Phase‐change materials (PCMs) are seeing tremendous interest for their use in reconfigurable photonic devices; however, the most common PCMs exhibit a large absorption loss in one or both states. ...Here, Sb2S3 and Sb2Se3 are demonstrated as a class of low loss, reversible alternatives to the standard commercially available chalcogenide PCMs. A contrast of refractive index of Δn = 0.60 for Sb2S3 and Δn = 0.77 for Sb2Se3 is reported, while maintaining very low losses (k < 10−5) in the telecommunications C‐band at 1550 nm. With a stronger absorption in the visible spectrum, Sb2Se3 allows for reversible optical switching using conventional visible wavelength lasers. Here, a stable switching endurance of better than 4000 cycles is demonstrated. To deal with the essentially zero intrinsic absorption losses, a new figure of merit (FOM) is introduced taking into account the measured waveguide losses when integrating these materials onto a standard silicon photonics platform. The FOM of 29 rad phase shift per dB of loss for Sb2Se3 outperforms Ge2Sb2Te5 by two orders of magnitude and paves the way for on‐chip programmable phase control. These truly low‐loss switchable materials open up new directions in programmable integrated photonic circuits, switchable metasurfaces, and nanophotonic devices.
New optical phase‐change materials are demonstrated, with the ability to realize on‐chip programmable phase control with very low optical losses. The chalcogenides Sb2S3 and Sb2Se3 exhibit a large refractive index contrast between their crystalline and amorphous phases. With reversible switching over thousands of cycles and easy integration with silicon, these materials pave the way for low‐loss reconfigurable and programmable nanophotonics.
Field-Effect Transistor sensors (FET-sensors) have been receiving increasing attention for biomolecular sensing over the last two decades due to their potential for ultra-high sensitivity sensing, ...label-free operation, cost reduction and miniaturisation. Whilst the commercial application of FET-sensors in pH sensing has been realised, their commercial application in biomolecular sensing (termed BioFETs) is hindered by poor understanding of how to optimise device design for highly reproducible operation and high sensitivity. In part, these problems stem from the highly interdisciplinary nature of the problems encountered in this field, in which knowledge of biomolecular-binding kinetics, surface chemistry, electrical double layer physics and electrical engineering is required. In this work, a quantitative analysis and critical review has been performed comparing literature FET-sensor data for pH-sensing with data for sensing of biomolecular streptavidin binding to surface-bound biotin systems. The aim is to provide the first systematic, quantitative comparison of BioFET results for a single biomolecular analyte, specifically streptavidin, which is the most commonly used model protein in biosensing experiments, and often used as an initial proof-of-concept for new biosensor designs. This novel quantitative and comparative analysis of the surface potential behaviour of a range of devices demonstrated a strong contrast between the trends observed in pH-sensing and those in biomolecule-sensing. Potential explanations are discussed in detail and surface-chemistry optimisation is shown to be a vital component in sensitivity-enhancement. Factors which can influence the response, yet which have not always been fully appreciated, are explored and practical suggestions are provided on how to improve experimental design.
Unlike MoS2 ultra-thin films, where solution-based single source precursor synthesis for electronic applications has been widely studied, growing uniform and large area few-layer WS2 films using this ...approach has been more challenging. Here, we report a method for growth of few-layer WS2 that results in continuous and uniform films over centimetre scale. The method is based on the thermolysis of spin coated ammonium tetrathiotungstate ((NH4)2WS4) films by two-step high temperature annealing without additional sulphurization. This facile and scalable growth method solves previously encountered film uniformity issues. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to confirm the few-layer nature of WS2 films. Raman and X-Ray photoelectron spectroscopy (XPS) revealed that the synthesized few-layer WS2 films are highly crystalline and stoichiometric. Finally, WS2 films as-deposited on SiO2/Si substrates were used to fabricate a backgated Field Effect Transistor (FET) device for the first time using this precursor to demonstrate the electronic functionality of the material and further validate the method.
Laser processing is a highly versatile technique for the post-synthesis treatment and modification of transition metal dichalcogenides (TMDCs). However, to date, TMDCs synthesis typically relies on ...large area CVD growth and lithographic post-processing for nanodevice fabrication, thus relying heavily on complex, capital intensive, vacuum-based processing environments and fabrication tools. This inflexibility necessarily restricts the development of facile, fast, very low-cost synthesis protocols. Here we show that direct, spatially selective synthesis of 2D-TMDCs devices that exhibit excellent electrical, Raman and photoluminescence properties can be realized using laser printing under ambient conditions with minimal lithographic or thermal overheads. Our simple, elegant process can be scaled via conventional laser printing approaches including spatial light modulation and digital light engines to enable mass production protocols such as roll-to-roll processing.
Online training of deep neural networks (DNN) can be significantly accelerated by performing in situ vector‐matrix multiplication in a crossbar array of analog memories. However, training accuracies ...often suffer due to nonideal properties of synapses such as nonlinearity, asymmetry, limited bit precision, and dynamic weight update range within a constrained power budget. Herein, a fully scalable process is reported for digital and analog ferroelectric memory transistors with possibilities for both volatile and nonvolatile data retention and <4 V operation that would be suitable as programmable synaptic weight elements. Ferroelectric copolymer P(VDF‐TrFE) gate insulator and 2D semiconductor MoS2 as the n‐type semiconducting channel material make them suitable for flexible and wearable substrate integration. The ferroelectric‐only devices show excellent performance as digital nonvolatile memory operating at <±5 V while the hybrid ferroelectric–dielectric devices show quasi‐continuous resistive switching resulting from gradual ferroelectric domain rotation. Analog conductance states of the hybrid devices allow good linearity and symmetry of weight updates and produce a dynamic conductance range of 104 with >16 reproducible conducting states. Network training experiments with these ferroelectric field‐effect transistors show >96% classification accuracy with Modified National Institute of Standards and Technology (MNIST) handwritten datasets highlighting their potential for implementation in scaled DNN architectures.
Herein, ferroelectric field‐effect transistors are reported which are compatible with the complementary metal–oxide–semiconductor back‐end‐of‐line operate at <4 V, and can work efficiently as digital and analog memory or synaptic weight element with nonvolatile or volatile data retention capability based on their gate stack composition. Ferroelectric copolymer P(VDF‐TrFE) gate ferroelectric and 2D semiconductor MoS2 n‐type channel material make the devices suitable for flexible and wearable substrate integration.
A low cost thin-film transistor (TFT) nanoribbon (NR) sensor has been developed for rapid real-time detection of DNA amplification using an isothermal Recombinase Polymerase Amplification (RPA) ...method. The semiconductor chip measures DNA amplification through a pH change, rather than via fluorescence. The utility of the method was demonstrated by amplifying CTX-M and NDM, two genes that confer bacterial resistance to cephalosporins and carbapenems, respectively. It is shown that this approach provides extremely fast and sensitive detection. It can detect <10 copies of the gene in genomic DNA extracted from E. coli or K. pneumoniae clinical isolates within a few minutes. A differential readout system was developed to minimize the effect of primer-dimer amplification on the assay. The simple device has the potential for low cost, portable and real-time nucleic acid analysis as a Point of Care device.
•A simple to fabricate low cost Thin Film Transistor sensor.•Ultra fast isothermal DNA amplification and detection.•DNA amplification measured by pH change.•Detected genes coding for antimicrobial resistance.
We propose a reconfigurable and non-volatile Bragg grating in the telecommunication C-band based on the combination of novel low-loss phase-change materials (specifically Ge
2
Sb
2
Se
4
Te
1
and Sb
2
...S
3
) with a silicon nitride platform. The Bragg grating is formed by arrayed cells of phase-change material, whose crystallisation fraction modifies the Bragg wavelength and extinction ratio. These devices could be used in integrated photonic circuits for optical communications applications in smart filters and Bragg mirrors and could also find use in tuneable ring resonators, Mach–Zehnder interferometers or frequency selectors for future laser on chip applications. In the case of Ge
2
Sb
2
Se
4
Te
1
, crystallisation produces a Bragg resonance shift up to ∼ 15 nm, accompanied with a large amplitude modulation (insertion loss of 22 dB). Using Sb
2
S
3
, low losses are presented in both states of the phase change material, obtaining a ∼ 7 nm red-shift in the Bragg wavelength. The gratings are evaluated for two period numbers, 100 and 200 periods. The number of periods determines the bandwidth and extinction ratio of the filters. Increasing the number of periods increases the extinction ratio and reflected power, also narrowing the bandwidth. This results in a trade-off between device size and performance. Finally, we combine both phase-change materials in a single Bragg grating to provide both frequency and amplitude modulation. A defect is introduced in the Sb
2
S
3
Bragg grating, producing a high quality factor resonance (
Q
∼ 10
4
) which can be shifted by 7 nm via crystallisation. A GSST cell is then placed in the defect which can modulate the transmission amplitude from low loss to below -16 dB.
Flexible thermoelectric generators (TEGs) can provide uninterrupted, green energy from body-heat, overcoming bulky battery configurations that limit the wearable-technologies market today. ...High-throughput production of flexible TEGs is currently dominated by printing techniques, limiting material choices and performance. This work investigates the compatibility of physical vapour deposition (PVD) techniques with a flexible commercial process, roll-to-roll (R2R), for thermoelectric applications. We demonstrate, on a flexible polyimide substrate, a sputtered Bi
Te
/GeTe TEG with Seebeck coefficient (S) of 140 μV/K per pair and output power (P) of 0.4 nW per pair for a 20 °C temperature difference. For the first time, thermoelectric properties of R2R sputtered Bi
Te
films are reported and we demonstrate the ability to tune the power factor by lowering run times, lending itself to a high-speed low-cost process. To further illustrate this high-rate PVD/R2R compatibility, we fabricate a TEG using Virtual Cathode Deposition (VCD), a novel high deposition rate PVD tool, for the first time. This Bi
Te
/Bi
Sb
Te
TEG exhibits S = 250 μV/K per pair and P = 0.2 nW per pair for a 20 °C temperature difference.
In this review we present some of the recent advances in the field of silicon nitride photonic integrated circuits. The review focuses on the material deposition techniques currently available, ...illustrating the capabilities of each technique. The review then expands on the functionalisation of the platform to achieve nonlinear processing, optical modulation, nonvolatile optical memories and integration with III-V materials to obtain lasing or gain capabilities.
We describe a low cost thin-film transistor (TFT) nanoribbon sensor for detection of the inflammatory biomarker C-reactive protein (CRP) in human serum via a miniature bead-based enzyme-linked ...immunosorbent assay (ELISA). The TFT nanoribbon sensor measures the reaction products from the ELISA via pH changes. The bead-based ELISA decouples the protein functionalization steps from the sensor surface, increasing the signal and simplifying the assay. The ability to directly sense proteins in human serum in this way overcomes the Debye length limitation associated with nanowire and nanoribbon biosensors. Compared to classically fabricated nanowires, the TFT nanoribbon sensors are simple, extremely easy to fabricate, and should therefore be much cheaper to manufacture. TFT nanoribbon sensors, configured to measure pH, were used for quantitative detection of CRP spiked into human serum at concentrations as low as 0.2 ng/mL, which is 10 000 times lower than needed for diagnostic purposes, providing the potential for applications that require very high sensitivity.
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