Bottom Contact Research Articles

Superior P-Type Switching in InSe Nanosheets for Complementary Multifunctional Systems.

van der Waals (vdW) indium selenide (InSe) is receiving attention for its exceptional electron mobility and moderate band gap, enabling various applications. However, the intrinsic n-type behavior of InSe has restricted its use predominantly to n-type devices, constraining its application in complementary integrated microsystems. Here, we show superior ambipolar InSe transistors with vdW bottom contacts, achieving impressive p-type on/off current ratios greater than 109 and Schottky barrier heights approaching the ideal Schottky-Mott limit. By introducing a partially gate-coupled architecture, we also demonstrate an ambipolar-to-unipolar transition and reconfigurable complementary multifunctionality, including n-type and p-type transistors as well as negative and positive rectifiers and breakdown diodes. The rectification polarity and ratio are gate-tunable from 3.5 × 107 down to ∼10 without complex heterostructures, chemical doping, and multigate layouts. The negative and positive breakdowns are reversible, with both the breakdown voltage and switching ratio, which can exceed 108, also being electrically tunable.

Ultralow-Power Programmable 3D Vertical Phase-Change Memory with Heater-All-Around Configuration.

Recent advancements in phase-change memory (PCM) technology have predominantly stemmed from material-level designs, which have led to fast and durable device performances. However, there remains a pressing need to address the enormous energy consumption through device-level electrothermal solutions. Thus, the concept of a 3D heater-all-around (HAA) PCM fabricated along the vertical nanoscale hole of dielectric/metal/dielectric stacks is proposed. The embedded thin metallic heater completely encircles the phase-change material, so it promotes highly localized Joule heating with minimal loss. Hence, a low RESET current density of 6-8 MAcm-2 and operation energy of 150-200 pJ are achieved even for a sizable hole diameter of 300nm. Beyond the conventional 2D scaling of the bottom electrode contact, it accordingly enhances ≈80% of operational energy efficiency compared to planar PCM with an identical contact area. In addition, reliable memory operations of ≈105 cycles and the 3-bits-per-cell multilevel storage despite ultrathin (<10nm) sidewall deposition of Ge2Sb2Te5 are optimized. The proposed 3D-scaled HAA-PCM architecture holds promise as a universally applicable backbone for emerging phase-change chalcogenides toward high-density, ultralow-power computing units.

Benthic habitat mapping of the glass sponge (Vazella pourtalesii), and associated community composition on Sambro Bank, Scotian Shelf, Canada

Sponges have been identified as ecosystem engineers, providing habitat structure for many other benthic organisms, but are vulnerable to the impacts of bottom contact fishing. The Sambro Bank Sponge Conservation Area (SBSCA) protects a globally unique aggregation of the glass sponge (Vazella pourtalesii) off the east coast of Canada. Here, we present the first comprehensive, high-resolution mapping study of this site. Multispectral multibeam echosounder (MBES) mapping at three operating frequencies and benthic drop camera surveys were conducted at the SBSCA in 2022. Video data were analysed to quantify the abundance and location of V. pourtalesii and all associated benthic fauna and sediment characteristics. Using the MBES data as predictor variables, the study created a generalized linear mixed model of V. pourtalesii presence in the SBSCA, with 90.1% accuracy. Four seafloor benthoscape classes were identified from the video imagery, with statistically distinct benthic macrofaunal communities associated with each class. The study creates a baseline assessment of the current community composition and habitat characteristics of the site, which can be used for future ecological monitoring and management.

Design and analysis of central gate organic thin film transistor

Abstract This paper presents a novel central gate organic thin-film transistor (OTFT) with electrodes in top-bottom configuration and its comparative performance analysis with conventional single and dual gate OTFTs. The central gate OTFT is comprised of a single gate electrode configured to be the center thin film. A pair of identical dielectric layers viz. top dielectric layer and a bottom dielectric layer on both sides of gate electrode to facilitate the further deposition top and bottom organic semiconductor layer over them respectively. The organic semiconductor layers (OSC) are configured as top OSC layer and a bottom OSC to accommodate two independent conduction channels. The source and drain electrodes are also deposited in pairs in top and bottom configurations. Due to the subtle modifications in the architecture the resultant output drain current of the central gate (CG) OTFT has increased manifold. It has been found in the study that the CG OTFT produces 94%, 76.36%, 80.58% higher drain current than bottom gate bottom contact (BGBC), top gate bottom contact (TGBC) and bottom gate top contact (BGTC) OTFT respectively of similar size, operating under identical voltage regime. Similarly in the case of dual gate (DG) OTFT an improvement of 5.10% has been recorded without any additional gate electrode at the same operating voltages.

Paving the Way for Pass Disturb-Free Vertical NAND Storage via a Dedicated and String-Compatible Pass Gate.

In this work, we propose a dual-port cell design to address the pass disturbance in vertical NAND storage, which can pass signals through a dedicated and string-compatible pass gate. We demonstrate that (i) the pass disturb-free feature originates from weakening of the depolarization field by the pass bias at the high-VTH (HVT) state and the screening of the applied field by the channel at the low-VTH (LVT) state; (ii) combined simulations and experimental demonstrations of dual-port design verify the disturb-free operation in a NAND string, overcoming a key challenge in single-port designs; (iii) the proposed design can be incorporated into a highly scaled vertical NAND FeFET string, and the pass gate can be incorporated into the existing three-dimensional (3D) NAND with the negligible overhead of the pass gate interconnection through a global bottom pass gate contact in the substrate.

Bottom Contact Engineering for Ambient Fabrication of >25% Durable Perovskite Solar Cells.

The bottom contact in perovskite solar cells (PSCs) is easy to cause deep trap states and severe instability issues, especially under maximum power point tracking (MPPT). In this study, sodium gluconate (SG) is employed to disperse tin oxide (SnO2) nanoparticles (NPs) and regulate the interface contact at the buried interface. The SG-SnO2 electron transfer layer (ETL) enabled the deposition of pinhole-free perovskite films in ambient air and improved interface contact by bridging effect. SG-SnO2 PSCs achieved an impressive power conversion efficiency (PCE) of 25.34% (certified as 25.17%) with a high open-circuit voltage (VOC) exceeding 1.19V. The VOC loss is less than 0.34V relative to the 1.53eV bandgap, and the fill factor (FF) loss is only 2.02% due to the improved contact. The SG-SnO2 PSCs retained around 90% of their initial PCEs after 1000h operation (T90 = 1000h), higher than T80 = 1000h for the control SnO2 PSC. Microstructure analysis revealed that light-induced degradation primarily occurred at the buried holes and grain boundaries and highlighted the importance of bottom-contact engineering.

Improvement on the onset voltage for electroluminescent devices based in a SiOx/SiOy bilayer obtained by sputtering

Abstract This work is focused on the composition, optical and electroluminescent properties of silicon rich oxide (SiOx, x &lt; 2) films monolayers and bilayers (SiOx/SiOy) deposited by Sputtering with silicon excess between 6.2 to 10.7 at.% were deposited on p-type (100) silicon substrates. As-deposited SiOx films emit a broad photoluminescence (PL) band where the maximum peak shifts from 420 to 540 nm as the Si-excess increases from 6.2 to 10.7 at.%, respectively. The PL intensity strongly increases and the main PL peak shifts to the red region when the SiOx films are thermally annealed. The PL emission band was dependent on silicon excess and the presence of Si-O bonds defects working as emission centers. MOS-like devices were fabricated (N+ polysilicon was used as top contact and aluminum as bottom contact) to study the EL of SiOx monolayers and SiOx/SiOy bilayers. It was found that the required voltage to obtain EL was reduced when SiOx/SiOy bilayers were used in light emitting capacitors (BLECs) as compared to those with SiOx monolayers.

Ternary Content-Addressable Memory Based on a Single Two-Dimensional Transistor for Memory-Augmented Learning.

Ternary content-addressable memory (TCAM) is promising for data-intensive artificial intelligence applications due to its large-scale parallel in-memory computing capabilities. However, it is still challenging to build a reliable TCAM cell from a single circuit component. Here, we demonstrate a single transistor TCAM based on a floating-gate two-dimensional (2D) ambipolar MoTe2 field-effect transistor with graphene contacts. Our bottom graphene contacts scheme enables gate modulation of the contact Schottky barrier heights, facilitating carrier injection for both electrons and holes. The 2D nature of our channel and contact materials provides device scaling potentials beyond silicon. By integration with a floating-gate stack, a highly reliable nonvolatile memory is achieved. Our TCAM cell exhibits a resistance ratio larger than 1000 and symmetrical complementary states, allowing the implementation of large-scale TCAM arrays. Finally, we show through circuit simulations that in-memory Hamming distance computation is readily achievable based on our TCAM with array sizes up to 128 cells.

Simulation of perovskite solar cell with transparent contacts for solar windows

In recent years, halide-based perovskite solar cells (PSC) have caught worldwide attention since their power conversion efficiency (PCE) has surpassed 25% with low fabrication cost and high scalability. The semi-transparent PSC (ST-PSC) is suitable for building-integrated photovoltaic (BIPV) applications, especially for solar windows. The ST-PSC must demonstrate a reasonable balance between PCE and transparency in the visible region for solar windows, which is inversely proportional to each other. This work studies ST-PSC based on methylammonium lead triiodide (MAPbI3) as solar windows using the General-Purpose Photovoltaic Device Model (GPVDM) and OPAL 2 as the simulation platforms. Parameters such as methylammonium lead triiodide (MAPbI3) thickness, silver (Ag) contact thickness and indium tin oxide (ITO) transparent contact thickness are investigated in relation to the PCE and average visible transmission (AVT). The results demonstrate that the ST-PSC with MAPbI3 thickness of 500 nm and ITO bottom transparent contact of 100 nm leads to PCE of 22.85% and AVT of 11.36%. These parameters represent the best results obtained in this work.

Direct-Written Silver Electrodes for All-Solution-Processed Low-Voltage Organic Thin Film Transistors Towards Flexible Electronics Applications

Recent progress inprinted electronics has offered the possibility of fabricatingvarious organic-based electronic devices,such as organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs).As one of the important deposition methods inprinted electronics, an inkjet printing technique offers the deposition of solution-processable materials onto a variety of substrates using simpler fabrication steps at lower processing temperatures, which is suitable for flexible electronic applications. Despite being the leading choice in OTFT fabrication,the clogging issues that frequently occurred at the printhead nozzle havenot only limitedthe material selection but also restrained the efforts to bring organic electronic devices to the market. Apart from that, although remarkable progress has been made to enhance the performance of the OTFT, the high operating voltage resulting from the low gate capacitance density of the inorganic oxide-based dielectric layer remains a critical limitation that hinders the practical application of the OTFT. Hence, in this paper, we propose a simple solution-based method to develop a low-voltageOTFT. This work utilized a direct-write printing technique to print silver source/drain and gate electrodes incorporated into a bottomgate bottom contact OTFT structure, a spin-coating deposition method to deposit both small molecule TIPS-pentacene organic semiconducting layer and high-kPVA dielectric layer. Notably, the proposed OTFT achieved a micrometre channel length with a saturation mobility of 4.49 × 10-1cm2/Vs, a threshold voltage of -1.5V, an on/off current ratio of 108, and a subthreshold swing of 66.8mV/dec whilethe overall fabrication temperature and operating voltage arekept below 150 °Cand -15 V, respectively.The direct ink writing technology incorporated into the high-kdielectric layer provides a new strategy to fabricate organic-related components,particularly the OFTFs at lower manufacturing cost and temperature towardsflexible and low-operating voltage electronic devices.

Sustainable Mixed-Halide Perovskite Resistive Switching Memories Using Self-Assembled Monolayers as the Bottom Contact.

The complex ionic-electronic conduction in mixed halide perovskites enables their use beyond von Neumann architectures implemented in resistive switching memory devices. Although device fabrication based on perovskite compounds involves solution-processing at low temperatures, reducing further fabrication costs by eliminating expensive materials can improve their compatibility with upscalable deposition techniques. Notably, the substrate on which the perovskite active layer is developed has been reported to severely affect its quality and thus the overall device performance. Hereby, we demonstrate the sustainable manufacturing of memristive perovskite solar cells by replacing the expensive poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) that serves as a hole transporting layer (HTL) with a self-assembled monolayer (SAM), namely [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz). Multiple sequential memristive current-voltage characteristics of single devices are reported, and average data of multiple reference and targeted devices are compared. Resistive switching memory devices based on SAM exhibit improved performance having reduced average SET voltage values and narrower statistical variation compared to reference devices with PTAA. It is shown that both PTAA and SAM based devices exhibit high ON/OFF ratio of about 103 operating at low switching electric fields. Replacing an expensive polymer-based HTL with this approach reduces fabrication costs compared to PTAA.

Local Deformation Analysis and Optimization of Steel Box Girder during Incremental Launching

Due to the significant weight of the steel box girder and the substantial gap between temporary piers, the stress concentration and localized deformation of the girder’s bottom plate are pronounced during the incremental launching construction process. In this study, the multi-scale finite element method was employed to simulate the incremental launching process of the steel box girder, analyze the pattern of localized deformation in the bottom plate contact area, and propose corresponding optimization control measures. Additionally, the entire incremental launching process was monitored, and the improvement in localized deformation before and after the optimization of the incremental launching scheme was analyzed. The results illustrate that the original incremental launching scheme led to substantial localized deformation in the bottom plate contact area of the steel box girder. Optimal control measures were implemented for the four incremental launching construction schemes. The optimal scheme significantly mitigated the localized deformation of the steel box girder’s bottom plate, with an average decrease in deformation of 48.32%. These findings can provide robust technical guidance and data support for the control of localized deformation in large-span steel box girders during the incremental launching construction process.

Compressive failure and fragmentation of fused silica glass under quasi-static loading

This paper investigates the failure and post-failure fragmentation processes of fused silica glass cylinders under quasi-static compression, addressing the effects of surface finish on apparent strength. The compressive strengths of cylinders with side-polished sides under dry friction conditions (PSG-D) or lubricated conditions (PSG-L) were 2.52 GPa and 2.32 GPa, respectively. In situ observations showed that these specimens fractured from either the top or bottom contact surfaces, and that friction between the specimen and the loading anvil delayed the development of surface cracks. The unpolished rough side specimens (RSG-D) under dry friction conditions failed at a much lower level of 1.54 GPa, initiated by defects in the side surfaces. Specimens "explosively" fragmented upon failure. The propagation speed of the failure front ranged from 1800 to 2800 m/s. The average sizes and distributions of the fragments were determined through statistical analysis, with results showing reasonably close agreement with theoretical estimations.

Adsorption of Methylene Blue using Bottom Ash: Experimental Design, Isotherm Analysis, and Optimum Conditions

&lt;p&gt;&lt;span lang="EN-US" style="font-size:12.0pt"&gt;&lt;span style="line-height:107%"&gt;&lt;span style="font-family:&amp;quot;Times New Roman&amp;quot;,serif"&gt;&lt;span style="color:black"&gt;This study investigated the removal of methylene blue (MB) via adsorption using waste bottom ash.&amp;nbsp; The bottom ash, sourced from a waste storage site in the Çorlu district of Tekirdağ province, Thrace Region, was utilized as the adsorbent. The research examined the impact of several variables on MB removal, including bottom ash dosage, pH, contact time, and agitation speed. It was found that all parameters had a single-variable effect, while pH exhibited a quadratic effect on MB removal in a model-based analysis. The optimization of the model for maximum MB removal identified the optimal conditions as 0.978 g bottom ash dosage, pH 3, 15 minutes of adsorption time, and 50 rpm agitation speed. Under these conditions, the model predicted an MB removal efficiency of 71%, which was experimentally confirmed to be 72.5%. The adsorption process was found to fit with the Freundlich isotherm, indicating a multilayer adsorption mechanism on the heterogeneous surface of the adsorbent. This research not only highlights the feasibility of using bottom ash from coal combustion as an economical adsorbent for dye-contaminated wastewater but also underscores its potential to inform and inspire future studies on waste recycling and wastewater treatment.&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

Strain-induced polarization modulation at GaN/Ti interface for flexible thin-film sensor

We have demonstrated an effective piezoelectric polarized interface modulation in a GaN/Ti Schottky structure and fabricated a flexible GaN-based sensor using a double-transfer method. Chemical etching of the Ni sacrificial layer successfully removes the temporary substrate without damaging the metal electrodes. The fabricated flexible GaN-based sensor, with top and bottom Ti metal Schottky contacts, exhibits a current on/off characteristic under external strain. Specifically, the current shows a 53.9% reduction under 2.3% tensile strain and a 67.8% enhancement under −2.3% compressive strain at a 5 V bias voltage. It was found that the light/dark current ratio in the GaN/Ti Schottky junction significantly increases near zero-bias voltage under 2.3% tensile strain, likely indicating an enhanced built-in piezoelectric polarized field at the interface. This work advances the study of flexible sensors based on wurtzite III–V nitrides for wearable electronics and optoelectronics.

Direction Dependent Ferroelectricity and Conductivity in a Single Crystal 2D Halide Double Perovskite.

Halide ferroelectric materials have garnered a lot of interest because of their distinctive electrical and structural characteristics. In this study, the design and development of a new non-centrosymmetric 2D layered halide double perovskite material, Cl1.14Br2.86PA4AgInBr8 (CPAIn) is reported. This material shows ferroelectric properties above room temperature, with a Curie temperature of 190 °C. This behavior is achieved through the substitution of the halogenated A-site organic linker, 3-chloropropylammonium. CPAIn exhibits anisotropic ferroelectric behavior with higher spontaneous polarization of 6.25 µC cm-2 along the perpendicular direction to the octahedral layers, whereas the value decreases to 0.174 µC cm-2 between sheets. While using bottom contact to study the nature of polarity within a sheet, the P-E loop displays capacitive loop. The nature and value of polarization is highly direction dependent, and to further understand the mechanism of conduction, a combination of temperature-dependent impedance studies and poling dependent conductivity techniques are employed. These directional dependent properties hold immense potential in memory devices, sensors and photovoltaics, piezoelectric devices and energy storage.

Reducing invertebrate by-catch in a coastal fishery using a raised monofilament trammel net

Trammel nets are one of the least selective fishing gears and are known to catch a variety of species, many of which are discarded, including important invertebrates that are considered habitat-forming species. Although there are few studies focusing on this type of by-catch, these habitat-forming species include corals and sponges that are vulnerable to disturbances from fishing activities using bottom contact gear. Experimental fishing was conducted off the port of Portimão (southern Portugal) from November 2021 to April 2022 using standard and modified trammel nets rigged to be lifted off the bottom with the objective of reducing invertebrate by-catch and impacts on the bottom habitat. The modified lifted net caught 36% less by-catch of invertebrates in numbers than the standard net, with no significant decrease of biomass and value of target species. The results obtained with the two net types are discussed, as well as the necessity for good video recording equipment that can improve sampling accuracy, and the usefulness of interviewing the fishers on net performance after experimental fishing was conducted.

Enhanced photovoltaic response in WSe2 photodetector with asymmetric two-dimensional contacts

Asymmetric contact pairs with different work functions provide an efficient method to extract photogenerated carriers in optoelectrical devices. Specifically, vertical optoelectrical devices based on two-dimensional (2D) materials utilize graphene layers as the bottom and top contacts. Whereas an additional terminal is required for electrostatic doping in either top or bottom graphene to enlarge the built-in electric field. Herein, we present an enhanced photovoltaic response in a vertical WSe2 photodetector utilizing asymmetric 2D contacts. A graphite layer and a degenerate SnSe2 are used as the top and bottom contacts, respectively, with a significant difference in their work functions. By establishing a large built-in electric field across the vertical WSe2 layer, a strong photovoltaic effect is achieved, resulting in an open-circuit voltage of 0.37 V and a short-circuit current of 0.42 μA under 532 nm illumination. The device shows high-performance photodetection characteristics, with a responsivity of 32.04 A W−1, external quantum efficiency of 7475%, and specific detectivity of 3.61 × 1012 Jones. Furthermore, the device can generate a maximum output electrical power of 70.9 nW, enabling a high-power conversion efficiency of 3.5%.

Enhancement in electrical properties of dual-active-layer amorphous SiZnSnO/SiInZnO thin film transistors

Bi-layer thin film transistors (TFTs) have been fabricated with a channel structure comprising a dielectric layer, a semiconducting amorphous-Si-In-Zn-O (a-SIZO) layer, and a semiconducting amorphous-Si-Zn-Sn-O (a-SZTO) layer, aiming to improve field effect mobility and stability. These films were deposited using RF sputtering at room temperature. The TFTs with a bottom gate top contact, processed at 500 °C, exhibited high mobilities (>32 cm2 V−1 s−1) along with a current on/off ratio of approximately 108 and a subthreshold swing (SS) value below 0.5 V decade−1 primarily because of reduced trap density and presence of highly conducting ultrathin a-SIZO layer. Furthermore, the bi-layer TFTs demonstrated notable stability under negative and positive bias temperature stress conditions.

Vertical Schottky diode on (113) oriented homoepitaxial diamond

Vertical Schottky diodes were fabricated on (113) oriented diamond substrates produced from thick heavily boron doped (NA ∼ 3.5 × 1020 cm−3) diamond layers grown on HPHT-grown synthetic Ib diamond crystals. The p+-substrates were overgrown by a low doped p-epilayer whose surface layer was compensated up to the depth of 0.1 to 0.3 μm. The surface was then oxygen terminated and covered by evaporated Mo/Au Schottky contacts. The bottom ohmic contact to p+-substrate was formed by Ti/Au bi-layer. Current- and capacitance-voltage characteristics of the realized diodes were measured at temperatures ranging from 25 to 180 °C. At room temperature, the realized diodes show high forward current densities JF = 100 A/cm2 and low differential ON-state specific resistance Ron_sp = 3.7 mΩ.cm2 at forward voltage VF = 4 V and a very low leakage (JR < 10−9 A/cm2) in the blocking regime. At 180 °C, forward characteristics significantly improve (JF = 5 kA/cm2, Ron_sp = 0.2 mΩ.cm2 at VF = 4 V) while the blocking characteristics remain almost unchanged (JR = 6 × 10−8 A/cm2 at VR = 4 V). The breakdown electric field is about 3 MV/cm and the rectification ratio keeps at the level of 1011. Characteristics of realized diodes, which are fully comparable to those of Schottky-pn diodes prepared on (111) oriented boron doped diamond, confirm the suitability of (113) orientation for realization of vertical diamond power devices.