Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood.Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices.Heterostructures between metals and ceramics have been widely used for power electronic devices requiring both high thermal performance and reliability in harsh environments. Since the interfaces play critical roles in many properties such as mechanical strength, thermal conductivity and dielectric strength, a fundamental understanding of the interface structure and the interface formation mechanism is crucially important. So far, several experimental and theoretical studies on metal/ceramic interfaces have been performed, down to atomistic dimensions [1][2][3][4][5][6] . These studies suggested that there are several factors affecting the structures of heterointerfaces, such as lattice mismatches, chemical bonding states and dopant/impurity segregation. However, one of the most important aspects when considering the formation of heterointerfaces is the bonding process 1,7,8 . Thus, in order to understand and control the heterointerface structures and their resultant properties, the actual bonding processes must be considered.Aluminum nitride (AlN) is considered one of the most important materials for power electronic device applications due to its high thermal conductivity, low thermal expansion coefficient and nontoxic nature 9 . Metal aluminum (Al)/AlN heterostructures, fabricated by a direct bonding aluminum (DBA), are now widely used in automobiles as high power modules which can perform under harsh thermal stress conditions 10 . In DBA, the system is heated near the melting point of Al metal to facilitate liquid phase bonding between the molten Al and the AlN substrate. The melting temperature of Al metal can be decre...
Interactions between BaTiO, and three binary glasses were studied through the reaction of BaTiO, powder with glass powder. For PbO-B,O, and PbO-SiO, glasses, the reaction led to stable compound formation, the substitution of Pb in the BaTiO, structure, and noticeable grain growth of BaTiO,. The interaction phenomena for these two glass systems were very similar. The substitution of Pb into BaTiO, is assisted by chemical reactions in which BaB,O, or Ba,SiO, is formed. The substitution into BaTiO, also seems to be closely related to the grain growth of BaTiO,. On the other hand, only compound formation was observed during the processing of BaTiO, with Bi,O,-B,O, glass. Neither BaTiO, grain growth nor Bi substitution took place with the Bi,O,-B,O, glass system. Based on the observed reactions and the glass viscosity, several sintering aids for BaTiO, ceramic products are suggested in this paper.
Interaction between 96% alumina and three binary glassesfor this study. A penetration model of alumina by glass is used as frits in thick-film technology is studied. A possible proposed based on scanning electron microscopy (SEM) and interfacial reaction mechanism where a melt glass peneelectron probe microanalysis (EPMA) studies of the interfacial trates into the alumina through the grain boundaries dismicrostructure between alumina and glass. The degree of penesolving SiO 2 , one of the grain boundary components, is tration is discussed in terms of the viscosity and the surface suggested. The formulation expressing the glass penetration tension of the melt glass. rate into the alumina based on Poiseuille's law, assuming the driving force for the glass penetration is the capillary II. Experimental Procedure force, is consistent with the experimental growth rate of the reaction layer in the alumina. The formulation also clearly explains the relationship of the degree of glass penetration(1) Alumina to the viscosity and the surface tension of the melt glass. TheWell-sintered dense 96% alumina (Kyocera) was used for the extraordinary difference in K, designated as the coefficient alumina sample because it is commonly used for thick-film of penetration, between the calculated result and the expericeramic substrates. Table I shows the properties of the alumina. mental result suggests that the process of dissolving SiO 2As shown in Fig. 1, the alumina contains SiO 2 , MgO, and a into a melt glass at the alumina grain boundaries retards small amount of CaO as the minor components. the glass penetration.( 2) Glass Preparation 7,8Three binary glass systems with various ratios (mol%) of I. Introduction glass modifier to glass former were selected for the glass G LASS is an important constituent in thick-film materials that samples: 10PbOи90B 2 O 3 to 90PbOи10B 2 O 3 , 40PbOи60SiO 2 performs different functions according to the nature of the to 90PbOи10SiO 2 , and 10Bi 2 O 3 и90B 2 O 3 to 90Bi 2 O 3 и10B 2 O 3 . thick-film layer. In thick-film conductors, glass is added to These glasses are commonly used as bonding agents in thickpromote adhesion with the ceramic substrate and sintering of film materials. In the PbO-SiO 2 system, glasses with SiO 2 the conductive metal powders. In thick-film dielectrics, glass greater than 60 mol% were not used because of their high improves densification, dielectric strength, and adhesion, and it melting temperatures. provides passivation. In thick-film resistors, glass is vital as a Calculated amounts of reagent-grade chemicals (PbO, Bi 2 O 3 , matrix for the cermet structure, and it determines the electrical SiO 2 , and H 3 BO 3 ) for the various glass compositions were properties, such as resistivity, and the temperature coefficient.weighed, mixed, and melted in a platinum crucible in an Each application places its own unique set of demands on the air atmosphere at 1000ЊC for 3 h. The molten glasses were glass phase used. Therefore, the glass transition temperature, quenched on a plati...
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