Research Progress of High Thermal Conductivity Silicon Nitride Ceramics Prepared by Non-oxide Sintering Additives

doi:10.15541/jim20230530

Abstract

Abstract:

The development trend of high voltage, high current and high-power density of power semiconductor devices has raised the requirement for the heat dissipation capability and reliability of ceramic substrates in devices. Silicon nitride (Si₃N₄) ceramics, known for their high thermal conductivity and excellent mechanical properties, have emerged as a preferred thermal dissipation substrate material for high-power electronic devices. However, there is a significant gap between experimental and theoretical values of thermal conductivity in Si₃N₄ ceramics. The long period of heat preservation during preparation leads to excessive grain growth, compromising mechanical properties and increasing costs, which hinders large-scale application. Lattice oxygen defects act as main factor limiting thermal conductivity of Si₃N₄ ceramics. Now, researchers are exploring ways to promote removal of lattice oxygen and full development of bimodal morphology formation of Si₃N₄, by selecting non-oxide sintering additives to reduce the oxygen content in the system, adjusting the composition and properties of the liquid phase, constructing a “nitrogen-rich-oxygen-deficient” liquid phase, and regulating the dissolution and precipitation process in the liquid phase. These efforts aim to the synergistic optimization of thermal conductivity-mechanical properties of Si₃N₄ ceramics. Based on the elemental classification, we review the non-oxide sintering additives developed at domestic and abroad, explain how they improve the thermal conductivity of Si₃N₄ ceramics from liquid-phase modulation and microscopic morphology control, analyze the grain development and morphology evolution laws, and discusse the mechanism of lattice oxygen removal. The out look on future development of high thermal conductivity Si₃N₄ ceramics is also prospected.

Key words: Si₃N₄, thermal conductivity, mechanical property, liquid phase sintering, non-oxide sintering additive, review

CLC Number:

TQ174

WANG Weiming, WANG Weide, SU Yi, MA Qingsong, YAO Dongxu, ZENG Yuping. Research Progress of High Thermal Conductivity Silicon Nitride Ceramics Prepared by Non-oxide Sintering Additives[J]. Journal of Inorganic Materials, 2024, 39(6): 634-646.

Figures/Tables 19

Fig. 1 Schematic of typical packaging of power semiconductor device[1] (1200 V, chip area 9 mm×9 mm, encapsulated with Al2O3 DCB substrate)

Table 1 Properties of ceramic substrate materials[2]

Material	Thermal conductivity/ (W·m^-1·K^-1)	Fracture toughness/ (MPa·m^1/2)	Bending strength/ MPa
Al₂O₃	18-24	3.5-4.0	300-400
AlN	150-270	3.0-3.5	220-310
ZTA	28	4.5	650
Si₃N₄	80-177	6.5-7.5	600-800

Fig. 2 Schematic of the liquid phase sintering mechanism for Si3N4 ceramics[10]

Fig. 3 Effects of volume fraction of glassy phase, grain- boundary film thickness(δ), and grain size on the thermal conductivity of β-Si3N4[13]

Fig. 4 Effect of lattice oxygen content on the thermal conductivity of Si3N4 ceramics[17]

Fig. 5 Displacement-temperature curves of Si3N4 ceramics with MgF2 or MgO as sintering additives[19]

Fig. 6 XRD patterns of Si3N4 samples prepared with different LiF contents[20]

Fig. 7 Depolymerization mechanism of F atom in silicate melts[22] (a) F atom breaks the network structure by replacing the bridging oxygen atoms; (b) Solute atom solution-diffusion-precipitation mechanism during liquid-phase sintering in samples YOMO and YFMF; (c) Free energy barriers overcome by solute atoms in melts Y-Si-O-N and Y-Si-O-N-F; (d) Mechanism of solute drag effect on grain boundary migration

Fig. 8 SEM morphologies of the polished surfaces of Si3N4 ceramics after gas pressure sintering (GPS) with different additives added[24] (a) MgO-doped for 2 h; (b) MgO-doped for 48 h; (c) MgSiN2-doped for 2 h; (d) MgSiN2-doped for 48 h

Fig. 9 Typical HRTEM images of Si3N4 ceramics added with Y2O3 (a) and Y2Si4N6C (b) as additives[31]

Fig. 10 Curves of relative displacement of the as-pressed specimens with temperature variation[32]

Fig. 11 Densification mechanism of Si3N4 ceramics with ZrSi2-MgO additive[36]

Fig. 12 Shrinkage curves of the Si3N4 ceramics[10]

Fig. 13 Schematic illustration of Si3N4-Y2O3-SiO2 phase at 1900 ℃[10]

Fig. 14 STEM-EDS characterizations of Si3N4 ceramics with the addition of ZrO2 and ZrH2[47] (a, d) Bright-field TEM images for Si3N4 ceramics with the addition of (a) ZrO2 and (d) ZrH2; (b, e) Elements distribution for Si3N4 ceramics with the addition of (b) ZrO2 and (e) ZrH2; (c) EDS analysis of the marked points in (a, d) images; (f) HRTEM image presenting the grain boundary film marked by the red rectangle in (d) image

Fig. 15 SEM images on the fracture surfaces of nitrided samples (a, b) and post-sintered samples (c, d) without (a, c) and with (b, d) graphite powder bed addition[57]

Fig. 16 TEM images of PDA-coated powder and schematic of Si3N4-C core-shell structure[59-60] (a, e) Overall morphologies of PDA-coated (a) and PDA-free (e) powder; (b, f) Partial magnified images of (a, e), respectively; (c, g) O distributions of PDA-coated (c) and PDA-free (g) powder; (d, h) Si and N distributions of PDA-coated (d) and PDA-free (h) powder; (i) Schematic of Si3N4-C core-shell structure

Fig. 17 (a) Shrinkage behaviors and densification mechanism of Si3N4 ceramics during sintering, and (b) relationship between β phase ratio and relative density[62]

Fig. 18 Evolution of microstructure and diameter of Si3N4 ceramics[10] (a-c) Without Si addition; (d-f) With Si addition

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