Abstract The influence of thermal aging on joint strength and fracture surface of PbSn and AuSn solders in laser module packages has been studied experimentally and numerically. Al2O3-Solder-Substrate assembled samples were aged at 150oC for one, four, nine, sixteen, twenty-five, thirty-six, and forty-nine days. It was found that the joint strength decreased as the aging time increased. This joint strength decrease is due to the increase of void and crack formations in solder joints. There is a correlation between the intermetallic compound (IMC) growth and the joint strength for PbSn and AuSn solders under aging test. The fracture surface of PbSn specimen is gradually changed from the ductile dominated morphology of as-soldered status to the brittle dominated morphology. The section view indicates Kirkendall voids appeared around the interface of bulk solder and IMC layers after 49 days of aging. However, AuSn specimen still shows a ductile dominated morphology and no Kirkendall voids observed even after 49 days of aging. Through 49 days of aging, the shear force drops of 2£gm Au-coated PbSn and AuSn specimens are 9.48kg and 7.65kg, respectively; the shear force drops of 10£gm Au-coated PbSn and AuSn specimens are 9.42kg and 5.88kg,respectively. A finite-element method (FEM) analysis was performed on the calculation of joint strength variation of PbSn and AuSn solders in thermal aging tests. Simulation results were in good agreement with the experimental measurements that the solder joint strength decreased as the aging time increased. Another study is based on the well-known result of thermal induced fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser diode package. It indicates fiber alignment shift under temperature cycling tests can be reduced significantly if the fiber can be located closer to the center of the ferrule. An approach to make an FSF with the minimum eccentric offset is studied, an in-house design machine set is used for this purpose, which includes a hot plate, a fiber fix stage, an image capture camera, and a PC with offset analysis program. A preliminary target is set to achieve a maximum 20£gm offset FSF. It was believed that a less than 0.5£gm fiber shift could be measured after 500 temperature cycles. After the practical experiment trial, FSF with around 10 and 12£gm offset is available. However, the continuous improvement is necessary for process stability.

Current requirements of nonvolatile memory (NVM) are the high density cells, low-power consumption, high-speed operation and good reliability for next-generation NVM application. However, all of the charges stored in the floating gate will leak into the substrate if the tunnel oxide has a leakage path in the conventional NVM during endurance test. Therefore, the tunnel oxide thickness is difficult to scale down in terms of charge retention and endurance characteristics. Nanocrystals (NCs) NVMs are one of the promising candidates to substitute for conventional floating gate memory since the discrete storage nodes as the charge storage media can effectively enable the improvement of data retention for the scaling down device. In this thesis, we try to overcome the limitation of conventional NVMs during the scaling down process and further increase the retention time by means of changing the structure of Nanocrystals NVMs. Firstly, we deposit a NiSi2 layer as the nanocrystal self-assembled layer and thereby apply it to Nanocrystals NVMs. In room temperature, we bombard NiSi2 target to form single layer and double layer charge trapping layer through sputtering system layer by layer, and the two charge trapping layers are separated by 30 Å silicon-oxide (SiO2). Next, we also deposit silicon oxide as control oxide. According to rapid thermal anneal (RTA) mix oxide gas, we improve the oxide quality and supply NiSi2 sufficient energy to reach the smallest Gibbs free energy so as to form uniform and high density NiSi nanocrystal. On account of the increasing of trapping center and the coulomb repulsion power, the double layer structure NiSi Nanocrystals NVMs has better memory window and retention than the single layer one. In the similar process, we sputter NiSi2 target with Ar gas mixes NH3 gas to form silicon-nitride compound layers. Then, we use the same RTA process to form nanocrystal and improve the oxide quality. In the light of TEM and XPS analysis, we may infer that the nanocrystal is formed by NiSi2 and SiNX compound. Further, based on our electronic analysis, we can observe that the retention of NiSi2/SiNX compound Nanocrystal NVMs after 104 sec rises from 50% to 72% in comparison with the traditional one due of the quantum well band structure contributes by NiSi2 and SiNX compound nanocrystals. The retention of NiSi2/SiNX compound Nanocrystal NVMs after 104 sec is even better than the double layer without NH3 mixed one, 68%. Furthermore, the threshold voltage of NiSi2/SiNX compound Nanocrystal NVMs has not been subject to change after endurance with 104 programming and erasing cycles continuously. Thus, by means of depositing nanocrystal charge trapping layer mixed with NH3 gas, we achieve the objective of simplifying the fabrication process. These fabrication techniques for the application of nonvolatile nanocrystal memory can also be applicable to the current manufacture process of the integrated circuit manufacture.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 221-249). Available also in a digital version from Dissertation Abstracts.

published_or_final_version / Physics / Master / Master of Philosophy

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This Thesis describes some [3,3] and [2,3] -sigmatropic rearrangements that can occur in a variety of polyfluoroaromatic and -heteroaromatic compounds. The presence of fluorine on the aromatic moiety precludes the normal rearomatization process. The work is conveniently divided into two parts. Part A concerns the preparation and thermal (Claisen) rearrangement of derivatives of allyl 5-fluoropyrimidin-4-yl ether. These rearrange upon thermolysis to give isomers in which the terminus for the migration of the allyl group is N-3, provided that there is no preceding reaction which localises a double- bond between C-4 and C-5 - in which case C-5 is the migration terminus. Hydrolysis of some of the N-allyl derivatives results in the formation of some new derivatives of 5-fluorouracil. Part B describes the reactions that occur when polyfluor - inated monocyclic, polycyclic and heterocyclic ring systems are treated with dimethylsulphoxide activated by dicyclohexycarbodi-imide or by trifluoroacetic anhydride. Fluorinated phenolic type compounds give products which are the result of a [2,3] sigmatropic rearrangement of the derived sulphoniumylide. Fluorinated anilines and thiophenols behave differently. Dearomatization occurs under very mild conditions. A number of reactions of the fluorinated cyclohexa-2,4-dienone products are described. The preparation and attempted rearrangement of 2,3,4,5,6- pentafluorobenzylmethylsulphoxide is also discussed.

New methods have been developed for the selective introduction of fluorine into benzenoid aromatic compounds involving the cleavage of aryl-metal bonds by various ‘electrophilic’ fluorinating agents. Cleavage of aryl-metal bonds has been achieved using trifluoromethyl hypofluorite (CF(_3)OF), caesium fluoroxysulphate (CsSO(_4)F) and elemental fluorine and, by the nature of the process, is regiospecific. Attempts have been made to extend this method to the introduction of fluorine into imidazole bases with some success. This approach has involved the synthesis of trialkylstannyl derivatives of several benzene derivatives and trimethylstannyl derivatives of 1,2-dimethylimidazole and N-methylimidazole. Prior to our attempts at selective introduction of fluorine into the sugar ring of 5-amino-l-(β-D-ribofuranosyl) imidazole-4-carboxamide (AICAR) a series of protection and selective deprotection reactions on the nucleoside were carried out and trifluoromethane sulphonate ester derivatives of the protected nucleoside were synthesized. Fluoride ion displacement of the trifluoromethane sulphonate group to give a fluorosugar has been attempted.

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