Fabrication and Characterization of Flexible AlGaN/GaN HEMTs on Kapton Tape

In this work, we successfully used wet etching to remove the Si substrate and transferred AlGaN/GaN high-electron mobility transistor (HEMT) film with a gate length of 2 mu m to the flexible Kapton tape. The transferred area of AlGaN/GaN epitaxial thin film reached 1.2 x 1.2 cm(2). The flexible HEMTs still exhibit excellent electrical characteristics with the maximum drain current density (J(DS,max)) of 290 mA/mm and the maximum transconductance (g(m, max)) of 108 mS/mm. Furthermore, we analyzed the physical mechanisms when devices were under bending. Under bending, the tensile strain enhances the piezoelectric field within the AlGaN layer, consequently increasing the 2-D electron density. In the condition that flexible HEMTs are bent with a curvature radius of 0.3 cm, JDS, max still reaches 346 mA/mm and gm, max achieves 125 mS/ mm. Besides, the main reason for the decrease in dc characteristics is verified by self-heating. As for the RF characteristics, the Si substrate removal can effectively decrease the output parasitic capacitances. Although gm, max becomes half after the transfer processes, the cutoff frequency and the maximum oscillation frequency of flexible HEMTs still reaches 3.8 and 6.5 GHz, respectively.