As I discussed in my last editorial,1 there are four criteria for judging whether a paper should be published in a given scientific journal: 1) does the paper’s content match the scope of the journal; 2) is the quality of the work and writing sufficiently high; 3) is there something novel being presented; and 4) is the paper sufficiently significant. This last criterion, paper significance, is a tricky one since significance lies in the mind of the reader. Still, editors and reviewers must do their best to judge both how important the problem being addressed by the work is, and how big of an advance over the prior literature this work represents.

We describe a method for fabricating an aperture on a fluidic cantilever device using SU-8 as a structural material. The device can ultimately be used for patch clamping, microinjections, fluidic delivery, fluidic deposition, and micromaterial removal. In the first generation of this device, the initial aperture diameter is 10  μm and is fabricated on a silicon-on-insulator (SOI) wafer that is structurally used to define the aperture. The aperture can be reduced in size through mask design. This self-aligned process allows for patterning on the sharp tip projecting out of the fluidic plane on the cantilever and is batch fabricated, reducing the cost and time for manufacture. The initial mask, SOI device layer thickness, and the width of the base of the tip define the size of the aperture. The SU-8 micromachined cantilever includes an electrode and a force sensing mechanism. The cantilever can be easily integrated with an atomic force microscope or an optical microscope.

The SPIE Advanced Lithography Symposium is the most important and widely attended symposium on lithography today, typically attracting over 2000 attendees from more than 30 countries. For anyone working in the field and looking to understand the most current trends, the event constantly attracts the most groundbreaking work in the field and attracts the attention of the industry’s key decision makers.

Reverse-tone step and flash imprint lithography (S-FIL/R) requires materials that can be spin-coated onto patterned substrates with significant topography and that are highly planarizing. Ideally, these planarizing materials must contain silicon for etch selectivity, be UV or thermally curable, and have low viscosity and low volatility. One such unique material, in particular, a branched and functionalized siloxane (Si-12), is able to adequately satisfy the above requirements. This paper describes a study of the properties of epoxy functionalized Si-12 (epoxy-Si-12) as a planarizing layer. An efficient synthetic route to epoxy-Si-12 was successfully developed, which is suitable and scalable for an industrial process. Epoxy-Si-12 has a high silicon content (30.0%), low viscosity (29 cP at 25°C), and low vapor pressure (0.65 Torr at 25°C). A planarizing study was carried out using epoxy-Si-12 on trench patterned test substrates. The material showed excellent planarizing properties and met the calculated critical degree of planarization (critical DOP), which is a requirement for a successful etch process. An S-FIL/R process using epoxy-Si-12 was demonstrated using an Imprio® 100 (Molecular Imprints Inc., Austin, Texas) imprint tool. The results indicate that epoxy-Si-12 works very well as a planarizing layer for S-FIL/R.

The nanoimprint lithography (NIL) process with its key elements molding and thin film pattern transfer refers to the established process chain of resist-based patterning of hard substrates. Typical processes for mass fabrication are either wafer-scale imprint or continuous roll-to-roll processes. In contrast to this, similar process chains were established for polymeric microelements fabricated by injection molding, particularly when surface topographies need to be integrated into monolithic polymer elements. NIL needs to be embedded into the framework of general replication technologies, with sizes ranging from nanoscopic details to macroscopic entities. This contribution presents elements of a generalized replication process chain involving NIL and demonstrates its wide application by presenting nontypical NIL products, such as an injection-molded microcantilever. Additionally, a hybrid approach combining NIL and injection molding in a single tool is presented. Its aim is to introduce a toolbox approach for nanoreplication into NIL-based processing and to facilitate the choice of suitable processes for micro- and nanodevices. By proposing a standardized process flow as described in the NaPANIL library of processes, the use of establish process sequences for new applications is facilitated.

Directed self-assembly (DSA) is a promising approach for extending conventional lithographic techniques by being able to print features with critical dimensions under 10 nm. The most widely studied block copolymer system is polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA). This system is well understood in terms of its synthesis, properties, and performance in DSA. However, PS-b-PMMA also has a number of limitations that impact on its performance and hence scope of application. The primary limitation is the low Flory-Huggins polymer-polymer interaction parameter (χ), which limits the size of features that can be printed. Another issue with block copolymers in general is that specific molecular weights need to be synthesized to achieve desired morphologies and feature sizes. Here we explore blending ionic liquid (IL) additives with PS-b-PMMA to increase the χ parameter. ILs have a number of useful properties that include negligible vapor pressure, tunable solvent strength, thermal stability, and chemical stability. The blends of PS-b-PMMA with an IL selective for the PMMA block allowed the resolution of the block copolymer to be improved. Depending on the amount of additive, it is also possible to tune the domain size and the morphology of the systems. These findings may expand the scope of PS-b-PMMA for DSA.

Application of the directed self-assembly of block copolymer to the hole shrink process has gained large attention because of the low cost and high potential for sublithographic patterning. In this study, we have employed a simplified model, called the Ohta-Kawasaki model to find the optimal process conditions, which minimize the morphological defects of the diblock copolymer, PS-b-PMMA. The model parameters were calibrated with cross-sectional transmission electron microscopy images. Our simulation results revealed that it is difficult to eliminate the morphological defects (i.e., PS residual layer) by only varying the shape of the guide hole. It turned out that changing the affinity of the bottom surface of the guide hole from “PMMA attractive” to “neutral” is a more effective way to obtain a reasonably wide, defect-free process window. Note that our simulations are not only computationally inexpensive, but are also comparable to the other detailed models such as the self-consistent field theory; they may also be feasible for large-scale simulations such as the hotspot analysis over a large area.

For proximity effect correction in 5 keV e-beam lithography, three elementary building blocks exist: dose modulation, geometry (size) modulation, and background dose addition. Combinations of these three methods are quantitatively compared in terms of throughput impact and process window (PW). In addition, overexposure in combination with negative bias results in PW enhancement at the cost of throughput. In proximity effect correction by over exposure (PEC-OE), the entire layout is set to fixed dose and geometry sizes are adjusted. In PEC-dose to size (DTS) both dose and geometry sizes are locally optimized. In PEC-background (BG), a background is added to correct the long-range part of the point spread function. In single e-beam tools (Gaussian or Shaped-beam), throughput heavily depends on the number of shots. In raster scan tools such as MAPPER Lithography’s FLX 1200 (MATRIX platform) this is not the case and instead of pattern density, the maximum local dose on the wafer is limiting throughput. The smallest considered half-pitch is 28 nm, which may be considered the 14-nm node for Metal-1 and the 10-nm node for the Via-1 layer, achieved in a single exposure with e-beam lithography. For typical 28-nm-hp Metal-1 layouts, it was shown that dose latitudes (size of process window) of around 10% are realizable with available PEC methods. For 28-nm-hp Via-1 layouts this is even higher at 14% and up. When the layouts do not reach the highest densities (up to 10∶1 in this study), PEC-BG and PEC-OE provide the capability to trade throughput for dose latitude. At the highest densities, PEC-DTS is required for proximity correction, as this method adjusts both geometry edges and doses and will reduce the dose at the densest areas. For 28-nm-hp lines critical dimension (CD), hole&dot (CD) and line ends (edge placement error), the data path errors are typically 0.9, 1.0 and 0.7 nm (3σ) and below, respectively. There is not a clear data path performance difference between the investigated PEC methods. After the simulations, the methods were successfully validated in exposures on a MAPPER pre-alpha tool. A 28-nm half pitch Metal-1 and Via-1 layouts show good performance in resist that coincide with the simulation result. Exposures of soft-edge stitched layouts show that beam-to-beam position errors up to ±7  nm specified for FLX 1200 show no noticeable impact on CD. The research leading to these results has been performed in the frame of the industrial collaborative consortium IMAGINE.

Directed self-assembly (DSA) of block copolymers (BCPs) proves to be a viable solution for the ultrahigh density bit-patterned media (BPM) application. However, servo design integration is still extremely challenging since the servo layouts require more complex patterns than the simple arrays naturally achieved by the DSA process. We present an integration scheme to create BPM servo patterns by utilizing the BCP dot-array patterns. This proposed method is based on an imprint guided two-step DSA process, combined with conventional optical lithography to define two separate zones. Both the data zone and servo zone consist of self-assembled hexagonal dot arrays: a regular pattern in the data zone and an arbitrary pattern in the servo zone. This method was successfully used to fabricate a servo-integrated BPM template with an areal density of 1.5  Teradot/inch² (Td/in.²) (L_o=22.3  nm). Using the fabricated quartz template, CoCrPt BPM media has been successfully patterned by nanoimprint lithography and subsequent ion-beam etching process on a 2.5 in. disk. Further, using patterned-in servo wedges on 1.5  Td/in.² patterned CoCrPt media, we are able to close the servo control loop for track-following on a spin-stand test. The standard deviation of repeatable run-out over the full revolution is calculated to be about 4% of the 38.6 nm track pitch. This method is currently being used to fabricate a template at a much higher density of 3.2  Td/in.² (L_o=15.2  nm).

One of the potentially most important issues in accurately modeling directed self-assembly of block copolymers (BCPs) is the fact that the real BCPs often have block energy and/or density asymmetry, meaning that each block has a different homopolymer density and/or cohesive energy density (CED). A simulation of BCP behavior based on molecular dynamics of coarse-grained polymer chains has been developed that can independently parameterize and control the density and the CED of each block to more accurately match this asymmetry. This model was used to study the effect on the order-disorder transition (ODT), domain scaling, and self-assembly of thin films of BCPs. BCPs whose blocks each have a different density show deviations from the mean-field ODT coexistence curve, exhibiting an asymmetric order-disorder transition curve. Self-assembly of thin films of BCPs with mismatches in CED shows significant changes in morphologies compared to BCPs with energetically symmetric blocks, because the lowest CED block has a strong propensity to segregate to and “wet” the free interface. This CED mismatch also gives rise to a large number of deviations from bulk behavior including changing vertical-to-horizontal morphologies through film depth, compression and expansion of domain sizes, and island and hole formations among others.

Escalating manufacturing cost and complexity is challenging the premise of affordable scaling. With lithography accounting for a large fraction of wafer costs, researchers are actively exploring several cost-effective alternative lithographic techniques, such as directed self-assembly, self-aligned multiple patterning, etc. However, most of the alternative lithographic techniques are restrictive, and it is important to understand the impact of such pattering restrictions on system-on-chip (SoC) design. To this end, we artificially restricted all layers in a 14 nm process to be pure gratings and observed that the pure gratings approach results in an inefficient SoC design with several process integration concerns. To come up with a technology definition that is mindful of designer requirements, it is essential to undertake a holistic design technology co-optimization (DTCO) considering several SoC design elements, such as standard cell logic, static random access memory bitcells, analog blocks, and physical synthesis. Our DTCO on the IBM 14 nm process with additional 10- and 7-nm node-like pattern restrictions leads us to converge on a set of critical pattern constructs that are required for an efficient and affordable SoC design.

We present a miniaturized polymer-based micro-optical detection unit for ultraviolet and visible laser-induced fluorescence (LIF) and absorbance (ABS) analysis with an interaction length of 3 mm. We use nonsequential optical ray tracing simulations to model the system and to optimize its performance with respect to optical efficiency and system complexity. The design features a compact optical system combining total internal reflection (TIR) mirrors and refractive optics. The detection module is prototyped with deep proton writing in 2-mm-thick polymethylmethacrylate and quantitatively characterized using a three-dimensional coordinate measurement machine. We demonstrate the proof-of-concept of this TIR mirror–based module for coumarin 480 obtaining limits of detection of 50 pM and 500 nM for LIF and ABS, respectively.

In a first study to analyze the feasibility of electron beam-induced deposition (EBID) for creating certain patterns in advanced lithography, line patterns were fabricated on silicon wafers using EBID. The growth conditions were such that the growth rate is fully determined by the electron flux (the current limited growth regime). It is experimentally verified that different patterning strategies, such as serial versus parallel patterning and single pass patterning versus multiple pass patterning, all lead to the same result in this growth regime. Images of EBID lines, imaged in a scanning electron microscope, were analyzed to determine the position of the lines, the width of the lines, and the linewidth roughness (LWR). The results are that the lines have an average width of 13.7 nm, an average standard deviation of 1.6 nm in the center position of the lines, and an average LWR of 4.5 nm (1σ value). As an example of the capabilities of EBID, a logic-resembling lithography pattern was fabricated.

This paper proposes an electrostatic stiffness correction method for the quadrature error (QUER) in a decoupled dual-mass gyroscope structure. The QUER is caused by the imperfections during the structure manufacturing process, and the two masses usually have different QUERs. The harm contribution to the Coriolis signal is analyzed and quantified. The generating forms of QUER motion in both masses are analyzed, the correction electrodes’ working principle is introduced, and a single mass individual correction method is proposed. The QUER stiffness correction system is designed based on a PI controller, and the experiments are arranged to verify the theoretical analysis. The bias stability decreases from 2.06 to 0.64 deg/h after the QUER correction, and the parameters of scale factor such as nonlinearly, asymmetry, and repeatability, reduce from 143, 557, and 210 ppm to 84, 242, and 175 ppm, respectively.

Dual-photoresist complementary lithography technique consisting of inorganic oxide photoresist and organic photoresist is applied to produce the submicron pit array patterns on a sapphire surface. The oxide photoresist is patterned by direct laser writing, and the developed pit size decreases to a smaller value than the laser spot size due to the thermal lithography. The oxide photoresist possesses strong etching resistance against oxygen plasma but shows no resistance against chlorine plasma. During the ion-coupled-plasma reactive-ion-etching process, chlorine plasma is a necessary component to etch the sapphire. Moreover, the characteristics of organic resist are opposite those of oxide photoresist and possess moderate resistance against chlorine plasma but no resistance against oxygen plasma. The thermal and developing characteristics of oxide photoresist are reported in this study. The dependence of laser power on the developed mark sizes and morphologies is examined by atomic force microscopy. The temperature distribution on the photoresist structure during the laser writing is simulated, and the thermal lithography concept is introduced to explain the effect of power on the developed oxide mark width. Images of patterned pit array on a commercial 4-inch-diameter sapphire substrate are also shown.

Contact holes (CHs) created by 193i lithography were shrunken by directed self-assembly of polystyrene-b-methylmethacrylate (PS-PMMA) block copolymers (BCPs). The placement error of these highly confined systems is determined both experimentally and by simulations. Good agreement between simulations (2 nm) and experiments was observed (2 nm). Extensive simulations show that the placement error is dependent on the length of the PS block only, indicating that the placement error is intrinsic to the BCP. This was explained by considering the BCPs as springs. For double CHs, a relation is found between the offset of the CH from the center of the CHs and the additional placement error.

Replicated polydimethylsiloxane (PDMS) micro/nanostructures are widely used in various research fields due to their inexpensiveness, flexibility, low surface energy, good optical properties, biocompatibility, chemical inertness, high durability, and easy fabrication process. However, the application of PDMS micro/nanostructures is limited when an accurate pattern shape or position is required because of the shrinkage that occurs during the PDMS curing process. In this study, we analyzed the effects of processing parameters in the PDMS replication process on the shrinkage of the final structure. Although the shrinkage can be decreased by decreasing the curing temperature, this reduction also increases the unnecessary curing time. To minimize the inherent shrinkage in the PDMS replica without an accompanying curing time increase, we propose a PDMS replication process on a high modulus substrate (glass and polymer films) with compression pressure, in which the adhesion force between the substrate and the PDMS, and the compression pressure prevent shrinkage during the curing process. Using the proposed method, a PDMS replica with less than 0.1% in-plane and vertical shrinkage was obtained at a curing temperature of 150°C and a curing time of 10 min.

A fast model is developed for the simulation of the mask diffraction spectrum in extreme ultraviolet lithography. It combines a modified thin mask model and an equivalent layer method and provides an analytical expression of the diffraction spectrum of the mask. Based on this model, we perform a theoretical analysis of the mask shadowing effect. Mathematical expressions for the best mask (object space) focus position and for the required correction of the mask pattern size are derived. When the mask focus is positioned in the equivalent plane of the multilayer, the amount of pattern shift is reduced. When the mask pattern size is corrected using the derived formula, taking a space pattern with a target critical dimension (CD) of 22 nm as an example, the imaging CD bias between different oriented features is below 0.3 nm.

An external-integrated biomimetic micropump for a microfluidic system is demonstrated. An “artificial leaf” is constituted, which mimics the stomatal transpiration process in plants and utilizes the negative pressure generated to drive the fluid flow. The biomimetic micropump integrated an SU-8 film with a micropore array, agarose gel, a flow rate control unit, and additional necessary operating auxiliaries. SU-8 film with micropores and agarose gel is used to mimic the stomata and the mesophyll cells in a leaf, respectively. The flow rate control unit can change the flow rate of the micropump by adjusting the number of micropores that participate in transpiration. Additional necessary operating auxiliaries can fix a microchip, provide a continuous fluid supply, and speed up the fluid flow rate. Experiments on a microchip are conducted to evaluate the performance of the micropump platform. Results have shown that the flow rate of the micropump can be increased by accelerating the wind speed or raising the temperature.

We investigated the off-line metrology for line edge roughness (LER) determination by using the discrete power spectral density (PSD). The study specifically addresses low-dose scanning electron microscopy (SEM) images in order to reduce the acquisition time and the risk of resist shrinkage. The first attempts are based on optimized elliptic filtering of noisy experimental SEM images, where we use threshold-based peak detection to determine the edge displacements. The effect of transversal and longitudinal filterings cannot be ignored, even when considering an optimized filter strength. We subsequently developed a method to detect the edge displacements without the use of a filter and thus avoiding biasing. This makes it possible to study how much image noise is acceptable and still determine the LER. The idea is to generate random images of line edges using the model of Palasantzas and the algorithm of Thorsos. We study the simulated PSDs as a function of the number of line edges and report on the convergence of the parameters (LER, correlation length, and roughness exponent) by fitting the Palasantzas model extended with a white noise term. This study demonstrates that a very noisy image with 12 line edges and about 2 electrons per pixel on average (charge density ≈10  μC) already produces an estimation for LER with a relative error (one-sigma) of about 10%. Furthermore, increasing the dose beyond 20 electrons per pixel does not significantly improve the LER determination.

In this work, we have investigated the evolution of line roughness from the photoresist (PR) to the poly-silicon gate etch based on the composite SiO₂ /Si₃ N₄ /SiO₂ (ONO) multilayer hard mask structure using a capacitively coupled plasma etcher. A severe line roughness could be observed during gate patterning when the PR pattern was directly transferred into the ONO hard mask. Then, the formation mechanisms of line roughness were the results of the effects of decomposed oxygen radical generated from the SiO ₂ mask because of ion bombardment and the rough surface morphology of poly-silicon that accelerates the etching of both the hard mask and the PR sidewalls by reflected ions. We found that a combination of an amorphous silicon (α -Si) capping layer and amorphous Si gate could effectively reduce the strong dependence of hard mask etch on PR and ions reflection effect from rough surface morphology of poly-silicon. Finally, our results have shown that the gate pattern with a fairly smooth line, without deformation, and with the gate length of 29 nm and the line width roughness of 3.4 nm can be achieved.

Thermoplastic nanoimprint lithography has been used for the first time, to the best of our knowledge, as a method for transferring nanoscale patterns to electroactive polymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)]. PVDF, its copolymers, and terpolymers cannot be processed using conventional lithography techniques because of their solubility in most organic solvents and photoresist developers. In this work, line-shaped patterns with widths of 60 to 100 nm were formed in the thermoplastic polymer by thermal compression using a previously patterned and treated silicon (Si) stamp. Annealing of the polymer under compression in a nanoimprinter following imprint resulted in a 10-fold improvement in the surface roughness of the polymer relative to spin-coated layers of P(VDF-TrFE-CFE). Patterning of distinct polymer structures on Si substrates (without residual layer) was achieved for micron scale structures. The processes presented here comprise a basis for the integration of P(VDF-TrFE-CFE) as an active material in nanoscale sensors and actuators.

A vibration-based piezoelectric energy harvester has received increasing attention as a potential power source for microelectronics because of its simplicity of design, operation, and fabrication of devices using microelectromechanical system (MEMS) technology. Energy harvesting provides unending sources of energy for low-power electronics such as wireless sensor nodes where replacement of batteries is not practically possible. Piezoelectric energy harvesters are widely considered because of their compact design, compatibility to MEMS devices, and ability to respond to a wide range of frequencies freely available in the environment. A model for cantilever-based piezoelectric energy harvester is designed and optimized by investigating the effect of seismic mass geometry on the potential generated. The effect of the shape geometry of the seismic mass on the resultant potential generated due to center of mass shift is calculated and compared. A seismic mass with a triangular-shaped geometry with fields concentrated at the tip of the triangle gives a resultant center of mass for a cantilever structure and the seismic mass at a higher point as compared with the rectangular or pyramidal shapes that were investigated. This shift in the center of mass of the combined geometry (cantilever beam and seismic mass) toward the applied pressure results in exerting a higher force and thus increasing the potential. This paper reports that an increased potential of 0.0533 V at a boundary load of 1 bar pressure (minimum feasible pressure) is generated by the energy harvester when a triangular-shaped seismic mass is used; this innovative shape is also compared with other geometries.

Numerous studies report the importance of nanoscale metallic features to increase the sensitivity of gas sensors, biodetectors, and for the fabrication of the new-generation plasmonic devices. So far, nanoimprint lithography has not shown the capability to pattern a metallic structure that would both be sub-15 nm and sufficiently thick to ensure electrical conductance. To overcome these limitations, we report a step and repeat nanoimprint lithography (SR-NIL) on a pre-spin-coated layer stack. This work reports the fabrication of sub-15-nm lines that are 15-nm thick and have a 50-nm-half-pitch grating with 35-nm-thick metal, which represents the new state of the art for SR-NIL.

Extreme ultraviolet (EUV) lithography is a promising candidate for next-generation lithography. To achieve an 11-nm node, a six-mirror EUV projection objective with a numerical aperture (NA) of 0.5 is designed with the grouping design method. In this design, pupil obscuration is introduced to decrease the angular spread on the mirrors, which still makes the six-mirror objective with aspheric surfaces sufficient for aberration correction. The grouping design allocates the complexity of designing a whole system to each of the mirror groups and could compatibly apply to designing EUV projection objectives with obscuration. The ×8 reduction design serves as an example for illustrating the grouping design principles for this type of system. In addition, the specific design forms with different reductions are presented and discussed. Design of these six-mirror objective systems provides potential solutions for 11-nm node EUV lithography.

A detailed analysis of the impact of pitch variations in block copolymer self-assembly patterns on defect density and placement errors inside lithographically defined trenches is presented. The presence of random variations in the pitch of nanopatterns resulting from the self-assembly of cylindrical phase block copolymer in open trenches (one-dimensional confinement) is experimentally demonstrated and confirmed by theoretical modeling. The simulations show that the intrinsic pitch spread is not affected when the same block copolymer is studied inside closed trenches (two-dimensional confinement) where the observed spread has a direct influence on placement and defectivity. The magnitude of the detrimental impact of the pitch variations on both defect density and placement accuracy in closed trenches is strongly dependent on trench length. These findings pose new design rules for future applications of directed self-assembly in semiconductor industry.

A lithography parametric yield estimation model is presented to evaluate the lithography distortion in a printed layout due to lithography hotspots. The aim of the proposed yield model is to provide a new metric that enables the possibility to objectively compare the lithography quality of different layout design implementations. Moreover, we propose a pattern construct classifier to reduce the set of lithography simulations necessary to estimate the litho degradation. The application of the yield model is demonstrated for different layout configurations showing that a certain degree of layout regularity improves the parametric yield and increases the number of good dies per wafer.

We have developed an extended gate field-effect-transistor (EGFET)-based carbon dioxide (CO₂) sensing system with a packaged Ti/Ag/AgCl/KCl-gel microreference electrode using microelectro-mechanical systems (MEMS) technology. The total dimensions of the proposed CO₂ sensing system are only 2.8×1.5×0.1  cm, which is approximately 30 times smaller than a conventional CO₂ sensing system (including the commercial Ag/AgCl RE). All of the manufacturing processes adopted in this work are compatible with standard planar technology and are very suitable for mass production. The presented planar reference electrode shows a very small offset voltage (−3.0  mV) and a very small potential drift (2.5 mV in 30,000 s) that is approximately equal to that of the commercial Ag/AgCl RE (1.6 mV in 30,000 s). Additionally, the implemented EGFET-based CO₂ microsensor with a coated CO₂ solid electrolyte and gas permeable membranes on the gate sensing area demonstrates a very high sensitivity (44.4  mV/decade) and very high sensing linearity (98.37%), while sensing CO₂ concentrations ranging from 0.25 to 50 mM. Furthermore, a very small hysteresis voltage (7.5 mV) was obtained during the sensing cycle of 2.5–5–25–50–25–5–2.5 mM; this result was achieved by improving the surface planarization and enlarging the sensing area of the EGFET to 1  mm².

This work reports our efforts on developing simple-to-use microfluidic devices for point-of-care diagnostic applications with recent extensions that include the trapping of microbeads using dielectrophoresis (DEP) and the modulation of the liquid flow using integrated microheaters. DEP serves the purpose of trapping microbeads coated with receptors and analytes for detection of a fluorescent signal. The microheater is actuated once the chip is filled by capillarity, creating an evaporation-induced flow tuned according to assay conditions. The chips are composed of a glass substrate patterned with 50-nm-thick Pd electrodes and microfluidic structures made using a 20-μm-thick dry-film resist (DFR). Chips are covered/sealed by low temperature (50°C) lamination of a 50-μm-thick DFR layer having excellent optical and mechanical properties. To separate cleaned and sealed chips from the wafer, we used an effective chip singulation technique which we informally call the “chip-olate” process. In the experimental section, we first studied dielectrophoretic trapping of 10-μm beads for flow rates ranging from 80  pL s⁻¹ to 2.5  nL s⁻¹ that are generated by an external syringe pump. Then, we characterized the embedded microheater in DFR-covered chips. Flow rates as high as 8  nL s⁻¹ were generated by evaporation-induced flow when the heater was biased by 10 V, corresponding to 270-mW power. Finally, DEP-based trapping and fluorescent detection of functionalized beads were demonstrated as the flow was generated by evaporation-induced flow after the microfluidic structures were filled by capillarity.

Point-of-care (PoC) biosensors continue to gain popularity because of the desire to improve cost performance in today’s health care industry. As cardiovascular disease (CVD) remains one of the top three leading causes of death in Asia, a tool that can help to detect CVDs is highly sought after. We present a high-sensitivity PoC biosensor that can be used to detect CVD biomarkers. To meet the requirements of a PoC biosensor, we adopted electrochemical methods as the basis of the detection. A more stable three-electrode configuration was miniaturized and put onto a biochip. To improve the detection sensitivity associated with the reduced size in the biochip, computer simulation was used to investigate several potential effective possibilities. We found that the electrolyte current density on the edge near the working electrode (WE) and counter electrode (CE) was higher. This was verified using an atomic force microscope to measure the surface potential. We then experimented with the configuration by lengthening the edge of the WE and CE without changing the area of the WE and CE and maintained the gap between the two electrodes. We found improved measurement efficiency with our newly developed biochip.