© 2020 IEEE. As for the IGBT power device based on Si used for the vehicle, the performance limit of the Si semiconductor has been pointed out, and the SiC semiconductor has been attracting attention as a next-generation semiconductor. The SiC semiconductor has advantages such as a wider band gap, a larger breakdown electric field, and high temperature operation (about 300 ° C.). If these features can be maximized, a SiC power semiconductor module that can be significantly improved in efficiency, downsized, and operable in a high-temperature environment as compared with a Si semiconductor can be more widely implemented.In this study, two sets of SiC-MOS and SiC-SBD devices are embedded in a ceramic substrate, and their electrodes and the copper electrodes of the substrate are interconnected by NMPB (Nickel Micro-plating Bonding) method, so that one-leg prototype inverter modules of a highly heat-resistant and ultra-small size (47x30x1.3mm) could be manufactured. The NMPB method is a technology that we have originally developed to connect a chip electrode and a lead formed in a chevron shape by Ni plating. High-temperature operation and excellent switching characteristics of the SiC power module were demonstrated.

There is an increasing expectation to incorporate silicon carbide (SiC) as inverter power modules for hybrid electric vehicles (HEVs) and electric vehicles (EVs). In order to maximize the performance of SiC devices, new packaging technologies that can realize high-temperature heat resistance by replacing solder joint or Al wire bonding, have been strongly demanded. In order to meet these demands, we have developed a new interconnection technology named Nickel micro-plating bonding (NMPB), that enables the interconnection in a narrow gap between electrodes of SiC devices and substrates via our newly designed lead frame, whose lead surface is formed into chevron shape. The plating bath for NMPB is a sulfamic acid bath consisting of nickel sulfamate and several additives, and was specifically prepared to plate narrow areas at the bonding interface without plating defects. It was found that when columnar crystal grains grow from both facing electrode surfaces, a strong bond without defects such as micro-voids at the interface is obtained. The bonding strength of NMPB was confirmed by shear test to be higher than that of Pb free solder joints and not to deteriorate even after high temperature storage (HTS) tests at 250 degrees C for 1000hrs and after 1000cycle thermal cycle tests (TCTs, 250 degrees C/-45 degrees C). The NMPB was applied to the manufacture of one leg SiC inverter power module using two pairs of SiC MOS-FETs and SBDs, which were interconnected with a newly designed lead frame for double sided cooling structure. After molding resin copper heat spreaders were formed on the outer surfaces of both sides of the NMPB leads by additive method. Our newly developed SiC power module showed stable I-V characteristics over 250 degrees C and lower switching loss. The reliability of the modules was confirmed by TCTs and power cycle tests.

Recently there are high expectations for incorporating silicon carbide (SiC) devices as power modules in hybrid electric vehicles (HEV) and electric vehicles (EV). The need fir new bonding technologies, which can deliver high-temperature thermal resistance that replaces solder bonding or Al wire bonding, has been strongly expected in order to maximize the performance of SiC power device. We developed a new micro plating interconnection technology named Nickel Micro Plating Bonding (NMPB) which enables the interconnection in a narrow space between electrodes and SiC devices via our new lead frame formed in chevron shape. As for the bonding strength of NMPB, sufficient joint strength value is confirmed by shear test. We also newly proposed low-temperature nickel nanoparticle sintering to form die bonding connections. We have confirmed that bonding at a bonding temperature of 400 degrees C or lower is possible, and that it is a bonding having long-term high heat resistance. We implemented heat resistant mounting of SiC schottky barrier diode (Slip) on the TO247 type package and confirmed the I-V characteristics even after the high temperature storage at 300 degrees C without any significant degradation. We clarified that these methods had adequate potential as an advanced heat resistant package in comparison with conventional interconnections.

The behavior of diffusion and phase transformation in a high temperature stable ferritic stainless steel (SUS444) nitrogen-absorbed at 1450 K for 4 hr under 0.4 MPa N₂ gas was investigated with EPMA mapping. While Cr content in the nitrogen absorption layer (NA layer: γ phase) increased, Mo discharged from NA layer was enriched in the grain boundary of α/γ. Using a 1D-phase field simulation (PFS), the phenomenon during the NA treatment in the Fe-19Cr-2Mo-0.5Mn-N alloy was discussed. In the case of PFS with impurity diffusion (lattice diffusion) coefficients in Fe, since the diffusion velocity in γ phase was smaller than that of α phase, concentration distribution between NA layer and matrix α phase is caused by local phase equilibrium in depending on the composition of NA layer. Additionally, diffusion of substitutional atoms is slower than the growing velocity of NA layer that is depended on nitrogen diffusivity. This is the reason why Cr content in the NA layer fluctuates and why the average compositions in α phase and NA layer has the opposite trend with thermodynamic calculated and experimental results. On the other hand, in the case of the simulation under D^γ > D^α in consideration of the grain boundary diffusion of substitutional elements, the segregation behavior of solute elements was in good agreement with the results of EPMA mapping. Thus, it was confirmed that not only the diffusion of N atoms but also the grain boundary diffusion contributes greatly to the growing phenomenon of NA layer in a high stable ferritic stainless steel.

Dots and lines consisting of LiNbO3 crystals are patterned on the surface of 1CuO40Li2O32Nb2O528SiO 2 (mole ratio) glass by irradiations of continuous-wave Nd:YAG laser (wavelength: λ=1064 nm), diode laser (λ=795 nm), and Yb:YVO 4 fiber laser (λ=1080 nm), and the feature of laser-patterned LiNbO3 crystal growth is examined from linearly polarized micro-Raman scattering spectrum measurements. LiNbO3 crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. The growth direction of an LiNbO3 along the laser scanning direction is the c-axis. It is proposed that the profile of the temperature distribution in the laser-irradiated region and its change along laser scanning would be one of the most important conditions for the patterning of crystals with a preferential growth orientation. Laser irradiation giving a narrow width is also proposed to be one of the important factors for the patterning of LiNbO3 crystal lines with homogeneous surface morphologies. © 2010 Elsevier Inc. All rights reserved.

情報生産システム研究科・先進材料研究室では、次世代ワイドバンドギャップ半導体デバイス向けの高耐熱実装技術として、金属ナノ粒子の低温焼結性に着目し、Niナノ粒子を接合材とする実装技術の研究に取り組んでいる。これまでNiナノ粒子接合材と半導体のAl電極面に対する接合性評価において、加熱雰囲気によって接合強度に大きな違いがあることが分かっている。そこで本課題では加熱雰囲気がAlとNiとの拡散挙動に与える影響を明らかにすることを目的とした。接合試料構造を模擬したAlとNi薄膜を積層した試料に対して異なる雰囲気下での熱処理を施し、オージェ電子分光装置を用い表面から内部への組成分析により拡散挙動の差異を明らかにした。

エネルギー利用システムのひとつを担うパワー半導体デバイス分野では、低炭素社会実現にむけ高性能化を図るためにSiCを用いたデバイス開発が行われている。SiCは高耐圧・高熱伝導率の特性から250℃程度の高温動作が見込まれており、従来の半導体実装に用いられている“はんだ”に替わる高耐熱性実装技術の開発が求められている。情報生産システム研究科・先進材料研究室ではメッキ技術を用いた新たな実装技術・Niマイクロメッキボンディング（NMPB）の開発に取り組んでいる。NMPBは被接合材両方向からNiメッキを成長させて接合するものである。本研究では接合のためのメッキ条件の確立に向け、メッキ条件が組織形態に与える影響を評価した。

　電気自動車や電鉄車両、送配電システムなどの電力変換機器にパワーデバイスが用いられている。これらの高効率化・小型化に向け、デバイスの半導体材料をSiからSiCに替えた次世代デバイスの開発が行われているなかで、SiCの高温動作特性を発揮するために従来の半導体実装で用いられてきた半田に替わる高耐熱実装技術が求められている。情報生産システム研究科・先進材料研究室（巽研究室）では電解Niメッキを実装手法とするNiマイクロメッキボンディング（NMPB）の開発に取り組んできた。NMPBは向かい合わせた被接合材両方向からNiメッキを成長させて接合する。本研究ではメッキ浴組成および電流密度がメッキ成長挙動や組織形態に与える影響を評価した。