Deep Reactive Ion Etching Technique Research Articles

Large-Area Self-Assembled Monolayer of Silica Microspheres by Convective Assembly

We reported here a convective assembly process for the formation of large-area self-assembled monolayers of silica microspheres on silicon and glass substrates. Uniformly coated monolayers of silica spheres were achieved on silicon wafers with and without coated SiN2 of 3 inch of diameter and large glass substrate of 6 × 6 in2 in size. The coating of large-area uniform monolayers of silica microspheres was characterized with scanning electron microscopy and optical microscopy. The mechanism of the convective assembly has been explained by the convective flux that is generated by capillary immersion force caused from the solution evaporation and hydrodynamic drag force. The patterns of silica microspheres were transferred to the silicon substrates using a deep reactive ion etching technique. It is found that textured silicon reduced the reflectance of silicon substrate from 52.2% to 33.2% around 400 nm and from 33.9% to 19.5% around 1,100 nm. The rapid self-assembled monolayer with silica microspheres provided a glimpse at the wide range of coating and photonic device applications where convective assembly can be used.

Memristive Biosensors Under Varying Humidity Conditions

We attempt to examine the potential of silicon nanowire memristors in the field of nanobiosensing. The memristive devices are crystalline Silicon (Si) Nanowires (NWs) with Nickel Silicide (NiSi) terminals. The nanowires are fabricated on a Silicon-on-Insulator (SOI) wafer by an Ebeam Lithography Technique (EBL) process that allows high resolution at the nanoscale. A Deep Reactive Ion Etching (DRIE) technique is used to define free-standing nanowires. The close alignment between Silicon (Si) and Nickel-Silicide (NiSi) terminals forms a Schottky-barrier at their junction. The memristive effect of the fabricated devices matches well with the memristor theory. An equivalent circuit reproducing the memristive effect in current-voltage (I-V) characteristics of our silicon nanowires is presented too. The memristive silicon nanowire devices are then functionalized with anti-human VEGF (Vascular Endothelial Growth Factor) antibody and I-V characteristics are examined for the nanowires prior to and after protein functionalization. The uptake of bio-molecules linked to the surface of the memristive NWs is confirmed by the increased voltage gap in the hysteresis curve. The effects of varying humidity conditions on the conductivity of bio-modified memristive silicon nanowires are deeply investigated.

Vibration interference analysis and verification of micro-fluidic inertial switch

The micro-fluidic inertial switch based on liquid metal utilizes the moving mercury droplet to close the switch under the action of acceleration, which is characterized by no moving parts, small contact resistance, long service life and large current. In addition to the requirement of response time, accuracy and reliability, the micro-fluidic inertial switch needs to overcome the impact of the ambient vibration. The influence of the ambient vibration on the performance of switch is investigated by loading pulse or sinusoidal interference signals in the X, Y and Z direction. The numerical results suggest that the performance of micro-fluidic inertial switch is greatly affected by impact interference signal in X sensitive direction as compared with low frequency harmonic signal. If the impact signal with high amplitude lasts only for a short time, the wrong operation might also occur. The interference signals in insensitive direction have a relatively small impact on the performance of switch, and the impact of interference signal can be reduced by reasonable structural design. Finally, anodic bonding, deep reactive ion etching (DRIE) and sputtering technique are adopted to fabricate the micro-fluidic inertial switch. The acceleration threshold of the prototype is tested. The experiment results agree with the numerical results, which indicate that the simulation method is valid.

Formation of Highly Ordered Silicon Nanowires by a High-Speed Deep Etching

We report the formation of highly ordered vertical silicon nanowires using a hydrogen-assisted deep reactive ion etching technique. Nanosphere lithography with 460- and 300-nm polystyrenes is employed to realize the etching mask for fabrication of sub-50-nm patterns. SiNWs can be achieved consequently with a top-down process using vertical etching of silicon where the underetching can be limited to 10 nm. By means of a patterned mesh-like structure, we have improved the arrangement order of the nanospheres and nanorods. The etching is performed using three gases of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> in two subsequences of etching and passivation, and in a low plasma density capacitive coupled RIE system. This process is capable of etching high aspect ratio nanometric features with high etching rate. Values for aspect ratio around 100 for sub-100-nm SiNW with etching rate of 0.8 μm/min are achieved. Applying proper process parameter can result in conical tip nanorods, which have the potential for large-scale fabrication of nanowire emitter arrays.

Wafer-Level Fabrication of a Fused-Quartz Double-Ended Tuning Fork Resonator Oscillator Using Quartz-on-Quartz Direct Bonding

In this letter, a novel process to fabricate high- $Q$ fused-quartz micromechanical resonators is demonstrated. Plasma-assisted quartz-on-quartz direct bonding at a low temperature in combination with quartz deep-reactive ion etching technique enables a simple wafer-level fabrication of self-mounted, electrostatically driven fused-quartz resonators. A 27-kHz capacitively transduced double-ended tuning fork fused-quartz resonator oscillator is successfully fabricated using the developed process. A high resonator $Q$ -factor of 68000 is obtained, and the constructed oscillator shows a signal-to-noise ratio of 70 dB.

Novel Projection Display Pixels Using Micro Vessel Structures

In this paper Electrochromic based micro-mirrors fabrication has been investigated on silicon substrates using a highlyprogrammable deep reactive ion etching technique. Silicon based micro structures have been used as micro containers for Li+ based electrolyte.Covering these micro vessels with WO3 coated ITO electrodes as electrochromic layer, leads to transparent or opaque interfaces which later will be used as image pixels. Passive addressing of micro-mirrors if feasible between mentioned ITO electrodes on top and silicon n+ doped lines at the bottom of micro structures. Desired image can be achieved by addressing each or a cluster of pixels.

Measurement of pressure drop and flow resistance in microchannels with integrated micropillars

In the present study, we investigate single phase fluid flow through microchannels with integrated micropillars to calculate the pressure drop and flow resistance. The microchannels, which contain micropillars arranged in square and staggered arrangement, are fabricated in silicon substrate using standard photolithography and deep reactive ion etching (DRIE) techniques. The DRIE technique results in precise and accurate fabrication with smooth and vertical wall profiles. Pressure drop measurements are performed on microchannels with integrated micropillars under creeping flow regime over a range of water flow rates from 50 to 600 μl/min. It is observed that the pressure drop varies linearly with increasing flow rates. Flow resistance ( $$\Updelta P/Q$$ ) is calculated using the pressure drop values and is found to be decreasing as the Darcy number ( $$\sqrt{K/h^2}$$ ) increases. In general, the square arrangement of pillars offers higher resistance to flow than their staggered counterparts. It is observed that the existing theoretical models fail to accurately predict the permeability of the microchannel with integrated micro-pillars, particularly for cases where the micropillars have smooth and accurate geometric conformity, as obtained in the microfabricated structures used in the present study.

Hydrodynamic chromatography separations in micro‐ and nanopillar arrays produced using deep‐UV lithography

We report on a series of hydrodynamic chromatography separations conducted in micropillar array columns with an interpillar distance spacing of, respectively, 1.00, 0.70, and 0.47 μm. The columns have been produced using state-of-the-art deep-UV lithography and deep reactive ion etching techniques. Despite the fact that the efficiency was smaller than theoretically possible (due to fabrication limitations and significant injection and detection band broadening), it was nevertheless possible to separate mixtures of fluorescein isothiocyanate (used as the t(0) -marker) and 20- and 40-nm polystyrene beads. With the smallest interpillar distance, a resolution of R(s) = 0.5 between the 20- and 40-nm particles could be obtained in 90s over a column length of 4 cm. The selectivity obtained in the pillar array columns was found to be very similar to that observed in packed-bed columns. By detecting the fluorescent signals in a 90-μm-deep detection groove at the end of the column, the signal-to-noise ratio could be enhanced up to 150 times.

Comparison of two experimental methods for the mechanical characterization of thin or thick films from the study of micromachined circular diaphragms

The purpose of this study was to compare two experimental methods and evaluate the effectiveness of a set of analytical models in order to measure the initial stress and the Young's modulus value of thin and thick film materials. Two types of experiments were performed on micromachined circular diaphragms: bulge testing and vibrometry. The range of validity and accuracy of the analytical models with respect to the vibration of the diaphragms was discussed from the finite element simulations. It was shown that the a/t ratio should be considered carefully to determine the value of the Young's modulus by vibrometry with an acceptable error. A relative error of approximately ±10% on E was obtained for a/t ≤ 750. For 750 ≤ a/t ≤ 1000, the value of the dimensionless parameter k must also be considered. It has been shown that the residual stress value can be obtained with an accuracy of 10% or less, given that k > 12. As an illustration, experimental methods and models were applied to the characterization of a thick electroplated gold film and a sputter-deposited Inconel thin film. Circular structures were defined by vertical sidewalls etched on the back of a Si wafer using the deep reactive ion etching technique. In addition to analytical models, parametric finite element simulations and a design optimization technique were used to determine the material's mechanical properties. The static deflections of the diaphragms were measured as a function of the applied pressure. The resonant frequencies and mode shapes of the vibrating structures were observed under vacuum by white-light interferometric microscopy. For gold, it was found that E = (53 ± 20) GPa and σ(0) = (180 ± 10) MPa. For Inconel, it was found that E = (157 ± 14) GPa and σ(0) = (172 ± 5) MPa.

Three-dimensional etching of silicon substrates using a modified deep reactive ion etching technique

We report realization of highly featured three-dimensional micro- and nano-structures on silicon substrates with a single masking layer using a hydrogen-assisted deep reactive ion etching process. Three gases of oxygen, hydrogen and SF6 are used in a sequential passivation and etching process to achieve high aspect ratio features. By controlling the flows of these gases and the power and timing of each subsequence, it is possible to achieve desired deep vertical etching with controlled underetching and recovery, yielding three-dimensional features directly on silicon substrates. Etch rates up to 0.75 µm min−1 have been obtained with a low plasma power density of 1 W cm−2. Also features with a controllable underetching with more than 8 µm in sidewall recession have been achieved. The three-dimensional structures can be used as a mold for polymers as well as a holding substrate for projection display applications where an electro-chromic material (WO3) has been used.

P‐184: Application of Deep Micromachining of Silicon Substrates to Realize a Novel Electrochromic Based Projection Display

AbstractIn this paper, we report on the realization of miniaturized projection displays on silicon substrates using a highly programmable deep reactive ion etching technique. The micro‐machined silicon substrates have been used to incorporate Liionic electro‐chromic solutions. The use of tungsten oxide (WO3) in conjunction with the ITO electrodes, leads to a transparent or opaque interfaces which can be used as a method to distinguish different spots in an image, provided an external light source is exploited. The formation of highly complex three‐dimensional structures is feasible during the deep reactive ion etching of silicon wafers, while desired under‐etching is achieved by controlling the etching parameters. The evolution of cup‐like micro‐mirrors can be carried out at micrometer sizes leading to ultra‐high resolution projection systems. A passive addressing is feasible between the top ITO‐lines placed on a glass substrate and the bottom cavity‐holding substrate. By addressing individual or clusters of pixels one can achieve desired images.

DESIGN AND FABRICATION OF MICRONOZZLES

Micronozzle, a key component in micropropulsion system, has been designed and fabricated. Quasi 1D inviscid theory was used in designing a series of conical micronozzles of different expander half-angles (10°-50°). Aerospike micronozzle, a promising candidate to achieve high performance propulsion system, was designed with Angelino method (or Approximate method). Both micronozzles were fabricated using soft lithography, an inexpensive and relatively simple technique comparing to well-established deep reactive ion etching (DRIE) technique, with polydimethylsiloxane (PDMS) as structural material. Micronozzles with two different nozzle throat width, 53.5µm and 107µm, were fabricated for comparison. Microscopic inspections reveal 107µm is the more producible nozzle throat width with current equipments. The PDMS-based micronozzle can be used as cold gas microthruster system for micro- and nanosatellites.

Macroporous silicon hydrogen diffusion layers for micro-fuel cells: From planar to 3D structures

In this study, we demonstrate the possibility of using macroporous silicon as a hydrogen diffusion layer in integrated planar and 3D proton exchange membrane micro fuel cells (PEMFC). In this context, silicon electrochemical etching is presented as an interesting alternative to costly deep reactive ion etching techniques. In the case of planar PEMFC, a maximum density power of 250mW/cm2 was measured. The second objective of our work is to enhance the fuel cell active surface. One way to increase power densities is to chemically texture the surface of the GDL supporting the fuel cell. Then, the porous silicon electrochemical etching process is applied to these 3D silicon substrates. Flow rates measured through these fully porous 3D structures are compared with planar diffusion layers.

Characterization of sidewall roughness for silicon microstructures in micro actuator

Thermal micro actuators are fabricated using deep reactive ion etching (DRIE) technique on silicon on insulator (SOI) substrates. The sidewalls of silicon microstructure in micro actuator are used as optical interfaces with the fibe rs. Line edge roughness (LER) of reflective sidewalls is essential to device performance. A method is presented through analyzing high-resolution top-down scanning electron microscope (SEM) images to characterize sidewall line edge roughness (LER) of Si microstructures in thermal micro actuator, only conventional SEM scanning technique is required.

Design and fabrication of a new two-dimensional pneumatic micro-conveyor

This paper presents the design, fabrication and testing of a new two-dimensional pneumatic conveyor for micro-chips manipulation. The conveyor can levitate and move flat objects to a desired position using controlled air-flow. The structure consists of a sandwich of silicon–silicon–Pyrex layers fabricated using MEMS technologies, in which deep reactive ion etching (DRIE) and ultrasonic micro-machining techniques were used for the fabrication of silicon and Pyrex chips, respectively. The silicon–silicon wafers and silicon–Pyrex wafers were bonded by gold eutectic bonding and anodic bonding techniques, respectively. The device array is about 9 mm × 9 mm of surface dimension and composed of 8 × 8 pneumatic micro-conveyors. A micro-conveyor has four nozzles that can generate inclined air-jets allowing four conveyance directions. We demonstrate experimentally that a 3 mm diameter object of 2 mg weight can be conveyed to a desired position with intermittent air-flow of 20 kPa.

Nanograss and nanostructure formation on silicon using a modified deep reactive ion etching

Silicon nanograss and nanostructures are realized using a modified deep reactive ion etching technique on both plane and vertical surfaces of a silicon substrate. The etching process is based on a sequential passivation and etching cycle, and it can be adjusted to achieve grassless high aspect ratio features as well as grass-full surfaces. The incorporation of nanostructures onto vertically placed parallel fingers of an interdigital capacitive accelerometer increases the total capacitance from 0.45 to 30 pF. Vertical structures with features below 100 nm have been realized.

BioMEA™: A versatile high-density 3D microelectrode array system using integrated electronics

Microelectrode arrays (MEAs) offer a powerful tool to both record activity and deliver electrical microstimulations to neural networks either in vitro or in vivo. Microelectronics microfabrication technologies now allow building high-density MEAs containing several hundreds of microelectrodes. However, dense arrays of 3D micro-needle electrodes, providing closer contact with the neural tissue than planar electrodes, are not achievable using conventional isotropic etching processes. Moreover, increasing the number of electrodes using conventional electronics is difficult to achieve into compact devices addressing all channels independently for simultaneous recording and stimulation. Here, we present a full modular and versatile 256-channel MEA system based on integrated electronics. First, transparent high-density arrays of 3D-shaped microelectrodes were realized by deep reactive ion etching techniques of a silicon substrate reported on glass. This approach allowed achieving high electrode aspect ratios, and different shapes of tip electrodes. Next, we developed a dedicated analog 64-channel Application Specific Integrated Circuit (ASIC) including one amplification stage and one current generator per channel, and analog output multiplexing. A full modular system, called BIOMEA™, has been designed, allowing connecting different types of MEAs (64, 128, or 256 electrodes) to different numbers of ASICs for simultaneous recording and/or stimulation on all channels. Finally, this system has been validated experimentally by recording and electrically eliciting low-amplitude spontaneous rhythmic activity (both LFPs and spikes) in the developing mouse CNS. The availability of high-density MEA systems with integrated electronics will offer new possibilities for both in vitro and in vivo studies of large neural networks.

Development and fabrication of nanoporous silicon-based bioreactors within a microfluidic chip

Multi-scale lithography and cryogenic deep reactive ion etching techniques were used to create ensembles of nanoporous, picolitre volume, reaction vessels within a microfluidic system. The fabrication of these vessels is described and how this process can be used to tailor vessel porosity by controlling the width of slits that constitute the vessel pores is demonstrated. Control of pore size allows the containment of nucleic acids and enzymes that are the foundation of biochemical reaction systems, while allowing smaller reaction constituents to traverse the container membrane and continuously supply the reaction. In this work, a 5.4 kb DNA plasmid was retained within the reaction vessels and labeled under microfluidic control with ethidium bromide as an initial proof-of-principle. Subsequently, a coupled enzyme reaction, in which glucose oxidase (GOX) and horseradish peroxidase (HRP) were contained and fed with a substrate solution of glucose and Amplex Red to produce fluorescent resorufin, was carried out under microfluidic control and monitored using fluorescent microscopy. The fabrication techniques presented are broadly applicable and can be adapted to produce devices in which a variety of high aspect ratio, nanoporous silicon structures can be integrated within a microfluidic network. The devices shown here are amenable to being scaled in number and organized to implement more complex reaction systems for applications in sensing and actuation as well as fundamental studies of biological reaction systems.

Influence of process route on membrane profile and Q-factor of an acoustic resonator sensor

Membranes for acoustic resonator sensors can be fabricated using deep reactive ion etching techniques. To produce the pattern a mask is needed. The most common materials used for the mask are photoresist and silicon dioxide. This paper explores what influence the choice of the mask material and etching parameters has on the profile of the membrane and as such on the Q-factor of the resonator. Results are presented for membranes fabricated using photoresist, silicon dioxide, aluminum, alumina, or combinations of these materials as etch masks. Best results were achieved using very thin (∼27 nm) alumina films patterned in a lift-off process as a mask and following the Bosch deep reactive ion etch by an isotropic etch to get a smoother surface.

Fabrication and Characterization of Vanadium Doped PbZr0.53Ti0.47O3 (PZTV) Force Sensors for Minimally Invasive Surgical Tools

Minimally invasive surgery (MIS) is the most exciting and rapidly developing area where force sensing is actually of central importance. Micro-machined piezoelectric sensors can be integrated onto MIS tools for improved diagnosis and treatment monitoring. A micro-machined freestanding vanadium doped-lead zirconate titanate (PZTV) force sensor is fabricated using five masks process incorporating deep reactive ion, ion beam and wet-chemical etching techniques. The PZTV sensor is designed as a parallel plate capacitor structure in which the sol-gel prepared 1-μ m thick PZTV film is sandwiched between top (Au/Cr) and bottom (Pt/Ti) metal electrodes mounted on a thin Si membrane. This paper also describes a new wet chemical approach for patterning vanadium doped-PbZr0.53Ti0.47O3 films. The etch recipe provided excellent etch control, minimized undercut, preserved the photoresist mask, and effectively removed the residues on the etched surfaces. A high etch rate (200 nm/min), high selectivity with respect to photoresist, and limited under-cutting (1.5:1, lateral : thickness) were obtained. The fabricated force sensor exhibited good ferroelectric properties. The current fabrication procedure and electrical analysis can be considered as a breakthrough for fabricating freestanding PZT force sensor in any desired shape and dimensions, as well as a good example of ferroelectric microdevices.