A co-fireable material system for ceramics and ferrites hetero-laminates in LTCC substrates

A method for solving the current challenges in manufacturing hetero-laminated material systems using Low Temperature Co-firing Ceramics (LTCC) technique is introduced in this paper. The system contains all three major materials that widely used in the LTCC industry, Zn2SiO4 ceramic, NiCuZn ferrite and silver. Previous reported methods either involve additional buffer layers which would increase the device thickness, or apply mechanical pressure during the co-firing which is not compatible to the standard LTCC process. Our method provides a facile route to manufacture hetero-laminated material systems that demands no buffer layer and follows the standard LTCC process. In this paper, four glass-free hetero-laminated material systems using LTCC technology, i.e. NiCuZn/Zn2SiO4/NiCuZn/Zn2SiO4/NiCuZn (termed “LTCC-5”), NiCuZn/Zn2SiO4-Ag/NiCuZn (termed “LTCC-3-NZAN”), NiCuZn/Ag/NiCuZn (termed “LTCC-3-NAN”) and NiCuZn/Zn2SiO4/NiCuZn (termed “LTCC-3-NZN”), have be were designed, manufactured and characterized. The shrinkage rates of these material systems show well-matched temperature spectrum. The sintering properties and interfacial diffusions of the material systems were characterized using optical microscopy, electron microscopy and Energy Dispersive Spectrometer (EDS) element mapping. Optical microscopy shows that all the material systems have well-defined multi-layered structure with controllable and tunable layer thickness. Electron microscopy images prove no microstructural cracks or defects at any of the hetero material interfaces. EDS analysis further proves that the inter-diffusions of the magnetic elements (Fe and Ni) at the NiCuZn/Zn2SiO4 interface is minimized. Such property is essential for achieving high performance devices for applications such as power inductors and DC/DC converters.