Hardness Of SiC Research Articles

Metallic glass coating for improving diamond dicing performance

This is the first report on the coating of diamond dicing blades with metallic glass (MG) coating to reduce chipping when used to cut Si, SiC, sapphire, and patterned sapphire substrates (PSS). The low coefficient-of-friction (CoF) of Zr-based MG-coated dicing blades was shown to reduce the number and size of chips, regardless of the target substrate. Overall, SiC, sapphire and PSS were most affected by chipping, due to the fact that higher cutting forces were needed for the higher hardness of SiC, sapphire and PSS. Compared to the bare blade, the MG coating provided the following reductions in chipping area: Si (~ 23%), SiC (~ 36%), sapphire (~ 45%), and PSS (~ 33%). The proposed coating proved particularly effective in reducing chips of larger size (> 41 µm in chipping width), as indicated by an ~ 80% reduction when cutting sapphire. Small variations in kerf angle and depth demonstrate the durability of the coated blades, which would no doubt enhance consistency in dicing performance and extend the blade lifespan. Finite-element modeling revealed significant reductions in tensile stress and elastic–plastic deformation during dicing, thanks to a lower CoF.

Rapidly Thinning Silicon Carbide By Anodization

SiC is a semiconductor material used to fabricate electronic devices that can operate under severe conditions, such as high temperatures, and which have some advantages over silicon-based devices (for example, high frequency and high power). The hardness of SiC is quite high (Mohs=9.5) and strong chemically inert, making it difficult be thinned. Up to now, since the majority carriers of n-type SiC are electrons, its application is more extensive, but it is also more difficult to thin. An effective etching method is by the reactive ion etching (RIE) method, which may produce satisfactory results in a smooth surface. In addition, according to reports, an efficiently etching processing can be performed by a high temperature (>700 C) molten alkali metal hydroxide (for example, NaOH). However, the equipment cost, operation convenience and thinning speed of these etching approaches are not as well as electrochemical etching, i.e., anodization. However, n-type SiC is very difficult to be anodized because of the lack of electric holes which are the key species for etching. In our report, we used a wafer bonding processing to form a temporary p-n junction by jointing to a p-type silicon, so that minority carriers, electric holes, in the mated p-type silicon can easily transfer to the SiC surface via a bias, resulting in a HF-based electrochemical etching. By the processing, the n-type SiC can be quickly thinned. After thinning, the p-type silicon subatrate can be easily removed without the chemical contamination on the thinned SiC substrate.Figure: The anodized surface of n-type SiC. Figure 1

E-SiCure Collaboration Project: Silicon Carbide Material Studies and Detector Prototype Testing at the JSI TRIGA Reactor

In 2016, the ”E-SiCure” project (standing for Engineering Silicon Carbide for Border and Port Security), funded by the NATO Science for Peace and Security Programme, was launched. The main objective is to combine theoretical, experimental and applied research towards the development of radiation-hard SiC-based detectors of special nuclear materials (SNM), and by that way, to enhance border and port security barriers. Along the plan, material modification processes are employed firstly to study, and secondly to manipulate the most severe electrically active defects (which trap or annihilate free charge carriers), by specific ion implantation and defect engineering. This paper gives an overview of the experimental activities performed at the JSI TRIGA reactor in the framework of the E-SiCure project. Initial activities were aimed at obtaining information on the radiation hardness of SiC and at the study of the energy levels of the defects induced by neutron irradiation. Several Schottky barrier diodes were fabricated out of nitrogen-doped epitaxial grown 4H-SiC, and irradiated under Cd filters in the PT irradiation channel in the JSI TRIGA reactor with varying neutron fluence levels. Neutron-induced defects in the material were studied using temperature dependent current-voltage (I-V), capacitance-voltage (C-V) and Deep-Level Transient Spectroscopy (DLTS) measurements. Our prototype neutron detectors are configured as 4H-SiC-based Schottky barrier diodes for detection of secondary charged particles (tritons, alphas and lithium atoms) which are result of thermal neutron conversion process in 10B and 6LiF layers above the surface of the 4H-SiC diodes. For field testing of neutron detectors using a broad beam of reactor neutrons we designed a standalone prototype detection system consisting of a preamplifier, shaping amplifier and a multichannel analyser operated by a laptop computer. The reverse bias for the detector diode and the power to electronic system are provided by a standalone battery-powered voltage source. The detector functionality was established through measurements using an 241Am alpha particle source. Two dedicated experimental campaigns were performed at the JSI TRIGA reactor. The registered pulse height spectra from the detectors, using both 10B and 6LiF neutron converting layers, clearly demonstrated the neutron detection abilities of the SiC detector prototypes.

Effect of Sintering Temperature on Microstructure and Hardness of SiC and Fly Ash Reinforced Copper Matrix Composite

Copper based composites with SiC and Fly ash as reinforcement is prepared by powder metallurgy process. During processing of composites the compaction pressure is maintained as 400MPa for all combination of materials. The prepared green compacts were sintered on both 700℃ and 900℃ and the results microstructure and hardness obtained through Brinell harness test were compared.

The effects of B4C addition on the microstructure and mechanical properties of SiC prepared using powders recovered from kerf loss sludge

Abstract In this study, high purity SiC powders (~ 99.3%), which were recycled from the kerf loss sludge using hydro-cyclone, classifier and direct carbonization and which have purity similar to the commercial SiC powders used to fabricate structural components, were used to investigate the effect of B4C addition on the microstructure and mechanical properties of the sintered SiC. B4C phase and graphite were observed on the grain boundaries between SiC grains, and the amount of B4C phase at the grain boundaries was increased with increasing B4C contents. Both the phases on the grain boundaries impeded the growth of SiC grains and led to the high porosity, which resulted in the decrease in density and hardness. The addition of B4C was found to have negative effect on the density and hardness of SiC. The fracture toughness, however, was enhanced with the increase in the B4C content. The impediment of crack propagation by the B4C phase was found to be related to the improvement of fracture toughness as the amount of B4C content was increased

Dense SiC containing strongly aligned plate-like grains by magnetic treatment

Dense SiC having strongly aligned plate-like grains was prepared by slip casting under strong magnetic field and subsequent densification using Al3BC3 additive. Irregular-shaped 6H-SiC powders in the green body were strongly aligned by the magnetic treatment. Subsequently, Al3BC3 additive induced the formation of aligned plate-like SiC grains during densification. The hardness of SiC could be tailored up to 11% by the strong alignment of the grains. Crack deflection was also strongly affected by the direction of the aligned plate-like grains. As a result, the length of the cracks which propagated parallel to the elongated grains was 18.6% shorter compared to that formed perpendicular to the grains.

Effects of Chromium Addition on Microstructure and Abrasion Resistance of Fe–B Cast Alloy

This research work studies the effects of chromium on microstructure and abrasion resistance of Fe–B cast alloy. The results show that eutectic boride changes from continuous network to less continuous and matrix changes from pearlite to martensite with the increase in chromium content in the alloy. Meanwhile, an increase in chromium addition in the alloy leads to an increase in the chromium content in M2B-type boride because chromium can enter boride by substituting for iron in Fe2B. Under two-body wear, Fe–B cast alloy exhibits excellent wear resistance. When alloys are tested against soft abrasive, chromium can markedly improve the wear resistance of Fe–B cast alloy, whereas excessive chromium can reduce the wear resistance. The wear resistance of Fe–B cast alloy increases first and then decreases with the increase in chromium. But when tested against hard abrasive, since the hardness of SiC is much higher than that of M2B boride, an increase in chromium content marginally increases the wear resistance. Weight losses of Fe–B cast alloy increase with the increase in the load and exhibit the linear relationship.

Strain rate dependence of hardness of AlN doped SiC

Tailored nanoindentation experiments were used to determine the strain rate dependence of the hardness of AlN doped SiC produced by spark plasma sintering. It is shown that in the nanoindentation regime, where cracking is limited, the hardness of SiC reduces by 0·8 GPa/decade reduction in strain rate. This measured variation in hardness is consistent with estimates for the strain rate dependence of the lattice resistance (Peierls stress) of SiC. These experiments therefore open up the possibility to determine real constitutive equations for plasticity in SiC and other armour ceramics.

Operation of Al-Implanted SiC Nuclear Detectors Subjected to High Radiation Fluences at Temperatures of up to 250 °C

The effect of a cycle "introduction of defects – annealing – introduction of defects" on the SiC properties has been studied to know the degradation of characteristics of p-n- nuclear radiation detectors. The irradiation with 8 МeV protons at fluences of about 3×1014 сm-2 was used. The annealing was carried out in two stages one-hour at temperatures of 600 and 700 °С. Nuclear spectrometric techniques with 5.8 MeV -particles were employed to test the detectors. The charge collection efficiency and features of the amplitude spectrum were determined to study the capture of charge carriers by radiation-induced defects. Measurements were made in the temperature range of 20–250 °С. It is shown that at 250 °С there is a decrease in the carriers capture. The form of the amplitude spectrum essentially improves. The first irradiation and the subsequent annealing do not change significantly the radiation hardness of SiC. During the second irradiation the effective concentration of the introduced centers is 1.3 times higher. This result may be due to the high total fluence of protons, 6×1014 cm-2.

Radiation hardness of SiC subjected to alternating irradiation and annealing

Effect of the cycle “introduction of defects, annealing, and repeated introduction of defects” on the SiC properties has been studied by means of nuclear spectrometry for an example of degradation of characteristics of a p-n nuclear radiation detector. The defects were introduced by irradiation with 8-MeV protons in two equal fluences of 3 × 10 14 cm−2. The total fluence of 6 × 1014 cm−2 corresponded to an introduction of 2.4 × 10 17 cm−3 primary knocked-out atoms. The annealing was made in two stages, each 1 h long, at temperatures of 600 and 700 °C. The detectors were tested with 5.4-MeV α particles, with the charge collection efficiency and specific features of the amplitude spectrum determined. The measurements were performed in the temperature range of 20–250 °C. It was shown that the effect of the first irradiation and the subsequent annealing does not significantly change the radiation hardness of SiC. The effective concentration of centers introduced in the course of the second irradiation (at the same fluence) is higher by a factor of 1.2. The nonequivalence of the fluences can also be attributed to the effect of the high total proton fluence of 6 × 1014 cm−2.

Surface hardness enhancement in sp3-bonded carbon doped SiC nanocomposite films

The sp3-bonded carbon/SiC composite films have been produced from electron beam-physical vapor deposition of SiC materials. The hardness of such films, measured using Hysitron indentation, reaches 50GPa, which is significantly higher than the hardness of SiC (28GPa). It appears that the superhardness of the thin films is due to the formation of nanocrystalline SiC/diamondlike carbon composites.

Effects of Very High Neutron Fluence Irradiation on p<sup>+</sup>n Junction 4H-SiC Diodes

In this work we analyzed the radiation hardness of SiC p+n diodes after very high 1 MeV neutron fluence. The diode structure is based on a p+ emitter ion implanted in n-type epilayer with thickness equal to 5 %m and donor doping ND = 3×1015 cm-3. Before irradiation, the average leakage current density at 100 V reverse bias was of the order of 3 nA/cm2. These devices were irradiated at four different fluence values, logarithmically distributed in the range 1014-1016 (1 MeV) neutrons/cm2. After irradiation the epilayer material became more resistive, as indicated by the reduction of the forward and reverse current density at a given voltage. In particular, after a neutron fluence of 1×1014 n/cm2 the epilayer active doping concentration decreased to 1.5×1015 cm-3. After irradiation at 1016 n/cm2, i.e. the highest fluence value, the average leakage current density at 100 V reverse bias decreased to values of the order of 0.1 nA/cm2. This very low noise even after very high fluence is very important to obtain a high signal to noise ratio even at room temperature.

High Rate Silicon Carbide Polishing to Ultra-smooth Surfaces

ABSTRACTSilicon Carbide has a unique combination of properties that include a nearly diamond-like hardness, intrinsic electrical semiconductivity and a high thermal conductivity. This combination of properties has led to it's use in a number of applications including substrates for Light Emitting Diodes (LEDs), power, RF (radio frequency) and other electronic devices in addition to mirror substrates and optical devices as well as stop layers in integrated circuit chip manufacture. In addition, the chemical inertness and high hardness of SiC has historically resulted in low removal rates during chemical mechanical Planarization (CMP). Recent efforts in our labs have led to being able to polish single crystal silicon carbide at removal rates up to 400 nm/hr yielding a root mean squared roughness on the order of a nanometer as determined by AFM and interferometry. The high rates and smoothness obtained are expected to translate to other types of silicon carbide. Fundamental studies by FTIR, streaming potential and ESCA have been done to elucidate the mechanism of silicon carbide polishing.

The fabrication process and mechanical properties of SiC p/Al–Si metal matrix composites for automobile air-conditioner compressor pistons

The fabrication process and mechanical properties of SiC p/Al–Si metal matrix composite (MMC) pistons for automobile air-conditioner compressor were investigated. The required material properties for automobile air-conditioner compressor pistons are high strength, good wear resistance and light weight. SiC p/Al–Si MMCs were fabricated by the powder metallurgy process of vacuum hot pressing at a temperature of 540–570°C with 30 MPa followed by hydrostatic extrusion at 500°C with an extrusion ratio of 8:1. The compressor pistons were made by the one-step forging of extruded bars at 400°C. The tensile strength and hardness of Al–10–12 wt.%Si alloys and 5–10 wt.%SiC p/Al–10–12 wt.%Si MMCs were increased by hydrostatic extrusion and forging, mainly due to a decrease of the grain size in the matrix through plastic deformation. The hardness of SiC p/Al–12 wt.%Si MMC was higher than that of SiC p/Al–10 wt.%Si MMC due to the higher Si content. The wear behavior of SiC p/Al–12 wt.%Si MMC was controlled by the surface hardening and cracking of the matrix, and the wear resistance increased with increase in the weight fraction of SiC particles. On the other hand, the wear behavior of SiC p/Al–10 wt.%Si MMC was controlled by the plastic deformation of the matrix and the wear resistance was almost independent of the SiC particle weight fraction.

SiC p/Mg composites made by low-energy mechanical processing

Composite powders containing 10, 20 and 30 vol% SiC p particulates in a Mg matrix were produced using mechanical processing. A small laboratory ball mill was used to achieve a uniform distribution of the reinforcements in the Mg matrix. The particle size distribution and the microstructure of the composite powders were studied as a function of processing time. Based on these observations, four successive stages of processing were identified. It was shown that a homogeneous distribution of SiC p in a Mg matrix may be obtained under low-energy milling conditions. The influence of milling time and concentration of SiC p on tensile strength, stiffness, elongation and impact properties of rods extruded from the resulting composite powders were investigated. The hardness of SiC p/Mg composites was also evaluated to determine the influence of SiC p content.