DEVELOPMENT OF NANO-CBN THIN FILM DEVICES WORKING AT HIGH-TEMPERATURES UNDER SEVERE CONDITIONS

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Increasing attention has been paid to the semiconductor devices that can work at high temperature. These devices will be applied to the control units for aircraft jet engines and giant power generators at higher operating temperatures, offering more efficient and reliable performances as the total system. Semiconductors with wide bandgap and high thermal conductivity can realize these applications in nature and GaN, SiC and Diamonds are listed as good candidates by many researchers. Among these, cubic boron nitride (cBN) has the widest bandgap in III-V and IV- group semiconductors as well as high chemical stability and thermal conductivity, and hence is considered to be the most suitable material for these applications. About 10 years ago, we succeeded to deposit such cBN thin films both by ICP-CVD and sputtering methods. Since then, we have been recognized as one of the leading groups. Based firmly on this proved track records in this field, important findings and advancements have be … More en achieved in this project.The first major achievement in this project is the fabrication of cBN thin films on silicon substrate suppressing amorphous interlayer formation. Such cBN growth only through the t-BN phase from silicon was realized by an invention of time-dependent-bias-technique (TDBT) using ICP-CVD method. Epitaxial growth of cBN on silicon will be a major breakthrough for the large area, high-quality synthesis of cBN in future, so this process will be essential to reach this goal.The discovery of the elastic deformation of boron nitride nano array (BNNA) in nano-scale is the second important finding, observed by the transmission electron microscopy (TEM). The peculiar deformation was caused in sp^2-bonded turbostratic boron nitride (tBN), built on a thin edge of silicon by ICP-CVD. The reversible minimum-bending curvature radius of the arrays was found to reach approximately 0.3 nm. Such an unique elastic deformation can not be explained by the conventional theory of deformation of ceramics and metals, and requires further investigation for thorough understandings of the mechanism. Still it can possess the potential of being applied in both MEMS and various nano-scale devices as shock absorber or relevant buffers.As the third major result, we have fabricated a prototype device of high temperature semiconductor with cBN to demonstrate the high potential and high quality of the films processed in a newly developed ultra-clean sputtering system. This device has the structure of heterojunction diode between cBN and silicon and has exhibited the rectification ratio over 10^4 at room temperature, capable of working up to 570K.From the above, it can be seen that considerable progress was made towards the overall goal of this project, and the results obtained so far clearly demonstrate the feasibility of this approach. Less