High density plasma etching of amorphous CoZrNb films for thin film magnetic devices

Inductively coupled plasma reactive ion etching of CoZrNb magnetic thin films was studied using a TiN hard mask in a Cl₂/O₂/Ar gas mix. The etch rates of CoZrNb films and TiN hard mask gradually decreased with increasing Cl₂ or O₂ gas concentrations. When O₂ gas was added in the Cl₂/Ar gas mix, the etch rate of TiN hard mask was suppressed effectively so that the etch selectivity of CoZrNb film to TiN hard mask was enhanced. The addition of O₂ into the gas mix also led to the anisotropic etching of the CoZrNb films and it was confirmed by Auger electron spectroscopy that there were no redeposited materials on the sidewall of the etched films. Highly anisotropic etching of CoZrNb films was achieved at room temperature under the optimized etching conditions.     

Simultaneous Fabrication of Very High Aspect Ratio Positive Nano‐ to Milliscale Structures

A simple and inexpensive technique for the simultaneous fabrication of positive (i.e., protruding), very high aspect (>10) ratio nanostructures together with micro‐ or millistructures is developed. The method involves using residual patterns of thin‐film over‐etching (RPTO) to produce sub‐micro‐/nanoscale features. The residual thin‐film nanopattern is used as an etching mask for Si deep reactive ion etching. The etched Si structures are further reduced in size by Si thermal oxidation to produce amorphous SiO₂, which is subsequently etched away by HF. Two arrays of positive Si nanowalls are demonstrated with this combined RPTO‐SiO₂‐HF technique. One array has a feature size of 150 nm and an aspect ratio of 26.7 and another has a feature size of 50 nm and an aspect ratio of 15. No other parallel reduction technique can achieve such a very high aspect ratio for 50‐nm‐wide nanowalls. As a demonstration of the technique to simultaneously achieve nano‐ and milliscale features, a simple Si nanofluidic master mold with positive features with dimensions varying continuously from 1 mm to 200 nm and a highest aspect ratio of 6.75 is fabricated; the narrow 200‐nm section is 4.5 mm long. This Si master mold is then used as a mold for UV embossing. The embossed open channels are then closed by a cover with glue bonding. A high aspect ratio is necessary to produce unblocked closed channels after the cover bonding process of the nanofluidic chip. The combined method of RPTO, Si thermal oxidation, and HF etching can be used to make complex nanofluidic systems and nano‐/micro‐/millistructures for diverse applications.     

Effect of BCl3 concentration and process pressure on the GaN mesa sidewalls in BCl3/Cl2 based inductively coupled plasma etching

GaN mesa etching is investigated using BCl₃/Cl₂ based inductively coupled plasma at constant ICP/RF powers for HEMT fabrication. The effect of chamber process pressure (5-15 mTorr) and BCl₃/Cl₂ flow rate ratio >1 on mesa sidewall profile is studied in detail using less complex photoresist mask. Mesa sidewall sharpness varied strongly with chamber pressure and deteriorated at lower pressure ∼5 mTorr. The etched GaN mesas resulted in severely damaged sidewalls with significant sidewall erosion at BCl₃/Cl₂ ratio of <1, which reduced gradually as BCl₃/Cl₂ ratio was increased to values >1 mainly due to decreased Cl ion/neutral scattering at the edges. Finally, the smooth and sharp mesa sidewalls with angle of ∼80° and moderate GaN etch rate of ∼1254 Å/min are obtained at BCl₃/Cl₂ ratio of 2.5:1 and 10 mTorr pressure due to a better balance between physical and chemical components of ICP etching.     

Dry etched mesas for buried heterostructure InGaAsP/InP lasers using electron cyclotron resonance Cl2/CH4/H2/Ar discharges

High-density, magnetically enhanced discharges of Cl₂/CH₄/H₂/Ar were shown to provide rapid dry etching of InGaAsP/InP laser structures for sample temperatures of greater than 130 C. The etch rates were ~1 m min^–1, and they were more than an order of magnitude faster than for conventional CH₄/H₂/Ar etching. Smooth, anisotropic mesa sidewalls were obtained when the direct-current (d.c.) self-bias was kept low (–80 V). The etched surfaces were suitable for epitaxial regrowth of current-blocking layers by either organo-metallic-vapour-phase epitaxy or metal-organic molecular-beam epitaxy. In the former technique, addition of CCl₄ to the growth chemistry was helpful in preventing deposition of polycrystalline InP on the dielectric mask.     

Texturization of ZnO:Al surface by reactive ion etching in SF<Subscript>6</Subscript>/Ar,CHF<Subscript>3</Subscript>/Ar plasma for application in thin film silicon solar cells

As-deposited sputtered ZnO:Al (AZO) thin films having high transparency (T?≥?85% at 550 nm of wavelength) and good electrical properties (ρ?=?2.59?×?10^?04 Ω cm) are etched to get suitable light trapping in thin film solar cells, using reactive ion etching method in sulfur hexafluoride–argon (SF₆/Ar) plasma and trifluoromethane–argon (CHF₃/Ar) plasma to texture their surface. Though the electrical properties of the films are not affected much by the etching process but significant increment in the average haze values in the wave length range of 350–1100 nm in the etched AZO films (19.21% for SF₆/Ar and 22.07% for CHF₃/Ar plasma etched) are found compared to as-deposited AZO films (5.61%). Increment in haze value is due to more scattering of light from the textured surface. These textured substrates are used as front transparent conducting oxide electrode for the fabrication of amorphous silicon solar cells. Solar cells fabricated on etched AZO substrates show 7.76% increase in conversion efficiency compared to as-deposited AZO substrates.     

Molecular beam epitaxial growth of high-quality InP layers from solid phosphorus using a valved phosphorus cracker cell

We report the molecular beam epitaxial (MBE) growth of epitaxial InP using a valved phosphorus cracker cell at a range of cracking-zone temperatures (T_cr = 875–950°C), V/III flux ratios (V/III = 1.2–9.3) and substrate temperatures (T_s = 360–500°C). The as-grown epitaxial InP on an InP (100) substrate is found to be n-type from Hall measurements. The background electron concentration and mobility exhibit a pronounced dependence on the cracking-zone temperature, V/III flux ratio and substrate temperature. Using a T_cr of 850°C, the highest 77 K electron mobility of 40 900 cm² (V s)⁻¹ is achieved at a V/III ratio of 2.3 and a T_s of 440°C. The correponding background electron concentration is 1.74 × 10¹⁵ cm⁻³. The photoluminescence (PL) spectra show two prominent peaks at 1.384 and 1.415 eV, with the intensity of the low-energy peak becoming stronger at higher cracking-zone temperatures. The lowest PL FWHM achieved at 5 K is 5.2 meV. Within the range of substrate temperatures investigated, the effect on the crystalline quality determined from X-ray diffraction (XRD) measurements is not significant.     

Observation of Self‐Assembled Core–Shell Structures in Epitaxially Embedded TbErAs Nanoparticles

Self‐assembled core–shell structured rare‐earth nanoparticles (TbErAs) are observed in a III–V semiconductor host matrix (In_0.53Ga_0.47As) nominally lattice‐matched to InP, grown via molecular beam epitaxy. Atom probe tomography demonstrates that the TbErAs nanoparticles have a core–shell structure, as seen both in the tomographic atom‐by‐atom reconstruction and concentration profiles. A simple thermodynamic model is created to determine when it is energetically favorable to have core–shell structures; the results strongly agree with the observations.     

In‐Plane Direct‐Write Assembly of Iridescent Colloidal Crystals

Materials made by directed self‐assembly of colloids can exhibit a rich spectrum of optical phenomena, including photonic bandgaps, coherent scattering, collective plasmonic resonance, and wave guiding. The assembly of colloidal particles with spatial selectivity is critical for studying these phenomena and for practical device fabrication. While there are well‐established techniques for patterning colloidal crystals, these often require multiple steps including the fabrication of a physical template for masking, etching, stamping, or directing dewetting. Here, the direct‐writing of colloidal suspensions is presented as a technique for fabrication of iridescent colloidal crystals in arbitrary 2D patterns. Leveraging the principles of convective assembly, the process can be optimized for high writing speeds (≈600 µm s^?1) at mild process temperature (30 °C) while maintaining long‐range (cm‐scale) order in the colloidal crystals. The crystals exhibit structural color by grating diffraction, and analysis of diffraction allows particle size, relative grain size, and grain orientation to be deduced. The effect of write trajectory on particle ordering is discussed and insights for developing 3D printing techniques for colloidal crystals via layer‐wise printing and sintering are provided.     

Fabrication of High‐Performance Silver Mesh for Transparent Glass Heaters via Electric‐Field‐Driven Microscale 3D Printing and UV‐Assisted Microtransfer

Great challenges remain concerning the cost‐effective manufacture of high‐performance metal meshes for transparent glass heaters (TGHs). Here, a high‐performance silver mesh fabrication technique is proposed for TGHs using electric‐field‐driven microscale 3D printing and a UV‐assisted microtransfer process. The results show a more optimal trade‐off in sheet resistance (R_s = 0.21 Ω sq^?1) and transmittance (T = 93.9%) than for indium tin oxide (ITO) and ITO substitutes. The fabricated representative TGH also exhibits homogeneous and stable heating performance, remarkable environmental adaptability (constant R_s for 90 days), superior mechanical robustness (R_s increase of only 0.04 in harsh conditions–sonication at 100 °C), and strong adhesion force with a negligible increase in R_s (2–12%) after 100 peeling tests. The practical viability of this TGH is successfully demonstrated with a deicing test (ice cube: 21 cm³, melting time: 78 s, voltage and glass thickness: 4 V, 5 mm). All of these advantages of the TGHs are attributed to the successful fabrication of silver meshes with high resolution and high aspect ratio on the glass substrate using the thick film silver paste. The proposed technique is a promising new tool for the inexpensive fabrication of high‐performance TGHs.     

Etch characteristics of magnetic tunnel junction stack with nanometer-sized patterns for magnetic random access memory

Etch characteristics of magnetic tunnel junction (MTJ) stack masked with TiN films were investigated using an inductively coupled plasma reactive ion etcher in Cl₂/Ar and BCl₃/Ar gases for magnetic random access memory. The effect of etch gas on the etch profile of MTJ stacks was examined. As Cl₂ and BCl₃ concentrations increased, the etch slope of etched MTJ stack became slanted and the dimensional shrinkage was observed. A high degree of anisotropic etching of MTJ stacks was achieved using Cl₂/Ar gas at the optimized etch conditions.     

Pores in III–V Semiconductors

The paper reviews electrochemically etched pores in III–V compound semiconductors (GaP, InP, GaAs) with emphasis on nucleation and formation mechanisms, pore geometries and morphologies, and to several instances of self‐organization. Self‐ organization issues include the formation of single‐crystalline two‐dimensional hexagonal arrays of pores with lattice constants as small as 100 nm found in InP, synchronized and unsynchronized diameter oscillations coupled to current and voltage oscillations, and pore domain formation. The findings are discussed in relation to pores observed in silicon. Some novel properties of the porous layers obtained in III–V compounds are briefly described.     

Etch characteristics of indium zinc oxide thin films using inductively coupled plasma of a Cl2/Ar gas

Inductively coupled plasma reactive ion etching of indium zinc oxide (IZO) thin films masked with a photoresist was performed using a Cl₂/Ar gas. The etch rate of the IZO thin films increased as Cl₂ gas was added to Ar gas, reaching a maximum at 60% Cl₂ and decreasing thereafter. The degree of anisotropy in the etch profile improved with increasing coil rf power and dc-bias voltage. Changes in pressure had little effect on the etch profile. X-ray photoelectron spectroscopy confirmed the formation of InCl₃ and ZnCl₂ on the etched surface. The surface morphology of the films etched at high Cl₂ concentrations was smoother than that of the films etched at low Cl₂ concentrations. These results suggest that the dry etching of IZO thin films in a Cl₂/Ar gas occurs according to a reactive ion etching mechanism involving ion sputtering and a surface reaction.     

Large‐Scale Plasmonic Hybrid Framework with Built‐In Nanohole Array as Multifunctional Optical Sensing Platforms

Light coupling with patterned subwavelength hole arrays induces enhanced transmission supported by the strong surface plasmon mode. In this work, a nanostructured plasmonic framework with vertically built‐in nanohole arrays at deep‐subwavelength scale (6 nm) is demonstrated using a two‐step fabrication method. The nanohole arrays are formed first by the growth of a high‐quality two‐phase (i.e., Au–TiN) vertically aligned nanocomposite template, followed by selective wet‐etching of the metal (Au). Such a plasmonic nanohole film owns high epitaxial quality with large surface coverage and the structure can be tailored as either fully etched or half‐way etched nanoholes via careful control of the etching process. The chemically inert and plasmonic TiN plays a role in maintaining sharp hole boundary and preventing lattice distortion. Optical properties such as enhanced transmittance and anisotropic dielectric function in the visible regime are demonstrated. Numerical simulation suggests an extended surface plasmon mode and strong field enhancement at the hole edges. Two demonstrations, including the enhanced and modulated photoluminescence by surface coupling with 2D perovskite nanoplates and the refractive index sensing by infiltrating immersion liquids, suggest the great potential of such plasmonic nanohole array for reusable surface plasmon‐enhanced sensing applications.     

Wear and corrosion studies of graphite‐aluminum composite reinforced with micro/nano‐TiB2 via spark plasma sintering

The demand for lightweight materials in the automobile and aerospace industries has led to various researches on graphite and graphite‐aluminum composites. The aim of this study was to investigate the effect of the addition of micron/nano TiB₂ particles on the properties of graphite‐aluminum composite particularly the wear resistance. The powders were sintered at 550 °C and 50 MPa with more attention on the effect of the sintering temperature on densification, microhardness, coefficient of thermal expansion, wear and frictional force. The results show that the addition of nano TiB₂ reduces the densification while improving the hardness of Gr?Al composite with the lowest value being 96.0 % of relative density and the highest microhardness of 43.58 HV 0.1. The coefficient of thermal expansion and frictional force of the composite materials increases with increasing TiB₂ content and heating rate (100 °C/min–150 °C/min). TiB₂ particles enhance the wear resistance of graphite‐aluminum composite. The addition of micro/nanoparticles of TiB₂ to graphite‐aluminum composite increases its corrosion rate with improved passivation behavior in 3.5 wt.% NaCl solution. Nevertheless, 5 wt.% nano (100 °C/min) TiB₂ additions do not affect the overall corrosion rate. This work has shown that we can take advantage of some of the properties of TiB₂ to improve the performance of graphite‐aluminum composite.     

Fabrication of Millimeter‐Scale,Single‐Crystal One‐Third‐Hydrogenated Graphene with Anisotropic Electronic Properties

Periodically hydrogenated graphene is predicted to form new kinds of crystalline 2D materials such as graphane, graphone, and 2D C_xH_y, which exhibit unique electronic properties. Controlled synthesis of periodically hydrogenated graphene is needed for fundamental research and possible electronic applications. Only small patches of such materials have been grown so far, while the experimental fabrication of large‐scale, periodically hydrogenated graphene has remained challenging. In the present work, large‐scale, periodically hydrogenated graphene is fabricated on Ru(0001). The as‐fabricated hydrogenated graphene is highly ordered, with a √3 × √3/R30° period relative to the pristine graphene. As the ratio of hydrogen and carbon is 1:3, the periodically hydrogenated graphene is named “one‐third‐hydrogenated graphene” (OTHG). The area of OTHG is up to 16 mm². Density functional theory calculations demonstrate that the OTHG has two deformed Dirac cones along one high‐symmetry direction and a finite energy gap along the other directions at the Fermi energy, indicating strong anisotropic electrical properties. An efficient method is thus provided to produce large‐scale crystalline functionalized graphene with specially desired properties.     

Stable Light‐Emitting Diodes Using Phase‐Pure Ruddlesden–Popper Layered Perovskites

State‐of‐the‐art light‐emitting diodes (LEDs) are made from high‐purity alloys of III–V semiconductors, but high fabrication cost has limited their widespread use for large area solid‐state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase‐pure 2D Ruddlesden–Popper (RP) halide perovskites with a formula (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_n?1Pb_nI_3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr^?1 cm^?2 at 744 nm with an ultralow turn‐on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase‐pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm^?2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.     

Chemical etching of InP (1 0 0) wafer based on a volcanic mineral water

We have successfully demonstrated that a solution of spa water [Tamagawa Spa water (TaSW):H₂O₂ = 1:1] etches InP (1 0 0) wafer. The TaSW is a colorless acidic liquid of pH ∼1.1. It contains a considerable amount of positive ions, such as H⁺, Al³⁺, and Ca²⁺. The Cl⁻, HSO₄²⁻, and SO₄²⁻ ions are the main anions. The TaSW-etchant system provides shiny flat surfaces on the etched bottoms. The spa-etchant system has reproducible etching rates and does not erode photoresist masks. The etching kinetics is reaction-rate limited. The spa-etchant system is also found to etch GaAs (1 0 0) wafer, but the etched surface is considerably roughened.     

Novel Tunnel‐Contact‐Controlled IGZO Thin‐Film Transistors with High Tolerance to Geometrical Variability

Thin insulating layers are used to modulate a depletion region at the source of a thin‐film transistor. Bottom contact, staggered‐electrode indium gallium zinc oxide transistors with a 3 nm Al₂O₃ layer between the semiconductor and Ni source/drain contacts, show behaviors typical of source‐gated transistors (SGTs): low saturation voltage (V_{D_SAT} ≈ 3 V), change in V_{D_SAT} with a gate voltage of only 0.12 V V^?1, and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry: the saturated current changes only 0.15× for 2–50 µm channels and 2× for 9‐45 µm source‐gate overlaps. A higher than expected (5×) increase in drain current for a 30 K change in temperature, similar to Schottky‐contact SGTs, underlines a more complex device operation than previously theorized. Optimization for increasing intrinsic gain and reducing temperature effects is discussed. These devices complete the portfolio of contact‐controlled transistors, comprising devices with Schottky contacts, bulk barrier, or heterojunctions, and now, tunneling insulating layers. The findings should also apply to nanowire transistors, leading to new low‐power, robust design approaches as large‐scale fabrication techniques with sub‐nanometer control mature.     

High‐Gain 200 ns Photodetectors from Self‐Aligned CdS–CdSe Core–Shell Nanowalls

1D core–shell heterojunction nanostructures have great potential for high‐performance, compact optoelectronic devices owing to their high interface area to volume ratio, yet their bottom‐up assembly toward scalable fabrication remains a challenge. Here the site‐controlled growth of aligned CdS–CdSe core–shell nanowalls is reported by a combination of surface‐guided vapor–liquid–solid horizontal growth and selective‐area vapor–solid epitaxial growth, and their integration into photodetectors at wafer‐scale without postgrowth transfer, alignment, or selective shell‐etching steps. The photocurrent response of these nanowalls is reduced to 200 ns with a gain of up to 3.8 × 10³ and a photoresponsivity of 1.2 × 10³ A W^?1, the fastest response at such a high gain ever reported for photodetectors based on compound semiconductor nanostructures. The simultaneous achievement of sub‐microsecond response and high‐gain photocurrent is attributed to the virtues of both the epitaxial CdS–CdSe heterojunction and the enhanced charge‐separation efficiency of the core–shell nanowall geometry. Surface‐guided nanostructures are promising templates for wafer‐scale fabrication of self‐aligned core–shell nanostructures toward scalable fabrication of high‐performance compact photodetectors from the bottom‐up.     

Inkjet‐Printed High‐Q Nanocrystalline Diamond Resonators

Diamond is a highly desirable material for state‐of‐the‐art micro‐electromechanical (MEMS) devices, radio‐frequency filters and mass sensors, due to its extreme properties and robustness. However, the fabrication/integration of diamond structures into Si‐based components remain costly and complex. In this work, a lithography‐free, low‐cost method is introduced to fabricate diamond‐based micro‐resonators: a modified home/office desktop inkjet printer is used to locally deposit nanodiamond ink as ?50–60 µm spots, which are grown into ≈1 µm thick nanocrystalline diamond film disks by chemical vapor deposition, and suspended by reactive ion etching. The frequency response of the fabricated structures is analyzed by laser interferometry, showing resonance frequencies in the range of ≈9–30 MHz, with Q ‐factors exceeding 10⁴, and (f₀ × Q) figure of merit up to ≈2.5 × 10¹¹ Hz in vacuum. Analysis in controlled atmospheres shows a clear dependence of the Q‐factors on gas pressure up until 1 atm, with Q ∝ 1/P. When applied as mass sensors, the inkjet‐printed diamond resonators yield mass responsivities up to 981 Hz fg^?1 after Au deposition, and ultrahigh mass resolution up to 278 ± 48 zg, thus outperforming many similar devices produced by traditional top‐down, lithography‐based techniques. In summary, this work demonstrates the fabrication of functional high‐performance diamond‐based micro‐sensors by direct inkjet printing.