Array Of Through-holes Research Articles

Fabrication of through alumina vias (TAV) by ultrasonic micromachining for advanced packaging applications

This article presents the fabrication of a high aspect ratio through alumina-vias (TAV) by combining ultrasonic micromachining (USM), electroless plating, and copper electrodeposition. Various horn designs, i.e., tapered, stepped, exponential, and hybrid horns, were analyzed to achieve a uniform longitudinal vibration in a 6 × 6 multi-tip tool assembly. The modal analysis determined the horn length, and harmonic analysis provided the stress distribution and vibrational amplitude. The tapered horn design was selected for its superior vibration amplification and reduced stresses. Finite element modeling predicted the geometric profiles of the microvias at various USM parameters. Experimental validation showed less than 5 % error in the depths of the microvias. Using the optimized USM parameters, a 6 × 6 array of blind and through-holes was created in a 3 mm thick alumina substrate with an average feed rate of 180 μm/min. The average tool wear was observed to be 0.5 mm when drilling through 3 mm thick alumina. Electroless deposition created a ∼100 nm seed layer on the alumina substrate and achieved good adhesion with via sidewalls. The through-holes were partially filled with a 60 μm thick copper layer by electrodeposition to create through-alumina vias (TAV) that can be used as 3D interconnects in the packaging of high-power electronics.

Effects of Heat Treatment on Anodic Porous Alumina Membranes for Mass Spectrometry

Abstract Desorption ionization using through-hole alumina membrane (DIUTHAME) method is a mass spectrometry imaging (MSI) method that uses an anodic porous alumina membrane (APAM) with an array of submicron-sized through-holes as a surface-assisted laser desorption/ionization (SALDI) substrate. The DIUTHAME method is particularly promising for MSI because it does not generate interfering peaks in the low-molecular-weight region. However, the SALDI effect cannot be obtained if the nanostructures of the substrate are destroyed owing to laser irradiation before sample vaporization. APAMs that maintain their structures after irradiation with a high-intensity laser must be fabricated to realize highly sensitive measurements. In this study, we investigated the role of heat treatment suppressing the laser irradiation induced fracture of APAMs. We found that heat treatment at higher temperatures more effectively suppressed APAM fracture associated with laser irradiation. This result was attributed to the reduction of anion-derived impurities in APAMs upon heat treatment. The resulting heat-treated APAM is expected to serve as a substrate for highly sensitive and robust MSI.

Localized surface roughening to improve adhesion of electroless seed layer in through-glass vias

This article reports the improvement of the adhesion of the electroless seed layer deposited on glass substrates used in creating through-glass vias (TGV) by localized surface roughening. Four glass substrates having varying roughness characteristics were prepared by electrochemical discharge machining (ECDM) and ultrasonic machining (USM). The electroless nickel seed layer was deposited directly on glass without any adhesion layer, followed by electrodeposited copper layers. In-depth surface topography and morphology analysis reveal the mechanism behind the improved adhesion during standard peel and cross-hatch adhesion tests, which were used to determine the interlayer adhesion.Localized roughening techniques generated specific microfeatures, i.e., microgrooves (in USM) or ridges (in ECDM), increasing the surface area. These features acted as interlocking/nucleation sites to hold the electroless nickel atoms, resulting in higher interfacial adhesion. USM-roughened samples exhibited stronger interfacial adhesion than their ECDM-roughened counterparts, which indicated that the interlayer adhesion depends on topography and the roughened surface's morphology. The surface with negative skewness and positive excess kurtosis promotes mechanical interlocking, offering a promising strategy for enhancing interlayer adhesion. Finally, conformal deposition in a 6 × 6 array of through-holes having an aspect ratio of ∼4 was also demonstrated.

MEMS nozzle for dry-capturing lily pollens in array and fixing on culture media for plasma bio-applications

A nozzle device featuring a micro-electromechanical system (MEMS) was developed to realize a series of advanced micromanipulation steps for capturing pollens from flower stamen and fixing them in arrays on culture media without cell damage. The MEMS nozzle, which has an array of through-holes with counterbores, was fabricated by the photolithography and Si etching. During the manipulation, the pollen in the air was captured in the counterbores due to the negative pressure applied from the nozzle backside. When the device with the captured pollen was moved into the liquid culture media of the gelatin, the liquid was sucked into each counterbore, so that the captured pollen was covered. By cooling the culture media down and switching off negative pressure, the controlled release of sucked cells without damage and the fixation in array on solid culture media were achieved. Through experiments implemented by the nozzle, the positive effect of plasma-treated water on the pollen growth was verified. The microarray strategy presented in this work made the cell experiments and result analysis more effective, especially for the plasma bio-applications.

Method to Change the Through-Hole Structure to Broaden Grounded Coplanar Waveguide Bandwidth.

A grounded coplanar waveguide (GCPW), as a millimeter wave special transmission line, can be used to calibrate broadband oscilloscope probes. A method to change the through-hole structure to widen the GCPW is investigated in this paper. The effect of the through-hole array on the band-width of the GCPW is investigated and verified using COMSOL Multiphysics simulation software. Finally, the S-parameters of the fabricated GCPWs are measured by a vector network analyzer, and the results show that they have an insertion loss > -3 dB and return loss < -10 dB in the frequency range of DC to 60 GHz, which satisfies the design requirements.

A polarization converter array based on microcavity patterned hydrophobic layer induced twisted-radial liquid crystals

We report a facile method to prepare an array of liquid-crystal polarization converters (LCPCA) based on hydrophobic microcavity arrays. The reactive ion etching (RIE) technique was chosen to treat the homeotropic polyimide (PI⊥) layers through a metal mask with a through-hole array. Under the selective RIE treatment, a hydrophobic–hydrophilic pattern is obtained due to the increase in surface energy in the etched area from ∼34.6 to ∼73.2 mN/m. The etched area forms a microcavity with a diameter of 520 μm, depth of ∼23 nm, and center distance of 690 μm, which is consistent with the dimensions of the metal mask. Since the walls of the microcavity retain hydrophobicity, the liquid-crystal (LC) molecules show a radial arrangement in the microcavity. Combining a substrate covered by a parallel rubbed homogeneous polyimide (PI∥) layer with the substrate covered by a microcavity-patterned PI⊥ layer can form a “sandwich” structure. The LC molecules in the microcavities are arranged in a twisted-radial texture, which can convert linearly polarized light to radially or azimuthally polarized light depending on the polarization direction of the incident light. The proposed method has the merits of simple steps, controllable size, and easy to fabricate large-area arrays. Our LCPCA has potential applications in tight focus, material processing, biological tissue analysis, particle capture, and optical data storage.

Process Optimization and Performance Evaluation of TSV Arrays for High Voltage Application.

In order to obtain high-quality through-silicon via (TSV) arrays for high voltage applications, we optimized the fabrication processes of the Si holes, evaluated the dielectric layers, carried out hole filling by Cu plating, and detected the final structure and electric properties of the TSVs. The Si through-hole array was fabricated in an 8-inch Si substrate as follows: First, a blind Si hole array was formed by the Si deep reactive etching (DRIE) technique using the Bosch process, but with the largest width of the top scallops reduced to 540 nm and the largest notch elimidiameternated by backside grinding, which also opens the bottom ends of the Si blind holes and forms 500-μm-deep Si through holes. Then, the sidewalls of the Si holes were further smoothed by a combination of thermal oxidation and wet etching of the thermal oxide. The insulating capability of the dielectric layers was evaluated prior to metal filling by using a test kit. The metal filling of the through holes was carried out by bottom-up Cu electroplating and followed by annealing at 300 °C for 1 h to release the electroplating stress and to prevent possible large metal thermal expansion in subsequent high-temperature processes. The TSV arrays with different hole diameters and spacing were detected: no visible defects or structure peeling was found by scanning electron microscopy (SEM) observations, and no detectable interdiffusion between Cu and the dielectric layers was detected by energy dispersive X-ray (EDX) analyses. Electric tests indicated that the leakage currents between two adjacent TSVs were as low as 6.80 × 10-10 A when a DC voltage was ramped up from 0 to 350 V, and 2.86 × 10-9 A after a DC voltage was kept at 100 V for 200 s.

Electrode wear prediction and offline compensation for micro-EDM drilling through-hole array using geometry simulation

Electrode wear prediction and offline compensation for micro-EDM drilling through-hole array using geometry simulation

Lightweight Through-Hole Copper Foil as a Current Collector for Lithium-Ion Batteries.

In the past few decades, much effort has been dedicated to improve electrochemical performance of lithium-ion batteries (LIBs) through material design. Less attention, however, has been paid to structure engineering of battery components, which is an effective way for improving the electrochemical performance of LIBs. In this work, a lightweight Cu current collector with a through-hole array and columnar crystal on the surface (CC/THCu) was designed and fabricated using a nanosecond ultraviolet laser and electrodeposition processing to enhance specific capacity and cycle stability of LIBs. The synergistic effect of the columnar crystal and through-hole structure for improving electrochemical performances of LIBs assembled with the CC/THCu current collector was investigated. The results show that the complex structure provides spaces for volume expansion and reduces volume variation. When the hole fraction reaches 20%, the weight loss of CC/THCu is 28.41%. The corresponding LIB with the 20% hole fraction CC/THCu shows a high residual capacity rate of 81.2% and enhanced specific capacity (55.9% compared to the LIB with a bare Cu current collector). At a high rate of 1 C, the remaining specific capacity of the LIB with the CC/THCu current collector is better than that with the bare Cu current collector after 200 cycles. The CC/THCu current collector effectively improves the specific capacity and cycle stability of LIBs in contrast to the bare Cu current collector.

Highly Ordered Alumina Through-Hole Membranes Having Reduced Hole Intervals: 30–50 nm

We investigated the dependence of the solubility of the oxide layer formed by anodization of Al on the concentration of sulfuric acid. As a result, it was found that the solubility of anodic porous alumina formed in sulfuric acid electrolyte could be controlled by adjusting the concentration of sulfuric acid. On the basis of these results, highly ordered alumina through-hole membranes with reduced hole intervals, 30–50 nm, were formed by two-layer anodization, where one of the oxide layers was selectively dissolved in accordance with the concentration of sulfuric acid used for anodization in the postetching treatment. The obtained ordered alumina through-hole membranes with reduced hole intervals are expected to be applied to various functional devices requiring a highly ordered through-hole array of reduced size.

Polydimethylsiloxane microfluidic films for in vitro engineering of small-scale neuronal networks

Polydimethylsiloxane microfluidic devices have become standard tools in cell engineering research. However, through-holes where cells access the microchannels are usually fabricated manually using biopsy punches, making it difficult to create a large array of sub-mm sized through-holes. Here, we present a fabrication process for a thin-film microfluidic device containing an array of through-holes, which are as small as 100 μm by 100 μm and span 10 mm by 10 mm. A proof-of-concept application of the device to neuronal patterning experiments shows that spatially complex network dynamics emerge when a non-random connectivity is imposed to cultured neuronal networks. We also demonstrate that the coupling strengths between neuronal modules, a major factor that defines the global network dynamics, can be effectively modulated by varying the microchannel widths. This work opens a new application of microfluidic devices to multicellular systems comprised of several tens to hundreds of neurons.

A novel two-layer-integrated microfluidic device for high-throughput yeast proteomic dynamics analysis at the single-cell level.

Current microfluidic methods for studying multicell strains (e.g., m-types) with multienvironments (e.g., n-types) require large numbers of inlets/outlets (m*n), a complicated procedure or expensive machinery. Here, we developed a novel two-layer-integrated method to combine different PDMS microchannel layers with different functions into one chip by a PDMS through-hole array, which improved the design of a PDMS-based microfluidic system. Using this method, we succeeded in converting 2×m×n inlets/outlets into m+n inlets/outlets and reduced the time cost of loading processing (from m×n to m) of the device for studying multicell strains (e.g., m-types) in varied multitemporal environments (i.e., n-types). Using this device, the dynamic behavior of the cell-stress-response proteins was studied when the glucose concentration decreased from 2% to a series of lower concentrations. Our device could also be widely used in high-throughput studies of various stress responses, and the new concept of a multilayer-integrated fabrication method could greatly improve the design of PDMS-based microfluidic systems.

Polishing tool with phyllotactic distributed through-holes for photochemically combined mechanical polishing of N-type gallium nitride wafers

In this work, we further developed the photochemically combined mechanical polishing (PCMP) method for finishing N-type gallium nitride (GaN) wafers. A core improvement is to design a novel polishing tool with phyllotactic distributed through-holes, through which the wafer surface underneath through-holes can receive ultraviolet (UV)-light for the photochemical oxidation, while the rest parts undergo mechanical polishing. During PCMP, the co-rotation of the wafer and polishing tool allows the wafer surface to undergo the uniform and high-frequency conversion of oxidation and polishing. Based on the designed PCMP system and apparatus, the fundamental issues arising from such an alternate processing mode, which is different from the parallel mode of conventional chemical mechanical polishing (CMP), were investigated. Results show that the technical features of PCMP depend on the nature of the photochemical oxidation of wafers themselves if the mechanical polishing procedure can sufficiently remove oxides in time. The material removal rate (MRR) is inversely proportional to the dislocation density of wafers. Under acidic conditions, the oxidation proceeds by the GaN monocrystal step orientation, allowing PCMP to clear surface/subsurface damages (SSDs) and to prepare step-terrace structures on the wafer surface. When the polishing solution (pH = 1.5) includes 0.1 M K2S2O8 oxidants and 10 wt% SiO2 abrasives, the surface roughness Sa attains 0.21 nm in 10 × 10 μm2, and the MRR reaches 275.3 nm/h. The present study shows that the phyllotactic distributed through-hole array structure designed for polishing tools offers rich possibilities for the innovation of polishing technologies combining with various oxidation approaches.

A Multiplexed Microarray Platform for Targeted Proteomics

A Multiplexed Microarray Platform for Targeted Proteomics

High filling rate digital PCR through-hole array chip with double independent S-shaped flow channels.

Sample digital technology is a powerful method for absolute quantification of target molecules such as nucleic acids and proteins. The excellent sample stability and mass production capability has enabled the development of microwell array-based sample digitizing methods. However, in current microwell array chips, samples are loaded by the liquid scraping method, which requires complex manual operation and results in a low filling rate and limited hole filling uniformity. Here, we perform sample loading of a through-hole array chip by a microfluidics-driven method and design a double independent S-shaped flow channels sandwiched through-hole array chip. Because of the capillary force and capillary burst pressure, the sample flowing in the channel can be trapped into through-holes, but cannot flow through the other side. Via air flow and displacement of the remaining sample in the channel, the sample can be partitioned consistently, with zero surplus sample residue in the channel. We evaluated the actual performance of the sample-loading process: the chip enables 99.10% filling rate of 18 500 through-holes, with a grayscale coefficient of variation value of 6.03% determined from fluorescence images. In performing digital polymerase chain reaction on chip, the chip demonstrates good performance for the absolute quantification of target DNA. The simple and robust design of our chip, with excellent filling rate and microsample uniformity, indicates potential for use in a variety of sample digitization applications.

Engineering of high quality factor THz metasurfaces by femtosecond laser ablation

We report on the realization of high Q metasurfaces operating in the THz frequency range by femtosecond laser ablation applied to a nanometric metallic layer over a silicon substrate. Two different fabrication methods are used to develop periodic patterns whose basic elements are in form of an array of through-holes or metallic islands. The response of the resulting structures is characterized using a time-domain spectrometer in the frequency range 0.3–1.5 THz. The experimental findings are compared with the predictions of full wave electromagnetic simulations. The fairly good agreement between simulation predictions and experimental findings evidences that the proposed approach can offer a facile way to the elaboration of THz metasurfaces.

Optical Directivity Design Using Through-hole Array Silicon Chip

In this letter, we report a method of designing the optical sensor directivity without using an optical lens. The directivity is realized by attaching the designed through-hole array chip on an optical sensor surface. The through-hole array chip can be formed by a conventional semiconductor manufacturing technique. The directivity can be designed by adjusting the through-hole size and the chip thickness. Its performance is evaluated using the manufactured test chip. For visible light, when the through hole width is $25~\mu \text{m}$ and the partition wall thickness between them is $10~\mu \text{m}$ , the directivity is about 4 ° and the light transmittance is about 31%. Although directivity is slightly broad for near-infrared light, it can be designed utilizing the trade-off between directivity and transmittance. The proposed method enables us to reduce the sensor size to one-tenth or less of that using optical lenses.

Bragg-Mirror Suppression for Enhanced Bandwidth in Terahertz Photonic Crystal Waveguides

Terahertz technology is being accelerated by photonic crystal waveguides that are implemented with an array of through-holes in an intrinsic silicon slab. Such waveguides show promise to realize compact terahertz systems. However, photonic crystal waveguides were originally developed in the infrared range, where small relative bandwidth is acceptable for communications applications. Greater relative bandwidth is desirable for the lower-frequency terahertz range, and hence our aim is to increase the bandwidth of terahertz photonic crystal waveguides. To this end, the defect-row structure of the photonic crystal waveguide track is adapted in order to suppress the Bragg-mirror effects that are typical of conventional photonic crystal waveguides. Specifically, the waveguide track is clad with semi-circular holes. The resultant structure is found to guide radiation efficiently over a bandwidth from 277 to 435 GHz—a six-fold increase in relative bandwidth over existing terahertz photonic crystal waveguides—and hence it may find applications in terahertz communications. Although simulations show that the waveguide is over-moded, experiments indicate that only the desired dominant mode is strongly excited in practice.

MEMS Flow Sensor Using Suspended Graphene Diaphragm With Microhole Arrays

This letter reports a miniature flow sensor using a suspended composite membrane of graphene and silicon nitride containing an array of microscale through-holes. As a fluid flow passes through these microholes, the graphene layer of the composite membrane is stressed to change its electrical resistance due to the piezoresistive effect of graphene. The creation of the microholes in graphene allows for a wide dynamic range of the sensor from 5 to 56 m/s of air flow velocity. The sensor also exhibits an air flow rate sensitivity of $\sim 7\times 10^{ {-8}}$ (m/s)−1. [2018-0133]

Crystallography on a chip - without the chip: sheet-on-sheet sandwich.

Crystallography chips are fixed-target supports consisting of a film (for example Kapton) or wafer (for example silicon) that is processed using semiconductor-microfabrication techniques to yield an array of wells or through-holes in which single microcrystals can be lodged for raster-scan probing. Although relatively expensive to fabricate, chips offer an efficient means of high-throughput sample presentation for serial diffraction data collection at synchrotron or X-ray free-electron laser (XFEL) sources. Truly efficient loading of a chip (one microcrystal per well and no wastage during loading) is nonetheless challenging. The wells or holes must match the microcrystal size of interest, requiring that a large stock of chips be maintained. Raster scanning requires special mechanical drives to step the chip rapidly and with micrometre precision from well to well. Here, a `chip-less' adaptation is described that essentially eliminates the challenges of loading and precision scanning, albeit with increased, yet still relatively frugal, sample usage. The device consists simply of two sheets of Mylar with the crystal solution sandwiched between them. This sheet-on-sheet (SOS) sandwich structure has been employed for serial femtosecond crystallography data collection with micrometre-sized crystals at an XFEL. The approach is also well suited to time-resolved pump-probe experiments, in particular for long time delays. The SOS sandwich enables measurements under XFEL beam conditions that would damage conventional chips, as documented here. The SOS sheets hermetically seal the sample, avoiding desiccation of the sample provided that the X-ray beam does not puncture the sheets. This is the case with a synchrotron beam but not with an XFEL beam. In the latter case, desiccation, setting radially outwards from each punched hole, sets lower limits on the speed and line spacing of the raster scan. It is shown that these constraints are easily accommodated.