Bottom Of Trench Research Articles

Formation of highly vertical trenches with rounded corners via inductively coupled plasma reactive ion etching for vertical GaN power devices

A trench-gate metal-oxide-semiconductor field-effect transistor (T-MOSFET) has great potential for use in gallium nitride (GaN)-based vertical power switching devices owing to its high blocking voltage and high current capability. To form an optimal trench shape that has highly vertical sidewalls and rounded corners, we developed a dry-etching technique using inductively coupled plasma reactive ion etching (ICP-RIE). A highly vertical trench was obtained by including SiCl4 reactive gas mixed with Cl2 gas in the ICP-RIE process, where Si-related byproducts suppressed the etching of the sidewall and allowed selective etching in the vertical direction. We found that the optimization of the bias power was a key to suppress the formation of subtrenches and to avoid an isotropic etching mode. The optimal etching condition leads to natural formation of rounded corners at the trench bottom. In addition, a multistep-bias etching technique was applied to reduce etching-induced damage. Cross-sectional transmission electron microscopy images revealed that lattice distortion on the sidewall surface was eliminated by multistep-bias etching. Based on the rectification properties of the Schottky barrier diodes formed on the trench sidewalls, the Schottky barrier height was comparable to the not-etched surfaces. This indicates that the gap states caused by etching-induced damage can almost be eliminated in the multistep-bias process. The proposed technique is suitable for GaN-based vertical T-MOSFETs.

Improved 4H-SiC UMOSFET with super-junction shield region* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61774052 and 61904045), the Youth Foundation of the Education Department of Jiangxi Province, China (Grant No. GJJ191154), and the Youth Foundation of Ping Xiang University, China (Grant No. 2018D0230).

This article investigates an improved 4H-SiC trench gate metal–oxide–semiconductor field-effect transistor (MOSFET) (UMOSFET) fitted with a super-junction (SJ) shielded region. The modified structure is composed of two n-type conductive pillars, three p-type conductive pillars, an oxide trench under the gate, and a light n-type current spreading layer (NCSL) under the p-body. The n-type conductive pillars and the light n-type current spreading layer provide two paths to and promote the diffusion of a transverse current in the epitaxial layer, thus improving the specific on-resistance (R on,sp). There are three p-type pillars in the modified structure, with the p-type pillars on both sides playing the same role. The p-type conductive pillars relieve the electric field (E-field) in the corner of the trench bottom. Two-dimensional simulation (silvaco TCAD) indicates that R on,sp of the modified structure, and breakdown voltage (V BR) are improved by 22.2% and 21.1% respectively, while the maximum figure of merit () is improved by 79.0%. Furthermore, the improved structure achieves a light smaller low gate-to-drain charge (Q gd) and when compared with the conventional UMOSFET (conventional-UMOS), it displays great advantages for reducing the switching energy loss. These advantages are due to the fact that the p-type conductive pillars and n-type conductive pillars configured under the gate provide a substantial charge balance, which also enables the charge carriers to be extracted quickly. In the end, under the condition of the same total charge quantity, the simulation comparison of gate charge and OFF-state characteristics between Gauss-doped structure and uniform-doped structure shows that Gauss-doped structure increases the V BR of the device without degradation of dynamic performance.

DESIGN AND CONSTRUCTION OF LINEAR MAIN PIPELINE ON WATER-LOGGED GROUNDS

The paper shows that the linear segments of the main pipelines laid on water-logged grounds are characterized by the floating parts 150–300 m long, with arch blowouts with a deflection of 1.0–1.5 m. This occurs due to the vertical axial loads and the temperature difference. The buckling stability of the floating part is calculated for the pipeline laid in a bog. It is shown that the loss of the buckling stability in the form of the floating parts and arch blowout can be explained by the fact that the project on the water-logged ground construction has no the analysis of the buckling stability under axial loads with regard to the topography of the trench bottom that describes the stress-strain state of the pipeline. At a design stage, it is necessary to conduct more detailed surveys on the pipeline laying with regard to the trench profile in calculating the pipeline buckling stability on water-logged grounds.

Superconformal Cobalt Electrodeposition with a Hydrogen Evolution Reaction Suppressing Additive

In this study, superconformal cobalt filling of submicron trenches by electrodeposition is investigated in the presence of 2-mercaptobenzimidazole (MBI), which suppresses both cobalt deposition and the hydrogen evolution reaction (HER). The mechanism through which this single additive enables superconformal cobalt filling is investigated. The formation and breakdown of the suppression layer are characterized by linear sweep voltammetry and chronoamperometry. The convection-driven local concentration of MBI exerts different suppressing effects on cobalt reduction and the HER, leading to a change in the deposition rate and the current efficiency of cobalt. These phenomena induce a deposition rate differential between the top and bottom of the submicron trench, enabling bottom-up cobalt filling with a V-shape profile.

Occurrence of Halogenated Organic Pollutants in Hadal Trenches of the Western Pacific Ocean.

The hadal trenches are the most remote and inaccessible habitats on earth and were once believed to be pristine. A recent study has reported the detection of high levels of persistent organic pollutants (POPs), including polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), in endemic amphipods from two hadal trenches (Mariana and Kermadec) in the Western Pacific, implicating that the trenches are indeed polluted. However, a fundamental question remains unanswered, if and to what extent such the physical environment of the trenches is polluted by POPs. In this study, we sampled Mariana, Mussau, and New Britain trenches and analyzed samples of amphipods, sediment, and suspended particulate matter (SPM). Our results show that the amphipods contained elevated levels of PCBs and PBDEs, comparable to those reported in the earlier study. We also detected significantly high concentrations (up to 1343 ng g-1 lw) of chlorinated pesticides, such as dichlorodiphenyltrichloroethanes and chlordanes. Furthermore, four brominated natural products (BNPs), which structurally resembled methoxylated brominated diphenyl ethers or polybrominated biphenyls, were identified in the endemic amphipods. However, neither POPs nor BNPs were detected in sediments or SPM. Taken together, we propose that the POPs detected in endemic amphipods likely resulted from bioaccumulation by feeding on polluted large detritus (e.g., carrion) falling to the trench bottoms from the surface ocean.

Investigations of internal stresses in high-voltage devices with deep trenches

Deep trenches, as essential elements of silicon chips used in electronic high-power and high-frequency devices, are known as starting points for dislocation generation under the influence of internal mechanical stresses resulting mainly from the difference in the thermal expansion coefficients between silicon and silicon dioxide. Since the electrical insulation of the devices requires a sequence of mechanical, chemical, and high-temperature processes during the preparation of the deep trenches, including the formation of an amorphous SiO2 edge layer, the emergence of the internal stresses is hardly avoidable. The method of cross correlation backscattered electron diffraction in the scanning electron microscope is used here to quantitatively determine the magnitude and local distribution of internal stresses in silicon around the deep trenches after four different process steps. For this purpose, Kikuchi diffraction images are recorded of the wafer cross section areas along lines perpendicular and parallel to the deep trenches. After Fourier transformation, these images are cross correlated with the Fourier transform of the diffraction image from a stressfree reference sample site. The well-established numerical evaluation of cross correlation functions provides the complete distortion tensor for each measuring point of the line scan, from which the stress tensor can be calculated using Hooke's law. It is found that the in-plane normal stress component σ11 perpendicular to the long edges of the deep trench is larger than the other stress components. That means it essentially determines the magnitude of the von-Mises stress, which was determined as a general stress indicator for all measuring points, too. A characteristic feature is the local distribution of the stress component σ11 with maximum tensile stresses of some hundred megapascals at transition between Si and amorphous SiO2 on the long edges of the deep trench, and with even higher maximum compressive stresses immediately below the bottom of the deep trench. At a distance of about 2 μm from the edges of a single deep trench, all stress components decrease to negligibly small values so that steep stress gradients occur. The range and distribution of tensile and compressive stresses are in accordance with finite element simulations; however, the measured stresses are higher than expected for all investigated states so that dislocation formation seems to be possible. The influence of the electron acceleration voltage on the determination of the internal stresses is discussed as well.

Impact of earthworks on the atmosphere during the reconstruction and overhaul of trunk pipelines

The paper discusses adverse atmospheric impact of earthworks during reconstruction and overhaul of trunk lines. The review of the trunk line insulation replacement process under normal and complex conditions helped identify the number of excavating machines adversely affecting the environment when operated simultaneously,. The point is made that the calculation of adverse impact should be performed in at least two stages to, first, estimate noxious emissions of operating machines and mechanisms; and, second, quantify the amount of fine-dispersed dust from cutting off the fertile soil layer, extracting the old pipeline, excavating the trench, leveling the trench bottom and other earthworks. It is further noted that the diversity of work techniques and the use of multi-criteria factors hinder the estimation of the adverse atmospheric impact of earthworks, as the engineering process does not consider the meteorological and other related conditions. Therefore, a “construction blockchain technology” (CBC technology) comprising GIS data is required. The CBC technology identifies the construction technologies, machines, equipment, mechanisms, resources etc., as well as software products to select the optimum work techniques, technology and organization, including scheduling. Over-all, the integration of CBC and BIM technologies should underline environmental safety of construction works including, among others, earthworks.

Lateral variation doped wide bottom trench gate IGBT for reduced on-resistance with improved gate charge

In this paper, novel concept of lateral variation doping profile in the drift region for IGBT is presented. The variation profile divides the drift region in four sections in such a way that highly doped p+ and n+ pillars are present at the center, while pillars with lesser concentration are situated at the drift region boundary. Higher concentration below the channel region, enables the presence of more free charges in the conduction path thereby reducing the specific resistance (Ron.A) in the conduction path. The p- and n- section reduces the critical electric field at the corner and maintains the similar breakdown voltage in comparison with the conventional design despite of higher concentration doping profile at the middle. Proposed structure offers 19% improvement in current density and 16% reduction in Ron.A. Lateral variation doped structure also able to reduce on-state voltage drop (Von) by 15.38%. Along with the lateral doping concept, Proposed structure utilizes the broad oxide at the gate region in order to improve the switching performance. The increment in the oxide thickness reduces the gate to collector capacitance (CGC) and leads to reduces the gate to collector charge (QGC) by 30%. Reduction in gate charge also improve the switching performance of the devices and reduces the energy losses during the turn-off period. The 20% improvement in turn-off losses at same on-state voltage drop is observed. Additionally, 5% improvement in the on-state voltage drop is also achieved. Additionally, various figure of merit (FOM) is also evaluated. The Baliga's FOM and industrial FOM is improved by 19% and 55% respectively as compared to conventional design.

Improved Deep Trench Super-junction LDMOS Breakdown Voltage By Shielded Silicon-Insulator-Silicon Capacitor

Deep trench LDMOS is widely used in high-voltage level power devices. This paper proposes and optimizes a deep trench super-junction LDMOS with triangular charge compensation layer (TCCL DT SJ LDMOS), which solves the problem of charge imbalance in the super-junction region due to the Silicon-Insulator-Silicon (SIS) capacitance at both ends of the trench and improves the Breakdown Voltage (BV) of the device. This structure also helps to deplete the drift region at the bottom of the deep trench by adding P-buffer under the N-Pillars, which improves the doping concentration and reduces the specific on-resistance of the device. The simulation results show that compared with the Con. DT SJ LDMOS, the BV of the TCCL DT SJ LDMOS has been increased from 498V to 730V, and the power figure of merit (FOM) has increased by 12.8 MW / cm2(FOM = BV2 / Ron, sp).

Sediment record of mining legacy and water quality from a drinking-water reservoir, Aztec, New Mexico, USA

The record of mining legacy and water quality was investigated in sediments collected in 2018 from four trenches in the Aztec, New Mexico, drinking-water reservoir #1. Bulk chemical analysis of sediments with depth in the reservoir revealed variable trace-element (uranium, vanadium, arsenic, copper, sulfur, silver, lead, and zinc) concentrations, which appear to coincide with historical mining and milling operations. Cesium-137 age dating, which identified the location of the 1963 radioactive fallout maximum, combined with the known age of the bottom and top of the sediment trenches, was used to estimate a polynomial sedimentation rate (average rate = 1.7 cm/yr). The clay size fraction (< 0.004 mm) was the dominant grain-size fraction of the sediments. Abundant fine-grained phyllosilicate (clay) minerals, predominantly montmorillonite and kaolinite, may explain sorption properties of trace elements. Scanning electron microscopy evaluation of sediments from two trenches showed copper and zinc associated with sulfur, and arsenic associated with iron and aluminum oxides. Results from laboratory batch experiments indicated that uranium, vanadium, and arsenic were released when sediments were reacted with a 150 mg/L sodium bicarbonate solution whereas copper was released when sediments were reacted with 2 mMol/L acetic acid. Observed concentrations from the two leach tests were below regulatory thresholds for delivery of solids to a landfill and were below drinking-water standards. Diatom relative abundance indicates that the water quality in the reservoir was not impaired by high metal concentrations.

Crystalline Quality Evaluation of SiC p/n Column Layers Formed by Trench-Filling-Epitaxial Growth

We evaluated crystalline quality of SiC p/n column layers over 20 μm thickness formed by trench-filling-epitaxial growth. Although threading dislocation density of trench-filling-epitaxial layer is almost same as flat n-type epitaxial layer, threading dislocations are localized in only trench-filled p-columns. We consider that threading dislocations migrated toward p-columns around trench bottom during trench-filling-epitaxial growth.

Investigations on the Resistance Reduction Effect of Double-Trench SiC MOSFETs under Repetitive Avalanche Stress

The unexpected resistance reduction effect of double-trench SiC MOSFETs under repetitive avalanche stress is investigated in this work. After enduring repetitive avalanche stress, the ON-state drain-source resistance (Rdson) of the device decreases. With the help of TCAD simulations, the dominant mechanism is proved to be the injection of positive charges into the gate trench bottom oxide, which is almost irreversible under zero-voltage bias condition at room temperature. For the injected positive charges attract extra electrons just beneath the gate trench bottom, where the carriers pass through under ON state, the resistivity there is reduced, improving the conduction capability of the device. Moreover, an optimization method is proposed. Since the impact ionization rate (I.I.) and the vertical oxide electric field (E⊥) along the gate trench bottom oxide interface contribute to the injection of positive charges, it is recommended to make the bottom oxide thicker to suppress this effect.

Numerical Study of 4H-SiC UMOSFETs with Split-Gate and P+ Shielding

In this paper, performances of a 4H-SiC UMOSFET with split gate and P+ shielding in different configurations are simulated and compared, with an emphasis on the switching characteristics and short circuit capability. A novel structure with the split gate in touch with the P+ shielding is proposed. The key design issues for 4H-SiC UMOSFETs are trench gate dielectric protection and reverse transfer capacitance Crss reduction. Based on simulation results, it is concluded that a UMOSFET with a gate structure combining split gate grounded to the trench bottom protection P+ shielding layer and a current spreading layer is achieved to yield the best compromise between conduction, switching, and short circuit performance. The split-gate design can effectively reduce Crss by shielding the coupling between the gate electrode and the drain region. The P+ shielding design not only protects the oxide at trench bottom corners but also minimizes the short channel effect due to drain-induced barrier lowing and the channel length modulation. Trade-off of the doping concentration of current spreading layer for UMOSFET is also discussed. A heavily doped current spreading layer may increase Crss and influence the switching time, even though RON,SP is reduced.

Failure Mechanism of Avalanche Condition for 1200-V Double Trench SiC MOSFET

Due to superior properties of silicon carbide (SiC), the unipolar conduction mechanism of metal-oxide-semiconductor-field-effect transistor (MOSFET), and the structural feature, double trench SiC MOSFETs have great potential to be one of the next-generation power switches. In this article, an avalanche safe operation area (SOA) is established, and a new failure behavior of 1200-V double trench SiC MOSFET is revealed timely through unclamped inductive switching (UIS) test (300 K of initial temperature). With comprehensive analyses involving terminal impedance measurement, monitoring of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gss</sub> before and after each avalanche test, inner electric field comparison by physics-based device modeling, maximum die temperature estimation, and decapsulation validation, the predominant failure mechanism (fracture of trench gate oxide) is identified for double trench SiC MOSFET under UIS test. Before the maximum die temperature approaches the melting point of source metal, the fracture of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer located at gate trench bottom and corner occurs, which is degraded by duration, excessive electric field, and elevated temperature. Accordingly, we propose I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gss</sub> as a predicting indicator of avalanche failure, which should be a key monitoring scheme in particular for trench type SiC MOSFET.

Impact of Si(100) doping methods on TiSi2 formation in vertical and horizontal FET structure areas with increasing aspect ratio

Due to the increasing complexity of FET structures and the preferred high trench aspect ratios, demanding process challenges exist, not only in the structuring of the contact trenches, but also in the uniform doping of the diffusion area. Previous investigations have mainly analyzed the doping of horizontal contact areas. For this reason, this paper demonstrates how vertical and horizontal contact areas can be doped through the side wall at the same time. For this purpose, relationships between structural geometry and doping methods are studied in order to structure a multitude of contact trenches next to each other in a functional way, which can realize source and drain trenches. By means of an ion implanted test structure, high doping concentrations of up to 1019 cm−3 could be achieved at a depth of approx. 250 nm below the 2.5 μm deep contact trench bottom. The concentration which can be obtained by PSG diffusion decreases rapidly with increasing Si depth. For the first time, it is shown that the dopant particle concentration of ion implantation increases with trench height and proximity to the trench side wall. Accordingly, the electrical conductivity is also higher and the SR value lower. A positive effect of the near-surface doping concentrations on the subsequent C49-TiSi2 formation could be demonstrated, which enables uniform film growth. In contrast, dopant deposition generates asymmetric dopant concentrations and prevents uniform silicide formation as the aspect ratio increases, thus causing higher diffusion area resistances.

Deformation characteristics of latticed diaphragm wall in revetment foundation trench for one immersed tunnel

In this paper, based on the excavation of revetment foundation trench of an immersed tunnel project in Guangzhou, China, the influence of the insertion ratio of latticed diaphragm wall, the thickness of muddy layer under the bottom of foundation trench, the grading excavation of foundation trench and the construction of undercrossing shield tunnel are considered respectively, to study the deformation characteristics of diaphragm wall by three-dimensional numerical simulation. In addition, the finite element strength reduction method is used to analyse the stability of the latticed diaphragm wall. The results show that: the maximum lateral deformation of the latticed diaphragm wall decreases with the increase of the insertion ratio. When the insertion ratio rises to about 0.63, the lateral deformation will change slightly from then on; The increasing thickness of muddy layer has more and more influence on the lateral deformation of diaphragm wall; The deformation of diaphragm wall mainly comes from the excavation of foundation trench, and is very little affected by the excavation of the shield tunnel; Under actual working condition, the safety factor of diaphragm wall calculated by strength reduction method is about 4.1 also.

Effect of U-shape trench etching process on electrical properties of GaN vertical trench metal-oxide-semiconductor field-effect transistor

As reported by several market analysts, GaN-based power devices show great potential applications in the low and medium voltage range ( &lt; 900 V). For high voltage ( &gt; 1200 V), including ship transportation and power grid, the future applications of GaN highly depend on the development of vertical devices based on GaN substrates. Several vertical devices have been reported, such as current aperture vertical electron transistors (CAVETs), U-shape trench metal-oxide-semiconductor field-effect transistors (UMOSFETs), and fin power transistors. And the UMOSFETs show potential advantages due to greater simplicity in material epitaxy and fabrication process. In the fabrication of UMOSFETs, the U-shape trench dry etching is the most critical process. The GaN sidewalls after dry etching directly affect the interface state characteristics in the MOS structure and the channel electron transport. In this work, etching optimization including etching radio-frequency (RF) power and etching mask is investigated and process-dependent electrical characteristics of GaN UMOSFETs are also studied. The appropriate decrease of RF power ensuring the steep sidewalls can effectively improve the channel electron mobility from 35.7 cm&lt;sup&gt;2&lt;/sup&gt;/(V·s) to 48.1 cm&lt;sup&gt;2&lt;/sup&gt;/(V·s) and consequently increase the ON-state current and reduce the ON-state resistance. Larger etching damage to the p-GaN sidewall caused by higher RF power leads the scattering effects to increase and the mobility of the channel carriers to decrease. The interface state density at the channel can be extracted by the subthreshold swing. The interface state density decreases to 1.90 × 10&lt;sup&gt;12&lt;/sup&gt; cm&lt;sup&gt;–&lt;/sup&gt;&lt;sup&gt;2&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; when the RF power is regulated to 50 W, which is only half of the interface state density when RF power is 135 W. Similar breakdown voltages (350－380 V) are measured for these devices with varying RF power, which are governed by gate early breakdown. Positive valence band offset is formed in the SiO&lt;sub&gt;2&lt;/sub&gt;/GaN MOS structure and the early breakdown occurs due to the holes accumulating at the SiO&lt;sub&gt;2&lt;/sub&gt;/GaN interface. The etching uniformity at the bottom of U-shape trench can be improved by using the SiO&lt;sub&gt;2&lt;/sub&gt; hard masks instead of photoresist masks. Sub-trenches at both ends of the trench bottom are observed in the device with photoresist masks, leading the carrier scattering to increase and ON-state current to decrease. Besides, the interface state density decreases from 3.42 × 10&lt;sup&gt;12&lt;/sup&gt; cm&lt;sup&gt;–2&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; to 2.46 × 10&lt;sup&gt;12&lt;/sup&gt; cm&lt;sup&gt;–2&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; with a SiO&lt;sub&gt;2&lt;/sub&gt; hard mask layer used. Compared with 1.6 μm photoresist mask, the thinner SiO&lt;sub&gt;2&lt;/sub&gt; mask with a thickness of 500 nm has a small sidewall area, which weakens the high-energy ion reflection in the inductively coupled plasma system. Consequently, the over-etching at the bottom ends of the trench is improved significantly and therefore the fabricated GaN UMOSFET has higher channel mobility and a lower interface state density.

Efficient sequestration of terrigenous organic carbon in the New Britain Trench

The fate of terrigenous organic carbon (OCterr) in the ocean remains an enigma for four decades. Hadal trenches, the deepest ocean realm (6–11 km deep), were recently proposed to be OC depocenters, but whether and how much OCterr was sequestrated there remain elusive. Here we conducted comprehensive analyses for four sediment cores from the New Britain Trench (NBT) close to Papua New Guinea to assess source, translocation and burial of OC. The bulk and molecular radiocarbon data suggest that the NBT landward slope and axis sediments mainly receive young and biogenic rather than petrogenic OC. The three-endmember mixing model based on Δ14C, δ13C and OC contents reveals that sediments of the NBT axis (8225 m) comprise relatively high OC contents (0.66 ± 0.08%), of which biogenic OCterr accounts for 62 ± 10%. The high proportion of biogenic OCterr was attributed to the selective translocation of OCterr-enriched coarse particles and rapid delivery of sediments supported by unique V-shape feature of the trench. In contrast, the sediment OC at the oceanward slope is primarily of a marine origin, suggesting that OCterr was efficiently trapped in the trench bottom. It is estimated that the burial rate is 2.75 ± 0.32 g C m−2 yr−1 for OC and 1.69 ± 0.41 g C m−2 yr−1 for OCterr in the NBT. Given a fact that many trenches are close to the landmasses, we propose that the hadal trenches may contribute significantly to the burial of OCterr in the ocean.

Microbial community and geochemical analyses of trans-trench sediments for understanding the roles of hadal environments

Hadal trench bottom (>6000 m below sea level) sediments harbor higher microbial cell abundance compared with adjacent abyssal plain sediments. This is supported by the accumulation of sedimentary organic matter (OM), facilitated by trench topography. However, the distribution of benthic microbes in different trench systems has not been well explored yet. Here, we carried out small subunit ribosomal RNA gene tag sequencing for 92 sediment subsamples of seven abyssal and seven hadal sediment cores collected from three trench regions in the northwest Pacific Ocean: the Japan, Izu-Ogasawara, and Mariana Trenches. Tag-sequencing analyses showed specific distribution patterns of several phyla associated with oxygen and nitrate. The community structure was distinct between abyssal and hadal sediments, following geographic locations and factors represented by sediment depth. Co-occurrence network revealed six potential prokaryotic consortia that covaried across regions. Our results further support that the OM cycle is driven by hadal currents and/or rapid burial shapes microbial community structures at trench bottom sites, in addition to vertical deposition from the surface ocean. Our trans-trench analysis highlights intra- and inter-trench distributions of microbial assemblages and geochemistry in surface seafloor sediments, providing novel insights into ultradeep-sea microbial ecology, one of the last frontiers on our planet.

Two-step potassium hydroxide etching to enhance aspect ratio in trench fabrication

Among various grating structure fabrication techniques, potassium hydroxide (KOH) wet anisotropic etching of Si(110) wafers offers low cost and impressive aspect ratio over large areas with high etch uniformity. The aspect ratio is ultimately limited by lateral etching that constantly widens the trenches. In this paper, the authors demonstrated a method to double the achievable aspect ratio using two-step KOH etching. After first KOH etching, the grating structure was grown with a thermal oxide; and after removing the oxide from the trench bottom using reactive ion etching, a second KOH etching was carried out with the original trench sidewall protected by the thermal oxide. The authors achieved the highest anisotropy [etching rate ratio of (110) and (111)] of 247 with 50 wt. % KOH at room temperature. Using the two-step KOH etching, it is possible to increase the aspect ratio by more than a factor of 2 while keeping the trench width almost unchanged.