High-Q inductors are realized on a 3-8 Ω•cm silicon substrate in the buildup of BCB/Cu. Anisotropic wet etching is utilized to remove the silicon in the cavities underneath the spirals from the backside. Examples of 3.5-turn spiral inductors with and without cavity are compared, and their parameter extractions are accomplished with an equivalent circuit model. Compared to the inductor without cavity, the measured peak quality factor of a 8.19-nH inductor with cavity increases from 24 at 0.8 GHz to 39 at 2.5 GHz by 67%, and the inductor with cavity has a wider bandwidth using the same equivalent model. The inductors utilizing this technique have a potential wide application in hand-held RF modules either as part of an off-chip device or as an integrated passive in a silicon interposer.
2. Rong, B., et al., "Surface-passivated high-resistivity silicon substrates for RFICs," IEEE Electron Device Letters, Vol. 25, No. 4, 176-178, 2004.
3. Gamble, H. S., et al., "Low-loss CPW lines on surface stabilized high-resistivity silicon," IEEE Microwave and Guided Wave Letters, Vol. 9, No. 10, 395-397, 1999.
4. Zoschke, K., et al., "Wafer level processing of integrated passive components using polyimide or polybenzoxazole/copper multilayer technology," IEEE Transactions on Advanced Packaging, Vol. 33, No. 2, 398-407, 2010.
5. Chen, C. H., C. S. Shih, T. S. Horng, and S.-M. Wu, "Very miniature dual-band and dual-mode bandpass filter designs on an integrated passive device chip," Progress In Electromagnetics Research, Vol. 119, 461-476, 2011.
6. Wu, S. M., et al., "Physical model extracting of spiral inductor on glass substrate, electronics packaging technology conference," 10th Electronics Packaging Technology Conference, EPTC 2008, 1028-1033, 2008.
7. Chong, K., et al., "High-performance inductors integrated on porous silicon," IEEE Electron Device Letters, Vol. 26, No. 2, 93-95, 2005.
8. Yook, J. M., D. Kim, and J. C. Kim, "High-Q trenched spiral inductors and low-loss low pass filters using through silicon via processes," Japanese Journal of Applied Physics, Vol. 53, No. 4S, 04EE11, 2014.
9. Hongrui, J., W. Ye, J. L. A. Yeh, and N. C. Tien, "On-chip spiral inductors suspended over deep copper-lined cavities," IEEE Transactions on Microwave Theory and Techniques, Vol. 48, No. 12, 2415-2423, 2000.
10. Gu, , L. and X. Li, "Concave-suspended high-Q solenoid inductors with an RFIC-compatible bulk-micromachining technology," IEEE Transactions on Electron Devices, Vol. 54, No. 4, 882-885, 2007.
11. Wang, T., M. Han, and L. Luo, "A folded slot antenna with pre-etched cavity and BCB support membrane on silicon wafer," Progress In Electromagnetics Research Letters, Vol. 39, 97-102, 2013.
12. Yue, C. P., et al., "A physical model for planar spiral inductors on silicon," IEEE International Electron Devices Meeting, IEDM'96, 155-158, 1996.
13. Xiao, H., K. J. Chen, and P. C. H. Chan, "Silicon-based high-Q inductors incorporating electroplated copper and low-K BCB dielectric," IEEE Electron Device Letters, Vol. 23, No. 9, 520-522, Sep. 2002.
14. Khoo, Y. M., et al., "Enhancement of silicon-based inductor Q-factor using polymer cavity," IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 2, No. 12, 1973-1979, 2012.