Characterization of Low Temperature Sintered Ferrite Laminates for High Frequency Point-of-Load (POL) Converters

Low profile magnetic components and associated integration techniques are desired for design and fabrication of highly integrated point-of-load (POL) converters working at high frequency. The multilayer low-fire ferrite inductors can be fabricated as the magnetic substrate in an integrated POL converter with active components on top. This paper reports the characterization of magnetic property, microstructure, and chemical composition of commercially available low-fire Ni-Cu-Zn ferrites (ESL 40010, 40011, and 40012) and their mixed laminates. Permeability and core loss density were measured on toroidal cores sintered at 885 ^° C for 3.5 h. The influence of superimposed dc bias on the magnetic property of ferrite laminates was also evaluated. The microstructure and chemical composition of low temperature sintered ferrite laminates were analyzed. The mixed laminate with alternating layers of ESL 40010 and ESL 40012 in 1:1 ratio presents the highest permeability and the lowest core loss density among all examined samples when dc bias is above 1000 A/m. Finally, a 12 V to 1.2 V, 15 A, high frequency (1.5-5 MHz) integrated POL converter with laminated ferrite inductor was fabricated and demonstrated to work at high efficiency with a power density as high as 1000 W/in³.