surface leakage current was also observed by BCB encapsulation between the two adjacent mesas. Due to the reduction of leakage currents, ~2-times increase of OFF-state breakdown voltage was observed. In addition, the 9-µm-thick BCB encapsulation layer also helps to have structurally stable air bridges. This work demonstrates the low-k dielectric BCB as a viable solution for the complete encapsulation of GaN HEMTs and ICs.