Impact of Bias Temperature Stress on IGZO/Ni/IGZO Steep Subthreshold Vertical Current Driver Fabricated at Room Temperature

Abstract

Impact of bias-temperature stress (BTS) has been assessed in a three-terminal vertical current driver fabricated by room temperature processing of IGZO/Ni/IGZO stack on a p-silicon substrate. Under normal working condition and at a low voltage, the driver exhibits 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ON-OFF current ratio with remarkable 46 mV/decade subthreshold slope, because of 0.89 eV Schottky barrier presented by the Ni/IGZO interfaces and linear superposition of thermionic-field, thermionic and diode currents of the driver as obtained by bias dependent variable energy offsets between the Ni and the IGZO Fermi energy levels. Furthermore, Schottky gate eliminates charge trapping induced threshold voltage instability as commonly found in planar IGZO thin film transistors, as a result of which excellent current stability under both ON and OFF states was found even when bias stress of more than 5 times the nominal working bias was applied to the driver for 12 hours. Employing accelerated stress bias progressive current degradation of the driver was further induced and assessed in detail