3D integration technologies for MEMS
This paper describes selected technologies for the 3D integration of MEMS devices. This comprises a Via Last approach for the formation of MEMS TSVs and a Cu based thermo-compression bonding method for the realization of small 3D-WLP devices. Moreover, the Aerosol Jet technique is discussed as method for the final assembly by means of printing conducting lines over 3D topography.
Low-Temperature Cu-Cu Wafer Bonding
Metal thermo-compression bonding is a process suitable for 3D interconnects applications at wafer level. The process requires typically bonding temperatures of ~400{degree sign}C and high contact pressure applied during bonding. Temperature reduction below such values is required in order to solve some issues regarding wafer-to-wafer misalignment after bonding and to minimize thermo-mechanical stresses. Low-temperature (LT) Cu-Cu wafer bonding was successfully demonstrated at 175{degree sign}C. The bond quality, bond strength, metal interface layers microstructure and chemical composition of Cu-Cu wafer pairs bonded under different process conditions were investigated. Experimental results on various Cu native oxide methods evaluation as well as results obtained for various bonding and annealing temperatures are presented.
High‐precision U‐Pb zircon age calibration of the global Carboniferous time scale and Milankovitch band cyclicity in the Donets Basin, eastern Ukraine
High‐precision ID‐TIMS U‐Pb zircon ages for 12 interstratified tuffs and tonsteins are used to radiometrically calibrate the detailed lithostratigraphic, cyclostratigraphic, and biostratigraphic framework of the Carboniferous Donets Basin of eastern Europe. Chemical abrasion of zircons, use of the internationally calibrated EARTHTIME mixed U‐Pb isotope dilution tracer, and improved mass spectrometry guided by detailed error analysis have resulted in an age resolution of <0.05%, or ∼100 ka, for these Carboniferous volcanics. This precision allows the resolution of time in the Milankovitch band and confirms the long‐standing hypothesis that individual high‐frequency Pennsylvanian cyclothems and bundles of cyclothems into fourth‐order sequences are the eustatic response to orbital eccentricity (∼100 and 400 ka) forcing. Tuning of the fourth‐order sequences in the Donets Basin to the long‐period eccentricity cycle results in a continuous age model for the Middle to Late Pennsylvanian (Moscovian‐Kasimovian‐Ghzelian) strata of the basin and their record of biological and climatic changes through the latter portion of the late Paleozoic Ice Age. Detailed fusulinid and conodont zonations allow the export of this age model to sections throughout Euramerica. Additional ages for Mississippian strata provide among the first robust radiometric calibration points within this subperiod and result in variable lowering of the base ages of its constituent stages compared to recent global time scale compilations.