Device Thickness Research Articles

Optimization of the electrospun-aligned microfiber composite with liquid crystal for terahertz wave variable phase shifters

AbstrcatIn this study, electrospun microfibers (MFs) were produced and used as key materials to optimize the composite with liquid crystal (LC) for terahertz (THz) wave phase shifters. These MFs, with an average diameter of 1.4 μm, were produced using the polymer solution concentration of 14 wt% and spinning voltage of 13 kV. When MFs were combined with LC, the measured results of the electrical characteristics showed that 14 wt% MFs provided an outstanding solution to the problem of a significant reduction in the natural birefringence of pure LC. The birefringence in the THz frequency range of the composite using 14 wt% MFs approached 90% compared with that using pure LC. Additionally, the decay time drastically shortened from hundreds of seconds for pure LC to hundreds of milliseconds for MF/LC composite and was independent of device thickness.

Synchrotron Radiation Study of Gain, Noise, and Collection Efficiency of GaAs SAM-APDs with Staircase Structure.

In hard X-ray applications that require high detection efficiency and short response times, such as synchrotron radiation-based Mössbauer absorption spectroscopy and time-resolved fluorescence or photon beam position monitoring, III–V-compound semiconductors, and dedicated alloys offer some advantages over the Si-based technologies traditionally used in solid-state photodetectors. Amongst them, gallium arsenide (GaAs) is one of the most valuable materials thanks to its unique characteristics. At the same time, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics, such as in the case of a very weak photon flux or when single-photon detection is required. Some GaAs-based avalanche photodiodes (APDs) were grown by a molecular beam epitaxy to fulfill these needs; by means of band gap engineering, we realised devices with separate absorption and multiplication region(s) (SAM), the latter featuring a so-called staircase structure to reduce the multiplication noise. This work reports on the experimental characterisations of gain, noise, and charge collection efficiencies of three series of GaAs APDs featuring different thicknesses of the absorption regions. These devices have been developed to investigate the role of such thicknesses and the presence of traps or defects at the metal–semiconductor interfaces responsible for charge loss, in order to lay the groundwork for the future development of very thick GaAs devices (thicker than 100 m) for hard X-rays. Several measurements were carried out on such devices with both lasers and synchrotron light sources, inducing photon absorption with X-ray microbeams at variable and controlled depths. In this way, we verified both the role of the thickness of the absorption region in the collection efficiency and the possibility of using the APDs without reaching the punch-through voltage, thus preventing the noise induced by charge multiplication in the absorption region. These devices, with thicknesses suitable for soft X-ray detection, have also shown good characteristics in terms of internal amplification and reduction of multiplication noise, in line with numerical simulations.

Fabrication of vertical-taper structures for silicon photonic devices by using local-thickness-thinning process

This paper describes a simple fabrication process of vertical-taper structures which can locally tune the thickness of silicon photonic devices. For low-loss spot-size conversion, taper angles less than 10° are required. To fabricate the gradual-slope shape of the vertical tapers, we have developed a step-and-exposure lithography process, which is realized by repeated light exposure to photoresist and movement of the wafer stage by using commercial steppers. The process is conducted at a lower temperature (∼120 °C) than the conventional process and is compatible with the complementary metal-oxide-semiconductor process. Also, we have made a model of the lithography to predict the angle of the taper. Theoretical angles are consistent with the experimental results. We demonstrate the conversion of a 400 nm thick silicon waveguide to 220 nm, whose length was 2.4 μm and insertion loss was measured to be less than 0.3 dB. The process enables us to choose the optimal thickness for each silicon-photonic device.

ZnO/MoO3 Heterojunction Thick Films to Detect ppb Level Volatile Organic Compounds

The development of a fast, stable metal oxide-based VOC sensor for the detection of trace-level ppb concentrations, remains a challenge. Recently, many composite materials have been investigated to try and develop sensors with these characteristics. Here, we report on the development of ZnO/MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> heterojunction thick film devices, fabricated by a spin-coating technique, to detect a wide range of VOCs at application relevant ppb level concentrations. For comparison, pristine ZnO and pristine MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> devices were also fabricated. Sensors were tested at different temperatures and resulting in an optimum temperature of 380°C. The sensors were tested towards 11 different VOCs at ppb concentrations. Of all the sensors tested, the heterojunction device showed the highest response to VOCs, with the highest sensitivity towards 200 ppb of ethanol (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 12.84). The results compared well with the pristine materials, with the response of the ZnO material being 6 times smaller and MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> 10 times smaller compared to their heterojunction counterpart. The response times of the heterojunction device were also faster, at around 30 sec compared with 120 sec for pristine materials.

Detailed microwave absorption performance of BaFe12O19 nano-hexaplates with a large variety of thicknesses

We successfully prepared BaFe12O19 (BaM) nano-hexaplates using the co-precipitation method followed by heat treatment. The hexaplate-like grain size varied in the range of 50–200 nm, while its crystalline size was ∼46 nm. Before investigating microwave absorption, structural and magnetic properties were studied by x-ray diffraction, Raman scattering, and a vibrating sample magnetometer. The structural studies showed a pure phase of BaM, while the magnetic studies revealed a ferro/ferrimagnetic behaviour with M s = 59.93 emu g−1, M r = 32.49 emu g−1, and H c = 5.16 kOe. Microwave dissipation features were systemically investigated for device thickness of 0.25–10 mm with a measured frequency range of 2–16 GHz. The study showed that the BaFe12O19 sample could absorb more than 99.9% of the incident microwave in the 12–14 GHz frequency range for 6.5 mm thickness. The effective absorption bandwidth was also fairly large, as ∼3 GHz in this frequency range. The microwave dissipation features of BaM in this work were better than pure BaM ones in other studies and relatively comparable with BaM-based microwave absorbers. The magnetic loss originated from natural resonance, while the dielectric loss resulted from multi-interface, interface, and dipolar polarization. Overall, the BaFe12O19 sample in this study could be used as a promising microwave absorber in the Ku waveband.

On-chip integrated process-programmable sub-10 nm thick molecular devices switching between photomultiplication and memristive behaviour

Molecular devices constructed by sub-10 nm thick molecular layers are promising candidates for a new generation of integratable nanoelectronic applications. Here, we report integrated molecular devices based on ultrathin copper phthalocyanine/fullerene hybrid layers with microtubular soft-contacts, which exhibit process-programmable functionality switching between photomultiplication and memristive behaviour. The local electric field at the interface between the polymer bottom electrode and the enclosed molecular channels modulates the ionic-electronic charge interaction and hence determines the transition of the device function. When ions are not driven into the molecular channels at a low interface electric field, photogenerated holes are trapped as electronic space charges, resulting in photomultiplication with a high external quantum efficiency. Once mobile ions are polarized and accumulated as ionic space charges in the molecular channels at a high interface electric field, the molecular devices show ferroelectric-like memristive switching with remarkable resistive ON/OFF and rectification ratios.

A Measuring Device for Residual Thickness of Brake Shoe of Railcar Based on Deep Learning

At present, the residual thickness of brake shoe of metro vehicles is mainly measured manually by naked eyes or simple ruler, which has some problems such as low detection efficiency, large subjective randomness and poor engineering applicability. Therefore, this paper proposes a device for measuring the residual thickness of brake shoes of railcar based on deep learning method. Firstly, a residual thickness measuring device includes parts of image acquisition module, image positioning and segmentation module, and image correction module. Then for each module, the article conducted the related experiments for verifying the accuracy of the system. The results show that the brake shoe residual thickness measurement device proposed in this paper has higher accuracy and better robustness than manual detection, and has obvious advantages in detection time consumption.

Regulation of Crystallinity and Vertical Phase Separation Enables High‐Efficiency Thick Organic Solar Cells

AbstractThick film organic solar cells have great potential for preparing large‐area devices in the future. However, unsuitable vertical donor/acceptor distribution, poor crystallinity of materials, and voltage losses remain unclear, limiting the performance of thick film devices. Here, a target ternary strategy by introducing a nematic liquid crystalline small molecule donor BTR‐Cl into the PM6:Y6 host system is used to reduce the performance degradation caused by the increase of active layer thickness. By incorporating 10% BTR‐Cl into the blend film, the voltage loss is minimized in both thin and thick ternary devices. Moreover, the power conversion efficiency of the ternary device is maintained at 15.28% compared to 12.94% of binary devices with an active layer thickness of 300 nm. It is benefited from the optimized crystallization behavior and more suitable vertical phase distribution driven by differences in miscibility between components. While ensuring sufficient phase separation, the charge transport is improved, it also prompts the balance of charge transport and reduces the non‐radiative recombination. This work demonstrates that the use of the third component to enhance the crystallization of the active layer and improve the vertical phase distribution is an effective method to build thick films for future large‐scale printing techniques.

Ultra-Thin Terahertz Deflection Device Based on Laser Direct Writing Graphene Oxide Paper.

In the world of terahertz bands, terahertz beam deflection has gradually attracted substantial attention, due to its great significance in wireless communications, high-resolution imaging and radar applications. In this paper, a low-reflection and fast-fabricated terahertz beam deflection device has been realized by utilizing graphene oxide paper. Using laser direct writing technology, graphene oxide has been patterned as a specific sample. The thickness of the graphene oxide-based terahertz devices is around 15–20 μm, and the processing takes only a few seconds. The experimental results show that the beam from this device can achieve 5.7° and 10.2° deflection at 340 GHz, while the reflection is 10%, which is only 1/5 of that of existing conventional devices. The proposed device with excellent performance can be quickly manufactured and applied in the fields of terahertz imaging, communication, and perception, enabling the application of terahertz technology.

Synthesis, characterizations and photovoltaic applications of a thickness-insensitive benzodifuran based copolymer

Low toleration of thickness variations in the organic solar cells (OSCs), is currently becoming bottleneck challenges to achieve power conversion efficiencies (PCE) and large-scaled roll-to-roll device fabrication. In this work, a new thienyl-free furan-based copolymer of PBDFDFBO was synthesized via Stille copolymerization of benzodifuran (BDF) and 4,7-di(furan-2-yl)benzo[c][1,2,5]oxadiazole monomers. It exhibited a high hole mobility of 2.46 × 10−3 cm2 V−1 S−1, which could be attributed to a planar molecular conformation of the polymer. When the polymer was selected as donor and small molecular ITIC-F as acceptor, the photovoltaic device results showed a champion PCE of 11.53% with a high Voc and FF. Impressively, device efficiency is insensitive to the variation of photoactive layer thickness and can maintain over 10.98% efficiency as film thickness increases to 600 nm, which is the best result for furan-based OSCs. The features of all furan-based polymer of PBDFDFBO provide great potential in developing thick film photovoltaic device and the efficient molecular design strategy also could be referenced to other photovoltaic materials.

On-chip integration of 2D Van der Waals germanium phosphide (GeP) for active silicon photonics devices.

The outstanding performance and facile processability turn two-dimensional materials (2DMs) into the most sought-after class of semiconductors for optoelectronics applications. Yet, significant progress has been made toward the hybrid integration of these materials on silicon photonics (SiPh) platforms for a wide range of mid-infrared (MIR) applications. However, realizing 2D materials with a strong optical response in the NIR-MIR and excellent air stability is still a long-term goal. Here, we report a waveguide integrated photodetector based on a novel 2D GeP. This material uniquely combines narrow and wide tunable bandgap energies (0.51-1.68 eV), offering a broadband operation from visible to MIR spectral range. In a significant advantage over graphene devices, hybrid Si/GeP waveguide photodetectors work under bias with a low dark current of few nano-amps and demonstrate excellent stability and reproducibility. Additionally, 65 nm thick GeP devices integrated on silicon waveguides exhibit a remarkable photoresponsivity of 0.54 A/W and attain high external quantum efficiency of ∼ 51.3% under 1310 nm light and at room temperature. Furthermore, a measured absorption coefficient of 1.54 ± 0.3 dB/µm at 1310 nm suggests the potential of 2D GeP as an alternative infrared material with broad optical tunability and dynamic stability suitable for advanced optoelectronic integration.

Thermoelectric coolers for high-power-density 3D electronics heat management

Future advancements in three-dimensional (3D) electronics require robust thermal management methodology. Thermoelectric coolers (TECs) are reliable and solid-state heat pumping devices with high cooling capacity that can meet the requirements of emerging 3D microelectronic devices. Here, we first provide the design of TECs for electronics cooling using a computational model and then experimentally validate the main predictions. Key device parameters such as device thickness, leg density, and contact resistance were studied to understand their influence on the performance of TECs. Our results show that it is possible to achieve high cooling power density through optimization of TE leg height and packing density. Scaling of TECs is shown to provide ultra-high cooling power density.

Mixed-Voltage I/O Buffer Using NMOS Blocking Considering Gate Oxide Reliability

This paper presents a [Formula: see text] tolerant I/O buffer with low voltage (VDD) devices. A novel bootstrap circuit for mixed voltage I/O buffer is proposed to solve the unwanted leakage paths and gate oxide reliability issues. The proposed circuit is designed using 1.8[Formula: see text]V thick gate devices in 22-nm FinFET technology with 1.8[Formula: see text]V signaling and tolerant to 3.3[Formula: see text]V. The structure can be used in any CMOS technology for [Formula: see text] tolerant I/O buffer.

Investigation of recombination processes in bulk-heterojunction organic solar cell by extraction of injected charge carriers

In this paper, we used extraction of injected charge carriers technique and time-of-flight method to establish recombination rate dependency on carrier concentration and thickness in a bulk-heterojunction organic solar cell with the active layer blend consisting of poly(3-hexylthiophen-2,5-diyl) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT: PCBM). Using aforementioned techniques and numerical calculations, we determined that 1.8-diiodiooctane processing additive in combination with chlorobenzene solvent in solution-processed P3HT: PCBM samples causes charge carrier transport and recombination rate changes with increasing device thickness. Also, recombination velocities of P3HT: PCBM blends obtained with the extraction of injected charge carriers technique have a two-component dependency on charge carrier concentration governed by interfacial states between two pure phases.

Effect on coupling coefficient of diamond-based surface acoustic wave devices using two layers of piezoelectric materials of different widths

With the advent of 5G massive data, it is critical to improve the frequency and bandwidth of surface acoustic wave devices. In this work, ZnO, AlN and LiNbO3 piezoelectric materials were applied to a three-layer structure based on diamond as the substrate. Unlike conventional structures, widths of two piezoelectric materials are different. The electromechanical coupling coefficient based on the ZnO/ZnO/diamond structure can be remarkably improved to 8.26%, while a high frequency of 2 GHz can also be obtained. The structure based on the AlN/AlN/diamond structure is more inclined to obtain a high frequency of 3.76 GHz and an electromechanical coupling coefficient of 4.64%. Rational selection of piezoelectric materials and film thickness of surface acoustic wave devices can achieve different degrees of enhancement of electromechanical coupling coefficients and frequency. Finally, it was found that the larger electric potential on the surface of diamond will result in a larger electromechanical coupling coefficient when the first layer of piezoelectric material is identical.

Transmitting Performance Simulation of Piezoelectric Transducer for Underwater Application

This paper reports transmitting performance simulation of the circular piezoelectric transducer using finite element analysis (FEA) approach. The 3D model of the transducer is designed and simulated using six different piezoelectric materials. FEA simulation and modelling had been carried out using the COMSOL Multiphysics 5.0 software. The thickness and radius of the piezoelectric material layer were varied and transmitting performance were compared and analysed. From this simulation, the transmitting performance of the Piezoelectric Micro Ultrasonic Transducer (PMUT) is decreased as the membrane radius increased, while it increased as the thickness of the piezoelectric material layer increased. The total device thickness at 430 µm with the membrane radius at 1500 µm, show the best performance at 240 kHz of frequency, tailored for many underwater applications. The thickness and radius have contributed significantly to the mechanical stress generated at the surface of the piezoelectric material layer, in contact with the electrode. Hence, the device radius and thickness of the piezoelectric layer are considered, regardless of the type of piezoelectric material used.

Device study and optimisation of CZTS/ZnS based solar cell with CuI hole transport layer for different conduction band offset

The copper zinc tin sulphide (CZTS) is a promising candidate for solar cell application. The CZTS/ZnS-based heterojunction provides a high conduction band offset at the junction. The three types of conduction band offset (spike, flat, and cliff) are discussed in the study, and the comparison of cell output variation is also discussed. In this simulation-based study, we have performed optimisation of the device for layer thickness, carrier mobility, defects, front contact transmission profile, and both the series and shunt resistance. A high acceptor type defect density in CZTS increases open-circuit voltage by shifting the Fermi level towards the valance band maximum. The introduction of CuI as a hole transport layer (HTL) offers a low Schottky barrier and delivers high efficiency compared to the same without the CuI layer, while a higher CuI thickness produce a barrier to back reflection. The finally optimised cell gives the highest power conversion efficiency of 15.53% for a spike like conduction band offset of 0.06 eV. This simulation paves a way to fabricate realistic CZTS solar cells based on the present cell model.

Broadband Silicon Nitride Power Splitter Based on Bent Directional Couplers with Low Thermal Sensitivity.

Directional couplers, as power splitters, have provided a significant contribution for light splitting and combining in silicon photonics. However, the splitting ratio of conventional directional couplers is very sensitive to wavelength, which limits the bandwidth and the transmission performance of the devices. In this work, a silicon nitride bent directional coupler with large bandwidth, large fabrication tolerance, and low thermal sensitivity is proposed and demonstrated through simulation analysis and experiments. Moreover, the fabrication process of 400 nm thick silicon nitride photonic devices is described, which are compatible with complementary metal–oxide–semiconductor technology. The 1 dB bandwidth of the bent waveguide coupler can reach 80 nm, and the thermal sensitivity is reduced by 85% compared to the silicon-based devices.

Ultra-thin mid-infrared silicon grating coupler.

Mid-infrared (mid-IR) silicon photonics has been attracting great attention due to its tremendous potential applications in nonlinear optics, ranging, sensing, and spectroscopy. To date, mid-IR silicon devices have usually been developed based on silicon wafers with top-layer silicon thicknesses of hundreds of nanometers. Compared with the thick silicon devices, tens-of-nanometers thin silicon devices can provide giant evanescent-field energy proportions and optical mode areas, being significant for many biochemical sensing and nonlinear optics applications. However, ultra-thin mid-IR silicon devices have seldom been studied due to the difficulty of light coupling. Here, we demonstrated an ultra-thin focusing subwavelength-grating coupler for mid-IR ultra-thin suspended subwavelength-grating-cladding waveguide coupling. The results show that the grating has a maximum coupling efficiency of -7.1 dB at a center wavelength of 2200 nm with a 1-dB bandwidth of ∼115 nm and back reflection of -19.9 dB. We also measured the fiber alignment tolerance of 12 µm for 3-dB coupling efficiency reduction and bending optical loss of 0.25 dB/90°. Our results pave the way to developing mid-IR ultra-thin photonic integrated circuits.

Thin diffusion bonded flat loop heat pipes for electronics: Fabrication, modelling and testing

Diffusion bonding process was used to manufacture three different thin flat loop heat pipes (LHP), two with 1.52 mm and one with 0.92 mm of thickness. The proposed LHPs were designed to be candidates for thin electronics cooling applications, such as smartphones. The devices attended to the following heat transfer requirements, based on recent electronic technologies: dissipation of both low (2 W/cm2) and high heat fluxes (8 W/cm2) at natural air convection. A workbench, capable of evaluating the LHP thermal performance, was developed to simulate the operating condition of a chip processor with 1 cm2. The LHPs were investigated experimentally using ethanol as the working fluid in three orientations: horizontal, gravity-assisted and against-gravity. As the main problem of operating thin LHPs with low heat fluxes is the heat leakages from the evaporator, a theoretical model was proposed to predict the conduction heat transfer between the evaporator and the liquid line. The minimum thermal resistance of 0.2 °C/W was achieved for the 1.52 mm thick device at 8 W/cm2. Experimental results confirmed that the thickness reduction of heat pipes leads to a decrease in their thermal performance. The heat leakage of the thinner LHP to the liquid line was approximate 17% of the total heat transferred, while the thicker LHP showed a heat leakage of 10%. Although still demands development, two of the three proposed loop heat pipes showed good heat transfer capacity, keeping the evaporator temperature, supposedly in contact with the electronic component in actual applications, below 100 °C. This device is shown to be suitable for the thermal management of thin electronic devices, especially mobile phones.