High-performance single-turn interlaced-stacked transformers for Ka-Band CMOS RFIC applications

In this article, we demonstrate that high-coupling and ultra-low-loss transformers for Ka-Band (26-40 GHz) CMOS RFIC applications can be achieved by using single-turn in/erlaced-stacked (STIS) structure implemented in a standard 0.18-μm CMOS technology. State-of-the-art G_Amax of 0.777, 0.852, and 0.799 (i.e., NF_min of 1.097, 0.695, and 0.977 dB) were achieved at 30. 36, and 40 GHz, respectively, for a 2-layer STIS transformer with an inner dimension of 100 × 100 μm² and a metal width of 10 μm, mainly due to the high magnetic-coupling factor and the high resistive-coupling factor. Furthermore, the reasons why the STIS transformer exhibits better performances than the traditional bifilar and the traditional stacked transformer are explained. These results show that the STIS transformers are very promising for high-performance Ka-Band CMOS RFIC applications.