High-temperature Retention Research Articles

Reliable restriction of conductive filament in graphene oxide based RRAM devices enabled by a locally graphitized amorphous carbon layer

In this work, a locally graphitized amorphous carbon (LGAC) film was successfully prepared through catalytic graphitization process. Taking advantage of its locally conductive characteristic, we demonstrate an effective and repeatable method to improve the reliability of graphene oxide based RRAM devices. The above method is responsible for a fluctuation decrease of high/low resistance states (HRS/LRS) and SET/RESET voltage from 139.6%/76.9% to 31.4%/7.5% and 50.5%/47.7% to 7.7%/6.9%, respectively. The migration of oxygen ions during both the SET and RESET processes were well restrained within the narrow conductive areas thanks to the LGAC insertion layer. In addition, the optimized memory devices also showed pretty good cycling endurance and high temperature retention characteristics. This approach may be promising for developing reliable graphene oxide based RRAM devices.

Development of 2T-SONOS Cell Using a Contamination-Free Process Integration for a Highly Reliable Code Storage eNVM

We report a low-cost and highly reliable 2T-SONOS embedded nonvolatile memory (eNVM) using a novel contamination-free process integration. The proposed 2T-SONOS cell is fabricated on a 90-nm high-voltage CMOS process for a touch screen controller embedded display driver IC applications. For a code storage purpose, eNVM with moderate memory density, simple integration, platform logic and process compatibility, and sufficient retention lifetime are critically important. Thanks to the contamination-free charge trap layer and optimized junction, we have achieved enough retention lifetime without using any special materials for the charge trap layer. The 120 °C data retention lifetime of over 10 years is verified using 77 $\times \,\,{3}$ samples of 32-kB memory density intellectual property. By correlating high-temperature retention bake results with technology computer-aided design simulations, we can understand long-term charge redistribution behavior inside trap nitride, which is significantly different from floating gate type NVM.

Protein Nanosphere Anchors for Stabilizing Hydroxylated Polymer Chains in Organic Memory Transistors with Outstanding Retention Characteristics

AbstractIt is demonstrated that a heme protein (cytochrome c [Cyt c]) nanosphere plays a strong anchoring role in binding hydroxyl groups of poly(vinyl alcohol) (PVA) leading to outstanding high‐temperature (100 °C) retention characteristics of transistor‐type organic memory devices (TOMDs). The PVA:Cyt c layers are spin‐coated on indium tin oxide gate electrodes from aqueous solutions with various Cyt c contents up to 50 wt%, followed by the formation of poly(3‐hexylthiophene) (P3HT) channel layers and nickel/aluminum top source/drain electrodes in TOMDs. Results show that adding 20 wt% Cyt c improves the drain current of devices in the presence of good hysteresis characteristics, which are maintained even after exposure to high‐temperature conditions (100 °C). The excellent conservation of hysteresis characteristics is attributed to the formation of Cyt c nanospheres that act as an anchoring point to retard the relaxation of PVA chains via specific interactions (hydrogen bonding etc.) between amino groups in the Cyt c nanosphere surfaces and hydroxyl groups in the PVA chains. The optimized PVA:Cyt c layers (20 wt% Cyt c, thermal treatment at 100 °C) deliver excellent retention characteristics to TOMDs, whereas no memory function is measured in the case of the pristine PVA layers at 100 °C.

Trees – The Perpetual Carbon Traders

The Carbon trading is one of the fastest growing financial markets in the world. It is the most visible result of early regulatory efforts to mitigate climate change, and grew out of the Kyoto Protocol, which was adopted in 1997. The protocol requires that developed countries will achieve greenhouse gas emission reductions of at least 5% against baseline levels of 1990. To help countries achieve that goal it established the Clean Development Mechanism (CDM), which promotes sustainable development in developing countries while spurring cost-effective reductions in greenhouse gas emissions in the more polluting developed countries. India offers a large potential for CDM because of its inherent dependence on fossil fuels for development. So countries with relatively low abatement and transaction costs like India are a major attraction for CDM projects. Forestry activities and land use changes contribute about 22% carbon emission in the tropics. On the other hand trees also have the ability to remove equal amount of carbon dioxide from the atmosphere through photosynthetic activity. Trees play a key role in carbon trading in the tropics and the forests are often called as ‘carbon sinks’. According to one estimate about 1000 G. t. of Carbon is stored in the forests of the world and 50 per cent of the dry weight of a tree is carbon. However the denudation of the forests at a faster rate and illicit felling of trees for various usages have indirectly disturbed the carbon trading and there by leading to accumulation of CO2 in the atmosphere which in turn aids global warming as CO2 is one of the dangerous Green House Gases (GHGs), which play a key role in retention of high temperature on the earth surface.

Characteristics of AlGaN/GaN high electron mobility transistor temperature sensor

Semiconductor temperature sensors have been widely used in medical, industrial, aviation and civil fields due to their advantages such as high sensitivity, small size, low power consumption and strong anti-interference ability. However, most Si-based temperature sensors are not suitable for the application in high-temperature environments. The new AlGaN/GaN heterojunction material not only has a wide band gap, but also has a high two-dimensional electron gas concentration and carrier mobility. Therefore, the device made with it not only has good electrical properties, but also can be applied in ultra-high environments. In this paper, a temperature sensor based on gateless AlGaN/GaN high electron mobility transistor structure was fabricated and its temperature-dependent electrical properties were characterized. The temperature dependence of current-voltage characteristics of the device were tested from 50 to 400 °C. The sensitivity of the device was studied as a function of the channel aspect ratio of the device. The stability of electrical properties was characterized after heating in air and nitrogen at 300—500 °C for 1 hour. The theoretical and experimental results show that as the aspect ratio of the device increases, the sensitivity of the device increases. At a fixed current of 0.01 A, the average sensitivity of the device voltage with temperature changes is 44.5 mV/°C. Meanwhile, the good high temperature retention stability is shown during stability experiments.

Electrical insulation improvements of ceramic coating for high temperature sensors embedded on aeroengine turbine blade

Intelligent aeroengine requires high temperature sensors, especially MEMS thin film sensors directly fabricated on the surface of turbine blade. For this purpose, an electrical insulation layer is needed on blade substrate metals. However, the electrical insulation of ceramic materials will degrade at high temperatures, thereby affecting the characteristics of the sensor. In this paper, ceramic material of YSZ thermal barrier coating (TBC) formulation was modified by adding a certain amount of Al2O3 to improve its insulation at high temperatures. Micro processing was carried out on the surface of the TBC, including the fabrication of platinum-point thermocouples and thermal resistor on TBC surface, and high temperature electrical insulation properties of the modified TBC were studied. Results show that electrical insulation can be improved several orders of magnitude with adding Al2O3 which meets the requirement to build reliable thin film sensors on the top of TBC surface coated on turbine blade metals. Several verification experiments were carried out to ensure the working ability of TBC layer, including robustness test, thermal shock test and high temperature retention test.

Nano‐Graphite Clusters Regulation for Reliability Improvement of Amorphous Carbon‐Based Resistive Random Access Memory

Herein, the influence of nano‐graphite clusters on amorphous carbon‐based memories reliability is studied in detail. The size of nano‐graphite clusters is effectively controlled through vacuum annealing process, which is experimentally verified by Raman spectra. Taking advantage of the local electric‐field enhancement around the nano‐graphite clusters, the relative fluctuation of high‐resistance state/low‐resistance state (HRS/LRS) and SET/RESET voltage reduce from 66.5%/41.2% to 25.3%/19.7% and 43.2%/21.4% to 18.8%/15.4%, respectively. In addition, highly reliable write‐once‐read‐many (WORM) memories with excellent anti‐interference and high temperature (300 °C) retention capacity are also prepared thanks to the electrical modulating characteristic of graphite clusters to amorphous carbon (a‐C) film.

Investigation on greenhouse gas emissions and compost dynamics during in-vessel co-composting of septage and mixed organic wastes

Greenhouse gas emission during composting process is inevitable, although it relies on natural degradation. A good balance on carbon-to-nitrogen (C/N) ratio as well as the aeration mode could significantly control the emissions. The C/N ratio can be adjusted using optimal feedstock composition. The aeration can be done using passive and active modes. In the present study, greenhouse gas emissions during in-vessel co-composting of septage and organic waste with active and passive modes of aeration were investigated. This fills the gap in implementing suitable septage treatment practice. Retention of high temperature (> 55 °C) for prolonged period ensured the compost hygienization. The active aeration system showed significantly lower greenhouse gas emission compared to that of passive system. The contribution of CH4 and N2O to the total greenhouse gas was estimated to be 2.5% and 7.4% in the passive and 0.9% and 3.8% in the active aeration modes while > 90% was CO2. The resulted compost maturity was confirmed by seed germination index (> 80%) and NO3−/NH4+ index (> 6.25). Our study highlight that in-vessel co-composting with active aeration is a suitable option to convert waste to a nutrient-rich fertilizer in a shorter period compared to other septage treatment options.

A comparative study on the cesium retention ability up to 1750 °C in Cs–Zr–Si–O, Cs–Al–Si–O, and Cs–Si–O

Abstract As cesium-trapping agents in an accident-tolerant fuel (ATF) that reduces fission gas release (FGR), Al–Si–O and Zr–Si–O (resulting in Cs–Al–Si–O and Cs–Zr–Si–O) are considered promising due to their good cesium retention ability up to high temperatures. However, in previous research, there is a lack of experimental data to compare them and determine which material is superior. In this study, the cesium retention ability of these materials was assessed by observing their weight loss behaviors up to 1750 °C. Other cesium compounds, such as pollucite (CsAlSi2O6) and Cs–Si–O possibly formed in the real fuel environment were also compared. As a result, Cs–Al–Si–O (CsAlSiO4) exhibited the most favorable result. It released cesium at higher temperatures and showed lower loss rate: only 2.36% of captured cesium was released at 1750 °C when sufficiently homogenized at 1050 °C. The real nuclear fuel environment in the light water reactor (LWR) was taken into account for the interpretation of comparative results, demonstrating that Al–Si–O is the most advantageous trapping agent in terms of high-temperature cesium retention ability.

Synthesis and thermal stability of a novel acetylene end-capped silicon-containing polyimide coupling agent with a silane pendant group

In this study, a novel heat-resistant polyimide macromolecular coupling agent (PSI-C) was designed and synthesized. Silicon-containing diamine was one of the monomers used to increase the solubility of the polyimide, and m-aminophenylacetylene was the end-capping reagent that copolymerized with the resin matrix. A silane coupling group was introduced into the side chain to match the reinforced fiber. Thermogravimetric analysis revealed that the 5% thermal decomposition temperature ( T d5) of the cured PSI-C could reach 454°C and the residual rate at 800°C was 53%. Thermal pyrolysis of the vaporized resin showed that the heat-resistant functional group was still detectable at 550°C. The thermal stability of the alkynyl-terminated silicon-containing polyimide silane coupling agent was higher than those of conventional silane coupling agents. The curing process of the composite system was not affected when adding the coupling agent PSI-C to the quartz fiber/alkynyl resin composite. The interlaminar shear strength and bending strength of the composite were increased by 55% and 61%, respectively, at room temperature. The high-temperature retention rate at 500°C reached 58% and 63%.

Enhancing the Performance of Phase Change Memory for Embedded Applications

Focusing on meeting the requirements for embedded applications of faster switching and sensing, lower‐power consumption, higher reliability, longer cycling endurance, and higher temperature retention, a lot of progress in the phase change memory (PCM) field has been made, including materials improvement, process optimization, new circuits design, and better operation algorithms. Finally, a 128 MB embedded PCM chip has been demonstrated in 40 nm node. Using carbon‐doped Ge2Sb2Te5 phase change material and 3 nm thick heating bottom electrode contact (BEC) with nitride coating, a resistance ratio of more than two orders of magnitude has been achieved in Reset and Set states. Combined with the parasitic matched sensing circuit, optimized ramp‐down SET pulses, adaptive pre‐read and write‐verify methods, and automatic configure and test procedures, the chip exhibits excellent data retention and endurance characteristics with minimum program time of 200 ns, and the Reset/Set resistance ratio becomes even larger after 260 °C soldering test. The estimated data retention time is 10 years at 128 °C, and in a 128 MB full integrated chip the endurance over 109 cycles is achieved. It is confirmed that this PCM technology is suitable for embedded applications, especially for those with crucial requirements of high access speed, high thermal stability, and cycling endurance.

An atomic switch using oxygenated amorphous carbon as solid electrolyte

Atomic switches based on carbon films as electrolyte have received great attention due to the many advantages of carbon, but their low high-resistance state and poor thermal stability of the device have greatly limited their further development. Here, we have constructed an atomic switch in which we use an oxygenated amorphous carbon (a-COx) film as a solid electrolyte through introducing O2 gas during the sputtering of a graphite target. The reversible and steady resistive switching effect with a resistance ratio over two orders of magnitude was achieved. While the sputtered pure C film has a low resistivity, which is not suitable for an atomic switch, the resistance of a-COx increases substantially with the partial pressure of O2. More importantly, we found that the higher the partial pressure of O2, the better the high temperature retention. In combination with the two-step reset process in which the heat and electric fields respectively act and mutable forming voltage with temperature, the achieved high temperature retention for more oxidized carbon films is most likely due to the more reduction of structural defects caused by the greater addition of oxygen during the deposition process and the chemical inertness of a-COx.

Structural and electrochemical characteristics of Al2O3-modified LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a potential cathode material for lithium-ion batteries with outstanding energy density and power density. Here, we document a facile approach to prepare Al2O3-modified LNMO cathode materials. The Al2O3-modified LNMO materials were synthesized via a one-step solid-state reaction and then modified with Al2O3 via a wet chemical technique. The impacts of Al2O3 modification on the structure and electrochemical properties of LNMO materials were examined by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, charge-discharge tests, cyclic voltammetry measurements, electrochemical impedance spectroscopy, and aging tests. Throughout the modification process, several Al3+ were noted to substitute for Ni2+, resulting in a decrease of Mn4+ to Mn3+; this increased the electronic conductivity and lowered the electrochemical polarization of the LNMO material. An amorphous Al2O3 coating layer developed on the surface of the LNMO particles in the modification, and this could alleviate the strike of HF caused by electrolyte decomposition as well as the development of a solid electrolyte interphase. Thus, the 0.5 wt% Al2O3-modified LNMO material had decreased Rsf and Rct and greater DLi values with a rate capability and cycling stability better than LNMO. The rate capability was 105.6 and 83.3 mAh g–1 at high C rates of 5 C and 7 C, as opposed to 83.3 and 54.9 mAh g–1, respectively; the room temperature (25 °C) capacity retention was 92.6% at 1 C after 200 cycles, as opposed to 87.0%. The high-temperature (55 °C) capacity retention was 90.9% at 1 C rate after 200 cycles as opposed to 86.5%. Thus, this is an easy and feasible method to improve the electrochemical performance of LNMO cathode materials for industrialization.

High Endurance Ferroelectric Hafnium Oxide-Based FeFET Memory Without Retention Penalty

We report the integration of a ferroelectric (FE) silicon-doped hafnium oxide material in ferroelectric field-effect transistor (FeFET) devices fabricated with an optimized interfacial layer in a gate-first scheme. The effect of increasing the permittivity (k) value of the interface layer on the performance of the metal–ferroelectric–insulator–semiconductor (MFIS)-FE-HfO2 FeFET is studied in terms of its switching characteristics, endurance, and retention. In contrast to the previous work, the FE Si:HfO2-integrated FeFET devices show a low-power operation capability as well as an improved endurance characteristics without jeopardizing high-temperature retention. The utilization of an optimized SiON interface layer for MFIS-HfO2 FeFET stack is discussed, and the improvements are outlined with reference to a standard low-k SiO2 interface.

Al-Sb-Ge phase change material: A candidate for multilevel data storage with high-data retention and fast speed

The phase change memory with Al-Sb-Ge alloy is investigated for the feasibility of embedded system and the potential possibility of multilevel data storage. The Al15Sb53Ge32 compound has a high crystallization temperature (333 °C) and outstanding data retention ability (260 °C). Ge atoms inhibit crystal growth to enhance thermal stability and Al15Sb53Ge32 contains sequential crystallization of Sb-rich and Ge regions in two-step crystallization process. Remarkably, the device presents a fast speed of 50 ns and endurance up to 2.3 × 104 cycles. At the same time, a reliable tripe-level resistance state of the phase change memory cell is observed.

Low leakage current resistive memory based on Bi1.10 (Fe0.95Mn0.05) O3 films

The bipolar resistance switching characteristics were confirmed in a resistive memory device with an Ag/Bi1.10(Fe0.95Mn0.05)O3/SRO/Pt/TiO2/SiO2/Si(100) structure, in which the limiting current was 1 mA. In comparison with BiFeO3—based memory, it was found that doping with Mn effectively reduced the leakage current of the device and thus improved the device endurance (200 cycles-1000 cycles). The high-temperature retention test demonstrated that the device could be used for 10 years without losing data. Through x-ray photoelectron spectroscopy analysis of Bi1.10(Fe0.95Mn0.05)O3 thin film elements, it was inferred that both the oxygen vacancies, which are produced by high-temperature conditional growth, and the doped Mn change the Fe valence, thereby reducing the leakage current. Finally, through fitting analysis of the I–V diagram and temperature tests in the low-resistance state, we inferred that the behavior of the resistance conversion is due to the formation of Ag conductive filaments.

Investigation of the Coupled Effect of Liquid and Solid Inorganic Additives on Thermal Stability and Water Retention of PFSA Composite

Here, investigation of the high-temperature water retention property of new composites, which contain perfluorosulfonic acid (PFSA) polymer as matrix, a mineral acid, and MgF2 nanoparticles as inorganic additives, is done based on structural analysis. The composite shows an improvement in the water removal temperature from 50 to 250 °C because the crystalline water molecules were attached on the surface of solid inorganic additives at 250 °C. To optimize the water retention property, the 1 wt % of sulfuric acid and 3–15 wt % of MgF2-coated glass particles in PFSA polymer composites as additives were investigated. From the Fourier transform infrared-attenuated total reflection studies of these composite membranes, two major phenomena related to structural details of PFSA polymer as a function of the polymer and the weight ratio of the solid additives are observed: (1) sulfonic acid group released the proton even with low humidity and (2) the conformation and/or the degree of the crystallinity of the poly(t...

Porous γ-(Y1-xHox)2Si2O7 thermal insulator with excellent high-temperature strength retention and very low thermal conductivity

High-temperature thermal insulation materials challenge extensive candidates with good mechanical, thermal and chemical reliability at high temperatures. Recently, porous γ-Y2Si2O7 was indicated a promising thermal insulator in harsh environment; however, its strength at 1300 °C reduced to 34% of that at room temperature. In this work, we significantly improved its high-temperature strength by doping Ho. Highly porous γ-(Y1-xHox)2Si2O7 solid solution was fabricated by in-situ foam-gelcasting method. Especially, porous γ-(Y2/3Ho1/3)2Si2O7 demonstrated the optimal high-temperature strength, for instance 65% retention at 1300 °C, as well as high compressive strength (13.9 MPa) and low thermal conductivity (0.186 W/(m K)) at room temperature, at the porosity of 79.3%. Interestingly, porous solid solution sample displayed obviously lower thermal conductivity than the two end pure-phase porous materials. Porous γ-(Y1-xHox)2Si2O7 solid solution is clearly highlighted as a promising high-temperature thermal insulator with outstanding high-temperature strength retention and optimal low thermal conductivity.

Carbon dots with multi-functional groups and the application in proton exchange membranes

It is of great necessity to achieve a proton exchange membrane (PEM) with high proton conductivity and low methanol permeability for the practical applications. Nafion modified carbon dots (NCDs) with multi-functional groups were successfully synthesized via the pyrolysis of citric acid (CA) with the existence of Nafion. The modification process is motivated by the hydrophilicity-to-hydrophobicity transformation of CA as well as the non-covalent hydrophilic-hydrophobic interaction during the pyrolysis procedure. Multi-functionalized NCDs with moderate hydrophilicity influence the aggregation structure of Nafion matrix of the composite membranes and effectively enhance the high-temperature water retention ability. Both the proton conductivity and the methanol resistance ability of the composite PEMs are significantly enhanced. 0.5-NCD-0.5 Nafion composite PEM presents a 5–10 times increase in proton conductivity and 50% percent decrease in methanol permeability than that of recast Nafion.

(Invited) Non Volatile Resistive and Magnetic Memories: Materials, Integration Challenges and Opportunities

Demand for on chip memories has increased due to the need for more data storage and the increasing gap between processor and off chip memory speed. One of the solutions proposed to improve power consumption and to fill the memory gap is to introduce non volatility at different levels of the memory hierarchy (storage class, main memory, cache memory). Several disruptive technologies have been proposed in the last decades for non-volatile memory (NVM) applications. The more investigated ones are Phase-Change Memories (PCM), Conducting-Bridge RAM (CBRAM), Oxide-based Resistive RAM (OxRAM), and Perpendicular Spin Transfer Torque Magnetic Memories (pSTTMRAM). Intensive studies and demonstrations have being carried out in order to develop and improve those emerging memory concepts. Some memory stacks have shown promising results in term of high speed, good endurance or retention but not necessarily all of the above. A survey of published results [1] as well as internal studies carried out at LETI [2, 3] using a memory test vehicle developed to evaluate various memory concepts using the same 130nm CMOS logic have led us to infirm that the universal memory ie an optimized memory stack that fits all requests of memory hierarchy does not exist. However, because requirements for cache memories (ie high speed, endurance, but low data retention) are completely different from requirements for embedded memories (ie high temperature or long data retention), different technology or optimized memory stacks can be targeted to fulfill specific applications. It will be shown that despite very different physical concepts, universal signatures can be extracted unifying the characteristics of different technologies and thus drawing conclusions on their behaviors and tradeoffs (such as programming window vs endurance, programming window vs data retention, and endurance vs data retention). This is illustrated in Fig 1 where the relation between the programming window and the endurance capabilities of the different technologies is presented. It is shown that high programming window is typically associated to poor endurance capabilities, (as shown by some classes of chalco-based CBRAM or non-polar OxRAM). For these technologies the overall filament is believed to participate to the creation and the dissolution events. On the contrary, displacing very few atoms/ions, or spins, during the write or erase event allows to guarantee a long-lasting endurance (examples are certain class of polar OxRAM and STT MRAMs). Data also show that a universal tradeoff exists between the endurance and data retention itself. The better the performances in endurance, the lower the data retention capabilities at high temperature. Write latency speed will be discussed and ultra fast (<1ns) writing MRAM technology based on a recently discovered effect Spin Orbit torque (SOT MRAM) will be discussed. The characteristics and performances of the different emerging will be presented (materials, integration, speed, endurance, consumption and scalability) in regards of the needed specifications required for potential applications. [1] ] H.-S. P. Wong, C. Ahn, J. Cao, et al., “Stanford Memory Trends,” https://nano.stanford.edu/stanford-memory-trends, accessed Nov 11, 2015 [2] C. Nail; G. Molas; P. Blaise et al “ Understanding RRAM endurance, retention and window margin trade-off using experimental results and simulations”: IEDM 2016 Pages: 4.5.1 - 4.5.4, DOI: 10.1109/IEDM.2016.7838346[3] V. Sousa, G. Navarro, N. Castellani et al., “Operation Fundamentals in 12Mb Phase Change Memory Based on Innovative Ge-rich GST Materials Featuring High Reliability Performance”, VLSI Tech. Symp., pp.98-99, 2015 Figure 1