Wet Etching Research Articles

Comparative study of pool boiling heat transfer on different subtractive surfaces

• The subtractive micro-nano structured surfaces based on sandblasting were prepared. • The structured surface facilitates heat transfer depends on synergistic benefit of the influencing factors. • The characteristic parameters of the micro-nano surface have been quantitatively analyzed. • The visualization study has been carried out on the micro-nano structured surface. The preparation of stable surfaces to improve the heat transfer performance can make the equipment operate safely and bring significant economic benefits. Using sandblasting and ultrasonic wet etching techniques, copper surfaces were subtracted to prepare the microscale structures (MS) and nanoscale structures (NS) in this study. Then, these two special subtractive structures were composited together to form a hybrid micro-nano structured (HMS) surface. Nucleate pool boiling experiments were carried out on the prepared surfaces with different structures at atmospheric pressure. The effect of surface modification on key parameters such as critical heat flux (CHF) and heat transfer coefficient (HTC) were investigated. Through the quantitative analysis of roughness, surface area ratio and apparent contact angle, potential mechanisms affecting nucleate boiling were explored. Meanwhile, the surfaces were visualized and their enhancement mechanisms were analyzed from the perspective of bubble dynamics. The results show that compared with the smooth plain (SP) surface, the CHFs on NS surface, MS surface and HMS surface are improved by 22.8%, 48.2% and 33.8%, respectively. The maximum HTCs are improved by 42.9%, 83.7% and 77.6%, respectively. However, the boiling heat transfer performance of HMS surface is not improved compared with MS surface. According to the characterization results, this is the result of the combined effect of roughness, surface area ratio and wettability.

P‐5.3: Customization of Metal Wire Taper Specifications

GE(M1) and SE (M2) two metal film layers need to be patterned by wet etching solution. If the taper is too high after etching, it will lead to light leakage from the metal edge, which will reduce the contrast (GE only) and poor coverage of the insulating layer. If it is too low, the resistance value of the fanout will change greatly, and the photoresist will fall and lead to the failure of the metal line. In this article, we mainly analyze how to develop the specification of the taper for GE/SE layer metal wet etchant.

P‐5.6: Analysis of ITO Residue in 4mask process applied in Extra large‐size FFS LCDs

Indium tin oxide (ITO) residue is a serious problem in 4mask process applied in Fringe Field Switching (FFS) mode LCDs. In this paper, we analyzed the composition and structure of the residues and the reasons for their formation. ITO grains grow with increasing temperature during copper sputtering. As a result, it is hardly etched in the subsequent wet etching process, resulting in residues.

Refractive index sensing performance of stepped-mTFBG fabricated by flexibly-regulating wet etching process

In this paper, an interesting method was proposed to flexibly prepare the micron titled fiber Bragg grating (mTFBG) by using a quartz capillary. The etching region of mTFBG can be precisely controlled by inserting in and moving it out from the protection of the quartz capillary. In this way, the mTFBG with stepped diameter has been fabricated and demonstrated with its refractive index sensing performance. Compared with the uniformly-etched mTFBG, the refractive index sensitivity of stepped-mTFBG has been significantly-improved from 5.785 nm/RIU to 17.077 nm/RIU. Although this sensitivity is much lower than other types of refractive index optical fiber sensors, it provides the new method for the flexible design of FBG structures. Furthermore, it reveals that the transmission spectrum of mTFBG can be modulated continuously during the etching process, which suggests a new way to adjust the transmission spectra of optical fibers.

Quasi-periodic micro-lens array via laser-assisted wet etching

A close-packed micro-lens array (MLA) is widely used not only in novel optical systems but also in various engineering fields, such as semiconductors and display devices. In this paper, we present a simple and efficient method for fabricating MLAs on a glass substrate via laser ablation with a single femtosecond laser pulse and chemical wet etching in a hydrofluoric acid solution. The shapes of concave micro-lenses were optimized for laser pulse energy and etching time, and ∼70 000 micro-lenses with 15 µm diameter were formed. The shape of the micro-lens varies significantly with respect to the etching time in accordance with an initial ablated area (or laser energy), which is a key feature in fabricating micro-lenses of several tens of μm. Using the glass MLA as a mold, a polydimethylsiloxane convex-plano lens array was replicated, and the performance of the optical imaging and beam integrator was then examined.

(Invited, Digital Presentation) Ion Implantation for Amorphous-InGaZnO Sheet Resistance Control Technique

As a next-generation electronics material, amorphous-InGaZnO (a-IGZO) film devices were investigated. In order to further utilize a-IGZO films, we carried out conventional ion of boron (B+) or neon (Ne+) implantations in a-IGZO thin films on glass and analyzed the implanted a-IGZO via Hall measurement with wet etching. In addition, a-IGZO thin film transistor processes with the implantation were carried out. As a result, we find that both ions drastically decrease a-IGZO sheet resistances. However, we observed oxygen vacancy area increase in the case of Ne+ implanted a-IGZO in 300 oC post annealing, which indicates Ne diffuses in a-IGZO film. On the other hand, B diffusion was not observed by depth profile comparison between the implanted samples with and without annealing. Furthermore, we extract key device parameters, such as effective channel length and ON/OFF current ratio, which can be applied to a-IGZO device processing.

Chalcogenide Glass IR Artificial Compound Eyes Based on Femtosecond Laser Microfabrication

AbstractThe compact and lightweight infrared (IR) optics devices are highly demanded in booming applications. However, fabrication of IR optics devices with high efficiency is still technically challenging, especially artificial compound eyes (ACE) with low aberration imaging and large field of view. In this work, a method of femtosecond laser wet etching combining with the “two‐step” precision glass molding based on chalcogenide glass is proposed to fabricate glass IR ACE. The as‐prepared consists of 6000 ommatidia (diameter of 88 µm and the sag height of 11 µm) arranged in a hexagonal manner with perfect parabolic morphology and high uniformity. The chalcogenide glass IR ACE exhibits excellent optical performance both in IR active imaging and IR passive imaging with high transmittance (60–70%) ranging from 2.5 to 15 µm. The ommatidia have a high resolution up to 20.16 lp mm−1, and imaging with large field of view up to 60° and low aberration can be achieved. Furthermore, the proposed technology shows advantages to fabricate glass IR ACE with low cost and high efficiency, and glass IR ACE shows great potential in IR imaging, robot vision, IR 3D motion tracking, and so on.

Broadband absorber coupled with anti-reflection inverted pyramid type all-dielectric microstructure

In order to improve the absorption efficiency and absorption bandwidth, we propose an inverted pyramid type all-dielectric absorber. Using the anti-reflection interface characteristics of the inverted pyramid microstructure, the designed absorber can achieve 100% perfect absorption in the range of 1.5THz to 1.7THz. Based on the structural diffraction analysis and electromagnetic field distribution characteristics, we have deeply explored the physical mechanism of wave absorption of the designed structure, and revealed the dual physical mechanism of electromagnetic wave diffraction conversion and resonance absorption. Based on the unique wet etching technology, we have experimentally prepared this inverted pyramid type all-dielectric absorber. Through experimental measurement, the consistency of the theoretical design and experimental test was confirmed.

Fabrication and diameter analysis of a single-ended SMF tip structure.

Optical fiber technology combined with surface plasmon resonance enables rapid, precise detection of chemical, biochemical, and biological parameters. Many hybrid optical fiber structures have been suggested in recent decades to increase the sensitivity of optical fiber biosensors. In this work, an optical fiber tip structure is fabricated on single-mode fiber (SMF) by etching in a hydrofluoric acid (40%) solution at room temperature. The proposed method of tip formation utilizing wet etching is efficient for fabricating the highly sensitive fiber structures that are required for the development of optical fiber-based biosensors. The diameter measurement of fabricated fiber tip formation is done using a compound microscope.

Preparation Technology of Stretchable Electrode Based on Laser Cutting

Wearable electronics have showed their profound impact in military, sports, medical and other fields, but their large-scale applications are still limited due to high manufacturing costs. As an advanced micro-fabrication process, laser processing technology has the advantages of high speed, high flexibility, strong controllability, environmental protection and non-contact in preparing micro-nano structures of wearable electronics. In this paper, a 355 nm ultraviolet laser was used to pattern the copper foil pasted on the flexible substrate, and the interconnection electrodes and wires were constructed. A processing method of multi-parallel line laser cutting and high-speed laser scanning is proposed to separate and assist in peeling off excess copper foil. The process parameters are optimized. A stretchable 3 × 3 light-emitting diode (LED) array was prepared and its performance was tested. The results showed that the LED array can work normally under the conditions of folding, bending and stretching, and the stretch rate can reach more than 50%. A stretchable temperature measurement circuit that can be attached to a curved surface was further fabricated, which proves the feasibility of this process in the fabrication of small-scale flexible wearable electronic devices. Requiring no wet etching or masking process, the proposed process is an efficient, simple and low-cost method for the fabrication of stretchable circuits.

Textured Stainless Steel as a Platform for Black Mg2Si/Si Heterojunction Solar Cells with Advanced Photovoltaic Performance.

This paper reports on a facile bottom-up method for the direct integration of a silicon (Si)-magnesium silicide (Mg2Si) heterojunction solar cell (HSC) with a textured rear reflector made of stainless steel (SS). Modified wet chemical etching and post processing of SS substrates resulted in the formation of both a rough surface texture and diffusion barrier layer, consisting of magnetite (Fe3O4) with reduced optical reflection. Then, Si, Mg2Si and CaSi2 layers were stepwise thermally evaporated onto the textured SS surface. No traces of Fe and Cr silicide phases were detected by Raman spectroscopy, confirming effective suppression of impurity diffusion from the SS to the upper layers at least at temperatures required for Si deposition, as well as Mg2Si and CaSi2 formation. The obtained black-SS/Fe3O4/Si/Mg2Si/CaSi2 sample preserved, to some extent, its underlying textured morphology and demonstrated an averaged reflection of 15% over the spectral range of 200–1800 nm, while its prototype HSC possessed a wideband photoresponse with a photoelectric conversion efficiency of 7.5% under AM1.5 illumination. Moreover, Si layers deposited alone onto a black-SS substrate demonstrated competitive antireflection properties compared with black Si (b-Si) obtained by traditional top-down etching approaches, and hybrid b-Si/textured-SS structures with a glue-bonded interlayer.

Flexible GaN-based microscale light-emitting diodes with a batch transfer by wet etching.

Flexible inorganic GaN-based microscale light-emitting diodes (µLEDs) show potential applications in wearable electronics, biomedical engineering, and human-machine interfaces. However, developing cost-effective products remains a challenge for flexible GaN-based µLEDs. Here, a facile and stable method is proposed to fabricate flexible GaN-based µLEDs from silicon substrates in an array-scale manner by wet etching. Circular and square µLED arrays with a size and pitch of 500 µm were fabricated and then transferred to a flexible acrylic/copper substrate. The as-fabricated flexible µLEDs can maintain their structure intact while exhibiting a significant increase in external quantum efficiency. This Letter promotes the application of simple and low-cost flexible µLED devices, especially for virtual displays, wearables, and curvilinear displays.

Electrohydrodynamic Direct‐Writing Fabrication of Microstructure‐Enhanced Microelectrode Arrays for Customized and Curved Physiological Electronics

AbstractMetal‐based patterned conductors have a key role in flexible and curved micro/nanodevices. However, the fabrication of micro/nanoscale metal‐based electrodes with excellent electrical conductivities and well‐organized flexible/curved polymeric substrates remains a major challenge associated with a posttreatment. In this study, a maskless and direct‐writing method of electrohydrodynamic jet (e‐jet) printing combined with the conventional wet etching process is developed for fabrication of microscale conductive features of microstructure‐enhanced patterned electrodes without high‐temperature treatment. Customized metal‐patterned electrodes and various metal‐patterned electrode arrays are fabricated on a flexible/curved polyethylene terephthalate substrate. In addition, ultraviolet‐curable hierarchical micro/nanostructures can be fabricated by stable cone‐jet and electrospray modes. The results of electrocardiography (ECG) and electromyography signal measurements show that the added microstructures can increase the contact between the metal microelectrodes and skin surface, which yield lower disturbance and baseline drift and enable a stable ECG signal acquisition. Overall, e‐jet printing is a promising mask‐free approach for fabrication of conductive metal patterns for flexible and stretchable devices.

Wet Etching of Quartz Using a Solution Based on Organic Solvents and Anhydrous Hydrofluoric Acid.

The quartz-crystal resonator is the core device for frequency control in modern communication systems and network technology. At present, in modern resonator blanks manufacturing, BOE solution is usually used as the etching solution, but its etching rate is relatively volatile, and the surface morphology of the blanks is prone to defects after etching, which brings certain difficulties to the deep-etching process of the wafer. To solve the above challenges, this paper systematically compares a BOE solution and anhydrous etching solution in terms of etching rate, surface morphology, and electrical properties of the blanks after etching. Seven groups of blanks were etched using different etching solutions with different etching conditions to verify their effect on the surface morphology and electrical properties of quartz blanks. The experimental results suggest that the application of anhydrous etching solution has achieved better surface morphology and electrical properties and can be more suitable for application in batch manufacturing. In general, when using anhydrous etching solution, it is possible to reduce surface roughness by up to 70% and equivalent resistance by 32%, and the etch rate is almost 10 times lower than BOE solution under the same temperature, which is more conducive to the rate control of wafers in the etching process.

Development of substrate engineered Si-/[100] Patterned Features by anisotropic wet etching with Pt/Pt3Si mask

In the current article, a substrate engineered patterned array of square-shaped features of size 1.5 μm × 1.5 μm comprising of <111>/[100]-planes of p-Si substrate has been developed by employing electron beam lithography assisted selective anisotropic wet etching. The etching of such planes is performed by combining the effect of KOH as the chemical etchant and Pt/Pt3Si as the mask with its catalyzing properties for the etching reaction. The regular array of exposed <111>/[100]-planes is confirmed by FESEM imaging and X-ray diffraction study. The formation of a ‘virtual hetero-junction’ at <111>/[100] interface is characterized by in-situ current-voltage measurement within the FESEM chamber. Such surface engineered Si-substrates can be utilized for multifaceted applications by fabricating different types of electronic, optoelectronic and bio-sensing devices.

Coupling of Photonic Waveguides to Integrated Detectors Using 3D Inverse Tapering

We report on the design, fabrication, and characterization of a Silicon Nitride (SiN)-based integrated photonic chip in which the dielectric waveguides are coupled to photodetectors integrated homogeneously into the Silicon substrate. The photonic-electronic coupling was realized by a 3D inverse tapering of SiN waveguides. The novelty of our approach consists in tapering the waveguide in the vertical direction by means of an engineered wet chemical etching. This allows for a smooth transition from a full-height to an arbitrarily thin waveguide thickness at the detector location, expanding adiabatically the optical mode towards the latter. The measured chips showed a responsivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R\approx 109\;\mu$</tex-math></inline-formula> A/mW and a corresponding quantum efficiency of 16% at an excitation wavelength of 850 nm. Our technological solution offers a versatile method for a top-down monolithic integration of lightwave circuitries with substrate-located photon sensing devices.

Ultrasonically assisted surface modified CeO2 nanospindle catalysts for conversion of CO2 and methanol to DMC

This study developed a facile and effective approach to engineer the surface properties of cerium oxide (CeO2) nanospindle catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol. CeO2 nanospindles were first prepared by a simple precipitation method followed by wet chemical redox etching with sodium borohydride (NaBH4) under high intensity ultrasonication (ultrasonic horn, 20 kHz, 150 W/cm2). The ultrasonically assisted surface modification of the CeO2 nanospindles in NaBH4 led to particle collisions and surface reduction that resulted in an increase in the number of surface-active sites of exposed Ce3+ and oxygen vacancies. The surface modified CeO2 nanospindles showed an improvement of catalytic activity for DMC formation, yielding 17.90 mmol·gcat−1 with 100 % DMC selectivity. This study offers a simple and effective method to modify a CeO2 surface, and it can further be applied for other chemical activities.

Electrical Properties of the Base‐Substrate Junction in Freestanding Core‐Shell Nanowires

AbstractWell‐defined hetero‐interfaces with controlled properties are crucial for any high‐performance, semiconductor‐based, (opto‐)electronic device. They are particularly important for device structures on the nanoscale with increased interfacial areas. Utilizing a ultrahigh‐vacuum based multi‐tip scanning tunneling microscope, this work reveals inadvertent conductivity channels between the nanowire (NW) base and the substrate, when measuring individual vertical core‐shell III‐V‐semiconductor NWs. For that, four‐terminal probing is applied on freestanding, epitaxially grown coaxial p‐GaAs/i‐GaInP/n‐GaInP NWs without the need of nanoscale lithography or deposition of electrical contacts. This advanced analysis, carried out after composition‐selective wet chemical etching, reveals a substantially degraded electrical performance of the freestanding NWs compared to detached ones. In an electron beam induced current mode of the nanosensor, charge separation at the substrate‐to‐NW base junction is demonstrated. An energy dispersive X‐ray spectroscopic linescan shows an unintended compositional change of the epitaxially grown NW toward the planar layers caused by different incorporation mechanisms of Ga and In at the NW base. This approach provides direct insight into the NW‐substrate transition area and leads to a model of the conductivity channels at the NW base, which should, in principle, be considered in the fabrication of all NW heterostructures grown bottom‐up on heterogeneous substrate materials.

Inverted pyramid structure on monocrystalline silicon processed by wet etching after femtosecond laser machining in air and deionized water

The micro-structured silicon has been preliminarily applied to improve the surface and optical properties of micro-solar cells, micro-optical systems, and aerospace engineering. However, the morphological changes and optical properties of monocrystalline silicon during femtosecond laser machining assisted with chemical etching are not clear, especially in a liquid environment. In this paper, monocrystalline silicon was ablated by femtosecond laser in air and deionized water respectively and then etched by alkaline potassium hydroxide (KOH). The reflectivity, absorptivity, and transmissivity of monocrystalline silicon were tested. Experimental results showed that inverted pyramid (IP) structure could be processed on a monocrystalline silicon wafer by ablating the surface with a high-power laser under the air environment and a low-power laser under the deionized water environment, followed by KOH etching. Meanwhile, the optical properties of the monocrystalline silicon with IP structure were effectively improved.

Fabrication of hexagonal microstructure on gallium nitride films by wet etching assisted femtosecond laser ablation

Nitride-based microstructures are highly desirable for next-generation photonic and micro-electronic technologies. However, the efficient realization of regular microstructures for gallium nitride (GaN) is still technically challenging. This paper demonstrates the formation of hexagonal microstructures on GaN films via femtosecond laser ablation and wet chemical (hot KOH) etching. The fabricated hexagonal microstructures are shown to undergo anisotropic ablation. The structures with tunable profiles and dimensions are obtained by varying the laser energy and etching time. Additionally, we demonstrate that the microstructures were formed by selectively etching away the laser-irradiated region. This work could lead to a new approach to fabricating nitride-based microstructures using wet etching-assisted ultrafast laser processing technologies.