RF On-chip Spiral Inductor And Its Applications In Passive Filters Based On STI Technology And Copper Process

In RF communication circuits, inductors are widely used in each module of RF transceivers, such as low-noise amplifier (LNA), voltage-controlled oscillator (VCO), impedance matching networks and filters. Especially, with the increasing operating frequency of modern communication systems, the performance of inductors at high frequencies will directly affect the quality of mobile communication systems. In this context, the realization of RF spiral inductors and the related RF circuit modules has become a very important research topic. At present, the advantages are copper process, mainly in:copper conducts electricity better than the currently used aluminum and the resistance of copper is small. Besides, it emits a small amount of heat; Below 0.13μm, chip manufacturing technology using copper process will effectively increase the operating frequency of chips. Thus, using advanced CMOS copper process technology to produce RFICs on standard silicon substrates is in line with the low-cost and fully integrated development requirements in RFICs.In this paper, based on circuit and electromagnetic field theory, we analyzed the factors which affect the value of Q, such as the substrate loss, ohmic loss, eddy current loss, skin effect and proximity effect. Considering all factors, we applied three-dimensional electromagnetic simulation software HFSS to analyze how to improve the inductor performance by different methods, such as changes in shape of spiral inductors, substrate structure optimization and the copper process. We focused on the design and measurement of spiral inductors using copper process. Both the inductors with conventional structure and gradually changed structure have been fabricated using copper process. Then, we focused on the optimizing method of patterned trench isolation. The results show that the appropriate STI in the substrate below the inductor can improve the Q factor and the realization of the trench isolation process is compatible with the standard CMOS process. For a 3.5-turn inductor on low-resistivity silicon, Qmax of the inductor with 10μm depth of patterned trench isolation is 12.4% higher than the inductor without patterned trench isolation.fSR of the inductor with patterned trench isolation is 16.5GHz while fSR of the inductor without patterned trench isolation is 15.3GHz, which has nearly improved by 1GHz.In addition, we have applied inductors with trench isolation structure in the LC passive filters. We analyzed and compared the low-pass filter performances. Experiments show that LC low-pass filter performances have been improved to varying degrees by using the proposed optimizing method of patterned trench isolation. For example, the LC low-pass filter whose cutoff frequency is 2.4GHz has a perfect performance considering actual process conditions. Under low frequencies, the LC low-pass filters with patterned trench isolation have a better performance than the LC low-pass filters without patterned trench isolation.