Four-Dimensional Physical Unclonable Functions and Cryptographic Applications Based on Time-Varying Chaotic Phosphorescent Patterns.

Physical unclonable functions (PUFs) have attracted interest in demonstrating authentication and cryptographic processes for Internet of Things (IoT) devices. We demonstrated four-dimensional PUFs (4D PUFs) to realize time-varying chaotic phosphorescent randomness on MoS2 atomic seeds. By forming hybrid states involving more than one emitter with distinct lifetimes in 4D PUFs, irregular lifetime distribution throughout patterns functions as a time-varying disorder that is impossible to replicate. Moreover, we established a bit extraction process incorporating multiple 64 bit-stream challenges and experimentally obtained physical features of 4D PUFs, producing countless random 896 bit-stream responses. Furthermore, the weak and strong PUF models were conceptualized and demonstrated based on 4D PUFs, exhibiting superior cryptological performances, including randomness, uniqueness, degree of freedom, and independent bit ratio. Finally, the data encryption and decryption in pictures were performed by a single 4D PUF. Therefore, 4D PUFs could enhance the counterfeiting deterrent of existing optical PUFs and be used as an anticounterfeiting security strategy for advanced authentication and cryptographic processes of IoT devices.

Nanoporous MoS2 Field-Effect Transistor Based Artificial Olfaction: Achieving Enhanced Volatile Organic Compound Detection Inspired by the Drosophila Olfactory System.

Olfaction, a primal and effective sense, profoundly impacts our emotions and instincts. This sensory system plays a crucial role in detecting volatile organic compounds (VOCs) and realizing the chemical environment. Animals possess superior olfactory systems compared to humans. Thus, taking inspiration from nature, artificial olfaction aims to achieve a similar level of excellence in VOC detection. In this study, we present the development of an artificial olfaction sensor utilizing a nanostructured bio-field-effect transistor (bio-FET) based on transition metal dichalcogenides and the Drosophila odor-binding protein LUSH. To create an effective sensing platform, we prepared a hexagonal nanoporous structure of molybdenum disulfide (MoS2) using block copolymer lithography and selective etching techniques. This structure provides plenty of active sites for the integration of the LUSH protein, enabling enhanced binding with ethanol (EtOH) for detection purposes. The coupling of the biomolecule with EtOH influences the bio-FETs potential, which generates indicative electrical signals. By mimicking the sniffing techniques observed in Drosophila, these bio-FETs exhibit an impressive limit of detection of 10-6% for EtOH, with high selectivity, sensitivity, and detection ability even in realistic environments. This bioelectric sensor demonstrates substantial potential in the field of artificial olfaction, offering advancements in VOC detection.

Facile Transfer of Spray-Coated Ultrathin AgNWs Composite onto the Skin for Electrophysiological Sensors.

Disposable wearable sensors that ultrathin and conformable to the skin are of significant interest as affordable and easy-to-use devices for short-term recording. This study presents a facile and low-cost method for transferring spray-coated silver nanowire (AgNW) composite films onto human skin using glossy paper (GP) and liquid bandages (LB). Due to the moderately hydrophobic and rough surface of the GP, the ultrathin AgNWs composite film (~200 nm) was easily transferred onto human skin. The AgNW composite films conformally attached to the skin when applied with a LB, resulting in the stable and continuous recording of wearable electrophysiological signals, including electromyogram (EMG), electrocardiogram (ECG), and electrooculogram (EOG). The volatile LB, deposited on the skin via spray coating, promoted rapid adhesion of the transferred AgNW composite films, ensuring stability to the AgNWs in external environments. The AgNWs composite supported with the LB film exhibited high water vapor breathability (~28 gm-2h-1), which can avoid the accumulation of sweat at the skin-sensor interface. This approach facilitates the creation of rapid, low-cost, and disposable tattoo-like sensors that are practical for extended use.

An Aqueous Route to Oxygen-Deficient Wake-Up-Free La-Doped HfO2 Ferroelectrics for Negative Capacitance Field Effect Transistors.

The crucial role of nanocrystalline morphology in stabilizing the ferroelectric orthorhombic (o)-phase in doped-hafnia films is achieved via chemical solution deposition (CSD) by intentionally retaining carbonaceous impurities to inhibit grain growth. However, in the present study, large-grained (>100 nm) La-doped HfO2 (HLO) films are grown directly on silicon by adopting engineered water-diluted precursors with a minimum carbonaceous load and excellent shelf life. The o-phase stabilization is accomplished through a well-distributed La dopant, which generates uniformly populated oxygen vacancies, eliminating the need for oxygen-scavenging electrodes. These oxygen-deficient HLOs show a maximum remnant polarization of 37.6 µC/cm2 (2Pr) without wake-up and withstand large fields (>6.2 MV/cm). Furthermore, CSD-HLO in series with Al2O3 improves switching of MOSFETs (with an amorphous oxide channel) based on the negative capacitance effect. Thus, uniformly distributed oxygen vacancies serve as a standalone factor in stabilizing the o-phase, enabling efficient wake-up-free ferroelectricity without the need for nanostructuring, capping stresses, or oxygen-reactive electrodes.

Colorimetric Multigas Sensor Arrays and an Artificial Olfactory Platform for Volatile Organic Compounds.

Herein, we develop colorimetric multigas sensor arrays assembling chemo-reactive fluorescent patch arrays and 10 × 10 indium gallium zinc oxide phototransistor arrays and apply them to an artificial olfactory platform to recognize five different volatile organic compounds (VOCs). Porous nanofibers, coupled with two organic emitters and emitting fluorescence, rapidly respond to gas-phased VOCs and offer unique fluorescent patterns associated with particular gas conditions, including gas kinds, concentrations, and exposure times by forming patch arrays with different fluorophore component ratios. These VOC-induced fluorescent patterns could be quantified and amplified by indium gallium zinc oxide (IGZO) phototransistor arrays functioning as a signal-generating component, resulting in gas-fingerprint patterns regarding electrical signals. Thus, the pattern library associated with VOCs and their concentration enables us to determine each airborne analyte as the artificial olfactory platform. Therefore, this system could achieve rapid, early quantitative recognition of hazardous gases and be applied as a preventative, portable, and wearable multigas identifier in various fields.

Highly Sensitive and Selective Gas Sensors Based on Metal Iodates: Material Characterization and Sensor Performance Evaluation.

This study proposes the possibility of employing metal iodates as novel gas-sensing materials synthesized using a facile chemical precipitation method. An extensive survey of a library of metal iodates reveals that cobalt, nickel, and copper iodates are useful for gas sensor applications. Material analysis conducted using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermal gravity differential temperature analysis, and Raman spectroscopy enables us to understand the thermal behavior and optimize post-annealing conditions. The evaluation of the gas-sensing performance of the specified metal iodates indicates that all of them display p-type sensing behavior and exhibit a high gas response toward different gases: a gas response of 18.6 by cobalt iodate to 1.8 ppm of acetone, a gas response of 4.3 by nickel iodate to 1 ppm of NO2, and a gas response of 6.6 by copper iodate to 1.8 ppm of H2S. Further investigation of the temperature-programmed reduction of H2 and polarization-electric field hysteresis analyses elucidates that the high gas response originates from the inherent characteristics of metal iodates, such as the high oxygen-reduction ability of iodine, highlighting the potential of the iodates as novel gas-sensing materials.

Optical Enhancement of Indirect Bandgap 2D Transition Metal Dichalcogenides for Multi-Functional Optoelectronic Sensors.

The unique electrical and optical properties of transition metal dichalcogenides (TMDs) make them attractive nanomaterials for optoelectronic applications, especially optical sensors. However, the optical characteristics of these materials are dependent on the number of layers. Monolayer TMDs have a direct bandgap that provides higher photoresponsivity compared to multilayer TMDs with an indirect bandgap. Nevertheless, multilayer TMDs are more appropriate for various photodetection applications due to their high carrier density, broad spectral response from UV to near-infrared, and ease of large-scale synthesis. Therefore, this review focuses on the modification of the optical properties of devices based on indirect bandgap TMDs and their emerging applications. Several successful developments in optical devices are examined, including band structure engineering, device structure optimization, and heterostructures. Furthermore, it introduces cutting-edge techniques and future directions for optoelectronic devices based on multilayer TMDs.

Back-End-of-Line Compatible Large-Area Molybdenum Disulfide Grown on Flexible Substrate: Enabling High-Performance Low-Power Memristor Applications.

Transition-metal dichalcogenides (TMDs) in flexible technology can offer large-area scalability and high-density integration with a low power consumption. However, incorporating large-area TMDs in a flexible platform is lacking in state-of-the-art data storage technology owing to the high process temperature of TMDs. Low-temperature growth of TMDs can bridge mass production in flexible technology and reduce the complexity of the transferring process. Here, we introduce a crossbar memory array enabled by low-temperature (250 °C) plasma-assisted chemical vapor deposited MoS2 directly grown on a flexible substrate. The low-temperature sulfurization induces nanograins of MoS2 with multiple grain boundaries, allowing the path for charge particles, which leads to the formation of conducting filaments. The back-end-of-line compatible MoS2-based crossbar memristors exhibit robust resistance switching (RS) behavior with a high on/off current ratio of approximately ∼105, excellent endurance (>350 cycles), retention (>200000 s), and low operating voltage (∼±0.5 V). Furthermore, the MoS2 synthesized at low temperature on a flexible substrate facilitates RS characteristics demonstrated under strain states and exhibits excellent RS performance. Thus, the use of direct-grown MoS2 on a polyimide (PI) substrate for high-performance cross-bar memristors can transform emerging flexible electronics.

Se-Vacancy Healing with Substitutional Oxygen in WSe2 for High-Mobility p-Type Field-Effect Transistors.

Transition-metal dichalcogenides possess high carrier mobility and can be scaled to sub-nanometer dimensions, making them viable alternative to Si electronics. WSe2 is capable of hole and electron carrier transport, making it a key component in CMOS logic circuits. However, since the p-type electrical performance of the WSe2-field effect transistor (FET) is still limited, various approaches are being investigated to circumvent this issue. Here, we formed a heterostructural multilayer WSe2 channel and solution-processed aluminum-doped zinc oxide (AZO) for compositional modification of WSe2 to obtain a device with excellent electrical properties. Supplying oxygen anions from AZO to the WSe2 channel eliminated subgap states through Se-deficiency healing, resulting in improved transport capacity. Se vacancies are known to cause mobility degradation due to scattering, which is mitigated through ionic compensation. Consequently, the hole mobility can reach high values, with a maximum of approximately 100 cm2/V s. Further, the transport behavior of the oxygen-doped WSe2-FET is systematically analyzed using density functional theory simulations and photoexcited charge collection spectroscopy measurements.

A Wafer-Scale Nanoporous 2D Active Pixel Image Sensor Matrix with High Uniformity, High Sensitivity, and Rapid Switching.

2D transition-metal dichalcogenides (TMDs) have been successfully developed as novel ubiquitous optoelectronics owing to their excellent electrical and optical characteristics. However, active-matrix image sensors based on TMDs have limitations owing to the difficulty of fabricating large-area integrated circuitry and achieving high optical sensitivity. Herein, a large-area uniform, highly sensitive, and robust image sensor matrix with active pixels consisting of nanoporous molybdenum disulfide (MoS2 ) phototransistors and indium-gallium-zinc oxide (IGZO) switching transistors is reported. Large-area uniform 4-inch wafer-scale bilayer MoS2 films are synthesized by radio-frequency (RF) magnetron sputtering and sulfurization processes and patterned to be a nanoporous structure consisting of an array of periodic nanopores on the MoS2 surface via block copolymer lithography. Edge exposure on the nanoporous bilayer MoS2 induces the formation of subgap states, which promotes a photogating effect to obtain an exceptionally high photoresponsivity of 5.2 × 104 A W-1 . A 4-inch-wafer-scale image mapping is successively achieved using this active-matrix image sensor by controlling the device sensing and switching states. The high-performance active-matrix image sensor is state-of-the-art in 2D material-based integrated circuitry and pixel image sensor applications.

In Situ Synthesis of Two-Dimensional Lateral Semiconducting-Mo:Se//Metallic-Mo Junctions Using Controlled Diffusion of Se for High-Performance Large-Scaled Memristor.

Two-dimensional (2D) materials are favorable candidates for resistive memories in high-density nanoelectronics owing to their ultrathin scaling and controllable interfacial characteristics. However, high processing temperatures and difficulties in mechanical transfer are intriguing challenges associated with their implementation in large areas with crossbar architecture. A high processing temperature may damage the electrical functionalities of the bottom electrode, and mechanical transfer of 2D materials may introduce undesirable microscopic defects and macroscopic discontinuities. In this study, an in situ fabrication of an electrode and 2D-molybdenum diselenide (MoSe2) is reported. The controlled diffusion of selenium (Se) in the predeposited molybdenum (Mo) produces Mo//Mo:Se stacks with a few layers of MoSe2 on top and MoSex on the bottom. Diffusion-assisted Mo//Mo:Se fabrication is observed over a large area (4 in. wafer). Additionally, a 5 × 5 array of crossbar memristors (Mo//Mo:Se//Ag) is fabricated using the diffusion of Se in patterned Mo. These memristors exhibit a small switching voltage (∼1.1 V), high endurance (>250 cycles), and excellent retention (>15 000 s) with minimum cycle-to-cycle and device-to-device variation. Thus, the proposed nondestructive in situ technique not only simplifies the fabrication but also minimizes the number of required stages.

Surface Passivation of Layered MoSe2 via van der Waals Stacking of Amorphous Hydrocarbon.

Development of efficient surface passivation methods for semiconductor devices is crucial to counter the degradation in their electrical performance owing to scattering or trapping of carriers in the channels induced by molecular adsorption from the ambient environment. However, conventional dielectric deposition involves the formation of additional interfacial defects associated with broken covalent bonds, resulting in accidental electrostatic doping or enhanced hysteretic behavior. In this study, centimeter-scaled van der Waals passivation of transition metal dichalcogenides (TMDCs) is demonstrated by stacking hydrocarbon (HC) dielectrics onto MoSe2 field-effect transistors (FETs), thereby enhancing the electric performance and stability of the device, accompanied with the suppression of chemical disorder at the HC/TMDCs interface. The stacking of HC onto MoSe2 FETs enhances the carrier mobility of MoSe2 FET by over 50% at the n-branch, and a significant decrease in hysteresis, owing to the screening of molecular adsorption. The electron mobility and hysteresis of the HC/MoSe2 FETs are verified to be nearly intact compared to those of the fabricated HC/MoSe2 FETs after exposure to ambient environment for 3 months. Consequently, the proposed design can act as a model for developing advanced nanoelectronics applications based on layered materials for mass production.

Probing the Efficacy of Large-Scale Nonporous IGZO for Visible-to-NIR Detection Capability: An Approach toward High-Performance Image Sensor Circuitry.

The technological ability to detect a wide spectrum range of illuminated visible-to-NIR is substantially improved for an amorphous metal oxide semiconductor, indium gallium zinc oxide (IGZO), without employing an additional photoabsorber. The fundamentally tuned morphology via structural engineering results in the creation of nanopores throughout the entire thickness of ∼30 nm. See-through nanopores have edge functionalization with vacancies, which leads to a large density of substates near the conduction band minima and valence band maxima. The presence of nanoring edges with a high concentration of vacancies is investigated using chemical composition analysis. The process of creating a nonporous morphology is sophisticated and is demonstrated using a wafer-scale phototransistor array. The performance of the phototransistors is assessed in terms of photosensitivity (S) and photoresponsivity (R); both are of high magnitudes (S = 8.6 × 104 at λex = 638 nm and Pinc = 512 mW cm2-; R = 120 A W1- at Pinc = 2 mW cm2- for the same λex). Additionally, the 7 × 5 array of 35 phototransistors is effective in sensing and reproducing the input image by responding to selectively illuminated pixels.

Resistive Water Level Sensors Based on AgNWs/PEDOT:PSS-g-PEGME Hybrid Film for Agricultural Monitoring Systems.

Recently, an agricultural monitoring system using the Internet of Things has been developed to realize smart farming. The high performance of various sensors in agricultural monitoring systems is essential for smart farming to automatically monitor and control agricultural environmental conditions such as temperature and water level. In this study, we propose resistive water level sensors based on an AgNWs/PEDOT:PSS-g-PEGME hybrid structure to improve the already high conductivity and water stability of PEDOT:PSS. After spin-coating the AgNWs/PEDOT:PSS-g-PEGME hybrid film, a laser treatment method successfully patterns the resistive water level sensor with areas of higher resistance. When water contacts the sensor, the variation in resistance caused by the water level changes the current flow of the sensor, allowing it to be used to detect the water level. Finally, we develop a water level sensor module as a component of the agricultural monitoring system by connecting the sensor to a microcontroller for water level monitoring in real time. The proposed water level sensors may be a new solution for detecting water levels in agricultural monitoring systems.

Highly enhanced ferroelectricity in HfO2-based ferroelectric thin film by light ion bombardment.

Continuous advancement in nonvolatile and morphotropic beyond-Moore electronic devices requires integration of ferroelectric and semiconductor materials. The emergence of hafnium oxide (HfO2)-based ferroelectrics that are compatible with atomic-layer deposition has opened interesting and promising avenues of research. However, the origins of ferroelectricity and pathways to controlling it in HfO2 are still mysterious. We demonstrate that local helium (He) implantation can activate ferroelectricity in these materials. The possible competing mechanisms, including He ion-induced molar volume changes, vacancy redistribution, vacancy generation, and activation of vacancy mobility, are analyzed. These findings both reveal the origins of ferroelectricity in this system and open pathways for nanoengineered binary ferroelectrics.

Whey Protein Isolate Film and Laser-Ablated Textured PDMS-Based Single-Electrode Triboelectric Nanogenerator for Pressure-Sensor Application.

The use of biopolymers for realizing economical and eco-friendly triboelectric nanogenerators (TENGs) widens the application prospects of TENGs. Herein, an animal-sourced whey protein isolate (WPI) film, processed and prepared by a simple aqueous solution preparation and drop-casting technique, is applied to demonstrate its potential use in bio-TENGs. With the addition of formaldehyde in WPI, the films result in a free-standing and flexible film, whereas the pure WPI films are difficult to handle and lack flexibility. A TENG device based on the WPI and the laser-ablated textured polydimethylsiloxane (PDMS) for pressure-sensor application were developed. The output voltage of the TENG comprising WPI increased nearly two-fold compared to the TENG without WPI. A simple single-electrode TENG device configuration was adopted so that it could be easily integrated into a wearable electronic device. Moreover, WPI film exhibited tribo-negative-like material characteristics. This study provides new insights into the development of biocompatible and eco-friendly biopolymers for various electronic devices and sensors.

Nonvolatile High-Speed Switching Zn-O-N Thin-Film Transistors with a Bilayer Structure.

Zinc oxynitride (ZnON) has the potential to overcome the performance and stability limitations of current amorphous oxide semiconductors because ZnON-based thin-film transistors (TFTs) have a high field-effect mobility of 50 cm2/Vs and exceptional stability under bias and light illumination. However, due to the weak zinc-nitrogen interaction, ZnON is chemically unstable─N is rapidly volatilized in air. As a result, recent research on ZnON TFTs has focused on improving air stability. We demonstrate through experimental and first-principles studies that the ZnF2/ZnON bilayer structure provides a facile way to achieve air stability with carrier controllability. This increase in air stability (e.g., nitrogen non-volatilization) occurs because the ZnF2 layer effectively protects the atomic mixing between ZnON and air, and the decrease in the ZnON carrier concentration is caused by a shallow-to-deep electronic transition of nitrogen deficiency diffused from ZnON into the interface. Further, the TFT based on the ZnF2/ZnON bilayer structure enables long-term air stability while retaining an optimal switching property of high field-effect mobility (∼100 cm2/Vs) even at a relatively low post-annealing temperature. The ZnF2/ZnON-bilayer TFT device exhibits fast switching behavior between 1 kHz and 0.1 MHz while maintaining a stable and clear switching response, paving the way for next-generation high-speed electronic applications.

Ultrasensitive and Selective Field-Effect Transistor-Based Biosensor Created by Rings of MoS2 Nanopores.

The ubiquitous field-effect transistor (FET) is widely used in modern digital integrated circuits, computers, communications, sensors, and other applications. However, reliable biological FET (bio-FET) is not available in real life due to the rigorous requirement for highly sensitive and selective bio-FET fabrication, which remains a challenging task. Here, we report an ultrasensitive and selective bio-FET created by the nanorings of molybdenum disulfide (MoS2) nanopores inspired by nuclear pore complexes. We characterize the nanoring of MoS2 nanopores by scanning transmission electron microscopy, Raman, and X-ray photoelectron spectroscopy spectra. After fabricating MoS2 nanopore rings-based bio-FET, we confirm edge-selective functionalization by the gold nanoparticle tethering test and the change of electrical signal of the bio-FET. Ultrahigh sensitivity of the MoS2 nanopore edge rings-based bio-FET (limit of detection of 1 ag/mL) and high selectivity are accomplished by effective coupling of the aptamers on the nanorings of the MoS2 nanopore edge for cortisol detection. We believe that MoS2 nanopore edge rings-based bio-FET would provide platforms for everyday biosensors with ultrahigh sensitivity and selectivity.

Expeditiously Crystallized Pure Orthorhombic-Hf0.5Zr0.5O2 for Negative Capacitance Field Effect Transistors.

Ultralow-power logic devices are next-generation electronics in which their maximum efficacies are realized at minimum input power expenses. The integration of ferroelectric negative capacitors in the regular gate stacks of two-dimensional field-effect transistors addresses two intriguing challenges in today's electronics; short channel effects and high operating voltages. The complementary-metal-oxide-semiconductor-compatible Hf0.5Zr0.5O2 (HZO) is an excellent ferroelectric material crystallized in a noncentrosymmetric o-phase. The present work is the first to utilize pulsed laser deposition (PLD)-grown phase-pure ferroelectric HZO to achieve steep slope negative capacitance (NC) in field effect transistors (FETs). A dual-step growth strategy is designed to achieve phase-pure orthorhombic HZO on silicon and other conducting substrates. The room-temperature PLD-grown amorphous HZO is allowed to crystallize using rapid thermal annealing at 600 °C. The polycrystalline orthorhombic HZO is further integrated with atomic layer deposition-grown HfO2 to achieve a stable NC transition. The stack is further integrated into the molybdenum disulfide channel to achieve steep switching and a hysteresis-free operation of the resulting FETs. The subthreshold swings of the FETs are 20.42 and 26.16 mV/dec in forward and reverse bias conditions, respectively.