Silicon oxide and silicon nitride are the two key dielectrics used in modern silicon devices. The memory properties of SiOx- and SiNx-based memristors obtained by plasma-enhanced chemical vapor deposition, pyrolysis, and high-frequency reactive sputtering are reviewed. The nitrides obtained by high-frequency reactive sputtering have the best memory properties: a memory window of 102, a memristor endurance of up to 109 cycles at the same memory window, and a memristor retention of up to 105 s at the same memory window.

Silicon oxide and silicon nitride are the two key dielectrics used in modern silicon devices. The memory properties of SiO x - and SiN x -based memristors obtained by plasma-enhanced chemical vapor deposition, pyrolysis, and high-frequency reactive sputtering are reviewed. The nitrides obtained by high-frequency reactive sputtering have the best memory properties: a memory window of 10 2 , a memristor endurance of up to 10 9 cycles at the same memory window, and a memristor retention of up to 10 5 s at the same memory window.

In this study we investigated the influence of kind of metal on memristor effect in metal-insulator-semiconductor (MIS) structure. First, different metals have different work functions. This parameter can affect the flow of current through the MIS structure. Secondly, different metals have different binding energies of atoms. In this case, the bond energy consists of the energy of the metallic bond and the energy of the covalent bond. If we consider the model of the conductivity switching effect, in which a metal filament appears, this can affect the probability of its appearance. Thirdly, different metals and different methods of their deposition have different technological compatibility and ease of use. Two types of dielectrics were used for the experiments - silicon oxide and silicon nitride. Thin dielectric films were deposited on ptype monocrystalline silicon wafers. It was found that the best results among the tested metals were obtained using nickel deposited by electron beam evaporation. Copper proved to be poorly compatible with silicon oxide, since it easily diffuses into it and silicon. The other metals demonstrated the possibility of the appearance of the memristor effect. However, the yield was generally less than when nickel was used.

Рассматриваются перспективные направления развития памяти ReRAM. Нитрид кремния является перспективным резистивным переключающим слоем для мемристоров; проведено экспериментальное исследование изготовленных МНОП-структур (мемристоров) и переноса заряда в них в диапазоне температур 298-450 K.

Metal-nitride-oxide-silicon structures that exhibit memristor properties were obtained using the low-pressure chemical vapor deposition at 700° C. The fabricated metal-nitride-oxide-silicon memristor structure does not require a forming procedure. In addition, the metal-nitride-oxide-silicon memristor has a memory window of about 3 orders of magnitude. In our work, the charge transport of high and low resistive states in a metal-nitride-oxide-silicon memristor is analyzed with two contact-limited models and six bulk-limited charge transport models. It is established that the Schottky effect model, thermally assisted tunneling model, Frenkel model of Coulomb traps ionization, Hill-Adachi model of overlapping Coulomb traps, Shklovskii-Efros percolation model, Makram-Ebeid and Lannoo model of multiphonon isolated traps ionization and the Nasyrov-Gritsenko model of phonon-assisted tunneling between traps, quantitatively, do not describe the charge transport of metal-nitride-oxide-silicon memristor. We found that the main charge transport mechanism in the metal-nitride-oxide-silicon memristor in a high resistive state is the model of space-charge-limited current with traps. In a low resistive state, the charge transport mechanism is described by the space-charge-limited current model with filled traps.

Издательство Новые технологии выпускает журналы: Инфомационные технологии; Мехатроника, Автоматизация, Управление; Горные машины и автоматика; Микросистемная техника; Безопасность жизнедеятельности. Все журналы входят в перечень изданий, рекомендованных ВАК

Рассматриваются перспективные направления развития памяти ReRAM. Нитрид кремния является перспективным резистивным переключающим слоем для мемристоров; проведено экспериментальное исследование изготовленных МНОП-структур (мемристоров) и переноса заряда в них в диапазоне температур 298-450 K.

The discovery of ferroelectric properties in hafnium oxide has brought back the interest in the ferroelectric non-volatile memory as a possible alternative for low power consumption electronic memories. As far as real hafnium oxide-based materials have defects like oxygen vacancies, their presence might affect the ferroelectric properties due to oxygen atom movements during repolarization processes. In this work, the transport experiments are combined with the modeling to study evolution of the oxygen vacancy concentration during the endurance and to determine the optimal defect density for a higher residual polarization in lanthanum-doped hafnium oxide.

Silicon oxide and silicon nitride are two key dielectrics in silicon devices. The advantage of Si3N4 over other dielectrics is that silicon nitride is compatible with silicon technology. It is required to study in detail the charge transport mechanism in a Si3N4-based memristor to further improve the cell element and to create a matrix of these elements. Despite many research activities carried out, the charge transport mechanism in Si3N4-based memristors is still unclear. Metal–nitride–oxide–silicon structures that exhibit memristor properties were obtained using low-pressure chemical vapor deposition at 700 °C. The fabricated metal–nitride–oxide–silicon memristor structure does not require a forming procedure. In addition, the metal–nitride–oxide–silicon memristor has a memory window of about five orders of magnitude. We found that the main charge transport mechanism in the metal–nitride–oxide–silicon memristor in a high resistive state is the model of space-charge-limited current with traps. In a low resistive state, the charge transport mechanism is described by the space-charge-limited current model with filled traps. Trap parameters were determined in the Si3N4-based memristor in the high resistive state.

Мемристорная резистивная память с произвольным доступом (ReRAM, Resistive Random Access Memory) вместе с памятью с изменением фазового состояния (PCM, Phase Change Memory), магниторезистивной памятью с произвольным доступом (MRAM, Magnetoresistive Random Access Memory), сегнетоэлектрической памятью (FeRAM, Ferroelectric Memories) [4] являются востребованными видами энергонезависимой памяти на новых альтернативных принципах. Нитрид кремния является перспективным резистивным переключающим слоем для мемристоров. В данной работе проведено экспериментальное исследование эффекта переключения и переноса заряда в мемристоре на основе нитрида кремния для разных типов металла (Ni, Co, Cu) верхнего электрода.

Main characteristics of ReRAM cells based on hafnium oxide were studied. A significant variation of these characteristics was observed from both cycle-to-cycle and cell-to-cell. Specialized methods should be applied for improving the cells characteristics reproducibility. The results of the experimental investigation of ReRAM 1T-1R cells are presented in this work.

For the memory element based on a Si/HfO2/multilayer graphene/SiO2/Si structure, the write/erase and charge storage characteristics are evaluated. A sufficiently large work function of electrons in multilayer graphene (MLG) makes it possible to increase the time of storing the charge injected into it. Using MLG in flash memory devices allows one to increase the speed and/or reduce the voltage of reprogramming such devices.

The discovery of ferroelectricity in hafnium oxide has revived the interest in ferroelectric memories as a viable option for low power non-volatile memories. However, due to the high coercive field of ferroelectric hafnium oxide, instabilities in the field cycling process are commonly observed and explained by the defect movement, defect generation and field induced phase transitions. In this work, the optical and transport experiments are combined with ab-initio simulations and transport modeling to validate that the defects which act as charge traps in ferroelectric active layers are oxygen vacancies. A new oxygen vacancy generation leads to a fast growth of leakage currents and a consequent degradation of the ferroelectric response in Hf0.5Zr0.5O2 films. Two possible pathways of the Hf0.5Zr0.5O2 ferroelectric property degradation are discussed.

Before 2011, hafnium oxide was considered as a paraelectric material until the observation of the ferroelectric effect in doped thin HfO2 films after high­temperature annealing [T.S. Böscke et al., Appl. Phys. Lett. 99, 102903 (2011); S. Mueller et al., Adv. Function. Mater. 22, 2412 (2012)]. Dopping by lantanum leads to the largest remanent polarization of HfO2 films [U. Schroeder et al., Jpn. J. Appl. Phys. 53, 08LE02 (2014)]. Ferroelectricity in these materials is associated with the ability to stabilize noncentrosymmetric orthorhombic phase Pbc21 [J. Müller et al., Nano Lett. 12, 4318 (2012)]. It should be noted that hafnia-­based materials have a number of advantages over conventional ferroelectric regarding compatibility with the technological processes used in microelectronics, and they have already demonstrated their ability to provide a very high density of elements. Considering the advantages of ferroelectric random access memory (FRAM) as non­volatile, high­speed performance, high number of switching cycles, the discovery of ferroelectric effect in these materials gave an impetus for the development of the universal memory concept which may lead to a significant breakthrough in the development of memory devices [M.H. Park et al., Adv. Mater. 27, 1811 (2015)]. An unsolved problem in the way of development of FRAM­-based memory are is a reason of memory window of FRAM instability during set/reset cycling, i.e. endurance. One of the possible reasons for these effects is the presence of defects in HfO2:La thin films. The purpose of the present work is to study the evolution of charge trap density in ferroelectric HfO2:La after set/reset cycling. Transport measurements were performed for TiN/HfO2:La/TiN structures. Test structures were fabricated with the atomic layer deposition (ALD) technique. A 10-­nm­-thick TiN layer was deposited on the oxidized Si (100) substrate. Then the 10­-nm­-thickHfO2:La films were deposited at 235°C from TEMAH (heated to 100°С) and La(iPrCp)3 + (heated to 170°С) precursors using O2+Ar plasma. Laser ellipsometry and Rutherford backscattering spectroscopy confirmed the thickness and stoichiometry of HfO2:La films. TiN top layer (10 nm thick) was deposited using the ALD technique. For transport measurements, round (area is 7.854×103 μm2) electrodes were formed by the photolithography process. The presence of ferroelectric properties ofHfO2:La films is confirmed by observing the characteristic hysteresis on the polarization­voltage (P-­V) plate for TiN/HfO2:La/TiN structures. The P-­V and current-­voltage (I-­V) dependences were measured by the standard PUND technique at room temperature. The first “Positive” and the third “Negative” impulses aligned dipoles in the ferroelectric films (set and reset, respectively) and they were used to measure polarization, while, during the second “Up” and the forth “Down” impulses, the leakage currents were measured. The leakage currents were extracted from the current responses by removing displacement currents. The trap density was extracted from the leakage currents within phonon-assisted tunnelling between traps model [K. Nasyrov et al., J. Appl. Phys. 109 097705 (2011)].

The properties and applications of materials with non-volatile memory based on HfO2 were briefly considered. In addition, an overview of the obtained results was given. On the basis of these results, the possibility of use of the structures TiN/ Hf0.5Zr0.5O2/ TiN/ SiO2/ Si and TiN/ HfxAl1-xOy/ Pt/ SiO2/ Si for the non-volatile memory of FeRAM and ReRAM types obtained by the atomic-layer deposition was shown. In addition, the scalability of these elements and opportunity to create promising submicron integrated circuits for ferroelectric and resistive memory were demonstrated.

В работе будут представлены экспериментальные данные, демонстрирующие наличие проблемы с повторяемостью и воспроизводимостью электрофизических характеристик ячеек ReRAM. Также будет представлен обзор методов улучшения стабильности характеристик, произведен анализ их применимости к имеющимся образцам памяти. Будут предложены различные схемотехниченские и структурные изменения ячеек для повышения стабильности характеристик. Ключевые слова: энергонезависимая память; резистивная память; ReRAM; оксид гафния. This paper presents experimental data demonstrating the problem of the repeatability and reproducibility of electrophysical characteristics of ReRAM cells. An overview of methods for improving the stability of the characteristics will also be presented, and an analysis will be made of their applicability to the available memory samples. Some circuit and structural approaches to improving the stability of characteristics will be proposed.