Low-temperature Fabrication Process Research Articles

Design Automation and Test Solutions for Monolithic 3D ICs

Monolithic 3D (M3D) is an emerging heterogeneous integration technology that overcomes the limitations of the conventional through-silicon-via (TSV) and provides significant performance uplift and power reduction. However, the ultra-dense 3D interconnects impose significant challenges during physical design on how to best utilize them. Besides, the unique low-temperature fabrication process of M3D requires dedicated design-for-test mechanisms to verify the reliability of the chip. In this article, we provide an in-depth analysis on these design and test challenges in M3D. We also provide a comprehensive survey of the state-of-the-art solutions presented in the literature. This article encompasses all key steps on M3D physical design, including partitioning, placement, clock routing, and thermal analysis and optimization. In addition, we provide an in-depth analysis of various fault mechanisms, including M3D manufacturing defects, delay faults, and MIV (monolithic inter-tier via) faults. Our design-for-test solutions include test pattern generation for pre/post-bond testing, built-in-self-test, and test access architectures targeting M3D.

MORPHOLOGICAL AND PHYSICAL PROPERTIES OF ZnO NANOSTRUCTURES GROWN ON Sb-DOPED ZnO SEEDING FILMS ANNEALED UNDER DIFFERENT ATMOSPHERES

In this work, morphological and physical properties of pyramid-like ZnO nanostructures fabricated on Sb-doped ZnO seeding films annealed under different atmospheres are extensively studied. The Sb-doped ZnO seeding films were first prepared by sol–gel spin coating technique onto glass substrate then annealed in nitrogen, air and argon followed by low-temperature hydrothermal process for ZnO nanostructures fabrication. The morphological results exhibit the growth of pyramid-like ZnO nanostructure with increasing density of the ZnO nanostructures. The crystal structure shows pyramid-like ZnO wurtzite hexagonal growth along the c-axis without any impurity phase. The growth of pyramid-like ZnO nanostructures is due to the high growth rate of (002) plane. Photoluminescence spectra exhibit the near-band-edge of all samples while the red emission appears in ZnO nanostructures after the hydrothermal process due to the imperfection in the crystal. The reflectance of ZnO nanostructures covers the visible region with the absorption edge of 375[Formula: see text]nm. The calculation shows the relevant energy band gaps in the range of 3.26–3.28[Formula: see text]eV. The difference in hydrothermally grown ZnO nanostructures is significantly affected by different annealing atmospheres.

Enhanced efficiency of low-temperature fabricated dye-sensitized solar cells by incorporating upconversion nanoparticles

Upconversion nanoparticles (UCNPs) can effectively assist solar cells in utilizing near infrared through the anti-Stokes’ emission mechanism. We incorporate UCNPs, for the first time, into the mesoporous TiO2 of dye-sensitized solar cells (DSSCs) in a low-temperature fabrication process. The mesoporous TiO2 is designed as a two-layer structure, where the lower layer is prepared from reactive anatase TiO2 chelated by acetic acid (h-TAc). The UCNP incorporation into the lower layer displays a significant improvement in photovoltaic performance. For an optimized UCNP incorporation, the power conversion efficiency (PCE) of the DSSCs can increase from 6.49 to 7.98%, an enhancement of 23%, further exceeding most of the improvement on low-temperature fabricated DSSCs reported in the literature. The enhanced PCE may be ascribed to the increase of photocurrent. We find that the hydrophobic UCNPs reveal better enhancement than hydrophilic UCNPs due to the prevention from the electrolyte penetration. However, the hydrophobic UCNP incorporation may cause the cracking of the mesoporous TiO2 layer. The strong bonding ability of h-TAc effectively alleviates the cracking issue.

Interfacial-engineering enhanced performance and stability of ZnO nanowire-based perovskite solar cells

Perovskite solar cells (PSCs) have attracted extensive attention due to their convenient fabrication and excellent photoelectric characteristics. The highest power conversion efficiency (PCE) of over 25% has been realized. However, ZnO as electron transport layer based PSCs exhibit inferior PCE and stability because of the mismatched energy-band and undesirable interfacial recombination. Here, we introduce a thin layer of SnO2 nanocrystals to construct an interfacial engineering with gradient energy band and interfacial passivation via a facile wet chemical process at a low temperature. The best PCE obtained in this study reaches 18.36%, and the stability is substantially improved and maintains a PCE of almost 100% over 500 h. The low-temperature fabrication process facilitates the future application of ZnO/SnO2-based PSCs in flexible and stretchable electronics.

Synergy of mesoporous SnO2 and RbF modification for high-efficiency and stable perovskite solar cells

Electron transport layer (ETL) is very critical to the performance of perovskite solar cells (PSCs), and optimization work on ETL has received extensive attentions especially on tin oxide (SnO2) since it is an excellent ETL material widely applied in high-efficiency PSCs. Thereinto, introducing mesoporous structure and surface modification are two important approaches which are commonly applied. Herein, based on the previous work in low-temperature fabrication process of mesoporous SnO2 (m-SnO2), we introduced a modification process with rubidium fluoride (RbF) to the m-SnO2 ETL, and successfully achieved a synergy of the m-SnO2 and RbF modification: not only the shortcoming of the m-SnO2 in interfacial traps was overcome, but also the carrier collection efficiency was further improved. The PSCs based on the m-SnO2 ETL with RbF modification demonstrated outstanding performances: a champion power conversion efficiency (PCE) of 22.72% and a stability performance of maintaining 90% of the initial PCE after 300 h of MPP tracking were obtained without surface passivation of perovskite film. Hence, utilizing the abovementioned synergy is a cost-effective and feasible strategy for fabricating high-efficiency and stable PSCs since the fabrication process of the m-SnO2 ETL is a kind of low temperature process and RbF is cheap.

Diluted-CdS Quantum Dot-Assisted SnO2 Electron Transport Layer with Excellent Conductivity and Suitable Band Alignment for High-Performance Planar Perovskite Solar Cells.

An electron transport layer (ETL) with excellent conductivity and suitable band alignment plays a key role in accelerating charge extraction and transfer for achieving highly efficient planar perovskite solar cells (PSCs). Herein, a novel diluted-cadmium sulfide quantum dot (CdS QD)-assisted SnO2 ETL has been developed with a low-temperature fabrication process. The slight addition of CdS QDs first enhances the crystallinity and flatness of SnO2 ETLs so that it provides a promising workstation to obtain high-quality perovskite absorption layers. It also amazingly increases the conductivity of the SnO2 ETL by an order of magnitude and regulates the energy level matching between the SnO2 ETL and perovskite. These outstanding properties greatly accelerate the charge extraction and transfer. Thus, the MAPbI3-based PSCs with such a diluted-CdSQD-assisted SnO2 ETL achieve a maximum power conversion efficiency of 20.78% and obtain a better stability of devices in air. These findings testify the importance and potential of semiconductor QD modification on ETLs, which may pave the way for developing such composite ETLs for further enhancing photovoltaic performance of planar PSCs.

Solution-based CdS thin film transistors with low temperature-processed Al2O3-GPTMS-PMMA as hybrid dielectric gate

Herein, we report the low-temperature fabrication process and the electrical response of n-type cadmium sulfide (CdS)-based thin-film transistors (TFTs) with an Al2O3-GPTMS-polymethylmethacrylate (PMMA) hybrid dielectric gate. The TFTs with bottom-gate structure were assembled on ITO (indium-tin-oxide)-coated glass substrates employing solution processes for the deposition of both the dielectric gate and semiconductor layers. The hybrid dielectric layers were deposited by the sol-gel process and subsequently annealed at 150 °C. The FTIR and XPS analysis of the hybrid films demonstrated a proper link between Al2O3 and PMMA through the cross-linking agent 3-glycidoxy(propyltrimethoxysilane) silane (GPTMS). The surface characteristics were obtained by contact angle and atomic force microscope studies, the results show that the surface of hybrid films displays a hydrophobic behavior with a smooth surface. The CdS active layer was deposited on the hybrid dielectric gate at room temperature by a simple photochemical bath deposition using a 313 nm UV lamp. The CdS-TFTs showed outstanding electrical performance with a low threshold voltage of 1.3 V, I ON /I OFF of 104, subthreshold swing of 440 mV dec−1, and remarkable high mobility value of 64.4 cm2 V−1 s−1. Ultimately, the feature of these completely solution-based CdS TFTs is the maximum processing temperature of 150 °C, and the findings of this study are very promising for potential low-cost solution-processed TFTs.

Material- and Process-Tolerant High-Efficiency Solar Cells With Dynamic Recovery of Performance

Low cost, highly efficient, and stable solar cells demand low temperature processing, less stringent criteria on materials, and possibility of dynamic recovery from long term degradation: a combination of features unachievable from the perspectives of current cSi technology. To this end, here we propose a novel solar cell architecture with an additional control gate. Our simulation results indicate that the proposed device can achieve excellent efficiency even if the back-surface passivation is sub-optimal; thus allowing exploration of a wide variety of materials and low temperature fabrication processes. Importantly, such solar cells can dynamically offset efficiency loss due to elevated temperature and interface degradation associated with long term field operation and hence could be of broad interest to the PV community.

One-Volt TiO₂ Thin Film Transistors With Low-Temperature Process

We report one-volt TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film transistors (TFTs) with a low-temperature fabrication process. The TFTs with the 300 °C-annealed TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channel exhibit a high on/off current ratio ( I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ) of 5.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , a low subthreshold swing (SS) of 75 mV/dec and a saturation field effect mobility ( μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> ) of 2.13 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> under an ultra-low voltage of 1 V. In contrast, the TFTs with the 200 °C-annealed TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channel show no appreciable currents. Such a distinct conductivity difference is attributed to the crystallinity transformation of stoichiometric TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the charge transport of which can be well explained by the multiple-trapping-and-release (MTR) model. The channel/dielectric interfaces of these one-volt TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TFTs are further investigated by transmission electron microscopy (TEM), multi-frequency ( f) capacitance-voltage (C-V), and conductance-voltage (G-V) measurements. The interface trap density ( D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) values of ~ 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ·eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> obtained from both C-V and G-V measurements are in good agreement, suggesting a high-quality channel/dielectric interface. These one-volt TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TFTs show a great potential in emerging applications, such as foldable displays and wearable sensors, where a battery-powered operation is required.

Performance Enhancement and Bending Restoration for Flexible Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors by Low-Temperature Supercritical Dehydration Treatment.

For high-performance and high-lifetime flexible and wearable electronic applications, a low-temperature posttreatment method is highly expected to enhance the device performance and repair the defects induced by the low-temperature fabrication process intrinsically. Particularly, if the method can repair the traces induced by the multiple cycles of bending or deforming, it would overcome current fatal obstacles and provide a vital solution to the rapid development of flexible electronics. In this work, we propose a method to apply low-temperature supercritical CO2 fluid with a dehydration function to improve or even restore the performance of flexible amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). After the treatment, the a-IGZO TFT exhibits 3 times improvement drivability up to 0.24 μA/μm, a smaller subthreshold swing of 0.18 V dec-1, a smaller Vth of 0.25 V, and a larger Ion/Ioff ratio of 3.8 × 107. Additionally, the posttreated a-IGZO TFTs possess relatively good uniformity and reproducibility with an on-current standard deviation of 0.047 μA/μm, and the performance of the a-IGZO TFT after the treatment remains almost unchanged even after bending 2500 times at a bending radius of 5 mm. These characteristics are attributed to the improved quality of the channel and gate dielectric. It is worth noting that when this is applied to a flexible TFT-driven organic light-emitting diode lighting system, this treatment method can restore the performance of not only the TFT but also the lighting system, even after the system has been bent more than 600 times and has failed. To date, this is the first time that the bending-track erasing function of the supercritical fluid for flexible systems has been reported, which has the potential to prolong the lifetime of flexible electronics.

Dielectric properties and potential applications of alizarin yellow GG-Cu(II) complex film blended with polyvinyl alcohol

The films of alizarin yellow GG (AYGG)–CuCl2 blended with polyvinyl alcohol (PVA) have been successfully synthesized by casting method. The results show that the dielectric properties of AYGG–Cu(II) blended with PVA are enhanced by lowering selected frequency while σac(ω) increases monotonically with frequency, acting in accordance with the correlated barrier hopping model. At low temperature, the DC electrical resistivity of AYGG–Cu(II) blended with PVA film is temperature independent, while it is decreasing with high temperature. Aℓ/(AYGG – Cu(II) blended with PVA)/ITO is fabricated as organic photovoltaic cell, concluding that there are many mechanisms can control the current flow. Aℓ/(AYGG – Cu(II) blended with PVA)/ITO solar cell under illumination of green light be most effective compared to illuminations of others. It is concluded that Aℓ/(AYGG – Cu(II) blended with PVA)/ITO solar cell is very important, with potential advantages such as low cost and low-temperature fabrication processes. It is recommended that this material can be used in different applications such as temperature sensors, inrush current limiters, thermistors, and NO2 sensor.

Zinc Silicate Thin Film Composites Obtained by a Sputtering Based Approach: Structural, Dielectric and Photovoltaic Properties

This study deals with the production of zinc silicate thin films employing a solid-state reaction at temperatures ranging from 300 °C to 560 °C, to develop new inorganic, n-type materials with seemingly incompatible properties as low work function, high mobility, and high visible transmittance. Depending on a careful reaction control, zinc silicates can preserve reagents (silicon and/or ZnO) as nanoaggregate guests, exhibiting tunable light absorption and emission properties that make them useful for different applications, e.g., LED phosphors, photovoltaic windows, mesoporous photocatalytic materials for solar fuel production, etc. The main aim of this work is to obtain a zinc silicate single-phase and then determine its dielectric properties through ellipsometry. Simultaneously, as an example of application, a p-n photovoltaic junction is fabricated that exhibits a remarkable collection of photo-generated charge carriers at very high bandgaps (&gt;2 eV). The obtained results are promising in tailoring the zinc silicate guest-host composition (appropriate Si nanostructures sizing and quantity, improved charge carrier transport properties due to the simultaneous presence of bulk zinc oxide islands) in the function of the desired application, and taking into account that proposed selected low-temperature fabrication process is strategic for safeguarding the underlying junctions of tandem devices.

Low-temperature fabrication of calcium deficient hydroxyapatite bone scaffold by optimization of 3D printing conditions

We herein propose a novel low-temperature fabrication process of calcium deficient hydroxyapatite (CDHA) 3D scaffolds for bone tissue regeneration through a combination of material extrusion type 3D printing process and bone cement chemistry. The CDHA scaffolds with high porosity of 70% showed excellent mechanical property of 25 MPa (compressive strength), without any sintering process after 3D printing. By using this method, the final structures do not show size shrinkage, which must be considered in conventional ceramic sintering processes. We could therefore achieve both size- and 3D architecture-controlled porous CDHA scaffolds with high accuracy. In addition, the resulting ceramic cement scaffolds were not brittle and could be machined without chipping or fracturing the scaffold. The complete process takes place at physiological conditions (37 °C, pH=7), and heat sensitive drugs and biomolecules could be directly loaded onto the raw powder and achieve homogeneous distribution throughout the CDHA scaffold. In this study, we discuss various key factors to complete this low-temperature 3D printing fabrication of calcium phosphate, such as the pre-treatment conditions of particles, liquid-to-powder ratio, relationships between strut sizes, infill of structures, setting temperatures and the properties of 3D printed scaffolds. The low-temperature fabrication process of calcium phosphate scaffolds developed in this study has excellent potential for use in bone tissue engineering.

Multi-stack insulator to minimise threshold voltage drift in ZnO FET sensors operating in ionic solutions

FET biosensors operating in an electrolyte experience a monotonic, temporal and relatively slow change in threshold voltage caused by the hydration of the insulator layer between the electrolyte and the FET's channel. Minimising this temporal change in threshold voltage is critical as, over time, the drain current of n-channel FETs decreases, making it difficult to distinguish between the signal generated in response to analyte - receptor binding events and the background noise generated by the electrolyte and the FET biosensor. While Rapid Thermal Annealing of the insulator layer is known to diminish threshold voltage drift and its negative effects, it is not compatible with a low temperature fabrication process of 200oC. Our low temperature approach to minimising threshold voltage drift involves depositing a tri-layer insulator stack, consisting of a layer of HfO2 between two Al2O3 layers. Wetting ZnO NWFETs with PBS (10 mM phosphate, 150 mM KCl, pH 7.4) for an hour, showed that ZnO NWFETs with a stack insulator layer experienced a much smaller threshold voltage and drain current drift (100 mV, 0.064 nA) than ZnO NWFETs with a single material insulator layer (≥4300mV, 2.72 nA), Aluminium oxide in this case. Having established the resilience enhancing properties of the stack insulator layer on FETs operating in electrolytes of physiological relevant ionic concentrations; ZnO NWFETs with a stack insulator layer were shown to be capable of detecting the presence of the miDNA-21 strands. This, in effect, paves the way for miRNA sensing experiments in the near future and for exploring the potential of ZnO NWFETs as a diagnostic tool.

Low-temperature mineralization sintering process for fabrication of fluoridated hydroxyapatite-containing bioactive glass

Bioactive glasses and glass-ceramics are receiving wide attention for their biomedical applications. We present a novel route to obtain fluoridated hydroxyapatite-containing bioactive glass (FHBG) through a low-temperature mineralization sintering process (LMSP). LMSP is a low-temperature densification procedure that can provide a functionalization of pristine materials through the formation and growth of new phases induced by mineralization. Here, SiO2–CaO–P2O5 bioactive glass nanoparticles (BGNPs) were prepared and mixed with fluorine-containing simulated body fluid (F–SBF) to induce mineralization. Under a uniaxial pressure of 330 MPa and temperature of 120 °C, BGNPs were densified up to 89% of their theoretical density, and the Vickers hardness and fracture toughness of the sintered BGNPs increased to 4.15 ± 0.11 GPa and 1.32 ± 0.12 MPa m1/2, respectively. This densification behavior was strongly influenced by the mineralization that forms nanoscale crystalline phase such as carbonated fluoridated hydroxyapatite (HAp), where part of PO43− and OH− in HAp (Ca10(PO4)6(OH)2) was replaced by CO32− and F−, respectively. The fluorides formed as minor phases in the sintered BGNPs by mineralization were identified as calcium fluorosilicate (CaSiF6) and calcium fluoride (CaF2). After an acid resistance test, because of the presence of fluorides, the sintered BGNPs containing fluorides presented a 38% weight loss, which is lower than that of sintered BGNPs containing no fluorides (54% weight loss). By employing LMSP, we successfully fabricated FHBG from non-fluoride-containing BGNPs and F–SBF at an extremely low temperature at 120 °C. Therefore, this study offers a more efficient method for the manufacturing of glasses and glass-ceramics.

Fabrication of high efficiency, low-temperature planar perovskite solar cells via scalable double-step crystal engineering deposition method fully out of glove box

Halide perovskite solar cells designed using planar architectures are rapidly becoming of high interest due to their low-temperature fabrication process. As the Electron Selective Layer, SnO2 can enhance charge transfer from perovskite to electron transport layers leading to the reduction of charge accumulation at the interface exploiting the larger band offset with perovskite and a higher electron mobility compared with traditional TiO2. Herein, we developed a method for the fabrication of low-temperature planar PSCs under ambient conditions. The scalable Crystal Engineering approach was successfully applied to fabricate the CH3NH3PbI3 absorbing layer on low-temperature planar SnO2 under atmospheric conditions (fully out of glove-box). Photovoltaic characterization showed high-reproducible hysteresis-free planar perovskite solar cells with a maximum power conversion efficiency of 17.6%. The photophysical properties of the PSCs, evaluated by transient photovoltage and photocurrent analysis, showed the excellent capability of SnO2 to extract charge for perovskite. Non-encapsulated n-i-p planar solar cells indicated promising stability under atmospheric conditions, maintaining 90% of the initial efficiency for more than 1000 h. We demonstrate that the scalable air insensitive crystal engineering method is a promising approach for industrialization and fabrication of high efficiency, air-stable, and low-temperature planar perovskite solar cells with high reproducibility fabrication.

Improving the optical properties of organic light-emitting diodes using random nanoscale rods with a double refractive index

In this study, random nanoscale rods (RNRs) with a double refractive index were fabricated via spin coating, dry etching, and sputtering, which are processes that are extensively applied in industry. With regard to optical properties, the RNRs with a double refractive index (RNRsD) exhibited a total transmittance that was >90% in the visible range and an optical haze in the range of 42%–50% at a wavelength of 520 nm. Organic light-emitting diodes (OLEDs) with RNRsD, where SiO2 was deposited on the RNRs via radiofrequency sputtering, exhibited an enhancement of 34.5% in the external quantum efficiency compared with OLEDs with the bare substrate. Furthermore, the color variation of the OLEDs with the optimal RNRsD with respect to a change in the viewing angle was improved from color coordinates of Δ(x, y) = (0.032, 0.034) to Δ(x, y) = (0.014, 0.014). Therefore, the proposed film can be used as a scattering layer for enhancing the light extraction and viewing angle of OLEDs by reducing the substrate mode light loss and changing the direction of light. In addition to using a low-temperature fabrication process that does not employ a photomask and a lithographic template, the proposed method is applicable to flexible devices because it uses a polymer and a thin inorganic film.

Low-Temperature Solution Approaches for the Potential Integration of Ferroelectric Oxide Films in Flexible Electronics.

This technical review presents the state of the art in low-temperature chemical solution deposition (CSD) processing of ferroelectric oxide thin films. To achieve the integration of multifunctional crystalline oxides with flexible and semiconductor devices is, today, crucial to meet the demands of coming electronic devices. Hence, amorphous metal-oxide-semiconductors have been recently introduced in thin-film electronics. However, their benefits are limited compared with those of ferroelectric oxides, in which intrinsic multifunctionality would make possible multiple operations in the device. However, ferroelectricity is linked to a noncentrosymmetric crystal structure that is achieved, in general, at high temperatures, over 500 °C. These temperatures exceed the thermal stability of flexible polymer substrates and are not compatible with those permitted in the current fabrication routines of Si-based devices. In addition, the manufacturing of flexible electronic devices not only calls for low-temperature fabrication processes but also for deposition techniques that scale easily to the large areas required in flexible devices. In this regard, CSD processes are the best positioned today to integrate metal oxide thin films with flexible substrates as a large-area, low-cost, high-throughput fabrication technique. Here, we review the progress made in the last years in fabricating at low-temperature crystalline ferroelectric oxide thin films via CSD methods, highlighting the recent work of our group in the preparation of ferroelectric oxide thin films on flexible polyimide substrates.

WITHDRAWN: Multi-stack insulator to minimise threshold voltage drift in ZnO FET sensors operating in ionic solutions

Abstract FET biosensors operating in an electrolyte experience a monotonic, temporal and relatively slow change in threshold voltage caused by the hydration of the insulator layer between the electrolyte and the FET's channel. Minimising this temporal change in threshold voltage is critical as, over time, the drain current of n-channel FETs decreases, making it difficult to distinguish between the signal generated in response to analyte - receptor binding events and the background noise generated by the electrolyte and the FET biosensor. While Rapid Thermal Annealing of the insulator layer is known to diminish threshold voltage drift and its negative effects, it is not compatible with a low temperature fabrication process of 200 °C. Our low temperature approach to minimising threshold voltage drift involves depositing a tri-layer insulator stack, consisting of a layer of HfO2 between two Al2O3 layers. Wetting ZnO NWFETs with PBS (10 mM phosphate, 150 mM KCl, pH 7.4) for an hour, showed that ZnO NWFETs with a stack insulator layer experienced a much smaller threshold voltage and drain current drift (100 mV, 0.064 nA) than ZnO NWFETs with a single material insulator layer (≥4300mV, 2.72 nA), Aluminium oxide in this case. Having established the resilience enhancing properties of the stack insulator layer on FETs operating in electrolytes of physiological relevant ionic concentrations; ZnO NWFETs with a stack insulator layer were shown to be capable of detecting the presence of the miDNA-21 strands. This, in effect, paves the way for miRNA sensing experiments in the near future and for exploring the potential of ZnO NWFETs as a diagnostic tool.

Hybrid Perovskite‐Organic Flexible Tandem Solar Cell Enabling Highly Efficient Electrocatalysis Overall Water Splitting

AbstractPerovskite‐organic tandem solar cells are attracting more attention due to their potential for highly efficient and flexible photovoltaic device. In this work, efficient perovskite‐organic monolithic tandem solar cells integrating the wide bandgap perovskite (1.74 eV) and low bandgap organic active PBDB‐T:SN6IC‐4F (1.30 eV) layer, which serve as the top and bottom subcell, respectively, are developed. The resulting perovskite‐organic tandem solar cells with passivated wide‐bandgap perovskite show a remarkable power conversion efficiency (PCE) of 15.13%, with an open‐circuit voltage (Voc) of 1.85 V, a short‐circuit photocurrent (Jsc) of 11.52 mA cm−2, and a fill factor (FF) of 70.98%. Thanks to the advantages of low temperature fabrication processes and the flexibility properties of the device, a flexible tandem solar cell which obtain a PCE of 13.61%, with Voc of 1.80 V, Jsc of 11.07 mA cm−2, and FF of 68.31% is fabricated. Moreover, to demonstrate the achieved high Voc in the tandem solar cells for potential applications, a photovoltaic (PV)‐driven electrolysis system combing the tandem solar cell and water splitting electrocatalysis is assembled. The integrated device demonstrates a solar‐to‐hydrogen efficiency of 12.30% and 11.21% for rigid, and flexible perovskite‐organic tandem solar cell based PV‐driven electrolysis systems, respectively.