Abstract
This paper presents the development, characterization and application of a microtransformer with a bar magnetic core fabricated on silicon substrate using thin-film technology. The magnetic core, coils, and insulation layers were deposited using only sputtering PVD (physical vapor deposition) or CVD (chemical vapor deposition) processes. As insulation materials, silicon dioxide and silicon nitride are only used. The device is small with a chip size of 1600 µm x 800 µm. The transformer has a turns ratio of 1:1 and achieves a self-inductance of about 40 nH. The minimum measured breakdown voltage of the microtransformer is 1250 V(DC). The microtransformer device is applicable for frequencies up to 20 MHz. The device was fabricated on 12-inch silicon substrates on mass production equipment.
Highlights
One of the most important development challenges for monolithic solutions for Internet of Things (IoT), wireless communication, and many portable devices is the integration of on-chip inductors and transformers with magnetic materials on silicon
Closed toroidal core designs can be fabricated in one deposition step and allows flux to flow in the plane but uniaxial anisotropy can not be realized, resulting in poor efficiency
This paper showed the feasibility of fabricating a small signal microtransformer on 12-inch silicon substrates on mass production equipment
Summary
One of the most important development challenges for monolithic solutions for Internet of Things (IoT), wireless communication, and many portable devices is the integration of on-chip inductors and transformers with magnetic materials on silicon. Most recent works in this technical field do show big improvement in integration technology and magnetic material research and the development of new micro inductors and microtransformers and their implementation in many applications. New magnetics materials with high magnetic flux density like CoFe and materials with low core losses like CoZrTa, CoFeB were developed and used in microinductors and transformers. Most recent works in this technical field do show big improvement in integration technology and magnetic material research and the development of new micro inductors and microtransformers and their implementation in many applications.. New magnetics materials with high magnetic flux density like CoFe and materials with low core losses like CoZrTa, CoFeB were developed and used in microinductors and transformers. Microinductors and microtransformers were realized using different design approaches such as using bar core, closed toroidal cores or racetrack core.. The bar magnetic core design is used frequently due to its ease of implementation since only one magnetic layer is used and be fabricated in one process step. Closed toroidal core designs can be fabricated in one deposition step and allows flux to flow in the plane but uniaxial anisotropy can not be realized, resulting in poor efficiency. Microtransformers can be used in many applications at high switching frequency of tens of MHz. The most common applications are dc-dc converters (isolated and non-isolated) and digital isolators in SiC or GaN applications
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