Si Micro Research Articles

Study of Proton Radiation Damage Effects in Si microstrip Detector for New and Fast Tracking System of pCT

A new and fast radiation hard p-Si micro strip detector requires for the high proton imaging performance using the Proton Computed Tomography (pCT) system. Silicon trackers of the pCT have been measured the actual proton dose delivered to the cancer patient during the medical treatment. In this paper, several proton cancer doses up to 9.62x 1014 neq,/cm2 are used for the SRH modelling of the full depletion voltage and leakage current at 293 K of the Si micro-strip detector using microscopic radiation damage model. Radiation hard thin (150μm) p-type MCz Si micro strip detector design is proposed for the pCT that can work up to 800V for very high-irradiated proton cancer doses.

Experimental considerations for integration method of Si thin-film microchips for fluidic self-assembly

Fluidic self-assembly is a technique in which numerous semiconductor chips are integrated spontaneously. Here, we demonstrate that the integration efficiency is significantly improved by optimizing the separation conditions and appropriately controlling the external forces to which the microchips are subjected to the solution. In particular, an external drag force was found to prevent the Si microchips from forming aggregations and prompting transfer to the Si receiver pockets. This resulted in a significant improvement in the integration selectivity. Moreover, experiments with various microchip sizes statistically determined the effect of the Si receiver chip rinse on the evaluation functions: deposition selectivity, yield, and overall yield. While rinsing was effective for fluidic self-assembly of 10 μm scale Si microchips, rinsing of 800 nm scale chips is indicated to have different integration mechanisms. Our quantitative analysis indicated the potential applicability of the fluidic self-assembly technique to the integration technologies of Si micro semiconductor devices.

Analysis of Bulk and Surface Radiation Damage in n+ in p SFz Si Micro Strip Detectors for the Future High Luminosity Collider Experiments: TCAD Simulation and Measurements

Within the framework of CERN RD50 collaboration, several radiation damage models for n/p-SFz, n-MCz Si have been explored for the better understanding of the experimental results in radiation damage analysis of the irradiated Si detectors. In the present paper, the important review on the microscopic radiation damage model for the p-type SFz Si detector combining the surface and radiation damage effects that can be used to simulate radiation damages effects in the heavily irradiated detectors for the good comparison of the experimental data and simulation result. The surface radiation damage models were extracted from the experimental measurements on the p-MOS capacitor and Gate-Controlled Diodes irradiated by Gamma or X-ray radiations in the range of 10 to 500 Mrad (Si). Whereas, the bulk damage model microscopic parameter was extracted from the experimental (TSC, DLTS) measurements on the n in p-SFz Si microstrip detector. The radiation damage (surface and bulk) models can be fed into the commercial Synopsys TCAD device simulator program for the designing and optimization of the detector, which can be used in the very harsh radiation environment of the HL-LHC, or FCC experiment. The objective of this analysis was to verify the experimental results using the new microscopic radiation damage models on the p-SFz Si for the radiation damage analysis of p- SFz Si detectors irradiated by proton, neutron or mixed at very high fluences. The results were verified by comparison of the experimental data with TCAD simulation.

TCAD simulation of radiation hard n-MCz and n-Fz Si microstrip detector for the HL-LHC

A radiation hard Si detector is used in the new CMS tracker detector at HL-LHC. It has been observed that n-MCz and n-Fz Si as a material can be used for the Si micro strip detector. The detector design for this material should be simulated and optimized to get high CCE. In order to understand the charge collection behavior of the n-MCz/n-FzSi detector, it is required to simulate and compare the radiation damage effects in the mixed irradiated n-MCz Si and proton irradiated n-Fz Si micro strip detector equipped with metal overhang and multiple guard rings. In this paper, we have done analysis and optimization of the radiation hard n-MCz Si/n-Fz Si strip detector design for the HL-LHC experiment in order to get high CCE.

Defect Mediated Improvements in the Photoelectrochemical Activity of MoS2/SnS2 Ultrathin Sheets on Si Photocathode for Hydrogen Evolution.

Solar-driven water electrolysis to produce hydrogen is one of the clean energy options for the current energy-related challenges. Si as a photocathode exhibits a large overpotential due to the slow hydrogen evolution reaction (HER) kinetics and hence needs to be modified with a cocatalyst layer. MoS2 is a poor HER cocatalyst due to its inert basal plane. Activation of the MoS2 basal plane will facilitate HER kinetics. In this study, we have incorporated SnS2 into MoS2 ultrathin sheets to induce defect formation and phase transformation. MoS2/SnS2 composite ultrathin sheets with a Sn2+ state create a large number of S vacancies on the basal sites. The optimized defect-rich MoS2/SnS2 ultrathin sheets decorated on surface-modified Si micro pyramids as photocathodes show a current density of -23.8 mA/cm2 at 0 V with an onset potential of 0.23 V under acidic conditions, which is higher than that of the pristine MoS2. The incorporation of SnS2 into 2H-MoS2 ultrathin sheets not only induces a phase but also can alter the local atomic arrangement, which in turn is verified by their magnetic response. The diamagnetic SnS2 phase causes a decrease in symmetry and an increase in magnetic anisotropy of the Mo3+ ions.

Optical Sensing of Chlorophyll(in) With Dual-Spectrum Si LEDs in SOI-CMOS Technology

Small and low-cost chlorophyll sensors are popular in agricultural sector and food-quality control.Combining such sensors with silicon CMOS electronics is challenged by the absence of silicon-integrated light-sources.We experimentally achieve optical absorption sensing of chlorophyll based pigments with silicon (Si) micro light-emitting diodes (LED) as light-source, fabricated in a standard SOI-CMOS technology.By driving a Si LED in both forward and avalanche modes of operation,we steer its electroluminescentspectrum between visible (400–900 nm) and near-infrared (~1120 nm). For detection of chlorophyll in solution phase, the dualspectrum light from the LED propagates vertically through glycerol micro-droplets containing sodium copper chlorophyllin at varying relative concentrations. The transmitted light is detected via an off-chip Si photodiode. The visible to near-infrared color ratio (COR) of the photocurrent yields the effective absorption coefficient. We introduce the LED-specificmolar absorption coefficient as ametric to compute the absolute pigment concentration (~0.019 ± 0.006 mol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) and validate the results by measurements with a hybrid spectrophotometer. With the same sensor, we also show noninvasive monitoring of chlorophyll in plant leaves. COR sensitivities <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 3.9 \times 10^{4}$ </tex-math></inline-formula> mol <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> L and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 5.3 \times 10^{4}$ </tex-math></inline-formula> mol <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> L are obtained for two leaf species, where light from the LED propagates diffusely through the thickness of the leaf prior to detection by the photodiode. Our work demonstrates the feasibility of realizing fully CMOS-integrated optical sensors for biochemical analyses in food sector and plant/human health.

Reduction of anchor loss in high quality factor silicon nano-resonator for gas sensors

Micro / Nano electromechanical system (MEMS / NEMS) resonators can achieve high-resonance quality factor (Q-factor), which can be advantageous in applications for ultra-sensitive gas sensing. Q-factor is being considered as an important parameter of such sensing devices, and is enhanced by reducing the dissipation of mechanical energy stored in the resonator arising from various sources including air damping, thermoelastic damping, anchor loss, etc. In this study, anchor loss is investigated because it can emerge as the dominant mechanism of energy dissipation in ultra-high-quality factor resonators operated in high vacuum and low temperature. By numerical analysis via finite element method using perfectly matched layer (PML) technique, several anchor geometries are proposed to reduce anchor loss. Among them, a design with additional mass at the anchor point gives the highest simulated Q-factor. We also fabricated Si micro resonators having 300–500 μm length, 2 μm width and 7.5 μm thickness from silicon-on-insulator wafer. Q-factor of the fabricated micro resonators is evaluated in a vacuum chamber (~1 Pa) and at room temperature by the ring-down method with a digital lock-in-amplifier.

Light Emitting Properties of Si Micro Single Crystal Grown by Mixed-Source HVPE Method

Light Emitting Properties of Si Micro Single Crystal Grown by Mixed-Source HVPE Method

Estimation of the Electricity Storage Volume Density of Compact SMESs of a New Concept Based on Si Microfabrication Technologies

A compact superconducting magnetic energy storage system (SMES) produced by Si micro fabrication technologies has been proposed to improve electricity storage volume density, w, in the sub-Wh/L range of conventional SMESs and to produce them at a low cost by mass production. In parallel with the experimental development reported previously, a series of trials was performed to estimate a feasible value of w based on the calculation of the magnetic field generated by the compact SMES by improving the calculation models step by step. In this work, the experimentally obtained magnetic flux density dependence of superconductive critical current density was taken into consideration for the first time in this series of trials, together with the additional improvement of the calculation models. The results of the estimation indicated that a compact SMES produced by the proposed concept can attain a w in the Wh/L range or more, ranking with or surpassing that of presently used capacitors.

Large-Scale Synthesis of Highly Uniform Silicon Nanowire Arrays Using Metal-Assisted Chemical Etching.

The combination of metal-assisted chemical etching (MACE) with colloidal lithography has emerged as a simple and cost-effective approach to nanostructure silicon. It is especially efficient at synthesizing Si micro- and nanowire arrays using a catalytic metal mesh, which sinks into the silicon substrate during the etching process. The approach provides a precise control over the array geometry, without requiring expensive nanopatterning techniques. Although MACE is a high-throughput solution-based approach, achieving large-scale homogeneity can be challenging because of the instability of the metal catalyst when the experimental parameters are not set appropriately. Such instabilities can lead to metal film fracture, significantly damaging the substrate and thus compromising the nanowire array quality. Here, we report on the critical parameters that influence the stability of the metal catalyst layer for achieving large-scale homogeneous MACE: etchant composition, metal film thickness, adhesion layer thickness, nanowire diameter and pitch, metal film coverage, Si/Au/etchant interface length, and crystalline quality of the colloidal template (grain size and defects). Our results investigate the origin of the catalyst film fracture and reveal that MACE experiments should be optimized for each Si wire array geometry by keeping the etch rate below a certain threshold. We show that the Si/Au/etchant interface length also affects the etch rate and should thus be considered when optimizing the MACE experimental parameters. Finally, our results demonstrate that colloidal templates with small grain sizes (i.e., <100 μm2) can yield significant problems during the pattern transfer because of a high density of defects at the grain boundaries that negatively affects the metal film stability. As such, this work provides guidelines for the large-scale synthesis of Si micro- and nanowire arrays via MACE, relevant for both new and experienced researchers working with MACE.

Morphology control of c-Si via facile copper-assisted chemical etching: Managements on etch end-points

Abstract Micro-/nano-structures enable crystalline silicon (c-Si) to be prominent in many fields. In this work, an elaborate study on texturing c-Si via copper-assisted chemical etching (Cu-ACE) is reported. Various large-area craters arrays including gyro-like craters arrays, standard inverted pyramids arrays and deformed inverted pyramids arrays, together with mesoporous surfaces and polished-like surfaces are synthesized on Si wafers with Cu-ACE. An electrokinetic “H2O2 consumption” model and an energy band model are proposed to explain the synergetic effects between isotropic and anisotropic etching on preparing Si micro-/nano-structures during etching. It is demonstrated that the etched morphology is determined by the temporal H2O2 relative concentration at etch end-points, which is accurately controlled by etching conditions. A “curved sidewalls” model is put forward, for the first time, to illustrate the nuances among etched craters arrays. Based on this model, the local H2O2 relative concentration determines local curvatures of sidewalls. Textured Si wafers with inverted pyramids arrays exhibit excellent anti-reflection abilities and are promising for solar cells, photodiodes or other optoelectronic applications. Notably, our work provides a facile and controllable approach to produce various Si micro-/nano-structures which are of practical values in many domains.

Organic-inorganic composite nanocoatings with superhydrophobicity and thermal stability

PurposeThis paper aims to investigate the thermal stability and hydrophobicity of difference alkyl chain of silanes with silicon (Si) micro- and nanoparticles.Design/methodology/approachSol-gel methods have been used to design superhydrophobic glass substrates through surface modification by using low-surface-energy Isooctyl trimethoxysilane (ITMS) and Ethyl trimethoxysilane (ETMS) solution. Hierarchical double-rough scale solid surface was built by Si micro- and nanoparticles to enhance the surface roughness. The prepared sol was applied onto glass substrate using dip-coating method and was dried at control temperature of 400°C inside the tube furnace.FindingsThe glass substrate achieved the water contact angle as high as 154 ± 2° and 150.4 ± 2° for Si/ITMS and Si/ETMS films, respectively. The Si/ITMS and Si/ETMS also were equipped with low sliding angle as low as 3° and 5°, respectively. The Si micro- and nanoparticles in the coating system have created nanopillars between them, which will suspend the water droplets. Both superhydrophobic coatings have showed good stability against high temperature up to 200°C as there are no changes in WCA shown by both coatings. Si/ITMS film sustains its superhydrophobicity after impacting with further temperature up to 400°C and turns hydrophobic state at 450°C.Research limitations/implicationsFindings will be useful to develop superhydrophobic coatings with high thermal stability.Practical implicationsSol method provides a suitable medium for the combination of organic-inorganic network to achieve high hydrophobicity with optimum surface roughness.Originality/valueApplication of different alkyl chain groups of silane resin blending with micro- and nanoparticles of Si pigments develops superhydrophobic coatings with high thermal stability.

Three-Dimensional Electrochemical Axial Lithography on Si Micro- and Nanowire Arrays.

A templated electrochemical technique for patterning macroscopic arrays of single-crystalline Si micro- and nanowires with feature dimensions down to 5 nm is reported. This technique, termed three-dimensional electrochemical axial lithography (3DEAL), allows the design and parallel fabrication of hybrid silicon nanowire arrays decorated with complex metal nano-ring architectures in a flexible and modular approach. While conventional templated approaches are based on the direct replication of a template, our method can be used to perform high-resolution lithography on pre-existing nanostructures. This is made possible by the synthesis of a porous template with tunable dimensions that guides the deposition of well-defined metallic shells around the Si wires. The synthesis of a variety of ring architectures composed of different metals (Au, Ag, Fe, and Ni) with controlled sequence, height, and position along the wire is demonstrated for both straight and kinked wires. We observe a strong enhancement of the Raman signal for arrays of Si nanowires decorated with multiple gold rings due to the plasmonic hot spots created in these tailored architectures. The uniformity of the fabrication method is evidenced by a homogeneous increase in the Raman signal throughout the macroscopic sample. This demonstrates the reliability of the method for engineering plasmonic fields in three dimensions within Si wire arrays.

Thermal performance optimization of Si micro flat heat pipes by Box–Behnken design

Si micro heat pipe (MHP) is become an excellent passive cooling device for thermal management of micro electronics packages because of its considerable thermo-mechanical matching and fabrication feasibility with micro machining methods. The structural and operational parameters have nonlinear relationship which effect on thermal performance of MHP. In this experimental study, three different Si MHPs with same dimensions and hydraulic diameter of 120 μm, and various cross-sections are fabricated by micro fabrication methods and tested under different conditions of fluid charge ratios and input powers. To obtain optimal condition among effective input variables of fluid ratio, input power and cross-section’s shape, statistical method of Box–Behnken design (BBD) from response surface method family is used and experiments are performed according to BBD. Comparison between experiments and optimized model, demonstrated BBD method can establish acceptable relationship between effective input/output parameters, without solving the nonlinear and complex equations. Both theoretical and experimental methods confirmed that the trapezoidal MHP associated with rectangular artery which was charged with 40% of its vapor chamber’s volume had the best thermal performance.

Cycling Behavior of Silicon-Containing Graphite Electrodes, Part B: Effect of the Silicon Source

Silicon (Si) is a promising candidate to enhance the specific charge of graphite electrode, but there is no consensus in the literature on its cycling mechanism. Our aim in this study was to understand Si electrochemical behavior in commercially viable graphite/Si electrodes. From the comparison of three types of commercial Si particles with a producer-declared particle sizes of 30–50 nm, 70–130, and 100 nm, respectively, we identified the presence of micrometric Si agglomerates and the Si micro- and mesoporosity as the main physical properties affecting the cycling performance. Moreover, ex situ SEM, XRD, and Raman investigations allowed us to understand the lithiation/delithiation mechanism for each type of Si particles. For nanoscale Si particles, the entire Si particle is utilized, resulting in high specific charge, and the stress induced by the formation of Li15Si4 alloy upon deep lithiation is well managed within the Si mesoporosity. This leads to reversible cycling behavior and, thus, to good cycli...

Electrochemical Deposition of Conformal and Functional Layers on High Aspect Ratio Silicon Micro/Nanowires.

Development of new synthetic methods for the modification of nanostructures has accelerated materials design advances to furnish complex architectures. Structures based on one-dimensional (1D) silicon (Si) structures synthesized using top-down and bottom-up methods are especially prominent for diverse applications in chemistry, physics, and medicine. Yet further elaboration of these structures with distinct metal-based and polymeric materials, which could open up new opportunities, has been difficult. We present a general electrochemical method for the deposition of conformal layers of various materials onto high aspect ratio Si micro- and nanowire arrays. The electrochemical deposition of a library of coaxial layers comprising metals, metal oxides, and organic/inorganic semiconductors demonstrate the materials generality of the synthesis technique. Depositions may be performed on wire arrays with varying diameter (70 nm to 4 μm), pitch (5 μ to 15 μ), aspect ratio (4:1 to 75:1), shape (cylindrical, conical, hourglass), resistivity (0.001-0.01 to 1-10 ohm/cm2), and substrate orientation. Anisotropic physical etching of wires with one or more coaxial shells yields 1D structures with exposed tips that can be further site-specifically modified by an electrochemical deposition approach. The electrochemical deposition methodology described herein features a wafer-scale synthesis platform for the preparation of multifunctional nanoscale devices based on a 1D Si substrate.

A micro test platform for in-situ mechanical and electrical characterization of nanostructured multiferroic materials

This paper presents a novel approach to simultaneously fabricate a Si micro test platform and a nanostructured test specimen of a multiferroic material with critical dimension of 200nm and lateral aspect ratio of 33 for in-situ characterization in a scanning electron microscope (SEM). The design is adjusted to allow for electrical resistance measurements and tensile tests. We report on a fabrication process comprising e-beam lithography and dry etching technology and, as a proof of concept, on the measurement of the force-displacement characteristics of Ni nanobeams.

Bi-modal nanoheteroepitaxy of GaAs on Si by metal organic vapor phase epitaxy

Nano-heteroepitaxial growth of GaAs on Si(001) by metal organic vapor phase epitaxy was investigated to study emerging materials phenomena on the nano-scale of III–V/Si interaction. Arrays of Si nano-tips (NTs) embedded in a SiO2 matrix were used as substrates. The NTs had top Si openings of 50–90 nm serving as seeds for the selective growth of GaAs nano-crystals (NCs). The structural and morphological properties were investigated by high resolution scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, x-ray diffraction, and high resolution scanning transmission electron microscopy. The GaAs growth led to epitaxial NCs featuring a bi-modal distribution of size and morphology. NCs of small size exhibited high structural quality and well-defined {111}–{100} faceting. Larger clusters had less regular shapes and contained twins. The present work shows that the growth of high quality GaAs NCs on Si NTs is feasible and can provide an alternate way to the integration of compound semiconductors with Si micro- and opto-electronics technology.

The effects of Ag particle morphology on the antireflective properties of silicon textured using Ag-assisted chemical etching

Metal assisted chemical etching (MaCE) of silicon wafers is of interest for fabrication of antireflective layers for single-crystal Si solar cells. This paper presents an Ag-assisted chemical etching approach for single-crystal Si that generates wafer scale micro- and nano-porous textures with controlled surface morphologies and reflectance properties. The approach begins with an Ag thin film annealing process to form Ag micro- and nanoparticles on the Si substrate. This is followed by MaCE, where the Ag particles serve as a catalyst to produce a micro- and nano-porous texture on the Si surface. The morphology of the fabricated Si micro- and nanopores is controlled in accordance with the size and shape of the Ag particles, which are tuned by annealing the Ag films at different temperatures from 300 to 800 °C. The reflectance of the Si surface is in turn determined by the morphology of the etched texture. The fabricated Si antireflective textures have compound hierarchical structures, and an average reflectance of ∼4.7% is obtained when the Ag film is annealed at 600 °C.

Height reversal of Si micro dot and well patterns during Si nanowire formation by Ag-assisted chemical etching

The Si nanowire (Si-NW) formation process has been studied to develop a new anode material for lithium ion batteries. Si-NWs were prepared by a combination of electroless metal deposition (EMD) of Ag and metal-assisted chemical etching (Mac etching) on Si substrates that have micro dot and well patterns with respect to their height. During the fabrication of Si-NWs, height reversal occurred in the micro dot and well patterns, and Si micro- and nano-hybrid systems were fabricated. We also observed structural changes of the Si micro- and nano-hybrid structures during the electrochemical charge/discharge process of lithium ions, and showed that this hybrid system is robust for the volume change accompanied with the lithiation/delithiation reaction.