Optimization of MIS type Non-Volatile Memory Device with Al-Doped HfO ₂ as Charge Trapping Layer

Abstract

The reduction in physical size of the Non-volatile memory (NVM) demands the use of high-k dielectrics due to loss in charge trapping behavior. The large bandgap of Al 2 O 3 (∼7.0 eV) proves it suitable for blocking and tunneling layer, while the high dielectric constant of HfO 2 proves it suitable for charge trapping layer (CTL). In this paper, we propose the application of Al doped HfO 2 used as CTL. The doping concentration has been varied by varying the number of sub-cycles (sequential cycles of HfO 2 , Al 2 O 3 ) by ALD system. The optical energy bandgap of Al doped HfO 2 observed to be increases from 4.91−5.20 eV as the Al incorporation content increases with 1:9−1:4 ALD sub-cycles. Oxygen vacancy defect in the thin film decreased to 17.87% for 1:4-Al doped HfO 2 sample as verified from the XPS. The increase in Al incorporation leads to charge loss towards silicon substrate due to high bandgap energy. In addition, charge traps are not well performed due to reduction of internal defects in the film. After 10 years, the NVM device with Al doped HfO 2 (1:9) CTL has improved charge retention characteristics by 14% as compared to a normal HfO 2 charge trap layer NVM device.