Hole and electron trapping in HfO₂/Al₂O₃ nanolaminated stacks for emerging non-volatile flash memories

Abstract

HfO 2 /Al 2 O 3 nanolaminated stacks prepared by atomic layer deposition have been investigated in terms of their charge storage characteristics for possible application in charge trapping memories. It is shown that the memory window, electron and hole trapping and leakage currents depend strongly on Al 2 O 3 thickness and post-deposition oxygen annealing. Depending on the Al 2 O 3 thickness, postdeposition annealing in O 2 creates different electrically active defects (oxide charge and traps) in the stacks. O 2 annealing increases electron trapping, thus giving rise to a larger memory window and enhanced charge storage characteristics, i.e. 65% of charge is retained after ten years and the memory window decreases by 6% after 2.5 × 10 4 program/erase cycles.

Electrical characterization of memory capacitors for nonvolatile memory applications based on nanolaminated HfO2/Al2O3 and Al-doped HfO2 stacks

“…A simulation with the Band diagram tool [14] reveals that an oxide charge of about −6×10 12 cm -2 with a centroid situated in the middle of the BO layer, combined with the dipole potential, could explain the observed Vfb. Note that a negative Qox (−6.4×10 12 cm -2 ) was detected earlier [5] for HfO2/Al2O3 nanolaminates with thicker (~3 nm) Al2O3 sublayers. Hence, it could be suggested that the Al2O3 sublayers contribute a negative charge that is thickness-dependent; for certain thicknesses it might prevail over the positive charge associated with HfO2 and SiO2, thus determining the net negative Qox.…”

“…Since the modern MOSFET technology for ultra-high-density circuits requires the employment of high-k dielectrics in the gate stacks, it is quite tempting to use these materials as charge storage media; moreover, the high-k insulators turned out to be trap-rich materials. Among the various high-k dielectrics, HfO2-based dielectric stacks have been recently pointed out as very promising candidates for replacing Si3N4 in the future CTM generations [1,[3][4][5][6]. The attractiveness of employing HfO2 as a charge-trapping material is additionally reinforced by the fact that the HfO2 MOSFET technology has already reached a state of maturity.…”

“…The attractiveness of employing HfO2 as a charge-trapping material is additionally reinforced by the fact that the HfO2 MOSFET technology has already reached a state of maturity. Previously, we have reported some very promising from a CTM point of view charge trapping and storage results for HfO2/Al2O3 nanolaminated stacks [3][4][5] considering the influence of the annealing ambient and the stack structure on their ability to accumulate and store electrical charges. One of the issues which are still not clarified is the relation of Al with the charge trapping sites in the layer and their spatial distribution, as well as its impact on the stack's electrical characteristics.…”

High-Performance Non-Volatile InGaZnO Based Flash Memory Device Embedded with a Monolayer Au Nanoparticles

“…Meanwhile, the floating gate layer is also anticipated to be a promising constituent in the three-terminal NVM device’s structure for higher charge storage capacity and suitable endurance/retention memory operations [ 8 , 9 , 19 , 20 , 26 ]. Additionally, the charge-trap layer such as HfO 2 , SiN, and redox state molecule has been introduced in the NVM device’s structure to store and erase the charge according to the memory state controlled by a swing in the threshold voltage (V th ) [ 27 , 28 , 29 , 30 , 31 ]. On the contrary, NVM devices based on metallic nanoparticles as a floating gate have gained more advantages, such as higher tapping probability of charges, ensuring the stable probability of retention property in case of defects in the tunneling or control oxide layer, and larger memory window [ 8 , 32 , 33 , 34 ].…”

Self-Assembled Sn Nanocrystals as the Floating Gate of Nonvolatile Flash Memory

“…Because of the discrete nature of the NC-based floating-gate, charge leakage due to defects in the underlying thin tunnel-oxide is limited only to a small number of NCs, thus improving the charge retention and endurance characteristics. Moreover, the discreteness of the charge-storage nodes enables multibit-per-cell storage, without resorting to the multilevel approach. , In the recent past, many research efforts have therefore focused on the use of NCs of semiconductors, − metals, ,− metal silicides, or high-k dielectrics − to form the discrete floating-gate of NVMs. As one of the candidates for discrete charge-storage nodes, metal NCs provide several advantages over their semiconductor counterparts .…”