Reliability assessment on new reprogrammable non-volatile memory devices based on SiCr–O

The reliability of SiCr–O based reprogrammable non-volatile resistive memory devices is investigated. Superior data retention performances are confirmed with a lifetime of 10 k h at 245 °C. The activation energy is determined by experiments as 1.28 eV, projecting an intrinsic data retention lifetime of more than 100 years at 175 °C. An endurance life of a thousand program/erase cycles is achieved. The impact of dielectric in direct contact with the SiCr–O film, the layout of the device and the preconditioning step on endurance life are studied. Transmission electron microscopy cross-sections are made to understand the mechanism of the endurance failure. Electro-thermal simulations are performed to gain insight on the observed phenomena and to give directions for further improvements.     

All-printed and highly stable organic resistive switching device based on graphene quantum dots and polyvinylpyrrolidone composite

We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope.     

Charge transport and recombination in heterostructure organic light emitting transistors

Light-emitting field effect transistors (LEFETs) are a class of organic optoelectronic device capable of simultaneously delivering the electrical switching characteristics of a transistor and the light emission of a diode. We report on the temperature dependence of the charge transport and emissive properties in a model organic heterostructure LEFET system from 300 K to 135 K. We study parameters such as carrier mobility, brightness, and external quantum efficiency (EQE), and observe clear thermally activated behaviour for transport and injection. Overall, the EQE increases with decreasing temperature and conversely the brightness decreases. These contrary effects can be explained by a higher recombination efficiency occurring at lower temperatures, and this insight delivers new knowledge concerning the optimisation of both the transport and emissive properties in LEFETs.     

Study of radiation hardness of HfO2-based resistive switching memory at nanoscale by conductive atomic force microscopy

A resistive switching random access memory (RRAM) with an HfO₂/Ti structure grown on a molybdenum (MO) substrate was fabricated, and a gold (Au) conductive atomic force microscopy (CAFM) tip was used as the top electrode such that the cell area of the resulting RRAM device is as small as 3 × 10⁻¹² cm². The pre- and post-irradiated resistive switching behaviors of the RRAM device with various HfO₂ layer thicknesses were investigated after being subjected to Co⁶⁰ γ-ray irradiation with different radiation doses. It is found that the forming voltage (V_forming), set voltage (V_set), resistance of high resistance state (RHRS) and resistance of low resistance state (RLRS) of the RRAM device are all radiation dose-dependent. The V_forming, V_set, RHRS and RLRS all decrease as the radiation dose increases due to increasing radiation-induced oxygen vacancies or defects inside the HfO₂ layer. Our experimental results indicate that the HfO₂-based RRAM cell with an extremely small cell area is not actually radiation hard since the operating voltage will change with V_forming and V_set after irradiation.     

Thermal optimization of GaN-on-Si HEMTs with plastic package

In this paper, the degradation of a GaN-on-Si based RF power amplifier is investigated by means of electrical characterization. The reliability issues identified during this work are clearly related to the high thermal resistance between the device and the heat sink, which causes gate-leakage current and output power degradation. Moreover, we have demonstrated a low cost thermal optimization approach by increasing the thermal dissipation area and reducing the device carrier thickness. Measurement results show that the saturated output power can be increased from 1 W up to 5 W without device degradation at 3.8 GHz.     

Reliability of Diode-Integrated SiC Power MOSFET(DioMOS)

Status of the reliability study on silicon carbide (SiC) power MOS transistors is presented. The SiC transistors studied are diode-integrated MOSFETs (DioMOS) in which a highly doped n-type epitaxial channel layer formed underneath the gate oxide acts as a reverse diode and thus an external Schottky barrier diode can be eliminated. The novel MOS device can reduce the total area of SiC leading to potentially lower cost as well as the size of the packaging. After summarizing the issues on reliability of conventional SiC MOS transistors, the improvements by the newly proposed DioMOS with blocking voltage of 1200 V are presented. The I–V characteristic of the integrated reverse diode is free from the degradation which is typically observed in conventional pn-junction-based body diode in SiC MOS transistors. The improved quality of the MOS gate in the DioMOS results in very stable threshold voltage within its variation less than 0.1 V even after 2000 h of serious gate voltage stresses of + 25 V and − 10 V at 150 °C. High temperature reverse bias test (HTRB) shows very stable off-state and gate leakage current up to 2000 h under the drain voltage of 1200 V at 150 °C. These results indicate that the presented DioMOS can be applied to practical switching systems free from the reliability issues.     

LER and spacing variability on BEOL TDDB using E-field mapping: Impact of field acceleration

Understanding the impact of process variability on TDDB is crucial for assuring robust reliability for current and future technology nodes. This work introduces a lifetime prediction model that considers local field enhancement to assess the combined impact of die-to-die spacing variability and line edge roughness. The model is applied to 16 nm half-pitch BEOL interconnects assuming either the power law or the root-E as field acceleration model and the impact on lifetime reduction is discussed. In comparison with the ideal case of a straight line with a nominal spacing of 16 nm, a 1-sigma spacing variation of 0.6 nm and 1-sigma LER of 1 nm leads to ~ 3 orders of magnitude lifetime reduction when assuming power-law whereas this value is ~ 1 order of magnitude when assuming root-E.     

Prognostic methodology for remaining useful life estimation of retention loss in nanoscale resistive switching memory

Noise is a key indicator of the physical phenomenon underlying device operation, defect density and degradation trends. The analysis of noise in the frequency domain and the exponent (value of slope, α on logarithmic scale) of the power spectral density (PSD) can provide useful insight on the operating and failure mechanism of any device/system. We shall use this noise as a prognostic indicator to detect the instant at which the retention loss of a non-volatile memory device begins to occur. A qualitative perspective to prognostic management of a resistive random access memory (RRAM) device is provided in this work. Our method of detecting retention loss involves the unique observation of a slope of α = 3/2, which arises due to diffusion or ionic migration phenomenon.     

Lifetime tests of 600-V GaN-on-Si power switches and HEMTs

We present the first systematic lifetime tests which show excellent long-term reliability for 600 V GaN-on-Si power switches.High voltage accelerated life testing in the OFF-state yields a field related mean-time-to-failure (MTTF) greater than 3 × 10⁸ h for a 600 V operating condition. High temperature accelerated testing in the ON-state gives an MTTF of about 6 × 10⁸h at a 150 °C use condition. High temperature operating life testing using hard switched boost converters at 175 °C shows no measurable device degradation after 3000 h of operation. These results show that the intrinsic reliability of the new device technology is more than adequate for commercial and industrial power electronics applications.     

Experimental study on the influence of junction temperature on the relationship between IGBT switching energy loss and device current

Accurate determination of power losses in semiconductor devices is important for optimal design and reliable operation of a power converter. The switching loss is an important component of the total device loss in an insulated-gate bipolar transistor (IGBT) in a voltage source inverter. The objective here is to study experimentally the influence of junction temperature on the turn-on switching energy loss E_on and turn-off switching energy loss E_off. More specifically E_on and E_off are both related to device current I_c; the influence of junction temperature on the relationship between E_on and I_c and that between E_off and I_c is studied. As the operating environmental conditions and load conditions of power converter vary widely, a wide range of junction temperatures between − 35 °C and + 125 °C is considered here. The experimental data enable precise determination of the switching loss in each device in a high-power converter at any practical operating condition. This leads to precise estimation of total device loss and optimal thermal design of the converter. This further helps off-line and/or on-line estimation of device junction temperatures required for study of thermal cycles and reliability.     

Ultra-thin alumina layer encapsulation of bulk heterojunction organic photovoltaics for enhanced device lifetime

Successful organic photovoltaic (OPV) device fabrication is contingent on selecting an effective encapsulation barrier layer to preserve device functionality by inhibiting atmosphere-induced degradation. In this work, ultra-thin AlO_x layers are deposited by atomic layer deposition (ALD) to encapsulate pre-fabricated OPV devices. A summary of ALD recipe effects (temperature, cycling time, and number of cycles) on AlO_x film growth and device longevity is presented. First, AlO_x film growth on the hydrophobic OPV surface is shown to occur by a 3D island growth mechanism with distinct nucleation and cluster growth regions before coalescence of a complete encapsulation layer with a thickness ⩾7 nm by 500 cycles. Encapsulated device performance testing further demonstrates that reducing ALD processing temperature to 100 °C minimizes OPV phase segregation and surface oxidation loss mechanisms as evidenced by improved short circuit current and fill factor retention when compared with the conventional 140–150 °C range. Ultra-thin AlO_x encapsulation by ALD provides significant device lifetime enhancement (∼30% device efficiency after 2000 h of air exposure), which is well beyond other ALD-based encapsulation works reported in the literature. Furthermore, the interfacial bonding strength at the OPV–AlO_x interface is shown to play a crucial role in determining film failure mode and therefore, directly impacts ultimate device lifetime.     

A novel 1,1′-bis[4-(5,6-dimethyl-1H-benzimidazole-1-yl)butyl]-4,4′-bipyridinium dibromide (viologen) for a high contrast electrochromic device

A new electrochromic viologen, 1,1′-bis-[4-(5,6-dimethyl-1H-benzimidazole-1-yl)-butyl]-4,4′-bipyridinium dibromide (IBV) was synthesized by di-quaternization of 4,4′-bipyridyl using 1-(4-bromobutyl)-5,6-dimethyl-1H-benzimidazole. X-ray photoelectron spectroscopy confirmed the formation of the IBV (viologen) salt as distinct signals due to quaternary nitrogen and neutral nitrogen, and ionic-bonded bromide were identified. An electrochromic device encompassing a dicyanamide ionic liquid based gel polymeric electrolyte with high ionic conductivity, a thermal decomposition temperature above 200 °C, and a stable voltage window of ～4 V with the IBV viologen dissolved therein, was constructed. IBV is a cathodically coloring organic electrochrome and the device underwent reversible transitions between transparent and deep blue hues; the color change was accompanied by an excellent optical contrast (30.5% at 605 nm), a remarkably high coloration efficiency of 725 cm² C^?1 at 605 nm and switching times of 2–3 s. Electrochemical impedance spectroscopy revealed an unusually low charge transfer resistance at the IBV salt/gel interface, which promotes charge propagation and is responsible for the intense coloration of the reduced radical cation state. The device was subjected to repetitive switching between the colored and bleached states and was found to incur almost no loss in redox activity, up to 1000 cycles, thus ratifying its suitability for electrochromic window/display applications.     

The critical impact of temperature gradients on Pt filament failure

This work established the correlation between the location of temperature gradients and the positions where breakdown is observed on different Pt filament layouts in cantilever and full membrane type micro-hotplates. Focusing on practical aspects like in real operation, self-heating was applied to investigate the limitations of high temperature application and to reveal the fatal failure mechanisms. Besides electromigration, another phenomenon playing dominant role in the breakdown of the filaments, the temperature gradient driven thermomigration of Pt was identified. This limits the local allowable temperature gradient to < 0.4 °C/μm for operation temperature above 700 °C.     

A methodology for projecting SiO2 thick gate oxide reliability on trench power MOSFETs and its application on MOSFETs VGS rating

In this work, a methodology based on the E-model for the reliability projection of a thick (> 20 nm) SiO₂ gate oxide on a vertical trench power MOSFET, is presented. Experimental results suggest that a Logic Level (LL) trench MOSFET with 35 nm of gate oxide can be rated at V_GS = + 12 V if one assumes continuous DC Gate-Source bias of V_GS = + 12 V at T = 175 °C for 10 years at a defect level of 1 Part Per Million (PPM). We will demonstrate that if we take into account MOSFET device lifetime as dictated by the Automotive Electronics Council (AEC Q101) mission profile, then devices can be rated higher to V_GS = + 14.7 V at T = 175 °C for the same PPM level (1 PPM). The application of the methodology for establishing the oxide thickness, t_ox, for any required voltage rating, is discussed.     

Wavelength-tunable thulium-doped single mode fiber laser based on the digitally programmable micro-mirror array

We propose a wavelength-tunable thulium-doped single mode fiber laser with a digitally controlled micro-mirror array device. The fast and flexible lasing wavelength switching property was achieved by the pixelated spatial modulation of the micro-mirror array. The proposed laser provides a maximum output power of 160 mW with 24% slope efficiency and a narrow output linewidth of less than 0.03 nm. The operating wavelength is continuously tunable from 1863 nm to 1937 nm with a wavelength selectivity accuracy of less than 0.4 nm and a fast switching time of ∼75 μs.     

Deep trap-induced dynamic on-resistance degradation in GaN-on-Si power MISHEMTs

Identification and characterization of a single, deep trap causing large increases in the on-resistance of GaN-on-Si power metal-insulator-semiconductor-high electron mobility transistors (MISHEMTs) is reported. This is achieved by using HEMT-based deep level optical spectroscopy (DLOS) and related methods in conjunction with high voltage off-state V_DS switching up to 400 V. A trap with an activation energy of ~ E_C − 2 eV that is physically located in the drain-access region of the MISHEMT is shown to be the primary source of an increase of the dynamic on-resistance increase by as much as ~ 9 times at 400 V operation. Comparisons of trap signatures extracted from the MISHEMT with capacitance-based DLOS measurements of simple Schottky-diode test-structures showing the same, dominant trap signature suggests that the physical defect is located within the GaN buffer and is not a surface or insulator-related defect. A buffer trap based model is presented to explain the observed on-resistance degradation effects in the MISHEMTs during high voltage switching.     

Radiation induced loss properties and hardness enhancement technique for ErYb doped fibers for avionic applications

We present radiation reliability properties and their enhancement of ErYb doped optical fibers in terms of induced loss and lifetime prediction via master curve analysis method. In this study, we are primarily concerned with the effects of ionizing radiation on the performance of double cladded ErYb doped optical fibers in an accelerated low dose γ-radiation environment (i.e. <120 rad/h rate) for high power optical amplifiers to be used in satellite communication systems. We demonstrate a novel method that utilizes pre-radiation exposure and thermal annealing, for enhancing radiation hardness of the fibers with respect to induced optical loss and lifetime prediction. Based on this method, we are able to modify radiation induced loss-rate properties of the fiber with an initial loss penalty, realizing overall loss-budget improvement for relatively long-term deployment (i.e. >5 years). In a direct comparison to non-hardened ErYb doped fibers, we demonstrate approximately 0.16 dB/m of radiation induced loss improvement including an initial loss penalty of 0.14 dB for radiation-hardened fibers over a 10-year duration in a natural low dose (i.e. <0.3 rad/h) radiation environment, i.e. low earth orbit.     

A new erase method for scaled NAND flash memory device

A suitable bird-beak thickness is crucial to the cell reliability. However, the process control for bird-beak thickness in the edge region is very difficult. A new erase method is proposed in this work to modulate the electron tunneling region of 40 nm floating gate NAND flash memory device. The erasing electron can move to gate center from gate edge under back bias at 0.3 V/− 0.8 V. The Fowler-Nordheim (FN) current of erase operation distributes on the whole channel region, not located at the gate edge region. Results show that the proposed method can improve cell reliability about 33%. TCAD analysis is employed to explain and prove the mechanism. This new erase method is promising for scaled NAND flash memory.     

Degradation behaviors of GaN light-emitting diodes under high-temperature and high-current stressing

A number of commercially available multiple-quantum well (MQW) InGaN/GaN blue LEDs with wavelengths of about 460 nm and a power of 1 mW were stressed at temperatures ranging from 25 to 120 °C at several accelerated DC currents. Both the forward and reverse current voltage characteristics as well as the electroluminescent spectra of the LEDs were monitored. These effects also resulted in the pronounced degradation of light efficiency and device operation lifetime. We found that the degradation of photonic characteristics, correlated very well with the generation-recombination current which is governed by the defect density. The device degradation is much faster at high temperatures. At nominal operation current and at room temperature, the light intensity degradation reaches a saturation level before the light dyes out. These results shed new lights upon the design and lifetime specifications for the emerging commercial solid-state lighting devices.     

A fast switching bistable electromagnetic microactuator fabricated by UV-LIGA technology

A fast switching electromagnetic microactuator with two stable positions is presented. The actuator consists of a cantilever beam with two free ends, a torsional beam with two fixed ends, planar coils and permanent magnets. The cantilever beam has two stable positions due to the use of the permanent magnets. With electromagnetic actuation arising from the planar coils, the cantilever beam will switch from one stable position to the other. The behaviour of the microactuator is studied using a coupled electromagnetic-mechanical FEM-simulation with ANSYS software. The working mechanism for the bistability of the actuator is analysed. The device with a size of 2.0 mm × 2.2 mm is fabricated by UV-LIGA technology using sacrificial layer. The results of test show that a current pulse with an amplitude of 50 mA is needed for actuator’s switching between two stable states, and the switching time is approximately 20 μs. The displacement of the end of cantilever is about 17 μm.