Tham khảo tài liệu 'the materials science of thin films episode 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 678 Emerging Thln-Fllm Materials and Applications oxidation and sputter rates are equal and the oxide thickness is self-limiting. After the terminal oxide is established new oxide continually sputters off. The result is removal of contaminants and uniform thickness on all base electrodes. A further materials problem aired in Section concerns barrier mechanical stability during thermal cycling. The use of Sb in the Pb electrode Fig. 14-22 is to harden it in order to prevent hillock formation. Finally it must have occurred to the reader well before this point that high-Tc Josephson junction devices should offer significant benefits relative to low-Tc devices. Unfortunately very small coherence lengths and unstable surfaces coupled with fabrication and lithography difficulties has hindered progress. Nevertheless Josephson tunneling across grain boundaries serving as weak links has been reported Ref. 51 . High-Tc Josephson devices will probably not approach the sensitivities reached by low-Tc devices because of thermal noise in measurement. . Conclusion This appears to be an opportune time to end the book or more truthfully to abandon it. Much remains to be said about other thin-film applications including displays sensors and assorted electronic optical thermal and surface acoustic devices. The book by Chopra and Kaur Ref. 52 is recommended for these and other applications. LU Exercises U-1 1. A 100 Si wafer is covered with a SiO2 mask film. A square window in the SiO2 is opened to the bare Si surface by photolithography methods. If the sides of the square lie along 110 directions sketch the shapes of the holes produced in the Si after etching in KOH-H2O if a. etching is isotropic. b. etching is anisotropic Note Anisotropic etchants create faceted holes composed of crystal planes that are etched slowest. c. the initial square mask window is widened and the etching time is reduced. d. What shapes are produced if the initial window has a rectangular shape .
