Device Fabrication Process Research Articles

Characteristics of Piezoelectric Nanogenerators Based on Cr-Doped ZnO Nanorods for NO Gas Sensing

Abstract In this investigation, chromium-doped ZnO nanorod (NR) arrays were grown on ITO/PET substrates using a hydrothermal method. Subsequently, self-powered gas sensors based on piezoelectric nanogenerators (PENGs) were fabricated and characterized. The chromium doping concentration in the ZnO NRs was estimated to be 0.26 at% measured by energy-dispersive X-ray spectroscopy (EDS). Additionally, transmission electron microscope (TEM) results revealed that the as-grown ZnO NRs exhibited a hexagonal wurtzite structure. During the device fabrication process, the top electrode patterns were defined through laser engraving, and silver thin films were deposited on the ITO-PET substrates using the RF-sputtering technique. The piezoelectric nanogenerators (PENGs) were composed of the silver top electrodes and the bottom of chromium-doped ZnO NRs. A specialized impacting system has been employed to drive the fabricated PENGs with a fixed frequency. By the doping concentration of 0.5 mM chromium nitrate, it can be found that the output voltages of the PENG were measured at 1.447 V and 2.323 V respectively, without and with introducing 100 ppm of nitric oxide (NO). Clearly, such a PENG device exhibits an excellent self-powered characteristic and demonstrates a good sensitivity to NO gas.

Emergence of Low-Cost and High-Performance Nonfused Ring Electron Acceptors.

ConspectusOrganic solar cells (OSCs) have garnered significant attention in academic and industrial circles due to their advantages such as lightweight, excellent bending performance, and the ability to be fabricated into semitransparent devices. Since the proposal of the bulk heterojunction concept by Heeger et al. in 1995, conjugated polymer/fullerene pairs have gradually emerged as the optimal choice for active layer materials in OSCs. Fullerene derivatives were preferred as electron acceptors in OSCs because of their high electron mobility. However, due to limitations such as insufficient light absorption, limited derivative potential, and poor energy level tunability, the power conversion efficiency (PCE) of OSCs based on fullerene derivatives has encountered a bottleneck of approximately 12%, despite the continuous updates in polymer donor materials over nearly two decades of development, leading to a gradual decline in their importance. By contrast, nonfullerene electron acceptors (NFAs) have gradually gained dominance in this field since first appearing in 2015, thanks to their advantages of tunable absorption spectrum, adjustable energy levels, and modifiable chemical structure. Among nonfullerene acceptors, fused-ring electron acceptors (FREAs) such as ITIC and Y6 have achieved significant progress, boosting the PCE of OSCs to 20%. This milestone achievement indicates the potential of their commercial applications. However, the synthesis process of FREA is complex and often constrained by low-yield ring-closure reactions, resulting in high costs.The molecular backbone of nonfused ring electron acceptors (NFREAs) is composed of single bonds, which enables the adoption of modular synthesis mainly via Stille (based on organotin reactant) and/or Suzuki (based on organoboron reactant) coupling or C-H activation (without prefunctionalization) and avoids low-yield ring-closing reactions, thus making them a potential alternative to fused-ring acceptors. To achieve a planar molecular backbone and minimize energy loss due to conformational rotation, our team innovatively used intramolecular noncovalent interactions as a replacement for traditional covalent bonds. Furthermore, to address the issues of poor solubility and excessive aggregation during film formation for NFREAs, we strategically introduced sterically hindered side groups, such as 2,6-bis(alkyloxy)phenyl and diphenylamino, into the molecular design, effectively mitigating these problems. These innovative design concepts have significantly advanced the development of high-performance NFREAs and have garnered increasing attention from the research community. The PCEs of OSCs based on NFREAs have significantly improved from less than 10% to close to 20% since their initial discovery. By optimizing the device fabrication process, we have achieved a PCE of over 19%, which is comparable to that of FREAs. This article will delve into the evolution and latest research progress of NFREAs, aiming to provide valuable insights and guidance for the design of cost-effective and high-performance NFREA materials.

Neural Network Methods in the Development of MEMS Sensors.

As a kind of long-term favorable device, the microelectromechanical system (MEMS) sensor has become a powerful dominator in the detection applications of commercial and industrial areas. There have been a series of mature solutions to address the possible issues in device design, optimization, fabrication, and output processing. The recent involvement of neural networks (NNs) has provided a new paradigm for the development of MEMS sensors and greatly accelerated the research cycle of high-performance devices. In this paper, we present an overview of the progress, applications, and prospects of NN methods in the development of MEMS sensors. The superiority of leveraging NN methods in structural design, device fabrication, and output compensation/calibration is reviewed and discussed to illustrate how NNs have reformed the development of MEMS sensors. Relevant issues in the usage of NNs, such as available models, dataset construction, and parameter optimization, are presented. Many application scenarios have demonstrated that NN methods can enhance the speed of predicting device performance, rapidly generate device-on-demand solutions, and establish more accurate calibration and compensation models. Along with the improvement in research efficiency, there are also several critical challenges that need further exploration in this area.

Investigation of self-selective RRAM based on V/ITO structure with rapid thermal annealed ITO for synapse emulation

This paper focuses on the investigation of V/ITO (O2 Rapid Thermal Annealing)-based Self-Selective Resistive Random-Access Memory (RRAM) device. In this study, the natural oxidation of Vanadium top electrode and the rapid thermal annealing (RTA) process greatly simplified the device fabrication process. The VO2-based Selector, formed by the natural oxidation of the Vanadium electrode, effectively suppresses current and is directly integrated with the ITO layer, eliminating the need for additional serial Selector. The oxygen content of the ITO film is significantly increased by the RTA process, enabling the previously conductive ITO material to be used as the RRAM insulating layer without the need for additional deposition of insulating layer. This V/ITO (O2 RTA) structure not only exhibits highly uniform resistance distributions (σ/μ<2.8 %) and endurance stability (10000 cycles), but also effectively simulates synaptic plasticity, exhibiting both short-term and long-term memory behaviors. Notably, potentiation and depression characteristics are displayed by the device when continuous pulse voltage is applied. These advancements underscore the innovation and applicability of RTA-treated ITO films in next-generation memory technologies.

Terahertz refractive index control of 3D printing materials by UV exposure

Recently, significant progress has been made in the development of THz optics based on metamaterials to overcome the limited availability of suitable materials for conventional optics. Although 3D printing technology is a promising method for rapidly fabricating these subwavelength structures, the structural degree of freedom for 3D printed metamaterials is still limited by the optical properties of printing materials. In this study, we controlled the THz refractive index and extinction coefficient of the 3D printing resin by UV exposure doses during the printing process. Samples were fabricated as uniform plates under different curing conditions in printing, and their optical properties were measured in the range between 0.3 THz and 2.0 THz using THz time-domain spectroscopy (THz-TDS). The refractive index and extinction coefficient were changed from 1.65 to 1.80, and from 0.04 to 0.12, respectively, with increasing UV doses from 1 mJ/cm2, which allows resin to solidify and become printable, to 100 mJ/cm2, where the optical changes become almost saturated. The results provide insights into optimizing the fabrication process of THz devices, even those with a gradient and complex refractive index profile, by utilizing 3D printing technology for a broad range of applications.

Biosensing beyond Debye screening length using epitaxial graphene field-effect transistors on SiC substrate

We demonstrated the antigen detection beyond Debye screening length using antibody-modified epitaxial graphene field-effect transistors (FETs), which have been considered to be impossible because of the Debye screening length. The transfer characteristics of the graphene FETs with a single crystal epitaxial graphene film showed no concentration dependence of buffer solutions. The capacitance measurements in an epitaxial graphene FET also showed no concentration dependence, indicating that the solution-gate capacitance of the epitaxial graphene FET was independent on the Debye screening length. In addition, the minimum capacitance values were also almost independent for the concentration change. Since the Debye screening length depends on the ionic strength of the solution, which is proportional to the buffer solution concentration, the electrical characteristics of solution-gated epitaxial graphene FETs are almost independent on the Debye screening length owing to their small quantum capacitance. The antibody-modified epitaxial graphene FETs indeed detected the antigen, indicating that the epitaxial graphene FETs can detect the target beyond the Debye screening length without any complicated device fabrication processes and other desalted apparatuses.

Effect of Guanidinium Salt for Stress-Relaxation and Interfacial Engineering in Antisolvent Free Perovskite Solar Cells Fabricated Under Air Ambient.

In perovskite solar cells, the presence of stress and defects at interfaces promotes performance degradation and poor stability of the devices. The formation of these defects is more prominent in two-step antisolvent-free perovskite film fabrication. This study addresses these challenges by introducing guanidine sulfate (Gua-S) at the tin oxide/formamidinium lead iodide perovskite interface, fabricated without antisolvent under ambient air. Interfacial Gua-S enhanced morphology by forming bonds between uncoordinated Pb2+ ions and I- vacancies at the interface and showed improvement in the crystallinity and quality of the perovskite film. Microstructural stress analysis indicated a substantial reduction in stress, decreasing from 50.6 to 20.72 MPa with the application of Gua-S. Moreover, the Gua-S treated solar cells showed significant improvements and achieved an open circuit voltage of 1.08 V and 22.34% efficiency. Further, electrochemical impedance spectroscopic analysis showed improved built-in potential, carrier lifetime, and charge recombination lifetime for treated devices. The devices retained over 87% of the initial power conversion efficiency after 2000 hours of operation. This comprehensive study addresses the fundamental issues of interfacial stress and defects in perovskite solar cells and demonstrates the efficacy of Gua-S salt in enhancing both the structural and functional aspects of the antisolvent-free device fabrication process.

Enhanced Nonlinear Optical Responses in MoS2 via Femtosecond Laser‐Induced Defect‐Engineering

Abstract2D materials are a promising platform for applications in many fields as they possess a plethora of useful properties that can be further optimized by careful engineering, for example, by defect introduction. While reliable high‐yield defect engineering methods are in demand, most current technologies are expensive, harsh, or non‐deterministic. Optical modification methods offer a cost‐effective and fast mechanism to engineer the properties of 2D materials at any step of the device fabrication process. In this paper, the nonlinear optical responses of mono‐, bi‐, and trilayer molybdenum disulfide (MoS2) flakes are enhanced by deterministic defect‐engineering with a femtosecond laser. A 50‐fold enhancement in the third harmonic generation (THG) and a 3.3‐fold increase in the second harmonic generation (SHG) in the optically modified areas is observed. The enhancement is attributed to resonant SHG and THG processes arising from optically introduced mid‐band gap defect states. These results demonstrate a highly controllable, sub‐micrometer resolution tool for enhancing the nonlinear optical responses in 2D materials, paving the way for prospective future applications in optoelectronics, quantum technologies, and energy solutions.

Taguchi Method Statistical Analysis on Characterization and Optimization of 18-nm Double Gate MOSFETs

A bi-layer graphene with a multigate structure was intensified and analysed on an 18-nm Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) device to obtain an optimal performance parameter. The device has a gate structure made of Titanium Dioxide (TiO2) that serves as a high-k material and a metal gate made of Tungsten Silicide (WSix). The Silvaco TCAD Software which are ATHENA and ATLAS modules were used to enhance the fabrication process of virtual devices and to verify the electrical properties of a specific device. According to the International Technology Roadmap Semiconductor (ITRS) specifications of 0.179 V ± 12.7% for threshold voltage (VTH) and 20 nA/m for leakage current (ILEAK), the Taguchi L9 orthogonal array strategy was used to improve the device process parameters for optimum VTH and ILEAK. For the NMOS device, the process parameter of VTH Adjust Implant Dose was used as the dominant factor while Source/Drain (S/D) Implant Energy was used as the adjustment factor whereby for PMOS device, S/D Implant Energy was the dominant factor while S/D Implant Tilt was the adjustment factor in order to achieve a robust design through the Taguchi method implementation. The percentage affecting the process parameter is then applied to the results of the signal to noise ratio (SNR) of Nominal-the-best (NTB) for VTH and Smaller-the-better (STB) for ILEAK.

Structural and morphological properties of CeO2 films deposited by radio frequency magnetron sputtering for back-end-of-line integration

Cerium oxides have potential applications ranging from low-temperature gas sensing to photodetection. A back-end-of-line integration of the material into complementary metal-oxide-semiconductor device fabrication processes has many advantages but places limits on material deposition, most notably the thermal budget for deposition and annealing. Here, we investigate thin cerium oxide films deposited by radio frequency (RF) magnetron sputtering at substrate temperatures of 300 °C and RF magnetron powers between 30 W and 70 W without any post-deposition annealing steps. Our investigation of the structural and morphological properties reveals a columnar texture of the thin films, and we find that the material is composed predominantly of CeO2 (111), with a large degree of crystallinity. We discuss implications for resistive gas sensing applications.

Eliminating performance loss from perovskite films to solar cells.

Preoptimizing perovskite films may generally improve the performance of the final perovskite solar cells (PSCs). However, the research on whether the film optimization fully contributes to the enhancement of the final PSCs has been long neglected. We demonstrated that the preparation of metal electrodes by high-vacuum thermal evaporation, an unavoidable step in almost all device fabrication processes, will damage the surface of perovskite films, resulting in component escape, defect density rebound, carrier extraction barrier, and film stability deterioration. Therefore, the prepared perovskite film and the final film actually working in devices are not exactly the same, and the contribution of film optimization to the device improvement was weakened. We designed a bilayer structure composed of graphene oxide and graphite flakes to eliminate the unwanted film inconsistencies and thus save the film optimization loss. Therefore, the efficient PSCs with power conversion efficiency of 25.55% were obtained, which demonstrated negligible photovoltaic performance loss after operating for 2000 hours.

On-Chip Thermoelectric Devices Based on Standard Silicon Processing.

The strong reduction of thermal conductivity with respect to bulk silicon makes nanostructured silicon one of the best materials for highly efficient direct conversion of heat into electrical power and vice-versa. The widespread technologies for the integration of silicon devices can be used to define on-chip micro thermoelectric generators (scavengers); similar structures could also be used for precise and well-localized cooling through the reverse process of heat pumping. However, the road to the fabrication of integrated thermal energy scavengers or cooler, based on silicon, is still very long. In this work, the design and the fabrication process of on-chip thermoelectric devices based on a large number of interconnected monocrystalline silicon nanobeams, very tall (>1 µm) and thin (less than 200 nanometers), arranged in large areas combs is shown. The small width of the nanobeams gives a reduced thermal conductivity, and the height perpendicular to the substrate allows the definition of a highly dense collection of nanostructures. The total cross-sectionis far broader than that of other nanostructures, a characteristic that guarantees both mechanical stability and larger deliverable power per unit area.

Dual-Mode Reconfigurable Split-Gate Logic Transistor through Van der Waals Integration.

As silicon-based transistors approach their physical size limitations, two-dimensional material-based reconfigurable functional electronic devices are considered the most promising novel device architectures beyond Moore strategies. While these devices have garnered significant attention, they often require complex device fabrication processes and extra electric fields. Additionally, the device performance is usually limited by the metal-semiconductor interface properties. In this Letter, we have constructed a reconfigurable logic device based on a WSe2 transistor with a nanofloating gate and split-gates through van der Waals integration. This device achieves a small Schottky barrier height due to the van der Waals contacts. By varying the split-gate biases, we can realize volatile reconfigurable homojunctions as well as AND, OR, NOR, and NAND logic operations with just a single device. Furthermore, with the charge trapping effect of nanofloating gate, we can also achieve nonvolatile reconfigurable homojunctions, as well as AND and OR logic operations. The volatile and nonvolatile logic operations are similar to the short-term plasticity and long-term plasticity, respectively, of synapses in the human brain. This work offers a potential approach for creating novel reconfigurable functional electronic devices with a simple fabrication process and low cost.

Advancing semantic segmentation of two-dimensional materials using a semantic-adaptive transformer model

Accurate detection and characterization of two-dimensional (2D) materials are essential for their effective utilization in various applications. Traditional techniques, such as chemical vapor deposition, often produce materials with high defect density, while mechanical exfoliation is hindered by its labor-intensive and time-consuming nature. In this Letter, we propose a semantic-adaptive transformer model, termed Semptive, designed specifically for the precise detection of monolayer MoS2. Our approach integrates a semantic adaptation module with a multi-head self-attention mechanism, incorporating deep supervision and leveraging prior knowledge to enhance model performance. The model was trained on a dataset obtained through mechanical exfoliation and validated using photoluminescence spectroscopy. The experimental results reveal that Semptive significantly enhances segmentation performance compared to conventional models, achieving higher Intersection over Union and Dice scores while reducing computational demands. This method represents a notable advancement in the efficient and precise identification of 2D materials, providing substantial improvements for material characterization and device fabrication processes.

Memristors with Monolayer Graphene Electrodes Grown Directly on Sapphire Wafers.

The development of the memristor has generated significant interest due to its non-volatility, simple structure, and low power consumption. Memristors based on graphene offer atomic monolayer thickness, flexibility, and uniformity and have attracted attention as a promising alternative to contemporary field-effect transistor (FET) technology in applications such as logic and memory devices, achieving higher integration density and lower power consumption. The use of graphene as electrodes in memristors could also increase robustness against degradation mechanisms, including oxygen vacancy diffusion to the electrode and unwanted metal ion diffusion. However, to realize this technological transformation, it is necessary to establish a scalable, robust, and cost-effective device fabrication process. Here we report the direct growth of high-quality monolayer graphene on sapphire wafers in a mass-producible, contamination-free, and transfer-free manner, using a commercially available metal-organic chemical vapor deposition (MOCVD) system. By taking advantage of this approach, graphene-electrode based memristors are developed, and all the processes used in the device fabrication incorporating graphene electrodes can be performed at wafer scale. The graphene electrode-based memristor demonstrates promising characteristics in terms of endurance, retention, and ON/OFF ratio. This work presents a possible and viable route to achieving robust graphene-based memristors in a commercially and technologically sustainable manner, paving the way for the realization of more powerful and compact integrated graphene electronics in the future.

An amplitude-based temperature compensated MEMS resonant pressure sensor with single resonator

Temperature compensation is a common concern of MEMS sensors. This paper presents an amplitude-based temperature compensated MEMS resonant pressure sensor. An AGC (automatic gain control) closed-loop circuit with a constant-amplitude drive was designed, enabling the real-time sampling of resonant frequencies and amplitudes. Under the constant-amplitude drive, the amplitude of the resonator changes monotonously with temperature. Thus, pressure and temperature can be decoupled using a single resonator, achieving high accuracy in pressure measurements. Experimental results demonstrated that the fabricated microsensor achieved high performance with the amplitude-based temperature compensation. Within a pressure range of 10 kPa to 100 kPa and a temperature range of −20℃ to 60℃, the pressure accuracy of the microsensor reached ± 0.012 %FS (full scale), with a repeatability error of 0.009 %FS and a pressure hysteresis error of 0.007 %FS. Based on single resonator, the developed microsensor is expected to reduce device sizes, simplify design and fabrication processes, and decrease the power consumption of the system.

Triadic Halobenzene Processing Additive Combined Advantages of Both Solvent and Solid Types for Efficient and Stable Organic Solar Cells.

Solvent additives with a high boiling point (BP) and low vapor pressure (VP) have formed a key handle for improving the performance of organic solar cells (OSCs). However, it is not always clear whether they remain in the active-layer film after deposition, which can negatively affect the reproducibility and stability of OSCs. In this study, an easily removable solvent additive (4-chloro-2-fluoroiodobenzene (CFIB)) with a low BP and high VP is introduced, behaving like volatile solid additives that can be completely removed during the device fabrication process. In-depth studies of CFIB addition into the D18-Cl donor and N3 acceptor validate its dominant non-covalent intermolecular interactions with N3 through effective electrostatic interactions. Such phenomena improve charge dynamics and kinetics by optimizing the morphology, leading to enhanced performance of D18-Cl:N3-based devices with a power conversion efficiency of 18.54%. The CFIB-treated device exhibits exceptional thermal stability (T80 lifetime = 120h) at 85°C compared with the CFIB-free device, because of its morphological robustness by evolving no residual CFIB in the film. The CFIB features a combination of advantages of solvent (easy application) and solid (high volatility) additives, demonstrating its great potential use in the commercial mass production of OSCs.

Simultaneous Characterization of In-Plane and Cross-Plane Resistivities in Highly Anisotropic 2D Layered Heterostructures.

Understanding and characterizing the intrinsic properties of charge carrier transport across the interfaces in van der Waals heterostructures is critical to their applications in modern electronics, thermoelectrics, and optoelectronics. However, there are very few published cross-plane resistivity measurements of thin samples because these inherently 2-probe measurements must be corrected for contact and lead resistances. Here, we present a method to extract contact resistances and metal lead resistances by fitting the width dependence of the contact end voltages of top and bottom electrodes of different contact widths to a model based on current crowding. These contributions are then subtracted from the total 2-probe cross-plane resistance to obtain the cross-plane resistance of the material itself without needing multiple devices and/or etching steps. This approach was used to measure cross-plane resistivities of a (PbSe)1(VSe2)1 heterostructure containing alternating layers of PbSe and VSe2 with random in-plane rotational disorder. Several samples measured exhibited a 4 order of magnitude difference between cross-plane and in-plane resistivities over the 6-300 K temperature range. We also reported the observation of charge density wave transition in the cross-plane transport of the (PbSe)1(VSe2)1 heterostructure. The device fabrication process is fully liftoff compatible, and the method developed enables the straightforward measurement of the resistivity anisotropy of most thin film materials with nm thicknesses.

Recent advances in portable devices for environmental monitoring applications.

Environmental pollution remains a major societal problem, leading to serious impacts on living organisms including humans. Human activities such as civilization, urbanization, and industrialization are major causes of pollution. Imposing stricter rules helps control environmental pollutant levels, creating a need for reliable pollutant monitoring in air, water, and soil. The application of traditional analytical techniques is limited in low-resource areas because they are sophisticated, expensive, and bulky. With the development of biosensors and microfluidics technology, environmental monitoring has significantly improved the analysis time, low cost, portability, and ease of use. This review discusses the fundamentals of portable devices, including microfluidics and biosensors, for environmental control. Recently, publications reviewing microfluidics and biosensor device applications have increased more than tenfold, showing the potential of emerging novel approaches for environmental monitoring. Strategies for enzyme-, immunoassay-, and molecular-based analyte sensing are discussed based on their mechanisms and applications. Microfluidic and biosensor platforms for detecting major pollutants, including metal ions, pathogens, pesticides, and antibiotic residues, are reviewed based on their working principles, advantages, and disadvantages. Challenges and future trends for the device design and fabrication process to improve performance are discussed. Miniaturization, low cost, selectivity, sensitivity, high automation, and savings in samples and reagents make the devices ideal alternatives for in-field detection, especially in low-resource areas. However, their operation with complicated environmental samples requires further research to improve the specificity and sensitivity. Although there is a wide range of devices available for environmental applications, their implementation in real-world situations is limited. This study provides insights into existing issues that can be used as references and a comparative analysis for future studies and applications.

Hardware-Efficient Configurable Ring-Oscillator-Based Physical Unclonable Function/True Random Number Generator Module for Secure Key Management.

The use of physical unclonable functions (PUFs) linked to the manufacturing process of the electronic devices supporting applications that exchange critical data over the Internet has made these elements essential to guarantee the authenticity of said devices, as well as the confidentiality and integrity of the information they process or transmit. This paper describes the development of a configurable PUF/TRNG module based on ring oscillators (ROs) that takes full advantage of the structure of modern programmable devices offered by Xilinx 7 Series families. The proposed architecture improves the hardware efficiency with two main objectives. On the one hand, we perform an exhaustive statistical characterization of the results derived from the exploitation of RO configurability. On the other hand, we undertake the development of a new version of the module that requires a smaller amount of resources while considerably increasing the number of output bits compared to other proposals previously reported in the literature. The design as a highly parameterized intellectual property (IP) module connectable through a standard interface to a soft- or hard-core general-purpose processor greatly facilitates its integration into embedded solutions while accelerating the validation and characterization of this element on the same electronic device that implements it. The studies carried out reveal adequate values of reliability, uniqueness, and unpredictability when the module acts as a PUF, as well as acceptable levels of randomness and entropy when it acts as a true random number generator (TRNG). They also illustrate the ability to obfuscate and recover identifiers or cryptographic keys of up to 4096 bits using an implementation of the PUF/TRNG module that requires only an array of 4×4 configurable logic blocks (CLBs) to accommodate the RO bank.