用于高效率高隔离功率传输的片上变压器

As the key device for galvanic isolation, opto-coupler has an annual market size of 1 billion US dollars. However, opto-coupler cannot transfer power. On the other hand, on-chip transformer not only provides power transfer capability, but also offers small size, low cost, high isolation capability, fast speed, and long lifetime. However, currently using on-chip transformer for isolated power transfer results in rather low efficiency. For example, Analog Devices, Inc. only achieved a power transfer efficiency of 33%. This is due to the low inductance to resistance ratio (L/R) of ADI's on-chip transformer, which results in a low transformer efficiency of 70% and a high operating frequency of 170 MHz. The high operating frequency in turn lead to large power loss in other circuit components such as power switches and rectifying diodes. Therefore, we have invented silicon-embedded coil as well as the interleaved and back-to-back stacked silicon-embedded coreless transformer structures. Simulations and unseccessful experimental trials show that the interleavd and back-to-back stacked silicon-embedded coreless transformer structures can achieve L/Rs that are 8 times and 10 times larger than ADI's on-chip transformer. demonstration of the interleaved structure has verified that its L/R can be 8 times larger than ADI's on-chip transformer, resulting in high efficiencies of 85% at a low frequency of 50 MHz. In this project, we will focus on addressing the key fabrication issues and experimentally demonstrate interleaved and back-to-back silicon-embedded coreless transformers for high efficiency high isolation power transfer. In order to improve the on-chip transformer design and optimization methodology, we will also analyze and compare the power loss of different isolated power transfer circuit topologies.

光耦作为实现隔离的重要器件年销售额10亿美元，但是不能进行功率传输。片上变压器不但能实现功率传输，而且体积小、成本低、隔离能力强、速度快、寿命长。但是，目前使用片上变压器进行隔离式功率传输效率很低，ADI公司仅取得33%的功率传输效率。这是由于电感电阻比（L/R）小导致变压器效率低（70%）、工作频率高（170MHz）,高工作频率又导致功率开关、整流二极管等电路元件的高功耗。因此，项目申请人发明了硅嵌入式线圈和以其为基础的交缠型和背靠背叠置型硅嵌入式无芯变压器。前期仿真和失败的实验尝试显示，交缠型和背靠背叠置型硅嵌入式无芯变压器L/R可达ADI公司的8倍和10倍，均可在50MHz的较低频率达到85%的高变压器效率。本项目的研究内容就是解决关键工艺问题，并实验展示可实现高效率高隔离功率传输的交缠型和背靠背叠置型硅嵌入式无芯变压器。本项目还将进行隔离式功率传输功耗分析和电路结构比较来完善设计。

“超越摩尔定律”将越来越多的功能集成到芯片上是半导体产业的发展趋势，而其中无源器件的集成是一个重要方向。目前变压器的集成落后于电阻和电容等无源器件，是国际研究热点。基于变压器的隔离式小功率传输在工业、汽车、发电、电信、医疗、仪器仪表、消费电子、航空航天等领域具有广泛的应用需求。传统上使用大电感/电阻比的分立变压器可实现高效率功率传输，但集成度低、系统尺寸大、成本高。ADI公司使用片上变压器实现了系统级封装，将系统尺寸显著减小（50倍以上），同时降低了成本。但传统片上变压器电感/电阻比很小，在170MHz的高工作频率下才能达到70%的变压器效率，导致了很大的开关管和整流管高频损耗，系统功率传输效率仅为34%。因此，本项目提出了改进的交缠型硅嵌入式无芯变压器、双面叠置型硅嵌入式无芯变压器、背靠背叠置型硅嵌入式无芯变压器三种新型片上变压器结构，并成功完成了工艺开发实现了样品制备。本项目开发的三种新型片上变压器均在10MHz到20MHz的低工作频率下取得了70%以上的变压器效率，达到了世界先进水平，最高效率超过80%，为目前报道的最高值。本项目开发的三种新型片上变压器还具有面积小（2mm^2）、工艺流程简单（3到5张掩膜版）、不需要磁芯、电感/电阻比大（达到ADI公司的20到40倍）等优点，背靠背叠置型变压器电感/电阻比达到0.40 μH/Ω，为目前报道的最高值。本项目开发的背靠背叠置型变压器隔离能力超过了6kV，可满足绝大部分产品级应用要求。本项目开发的交缠型变压器和双面叠置型变压器隔离能力分别达到0.78kV和1.05kV，可满足220V市电应用要求。本项目还分析比较了全桥、推挽、反激三种主要隔离式功率传输电路结构中的变压器功耗和效率，搭建了器件研究和电路应用之间的桥梁。本项目的上述成果具有巨大的应用前景。