A Novel Primary-Embedded On-Chip Transformer for 6-kV-Isolation High-Efficiency DC–DC Conversion

In this letter, a novel primary-embedded on-chip transformer (PEOCT) is proposed and demonstrated for ultra-high-isolation high-efficiency DC-DC conversion. The PEOCT has a silicon-embedded primary coil with a 100-μm thickness and a top-metal secondary coil with a 30-μm thickness for achieving large coil inductance/resistance ratios. The stacked coils of the PEOCT can be easily isolated with a flat polyimide isolation layer. The fabricated 4-mm
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PEOCT achieved record-high transformer efficiencies at low frequencies (78% at 10 MHz and 84% at 20 MHz), which is essential for achieving a high isolated DC-DC conversion efficiency. An ultra-high isolation capability of more than 6 kV was also measured.