Ultra-thin Glass Research Articles

Enhancing the sensitivity of flexible acoustic wave ultraviolet photodetector with graphene-quantum-dots decorated ZnO nanowires

Graphene quantum dots decorated zinc oxide nanowires (GQDs@ZnO-NWs) were applied to enhance sensing performance of highly flexible and transparent surface acoustic wave (SAW) ultraviolet (UV) photodetectors made on ultra-thin flexible glass. The developed flexible SAW sensors possess better performance than that of the previously developed polymer based flexible SAW devices, due to insignificant acoustic loss of flexible glass substrate. UV sensitivity of the flexible glass based SAW sensors was enhanced by three times, and the response time was shorten by four times after the sensor was coated with the GQDs@ZnO-NWs hybrid nanomaterials. These improvements are mainly attributed to: (1) large specific surface areas of ZnO NWs which can generate a large number of photon-generated carriers; (2) introduction of GQDs which can reduce the carrier recombination rate. The resonant frequency of flexible glass SAW UV photodetectors exhibited a good repeatability and stability in responses to cyclic changes of the UV lights at different wavelengths. They also maintained a good performance under a bending angle of ∼30° for 200 times without apparent degradation, showing the excellent flexibility and stability of the UV photodetector.

Highly flexible cover window using ultra-thin glass for foldable displays

The market for next-generation flexible displays is rapidly expanding with the launch of foldable electronic products. Consequently, the flexible electronic material and device industries are continuously growing. Specifically, the cover window used in foldable displays is a very important component that must have excellent optical, physical, and mechanical characteristics while withstanding high external stresses caused by the bending radius, unlike the existing rigid-type cover windows. Considerable research efforts have been dedicated toward improving their performance. In this study, a cover window substrate for a foldable display having high flexibility was developed. To this end, ultra-thin glass (UTG) with excellent flexibility and transparency was used to overcome the low surface hardness of the typical polymer substrate used in existing foldable substrates. In addition, for efficient stress control, the design of the multilayer structure was optimized by generating multiple neutral planes through the use of an optical clear adhesive (OCA) buffer layer. The structure of the cover window was designed using the finite element simulation technique, and actual samples of the cover window with the optimized structure were produced to evaluate their physical, mechanical, and optical characteristics. As a result, the optimized foldable cover window showed a surface hardness of 9 H and a light transmittance of 90 %; especially, it exhibited an excellent bending reliability with 200000 bending repetitions without failure at the small bending radius of 1.5 R.

Bottom-up cutting method to maximize edge strength in femtosecond laser ablation cutting of ultra-thin glass

In femtosecond laser cutting of ultra-thin glass sheets, subsurface and back-surface damage are known to degrade the strength of diced samples significantly. Subsurface damage is generated by refraction of the laser beam at the V-shaped ablation groove into the glass in typical top-down cutting processes. Furthermore, our analysis indicates that interference of the refracted beam with its reflected portion at the back surface induces back-surface damage. In this work, we propose a bottom-up cutting method to eliminate the damage, and thereby maximize the edge strength. Refraction of the beam is absent in the proposed bottom-up cutting method because the ablation grooves have an inverted V-shape. This work verified the concept of the bottom-up cutting method, demonstrating a substantial enhancement of the edge strength of ultra-thin glass by eliminating sub- and back-surface damage. The maximum front- and back-side edge strengths of borosilicate glass cut by the bottom-up cutting method are ~330 and ~380 MPa, respectively, which are substantially higher than those achieved in conventional top-down cutting.

Flexible electrochromic devices prepared on ultra-thin ITO glass

Electrochromic devices (ECDs) containing iron-based metallo-supramolecular polymers (Fe-MEPE) and Prussian blue (PB) as electrode materials, polymer electrolyte and flexible ultra-thin ITO glass as transparent conductive substrate are demonstrated.

Hybrid laser-assisted forming process for ultralight three-dimensional glass elements

As part of a research project, a new hybrid forming process for ultrathin three-dimensional glass elements was developed. In a continuous process chain, the three-part procedure enables large-area gravity-assisted bending of thin glass, partial deep-drawing of individual small structures using CO2 laser radiation and cutting of flexible inner and outer contours. Using an experimental setup with a laser scanning system, novel component designs can be generated in a highly flexible and reproducible manner. This can open up new application fields or expand existing ones, for example in the area of cover glasses for display technology.

Mechanical reliability of flexible encapsulation of III-V compound thin film solar cells

Flexible III-V compound thin film solar cells are promising candidates in the applications of Internet of Thing, electronics, civil, automotive and aerospace. In this study, theoretical, numerical and experimental methods are employed to investigate the mechanical reliability of the GaAs thin film solar cells with polymer film encapsulation. Experimental investigation by uniaxial tensile testing has revealed the stress failure of cell can be divided into the two different stages. For lower applied strain (<2.0%), the stress concentration caused the local plasticity of encapsulation material along the polymer-semiconductor interface (e.g. EVA-GaAs). For larger applied strain (>2.0%), semiconductor materials (e.g. junction and window) have shown brittle cracking failures. The observed brittle and ductile failures of the sublayer can be well-explained by analytical model based on theory of solid and fracture mechanics. It is also found that the interface stiffness mismatch plays an important role of encapsulation failure at lower strain level. The degree of the stiffness mismatch can be characterised by the proposed strain intensity factor. To overcome the mechanical failure, new encapsulation material such as ultra-thin glass can be promising in the future application.

Pulsed Magnetron Sputtering of Strongly Thermochromic VO2-Based Coatings with a Transition Temperature of 22 °C onto Ultrathin Flexible Glass

The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their performance, an industry-friendly preparation technique, and an industrially relevant substrate. We present a scalable sputter deposition technique for the preparation of strongly thermochromic ZrO2/V0.984W0.016O2/ZrO2 coatings on ultrathin flexible glass and standard glass at a relatively low substrate surface temperature (330 °C) and without any substrate bias voltage. The V0.984W0.016O2 layers were deposited by a controlled high-power impulse magnetron sputtering of a V target, combined with a simultaneous pulsed dc magnetron sputtering of a W target. We explain the fundamental principles of this technique using the discharge characteristics measured for both discharges. We characterize the coating structure (X-ray diffraction) and a wide range of optical properties (spectrophotometry and spectroscopic ellipsometry). We find that the coatings combine a transition temperature of 22 °C, a luminous transmittance approaching 50%, a modulation of the solar energy transmittance over 10% and a temperature-independent color. The results in general, and the successful transfer from a standard glass to the ultrathin flexible glass in particular, are crucial for future applications of the coatings on smart windows.

Solar Cell Technology Selection for a PV Leaf Based on Energy and Sustainability Indicators—A Case of a Multilayered Solar Photovoltaic Tree

Harnessing energy from the sunlight using solar photovoltaic trees (SPVTs) has become popular at present as they reduce land footprint and offer numerous complimentary services that offset infrastructure. The SPVT’s complimentary services are noticeable in many ways, e.g., electric vehicle charging stations, landscaping, passenger shelters, onsite energy generated security poles, etc. Although the SPVT offers numerous benefits and services, its deployment is relatively slower due to the challenges it suffers. The most difficult challenges include the structure design, the photovoltaic (PV) cell technology selection for a leaf, and uncertainty in performance due to weather parameter variations. This paper aims to provide the most practical solution supported by the performance prioritization approach (PPA) framework for a typical multilayered SPVT. The proposed PPA framework considers the energy and sustainability indicators and helps in reporting the performance of a multilayered SPVT, with the aim of selecting an efficient PV leaf design. A three-layered SPVT (3-L SPVT) is simulated; moreover, the degradation-influenced lifetime energy performance and carbon dioxide (CO2) emissions were evaluated for three different PV-cell technologies, namely crystalline silicon (c-Si), copper indium gallium selenide (CIGS), and cadmium telluride (CdTe). While evaluating the performance of the 3-L SPVT, the power conversion efficiency, thermal regulation, degradation rate, and lifecycle carbon emissions were considered. The results of the 3-L SPVT were analyzed thoroughly, and it was found that in the early years, the c-Si PV leaves give better energy yields. However, when degradation and other influencing weather parameters were considered over its lifetime, the SPVT with c-Si leaves showed a lowered energy yield. Overall, the lifetime energy and CO2 emission results indicate that the CdTe PV leaf outperforms due to its lower degradation rate compared to c-Si and CIGS. On the other side, the benefits associated with CdTe cells, such as flexible and ultrathin glass structure as well as low-cost manufacturing, make them the best acceptable PV leaf for SPVT design. Through this investigation, we present the selection of suitable solar cell technology for a PV leaf.

Ultrathin Ga2 O3 Glass: A Large-Scale Passivation and Protection Material for Monolayer WS2.

Atomically thin transition metal dichalcogenide crystals (TMDCs) have extraordinary optical properties that make them attractive for future optoelectronic applications. Integration of TMDCs into practical all-dielectric heterostructures hinges on the ability to passivate and protect them against necessary fabrication steps on large scales. Despite its limited scalability, encapsulation of TMDCs in hexagonal boron nitride (hBN) currently has no viable alternative for achieving high performance of the final device. Here, it is shown that the novel, ultrathin Ga2 O3 glass is an ideal centimeter-scale coating material that enhances optical performance of the monolayers and protects them against further material deposition. In particular, Ga2 O3 capping of monolayer WS2 outperforms commercial-grade hBN in both scalability and optical performance at room temperature. These properties make Ga2 O3 highly suitable for large-scale passivation and protection of monolayer TMDCs in functionalheterostructures.

Thermal stress cleaving of glass-based X-ray telescope lenses by heated wire to eliminate microdefects

Abstract The satellite borne X-ray telescope (XRT) is a key technical tool for studying major astronomical problems in the universe. During the fabrication of ultra-thin glass lenses for XRTs, conventional glass cutting technologies yield micro-cracks along the cut surface or micro-damage on the surfaces of the glass normal to the cut. These micro-defects will cause the lenses to be damaged by the strong vibration and jerk of the launch process. In this paper, we seek to resolve this issue by developing a non-destructive cutting technique for glass lenses. Specifically, in this study we propose a heated wire thermal stress cleaving method. We derived the principal parameters affecting the thermal stress fracture behavior of lenses and furthermore calculated the relationship between the length of the initial crack and the minimum temperature. Experimental studies are performed to investigate the process parameters that affect the propagation of a crack in the telescope lens during the thermal stress cleaving process. In particular, we have successfully achieved thermal stress cleaving of a 0.3mm thick lenses with a surface roughness Ra of less than 0.5nm. When assessed in a satellite launch vibration test with a maximum accelerations amplitudes of 5g and 6g in the Y- and Z-directions, respectively, no crack propagation or damage was observed on the surface of the obtained telescope lenses. The study lays a foundation for the manufacture of glass-based XRT.

Foldable Market Expands with Samsung, Microsoft Offerings

Foldable Market Expands with Samsung, Microsoft Offerings

Room‐temperature bonding method of bioactive ultrathin glass film on titanium by a dissolution‐polymerization reaction

AbstractFreestanding ultrathin glass film (UGF) of 45S5 bioglass was successfully bonded on a Ti substrate by the room‐temperature bonding method. 45S5 UGFs with a thickness of 1~4 μm were fabricated by the glass‐blowing technique, and the UGF was attached on the Ti plate at room temperature with a water layer between them. The bonding strength was about 370 mJ/m2 just after bonding, and it increased during storing in the ambient atmosphere at room temperature and reached about 900 mJ/m2 after 9 hours storage. The interfaces of the UGF and Ti substrate during the bonding process were analyzed by an X‐ray photoelectron spectroscopy. The as‐prepared UGF was found to have surface layers with a high content of Na2O and low content of SiO2, and the dissolution of Na2O‐rich component into water layer induced depolymerization and polymerization of SiO2 network to form Si‐O‐Si bonds between the UGF and Ti plate and then to increase the bonding strength during storage. This work presents the simple technique to laminate the bioactive glass layer on the surface of the metal without post heat treatment.

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

AbstractFor applications to semi‐transparent and/or bifacial solar cells in building‐integrated photovoltaics and building‐applied photovoltaics, studies are underway to reduce the processing cost and time by decreasing the thickness of Cu(In1−x,Gax)Se2 (CIGSe) absorber to the ultra‐thin scale (≤500 nm). To dynamically and affordably meet the growing demand for electric power, daylighting, and architectural aesthetics of buildings in urban area, flexible semi‐transparent ultra‐thin (F‐STUT) CIGSe solar cells are proposed on flexible ultra‐thin glass (UTG) and compared with rigid semi‐transparent ultra‐thin (STUT) CIGSe solar cells fabricated on soda‐lime glass (SLG). At all the tested deposition temperatures of CIGSe, the F‐STUT CIGSe solar cells exhibit superior performance compared to the rigid STUT CIGSe solar cells. Furthermore, through realistic measurement under ≈1.3‐sun illumination, maximum bifacial power conversion efficiency of 11.90% and 13.23% are obtained for SLG and UTG, respectively. The major advantages of using UTG instead of SLG are not only the intrinsic characteristics of UTG, such as flexibility and high transmittance, but also collateral benefits such as the larger CIGSe grain size at the deposition temperature, better CIGSe crystalline quality, more precise controllability of the alkali element, and reduced thickness of the interfacial GaOx layer, which enhance the photovoltaic parameters.

Temperature difference in close-spaced sublimation (CSS) growth of CdTe thin film on ultra-thin glass substrate

In this study, cadmium telluride (CdTe) thin films were grown for the first time ever on ultra-thin (100 µm) Schott D263T glass substrates via high temperature deposition process namely close-spaced sublimation (CSS). CdTe thin films were deposited under different source and substrate temperatures ranging from 500 ℃ to 700 ℃ to investigate the influence of deposition temperature on the properties of CdTe thin films grown on ultra-thin Schott glass substrates. X-ray diffraction (XRD) analysis illustrated cubic CdTe structure with a sharp peak at (111) orientation. The scanning electron microscope (SEM) study elucidated that the grain growth and surface morphology were highly dependent on the deposition temperature. UV–Vis results showed approximate optical band gap range of 1.61–1.66 eV. Carrier concentration and resistivity were found in the order of 1013 cm−3 and 105 Ω-cm, respectively. Structural and opto-electronic characteristics were optimized for the best temperature range to be used for CdTe film deposition in CSS growth. Optimum conditions for CdTe film growth on ultra-thin (100 µm) substrate were found in the range of 500 ℃–600 ℃ for substrate and source temperature.

Hydrophilic direct bonding and debonding of ultrathin glass substrates for high-temperature devices

The direct hydrophilic bonding and debonding of ultrathin glass substrates onto and off from a glass carrier has been investigated, and a methodology is presented to reduce the excessive bonding strength after high-temperature annealing to facilitate the debonding process. It is found that with a preliminary surface conditioning of glasses at 300 °C and 400 °C in vacuum at 1 mbar before bonding, the specific surface energy of bonded wafers after high-temperature annealing for 30 min reduces to about 72% and 50% as compared to the control samples that have been surface-conditioned at room temperature instead.

Study on bending deformation of ultra-thin floating glass plate

The bending deformation caused by chemical strengthening is often thought as a negative factor on the performance of the ultra-thin glass plate. It becomes serious with the thickness of the ultra-thin glass plate getting smaller. The mechanism of the bending deformation was analyzed in this paper. The key factors including thermal history and micro structure variation caused by tin penetration were discussed accordingly. A numerical model was proposed to predict the bending deformation during manufacturing and chemical strengthening procedures. It was validated by bending deformation measurement. It is shown that after chemical strengthening the glass plate bends toward the upper (atmosphere) surface. The tin ion penetration during floating is an important factor to cause bending deformation in chemical strengthening stage.

Boson peak in ultrathin alumina layers investigated with neutron spectroscopy

Bulk glasses exhibit extra vibrational modes at low energies, known as the boson peak. The microscopic dynamics in nanoscale alumina impact the performance of qubits and other superconducting devices, however the existence of the boson peak in these glasses has not been previously measured. Here we report neutron spectroscopy on Al/Al$_2$O$_{3-x}$ nanoparticles consisting of spherical metallic cores from 20 to 1000 nm surrounded by a 3.5 nm thick alumina glass. An intense low-energy peak is observed at $\omega_{BP}$ = 2.8 $\pm$ 0.6 meV for highly oxidised particles, concurrent with an excess in the density of states. The intensity of the peak scales inversely with particle size and oxide fraction indicating a surface origin, and is red-shifted by 3 meV with respect to the van-Hove singularity of $\gamma$-phase Al$_2$O$_{3-x}$ nanocrystals. Molecular dynamics simulations of $\alpha$-Al$_2$O$_{3-x}$, $\gamma$-Al$_2$O$_{3-x}$ and a-Al$_2$O$_{3-x}$ show that the observed boson peak is a signature of the ultrathin glass surface, and the frequency is softened compared to that of the hypothetical bulk glass.

Self-Induced Passive Nonreciprocal Transmission by Nonlinear Bifacial Dielectric Metasurfaces

The breaking of Lorentz reciprocity law is a non-trivial task, since it usually requires bulky magnets or complicated time-modulation dynamic techniques to be accomplished. In this work, we present a simple and compact design of a nonlinear bifacial dielectric metasurface to achieve strong self-induced passive nonreciprocal transmission without the use of external biases. The proposed design is ideal for free space optics applications, can operate under both incident polarizations, and require very low input excitation power to reach the nonreciprocal regime. It is composed of two passive silicon-based metasurfaces exhibiting Fano and Lorentzian resonances embedded in an ultrathin glass substrate. Highly asymmetric field enhancement is achieved with the proposed design that leads to strong nonreciprocity at low excitation intensities due to the large Kerr nonlinearity of silicon. Moreover, cascade designs are presented to further improve the insertion loss, broaden the nonreciprocal intensity range, and increase the isolation ratio by enhancing the transmission contrast. Finally, it is demonstrated that the proposed nonlinear metasurface is robust to fabrication imperfections and can achieve large isolation for a relative broad input power range even in the case of two incident waves impinging at the same time from both directions. The current work is expected to lead to new compact nonreciprocal nanophotonic devices, such as all-optical diodes, isolators, circulators, and ultrathin protective layers for sensitive optical components.

Ultra-thin glass as a substrate for flexible photonics

Flexible photonics is an emerging field in optical materials for several frontier applications. New ultra-thin glasses with thicknesses ranging from tens to hundreds of microns are potential candidates as substrates for flexible photonics applications. The improvement in mechanical performance, specifically retained strength, for such glasses is achieved by composition design and ion exchange post-processing. The main physical effects to be considered are the introduction of residual stress profiles and refractive index modifications. Both aspects may interfere with flexible photonics application of these glass substrates. The physics of stress buildup and relaxation are discussed, as well as the impact on refractive index. The discussion also considers promising glass compositions widely used in consumer electronics applications.

Ultra-thin phosphate glass exhibiting high proton conductivity at intermediate temperatures

Ultra-thin proton-conducting phosphate glass was fabricated by press-forming at high temperature. The glass was evaluated for its ohmic loss reduction when installed as an electrolyte in intermediate-temperature fuel cells. The 36HO1/24NbO5/22BaO4LaO3/24GeO21BO3/249PO5/2 glass (36H-glass) was prepared by alkali-proton substitution. Herein, 3–4 mg of 36H-glass was placed onto a 50 μm-thick stainless steel or Pd support and then sandwiched by a glassy carbon plate, whereupon a 600 kg load was applied at temperatures varying as 333–391 °C. Ultra-thin 36H-glass with a thickness of 16 μm was successfully obtained without degradation of proton conductivity. A fuel cell incorporating the Pd-supported ultra-thin 36H-glass was successfully operated at 300 °C, and the ohmic loss of the fuel cell was reduced down to 2.7 Ω cm2 from the previous reported value of several tens of Ω·cm2.