Thin Silicon Research Articles

Аморфизация кремниевых нанонитей при облучении ионами аргона

The irradiation of silicon nanowires with Ar+ ions with an energy of 250 keV and fluences from 1013 cm^-2 to 10^16 cm^-2 was carried out. The dependence of the destruction of the structure under the action of ion irradiation on the fluence is investigated by the Raman spectroscopy. It is shown that the amorphization of porous silicon occurs at higher dpa values than in thin silicon thin films.

Numerical Simulation and Experiment of a High-Efficiency Tunnel Oxide Passivated Contact (TOPCon) Solar Cell Using a Crystalline Nanostructured Silicon-Based Layer

We report on the tunnel oxide passivated contact (TOPCon) using a crystalline nanostructured silicon-based layer via an experimental and numerical simulation study. The minority carrier lifetime and implied open-circuit voltage reveals an ameliorated passivation property, which gives the motivation to run a simulation. The passivating contact of an ultra-thin silicon oxide (1.2 nm) capped with a plasma enhanced chemical vapor deposition (PECVD) grown 30 nm thick nanocrystalline silicon oxide (nc-SiOx), provides outstanding passivation properties with low recombination current density (Jo) (~1.1 fA/cm2) at a 950 °C annealing temperature. The existence of a thin silicon oxide layer (SiO2) at the rear surface with superior quality (low pinhole density, Dph < 1 × 10−8 and low interface trap density, Dit ≈ 1 × 108 cm−2 eV−1), reduces the recombination of the carriers. The start of a small number of transports by pinholes improves the fill factor (FF) up to 83%, reduces the series resistance (Rs) up to 0.5 Ω cm2, and also improves the power conversion efficiency (PEC) by up to 27.4%. The TOPCon with a modified nc-SiOx exhibits a dominant open circuit voltage (Voc) of 761 mV with a supreme FF of 83%. Our simulation provides an excellent match with the experimental results and supports excellent passivation properties. Overall, our study proposed an ameliorated knowledge about tunnel oxide, doping in the nc-SiOx layer, and additionally about the surface recombination velocity (SRV) impact on TOPCon solar cells.

Monolithically integrated optical interference and absorption filters on thin film amorphous silicon photosensors for biological detection

High selectivity of photosensors is needed for targeted biological detection. Optical interference filters are monolithically integrated with hydrogenated amorphous silicon thin film photosensors for fluorescence measurements in lab-on-chip applications using a methodology that enables customization of fluorescence detection for various applications. The design of the optical interference filters is tailored to match the requirements of each application and the filters are fabricated as nitride-oxide multilayers. The interference filters are combined with hydrogenated amorphous silicon-carbon alloys, which serve as long-pass absorption filters, depending on the spectral requirements. In this work we demonstrate the development of these filters, through simulations and design, followed by experimental fabrication and characterization of transmission spectra, and finally, integration with photosensors which are implemented in measurements to detect fluorescence in three different applications, including bacteriophage fluorescence, quantum dot and Cy3 fluorophores, and grape fluorescence for grape maturation monitoring, in a novel methodology that allows for simplification and greater portability of the measurement setup and negates the need to stack optical filters in fluorescence applications.

GaN-based heterostructures with CVD diamond heat sinks: A new fabrication approach towards efficient electronic devices

A new approach to the fabrication of efficient heat sinks for GaN-based transistors is demonstrated. A key feature of this work is the growth of polycrystalline diamond coating on the functional silicon layer of SOI wafers followed by etching of a thick silicon substrate and a thin thermal oxide. As a result, composite epi–ready substrates consisting of a thin (410 nm) monocrystalline silicon functional layer on top of the 150 µm-thick polycrystalline diamond heat sink were fabricated. GaN heterostructures were grown on top of the silicon layer, which resulted in an effective thermal contact between CVD diamond and GaN structure. The packaged ungated transistors were made to analyze the efficiency of the developed heat sink. Improved heat removal structures showed the decrease in surface temperature by more than 50 °C at base temperature of Tb=85 °C and dissipation power of Pdiss=6.9 W/mm compared to conventional GaN-on-SiC technology and by more than 20 °C at Tb=25 °C, Pdiss=6.9 W/mm compared to up-to-date GaN-on-Diamond equivalent transistors reported by other groups. New substrate fabrication technology positively impacts GaN-based device output characteristics and reliability, which is important in improving communication systems, radars, and secondary power supply systems.

Accuracy of metal 3D printed frameworks for removable partial dentures evaluated by digital superimposition

ObjectivesTo evaluate the accuracy of metal 3D printed frameworks (MEP group) for removable partial dentures (RPDs) by digital superimposition, in comparison to that of frameworks produced by the conventional (CON group) and resin printing/casting (RPC group) workflows. MethodsA partially edentulous maxillary dentiform was prepared with rest seats and guiding planes on the right canine, left first premolar, and left second molar. Thirty master casts were prepared via repeated impressions of the dentiform. Frameworks were fabricated by three different workflows (n = 10 for each group). The internal discrepancies of the frameworks were assessed at 12 points by digital scanning with an optical triangulation principle-based tabletop scanner and superimposition using a reference best-fit alignment method. First, the master cast was scanned alone. Subsequently, a thin silicone material was applied to the framework and fitted onto the master cast, after which the framework was removed. Finally, the master cast with the silicone material attached was rescanned. The data from the two scans were matched, with the reference being the area not occupied by the silicone. ResultsFor the CON, MEP, and RPC groups, respectively, the mean overall internal discrepancies (279.72 µm, 241.02 µm, and 331.70 µm), and the mean internal discrepancies on palate areas (292.92 µm, 250.72 µm, and 355.84 µm) and rest seat areas (240.12 µm, 211.91 µm, and 259.26 µm) did not significantly differ among the three fabrication methods (p = 0.558, 0.542, and 0.774). SignificanceThe reference best-fit alignment of scan datasets is a useful approach to evaluate the internal discrepancy of frameworks. Metal 3D printing produces RPD frameworks that are comparable to conventional frameworks and meet clinical standards.

An integrated device for fast and sensitive immunosuppressant detection

The present paper describes a compact point of care (POC) optical device for therapeutic drug monitoring (TDM). The core of the device is a disposable plastic chip where an immunoassay for the determination of immunosuppressants takes place. The chip is designed in order to have ten parallel microchannels allowing the simultaneous detection of more than one analyte with replicate measurements. The device is equipped with a microfluidic system, which provides sample mixing with the necessary chemicals and pumping samples, reagents and buffers into the measurement chip, and with integrated thin film amorphous silicon photodiodes for the fluorescence detection. Submicrometric fluorescent magnetic particles are used as support in the immunoassay in order to improve the efficiency of the assay. In particular, the magnetic feature is used to concentrate the antibody onto the sensing layer leading to a much faster implementation of the assay, while the fluorescent feature is used to increase the optical signal leading to a larger optical dynamic change and consequently a better sensitivity and a lower limit of detection. The design and development of the whole integrated optical device are here illustrated. In addition, detection of mycophenolic acid and cyclosporine A in spiked solutions and in microdialysate samples from patient blood with the implemented device are reported.Graphical abstract

An LGAD-Based Full Active Target for the PIONEER Experiment

PIONEER is a next-generation experiment to measure the charged pion branching ratios to electrons vs. muons Re/μ=Γπ+→e+ν(γ)Γπ+→μ+ν(γ) and pion beta decay (Pib) π+→π0eν. The pion to muon decay (π→μ→e) has four orders of magnitude higher probability than the pion to electron decay (π→eν). To achieve the necessary branching-ratio precision it is crucial to suppress the π→μ→e energy spectrum that overlaps with the low energy tail of π→eν. A high granularity active target (ATAR) is being designed to suppress the muon decay background sufficiently so that this tail can be directly measured. In addition, ATAR will provide detailed 4D tracking information to separate the energy deposits of the pion decay products in both position and time. This will suppress other significant systematic uncertainties (pulse pile-up, decay in flight of slow pions) to <0.01%, allowing the overall uncertainty in to be reduced to O (0.01%). The chosen technology for the ATAR is Low Gain Avalanche Detector (LGAD). These are thin silicon detectors (down to 50 μm in thickness or less) with moderate internal signal amplification and great time resolution. To achieve a 100% active region several emerging technologies are being evaluated, such as AC-LGADs and TI-LGADs. A dynamic range from MiP (positron) to several MeV (pion/muon) of deposited charge is expected, the detection and separation of close-by hits in such a wide dynamic range will be a main challenge. Furthermore, the compactness and the requirement of low inactive material of the ATAR present challenges for the readout system, forcing the amplifier chip and digitizer to be positioned away from the active region.

Enhancing Si Solar Cells Efficiency by Adding SiO2 / TiO2 Thin Films Using Transfer Matrix Method

Thin film silicon solar cells are nowadays the best choice to get electricity due to their low cost compared to the crystalline solar cells. However, thin film silicon solar cells have weak absorption of incident light. To deal with such a weakness and get better efficiency of these cells, an efficient back reflector composed of multilayer thin films (Silver, Silicon dioxide (SiO2) and Titanium dioxide (TiO2)) will be used. The transmitted light from the first silicon layer will be reflected by the next layer, and the reflected light will go back to the first silicon layer. By this way, the absorbance of the silicon solar cell can be increased by an increase in the probability of the light reflection from the SiO2, TiO2 and Ag. The transfer matrix method (TMM) by Matlab program will be used to analyze the results of the reflectance, transmittance and absorbance of the thin film layer and these results can prove the efficiency of the cells by using MATLAB codes.

Fracture strength of silicon solar wafers with different surface textures

Surface texturing is widely used in modern photovoltaic converters to improve light capture and increase efficiency. This paper focuses on the influence of the surface texture on the mechanical strength of silicon wafers. Various existing test methods and approaches for measuring the mechanical strength of silicon wafers are discussed and reviewed. The surface morphology of silicon wafers with different textures is characterized by scanning electron microscopy (SEM). The mechanical strength of thin (<200 μm) silicon wafers with different surface textures is measured with a ring-on-ring bending test. A finite element method (FEM) is used to calculate the maximum stress. Weibull statistical theory is applied to the measured fracture stresses. The mean fracture strength, its standard deviation, the Weibull characteristic strength, and the Weibull modulus are obtained for silicon wafers with various surface textures. The fracture strength of silicon wafers is strongly affected by the surface texture. It is found that the fracture strength of silicon wafers with pyramidal textures increases with decreasing size of the pyramids. A new type of surface texture produced by a V2O5 selective oxidation exhibited fracture comparable or higher than that of the wafers with conventional pyramidal textures produced by alkaline etching.

Amorphous Silicon Thin Film Deposition for Poly-Si/SiO2 Contact Cells to Minimize Parasitic Absorption in the Near-Infrared Region

Tunnel oxide passivated contact (TOPCon) solar cells are key emerging devices in the commercial silicon-solar-cell sector. It is essential to have a suitable bottom cell in perovskite/silicon tandem solar cells for commercial use, given that good candidates boost efficiency through increased voltage. This is due to low recombination loss through the use of polysilicon and tunneling oxides. Here, a thin amorphous silicon layer is proposed to reduce parasitic absorption in the near-infrared region (NIR) in TOPCon solar cells, when used as the bottom cell of a tandem solar-cell system. Lifetime measurements and optical microscopy (OM) revealed that modifying both the timing and temperature of the annealing step to crystalize amorphous silicon to polysilicon can improve solar cell performance. For tandem cell applications, absorption in the NIR was compared using a semitransparent perovskite cell as a filter. Taken together, we confirmed the positive results of thin poly-Si, and expect that this will improve the application of perovskite/silicon tandem solar cells.

Efficient thin crystalline silicon photoanode with lithium fluoride based electron contacts

Thin c-Si-based photoelectrochemical cells are regarded as one of the most promising alternatives to ensure cost-effectiveness of water-splitting systems. In this work, we demonstrate a lithium fluoride (LiFX) layer as an electron-selective contact for cost-competitive 30-µm thick c-Si photoanode devices. To ensure low contact resistance through LiFX/Al contacts on c-Si substrates is demonstrated; due to this low-resistance contact, efficient oxygen-evolution reactions might increase. We achieve an onset-voltage reduction with a cathodic shift of approximately 233 mV and an overpotential reduction of approximately 270 mV at 10 mA/cm2 in a 1 M KOH solution. These results offer a cost-effective enhancement of thin c-Si photoelectrodes for water-splitting systems.

Tuning the optoelectronic properties of AZO thin films for silicon thin film solar cell applications

Al-doped ZnO (AZO) thin films are deposited using dc magnetron sputtering and the process conditions are optimized to obtain transparent conducting electrode (TCE) with desirable properties suitable for photovoltaic applications. In the course, the effects of deposition parameters such as growth temperature, deposition time and plasma power density on the structural and optoelectronic properties were investigated using suitable characterization techniques. XRD analysis of the deposited films at different process conditions showed a strong c-axis preferred orientation. The surface roughness of the deposited films was examined using AFM analysis. Elemental analysis was carried out using XPS. The resistivity and sheet resistance of the thin films decreased with increase in temperature, deposition time and power density. The optimized films deposited at 250 °C resulted in electrical resistivity of 6.23 × 10−4 Ωcm, sheet resistance of 9.2 Ω/□ and exhibited an optical transmittance of &gt;85% in the visible range. Figure of merit (FOM) calculations were carried out to analyze the suitability of deposited thin films for thin film amorphous silicon solar cell applications. The photogain of optimized intrinsic a-Si:H layer was in the range of 104, whereas no photogain was observed in doped a-Si:H layers. The thin film solar cell fabricated using the optimized AZO film as TCE exhibited power conversion efficiency of 6.24% when measured at AM 1.5 condition.

Design, Fabrication, and Characterization of a Micro Coriolis Mass Flow Sensor Driven by PZT Thin Film Actuators

A micro Coriolis flow sensor accurately measures small mass flows without being affected by properties of the fluid. This paper presents a micro Coriolis mass flow sensor driven by PZT thin film piezoelectric actuators, which allows a combination of large actuation force, low power dissipation and virtually no self-heating. The sensor was fabricated using surface channel technology, resulting in a tube diameter of 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and a thin silicon-rich silicon nitride tube wall of 1.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> thick, with a few additional steps to form the integrated piezoelectric actuators. The integrated actuators can actuate the sensor into both swing mode and twist mode. Both actuation modes were evaluated for different fluids and the results are presented in this paper. In the case of swing mode actuation, an optical readout was used to detect the resulting Coriolis movement, resulting in a relatively low sensitivity. In the case of twist mode actuation, a capacitive readout was used and, in comparison to previously published devices, a high mass flow sensitivity was achieved thanks to an optimized readout design. The measurement results show the read-out noise has a standard deviation of 0.15% of the full scale of 1.8 gh <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> when actuated in the twist mode. [2020-0392]

Investigating Thin Silicone Oil Films Using Four-Wave Mixing Spectroscopy and Sum Frequency Generation Vibrational Spectroscopy.

This article applies four-wave mixing (FWM) spectroscopy, a third-order nonlinear optical spectroscopic technique which is not intrinsically surface- or interface-sensitive, to study silicone oil thin films, supplemented by second-order nonlinear-optical sum frequency generation (SFG) vibrational spectroscopy. Although studies of thin organic films using coherent antistokes Raman spectroscopy (CARS), a special case of FWM, have been reported previously, in this study we demonstrate the feasibility of using a more general FWM process which involves three independent excitation laser beams to investigate silicone oil thin films. The results show that the FWM method has the potential to detect and provide molecular-level information on ultrathin silicone oil layers, down to a film thickness of 1 nm. This developed FWM methodology is widely applicable and can be utilized to study important issues in the biopharmaceutical field, e.g., to examine the distribution of silicone oil on syringe glass surfaces with subnanometer sensitivity. It can also be used to study the potentially slow reactions between silicone oil and glass surfaces as proposed in the literature but without direct molecular-level information.

Correction factors to strength of thin silicon die in three- and four-point bending tests due to nonlinear effects

The thin silicon dies have been widely used in the three-dimensional integrated circuits (3DIC), stacked-die or wearable electronic packages to meet the requirements of small size, low-profile features, high-pin count, high performance, low-power consumption or even flexibility. The bending strengths of the thin dies cut from silicon wafers have to be determined to ensure no reliability problems, mostly resulting from packaging process handling, reliability testing, and operations. Three-point bending (3PB) and four-point bending (4PB) tests are commonly used for measuring die bending strength; however, both tests are still problematic for testing the thin silicon dies. Therefore, the mechanics of both tests are reevaluated in this study by a nonlinear finite element method (NFEM) with taking into account geometric nonlinearity (or large deflection), associated with the related theoretical formulations. The nonlinear mechanics of both tests are discussed in detail. NFEM results-based correction factors to the linear beam solutions are further proposed in the form of the polynomial fitting equations in this study. Those polynomial fitting equations of the correction factors are proved to be workable and easy to use with an engineering acceptable accuracy. Those correction factors are also found highly dependent on the deflection (δ), span length (L) and radius of roller support (r), but not on test specimen thickness (t) and elastic modulus (E).

Enhanced absorption in thin and ultrathin silicon films by 3D photonic band gap back reflectors

Since thin and ultrathin silicon films have limited optical absorption, we explore the effect of a nanostructured back reflector to recycle the unabsorbed light. As a back reflector, we investigate a three-dimensional (3D) photonic band gap crystal made from silicon that is readily integrated with the thin silicon films. We numerically obtain the optical properties by solving the 3D time-harmonic Maxwell equations using the finite-element method, and model silicon with experimentally determined optical constants. The absorption enhancement spectra and the photonic band gap generated current density are obtained by weighting the absorption spectra with the AM 1.5 standard solar spectrum. We study thin films in two different regimes, much thicker (L Si = 2400 nm) or much thinner (L Si = 80 nm) than the wavelength of light. For L Si = 2400 nm thin film, the 3D photonic band gap crystal enhances the spectrally averaged (λ = 680 nm to 880 nm) silicon absorption by 2.22 × (s −pol.) to 2.45 × (p −pol.), which exceeds the enhancement of a perfect metal back reflector (1.47 to 1.56 ×). The absorption is considerably enhanced by the (i) broadband angle and polarization-independent reflectivity in the 3D photonic band gap, and (ii) the excitation of many guided modes in the film by the crystal’s surface diffraction leading to greatly enhanced path lengths. For L Si = 80 nm ultrathin film, the photonic crystal back reflector yields a striking average absorption enhancement of 9.15 ×, much more than 0.83 × for a perfect metal. This enhancement is due to a remarkable guided mode that is confined within the combined thickness of the ultrathin film and the photonic crystal’s Bragg attenuation length. An important feature of the 3D photonic band gap is to have a broad bandwidth, which leads to the back reflector’s Bragg attenuation length being much shorter than the silicon absorption length. Consequently, light is confined inside the thin film and the remarkable absorption enhancements are not due to the additional thickness of the photonic crystal back reflector. We briefly discuss a number of high-tech devices that could profit from our results, including ultrathin film solar cells.

Silicon Nitride Interface Engineering for Fermi Level Depinning and Realization of Dopant-Free MOSFETs

Problems with doping in nanoscale devices or low temperature applications are widely known. Our approach to replace the degenerate doping in source/drain (S/D)-contacts is silicon nitride interface engineering. We measured Schottky diodes and MOSFETs with very thin silicon nitride layers in between silicon and metal. Al/SiN/p-Si diodes show Fermi level depinning with increasing SiN thickness. The diode fabricated with rapid thermal nitridation at 900 ∘C reaches the theoretical value of the Schottky barrier to the conduction band ΦSB,n=0.2 eV. As a result, the contact resistivity decreases and the ambipolar behavior can be suppressed. Schottky barrier MOSFETs with depinned S/D-contacts consisting of a thin silicon nitride layer and contact metals with different work functions are fabricated to demonstrate unipolar behavior. We presented n-type behavior with Al and p-type behavior with Co on samples which only distinguish by the contact metal. Thus, the thermally grown SiN layers are a useful method suppress Fermi level pinning and enable reconfigurable contacts by choosing an appropriate metal.

High-efficiency hybrid solar cell with a nano-crystalline silicon oxide layer as an electron-selective contact

The efficiency of silicon heterojunction solar cells is limited by various factors including low surface passivation, parasitic absorption, and recombination losses. Herein, the surface passivation quality of crystalline silicon solar cells is improved by a hybrid passivation structure including a silicon heterojunction contact at the front side and a stack of tunneling oxide with n-type nano-crystalline silicon oxide (nc-SiOx(n)) passivating contact at the rear side. A passivation contact with thin silicon oxide (SiO2) and poly-silicon was previously proposed to enhance the rear surface passivation. In our study, the poly-silicon layer is swapped with the nc-SiOx(n) layer to improve the effective surface passivation, electrical properties, recombination losses, and carrier selectivity. The hybrid passivation structure shows significant passivation improvement with lifetime (τeff) of 2696 μs and implied open-circuit voltage (i-Voc) of 735 mV as compared with both-sides traditional silicon heterojunction (1650 μs, 719 mV) and tunneling passivation contact (2146 μs, 725 mV). The hybrid solar cell shows a potential performance as; open circuit voltage (Voc) = 724 mV, short circuit current (Jsc) = 38.95 mA/cm2, fill factor (FF) of 75.9%, efficiency (η) = 21.4%. However, there is room to further improve the overall cell performance.

Implementation of SiN thin film in fiber-optic sensor working in telecommunication range of wavelengths

Mirrors are used in optical sensors and measurement setups. This creates a demand for mirrors made of new materials and having various properties tailored to specific applications. In this work, we propose silicon covered with a thin silicon nitride layer as a mirror for near-infrared measurements. SiN layer was deposited on a standard silicon wafer with a Low-Pressure Chemical Vapor Deposition furnace. Then, the created layer was investigated using ellipsometry and scanning electron microscope. Subsequently, the mirror was used as a reflecting surface in a Fabry–Perot fiber-optic interferometer. The mirror performance was investigated for wavelengths used in telecomunication (1310 nm and 1550 nm) and then compared with results obtained with the same measurement setup, with a silver mirror instead of silicon covered with SiN, as reference. Results showed that the proposed mirror can replace the silver one with satisfying results for investigated wavelengths.

Skin moisture measurement on stripping and pasted water by a handy-type electrostatic sensor.

There is a need to develop a new device to evaluate and monitor the condition of human skin and make it possible to measure the skin in the diary because the current accuracy of water content measurement in the stratum corneum by capacitance and conductance measurement sensor that are used as the gold standard is insufficient. The electrostatic sensor is composed of a thin silicone gum sheet and a copper film. In the experiment, skin conditions on six positions such as the forearm, upper arm, and face of a test subject before and after tape stripping are measured by the electrostatic sensor and a commercial sensor. Skin conditions on the forearm of five subjects before and after pasted distilled water were measured by their sensors. The voltages measured by the electrostatic sensor and moisture measured by a commercial sensor are increased with P<0.01 before and after skin stripping. There were increases in the voltage and the moisture with P<0.01 before and after pasted distilled water. It is suggested that it is possible to measure the moisture on the upper layer of the skin by the electrostatic sensor.