Role of the (Ta/Nb)Ox/Al2O3 interface on the flatband voltage shift for Al2O3/(Ta/Nb)Ox/Al2O3 multilayer charge trap capacitors

Abstract

The authors studied the characteristics of Si/Al2O3/(Ta/Nb)Ox/Al2O3/SiO2/Pt charge trap capacitors fabricated by atomic layer deposition and postmetallization annealing at 400 °C. Al2O3 and (Ta/Nb)Ox films are amorphous and have negligible fixed charges. In program mode, a flatband voltage (Vfb) drastically shifts toward the positive direction at a short program time of 10−4 s. A large Vfb shift of approximately 4 V arises after programming at 1 mC/cm2 because there is a large difference in the conduction band offset between the (Ta/Nb)Ox-charge trapping layer (TNO-CTL) and the Al2O3-blocking layer (AlO-BL) (1.8 eV). In the retention mode, most of the trapped electrons in the TNO-CTL transfers across the Al2O3-tunneling layer (AlO-TL) rather than the AlO-BL. The thickness of the AlO-TL affects the Vfb shift degradation behavior in the retention mode. The injected electrons are dominantly located at the TNO-CTL/ALO-BL interface, determined from the thickness dependence of the TNO-CTL on the Vfb shift.