Cell-line Engineering of Chinese Hamster Ovary Cells for Low-temperature Culture

Developments in mammalian cell culture and recombinant technology has allowed for the production of recombinant proteins for use as human therapeutics. Mammalian cell culture is typically operated at the physiological temperature of 37°. However, recent research has shown that the use of low-temperature conditions (30-33°) as a platform for cell-culture results in changes in cell characteristics, such as increased specific productivity and extended periods of cell viability, that can potentially improve the production of recombinant proteins. Furthermore, many recent reports have focused on investigating low-temperature mammalian cell culture of Chinese hamster ovary (CHO) cells, one of the principal cell-lines used in industrial production of recombinant proteins. Exposure to low ambient temperatures exerts an external stress on all living cells, and elicits a cellular response. This cold-stress response has been observed in bacteria, plants and mammals, and is regulated at the gene level. The exact genes and molecular mechanisms involved in the cold-stress response in prokaryotes and plants have been well studied. There are also various reports that detail the modification of cold-stress genes to improve the characteristics of bacteria or plant cells at low temperatures. However, there is very limited information on mammalian cold-stress genes or the related pathways governing the mammalian cold-stress response. This project seeks to investigate and characterise cold-stress genes that are differentially expressed during low-temperature culture of CHO cells, and to relate them to the various changes in cell characteristics observed in low-temperature culture of CHO cells. The gene information can then be used to modify CHO cell-lines for improved performance in the production of recombinant proteins.

Preliminary Characterisation of Low-Temperature Bonded Copper Interconnects for 3-D Integrated Circuits

Three dimensional (3-D) integrated circuits can be fabricated by bonding previously processed device layers using metal-metal bonds that also serve as layer-to-layer interconnects. Bonded copper interconnects test structures were created by thermocompression bonding and the bond toughness was measured using the four-point test. The effects of bonding temperature, physical bonding and failure mechanisms were investigated. The surface effects on copper surface due to pre-bond clean (with glacial acetic acid) were also looked into. A maximum average bond toughness of approximately 35 J/m² was obtained bonding temperature 300 C.

Effects of Platinum on NiPtSiGe/n-SiGe and NiPtSi/n-Si Schottky Contacts

Solid phase reaction of NiPt/Si and NiPt/SiGe is one of the key issues for silicide (germanosilicide) technology. Especially, the NiPtSiGe, in which four elements are involved, is a very complex system. As a result, a detailed study is necessary for the interfacial reaction between NiPt alloy film and SiGe substrate. Besides using traditional material characterization techniques, characterization of Schottky diode is a good measure to detect the interface imperfections or defects, which are not easy to be found on large area blanket samples. The I-V characteristics of 10nm Ni(Pt=0, 5, 10 at.%) germanosilicides/n-Si₀/₇Ge₀.₃ and silicides/n-Si contact annealed at 400 and 500°C were studied. For Schottky contact on n-Si, with the addition of Pt in the Ni(Pt) alloy, the Schottky barrier height (SBH) increases greatly. With the inclusion of a 10% Pt, SBH increases ~0.13 eV. However, for the Schottky contacts on SiGe, with the addition of 10% Pt, the increase of SBH is only ~0.04eV. This is explained by pinning of the Fermi level. The forward I-V characteristics of 10nm Ni(Pt=0, 5, 10 at.%)SiGe/SiGe contacts annealed at 400°C were investigated in the temperature range from 93 to 300K. At higher temperature (>253K) and larger bias at low temperature (<253K), the I-V curves can be well explained by a thermionic emission model. At lower temperature, excess currents at lower forward bias region occur, which can be explained by recombination/generation or patches due to inhomogenity of SBH with pinch-off model or a combination of the above mechanisms.