Design and optimization of on-chip thick-plated copper-transformers for galvanic isolated DC-DC converter achieving up to 38.9% peak efficiency

Abstract

In this article, an approach for on-chip coreless transformers design and optimization is proposed and demonstrated for isolated DC-DC converter applications. This available approach was successfully executed by one fabricated sample and then with the aid of measurement and simulation its accuracy has been validated. Using the provided guidelines by EM simulation, transformers with different geometrical parameters were simulated and optimized based on the provided analytic model. The on-chip transformers within 6 μm thick-plated copper were implemented by re-distribution layer technique on 0.35 μm BCD platform. The proposed architecture was ultimately benefited from these evidences and fabricated as a stand-alone die. Finally, the targeted coreless transformer was integrated with oscillator and rectifier to verify the combined work and their efficiency. Results show that the transformers strictly follow the derived rule-set and meet the desired expectation. The assembled DC-DC converter is able to work effectively. Thanks to the optimization of fabricated structure of transformer, designed DC-DC converter delivers an excellent 38.9% efficiency at 3.3 V regulated output voltage in room temperature, while exhibiting isolated rating of better than 5 kVrms over a minute duration with 16 μm polyimide.