On-Chip Thin-Film Microtransformer With Improved Coupling Factor For High Frequency Data Transmission

An on-chip thin-film microtransformer with an improved coupling factor is shown in this paper. In addition to the development of this component, the characterization of the microtransformer and its use in the data transmission application are presented. In comparison to previous work, this microtransformer device shows an improved coupling factor. The microtransformer is fabricated on silicon substrate using thin-film technology. The fabrication is based on damascene process and combines material deposition using only sputtering PVD (physical vapor deposition) or CVD a (chemical vapor deposition) processes and chemical-mechanical polishing (CMP) process for patterning. The microtransformer design is a solenoid type device with a magnetic bar core and interleaved winding style. For a magnetic core a CoFeB material is applied. As insulation materials, silicon dioxide and silicon nitride are implemented. The device chip size is 1.6 mm x 0.8 mm. A turns ratio of the microtransformer is 1:1, and the device shows a self-inductance of about 25 nH and an improved coupling factor with a value of 60%.