Influence of ferrite thin-film layer on property of stacked spiral thin-film transformer

Stacked spiral thin-film transformer is designed and fabricated. The mechanism of ferrite thin film is discussed. Primary spiral and secondary spiral are on the different layer and have the same shape. Air core transformer and magnetic core transformer are made with SiO2 or ferrite thin film in the middle of two spirals respectively. S-parameters are measured at 10MHz-20GHz. The result shows that the transmission efficiency of air core thin-film transformer more than 50% at 8GHz-16GHz, and the maximum is 60.6% at 11.95GHz; the transmission efficiency of magnetic core thin-film transformer more than 50% at 2.5GHz-20GHz, and the maximum is 78.0% at 9.85GHz.