Conventional Photolithography Research Articles

Machine Learning Predictions of Block Copolymer Self-Assembly.

Directed self-assembly of block copolymers is a key enabler for nanofabrication of devices with sub-10 nm feature sizes, allowing patterning far below the resolution limit of conventional photolithography. Among all the process steps involved in block copolymer self-assembly, solvent annealing plays a dominant role in determining the film morphology and pattern quality, yet the interplay of the multiple parameters during solvent annealing, including the initial thickness, swelling, time, and solvent ratio, makes it difficult to predict and control the resultant self-assembled pattern. Here, machine learning tools are applied to analyze the solvent annealing process and predict the effect of process parameters on morphology and defectivity. Two neural networks are constructed and trained, yielding accurate prediction of the final morphology in agreement with experimental data. A ridge regression model is constructed to identify the critical parameters that determine the quality of line/space patterns. These results illustrate the potential of machine learning to inform nanomanufacturing processes.

Organic Thin Film Transistors Fabricated by a Solution Process Using Direct Patterned Single-Layer Graphene Electrodes.

We propose the direct transfer method of single-layer graphene (SLG) from metal catalyst Cu-foil to a polymeric insulator and the direct patterning method of the SLG for electrodes of organic thin-film transistors (OTFTs) without contamination using soft-lithography. Through soft-lithography, SLG can be formed in various patterns relatively easily in comparison with the conventional photolithography method that has multiple complex process steps to make graphene patterns. Furthermore, the 6,13-bis(triisopropylsilylethynyl) pentacene OTFTs are fabricated in solution with SLG source and drain electrodes. As a result, the field-effect mobility of OTFTs based on SLG electrodes was enhanced about 4 times in comparison with that of OTFTs using typical metal electrodes due to the decrease in contact resistance.

Polarization insensitive, metamaterial absorber-enhanced long-wave infrared detector.

Detecting low energy photons, such as photons in the long-wave infrared range, is a technically challenging proposition using naturally occurring materials. In order to address this challenge, we herein demonstrate a micro-bolometer featuring an integrated metamaterial absorber (MA), which takes advantage of the resonant absorption and frequency selective properties of the MA. Importantly, our micro-bolometer exhibits polarization insensitivity and high absorption due to a novel metal-insulator-metal (MIM) absorber design, operating at 8-12 µm wavelength. The metamaterial structures we report herein feature an interconnected design, optimized towards their application to micro-bolometer-based, long-wave infrared detection. The micro-bolometers were fabricated using a combination of conventional photolithography and electron beam lithography (EBL), the latter owing to the small feature sizes within the design. The absorption response was designed using the coupled mode theory (CMT) and the finite integration technique, with the fabricated devices characterized using Fourier-transform infrared spectroscopy (FTIR). The metamaterial-based micro-bolometer exhibits a responsivity of approximately 198 V/W over the 8-12 µm wavelength regime, detectivity of ∼ 0.6 × 109 Jones, thermal response time of ∼ 3.3 ms, and a noise equivalent temperature difference (NETD) of ∼33 mK under 1mA biasing current at room-temperature and atmosphere pressure. The ultimate detectivity and NETD are limited by Johnson noise and heat loss with thermal convection through air; however, further optimization could be achieved by reducing the thermal conductivity via vacuum packaging. Under vacuum conditions, the detectivity may be increased in excess of two-fold, to ∼ 1.5 × 109 Jones. Finally, an infrared image of a soldering iron was generated using a single-pixel imaging process, serving as proof-of-concept of this detection platform. The results presented in this work pave the road towards high-efficiency and frequency-selective detection in the long-wave infrared range through the integration of infrared MAs with micro-bolometers.

Highly Stable and Scalable Blue QD‐LED via an Evaporated TiO2 Thin Film as an Electron Transport Layer

AbstractQuantum dot‐based light‐emitting diodes (QD‐LEDs) have excellent optical properties; however, their limitations of stability, reproducibility, and scalability due to the solution process are the major drawback. Herein, blue QD‐LEDs fabricated with the conventional vacuum process using an e‐beam‐evaporated TiO2 thin film as an electron transport layer (ETL) are demonstrated. CdZnS/ZnS‐based blue LEDs with a TiO2 thin film are fabricated under ambient conditions. They exhibit maximum external quantum efficiencies of 3.53% and a peak luminance of 2847 cd m−2. These values are retained, which minimizes performance degradation under high potential bias. In addition, the optimized evaporated TiO2 thin film has a negligible red shift (0.5 nm) of the peak wavelength between the photoluminescence spectrum and electroluminescence spectrum with stable full‐width at half‐maximum changing by less than 2 nm at high voltage. Finally, a blue QD‐LED is fabricated on a scalable emission area of 2 × 2 in. with a patterned cathode accompanied by an evaporated TiO2 thin film, which allows to perform conventional photolithography. A highly stable and reproducible vaporized inorganic thin film as the ETL supports the multilayer architecture to minimize the process damage.

Noble‐Metal‐Free Memristive Devices Based on IGZO for Neuromorphic Applications

AbstractAmorphous indium‐gallium‐zinc‐oxide (a‐IGZO) based memristive devices with molybdenum contacts as both top and bottom electrodes are presented aiming to be used in neuromorphic applications. Devices down to 4 µm2 are fabricated using conventional photolithography processes, with an extraordinary yield of 100%. X‐ray photoelectron spectroscopy and transmission electron microscopy performed on the developed structures confirm the presence of a thin intermixed oxide layer (4–5 nm) containing Mo6+ oxidation state at the interface with the bottom contact. This results in Schottky diode‐like characteristics at the pristine state with a rectification ratio of 3 orders of magnitude. The devices have electroforming‐free and area‐dependent analog resistive switching properties. Temperature analysis of resistive switching I–V data reveals barrier height variations of the junction. Several synaptic functions, such as synaptic potentiation and depression as response to programmed pulses, short‐ to long‐term plasticity transition (STP to LTP) and “learning experience” properties are presented. The Mo/IGZO/Mo memristive device shows potential application of an electronic synapse for brain‐inspired computing application. Integration in System‐on‐Panel architectures is possible at negligible cost, because all materials are used in commercial IGZO thin‐film transistor fabrication.

High-Resolution Three-Dimensional Sculpting of Two-Dimensional Graphene Oxide by E-Beam Direct Write.

On-demand switchable "additive/subtractive" patterning of two-dimensional (2D) nanomaterials is an essential capability for developing new concepts of functional nanomaterials and their device realizations. Traditionally, this is performed via a multistep process using photoresist coating and patterning by conventional photo or electron beam lithography, which is followed by bulk dry/wet etching or deposition. This limits the range of functionalities and structural topologies that can be achieved as well as increases the complexity, cost, and possibility of contamination, which are significant barriers to device fabrication from highly sensitive 2D materials. Focused electron beam-induced processing (FEBIP) enables a material chemistry/site-specific, high-resolution multimode atomic scale processing and provides unprecedented opportunities for "direct-write", single-step surface patterning of 2D nanomaterials with an in situ imaging capability. It allows for realizing a rapid multiscale/multimode approach, ranging from an atomic scale manipulation (e.g., via targeted defect introduction as an active site) to a large-area surface modification on nano- and microscales, including patterned doping and material removal/deposition with 2D (in-plane)/three-dimensional (3D) (out-of-plane) control. In this work, we report on a new capability of FEBIP for nanoscale patterning of graphene oxide via removal of oxygenated carbon moieties with no use of reactive gas required for etching complemented by carbon atom deposition using a focused electron beam. The mechanism of experimentally observed phenomena is explored using the density functional theory (DFT) calculations, revealing that interactions of e-beam that liberated reactive oxygen radicals with carbon atoms on the graphene basal plane lead to the creation of atomic vacancies in the material. The reaction byproducts are volatile carbon dioxides, which are dissociated and volatilized from the graphene oxide surface functional groups by interactions with an energetic focused electron beam. Along with selective subtractive patterning of graphene oxide, the same electron beam with increased irradiation doses can deposit out-of-plane 3D carbon nanostructures on top of or around the 2D etched pattern, thus forming a hybrid 2D/3D nanocomposite with a feature control down to a few nanometers. This in operando dual nanofabrication capability of FEBIP is unmatched by any other nanopatterning techniques and opens a new design window for forming 2D/3D complex nanostructures and functional nanodevices.

70‐2: Low Temperature Process and Material Development for Flexible/Stretchable Transparent Conductor

Flexible/stretchable electronics and displays have become the core technologies for future portable and wearable electronics due to its flexibility and light weight. Most of flexible electronics and display are built on the heat sensitive plastics substrates which is usually not well compatible with conventional photolithography processes that usually use high temperature and corrosive etchants. Therefore, there is a strong need to develop a novel low temperature process to realize flexible electronics and display on the conventional heat sensitive polymer substrate materials. In this paper, the recent development for the low temperature process compatible with plastic substrate will be reviewed in both materials and process aspects. Furthermore, very recent trends in stretchable electronics and transparent electronics will be discussed as well.

Expeditious and eco-friendly solution-free self-patterning of sol–gel oxide semiconductor thin films

Due to its simplicity and low-cost manufacturing, self-patterning has been considered a promising candidate to replace conventional photolithography. However, most solution-based self-patterning methods require toxic materials, lengthy processes and generate extensive material waste, thus hindering eco-friendly and also economic mass production. Therefore, this work presents an expeditious and eco-friendly solution-free self-patterning method to fabricate patterned indium gallium zinc oxide (IGZO) thin-film transistors (TFTs). This faster and simpler two-step process requires within only 10 min to generate the selective wetting and dewetting regions on the dielectrics via a simultaneous stamping and thermal treatment (SST) and then an ultraviolet ozone exposure. As a result, well-defined IGZO patterns were formed without residues. Extremely suppressed lateral and vertical leakage currents were obtained in self-patterned IGZO TFTs by eliminating leakage paths found in non-patterned devices (appx. 10−11 A versus 10−5 A, respectively). Furthermore, the recyclability of the surface energy modification stamp (SEMS) used in the proposed SST process was confirmed, as the IGZO patterns and uniform electrical performances remained clear through nine patterning processes using a single SEMS. Overall, the proposed solution-free self-patterning method will contribute to the realization of next-generation printed electronics by enabling their mass production.

Inkjet-printed MoS2-based field-effect transistors with graphene and hexagonal boron nitride inks

Field-effect transistors (FETs) are powerful devices in the semiconducting electronics industry and their manufacturing forms the basis of countless electronic devices. Most contemporary FETs rely on inorganic materials, mainly silicon that uses conventional photolithography, etching, and deposition techniques in sophisticated and expensive clean-room environments. An alternative route to fabricating FETs is via inkjet printing that offers the possibility of mass production and working with additively manufactured, low-cost materials, to form high functionality devices with applications in a wide array of fields. Although the inkjet-printed electrode-based sensor is widely reported, the number of all inkjet-printed FETs is still limited. Here, the authors report the design, fabrication, and characterization of an all inkjet-printed FET. Two-dimensional layered materials, such as electrically conducting graphene, semiconducting molybdenum disulfide (MoS2), and dielectric-hexagonal boron nitride (hBN), were used to construct the printed FET on an Si/SiO2 substrate. Here, the authors also present the annealing temperature analysis of the drop-cast hBN ink, which provided a clear outlook toward the printed dielectric layer fabrication of the transistor. To have an idea of the leakage current of the FET, the authors inkjet-printed a simple capacitor device first with graphene and hBN inks, which was characterized by using the small-signal impedance technique, capacitance-frequency (C-F), and capacitance-voltage (C-V), where the change in C was measured from F ∼ 1 kHz up to 5 MHz. At low frequency, ∼1 KHz, the maximum capacitance ∼36 pF was found at 20 V.

Cold Tribo-Nanolithography on Metallic Thin-Film Surfaces.

This paper demonstrates a modified tribo-nanolithgraphy (TNL), micro- to nanometer scale mechanical machining processes, on metallic thin film surfaces which have poor machinability in micro scale under several mN normal loads. TNL is one of the promising atomic force microscopy (AFM)-based lithography processes which is more effective fabrication technology, as compared to conventional photolithography due to its relatively simple processes, high resolution, short processing time, and low cost. We propose ultra-precision machining at sub-0 °C temperatures using a lab-made micro polycrystalline diamond (PCD) tool on a retrofitted piezo stage with a Peltier device. The workpiece, located on the stage, is cooled artificially, and a normal load of several mN is applied by a micro PCD tool for micro scale machining processes. The machining results indicated considerably different machinability when the work was performed at sub-0 °C, as opposed to the ambient surface temperature, due to the changed mechanical characteristics of surface by the forced cooling of the workpiece. Although the normal load, machining speed, and machining area remained constant, the width and depth of machined grooves are significantly increased at sub-0 °C temperature conditions. In addition, we analyzed the TNL characteristics when machining with the PCD tool in four different machining directions. The mechanical surface properties, surface topography, scanning electron microscope (SEM) images, chip formation and other physical properties are investigated for more discussions.

Direct polymer microcantilever fabrication from free-standing dry film photoresists

Traditionally, polymeric microcantilevers are assembled by a multitude of process steps comprising liquid spin-coated photoresists and rigid substrate materials. Polymer microcantilevers presented in this work rely instead on commercially available dry film photoresists and allowed an omittance of multiple fabrication steps. Thin, 5 μm thick dry film photoresists are thermally laminated onto prepatterned silicon substrates that contain AFM compatible probe bodies. Partially suspended dry film resists are formed between these probe bodies, which are patterned to yield microcantilevers using conventional photolithography protocols. A limited amount of thermal cycling is required, and sacrificial probe-release layers are omitted as microcantilevers form directly through resist development. Even 1 mm long polymeric cantilevers were fabricated this way with superior in-plane alignment. The general effects of post-exposure bake (PEB) and hardbake protocols on cantilever deflection are discussed. Generally, higher PEB temperatures limit out-of-plane cantilever bending. Hardbake improved vertical alignment only of high-PEB temperature cantilevers, while surprisingly worsening the alignment of low-PEB temperature cantilevers. The mechanism behind the latter is likely explained by complex interactions between the resist and the substrate related to differences in thermal expansion, heat conduction, as well as resist cross-linking gradients. We present furthermore multilayer structures of dry film resists, specifically cylindrical dry film resist pillars on the polymer cantilever, as well as the integration of metal structures onto the polymer cantilever, which should enable in future integrated piezoresistive deflection readout for various sensing applications. Finally, cantilever spring constants were determined by measuring force–displacement curves with an advanced cantilever calibration device, allowing also the determination of both, dry film resist cantilever density and Young’s modulus.

Micro- and Nanopatterning of Halide Perovskites Where Crystal Engineering for Emerging Photoelectronics Meets Integrated Device Array Technology.

Tremendous efforts have been devoted to developing thin film halide perovskites (HPs) for use in high-performance photoelectronic devices, including solar cells, displays, and photodetectors. Furthermore, structured HPs with periodic micro- or nanopatterns have recently attracted significant interest due to their potential to not only improve the efficiency of an individual device via the controlled arrangement of HP crystals into a confined geometry, but also to technologically pixelate the device into arrays suitable for future commercialization. However, micro- or nanopatterning of HPs is not usually compatible with conventional photolithography, which is detrimental to ionic HPs and requires special techniques. Herein, a comprehensive overview of the state-of-the-art technologies used to develop micro- and nanometer-scale HP patterns, with an emphasis on their controlled microstructures based on top-down and bottom-up approaches, and their potential for future applications, is provided. Top-down approaches include modified conventional lithographic techniques and soft-lithographic methods, while bottom-up approaches include template-assisted patterning of HPs based on lithographically defined prepatterns and self-assembly. HP patterning is shown here to not only improve device performance, but also to reveal the unprecedented functionality of HPs, leading to new research areas that utilize their novel photophysical properties.

Fabrication and Characterizations of Poly-Si Nanowire Biosensor using Conventional Photolithography Technique for Detection of Dengue Virus DNA Type 2 (DENV-2)

Nowadays, nanotechnology has become a vast expanding application which can be used all across the science field such as chemistry, biology, physic, material science and engineering. In this paper, a poly-Si nanowire biosensor was fabricated by using the conventional photolithography technique. In addition, this technique is used to define the initial poly-Si with the dimension of 1 μm. After the conventional photolithography process, the photoresist undergone the development using resist developer and etched with reactive ion etching (RIE). Meanwhile, for the electrical part, it was observable that there was an increase in current when the nanowire has been hybridized with Dengue DNA type-2 (DENV-2) ranging from 10 fM - 10 μM. The morphology of the poly-Si nanowire was characterized by optical microscopy whilst electrically characterized by measuring the two-terminal current-voltage (I-V) characteristic.

Fabrication of Freestanding Metallic Ni-Mo-W Microcantilever Beams With High Dimensional Stability

Recent studies have elucidated a promising balance of physical and mechanical properties of sputter deposited nickel-molybdenum-tungsten (Ni-Mo-W) films that have a unique nanotwinned microstructure and promising potential for use in high temperature microelectromechanical systems (MEMS). The current study was undertaken to establish the feasibility of making nanotwinned Ni-Mo-W microcantilevers with standard microfabrication processing, to assess their dimensional stability, and to demonstrate the possibility of using nanotwinned Ni-Mo-W in metal MEMS devices. Deposition of Ni-Mo-W films in commercial sputtering chambers revealed a wide processing window for the formation of the requisite nanotwinned microstructure. Conventional photolithography and etchants were employed to shape blanket Ni-Mo-W films into freestanding microcantilever beams. Monitoring microcantilever deflections via interferometry provided a direct measure of residual stresses and overall dimensional stability. Heat treatments of 200°C and 400°C were used to mimic wafer bonding temperatures. At 400°C, microcantilevers exhibited modest stress relaxation, yielding beam deflection profiles on the nanometer scale and portending dimensional stability and control for future metal MEMS devices.

All‐Solution Processed Multicolor Patterning Technique of Perovskite Nanocrystal for Color Pixel Array and Flexible Optoelectronic Devices

AbstractIn the present study, a new patterning method is introduced through the surface modification and stabilization of perovskite nanocrystals, which is compatible with conventional photolithography process based on all‐solution processes. Chemically designed gel‐type silica‐coated CsPbX3 (X = Br, I, etc.) perovskite nanocrystals combined with dip coating method are introduced to form stable and uniform films. Analyses of the physical and chemical states of nanocrystals and investigation of the kinetics in silica formation are conducted. In an optimized condition, physically uniform and chemically stable perovskite thin films are deposited on various substrates such as flexible, stretchable substrates, or even nonflat objects. By adopting these advantages and developing stable photolithographic chemicals, the high resolution patterns are successfully patterned with green and red emitting CsPbBr3 and CsPbBr3I3−x perovskites with the size down to 5 µm of radius and even a multicolor pixel array which can be used for the color filter, light converting or detecting applications. Flexible white light emitting diode is also fabricated with a large color gamut coverage. This work provides a fundamental understanding of perovskite nanocrystals, and also offers a technological breakthrough enabling various optoelectronic applications.

(Invited) Enzymatic Metal Oxide Electrolyte-Gated Field-Effect Transistors for Non-Invasive Glucose Biosensor

Fabrication of nano-scaled biosensors with high sensing performance is essential demand for a future biological sensing system. Detection of biomolecules is conducted in terms of change in electrical properties of the biosensor so that the consideration of semiconductor material becomes more crucial. Although a lot of attractive attentions are attempted such as utilizing silicon nanowire or carbon nanotube, studies for investigating the highly reliable and biocompatible materials still have been progressed. Metal oxide material for biosensing application has an advantages of relatively high electrical characteristics and provides environmental condition for immobilizing an enzyme. InGaZnO (IGZO) has high electron mobility and reliability which leads a high sensitivity for detecting biomolecules. Adapting field effect transistor (FET) structure is additional approach to enhance the signal response of the sensor. The fundamental principle of the FET biosensor relies on its sensitive response to the variation of electric field or potential at the sensor surface resulting from the electrical interaction between the semiconductor and glucose molecules captured at the glucose oxidase (GOx). The FET biosensor also could be effectively integrated with other application circuits through conventional photolithography technologies. In addition, electrolyte-gated FET structure, utilizing an electrolyte as a gate insulator, shows a high sensitivity to the glucose concentration originated from a large capacitance of the electrolyte.IGZO based electrolyte-gated FET (IGZO-EGFET) biosensor is fabricated. The pH sensing is tested for predicting the biosensing performance of IGZO-EGFET. The pH sensitivity is measured as 52.5 mV/pH within 3 to 9 pH range, which is comparable to other nano material pH sensors. Immobilization of GOx on the IGZO surface is conducted via crosslinking modification with (3-aminopropyl)triethoxysilane (APTES) and glutaraldehyde treatment. Finally, the variation of glucose concentration is successfully identified on the GOx immobilized IGZO-EGFET. This study shows the IGZO-EGFET biosensor could lead to the applications of portable and real-time detecting sensor.

Design 5.0 µm Gap Aluminium Interdigitated Electrode for Sensitive pH Detection

The aim of the research study to design high sensitive biosensor for medical applications. IDE pattern was designed using AutoCAD software with 5 µm ginger gap. The fabrication process was done using a conventional photolithography process and standard CMOS process. The fabricated electrode was physically characterized using a low power microscope (LPM) and a high power microscope (HPM). The electrically validated through I-V measurements and chemically tested with different pH buffer solutions. Al IDE was well fabricated with 0.1 µm tolerance between the design mask and fabricated IDEs. Electrical measurements confirmed that IDE was well fabricated without any shortage and results of similar IDE samples were confirmed that the repeatability of the device. The extremely small current variations in nano ampere range were quantitatively detected using an extra small volume of 2 µl for different pH buffer solutions. It is confirmed that IDEs are sensitive in both alkali and hydroxyl ions medium.

Sensitivity of Surface Acoustic Wave Sensors Based LiNbO3 128° Y-X and at-Quartz to PM10 and PM2.5

Introduction Particulate matter (PM) was estimated to cause around 7 million premature deaths worldwide per year according to World Health organization [1]. These particles can cause diseases leading to premature death [2]. Over the last decade, the monitoring of PM became an important issue on a worldwide scale. The miniaturization of the existing bulky systems has also become necessary to reduce their cost. To address this need, a new miniaturized system for PM monitoring was previously developed in our team [3]. It takes advantage of both a 3 Lpm cascade impactor and surface acoustic waves (SAW) sensors to respectively separate and measure particles. The present study aims to compare the sensitivity of two SAW devices. The first exploits Love waves on an AT cut Quartz substrate and the second is based on Rayleigh waves from a LiNbO3 Y-X 128° substrates. The latter presents a high electromechanical coupling factor that could be exploited for the self-cleaning of the device after the measurement. This could allow overcoming the fouling issue faced with impactors that wouldn’t be solved with quartz based sensors which suffer from an insufficient electromechanical coupling. Method In this study we used a dedicated 3 Lpm cascade impactor equipped with SAW delay lines as collecting plate. The Rayleigh wave sensor and the Love wave sensor were designed and fabricated respectively on LiNbO3 Y-X 128° cut and AT-Quartz cut substrates using a conventional photolithography process. The interdigital transducers (IDT) consist of double finger pairs made of 200 nm thick aluminum with a periodicity p=10 µm and a wavelength λ=40 µm. Hence, the working frequency is 125 MHz for the Love mode and 98 MHz for the Rayleigh mode. The propagation of Love wave needs a guiding layer. For that purpose, a silica layer was deposited using sputtering technique with shear velocity lower than the piezoelectric substrates. The region between the two IDTs constitutes the sensing area.Preliminary tests have been performed using candle smoke. As the obtained PM concentrations were unstable and difficult to reproduce, we have developed an experimental set-up bench consisting of a 1m3 chamber, a particle’s generator AGK 2000 and an optical system FIDAS® 100. Thus, sodium chloride (NaCl) was used to produce PM2.5 while PM10 were generated from silicon carbide (SiC) in the 0 to 200 μg/m3 concentration range. When the particles impact on the sensor surface, the velocity of the acoustic waves decreases due to the sensors’ high gravimetric sensitivity. Accordingly, the wave phase velocity shift is measured by monitoring the phase at constant frequency with an open loop interrogation [4]. It’s then correlated to the particles concentration. Results and Conclusions Figure 1 and 2 shows plots of phase derivative dϕ/dt of sensors based AT-Quartz (black) and LiNbO3 (red) with the concentration of PM10 and PM2.5 respectively measured with the optical system FIDAS®. As expected, the sensitivity of the Rayleigh wave sensor based on LiNbO3 is lower than the Love wave sensor based on quartz for both PM10 and PM2.5. The sensor’s sensitivity is estimated by applying a linear fit of the plotted data. The sensitivity of sensors based on quartz is 3.10-4 °/s.μg/m3 for PM 2.5 and 5.10-5 °/s.μg/m3 for PM10. For sensors based on LiNbO3, the sensitivity is 1.10-4 °/s.μg/m3 for PM2.5 and 1.10-5 °/s.μg/m3 for PM10. The feature that the sensors’ response is greater with PM2.5 than with PM10 can be explained by the fact that most adhesion forces are linearly dependent on particle diameter [5] which is often described as the rebound effect. As a result, the smaller particles settle more on the surface of the sensor resulting in a more significant slowdown of the wave. To ensure that each stage is measuring the targeted size range, we took images of the sensors surface at the end of the experiment using a microscope. Figures 3, 4 show the surface of the PM2.5 stage and figures 5, 6 the one of the PM10 stage. One can observe that, as expected, the PM2.5 contain more particles than the PM10 and that the particle sizes correspond well to the ranges [0.3 μm, 2.5 μm] and [2.5 μm, 10 μm]. It has therefore been shown that LiNbO3 sensors, although less sensitive, can also be used for fine particles detection. They still need work to improve their performance and limit the rebound effect, but they remain very promising for the development of self-cleaning systems.

Comparative Analysis on Dielectric Gold and Aluminium Triangular Junctions: Impact of Ionic Strength and Background Electrolyte by pH Variations

Field of generating a surface thin film is emerging broadly in sensing applications to obtain the quick and fast results by forming the high-performance sensors. Incorporation of thin film technologies in sensor development for the better sensing could be a promising way to attain the current requirements. This work predominantly delineates the fabrication of the dielectric sensor using two different sensing materials (Gold and Aluminium). Conventional photolithography was carried out using silicon as a base material and the photo mask of the dielectric sensor was designed by AutoCAD software. The physical characterization of the fabricated sensor was done by Scanning Electron Microscope, Atomic Force Microscope, High Power Microscope and 3D-nano profiler. The electrical characterization was performed using Keithley 6487 picoammeter with a linear sweep voltage of 0 to 2 V at 0.01 V step voltage. By pH scouting, I-V measurements on the bare sensor were carried out, whereby the gold electrodes conducts a least current than aluminium dielectrodes. Comparative analysis with pH scouting reveals that gold electrode is suitable under varied ionic strengths and background electrolytes, whereas aluminium electrodes were affected by the extreme acid (pH 1) and alkali (pH 12) solutions.

Microfabrication of Ni-Fe Mold Insert via Hard X-ray Lithography and Electroforming Process

In this research, a Ni-Fe mold insert for the efficient replication of high aspect-ratio microstructure arrays was fabricated via hard X-ray lithography and an electroforming process. For the X-ray exposure on a photoresist, a gold-based X-ray mask was prepared with conventional UV photolithography. The gold thickness was designed to be over 15 μm to prevent development underneath the absorber and to enhance the adhesion strength between the photoresist and substrate. By using the X-ray mask, a positive-type photoresist was selectively exposed to X-ray under an exposure energy of 4 kJ/cm3. Thereafter, the exposed region was developed in a downward direction to effectively remove the residual photoresist from the substrate. During the evaporation process, deionized water mixed with a surface additive prevented the bending and clustering of the photoresist microstructure arrays by lowering the capillary force, resulting in a defect-free mother structure for electroforming. Lastly, the mother structure was uniformly Ni-Fe electroformed on a conductive substrate without the formation of any pores or detachment from the substrate. Based on the proposed microfabrication process, a Ni-Fe mold insert with a 183 μm pattern size, 68 μm gap size, 550 μm height, 2116 microcavities and a hardness of 585 Hv was precisely manufactured. It can be utilized for the mass production of high aspect ratio metal and ceramic microstructure arrays in micro molding technologies.