Opportunity
Traditional transformers are electromagnetic devices consisting of magnetic cores and copper windings, which cannot be integrated into semiconductor-based integrated circuits. While coreless planar transformers have been developed for printed circuit boards (PCBs), they still rely on metallic conductors (e.g., aluminum or copper) for windings. This poses significant challenges due to the mismatch in thermal expansion coefficients between metals (e.g., aluminum: 23×10⁻⁶/K, copper: 17×10⁻⁶/K) and semiconductor materials like silicon (2.6×10⁻⁶/K). Such differences lead to mechanical stress at the metal-semiconductor interface, causing track breakage under thermal expansion. Additionally, depositing metallic materials on semiconductors is costly and complex. These limitations hinder the full integration of transformers into monolithic semiconductor circuits, especially for low-power and signal-transfer applications requiring electrical isolation.
Technology
The patent introduces a novel "semiconductor transformer" where primary and secondary windings are made of highly doped semiconductor materials (e.g., n++ or p++ silicon) instead of metallic conductors. This innovation leverages doped semiconductor paths, optionally enhanced with silicides or salicides (e.g., Cu₃Si, Fe₃Si), to achieve low resistivity while maintaining thermal expansion coefficients similar to the substrate (e.g., silicon dioxide). The windings are fabricated on opposite sides of an insulating substrate (e.g., SiO₂) using standard semiconductor processes like ion implantation or bonded silicon-on-insulator (SOI) techniques. Key advancements include:
- Material Compatibility: Semiconductor windings eliminate thermal stress issues by matching expansion coefficients with the substrate.
- Integration: The entire transformer can be fabricated within an integrated circuit (IC), enabling monolithic integration with other electronic components.
- Performance: Thin insulation layers (e.g., 20 µm SiO₂) provide high breakdown voltages (e.g., 12 kV) and low interwinding capacitance, reducing noise. Simulations show coupling coefficients up to 0.785 and resonant frequencies suitable for low-power applications (e.g., 21.7 MHz).
Advantages
- Full Circuit Integration: Enables transformers to be fabricated alongside other IC components, reducing stray elements and improving power density.
- Thermal Reliability: Eliminates mechanical stress from thermal expansion mismatches.
- Cost-Effective: Uses standard semiconductor manufacturing processes, avoiding expensive metal deposition.
- High Isolation: SiO₂ insulation offers high breakdown voltages (600 V/µm).
- Low Noise: Minimal interwinding capacitance reduces switching transients.
Applications
- Gate Drive Circuits: Isolated gate drives for power MOSFETs/IGBTs.
- Signal Transfer: Low-power communication interfaces requiring electrical isolation.
- Integrated Power Supplies: On-chip DC-DC converters for portable devices.
- Medical Electronics: Isolation in implantable or high-voltage medical equipment.
- Automotive Systems: Compact transformers for electric vehicle power systems.
