Thermal Conductivity Of Silicon Nitride Research Articles

Effect of a new nonoxide additive, Y3Si2C2, on the thermal conductivity and mechanical properties of Si3N4 ceramics

AbstractEnhancement of the thermal conductivity of silicon nitride is usually achieved by sacrificing its mechanical properties (bending strength). In this study, β‐Si3N4 ceramics were prepared using self‐synthesized Y3Si2C2 and MgO as sintering additives. It was found that the thermal conductivity of the Si3N4 ceramics was remarkably improved without sacrificing their mechanical properties. The microstructure and properties of the Si3N4 ceramics were analyzed and compared with those of the Y2O3‐MgO additives. The addition of Y3Si2C2 eliminated the inherent SiO2 and introduced nitrogen to increase the N/O ratio of the grain‐boundary phase, inducing Si3N4 grain growth, increasing Si3N4 grain contiguity, and reducing lattice oxygen content in Si3N4. Therefore, by replacing Y2O3 with Y3Si2C2, the thermal conductivity of the Si3N4 ceramics was significantly increased by 31.5% from 85 to 111.8Wm−1K−1, but the bending strength only slightly decreased from 704 ± 63MPa to 669 ± 33MPa.

Investigation on thermal conductivity of ceramic particles reinforced polymer composites

The hydroxyl group count in polymeric composites and amphiphilic investigators used as a function of Si3N4 orientation have been investigated by the thermal conductivity of Silicon Nitride (Si3N4), PVA and/or PVB. The thermal conductivity of the Si3N4 compounds in the structure seems to be greater than that of the Si3N4 outdoor compounds. The thermal conductivity of Si3N4/PVA in-plane composites was higher for a specific Si3N4 component compared to Si3N4/PVB in-plane. This could be attributable to Si3N4′s improved orientation because of the presence of a greater number of hydroxyl groups. The amphiphilic C14H6O8 treatments have shown higher temperature conductivity than C27H27N3O2 treatments. The evaluated thermal conductance of the composites equated to those predicted by several theoretic models.

The use of materials based on Si3N4 in the composition of composites for the design of high-temperature thermoelectric generators

The possibility of reducing the thermal conductivity of silicon nitride as a basis of high-temperature electrical converters was investigated in the thesis. Also, the values of thermoelectric figure of merit and efficiency of thermoelectric current generator for the case of refractory oxygen-free composites were simulated. During the study, the dependence between the m coefficient, which determines the maximum possible efficiency of the thermoelectric generator and the ZT thermoelectric figure of merit, was determined. It was shown that the coefficient of thermal conductivity of the studied materials ranges from 1,2 to 4·106 m2/s and is characterized by a negative temperature coefficient over the entire temperature range. It was found that the thermal conductivity of Si3N4-based materials varies from 2,1 to 5,1 W/(m·K) depending on the type of sintering activator. The use of Al2O3 as an activator makes it possible to obtain a 25% lower thermal conductivity value comparing to materials with the addition of MgO. For the first time, it was proved that currently it is not possible to achieve an efficiency of 0,5hT in Si3N4-based materials used as a composite basis for high-temperature thermoelectric generators development.

Effect of β-Si<sub>3</sub>N<sub>4</sub> Powder on Thermal Conductivity of Silicon Nitride Ceramics

To investigate the influence of β-Si3N4 powder on thermal conductivity of silicon nitride, coarse, fine β-Si3N4 powder and various β-Si3N4/α-Si3N4 ratios of starting powders were adopted to fabricate ceramics by spark plasma sintering at 1600°Cand subsequent high-temperature heat treatment at 1900°C with the sintering additives of Y2O3 and MgO. It is found that with more fine β-Si3N4 powder in the starting powder, β-Si3N4 grains exhibit high thermal conductivity, which is partly resulted from the compaction of β-Si3N4 grains.

High Thermal Conductivity Silicon Nitride Ceramics

This paper deals with the recent developments of high thermal conductivity silicon nitride ceramics. First, the factors that reduce the thermal conductivity of silicon nitride are clarified and the potential approaches to realize high thermal conductivity are described. Then, the recent achievements on the silicon nitride fabricated through the reaction bonding and post sintering technique are presented. Because of a smaller amount of impurity oxygen, the obtained thermal conductivity is substantially higher, compared to that of the conventional gas-pressure sintered silicon nitride, while the microstructures and bending strengths are similar to each other between these two samples. Moreover, further improvement of the thermal conductivity is possible by increasing β/α phase ratio of the nitrided sample, resulting in a very high thermal conductivity of 177 W/(m·K) as well as a high fracture toughness of 11.2 ㎫· m 1/2 .

Thermal analysis for fast thermal-response Si waveguide wrapped by SiN

A new type of Si waveguide wrapped by silicon nitride (SiN) is designed, and its optical and thermal analysis are presented. The thickness of SiN up-cladding should be larger than 1 μm in order to prevent the absorption of optical field by metal heater. Thermal response of the proposed waveguide structure is enhanced by the high thermal conductivity of SiN. Moreover, this thermal response can be further improved by a fast heat dissipation channel created in this structure. Our simulation results indicate that a rise time of about 110 ns can be achieved for the proposed waveguide structure, which is about two orders of magnitude less than that of the conventional Si waveguide. The influences of the thickness of up-cladding and the stretching width and etching depth on the thermal performance are also discussed. The simulation shows thin up-cladding, large stretching width and etching depth are critical to enhance the thermal response speed.

Dual material insulator SOI-LDMOSFET: A novel device for self-heating effect improvement

The silicon-on-insulator (SOI) power devices show good electrical performance but they suffer from inherent self-heating effect (SHE), which limits their operation at high current levels. The SHE effect is because of low thermal conductivity of the buried oxide layer. In this paper we propose a novel silicon on insulator lateral double diffused MOSFET (SOI-LDMOSFET) where the buried insulator layer under the active region consists of two materials in order to decrease the SHE. The proposed structure is called dual material buried insulator SOI-LDMOSFET (DM-SOI). Using two-dimensional and two-carrier device simulation, we demonstrate that the heat dissipation and the SHE can be improved in a conventional SOI-LDMOSFET by replacement of the buried oxide with dual material buried insulator (silicon nitride and silicon oxide) beneath the active region. The heat generated in the active silicon layer can be flowed through the buried silicon nitride layer to the silicon substrate easily due to high thermal conductivity of silicon nitride. Furthermore, the channel temperature is reduced, negative drain current slope is mitigated and electron and hole mobility is increased during high-temperature operation. The simulated results show that silicon nitride is a suitable alternative to silicon dioxide as a buried insulator in SOI structures, and has better performance in high temperature.

Effect of MgSiN2 addition on gas pressure sintering and thermal conductivity of silicon nitride with Y2O3

This paper reports the gas pressure sintering and thermal conductivity of silicon nitride with 2 mol% Y2O3 and varied contents of MgSiN2 in the range of 0 to 5 mol% at 1900°C under a nitrogen pressure of 1 MPa N2. It was found that the density curves show a typical "V" shape against the MgSiN2 content. The 1 mol% MgSiN2 hinders significantly the densification, but the 5 mol% MgSiN2 leads to complete densification. The inhibited densification is associated with the pronounced normal grain growth. However, the abnormal grain growth is inhibited with the addition of MgSiN2. After sintering for 12 h, the sample without MgSiN2 exhibits the coarsest and highest bimodal microstructure, whereas the one with 5 mol% MgSiN2 exhibits the finest microstructure. Although the MgSiN2 addition leads to a slightly enhanced thermal conductivity, it tends to reduce the thermal diffusivity. The thermal conductivity without porosity shows a decrease with the increase of MgSiN2 content because of the inhibited grain growth.

Mechanical and Thermal Properties of Silicon Nitride Hot Pressed with Adding Rare-Earth Oxides

Mechanical and thermal properties of Si3N4 ceramics with various rare-earth oxides (La2O3, CeO2, Lu2O3, Dy2O3, Sm2O3, Nd2O3, Yb2O3, and RuO2) were investigated. Flexural strength of silicon nitride with addition of 5vol% Nd2O3, CeO2, Dy2O3, and Sm2O3 showed higher value than that of silicon nitride with Lu2O3 and La2O3 added because they form denser microstructure and smaller elongated grain. Thermal conductivity of silicon nitride with an addition of 5vol% RuO2 was more enhanced than that of silicon nitride added with Nd2O3, Sm2O3, and Dy2O3 because the addition of RuO2 depressed grain growth. It is also associated with lattice oxygen governing thermal conductivity of Si3N4 when added rare-earth oxides.

Effect of inter-layer dielectric on thermal reliability in poly-silicon thin film transistors

Highly reliable polycrystalline silicon (poly-Si) thin film transistors (TFTs) were fabricated by silicon nitride as an inter-layer dielectric (ILD), where the thermal conductivity of silicon nitride is considerably higher than that of silicon oxide. The experimental results showed that the threshold voltage of the n-type poly-Si TFT with the proposed silicon nitride ILD was not degraded after high-power stress because the silicon nitride ILD may disperses the heat in the poly-Si TFT channels, which possibly improved the reliability of poly-Si TFTs without sacrificing the electrical characteristics.

Effect of MgSiN2 Additive for Thermal Conductivity of Silicon Nitride

Effect of MgSiN2 Additive for Thermal Conductivity of Silicon Nitride

Effect of sintering additive composition on the thermal conductivity of silicon nitride

The thermal conductivity of silicon nitride prepared with varying sintering additive compositions was studied. Samples of Si3N4 + 0.5 mol% Y2O3 + 0.5 mol% Nd2O3 and a further additional agent were gas pressure sintered at 2173 K. MgO or Al2O3 was employed as the additional agent. While both agents improved sinterability, the former promoted grain growth and the latter suppressed it. Thermal conductivity increased with increasing MgO content, and a maximum value of 128 Wm-1 K-1 was attained when 2 mol% MgO was added. In contrast, addition of Al2O3 degrades thermal conductivity. This is probably due to the suppression of grain growth and the dissolution of Al2O3 into Si3N4 grains.

Effect of Grain Growth on the Thermal Conductivity of Silicon Nitride

Thermal conductivity of sintered silicon nitride has been improved by grain growth of β-Si3N4. β-Si3N4 containing 0.5mol% Y2O3 and 0.5mol% Nd2O3 was gas-pressure sintered at 1973 to 2473K and the microstructures and the thermal conductivities were investigated. The materials sintered at temperatures higher than 2173K had a microstructure of “in-situ composite” with smaller β-Si3N4 matrix grains and a small amount of elongated β-Si3N4 grains. The grain size increased with increasing sintering temperature. Room temperature thermal conductivity increased with increasing sintering temperature; 122W·m-1·K-1 was produced by sintering at 2473K-this value was about two times higher than the values reported up to this time. Higher thermal conductivities were established by growth of Si3N4 grains and decrease in the amount of two-grain junctions.