Micromachining Process Research Articles

Manufacturability and surface characterisation of polymeric microfluidic devices for biomedical applications

Generally, machining of polymeric microfluidic devices is a one-step manufacturing process. It is economical compared to lithography and can be used for batch production and rapid prototyping. However, surface properties are modified during machining due to the viscoelasticity property of polymers and the mechanical nature of fractures. In this present work, the manufacturing capability of the mechanical micromachining process of polymers has been explored. Surface characteristics like surface roughness, surface energy, and burr formation are investigated. Surface quality is chosen as a contributing factor for defining the manufacturing capability as it is one of the significant factors influencing the physics of fluid flow in microchannels. In the present work, several manufacturing methods, such as 3D printing, hot embossing, photolithography, and mechanical micromachining, were considered. The surface energy of various surfaces machined using the abovementioned methods is evaluated and compared. It has been observed that mechanical micromachining is the most suitable methods as they have less wettability with lower surface energy. Further investigations are carried out by machining microfluidic devices using polymethylmethacrylate (PMMA) and polycarbonate (PC) materials, as they are extensively used in biomedical applications. Surface roughness was measured on the PMMA and PC surfaces after milling. The surface roughness values and surface energies are used for evaluating the suitability of the machining process to fabricate microfluidic devices. Microfluidic devices with serpentine channels were machined on PMMA with a depth of 50 µm and width of 200 µm for evaluating inertial focusing in the channels. These devices were further evaluated for blood cell separation at different dilution rates. It is observed that PMMA is the preferable choice for fabricating microfluidic devices using mechanical micro-milling.

Detection of cancer biomarkers CA125 and CA199 via terahertz metasurface immunosensor

The cancer biomarkers including AFP, CEA, CA199 and CA125, are of great importance in the diagnosis, prognostic prediction and recurrence monitoring of malignancies. However, in clinical practical applications, most tumor cancer biomarkers are lack of sensitivity and specificity. In this study, we propose a terahertz (THz) metasurface (MS) immunosensor coupled with gold nanoparticles (AuNPs), which have good biocompatibility and high specific surface area for biomarkers. Firstly, we added AuNPs to the surface of the sensor. And then, the surface is modified with Anti-CA125 or Anti-CA199 to improve the sensitivity and specificity to the target antigen. The biosensor was fabricated using a surface micromachining process and characterized by a THz-time-domain spectroscopy (TDS) system. The sensitivity of the resonance frequency of the sensor to the refractive index was 65 GHz/RIU (refractive index unit). The detection performance of the THz immunosensor was also verified with different concentrations of CA125 and CA199. The experimental results showed that the frequency shift of the resonance peak was linearly related to the concentration of CA125 and CA199. The detection limits for both CA125 and CA199 are 0.01 U/ml, which is better than that of other common methods. Finally, serum samples were collected and detected to explore whether this method is suitable for clinical detection. The results are consistent with the results of antigen recognition. This study proves that the practicability of the THz immunosensor, which potentially provides important techniques and equipment for improving the sensitivity and specificity of cancer biomarkers.

Bubble Behavior and Its Effect on Surface Integrity in Laser-Induced Plasma Micro-Machining Silicon Wafer

Abstract Laser-induced plasma micro-machining (LIPMM) process does well in fabricating high-quality surface microstructures of hard and brittle materials. However, the liquid medium is overheated to induce lots of bubbles to defocus the laser beam, reducing machining stability, and explosive behavior of bubbles destroys the surface quality. Thus, the static and dynamical behaviors of bubbles in LIPMM are comprehensively investigated in this article. First, a series of mechanisms including bubble generation and growth, bubble motion and explosion, and the effect of bubbles behavior on machining characteristics were explained. Second, a volume of fluid (VOF) model of bubble motions in laser-induced plasma micro-machining was established to simulate the dynamical behavior of bubbles under different depths of water layer, which reflect the growth of microbubbles, the aggregation of multiple bubbles, and the floating movement of bubbles. Then, a series of experiments were carried out to reveal bubble static behaviors, and further bubble explosion behaviors on surface integrity, surface defects, and hardness were analyzed. The increase of laser frequency leads to the increase of the maximum attached bubble size. Obstructed by bubble dynamical behaviors, a discontinuous section and the unablated area are observed in the microchannel. The elastic modulus and surface hardness of surface impacted by explosion bubbles are reduced. This research contributes to better understanding bubble behavior related to machining performances in LIPMM of single-crystal silicon.

Experimental Study on Gas Flow in a Rough Microchannel

The shape and relative roughness of a rough surface have an important influence on microscale flow and heat transfer. In this study, a rectangular silicon microchannel (0.8 mm width and 11.9 μm height) with a large width-depth ratio is fabricated by the MEMS micromachining process. The silicon surface of the microchannel and the two-dimensional rough contours of the glass surface are measured, and the fractal dimensions taken as the only quantitative parameter of the surface morphology are calculated. The three-dimensional morphology of the silicon surface is measured by a confocal laser microscope and atomic force microscope. On this basis, a microscale gas flow performance test system is designed and built, and the flow characteristics of nitrogen and helium in rough silicon microchannel are experimentally studied. The experimental results show that the rough profiles of the silicon surface and the glass surface have possessed self-affine characteristics. Both nitrogen and helium show a certain degree of boundary slip when they flow in a microchannel. The degree of slip of helium flow is larger than that of nitrogen flow, which verifies the rarefied effect of microscale gas flow.

Quasi-superhydrophobic microscale two-dimensional phononic crystals of stainless steel 304

Fabrication of metallic phononic and photonic crystals of characteristic size between 10 and 1000μm remains a challenge in precision using the conventional machining processes or too tedious for the cleanroom-based processes. We report the fabrication and elastodynamic bandgaps of two-dimensional phononic crystals (PhCs) machined on stainless steel 304 (SS304) substrates using the wire-electrochemical micromachining (wire-ECMM) process. Square arrays of pillars of length 400μm and cross section either 350×350μm2 or 250×250μm2 with periods 650 and 550μm, respectively, were micromachined on an SS304 homogeneous substrate. Based on these arrays, three types of PhCs were considered: air-SS304, water-SS304, and epoxy-SS304, where air, water, and epoxy are the hosts and SS304 pillars are the scatterers. We found that texturing the surface increased the contact angle of a 5-μl-water-droplet from 97.9° for an untextured SS304 substrate to a maximum of 145° for SS304 PhCs, making the latter quasi-superhydrophobic. Dispersion relations evaluated using the finite-element method revealed the presence of partial bandgaps in the 0.1–2.7 MHz for all PhCs and a complete bandgap for the epoxy-SS304 PhCs. Transmittance spectrums for incident plane waves also provided evidence for the occurrence of bandgaps. Furthermore, the buckling analysis indicated that these pillars do not undergo buckling until yield—making them mechanically robust.

Texturing design of WC-Co through laser parameter selection to improve lubricant retention ability of cutting tools

Laser Surface Texturing (LST) is widely used to modify hard material surfaces improving their physic-chemical and mechanical properties. This technology is particularly relevant for tungsten carbides, a material that requires high complexity methods when other micro-machining processes are used. LST allows innovative cutting tool designs that improve the machining behavior and enlarge the cutting tool lifetime.This research analyses the influence of LST parameters on the track dimensions, roughness, microstructure, hardness, and lubricant retention ability of the modified surfaces. Twelve combinations of energy density of pulse and scanning speed created different geometrical patterns on WC-Co surfaces. LST parameters were related to specific shape and dimensions of the linear grooves. Energy density was proven as the most influential parameter for dimensional characteristics and roughness values. Specific channel morphologies increased the lubricant expansion area up to 50%, leading the lubricant to a linear track direction. Low scanning speed and high energy density also increased the surface hardness up to 20%. The surface composition was also modified. The thermal effect of the laser treatments and the non-protective atmosphere increased the oxygen on the surface and modified the WC-Co microstructure. However, the thermal affected zone is considerably low compared to other texturing processes.

Microfluidic Thermal Flowmeters for Drug Injection Monitoring

This paper presents a microfluidic thermal flowmeter for monitoring injection pumps, which is essential to ensure proper patient treatment and reduce medication errors that can lead to severe injury or death. The standard gravimetric method for flow-rate monitoring requires a great deal of preparation and laboratory equipment and is impractical in clinics. Therefore, an alternative to the standard method suitable for remote, small-scale, and frequent infusion-pump monitoring is in great demand. Here, we propose a miniaturized thermal flowmeter consisting of a silicon substrate, a platinum heater layer on a silicon dioxide thin-membrane, and a polymer microchannel to provide accurate flow-rate measurement. The present thermal flowmeter is fabricated by the micromachining and micromolding process and exhibits sensitivity, linearity, and uncertainty of 0.722 mW/(g/h), 98.7%, and (2.36 ± 0.80)%, respectively, in the flow-rate range of 0.5–2.5 g/h when the flowmeter is operated in the constant temperature mode with the channel width of 0.5 mm. The measurement range of flow rate can be easily adjusted by changing the cross-sectional microchannel dimension. The present miniaturized thermal flowmeter shows a high potential for infusion-pump calibration in clinical settings.

Burr removal from high-aspect-ratio micro-pillars using ultrasonic-assisted abrasive micro-deburring

The demand for high-aspect-ratio microstructures is ever increasing in the fields of microelectromechanical systems, biomedicine, aerospace, telecommunication, and heat transfer. Mechanical micromachining processes have a distinct advantage over lithography-based processes for machining complex three-dimensional microstructures on a variety of materials with high accuracy and surface finish. But the tool-based micromachining operations face inherent issues in the form of excessive burr formation, which needs to be addressed by post-machining burr removal operations. In this study, an ultrasonic-assisted abrasive micro-deburring process employing a probe sonotrode and abrasive particles has been investigated for deburring high-aspect-ratio micro-pillars machined on aluminium 6061 and copper. Deburring of micromilled pillars of aspect ratio 5:1 has been achieved while maintaining pillar integrity. The mechanism of deburring has been observed to be mainly by the impact of the abrasive particles with a minor role played by liquid cavitation. Burr reduction as high as 88.75% for Al 6061 and 90.1% for copper has been achieved in a short processing time of 10 s. This is a significantly faster process than other ultrasonic cavitation-based deburring processes described in literature (deburring time ranging from 60 min to a few hours). With proper control of the process parameters like stand-off distance and power, burr removal has been achieved while maintaining the integrity of the micro-pillars. Pure water cavitation has also been studied for comparison, which has resulted in a burr removal by 51.5% and 53.1% for Al 6061 and copper, respectively. Upon proper selection of the process parameters, this process can be a viable alternative to existing deburring methods in terms of minimal processing time and structure damage.

Design and Testing of a Non-Contact MEMS Voltage Sensor Based on Single-Crystal Silicon Piezoresistive Effect.

The paper presents a novel non-contact microelectromechanical systems (MEMS) voltage sensor based on the piezoresistive effect of single-crystal silicon. The novelty of the proposed sensor design lies in the implementation of unique single-crystal silicon piezoresistive beams for voltage measurement. The sensitive structure of the sensor produces electrostatic force deformation due to the measured voltage, resulting in the resistance change of single-crystal silicon piezoresistive beams which support a vibrating diaphragm. The voltage can be measured by sensing the resistance change. Moreover, the sensor does not need an additional driving signal and has lower power consumption. The prototype of the sensor was fabricated using an SOI micromachining process. The piezoresistive characteristics of the sensor and the corresponding output response relationship were analyzed through theoretical analysis and finite element simulation. The voltage response characteristics of the sensor were achieved at power frequencies from 50 Hz to 1000 Hz in the paper. The experimental results showed that they were in good agreement with simulations results with the theoretical model and obtained good response characteristics. The sensor has demonstrated that the minimum detectable voltages were 1 V for AC voltages at frequencies from 50 Hz to 300 Hz and 0.5 V for AC voltages at frequencies from 400 Hz to 1000 Hz, respectively. Moreover, the linearities of the sensor were 3.4% and 0.93% in the voltage measurement range of 900–1200 V at the power frequency of 50 Hz and in the voltage measurement range of 400–1200 V at the frequency of 200 Hz, respectively.

Cavitation bubble removal by surfactants in Laser-Induced Plasma Micromachining

The Laser-Induced Plasma Micromachining (LIPMM) process results in higher material removal rates, lower heat affected areas, and is less influenced by materials properties in comparison to direct laser ablation. Despite these improved benefits, cavitation bubbles generated during the process that reflect, refract, and scatter the laser beam pose a challenge for processing materials in precision engineering applications. This work reports an effective solution to remove surface bubbles in LIPMM using surfactants. The force of repulsion between the surfactant molecules aids the buoyancy force in the bubbles to overcome the surface tension which causes the bubbles to detach from the surface.

Single-side micromachined ultra-small thermopile IR detecting pixels for dense-array integration

This paper presents a technology to fabricate ultra-small (100 × 100 μm) thermopile infrared (IR) sensing devices with a novel front-side micromachining process for integration of dense IR detection array. The thermopile IR detection unit is constructed into double-level suspending films, where the IR absorber and n/p-polysilicon thermopile are located at the central-supported upper level and the surrounding-supported lower level, respectively. The separated design for IR absorber and thermopile temperature-detection helps to achieve a high thermocouple fill-factor of 0.9 in terms of the structural area. A single-step wet etching method is proposed to simultaneously release the umbrella-shaped upper-level absorber and the thermal insulation cavity beneath the lower-level thermopile layer. By pre-depositing a polysilicon sacrificial layer, the etching method breakthroughs the restriction of anisotropic over-etch to the single crystalline silicon substrate, thereby maximizing the thermocouple number in the lower-layer film and minimizing the opened area of the etching holes. Finite-element-method simulation results show that the detector with 20 pairs of thermocouples exhibits maximized responsivity than those with more or less pairs of thermocouples. Benefit from the optimized heat dissipation design, the thermopile detection unit in atmospheric environment achieves a high normalized detectivity of 2.1 × 107 cm Hz1/2 W−1, a high responsivity of 52 V W−1 and sound respond time of 1.4 ms. Thanks to the ultra-small unit area, many unites can be densely integrated into IR detection arrays of various scales. As an example, an integrated 4 × 4 IR sensing array is herein fabricated. The 16 integrated pixels demonstrate good consistency in responsivity, with the deviation being less than ±7%. Featuring the tiny-size pixels for dense-array integration and the single-sided micromachining process that is compatible with integrated circuit fabrication, the proposed thermopile IR sensing devices are promising in IR detection applications including consumer-electronic level IR focal plane arrays.

Surface-Functionalized Terahertz Metamaterial Biosensor Used for the Detection of Exosomes in Patients.

Owing to their stability in bodily fluids, exosomes have attracted increased attention as colorectal cancer (CRC) biomarkers for early diagnosis. To validate the potential of the plasma exosomes as a novel biomarker for the monitoring of CRC, we demonstrated a terahertz (THz) metamaterials (MMs) biosensor for the detection of exosomes in this work. The biosensor with two resonant frequencies is designed using full wave electromagnetic simulation software based on the finite integration time domain (FITD) method and fabricated by a surface micromachining process. The biosensor surface is first modified using Au nanoparticles (AuNPs), and then, anti-KRAS and anti-CD147, which are specific to the exosomes, are modified on the AuNPs assembled with HS-poly(ethylene glycol)-COOH (HS-PEG-COOH). Exosomes used in the experiment are extracted via the instructions in the exosomes isolation and purification kit and identified by using transmission electron microscopy (TEM), Western blot (WB), and nanoparticle tracking analysis (NTA). The biosensor covered with plasma-derived exosomes of CRC patients has a different resonance frequency shift compared to that with healthy-control-derived exosomes. This study proposes an emerging and quick method for diagnosing the CRC.

Neural Network (NN)-Based RSM-PSO Multiresponse Parametric Optimization of the Electro Chemical Discharge Micromachining Process During Microchannel Cutting on Silica Glass

The production of miniature parts by the electrochemical discharge micromachining process ([Formula: see text]-ECDM) draws the most of attractions into the industrial field. Parametric influences on machining depth (MD), material removal rate (MRR), and overcut (OC) have been propounded using a mixed electrolyte (NaOH:KOH- 1:1) varying concentrations (wt.%), applied voltage ([Formula: see text]), pulse on time ([Formula: see text]s), and stand-off distance (SOD) during microchannel cutting on silica glass (SiO[Formula: see text]). Analysis of variances has been analyzed to test the adequacy of the developed mathematical model and multiresponse optimization has been performed to find out maximum MD with higher material removal at lower OC using desirability function analysis as well as neural network (NN)-based Particle Swarm Optimization (PSO). The SEM analysis has been done to find unexpected debris. MD has been improved with better surface quality using a mixed electrolyte at straight polarity using a tungsten carbide (WC) cylindrical tool along with [Formula: see text], [Formula: see text], and [Formula: see text] axis movement by computer-aided subsystem and combining with the automated spring feed mechanism. PSO-ANN provides better parametric optimization results for micromachining by the ECDM process.

Wet etching of AZ31B magnesium alloy with nitric acid

Wet etching is a micromachining process in which a material is immersed in liquid chemicals or etchants to remove unwanted sections from the surface. The process is generally known as cost-effective, reliable and suitable for high-production environments. Magnesium alloys are presenting a strong popularity in recent years since it is one of the lightest engineering alloys. Hence, the micromachining of these materials is becoming an important research area. One of the promising methods is wet etching. In this experimental study, two different concentrations (10 and 20 ml) of a nitric acid solution are used at room temperature. The wet etching characteristics of a selected magnesium alloy is determined by analysing the thickness reduction and surface roughness as well as colour degradation on the machined surfaces.

A Study on Weighted Aggregated Sum Product Assessment (WASPAS) w.r.t Multiple Criteria Decision Making

Advantages of the WASPAS method Weight Total Model (WSM) and Weight Product Model (WPM) Uses. Combining WSM and WPM improves the ranking accuracy of WASPAS alternatives. That At the moment, WASPAS calculates an optimal registration parameter, which will be given in detail later. The Weight the Product Assessment (WASPAS) system is a unique combination of Weight Gross Model (WSM) and Weight Product Model (WPM). Its mathematical simplicity and ability to deliver more accurate results compared to WSM and WPM methods Due to this, it is now widely accepted as an effective decision maker. In this paper, (a) a flexible production system, (b) a machine in a flexible production cell, (c) an automated guide vehicle and (d) an automation study. Structure and (c) an industrial robot. For all these five problems, the WASPAS method provides the most acceptable results. The optimal 1 value is determined for each issue considered and the effects of different values on the ranking of candidate alternatives in the WASPAS system are also analyzed. In this study, the compatibility of the Weighted the Product Evaluation (WASPAS) method is being explored as an effective MCDM tool, while eight production Decision making issues are resolved. Condition, Mac inability of objects and electro-discharge Micro-machining process parameters. The system has the ability to accurately sequence alternatives across the entire Selection issues are considered. In the ranking performance of the WASPAS system the effect of the parameter is also explored.

Self-Actuating Isothermal Nanomechanical Test Platform for Tensile Creep Measurement of Freestanding Thin Films

Microelectromechanical systems (MEMS) enable potent methods for nanomechanical testing. In many MEMS-based test platforms, high force polycrystalline silicon chevron-type thermal actuators are used as on chip actuators. Here, we implement thermal actuators using the refractory metal tantalum (Ta) as a new micromachined structural material in such a way that it can be integrated to test mechanical properties of a wide variety of metals. Because Ta’s coefficient of thermal expansion is more than double that of silicon, actuation is accomplished simply by raising the temperature. An isothermal condition is attained, while no force is lost to a heat sink. The platform is batch fabricated by conventional surface micromachining processes and is especially well suited to measure creep of thin films because the load spring is soft compared to the specimen uniaxially loaded in tension. This in turn gives rise to a slow stress relaxation and a large displacement range. Specimen alignment is excellent and handling procedures for thin films are simple and robust. As a validation of the apparatus, uniaxial Au tensile specimens of 110 nm thickness are fabricated and tested. Young’s modulus is measured and compares well with literature values, while creep rate is lower than other reported values for nanocrystalline Au, indicating that steady state creep is approached. This work demonstrates a powerful drift-free nanomechanical test platform for mechanical property measurement of freestanding thin films subjected to uniaxial tension. [2021-0171]

Electrochemical Micromachining of Linear Micropattern on Stainless Steel Surface

Maskless electrochemical micromachining process with SU-8 2150 masked tool has been introduced containing microstructures with higherprofile accuracy that are generated on SS-304. In this research work, to make maskless EMM method with more cost-effective, substantial adaptations are provided to this technique and an advanced version of EMM process is applied for microtexturing. In this modified technique, a special microtextured cell unit including (micromachining cell, electrical connection, and electrolyte flow scheme) is assembled by the mechanical force and perpendicular cross flow system has been developed inside the cell. Experimentation is conducted to explore the machining influence of the advanced maskless EMM process for fabricating linear micropattern. The machining outcomes of voltage, frequency, and duty ratio on MRR, dimensional accuracy, textured depth, and surface roughness are investigated during microtexturing. The investigational research reveals that this advanced maskless EMM technique can generate highly identical micropatterns having MRR of 2.2 mg/min, width overcut of 19.76μm, textured depth of 14.4μm and surface roughness of 0.0307μm.

Analysis of circuit current in electrochemical micromachining process under the application of different waveforms of pulsed voltage

Selection of optimal pulsed voltage parameters such as waveform, pulse rise and fall time, frequency, and duty ratio is very important to achieve the desired machining efficiency and accuracy in electrochemical machining (ECM). At present, this selection is done by conducting time-consuming and costly trial experiments. It is well understood that the volume and rate of material dissolution in ECM is dependent on the current flowing between the two electrodes. However, only a part of this current, called as Faradaic current, is responsible for the anodic dissolution and the rest of it, called as capacitive current, is consumed in charging the electrical double layer (EDL) capacitance which forms at the interface. Therefore, it is vital to understand the variation of Faradaic current in the system to arrive at optimal pulse parameters. An increase in the current flowing between the two electrodes does not ensures an increase in the Faradaic component of that current. To the best of authors' knowledge, there does not exists any method or device, to date, which can break the system current into its components and provide their variation explicitly. This research attempts to fill in this gap by provide a method of breaking the overall system current into its constituents by investigating the system under consideration using electrochemical impedance spectroscopy (EIS). The results of EIS are used to virtually construct an equivalent electrical circuit in MATLAB® Simscape and the current is simulated for different waveforms of pulsed voltage input. To access the correctness of the trends of Faradaic current obtained through simulations, an experimental study is conducted. Both simulation and experimental study is conducted for three waveforms of pulsed voltage namely: half wave rectified rectangular (RVW), sinusoidal (SVW), and triangular (TVW). For experimentation, these waveforms are obtained with the help of a rectification-cum-amplification circuit which is designed and developed in lab. Further optimization of triangular waveform is performed by varying its rise and fall time in five different cases. It is finally concluded that the trends of Faradaic current obtained from simulation study are in good agreement with the experimental results.

A model-based investigation of tool-chip friction during precision micro cutting of commercially pure titanium alloy

Understanding interaction between the cutting tool edge radius and the work material is essential to identify the conditions leading to superior surface finish during the micromachining process. The interaction between friction angle and effective rake angle has been investigated based on a slip-line field-based machining model from the literature. Machining forces and cut chip thickness values were obtained from orthogonal cutting tests and employed in the process model. The proposed model also allows for calculating material properties such as shear flow stress and fracture toughness. The proposed model can successfully simulate machining forces during shearing-dominated machining conditions. The results showed the importance of flank and rake face friction in micro-scale machining.

Etch Rates for Micromachining Process in Manufacturing Hybrid Microdevices Composed of Ni-Mn-Ga and Silicon Layers

Etch Rates for Micromachining Process in Manufacturing Hybrid Microdevices Composed of Ni-Mn-Ga and Silicon Layers