Application of Magnetic Ferrite Electrodeposition and Copper Chemical Mechanical Planarization for On-Chip Analog Circui
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Application of Magnetic Ferrite Electrodeposition and Copper Chemical Mechanical Planarization for On-Chip Analog Circuitry Cody Washburn1, Daniel Brown2, Jay Cabacungan1, Jayanti Venkataraman2 and Santosh K. Kurinec1 1 Microelectronic Engineering, 2Electrical Engineering Rochester Institute of Technology, Rochester, NY 14623 ABSTRACT Inductors are important components of analog circuit designs, from matching circuitry to passive filters. In this study, the application of electrophoretically deposited nano-ferrite material has been investigated as a technique to increase the inductance of integrated copper planar inductors fabricated using copper plating and chemical mechanical planarization. Sintered MnZn ferrite particles are suspended in a medium of isopropyl alcohol with magnesium nitrate and lanthanum nitrate salts. The transportation of the particles to the substrate surface is assisted by applied electric field and particles adhere to the substrate surface by a glycerol based surfactant. Electrophorectic deposition process forms a self aligned polymeric thin film on the surface of a p-type silicon substrate selectively with respect to copper. This ferrite deposition method yields high selectivity to the inductor coils and patterned silicon substrates compatible with standard silicon technology. INTRODUCTION Monolithic integration of passive circuit components such as inductors, capacitors and resistors can provide on-chip circuitry capable of performing a number of analog signal processing functions. When combined with CMOS technology, the integration of passives will result in greater device functionality along with reduced package size. The optimization of on chip passive components is critical to improve performance of silicon based analog technology. Planar inductor coils are a common configuration for incorporating highly inductive elements in silicon based technology. The planar structure is particularly easy to incorporate in a CMOS process, by utilizing the top level of metal interconnect. For optimal performance, copper is used to define the inductor pattern in order to minimize resistance. The mutual coupling of the magnetic field between adjacent traces of the inductor provides an opportunity to enhance the overall inductance by adjusting the material properties of the medium in which the magnetic field is present. The immersion of a planar coil in a material with a high permeability can greatly increase the inductance of the coil. This leads to a reduction in the layout area necessary for a given value of inductance [1-5]. The ability to integrate a material with a high permeability on chip, allows for magnetically coupled circuits and structures to be designed and incorporated along side CMOS circuitry. Devices ranging from A.C. transformers to magnetically driven MEMS structures can be designed and fabricated. An additional application is the incorporation of high frequency microwave ferrites on chip. This allows for the combination of devices such as circulators and other non-reciprocal
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