Simple Device Structure Research Articles

TID Effects Induced by ARACOR, 60Co, and ORIATRON Photon Sources in MOS Devices: Impact of Geometry and Materials

Total ionizing dose (TID) effects induced by different photon sources are studied in MOS devices. The dose factor (DF), defined as the ratio between dose deposition in dosimeter and actual dose deposition in MOS-sensitive oxides (SOs), is estimated using Monte-Carlo simulations of energetic photons striking simple device structures. An effective TID approach is proposed to account for both the real ionizing dose depositions in small volumes and the charge yield. This method is applied to a silicon-on-insulator (SOI) technology using three photon sources: the usual ARACOR and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co sources, which deliver several tens of kiloelectron volt photons and ~1.25-MeV photons, respectively, and a third facility named ORIATRON, a 6-MeV electron linear accelerator that produces photons on a wide energy spectrum. This topic, investigated intensively in the literature a few decades ago, is revisited in the context of several evolutions including: new radiation sources, novel simulation tools, and device scaling, which all impact ionizing dose deposition in microsensitive volumes of current electronic technologies. Dedicated numerical simulations demonstrate the importance of taking into account the entire stack of materials in order to get the most accurate estimations of TID in the SO. Descriptions of the back-end-of-line (BEOL) layers (especially when the technology uses copper), the polysilicon gate, the Buried OXide (BOX) (for SOI devices), but also of the substrate and package are mandatory in these simulations, since dose enhancement and/or backscattered photons can be a significant source of TID variation in the gate oxide. Also the package lid composition and its thickness can be major TID contributors. The results show that the use of a prefilter with lead and aluminum can optimize ionizing dose deposition

Facile Fabrication of Hybrid Perovskite Single‐Crystalline Photocathode for Photoelectrochemical Water Splitting

Recently, beyond various optoelectronic devices, lead halide perovskites have emerged as promising candidates for high‐performance photocatalysts owing to their excellent optoelectronic properties. However, most previous works on perovskite photocatalysts mainly used the forms of nanocrystals that need the perovskite‐saturated electrolyte or polycrystalline thin films that still suffer from the instability in water and low performance. Herein, the synthesis of high‐quality hybrid perovskite single crystals and their implementation as photocathodes for water splitting with a simple device structure are reported on. Optimized perovskite crystals exhibit a good water splitting photocurrent density of −0.51 mA cm−2 at 0 V versus reversible hydrogen electrode (RHE) under visible light illumination. Moreover, such devices as the p‐type photocathodes show improved stability, exhibiting no obvious decrease over 600 s. This work highlights the great potential of hybrid perovskite single crystals for photocatalyst applications in aqueous solution.

Resistive Switching of the Tetraindolyl Derivative in Ultrathin Films: A Potential Candidate for Nonvolatile Memory Applications.

Bipolar resistive switching using organic molecule is very promising for memory applications owing to their advantages, such as simple device structure, low manufacturing cost, stability, and flexibility. Herein we report Langmuir-Blodgett (LB) and spin-coated-film-based bipolar resistive switching devices using organic material 1,4-bis(di(1H-indol-3-yl)methyl)benzene (Indole1). The pressure-area per molecule isotherm (π-A), Brewster angle microscopy (BAM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to formulate an idea about the organization and morphology of the organic material onto thin films. On the basis of the device structure and measurement protocol, it is observed that the device made up of Indole1 shows nonvolatile resistive random access memory (RRAM) behavior with a very high memory window (∼106), data sustainability (5400 s), device yield (86.7%), and repeatability. The oxidation-reduction process and electric-field-driven conduction are the keys behind such switching behavior. Because of very good data retention, repeatability, stability, and a high device yield, the switching device designed using compound Indole1 may be a potential candidate for memory applications.

Precise Nucleation Regulation and Defect Passivation for Highly Efficient and Stable Carbon-Based CsPbI2Br Perovskite Solar Cells

Carbon-based all-inorganic CsPbI2Br perovskite solar cells (C-PSCs) are regarded as a promising photovoltaic candidate due to their low cost, simple device structure, and high stability. However, t...

On current blockade upon analyte translocation in nanopores

Nanopore sensing primarily concerns quantifying the amplitude and shape of blockage current as well as the frequency of translocation events by analyzing the variation of the ionic current upon analyte translocation in a nanopore that represents an extremely simple device structure. To facilitate such an analysis, most reported physical-phenomenological models focus on geometrical factors. Here, we systematically analyze several other factors that may influence the amplitude and waveform of the blockage current. Our theoretical analysis starts with an analytical model based on geometry. It is then extended to include effects of surface conductance, electroosmotic flow, ionic concentration polarization, and induced charge on nanopore membranes. This approach allows for the examination of related electrokinetic and electrohydrodynamic aspects of analyte translocation in nanopores. The model results are confirmed using numerical simulation. The principal outcome of our theoretical scrutiny includes the identification of the respective determinatives of various factors as well as criteria for safely neglecting some of them when correlating the amplitude and waveform of blockage current to the properties of the translocating analyte. Our attempt to categorize these factors can be of practical implications in understanding the translocation process and for developing advanced data analysis algorithms as an effort to promote nanopore sensor applications.

Controlled Biodegradation of an Additively Fabricated Capacitive Soil Moisture Sensor

Successful precision agriculture decision making requires characterizing soil heterogeneity at high spatiotemporal resolution in real-time in order to optimize input (such as water and nutrient) amounts and location. In order to achieve this goal, a printed soil moisture sensor fabricated from biodegradable materials is demonstrated. These devices are intended to function during the growing season and then harmlessly degrade afterward, enabling high-density deployment, eliminating the need for sensor retrieval, and enabling the use of simple device structures and low-cost materials and fabrication techniques. A capacitive structure is used with a water-soluble zinc electrode printed onto a biodegradable substrate. Rapidly degrading substrate and electrode are encapsulated in a slowly degrading wax blend that protects the device, reduces drift, and controls degradation time. A linear capacitance response is observed for soil samples with a volumetric water content from 0 to 72%. Accelerated degradation testing demonstrates that the sensor responds predictably and stably until the encapsulation is breached, at which point the sensor fails rapidly, providing a clear distinction between the functional and nonfunctional lifetimes of the sensor. These results demonstrate the potential of biodegradable sensors to allow maintenance-free, affordable, and real-time soil moisture measurement at high spatial density for precision irrigation control.

Solution‐Processed Organic/p‐Type Silicon Hybrid Heterojunction Solar Cells

Organic–inorganic hybrid heterojunction solar cells have gained extensive attention due to the simple device structure and low‐cost technological processes, and n‐type silicon has been mainly used as the inorganic absorber in previous research. Herein, hybrid heterojunction solar cells based on p‐type silicon are successfully prepared through a low‐temperature solution method. A preliminary power conversion efficiency over 4% is observed, via optimizing the organic thin‐film deposition and organic/inorganic interface, which enhance the built‐in field and promote the separation of photogenerated carriers in the heterojunction. Therefore, a new idea and possibility are provided for developing low‐cost, high‐performance solar cells.

High-power-efficiency thermally activated delayed fluorescence white organic light-emitting diodes based on asymmetrical host engineering

Developing thermally activated delayed fluorescence (TADF) white organic light emitting diodes (WOLED) featuring high power efficiencies faces a challenge in balancing carrier transport, energy transfer and quenching suppression. Here, we demonstrate that host matrix is crucial for the modification of optoelectronic process in emissive layers (EML) and the achievement of high power efficiency. Through asymmetrically introducing two or three diphenylphosphine oxide (DPPO) groups, three phosphine oxide (PO) hosts 24DBFDPO , 26DBFDPO and 248DBFTPO were constructed, in which dibenzofuran (DBF) chromophore is embedded by rationally spatial distribution of DPPO groups in 26DBFDPO and 248DBFTPO . Direct steric effect of DPPOs suppresses the host-dopant and dopant-dopant interaction induced quenching and mitigates excessive dopant-dopant energy transfer. Dually-doped white TADF films of 248DBFTPO reveal the improved white color purity with a high quantum yield of ~ 90%. Simultaneously, remote steric and electron-withdrawing effects of DPPOs remedy carrier transport in 248DBFTPO films. Based on a simple trilayer single-EML device structure, 248DBFTPO endowed its full-TADF WOLEDs with the state-of-the-art performance, especially the top-rank power efficiency beyond 70 lm W −1 . This work indicates host engineering can provide a feasible approach to realize the practical application of TADF daily lighting. • Host engineering based Asymmetric phosphine oxide hosts were implemented for white TADF diodes. • Intermolecular interactions in host matrixes are accurately adjusted with spatial asymmetry of phosphine oxide groups. • Carrier mobility of 10 −6 cm 2 V −1 s −1 for neat films and ~ 90% PLQYs of blue and white TADF doped films are achieved. • High power efficiency beyond 70 lm W −1 was realized by a simple trilayer single-emissive-layer TADF WOLED.

Effect of alkyl side chain length on the electroluminescent performance of blue light-emitting poly(fluorene-co-dibenzothiophene-S,S-dioxide)

In this manuscript, we report a simple strategy of tuning the alkyl side chain length of emissive polymer to realize blue polymer light-emitting diodes (PLED) with high efficiency and enhanced device lifetime. Two poly(fluorene-co-dibenzothiophene-S,S-dioxide) derivatives, PF16SO and PF8SO, comprising the same backbone but different side chains lengths (hexadecyl only or hexadecyl mixed with octyl), were synthesized, respectively. Attributing to the stronger rigidity caused by its shorter side chains, PF8SO exhibits high glass-transition temperature of 218 °C and photoluminescence quantum yield of 78%. Furthermore, the grazing incidence X-ray diffraction measurements reveal closer π-π packing for PF8SO, resulting in improved and more balanced charge carrier transport. As a result, an enhanced electroluminescence performance with a low turn-on voltage of 2.8 V, a high luminous efficiency of 8.36 cd A−1 (corresponding to an external quantum efficiency of 6.19%) with the Commission Internationale de L’E'clairage coordinates of (0.15, 0.18) was achieved based on a single-layer device structure of ITO/PEDOT:PSS/Emissive Layer/Ba/Al, which is among the best performance reported so far for pure blue light-emitting polymers based on this simple device structure. In addition, PF8SO based device exhibits longer lifetime than that of PF16SO. The result indicates the great potential of tuning the alkyl side chain length in enhancement of electroluminescent performance for blue light-emitting poly (fluorene-co-dibenzothiophene-S,S-dioxide).

Efficient green electroluminescent devices with low operation voltage and slow efficiency roll-off by utilizing hole transport material as host

We reported efficient electroluminescent (EL) devices with low operation voltage and slow efficiency roll-off based on green emitter Ir1 by utilizing hole transport material TAPC as host. Experimental results revealed our designed single light-emitting layer (EML) devices exhibit even lower operation voltage and slower efficiency roll-off compared with double-EMLs devices attributed to the reduced carriers' injection barriers, balanced carriers' distribution and well confined recombination zone. Ultimately, efficient green EL device realized the highest current efficiency (CE), power efficiency (PE), external quantum efficiency (EQE) and brightness of 71.6 cd/A, 75.0 lm/W, 22.9% and 36600 cd/m2, respectively. Excitedly, turn-on voltage was only 2.5 V. Even at a given brightness of 1000 cd/m2 (3.4 V), CE of 67.2 cd/A (EQE = 21.5%) and PE of 65.8 lm/W can still be retained. Our work offers a method to prepare efficient devices with slow efficiency roll-off, low operation voltage and simultaneously simple device structure.

Towards engineering in memristors for emerging memory and neuromorphic computing: A review

Resistive random-access memory (RRAM), also known as memristors, having a very simple device structure with two terminals, fulfill almost all of the fundamental requirements of volatile memory, nonvolatile memory, and neuromorphic characteristics. Its memory and neuromorphic behaviors are currently being explored in relation to a range of materials, such as biological materials, perovskites, 2D materials, and transition metal oxides. In this review, we discuss the different electrical behaviors exhibited by RRAM devices based on these materials by briefly explaining their corresponding switching mechanisms. We then discuss emergent memory technologies using memristors, together with its potential neuromorphic applications, by elucidating the different material engineering techniques used during device fabrication to improve the memory and neuromorphic performance of devices, in areas such as I ON/I OFF ratio, endurance, spike time-dependent plasticity (STDP), and paired-pulse facilitation (PPF), among others. The emulation of essential biological synaptic functions realized in various switching materials, including inorganic metal oxides and new organic materials, as well as diverse device structures such as single-layer and multilayer hetero-structured devices, and crossbar arrays, is analyzed in detail. Finally, we discuss current challenges and future prospects for the development of inorganic and new materials-based memristors.

Constructing Donor-Resonance-Donor Molecules for Acceptor-Free Bipolar Organic Semiconductors.

Organic semiconductors with bipolar transporting character are highly attractive as they offer the possibility to achieve high optoelectronic performance in simple device structures. However, the continual efforts in preparing bipolar materials are focusing on donor-acceptor (D-A) architectures by introducing both electron-donating and electron-withdrawing units into one molecule in static molecular design principles. Here, we report a dynamic approach to construct bipolar materials using only electron-donating carbazoles connected by N-P=X resonance linkages in a donor-resonance-donor (D-r-D) structure. By facilitating the stimuli-responsive resonance variation, these D-r-D molecules exhibit extraordinary bipolar properties by positively charging one donor of carbazole in enantiotropic N+=P-X- canonical forms for electron transport without the involvement of any acceptors. With thus realized efficient and balanced charge transport, blue and deep-blue phosphorescent organic light emitting diodes hosted by these D-r-D molecules show high external quantum efficiencies up to 16.2% and 18.3% in vacuum-deposited and spin-coated devices, respectively. These results via the D-r-D molecular design strategy represent an important concept advance in constructing bipolar organic optoelectronic semiconductors dynamically for high-performance device applications.

Highly stable and efficient cathode-buffer-layer-free inverted perovskite solar cells.

A simpler and less expensive fabrication process is one of the essential demands for the commercialization of perovskite solar cells (PeSCs). Especially, inverted PeSCs (I-PeSCs) require a cathode buffer layer (CBL) for fabricating highly efficient and stable PeSCs. However, this increases the number of fabrication step. Here, we demonstrate highly stable and efficient cathode-buffer-layer-free I-PeSCs via additive engineering on an ETL, which is based on phenyl-C61-butyric acid methyl ester (PC61BM) with a small amount of poly(methyl methacrylate) (PMMA). This modified ETL shows not only a simplified fabrication process but also effective extraction of charge from the perovskite to a high work function copper electrode (Cu) by formation of an interfacial dipole at the interfaces between the ETL and the Cu. Additionally, it exhibits good passivation of the trap density existing along the grain boundaries and surface of the perovskite layer, reducing the non-radiative recombination and consistent with the increases in open-circuit voltage (Voc). As a result, I-PeSCs with a blend PC61BM : PMMA ETL demonstrate an enhancement in the power conversion efficiency (PCE) from 13.55% (without PMMA) to 18.38%. Furthermore, they exhibit both burn-in-free behaviour in photostability measurements by maximum power-point tracking (MPPT) method and long-term air-stability (30 days for T90) in ambient air. Lastly, we obtained PCE of 15.03% and 16.83% for large-area (1 cm2) I-PeSCs with PC61BM and PC61BM : PMMA, respectively. This method provides an alternative route to reduce the fabrication time and budget for commercialization of I-PeSCs without sacrificing device performance.

Stable, High‐Efficiency Voltage‐Dependent Color‐Tunable Organic Light‐Emitting Diodes with a Single Tetradentate Platinum(II) Emitter Having Long Operational Lifetime

Voltage-dependent, color-tunable organic light-emitting diodes (OLEDs) are appealing tools that can be used for the visualization of electronic output signal of sensors. Nonetheless, the literature-reported color-tunable OLEDs that have a simple single-cell device structure suffer from relatively low efficiency, pronounced efficiency roll-off, color-aging, and short operation lifetime, all of which limit their practical applications. Here, a novel co-host-in-double-emissive-layer (CHIDEL) device, designed to enhance the performance of color-tunable OLEDs with the use of a single tetradentate Pt[O^ N^ C^ N] emitter, is described. When Pt-X-2 is used as a single emitter in an optimized CHIDEL device, a white OLED with tunable Commission International de I'Eclairage (CIE) coordinates from (0.47, 0.44) at 3V to (0.36, 0.48) at 11V, a high color rendering index of 82, and high external quantum efficiency (EQE) of up to 20.75% can be achieved. By using Pt-X-4 as a single emitter, the voltage-dependent color-tunable CHIDEL device, with CIE coordinates shifted from (0.56, 0.43) at 3V to (0.42, 0.55) at 11V, demonstrates a high luminance of beyond 90 000cd m-2 and a high EQE of 23.23% at a luminance of 1300cd m-2 . A long-lifetime time to 90% of the initial luminance (LT90 ) of almost 20000 h is demonstrated for the color-tunable OLED with Pt-X-4 emitting dopant.

In-plane spin-orbit torque magnetization switching and its detection using the spin rectification effect at subgigahertz frequencies

Inplane magnetization reversal of a permalloy/platinum bilayer was detected using the spin rectification effect. Using a sub GHz microwave frequency to excite spin torque ferromagnetic resonance (ST FMR) in the bilayer induces two discrete DC voltages around an external static magnetic field of 0 mT. These discrete voltages depend on the magnetization directions of the permalloy and enable detection of the inplane magnetization reversal. The threshold current density for the magnetization reversal is from 10 to 20 MA/cm^2, the same order as for known spin orbit torque (SOT) switching with in-plane magnetization materials. The magnitude of the signal is the same or larger than that of the typical ST FMR signal; that is, detection of magnetization switching is highly sensitive in spite of deviation from the optimal ST-FMR condition. The proposed method is applicable to a simple device structure even for a small ferromagnetic electrode with a width of 100 nm.

Fabrication of Amorphous SRVOX-Based Memristor for Neuromorphic Computing

Because resistive random access memory (RRAM) has advantages, such as fast switching speed, low energy consumption, and simple device structure, it is promising device architecture for memory, artificial intelligence, and neuromorphic computing. In particular, for RRAM for use in neuromorphic applications, it must be able to mimic synaptic behavior by pulse modulation. In order to have such a characteristic, the resistance state has to be gradually changed by the stress, e.g., potentiation and depression. High linearity is required because the linearity of RRAM obtained through each resistance state is evaluated as an especially important property for artificial synaptic applications.In this work, we performed the electrical properties of sputter-deposited amorphous strontium vanadate (a-SVO) RRAM with Pt bottom electrode and Ag top electrode. Sufficient reproducibility and uniformity between devices was realized. The highest resistance ratio of ~ 103 was observed and insignificantly changed for retention testing up to 2 × 104 s. In particular, the conduction filament generated from the a-SVO RRAM was adjusted according to the regulation of voltage stress to obtain a multi-level resistance state. It was confirmed by ToF-SIMS analysis and COMSOL Multiphysics simulation that the conduction filament was formed by Ag atoms. Hopfield Neural Network simulation was conducted to verify that the performance of analog resistive switching behavior of a-SVO RRAM is suitable for neuromorphic computing. The accuracy of our simulated device was saturated to 86.8 % for 100,000 asynchronous iterations. The results imply that our a-SVO RRAM is of great potential for use in neuromorphic computing.

Monolithic focus-tunable lens technology enabled by disk-type dielectric-elastomer actuators

We propose a monolithic focus-tunable lens structure based on the dielectric-elastomer actuator (DEA) technology. In our focus-tunable lens, a soft lens and radial in-plane actuator mimicking the ocular focal-tuning mechanism are constructed in a single body of an optimized dielectric-elastomer film. We provide device fabrication methods including elastomer synthesis, structure formation, and packaging process steps. Performance test measurements show 93% focal tunability and 7 ms response time under static and dynamic electrical driving conditions, respectively. These performance characteristics are substantially enhanced from the previous polylithic DEA tunable lens by a factor 1.4 for the focal tunability and a factor 9.4 for the dynamic tuning-speed limit. Therefore, we obtain greatly enhanced focal tuning control in a remarkably simple and compact device structure.

Two-Step Processed Efficient Potassium and Cesium-Alloyed Quaternary Cations Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) are continuously attracting much attention due to the poential applications in low-cost and flexible solar energy system. In this work, potassium (K+) and cesium (Cs+) were added into the perovskite (FAMA)Pb(IBr)3 (FA = CH(NH2)2+, MA = CH3NH3+) to prepare the high-quality quadruple-cation (KCsMAFA) perovskite film and PSCs via two-step solution process. The optoelectronic properties and stability of FAMA, CsFAMA and KCsFAMA perovskite film and PSC devices were systematically studied and analyzed. The power conversion efficiency (PCE) of champion KCsFAMA device reached 19.70%, and the steady output PCE was 19.40% with a simple device structure of ITO/SnO2/Perovskite/Spiro-OMeTAD/Ag. In addition, the stability of PSCs with quadruple-cation KCsMAFA was significantly improved as compared to the control ones. With the storage in air for 20 days (humidity ∼35%), the PCEs of PSCs without encapsulation could maintain 77% of the initial values, while the PCEs of PSCs with MAFA and CsMAFA only maintained 39% and 56% of their initial values, respectively. The improved efficiency and stability in PSCs with both K+ and Cs + were attributed to significant improvement in the film quality with large and dense grains, which could reduce grain boundaries and moisture immersion. Meanwhile, the incorporation of K+ and Cs+ could enhance the charge transfer resistance and suppress the charge recombination effectively, supporting in the improvement in the performance of PSCs.

Improving the Fill Factor of Perovskite Solar Cells by Employing an Amine-tethered Diketopyrrolopyrrole-Based Polymer as the Dopant-free Hole Transport Layer

Although rapid progress has been witnessed recently in regular perovskite solar cells (PSCs), one of the bottlenecks to delay their industrialization is the complicated and poor reproducible doping process of the widely used hole-transporting material (HTM) spiro-OMeTAD. To address this issue, herein, an unreported polymer, P25NH, has been synthesized and adopted as a dopant-free hole transport layer (HTL) in PSCs. Compared with the commonly used HTM poly(3-hexylthiophene), P25NH shows better aggregation property, enhanced ability of passivation to the perovskite surface, and higher mobility, which could greatly reduce series resistance and improve the fill factor. The PSCs with P25NH (1.6 mg/mL) as HTLs exhibited a decent power conversion efficiency (PCE) of 18.1% with a high fill factor of 81.9% (at 6 mg/mL, the fill factor is 83.2%). This work provides an alternative polymer for scalable dopant-free HTMs and a simple device structure for achieving high PCE.

Frequency-Enabled Decouplable Dual-Modal Flexible Pressure and Temperature Sensor

Multifunctional sensory devices are emerging as a new trend in skin-inspired flexible electronics. Multimodal sensors show advanced features of simple device structure and ease of integration. However, multimodal sensors usually involve various sensing mechanisms and have difficulty in signal decoupling. In this letter, we used chitosan as a multifunctional layer to create a dual-modal flexible sensor. The performance of the pressure sensing exhibited excellent linearity ( $\text{R}^{2} = 0.997$ ), short response time (~37 ms), and uniform sensitivity over a wide range based on the contact surface mechanism. The temperature-sensitive proton conductivity of chitosan allowed a capacitive sensitivity of ~2.56 pF/°C. The frequency dependency of the capacitive output enabled modulations of the responses and a simple yet effective approach for decoupling the pressure and temperature responses with an average accuracy of ~92.3%. Such frequency-enabled decouplable dual-modal sensors show the advantages of simple device structure and multifunctional capabilities in skin-inspired electronics.