H. Yazdani, S. Chevtchenko, I.  Ostermay and J. Würfl

Published in:

Semicond. Sci. Technol., vol. 36, no. 05, pp. 055018 (2021).

Abstract:

Mechanical stress/strain is altering the charging properties of piezoelectric materials. For AlGaN and GaN heterostructures, this phenomenon has been described theoretically (Ambacher et al 2000 J. Appl. Phys. 87 334-44). Recently it was shown that a mechanically stressed SiN_x passivation layer may produce local strain in the AlGaN/GaN layers underneath the gate at certain conditions. This results in a threshold voltage (V_th) shift (Osipov et al 2018 IEEE Trans. Electron Devices 65 3176-84). It is therefore straightforward to also investigate the influence of an intrinsically stressed gate metal on the device characteristics. In this study, AlGaN/GaN HFETs were fabricated on nominally identical wafers with variations of intrinsic stress in the gate metallization and in the first passivation. It is verified that the built-in mechanical stress of the gate metal can shift the threshold voltage. In detail we varied the intrinsic stress of both the first passivation layer (SiN_x) and the gate metallization (Ir) by about 1 GPa. These variations result respectively in 0.65 and 0.20 V threshold voltage shift. We have additionally analyzed the thermal stability of SiN_x and iridium films with respect to their mechanical properties and the resulting threshold voltage shift.

Keywords:

GaN HEMT, two-dimensional electrons gas (2DEG), strain engineering.

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