Device Design Strategies Research Articles

Progress on Light‐Emitting Electrochemical Cells toward Blue Emission, High Efficiency, and Long Lifetime

AbstractSince their emergence in the 1990s, light‐emitting electrochemical cells (LECs) have attracted much attention due to their unique properties and potential for use as an alternative technology for illuminations and displays. After decades of development, however, the performance of LECs remains far from satisfactory for practical applications, in particular for those requiring blue light. Efforts have been made to develop of highly efficient blue‐emitting materials and more advanced device structures, aiming at realizing blueshifted emission, enhancing efficiency, and extending prolonged device lifetimes. A timely review into the current state of blue LECs is deemed imperative, as a full understanding of the molecular and device design strategy and identification of the major challenges that must be addressed to realize practical applications is necessary. A specific summary of recent progress on blue LECs is provided, with the focus placed on design strategies for blue emitters for LECs and device structures with respect to color tuning, efficiency enhancement, and stability improvement. Finally, the direction of development strategies in the future is suggested.

Material strategies for on-demand smart transient electronics

Abstract

Ultra-high Photovoltage (2.45 V) Forming in Graphene Heterojunction via Quasi-Fermi Level Splitting Enhanced Effect.

SummaryOwing to the fast response speed and low energy consumption, photovoltaic vacuum-ultraviolet (VUV) photodetectors show prominent advantages in the field of space science, high-energy physics, and electronics industry. For photovoltaic devices, it is imperative to boost their open-circuit voltage, which is the most direct indicator to measure the photoelectric conversion capability. In this report, a quasi-Fermi level splitting enhanced effect under illumination, benefiting from the variable Fermi level of graphene, is proposed to significantly increase the potential difference up to 2.45 V between the two ends of p-Gr/i-AlN/n-SiC heterojunction photovoltaic device. In addition, the highest external quantum efficiency of 56.1% (under the VUV irradiation of 172 nm) at 0 V bias and the ultra-fast photoresponse of 45 ns further demonstrate the superiority of high-open-circuit-voltage devices. The proposed device design strategy and the adopted effect provide a referential way for the construction of various photovoltaic devices.

Vertical nanowire array-based biosensors: device design strategies and biomedical applications.

Biosensors have been extensively studied in the areas of biology, electronics, chemistry, biotechnology, medicine, and various engineering fields. The interdisciplinarity creates an ideal platform for scientists to analyze biological species and chemical materials in a direct, efficient, and sensitive manner; this is expected to revolutionize the life sciences, basic medicine, and the healthcare industry. To carry out high-performance biosensing, nanoprobes - with specific nanoscale properties - have been proposed for ultrasensitive and in situ monitoring/detection of tracer biomolecules, cellular behavior, cellular microenvironments, and electrophysiological activity. Here, we review the development of vertical nanowire (VNW) array-based devices for the effective collection of biomedical information at the molecular level, extracellular level, and intracellular level. In particular, we summarize VNW-based technologies in the aspects of detecting biochemical information, cellular information, and bioelectrical information, all of which facilitate the understanding of fundamental biology and development of therapeutic techniques. Finally, we present a conclusion and prospects for the development of VNW platforms in practical biomedical applications, and we identify the challenges and opportunities for VNW-based biosensor systems in future biological research.

Dynamic Blood Vessels and Implications for Medical Devices

The primary function of most vascular stents is to resist radial constriction after angioplasty, and the majority of stent grafts are meant to exclude aneurysms or dissected false lumens. These functions require radial force, however, these devices must also survive vascular deformations. Vascular deformation used to be an afterthought since experts once believed blood vessels had no significant movement aside from cardiac-induced radial pulsatility, but it is now known to be a critical consideration for medical device development. The main drivers of vascular deformation can include cardiac pulsatility, respiration, musculoskeletal motion, and external influences. Since long term implant durability came to the forefront of concern in the early 2000s, it is now entangled into device design, regulation, product positioning, marketing, sales, and corporate strategy. Investment in defining anatomic boundary conditions during the early stages of product development will improve product design and save time and money in the long run.

Air Curtain Dust Removal Device Design and Dust Prevention Strategy in Heading Face

Dust protection is a safety guarantee of heading face. The previous model of air curtain research was ideal, and the dust removal effect was rarely studied in the actual dust‐producing face. This paper presents a method of air curtain dust removal (ACDR) in the actual heading face. The author designed an air curtain dust removal device (ACDRD). The law of total dust concentration, respiratory dust concentration, and respiratory dust ratio is obtained. The minimum outlet airflow velocity is analyzed using the flat‐plane injection theory. The effect of the exhaust fan placement on the dust removal effectiveness is examined. Research indicates the following: The airflow speed at the upper, left, and right sides of the ∩‐shaped slot is 17.39 m/s, 12.04 m/s, and 13.66 m/s, respectively. The minimum dust removal speed of the air curtain is 5.48 m/s. The total dust concentration is the highest in the spot of roadheader operator, and the concentration of respiratory dust decreases sharply within 20 m. When the indentation air duct is 2.1 m away from the base plate, the dust‐proof effect is better. The results can provide theoretical bases and methods for air curtain analysis of the heading face.

Electrothermal performance limit of β-Ga2O3 field-effect transistors

A β-Ga2O3 field effect transistor (FET) outperforms a GaN FET in Baliga's figure of merit (FOM) by 400% and Huang's chip area manufacturing figure of merit by 330%, suggesting that β-Ga2O3 could be a substrate of choice for next generation power transistors. However, its low thermal conductivity leads to extreme self-heating, which deteriorates the device performance during high voltage operation. A holistic evaluation of performance from a material-device-circuit perspective is necessary before reaching any conclusion regarding the technological viability of β-Ga2O3. In this paper, we develop a multiphysics and multiscale model for a material-device-circuit analysis of β-Ga2O3 FETs. The framework allows us to explore the effectiveness of various device design strategies (e.g., thermal shunts) for mitigating the thermal chokepoints and compare the performance of improved β-Ga2O3 FETs against that of GaN and SiC FETs. We highlight the limitations of traditional FOMs to analyze the relative performance of the new generation of power transistors whose structure incorporates stacked layers of materials with different thermal conductivities, like those of β-Ga2O3 FETs. We suggest device design strategies, such as wafer thinning, incorporation of heat shunts, and improved channel mobility, so that β-Ga2O3 FETs can compete commercially with GaN and SiC technologies.

Electronic Fabry-Perot Cavity Engineered Nanoscale Thermoelectric Generators

In this work, we aim to design a heterostructure based nanoscale thermoelectric generator that can maximize the waste-heat conversion efficiency at a given output power. The primary objective to be achieved for this is to realize a boxcar-shaped (bandpass) electronic transmission function (R. S. Whitney, Phys. Rev. Lett. 112, 130601 (2014)). In order to achieve that, we propose the use of an electronic analog of optical Fabry-P\'erot cavity over a central resonant tunneling structure. We further explore the optimum design possibilities by varying the geometry of the cavity wall to ensure a nearly perfect bandpass energy filtering of electrons. Based on our findings, we propose a general design guideline to realize such transmission and demonstrate that such devices can be excellent thermoelectric generators compared to the existing proposals in terms of boosting the output power without a cost in efficiency. It is theoretically demonstrated using the non-equilibrium Green's function technique coupled with self-consistent charging effects that an enhancement in the maximum output power up to $116\%$ can be achieved through this scheme at a $10\%$ higher efficiency as compared to resonant tunneling based devices. Furthermore, an elaborate comparative study of the linear response parameters is also presented and explained in terms of the physical transport properties. This study suggests an optimal device design strategy for an improved thermoelectric generator and sets the stage for a new class of thermoelectric generators facilitated via transmission lineshape engineering.

Fiber-Based Energy Conversion Devices for Human-Body Energy Harvesting.

Following the rapid development of lightweight and flexible smart electronic products, providing energy for these electronics has become a hot research topic. The human body produces considerable mechanical and thermal energy during daily activities, which could be used to power most wearable electronics. In this context, fiber-based energy conversion devices (FBECD) are proposed as candidates for effective conversion of human-body energy into electricity for powering wearable electronics. Herein, functional materials, fiber fabrication techniques, and device design strategies for different classes of FBECD based on piezoelectricity, triboelectricity, electrostaticity, and thermoelectricity are comprehensively reviewed. An overview of fiber-based self-powered systems and sensors according to their superior flexibility and cost-effectiveness is also presented. Finally, the challenges and opportunities in the field of fiber-based energy conversion are discussed.

Steering second-harmonic radiation through local excitations of plasmon.

We propose an approach of steering the second harmonic (SH) emission from a single plasmonic structure, through local excitations of plasmon. The proposed idea is confirmed experimentally, by adjusting the incident beam position at the fundamental frequency, on a single plasmonic antenna. A significant directivity change ( ± 52°) for the SH emission is observed with submicrometer adjustment ( ± 250 nm) of the excitation beam position, over broadband SH frequencies. Providing a simple method of controlling the directivity of frequency-converted light, our approach paves the way to new design strategy for nonlinear optical devices with various nonlinear wavefronts.

Sub-nanosecond pulse programming and device design strategy for analog resistive switching in HfOx-based resistive random access memory

The analog switching behavior of resistive random access memory (RRAM) is crucial for its application in neuromorphic computing. This paper investigates the switching mechanism of RRAM under sub-nanosecond and nanosecond pulse programming, with selected device materials and structures, using the kinetic Monte Carlo simulation method. The microscopic distribution of oxygen vacancies is simulated in all three spatial dimensions and in the time dimension (four-dimensional). According to the simulation results, thermal effects are a critical factor affecting the switching behavior. The thermal effects inside the HfOx switching layer can be almost completely eliminated by using sub-nanosecond pulses with low voltage, finally leading to good analog behavior. When nanosecond pulses are applied, effective heat insulation is the key to realizing analog characteristics. In general, the switching process is proposed to involve three stages. Having the lowest energy consumption, the first stage shows the greatest potential for achieving analog behavior. The use of heat-isolating structures, like capping layers and side wall materials with lower thermal conductance, could be a solution to improve the analog behavior of RRAM at the first stage when down-scaling the device size.

Surface functionalization-induced photoresponse characteristics of monolayer MoS2 for fast flexible photodetectors.

Monolayered, semiconducting molybdenum disulfide (MoS2) is of considerable interest for its potential applications in next-generation flexible, wearable, and transparent photodetectors because it has outstanding physical properties coupled with unique atomically thin dimensions. However, there is still a lack of understanding in terms of the underlying mechanisms responsible for the photoresponse dynamics, which makes it difficult to identify the appropriate device design strategy for achieving a fast photoresponse time in MoS2 photodetectors. In this study, we investigate the importance of surface functionalization on controlling the charge carrier densities in a MoS2 monolayer and in turn the corresponding behavior of the photoresponse in relation to the position of the Fermi-level and the energy band structure. We find that the p-doping and n-doping, which is achieved through the surface functionalization of the MoS2 monolayer, leads to devices with different photoresponse behavior. Specifically, the MoS2 devices with surface functional groups contributing to p-doping exhibited a faster response time as well as higher sensitivity compared to that observed for the MoS2 devices with surface functional groups contributing to n-doping. We attribute this difference to the degree of bending in the energy bands at the metal-semiconductor junction as a result of shifting in the Fermi-level position, which influences the optoelectronic transport properties as well as the recombination dynamics leading to a low dark and thus high detectivity and fast decay time. Based upon these findings, we have also demonstrated the broad applicability of surface functionalization by fabricating a flexible MoS2 photodetector that shows an outstanding decay time of 0.7 s, which is the fastest response time observed in flexible MoS2 detectors ever reported.

Biomechanical research progress on sex differences of abdominal aortic aneurysm

The phenomenon of sex differences exists in patients who have abdominal aortic aneurysms (AAA). The occurrence rate of AAA is higher in male, while the rates of rupture and postoperative mortality are higher for female. This phenomenon of sex differences would affect the diagnosis, treatment and postoperative rehabilitation for AAA patients. This article reviewed the recent research status of sex differences on AAA, and explored the phenomenon of sex differences from the aspects of threshold determination, biomechanics and mechanobiology. This review points out that the sex differences on AAA could ascribe to the differences of biomechanical environment and biological properties induced by the vascular size, anatomy structure and structure components of abdominal aortic artery. The comprehensive investigations of the sex differences on AAA could help to optimize the diagnosis, treatment and device design, patient care and rehabilitation strategy of AAA based on sex differences phenomenon.

A general optimization approach for contact-separation triboelectric nanogenerator

Triboelectric nanogenerator (TENG) is a kind of mechanical energy harvesters based on triboelectric effect. Its output performance strongly depends on the structural design, material properties, circuit status, and mechanical loading process. In this work, we develop a new theoretical method for analysing the contact-separation mode TENG devices with dimensionless formulations which are based on the V-Q-x relationship with the TENG being treated as a parallel-plate capacitor. The correctness and accuracy of the proposed method and model are verified and validated via a series of experimental results. With the proposed method, the scaling laws between the performance and structure, material properties, circuit status and mechanical loading are established, and the output performance of the devices can be predicted with all the parameters being considered simultaneously. The developed model and formulas offer good guidance for structural design and optimization strategies for TENG devices, which could lead to the fast development of high performance of TENGs through accurate numerical analysis at low cost.

Highly efficient green and white fluorescent organic electroluminescent devices with co-doped electron transport material as both supplementary host and blue emitter

An alternative approach was exploited to achieve high performance fluorescent organic light-emitting diodes (OLEDs) by co-doping traditional electron transport material into hole dominant light-emitting layer as supplementary host and blue emitter. Experimental results demonstrated that in this device structure, the co-doping of supplementary host was beneficial in broadening recombination zone, improving carriers trapping and facilitating the balance of holes and electrons, due to its well matched energy levels and high electron mobility. Based on this device design strategy, the optimized green electroluminescent (EL) device obtained the maximum brightness and external quantum efficiency up to 21176 cd/m2 and 5.4%, respectively, which are higher than those of reference devices. In addition, bright white OLED with the maximum brightness, current efficiency and external quantum efficiency up to 17207 cd/m2, 10.47 cd/A and 4.4%, respectively, was realized by modulating the doping concentrations of blue-emitting electron transport material and orange-emitting material. Thus, our investigation provides a chance to construct high performance white OLEDs with simplified device structure.

Highly efficient green organic light-emitting devices based on terbium complex by employing hole block material as host

In this work, efficient green electroluminescent (EL) devices with simplified device structure were prepared by doping trivalent terbium complex Tb(PMIP)3 into hole block material TmPyPB. The high triplet energy of TmPyPB helps to confine excitons within light-emitting layer, while the electron transport characteristic of TmPyPB facilitates the balance of carriers on Tb(PMIP)3 molecules. By optimizing the doping concentration of Tb(PMIP)3 and the thickness of each functional layer, highly efficient green EL device with the structure of ITO/MoO3 (3 nm) /TAPC (50 nm) /Tb(PMIP)3 (30 wt%):TmPyPB (25 nm) /TmPyPB (60 nm) /LiF (1 nm) /Al (100 nm) displayed pure Tb3+ characteristic emission with maximum current efficiency, power efficiency and brightness up to 47.24 cd/A (external quantum efficiency (EQE) of 14.4%), 43.63 lm/W and 1694 cd/m2, respectively. At certain brightness of 100 cd/m2, the device still maintained a current efficiency of 19.96 cd/A (EQE=6.1%). Such a device design strategy helps to improve the EL performances of Tb(PMIP)3 and to simplify device fabrication processes, thus reduce the fabrication cost.

Monolithic magneto-optical oxide thin films for on-chip optical isolation

Abstract

Significantly enhanced energy density of amorphous alumina thin films via silicon and magnesium co-doping

The different Si-Mg co-doping content was explored to improve the dielectric properties of amorphous Al2O3 thin film. According to the analysis of DSC, FT-IR, and XPS spectra, it can be confirmed that a novel structure of glass network is formed in the co-doped Al2O3 thin film. More importantly, compared to Al2O3 thin film, the leakage current of (Al.97Si.02Mg.01)2Oy thin film is reduced by 2 orders of magnitude and the breakdown strength is improved from 276 MV/m to 544 MV/m. The corresponding energy density of the modified sample is up to 9.2 J/cm3, which is an enhancement of 6.2 J/cm3 over that of the undoped Al2O3 thin film. Based on finite element analysis, the simulation results show that the applied electric field is mainly focused on the glass network, which could strengthen the stability of Al2O3 structure and decrease the breakdown probability of the films. From the viewpoint of defect chemistry, another reason for the enhancement of the dielectric properties is that Si-Mg co-doping results in the generation of cation vacancies and thus the formation of oxygen vacancies could be effectively prevented. This work could provide a new design strategy for high-performance dielectric capacitor devices.

Curvy surface conformal ultra-thin transfer printed Si optoelectronic penetrating microprobe arrays

Penetrating neural probe arrays are powerful bio-integrated devices for studying basic neuroscience and applied neurophysiology, underlying neurological disorders, and understanding and regulating animal and human behavior. This paper presents a penetrating microprobe array constructed in thin and flexible fashion, which can be seamlessly integrated with the soft curvy substances. The function of the microprobes is enabled by transfer printed ultra-thin Si optoelectronics. As a proof-of-concept device, microprobe array with Si photodetector arrays are demonstrated and their capability of mapping the photo intensity in space are illustrated. The design strategies of utilizing thin polyimide based microprobes and supporting substrate, and employing the heterogeneously integrated thin optoelectronics are keys to accomplish such a device. The experimental and theoretical investigations illustrate the materials, manufacturing, mechanical and optoelectronic aspects of the device. While this paper primarily focuses on the device platform development, the associated materials, manufacturing technologies, and device design strategy are applicable to more complex and multi-functionalities in penetrating probe array-based neural interfaces and can also find potential utilities in a wide range of bio-integrated systems.

Electronic properties of tin iodide hybrid perovskites: effect of indium doping

For solution-processable tin iodide cubic perovskites, a small amount of indium doping reduced the conductivity without changing the band gap or the carrier concentration. We demonstrated another possibility of foreign metal doping in tin iodide cubic perovskites and displayed a design strategy for electronic devices using hybrid perovskites.