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

• Published in: IEEE transactions on electron devices 2021-07, Vol.68 (7), p.3320-3324
• Main Authors: Hsu, Keng-Li, Wu, Meng-Chyi
• Format: Article
• Language: English
• Subjects: Aluminum gallium nitride; Aluminum gallium nitrides; Bending machines; Electrical analysis; Electron density; flexible AlGaN/GaN high-electron mobility transistors (HEMTs); flexible substrate; Gallium nitrides; HEMTs; High electron mobility transistors; Kapton (trademark); Logic gates; MODFETs; Piezoelectricity; Polyimide resins; self-heating; Silicon; Silicon substrates; Substrates; Tensile strain; Thin films; Transconductance; Wide band gap semiconductors
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2021.3083475

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 \text{m} to the flexible Kapton tape. The transferred area of AlGaN/GaN epitaxial thin film reached 1.2\times1.2 cm 2 . The flexible HEMTs still exhibit excellent electrical characteristics with the maximum drain current density ( {J}_{\text {DS,max}} ) of 290 mA/mm and the maximum transconductance ( {g}_{\text {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, {J}_{\text {DS,max}} still reaches 346 mA/mm and {g}_{\text {m,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 {g}_{\text {m,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.