Heeyoung Jeon

Change in band alignment of HfO2 films with annealing treatments

Energy band alignment of a nitrided HfO2 film and dependence of the band gap (Eg) on annealing treatments with nitrogen plasma and ambient gases (N2 and O2) were studied by reflection electron energy loss spectra and x-ray photoelectron spectroscopy. We also investigated the nitrogen content in the film and its influence on the band alignment using medium energy ion scattering. The nitrogen incorporated into the HfO2 film by directed nitrogen plasma treatment significantly decreased the band gap and band offsets, i.e., the incorporated N in the film decreased both conduction and valance band offsets. The nitrogen content in depth direction was dependent on the postannealing conditions using O2 or N2.

Al2O3 multi-density layer structure as a moisture permeation barrier deposited by radio frequency remote plasma atomic layer deposition

Al2O3 films deposited by remote plasma atomic layer deposition have been used for thin film encapsulation of organic light emitting diode. In this study, a multi-density layer structure consisting of two Al2O3 layers with different densities are deposited with different deposition conditions of O2 plasma reactant time. This structure improves moisture permeation barrier characteristics, as confirmed by a water vapor transmission rate (WVTR) test. The lowest WVTR of the multi-density layer structure was 4.7 × 10−5 gm−2 day−1, which is one order of magnitude less than WVTR for the reference single-density Al2O3 layer. This improvement is attributed to the location mismatch of paths for atmospheric gases, such as O2 and H2O, in the film due to different densities in the layers. This mechanism is analyzed by high resolution transmission electron microscopy, elastic recoil detection, and angle resolved X-ray photoelectron spectroscopy. These results confirmed that the multi-density layer structure exhibits ver...

Resistive switching of a TaOx/TaON double layer via ionic control of carrier tunneling

Resistance random access memory (RRAM) is an attractive candidate for future non-volatile memory due to its superior features. As the oxide thickness is scaled down, the charge transport mechanism is also subject to the transition from hopping to tunneling dominant process, which is critically related to the interfacial electronic band structure. A TaOx/TaON double layer-based RRAM is fabricated and characterized in this work. Upon TaON insertion at the lower interface, the improved switching behavior is observed. The TaON at the bottom electrode interface blocks oxygen vacancy percolation due to strong N-O bonds and also modifies interfacial band alignment to lower the injected electron energy from bottom electrode due to higher tunneling barrier height than that of TaOx/Pt. This study suggested that a defect-minimized insertion layer like TaON with a proper interfacial band alignment is pivotal in RRAM for the effective ionic control of carrier tunneling resulting in non-linear I-V behavior with improved properties.

Effects of postnitridation annealing on band gap and band offsets of nitrided Hf-silicate films

The effects of film composition and postnitridation annealing on band gap and valence band offset were examined in nitrided Hf-silicate films prepared using direct plasma nitridation. Regardless of the composition of Hf-silicate films, the band gap characteristics were similar after direct plasma nitridation (4.5±0.1eV) and postnitridation annealing (5.6±0.1eV). The decrease in band gap after direct plasma nitridation was caused by the formation of Si–N and Hf–N bonds, while the recovery of band gap by postnitridation annealing was influenced by the dissociation of unstable Hf–N bonds. The difference in valence band offset was strongly related to the chemical states of Si–N bonds.

Charge trapping characteristics of Au nanocrystals embedded in remote plasma atomic layer-deposited Al2O3 film as the tunnel and blocking oxides for nonvolatile memory applications

Remote plasma atomic layer deposited (RPALD) Al2O3 films were investigated to apply as tunnel and blocking layers in the metal-oxide-semiconductor capacitor memory utilizing Au nanocrystals (NCs) for nonvolatile memory applications. The interface stability of an Al2O3 film deposited by RPALD was studied to observe the effects of remote plasma on the interface. The interface formed during RPALD process has high oxidation states such as Si+3 and Si+4, indicating that RPALD process can grow more stable interface which has a small amount of fixed oxide trap charge. The significant memory characteristics were also observed in this memory device through the electrical measurement. The memory device exhibited a relatively large memory window of 5.6 V under a 10/−10 V program/erase voltage and also showed the relatively fast programming/erasing speed and a competitive retention characteristic after 104 s. These results indicate that Al2O3 films deposited via RPALD can be applied as the tunnel and blocking oxides ...

Radio frequency plasma power dependence of the moisture permeation barrier characteristics of Al2O3 films deposited by remote plasma atomic layer deposition

In the present study, we investigated the gas and moisture permeation barrier properties of Al2O3 films deposited on polyethersulfone films (PES) by capacitively coupled plasma (CCP) type Remote Plasma Atomic Layer Deposition (RPALD) at Radio Frequency (RF) plasma powers ranging from 100 W to 400 W in 100 W increments using Trimethylaluminum [TMA, Al(CH3)3] as the Al source and O2 plasma as the reactant. To study the gas and moisture permeation barrier properties of 100-nm-thick Al2O3 at various plasma powers, the Water Vapor Transmission Rate (WVTR) was measured using an electrical Ca degradation test. WVTR decreased as plasma power increased with WVTR values for 400 W and 100 W of 2.6 × 10−4 gm−2day−1 and 1.2 × 10−3 gm−2day−1, respectively. The trends for life time, Al-O and O-H bond, density, and stoichiometry were similar to that of WVTR with improvement associated with increasing plasma power. Further, among plasma power ranging from 100 W to 400 W, the highest power of 400 W resulted in the best moi...

Spatially confined electric field effect for improved resistive switching behavior of a Ni/Ta-embedded TaOx/NiSi device

In this study, Ni/TaOx/NiSi and Ni/TaOx/Ta/TaOx/NiSi devices were fabricated, and the resistive switching (RS) behaviors were investigated. A 2 nm-thick Ta metal layer was deposited between two TaOx films to form a Ni/TaOx/Ta/TaOx/NiSi stack, which was analyzed using TEM. Based on a linear scale I–V curve and an R–V graph, both devices showed conventional bipolar conductive bridge random access memory (CBRAM) characteristics with formation/rupture of Ni conductive filaments (CFs). The Ta-embedded device showed lower forming/SET voltages and initial resistance due to the reduced effective thickness of TaOx films due to the inserted Ta metal layer. In addition, the Ta-embedded device exhibited improved endurance and resistance distribution due to suppression of the random formation of Ni CFs. In this study, Ni/TaOx/NiSi and Ni/TaOx/Ta/TaOx/NiSi devices were fabricated, and the resistive switching (RS) behaviors were investigated. A 2 nm-thick Ta metal layer was deposited between two TaOx films to form a Ni/TaOx/Ta/TaOx/NiSi stack, which was analyzed using TEM. Based on a linear scale I–V curve and an R–V graph, both devices showed conventional bipolar conductive bridge random access memory (CBRAM) characteristics with formation/rupture of Ni conductive filaments (CFs). The Ta-embedded device showed lower forming/SET voltages and initial resistance due to the reduced effective thickness of TaOx films due to the inserted Ta metal layer. In addition, the Ta-embedded device exhibited improved endurance and resistance distribution due to suppression of the random formation of Ni CFs.

Improvement of thermal stability of nickel silicide film using NH3 plasma treatment

In this study, the effects of NH3 plasma pre-treatment on the characteristics of NiSi films were investigated. Nickel film was deposited on a Si(100) substrate by meal-organic chemical vapor deposition (MOCVD) using Ni(iPr-DAD)2 as a Ni precursor and NH3 gas as a reactant. Before the Ni deposition, silicon substrate was treated by NH3 plasma with various flow rates to adjust the amount of inserted hydrogen and nitrogen atoms. The Ni films showed a considerable low sheet resistance around 12 Ω/, irrespective of the NH3 plasma pre-treatment conditions. The sheet resistance of the all Ni films was decreased after annealing at 500 °C due to formation of a low resistive NiSi phase. NiSi films with a high flow rate of NH3 plasma pre-treatment exhibited a lower sheet resistance and smoother interface between NiSi and the Si substrate than the low flow rate of the NH3 plasma pre-treated NiSi films because lots of nitrogen atoms incorporated at grain boundary of NiSi which result in reduce total surface/interface energy of NiSi and enhancement interface characteristics.

Nonlinear and complementary resistive switching behaviors of Au/Ti/TaOx/TiN devices dependent on Ti thicknesses

The fabricated Au/Ti/TaOx/TiN devices demonstrate nonlinear behavior at a low resistance state and a complementary resistive switching (CRS) behavior that is dependent upon the thickness of the Ti insertion layer. The nonlinear behavior can be explained by the presence of an ultrathin TiOx layer that acts as a tunnel barrier. In addition, the CRS behavior can be understood in relation to the redistribution of oxygen vacancies between the Ti/TaOx top interfaces. A thicker Ti insertion layer forms a thicker TiOx layer at the Ti/TaOx interface, which can serve as another switching layer. The Au/Ti/TaOx/TiN devices in this study are fabricated with fully complementary metal-oxide-semiconductor-compatible materials and exhibit nonlinear behavior at a low resistance state and a CRS behavior that present possible solutions for the suppression of the sneak current in the crossbar arrays.

Stabilization of Ni conductive filaments using NH3 plasma treatment for electrochemical metallization memory

In this study, NH3 plasma treatment was utilized to enhance the resistive switching (RS) properties. Au/Ni/TaOx/NiSi and Au/Ni/NH3 plasma-treated TaOx/NiSi resistance RAM (RRAM) devices were fabricated and the resistive switching (RS) properties of these devices were subsequently investigated. Both RRAM devices exhibited conventional electrochemical metallization memory (ECM) behaviors. However, the NH3 plasma-treated samples exhibited improved resistance distribution compared with that of non-treated samples due to the remaining Ni conductive filaments (CF), even following a RESET process. Additionally, superior retention properties longer than 104 s were observed due to the formation of stable Ni CFs. The formation of a defect-minimized TaON layer, observed via X-ray photoelectron spectroscopy (XPS), could be the source of stability for the Ni CFs, resulting in improved device behavior for the NH3 plasma-treated samples.