Influence of oxygen vacancies in ALD HfO_2-x thin films on non-volatile resistive switching phenomena with a Ti/HfO_2-x/Pt structure

Sokolov, Andrey Sergeevich,Jeon, Yu-Rim,Kim, Sohyeon,Ku, Boncheol,Lim, Donghwan,Han, Hoonhee,Chae, Myeong Gyoon,Lee, Jaeho,Ha, Beom Gil,Choi, Changhwan Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.434 No.-

<P><B>Abstract</B></P> <P>We report a modulation of oxygen vacancies profile in atomic layer deposition (ALD) HfO<SUB>2-x</SUB> thin films by reducing oxidant pulse time (0.7 s–0.1 s) and study its effect on resistive switching behavior with a Ti/HfO<SUB>2-x</SUB>/Pt structure. Hf 4f spectra of x-ray photoelectron microscopy (XPS) and depth profile confirm varied oxygen vacancies profiles by shifts of binding energies of Hf 4f5/2 and Hf 4f7/2 main peaks and its according HfO<SUB>2-x</SUB> sub-oxides for each device. The ultraviolet photoelectron spectroscopy (UPS) confirms different electron affinity (χ) of HfO<SUB>2</SUB> and HfO<SUB>2-x</SUB> thin films, implying that barrier height at Ti/oxide interface is reduced. Current transport mechanism is dictated by Ohmic conduction in fully oxidized HfO<SUB>2</SUB> thin films - Device A (0.7 s) and by Trap Filled Space Charge Limited Conduction (TF-SCLC) in less oxidized HfO<SUB>2-x</SUB> thin films - Device B (0.3 s) and Device C (0.1 s). A switching mechanism related to the oxygen vacancies modulation in Ti/HfO<SUB>2-x</SUB>/Pt based resistive random access memory (RRAM) devices is used to explain carefully notified current transport mechanism variations from device-to-device. A proper endurance and long-time retention characteristics of the devices are also obtained.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oxygen vacancies in ALD HfO<SUB>x</SUB> thin film were modulated by varying oxidant pulse time. </LI> <LI> Resistive switching behaviors are governed by connection/disruption of filament via reduction/oxidation. </LI> <LI> Conduction mechanism clearly depends on amount of oxygen vacancies. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The voltage–current and spectral characteristics of thin layers of Ag2S quantum dots and their mixtures with plasmon nanoparticles

Gurchenko Vladimir Sergeevich,Mazinov Alim Seit-Ametovich,Tyutyunik Andrey Sergeevich,Grevtseva Irina Gennadievna,Smirnov Mikhail Sergeevich,Chevychelova Tamara Andreevna,Ovchinnikov Oleg Vladimirovic 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.6

The paper presents a study of the structural and electrophysical parameters of sandwich structures of the conductive electrode type—a flm of colloidal quantum dots of silver sulfde (QDs Ag2S/SiO2) and Au plasmon nanoparticles—the second conductive electrode. The methods of transmission electron microscopy (TEM), including high-resolution TEM, IR absorption spectroscopy, were used, and the current–voltage characteristics were analyzed. It is shown that Ag2S/SiO2 QD reveals a crystalline cross section of 1.6 nm in the monoclinic modifcation and an amorphous SiO2 shell with a thickness of about 1.6 nm, which approximately corresponds to one monolayer of the organic ligand (3-mercaptopropyl)-trimethoxysilane. It is shown that the Al-Ag2S/SiO2-ITO sandwich structure has a barrier-type CVC, determined by the Schottky barrier that appears at the boundary of the Ag2S QD flm and aluminum. The use of plasmon-exciton Ag2S/SiO2/Au in the formation of sandwich structures Al-Ag2S/SiO2/Au-ITO changes the CVC to linear, which apparently determines the ohmic type of conductivity and the absence of barriers in such a structure. It was found that, in contrast to the structure based on Ag2S/ SiO2 QDs, the Al-Ag2S/SiO2/Au-ITO structure has photosensitivity. It is concluded that decorating Ag2S/SiO2 QDs with Au nanoparticles increases the photosensitivity of sandwich structures.

Application of Economic Risk Measures for a Comparative Evaluation of Less and More Mature Nuclear Reactor Technologies

Andrianov Andrey Alexseevich,Andrianova Olga Nikolaena,Kuptsov Ilya Sergeevich,Svetlichny Leonid Igorevich,Utianskaya Tatyana Vladimirovna 한국방사성폐기물학회 2018 방사성폐기물학회지 Vol.16 No.4

Less mature nuclear reactor technologies are characterized by a greater uncertainty due to insufficient detailed design information, operational data, cost information, etc., but the expected performance characteristics of less mature options are usually more attractive in comparison with more mature ones. The greater uncertainty is, the higher economic risks associated with the project realization will be. Within a comparative evaluation of less and more mature nuclear reactor technologies, it is necessary to apply economic risk measures to balance judgments regarding the economic performance of less and more mature options. Assessments of any risk metrics involve calculating different characteristics of probability distributions of associated economic performance indicators and applying the Monte-Carlo method. This paper considers the applicability of statistical risk measures for different economic performance indicators within a trial case study on a comparative evaluation of less and more mature unspecified LWRs. The presented case study demonstrates the main trends associated with the incorporation of economic risk metrics into a comparative evaluation of less and more mature nuclear reactor technologies.

Multi-criteria Comparative Evaluation of Nuclear Energy Deployment Scenarios With Thermal and Fast Reactors

Andrianov Andrey Alexseevich,Andrianova Olga Nikolaena,Kuptsov Ilya Sergeevich,Svetlichny Leonid Igorevich,Utianskaya Tatyana Vladimirovna 한국방사성폐기물학회 2019 방사성폐기물학회지 Vol.17 No.1

The paper presents the results of a multi-criteria comparative evaluation of 12 feasible Russian nuclear energy deployment scenarios with thermal and fast reactors in a closed nuclear fuel cycle. The comparative evaluation was performed based on 6 performance indicators and 5 different MCDA methods (Simple Scoring Model, MAVT / MAUT, AHP, TOPSIS, PROMETHEE) in accordance with the recommendations elaborated by the IAEA/INPRO section. It is shown that the use of different MCDA methods to compare the nuclear energy deployment scenarios, despite some differences in the rankings, leads to well-coordinated and similar results. Taking into account the uncertainties in the weights within a multi-attribute model, it was possible to rank the scenarios in the absence of information regarding the relative importance of performance indicators and determine the preference probability for a certain nuclear energy deployment scenario. Based on the results of the uncertainty/sensitivity analysis and additional analysis of alternatives as well as the whole set of graphical and attribute data, it was possible to identify the most promising nuclear energy deployment scenario under the assumptions made.

Structural engineering of tantalum oxide based memristor and its electrical switching responses using rapid thermal annealing

Abbas, Yawar,Sokolov, Andrey Sergeevich,Jeon, Yu-Rim,Kim, Sohyeon,Ku, Boncheol,Choi, Changhwan Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.759 No.-

<P><B>Abstract</B></P> <P>We have demonstrated the co-existence of reliable analog and digital switching characteristics with tantalum oxide based memristor by appropriate rapid thermal annealing (RTA). The device without RTA exhibits a digital SET and multilevel RESET for positive and negative sweeps, respectively. On the other hands, the device shows only analog switching characteristics such that current level increases and decreases gradually for successive positive and negative voltage sweeps, respectively, before any electroforming process with the RTA in the nitrogen ambient at the crystalline temperature of tantalum oxide which is 700 °C for 60 s. Once electroforming process is done, the device exhibits a reliable digital switching with SET at positive sweep and RESET at negative sweep voltages. In the analog state of the device we successfully emulate the synaptic characteristic of the device like spike-rate dependent plasticity (SRDP), pulse-paired facilitation (PPF) and post-tetanic potentiation (PTP). Finally, the Hermann Ebbinghaus forgetting curve is obtained from these devices. The conversion of the device from the digital SET and multilevel RESET to analogue switching is attributed to structural transition of amorphous tantalum oxide to polycrystalline tantalum oxide, different defect density and interface variation in the device.</P> <P><B>Highlights</B></P> <P> <UL> <LI> N<SUB>2</SUB> at 700 °C rapid thermal annealing (RTA) was carried out on the sputtered Ta<SUB>2</SUB>O<SUB>5</SUB>. </LI> <LI> RTA makes structural change from amorphous to polycrystalline state leading to pseudo-switching characteristics. </LI> <LI> Gradual change of current and conductance with RTA processed Ta<SUB>2</SUB>O<SUB>5-x</SUB> thin film is favorable for synaptic behaviors. </LI> </UL> </P>

The Effects of Etch Chemicals on the Electrical Properties of Metal-Oxide-Semiconductor (MOS) Device with Plasma Enhanced Atomic Layer Deposited (PEALD) TiN Metal Electrode

김영진,한훈희,임동환,손석기,Andrey Sergeevich,최창환 한국표면공학회 2015 한국표면공학회 학술발표회 초록집 Vol.2015 No.11

The Post Annealing to Control the Number of Layers of 2D MoS₂ and SnS₂

Choi, Moonsuk,Lim, Donghwan,Sergeevich, Andrey Sokolov,Son, Seok Ki,Kim, Young Jin,Han, Hoon Hee,Choi, Changhwan American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11

<P>We have demonstrated that post annealing could control the layer thickness of 2D MoS2 and SnS2 films transferred on a SiO2/Si substrate by varying the annealing temperature and time. Atomic force microscopy and Raman spectroscopy characterizations revealed that higher annealing temperature and longer treatment time led to thinner films, lower residues and fewer impurities on the surface of 2D materials. In addition, a higher possibility to attain few-layers on both 2D films was achieved using post annealing. The multiple layers of pristine films having the thickness over 15 nm were reduced down to bi-layers after annealing. We observed that the moderate annealing temperature of 450 degrees C on led to effective layer-thinning compared to the films annealed at 340 degrees C. The post annealing at 450 degrees C produced very smooth few-layers (<= 4 nm thickness, >1 mu m size) of 2D MoS2 and SnS2. However, the 2D films decomposed or disappeared at temperature greater than 650 degrees C. In addition, process time also affected the number of layers and the sweet spot turned out to be 2 to 3 hours in our experiment.</P>

Interface engineering of ALD HfO₂-based RRAM with Ar plasma treatment for reliable and uniform switching behaviors

Ku, Boncheol,Abbas, Yawar,Sokolov, Andrey Sergeevich,Choi, Changhwan Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.735 No.-

<P><B>Abstract</B></P> <P>The improved resistive switching (RS) characteristics of Pt/HfO<SUB>2</SUB>/Ti structured RRAM are demonstrated by engineering interface with argon (Ar) plasma irradiation. The Ar plasma treatment was intentionally carried out on the surface of atomic layer deposited (ALD) HfO<SUB>2</SUB> thin films to modulate the conducting filament size affecting RS behaviors. Compared to ALD HfO<SUB>2</SUB> RRAM without Ar plasma treatment, the Ar plasma treatment on the surface of ALD HfO<SUB>2</SUB> thin film leads to forming-free process, faster switching speed, tighter low resistance state (LRS) and high resistance state (HRS) current distribution, smaller variations of SET voltage and RESET voltage, and enhanced retention/endurance characteristics under HRS. These improvements are believed to be the generation of favorably modulated interface oxide layer between HfO<SUB>2</SUB> and Ti. In addition, current conduction mechanism is dominated by ohmic behavior in LRS while ohmic, space charge limited conduction (SCLC), and trap filled SCLC are observed at HRS with different field regions. The Ar plasma irradiation can be an easy and facile way to achieve the reliable and uniform RRAM characteristics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Argon plasma irradiation was conducted on the ALD HfO<SUB>2</SUB>. </LI> <LI> Ar plasma treatment produces faster switching, uniform and reliable resistive switching behaviors. </LI> <LI> Improved reliability depends on interface reaction at Ti/HfO<SUB>2</SUB>. </LI> </UL> </P>

Suppressed charge trapping characteristics of (NH₄)₂S_x passivated GaN MOS device with atomic layer deposited HfAlO_x gate dielectric

Han, Hoon Hee,Lim, Donghwan,Sergeevich, Andrey Sokolov,Jeon, Yu-Rim,Lee, Jae Ho,Son, Seok Ki,Choi, Changhwan ELSEVIER 2017 MICROELECTRONIC ENGINEERING Vol.178 No.-

<P><B>Abstract</B></P> <P>The charge trapping behaviors of ammonium poly-sulfide, (NH<SUB>4</SUB>)<SUB>2</SUB>S<SUB>x</SUB>, passivated GaN MOS device with atomic layer deposited HfAlO<SUB>x</SUB> gate dielectric and DC-sputtered TiN gate electrode are investigated and compared with those of GaN MOS device with hydrochloric acid, HCl, passivation. Compared to non-S passivated device, higher peak capacitance (>20% @1MHz), reduced frequency dispersion (~30% ↓), lower hysteresis (~34% ↓), higher breakdown (1.3×), lower stress induced flat-band voltage (V<SUB>FB</SUB>) shift (~30% ↓), and lower interface state density (D<SUB>it</SUB>), stronger immunity D<SUB>it</SUB> generation (ΔD<SUB>it</SUB>) against gate bias voltage are attained with S-passivated device. Further improved characteristics are observed with post deposition annealing at 400°C for 10min. These behaviors are mainly attributed to higher bond strength energy of SO and SN than those of ClO and ClN bonds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sulfur passivation induces higher C<SUB>ox</SUB>, reduced frequency dispersion, lower hysteresis, higher V<SUB>BD</SUB>, and lower D<SUB>it</SUB>. </LI> <LI> Stress induced ΔV<SUB>FB</SUB> and ΔD<SUB>it</SUB> are significantly suppressed with sulfur-passivation. </LI> <LI> Further improvement is still observed after post annealing at 400 <SUP>o</SUP>C. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The effects of process temperature on the work function modulation of ALD HfO₂ MOS device with plasma enhanced ALD TiN metal gate using TDMAT precursor

Kim, Young Jin,Lim, Donghwan,Han, Hoon Hee,Sergeevich, Andrey Sokolov,Jeon, Yu-Rim,Lee, Jae Ho,Son, Seok Ki,Choi, Changhwan Elsevier 2017 Microelectronic engineering Vol.178 No.-

<P><B>Abstract</B></P> <P>We have investigated the effects of metal gate process temperature on the effective work function (W<SUB>eff</SUB>) of MOS devices with all ALD HfO<SUB>2</SUB>/TiN gate stack and its correlation with grain size of PEALD TiN metal gate is presented with other electrical characteristics. Ti precursor and reactant were used with tetrakis-dimethyl-amino titanium (TDMAT) and H<SUB>2</SUB>/N<SUB>2</SUB> mixture for TiN while tetrakis-ethylmethyl-amino hafnium (TEMA-Hf) and H<SUB>2</SUB>O were used for HfO<SUB>2</SUB>. With increasing TiN deposition temperature, the W<SUB>eff</SUB> of TiN electrode is positively shifted up to ~200meV while EOT is kept as 1.2nm. These findings could be attributed to the combining effects from crystal structure change (i.e., increased grain size) and different chemical composition. Unlike PVD TiN system, in ALD TiN system, higher V<SUB>FB</SUB> is observed with increasing Ti ratio in the film, ascribed to the small amount of carbon residue (6–9at%) within the TDMAT precursor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> HfO<SUB>2</SUB>-MOS device with ALD TiN using TDMAT precursor and H<SUB>2</SUB>/N<SUB>2</SUB> mixture shows higher V<SUB>FB</SUB> by 200mV with 1.2nm EOT. </LI> <LI> TDMAT ALD TiN shows higher V<SUB>FB</SUB> with increasing [Ti]/[Ti+N<SUB>2</SUB>] ratio due to the combining effects of carbon residue from the precursor and increased grain size. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>