Comparison of Nonvolatile Memory Effects in Ni-Based Layered and Dotted Nanostructures Prepared through Atomic Layer Deposition

Abstract

Nano-floating gate memory devices were fabricated by using nickel nanocrystals as a charge-trapping portion embedded into Al 2 O 3 thin films. Ni nanocrystals were prepared via a thermal reduction of nanoscale NiO layers deposited by atomic layer deposition. Although the continuous deposition of insulating Al 2 O 3 and semiconducting NiO thin films allowed the facile fabrication of charge-trap, the corresponding retention feature suffers from inferior charge trapping/detrapping. On the other hand, the Ni nanocrystals enhanced the retention behavior and exhibited the largest memory window of 13.8 V with the stored charge density of 2.5 Â 10 13 traps/cm 2 , probably due to the isolated formation of charge-trapping centers.Next-generation non-volatile memories will have to meet stringent device performance requirements, such as higher speed, enhanced data storage density, limited device space, and lower power consumption, in addition to possessing nonvolatile features in data storage mode. In particular, nano-floating gate memories (NFGMs) are the dominant type of memory compared to their current competitors, such as phase-change random access memories (RAMs), resistive RAMs, polymer RAMs, magnetic RAMs etc. 1-7 NFGM performance far exceeds the currently-evolved flash memories and dynamic random access memories in terms of operation voltage, consumption power, and data volatility. Further, NFGMs can be effectively adapted to the pre-existing Si processing/technology through the incorporation of sophisticated thin dielectric layers. The performance of NFGMs depends largely upon the delicate function of the charge-trapping materials embedded into the high-k thin films. Furthermore, NFGMs should meet stringent requirements of nonvolatile memories: fast programming/erasing speed, high-number programming/easing cycles, and long-period charge retention.A typical strategy is to combine high-k dielectric materials (Al 2 O 3 , ZrO 2 , HfO 2 , etc. 8-22 ) with metallic and semiconducting nanocrystals such as Pt, Au, Co, Ge, Ni, and silicides. In particular, Ni-based nanocrystals were attempted in the combined form of physical deposition and post thermal treatments. 18-23 The formation of charge-trapping nanocrystals has been shown through physical and chemical deposition of metallic or semiconducting layers followed by thermal or optical annealing or chemical dispersion of nanocrystals onto the dielectric thin films. Those approaches suffer from the disadvantage that processing is discontinuous, while facile continuous processing would be preferred.Since the introduction of atomic layer deposition (ALD) by Suntola, 24 ALD has been gaining widespread attention in semiconductors and flat-panel displays, owing to conformal coverage in lowdimensional structures, superior control in film thickness and robust dielectrics. ALD was employed to continuously deposit insulating and charge-trapping layers without any process interruptions. 25 A semiconducting oxide, such as nickel oxide (NiO), has been proposed as a candidate for charge-...

Atomic Layer Deposition of Transparent p-Type Semiconducting Nickel Oxide Using Ni(tBu2DAD)2 and Ozone

“…Generally, NiO ALD processes have suffered from low GPCs with very few reports of greater than 0.05 nm/cycle (see Table ). We find that the GPC in the present work is among the highest of reported values for NiO, with reports of 0.13–0.14 nm/cycle for the Ni­(dmamb) 2 + H 2 O process ,, and 0.2 nm/cycle for the Ni­(acac)­2­(TMEDA) + O 3 process . However, both processes appear to exhibit a rather slow reaction kinetics with the Ni­(dmamb) 2 + H 2 O process space requiring long H 2 O and Ni­(dmamb) 2 pulses of >10 and >6 s, respectively, and the Ni­(acac) 2 (TMEDA) and O 3 process requiring a >4 s Ni­(acac) 2 (TMEDA) dose to reach saturating growth conditions.…”

Charge storage and tunneling mechanism of Ni nanocrystals embedded HfOx film

“…1 Compared to semi-conductive (Si,Ge) 2,3 and organic (C, graphene) 4,5 charge storage candidates, noble metal nanoparticles (Pt, 6 Au 7 and Ag 8 ) embedded in oxide dielectric films (Al 2 O 3 , HfO x , ZrO 2 , TiO 2 , HfAlO x ) have been highlighted due to their high work function and excellent charge properties, but they are not suitable for large-scale industrial applications due to their high cost. Ni nanocrystals (Ni-NCs) has a high work function of 5.35 eV, 9 stable chemical properties, and have been reported to exhibit a memory window width (flat-band voltage shift |∆ V FB |) ranging from 1 to 20 V, [10][11][12][13][14][15][16] showing excellent charge storage capacity. However, due to the oxidization of Ni-NCs in oxide matrix and diversify of nickel oxides, the endurance and retention properties for Ni-NCs-based memory cell need to be further improved.…”