Reliable Endurance Research Articles

Role of sulphur in resistive switching behavior of natural rubber-based memory

The rising environmental awareness has spurred the extensive use of green materials in electronic applications, with bio-organic materials emerging as attractive alternatives to inorganic and organic materials due to their natural biocompatibility, biodegradability, and eco-friendliness. This study showcases the natural rubber based resistive switching memory devices and how varying sulphur concentrations (0 - 0.8 wt.%) in natural rubber thin films impact the resistive switching characteristics. The natural rubber was formulated and processed into a thin film deposited on an ITO substrate as the bottom electrode and with an Ag film as the top electrode. The addition of sulphur modifies the degree of crosslinking in the natural rubber thin film, from which the concentration of -C=C- group and density of defect site (S+) are affected, and hence the resistive switching behavior of the memory device. The devices exhibit bipolar resistance with symmetric switching characteristics which are attributed to the formation of conductive paths facilitate by electron transport along -C=C- and S+ defect sites between the two electrodes. Notably, a sample with 0.2 wt.% sulphur exhibits a high ON/OFF ratio (104), a large memory window (5.5 V), prolonged data retention (10 years), and reliable endurance (120 cycles). These findings highlight the potential of natural rubber as a promising material for eco-friendly resistive-switching random access memory applications.&#xD.

High-performance memristor for energy-efficient artificial optoelectronic synapse based on BiVO4 nanosheets

Artificial optoelectronic synapses have drawn extensive attention owing to their ability to combine the optical and electrical responses. Those photosensitive materials that has been reported in memristors have the potential to be adopted in such optoelectronic synapses. Herein, optoelectronic synapses can be achieved based on two-terminal memristors by using two-dimensional (2D) BiVO4 with monoclinic scheelite (m-BiVO4) structure as the memristive layer. The fabricated memristors exhibit bipolar resistive switching (RS) characteristics with stable retention and reliable endurance performance. Furthermore, both electrical and optical synaptic functions can be achieved based on the memristors, such as long-term potentiation (LTP) and depression (LTD) stimulated by the voltages pulses as well as short-term and long-term memory under the light stimulation. More importantly, owing to the LTP and LTD functions with high symmetry, linearity and good repeatability of the LTP/LTD cycles, the artificial neural network can be simulated to achieve image recognition with a high accuracy for handwritten digits. Moreover, both the electrical and optical synapses can be used to emulate the “learning-forgetting” behaviors of human brain. Remarkably, the energy consumption per synaptic event in the optical and electrical modes can be calculated, indicating potential applications in energy-efficient synaptic devices. The m-BiVO4 nanosheets not only demonstrate good non-volatile RS behaviors but also implement energy-efficient optoelectronic synaptic functions, providing a promising strategy for applications in future neuromorphic computing.

Fabrication of Sb2S3/Sb2Se3 heterostructure for potential resistive switching applications

The exponential growth of large data and the widespread adoption of the Internet of Things (IoT) have created significant challenges for traditional Von Neumann computers. These challenges include complex hardware, high energy consumption, and slow memory access time. Researchers are investigating novel materials and device architectures to address these issues by reducing energy consumption, improving performance, and enabling compact designs. A new study has successfully engineered a heterostructure that integrates Sb2Se3 and Sb2S3, resulting in improved electrical properties. This has generated significant interest in its potential applications in resistive switching. In this study, we have demonstrated the fabrication of a device based on Sb2S3/Sb2Se3 heterostructure that exhibits resistive switching behavior. The device has different resistance states that can be switched between high and low resistance levels when exposed to an external bias (−1 V to 0 V to 1 V). It also has good non-volatile memory characteristics, including low power consumption, high resistance ratio (∼102), and reliable endurance (∼103). The device enables faster data processing, reduces energy consumption, and streamlines hardware designs, contributing to computing advancements amidst modern challenges. This approach can revolutionize resistive switching devices, leading to more efficient computing solutions for big data processing and IoT technologies.

In-Situ Observation of Adsorption Species on Platinum Catalyst in Oxygen Reduction Reaction Using High Energy Resolution XAFS

The oxygen reduction reaction (ORR) on Pt surfaces, for examples, Pt single crystals, polycrystalline Pt electrodes, Pt nanoparticles (NPs), Pt-based alloys, and core–shell Pt nanostructures, has been discussed in the last few decades.In polymer electrolyte fuel cells (PEFCs), hydrogen peroxide and its radicals are known to be fatal attacking species not only for electrode catalysts but also for carbon materials and polymer membranes.A thorough understanding of ORR schemes has led to the development of seamless four-electron reduction cathodes, contributing to improved endurance reliability of both anion-exchange membrane (AEM) and proton-exchange membrane (PEM) fuel cells.In this study, the reaction pathway, and intermediate species such as molecular oxygen, in the ORR were investigated in alkaline and acidic environments, respectively.In this work, High Energy Resolution Fluorescence Detection X-ray Absorption Spectroscopy (HERFD-XAS) at the Pt L III-edge, which enhances resolution by partially collecting fluorescent X-ray was employed.X-ray absorption fine structure (XAFS) can detect the electronic structure of Pt, and its high energy resolution makes it possible to distinguish between different adsorption species on the surface of Pt nanoparticles.In addition, photon-in photon-out experiments using hard X-ray with high penetrating ability make it relatively easy to perform in-situ/operando measurements in potential controlled solutions.Carbon-supported Pt nanoparticles as powder catalysts were used for measurement as more realistic conditions, and the species adsorbed on the Pt nanoparticles were analyzed while controlling under the potentials both in acidic and basic electrolyte solutions with N2 or O2 gas bubbling.In N2-saturated solutions, the XANES spectra of the Pt LIII-edge reflected the presence of the adsorption species such as Pt-O (*O), Pt-OH (*OH), Pt-H (*H), as well as PtO2 oxide and Pt metallic states without any adsorption, during the ORR with the potential change.In O2-saturated solutions, one additional adsorption species of molecular oxygen was observed in both acidic and basic electrolyte solutions. It was analyzed that the intermediate species adsorbed to platinum in a side-on configuration as a superoxide anion in an alkaline environment.This intermediate species is identified as hydrogen superoxide, also known as hydroperoxyl radical, with the chemical formula HO2 by being protonated in an acidic environment.The results of research on adsorption species using HERFD-XAS have provided important knowledge for designing catalysts that enable seamless four-electron reduction.The preferred cathode catalyst design will be discussed in detail in an oral presentation at the 244th ECS Meeting. Acknowledgments: The synchrotron radiation experiments were performed at the BL11XU in the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Numbers of 2012B3506, 2013A3506, 2014A3506, 2014B3506, 2015B3506, 2016A3556 2019A3508, 2019B3508, 2020A3508, 2021A3508, 2021B3508, 2022A3508 and 2022B3597 at BL11XU). This work was supported by JSPS KAKENHI Grant Number JP22H02188). Figure 1

Interface engineering in ZnO/CdO hybrid nanocomposites to enhanced resistive switching memory for neuromorphic computing

Resistive random-access memory (RRAMs) has attracted significant interest for their potential applications in embedded storage and neuromorphic computing. Materials based on metal chalcogenides have emerged as promising candidates for the fulfilment of these requirements. Due to its ability to manipulate electronic states and control trap states through controlled compositional dynamics, metal chalcogenide RRAM has excellent non-volatile resistive memory properties. In the present we have synthesized ZnO-CdO hybrid nanocomposite by using hydrothermal method as an active layer. The Ag/C15ZO/Pt hybrid nanocomposite structure memristors showed electrical properties similar to biological synapses. The device exhibited remarkably stable resistive switching properties that have a low SET/RESET (0.41/−0.2) voltage, a high RON/OFF ratio of approximately 105, a high retention stability, excellent endurance reliability up to 104 cycles and multilevel device storage performance by controlling the compliance current. Furthermore, they exhibited an impressive performance in terms of emulating biological synaptic functions, which include long-term potentiation (LTP), long-term depression (LTD), and paired-pulse facilitation (PPF), via the continuous modulation of conductance. The hybrid nanocomposite memristors notably achieved an impressive recognition accuracy of up to 92.6 % for handwritten digit recognition under artificial neural network (ANN). This study shows that hybrid-nanocomposite memristor performance could lead to efficient future neuromorphic architectures.

Synaptic Characteristics and Vector‐Matrix Multiplication Operation in Highly Uniform and Cost‐Effective Four‐Layer Vertical RRAM Array

AbstractThis study implements a highly uniform 3D vertically stack resistive random‐access memory (VRRAM) with a four‐layer contact hole structure. The fabrication process of a four‐layer VRRAM is demonstrated, and its physical and electrical properties are thoroughly examined. X‐ray photoelectron spectroscopy and transmission electron microscopy are employed to analyze the chemical distribution and physical structure of the VRRAM device. Multilevel capability, reliable endurance (>104 cycles), and retention (104 s) are successfully obtained. Synaptic memory plasticity, such as spike time‐dependent plasticity, spike rate‐dependent plasticity, excitatory post‐synaptic current, paired‐pulse facilitation, and long‐term potentiation and depression is presented. Finally, the vector‐matrix multiplication (VMM) operation is conducted on a 4 × 12 VRRAM array, according to the low resistance state ratio. It is ascertained that the accuracy drop, which can occur due to VMM error, can be limited to a decrease of less than 0.44% point. Utilizing the high‐density, multilevel, and biological characteristics of VRRAM, it is possible to implement high‐performance neuromorphic systems that require densely integrated synaptic devices.

Ag-dispersive chalcogenide media for readily activated electronic memristor

In this paper, we report a Ag-dispersive chalcogenide thin film as a resistance-switching material for memristive devices. The memristive device with Ag/Ge2Se3Te5/W showed an initial low resistance state in its pristine stage (electro-forming-free), a low power consumption of 60 nW, robust state retention in a harsh environment of 85 °C for 2 h, and reliable endurance. We used high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and electrical conduction characteristics to determine the microscopic origin of the memristive device. Comparative studies of different electrodes and resistive switching layers indicated that the diffusive Ag atom in the chalcogenide thin film plays a crucial role in realizing distinctive memristive characteristics. Further, we highlighted that the observed favorable performance of the memristive device is possible with a chalcogenide material, which can serve as an electrolyte for high ion diffusion and desirable electronic traps. Moreover, the memristive device exhibited an analogous conductance variation in a nonvolatile manner, which can be adopted as an artificial synaptic device. Based on the observed synaptic performance, an inference accuracy of ∼92% was achieved using handwritten numbers from the Modified National Institute of Standards and Technology database.

Effects of BiFeO3 Thickness on the Write‐Once‐Read‐Many‐Times Resistive Switching Behavior of Pt/BiFeO3/LaNiO3 Heterostructure

Thickness of the resistive switching materials is an essential factor to determine the integration density of resistive switching devices. Herein, the effect of the thickness of BFO on the write‐once‐read‐many‐times (WORM) resistive switching behavior of Pt/BFO/LNO‐based devices is investigated. The thicknesses of BFO thin films are controlled in the range of 70–220 nm. All the devices exhibit WORM resistive switching behavior with high ON/OFF ratio (≈10−2–10−4), long‐term data retention (>3600 s), and reliable endurance (>1000 cycles). The set voltages (Vset) of the devices exhibit an approximately linear relation to the BFO thicknesses, while the highest ON/OFF ratio appears in the device with BFO thickness of 150 nm. The thickness‐dependent resistive switching characteristic is attributed to the variation of oxygen vacancies and OFF state resistances with the increase of BFO thickness. The results underline the importance of the thickness of resistive switching materials for the future device applications.

Attack Resilient True Random Number Generators Using Ferroelectric-Enhanced Stochasticity in 2D Transistor.

By harnessing the physically unclonable properties, true random number generators (TRNGs) offer significant promises to alleviate security concerns by generating random bitstreams that are cryptographically secured. However, fundamental challenges remain as conventional hardware often requires complex circuitry design, showing a predictable pattern that is susceptible to machine learning attacks. Here, a low-power self-corrected TRNG is presented by exploiting the stochastic ferroelectric switching and charge trapping in molybdenum disulfide (MoS2 ) ferroelectric field-effect transistors (Fe-FET) based on hafnium oxide complex. The proposed TRNG exhibits enhanced stochastic variability with near-ideal entropy of ≈1.0, Hamming distance of ≈50%, independent autocorrelation function, and reliable endurance cycle against temperature variations. Furthermore, its unpredictable feature is systematically examined by machine learning attacks, namely the predictive regression model and the long-short-term-memory (LSTM) approach, where nondeterministic predictions can be concluded. Moreover, the generated cryptographic keys from the circuitry successfully pass the National Institute of Standards and Technology (NIST) 800-20 statistical test suite. The potential of integrating ferroelectric and 2D materials is highlighted for advanced data encryption, offering a novel alternative to generate truly random numbers.

A BN-Doped U-Shaped Heteroacene as a Molecular Floating Gate for Ambipolar Charge Trapping Memory.

Two wide-bandgap U-shaped polycyclic aromatic hydrocarbons with/without boron and nitrogen (BN-) doping (BN-1 and C-1) were synthesized to tune the electronic features to suit the performance requirements in organic field-effect transistor memory (OFET-NVM). The chemical structures were characterized by scanning tunneling microscopy and single crystal diffraction. Owing to the electron donor effect of N and the high electron affinity of B, the BN-1-based OFET-NVM displays large ambipolar memory windows and an enhanced charge storage density compared to C-1 and most of the reported small molecules. A novel supramolecular system formed via BN-1 and PMMA contributes to fabricating uniform films with homogeneous microstructures, which serve as a two-in-one tunnelling dielectric and charge trapping layer to realize long-term charge retention and reliable endurance. Our results demonstrate that both BN doping and supramolecular engineering are crucial for the charge trapping of OFET-NVM.

A BN‐Doped U‐Shaped Heteroacene as a Molecular Floating Gate for Ambipolar Charge Trapping Memory

AbstractTwo wide‐band gap U‐shaped polycyclic aromatic hydrocarbons with/without boron and nitrogen (BN‐) doping (BN‐1 and C‐1) were synthesized to tune the electronic features to suit the performance requirements for organic field‐effect transistor memory (OFET‐NVM). The chemical structures were characterized by scanning tunneling microscopy and single‐crystal diffraction. Owing to the electron‐donor effect of N and the high electron affinity of B, the BN‐1‐based OFET‐NVM displays large ambipolar memory windows and an enhanced charge storage density compared to C‐1 and most reported small molecules. A novel supramolecular system formed from BN‐1 and PMMA contributes to fabricating uniform films with homogeneous microstructures, which serve as a two‐in‐one tunnelling dielectric and charge‐trapping layer to realize long‐term charge retention and reliable endurance. Our results demonstrate that both BN doping and supramolecular engineering are crucial for the charge trapping of OFET‐NVM.

Ultrahigh Energy Storage Density in Superparaelectric-Like Hf0.2 Zr0.8 O2 Electrostatic Supercapacitors.

Electrostatic capacitors attract great interest in energy storage fields due to their advantages of high power-density, fast charge/discharge speed, and great reliability. Intensive efforts have been placed on the development of high-energy-density of capacitors. Herein, a novel supercapacitor with Hf0.2 Zr0.8 O2 /xAl2 O3 /Hf0.2 Zr0.8 O2 (HAHx) is designed to improve the breakdown strength (Eb ) through optimizing Al2 O3 (AO) film thickness. Low-temperature annealing is first proposed to enhance the polarization difference (Pm -Pr ) due to the formation of dispersed polar nanoregions, which is called "superparaelectric-like" similar to previous super-paraelectric behavior of perovskite structures. As results, both large Eb and Pm -Pr values are obtained, leading to an ultrahigh energy storage density of 87.66 Jcm-3 with a high efficiency of 68.6%, as well as a reliable endurance of 107 cycles. This work provides a feasible pathway to improve both the polarization difference and breakdown strength of HfO2 -based films by the combination of insulation insertion layer and low-temperature annealing. The proposed strategy can contribute to the realization of high-performance electrostatic supercapacitors with excellent microsystem compatibility.

Graphene Oxide-Based Memristive Logic-in-Memory Circuit Enabling Normally-Off Computing.

Memristive logic-in-memory circuits can provide energy- and cost-efficient computing, which is essential for artificial intelligence-based applications in the coming Internet-of-things era. Although memristive logic-in-memory circuits have been previously reported, the logic architecture requiring additional components and the non-uniform switching of memristor have restricted demonstrations to simple gates. Using a nanoscale graphene oxide (GO) nanosheets-based memristor, we demonstrate the feasibility of a non-volatile logic-in-memory circuit that enables normally-off in-memory computing. The memristor based on GO film with an abundance of unusual functional groups exhibited unipolar resistive switching behavior with reliable endurance and retention characteristics, making it suitable for logic-in-memory circuit application. In a state of low resistance, temperature-dependent resistance and I-V characteristics indicated the presence of a metallic Ni filament. Using memristor-aided logic (MAGIC) architecture, we performed NOT and NOR gates experimentally. Additionally, other logic gates such as AND, NAND, and OR were successfully implemented by combining NOT and NOR universal logic gates in a crossbar array. These findings will pave the way for the development of next-generation computer systems beyond the von Neumann architecture, as well as carbon-based nanoelectronics in the future.

Write-once-read-many-times memory device based on Pt/BiFeO3/LaNiO3 heterostructures

Nonvolatile memory devices based on resistive switching effects are promising candidates for next generation high performance nonvolatile data storage. Here, we report the write-once-read-many-times (WORM) resistive switching behavior for the first time in Pt/BiFeO3/LaNiO3 heterostructures. BiFeO3 thin films with (100) preferred orientation have been prepared by RF magnetron sputtering combined with annealing at temperature higher than 600 ℃, and show excellent WORM resistive switching behaviors with data retention for>3600 s and reliable endurance for>1000 cycles. The devices with BiFeO3 annealed at 650 ℃ exhibit extremely high ON/OFF ratio (>3 × 104) and low switching voltage (∼3 V) due to the high quality of BiFeO3 thin films. The observed resistive switching behavior is attributed to the formation of permanent conducting filaments that composed of oxygen vacancies. These results demonstrate that BiFeO3 is promising for novel WORM memory device applications.

Probabilistic modeling of threshold stress intensity factor for fatigue endurance reliability prediction

This study develops a probabilistic model for the threshold stress intensity factor range, which is a critical parameter in infinite fatigue life design under material flaws. The model is based on the proposed concept of probability of propagation in the probabilistic framework, allowing for deriving the probability density function of the threshold intensity factor range. The uncertainty in fatigue crack growth can naturally be incorporated into the resulting distribution. By further introducing the derived distribution into the Kitagawa–Takahashi diagram, the fatigue endurance reliability model can be established in a rational manner. With the first-order asymptotic approximation, the analytical form of fatigue endurance reliability index is obtained. The usefulness of the overall method is demonstrated using realistic engineering application examples.

Quaternary Logic Circuits Based on Low-Voltage Programmable/Erasable Four-Level Organic Transistor Nonvolatile Memories

Developing the multi-valued logic circuits, that can handle more data than the conventional binary logic circuits, is a promising strategy to break through the well-known Moore’s law. In this letter, we demonstrate quaternary logic circuits, for the first time, based on the four-level organic thin-film transistor nonvolatile memories (OTFT-NVMs) as the core components. High-performance four-level OTFT-NVMs are achieved, with the low programming/erasing voltages of ±15 V, high mobility up to 7.4 cm2/Vs, reliable endurance, and stable retention capabilities. By connecting the four-level OTFT-NVMs with a load resistance in the reasonable ways, we build the logic circuits to reliably perform quaternary logic operations of NOT, NAND and NOR, respectively. Our works lay the foundation to develop the novel quaternary integrated circuits in hardware.

Development of Reflow Fill of CGeSbTe Films for Sub‐20 nm Cells in 3D Cross‐Point Memory

AbstractTo obtain reliable and scalable cells in 3D cross‐point memory, endurance failures caused by voiding from etching damage to memory cells should be resolved to preserve the properties of GeSbTe (GST) phase‐change materials. Herein, the fabrication of a damascene cell without patterning, which relies on the bottom‐up fill of carbon‐doped GST layers into confined cells, is proposed as a promising solution. The reflow fill of the sputtered carbon‐doped GST films into confined cells at high‐temperature and low‐power conditions is demonstrated, and a mechanism in which Sb and Te transfer into the cell through vapor transfer and viscous flow due to capillary pressure is verified. The aspect ratio increases from 2 to 7.7 under enhanced vaporization of Sb and Te as well as the capillary force. The advanced reflow‐fill process using a laser can overcome the limit of the conventional reflow‐fill technology by increasing the atomic mobility above the melting temperature. Based on the proposed method, 19 nm cross‐point memory devices are successfully integrated together with the Ovonyx threshold switch and appropriate memory windows are secured. Furthermore, the 9 nm cells exhibit reliable endurance cycles over 108.

High-speed, low-voltage programmable/erasable flexible 2-bit organic transistor nonvolatile memory with a monolayer buffered ferroelectric terpolymer insulator

Achieving multi-bit data storage in one transistor is a promising strategy to further multiply the storage density of the nonvolatile memories (NVMs). Low-voltage programming/erasing (P/E) operation is a prerequisite for the commercialization of the multi-bit NVMs. And, the fast P/E switching is also a desirable figure of merit for the practical NVMs. Here, we develop a route to achieve a high-speed, low-voltage P/E flexible organic transistor-based NVM, by processing a monolayer buffered ferroelectric terpolymer insulator. The physical mechanisms for achieving the high-speed, low-voltage P/E properties in the organic transistor-based NVMs are investigated. As a result, high-performance flexible 2-bit NVMs are achieved, with the low P/E voltage of ±15 V, fast P/E switching capability of 50 ns, high mobility up to 7.4 cm2 V−1 s−1, high stable retention time up to 10 years, reliable endurance over 200 cycles, good mechanical bending durability, and atmosphere stability.

New ternary inverter with memory function using silicon feedback field-effect transistors

In this study, we present a fully complementary metal–oxide–semiconductor-compatible ternary inverter with a memory function using silicon feedback field-effect transistors (FBFETs). FBFETs operate with a positive feedback loop by carrier accumulation in their channels, which allows to achieve excellent memory characteristics with extremely low subthreshold swings. This hybrid operation of the switching and memory functions enables FBFETs to implement memory operation in a conventional CMOS logic scheme. The inverter comprising p- and n-channel FBFETs in series can be in ternary logic states and retain these states during the hold operation owing to the switching and memory functions of FBFETs. It exhibits a high voltage gain of approximately 73 V/V, logic holding time of 150 s, and reliable endurance of approximately 105. This ternary inverter with memory function demonstrates possibilities for a new computing paradigm in multivalued logic applications.

Optimizing Ferroelectric and Interface Layers in HZO-Based FTJs for Neuromorphic Applications

Nonvolatile memories especially the ferroelectric (FE)-based ones such as ferroelectric tunnel junctions (FTJs) and ferroelectric field-effect transistors (FeFETs) have recently attracted a lot of attention. FTJs have been intensively researched for the last decade and found to be very promising memory devices due to their significant nondestructive readout advantage as compared to conventional ferroelectric random access memory (FRAM). However, more research is needed on FTJ devices to obtain reliable endurance and retention behavior. In this article, we demonstrate the characteristics and performance of zirconium-doped hafnium oxide-based FTJ devices in terms of FE switching and reliability. This is investigated for FTJ stack structure tuning as well as for the FE switching process in FTJ devices. The FTJ memory switching characteristics, the effects of polarization switching on the write conditions, and the impact of pulse width and pulse amplitude on switching are investigated. The impact of FE layer thickness and interface layer type/thickness are reported to obtain a maximum FTJ <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio (memory window) and reliable performance. The maximum <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio changes depending on the FE layer (zirconium-doped HfO₂ layer) thickness (12, 8, 6, and 4 nm), the interface layer type (SiO₂, Al₂O₃), and thickness (1 and 2 nm), indicating the maximum value of <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio for a 1 nm SiO₂ interface layer stack. Moreover, a stable endurance of 10⁴ cycles is reported and extrapolated measurements suggest stable retention for more than ten years. Time-dependent breakdown analysis was performed to investigate the reliability of devices indicating a lifetime of ten years.