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Selective removal of the silicon underneath a set of single-turn multilayer interlaced stacked (SMIS) radio-frequency (RF) transformers with nearly perfect magnetic-coupling factor (kIM~1) and high resistive-coupling factor (kRe) is demonstrated. This process is based on the inductively coupled-plasma (ICP) deep trench technology. Improvement of 20.6 and 15.7 dB in isolation (S21) were achieved at 5.2 and 8 GHz, respectively, for a dummy open device after the backside ICP etching. Q-factor increases of 102% (from 4.96 to 10.03) and 23.2% (from 2.24 to 2.76), GAmax increases of 11.8% (from 0.76 to 0.85) and 4.5% (from 0.88 to 0.92), and NFmin decreases of 0.49 dB (from 1.22 to 0.73 dB) and 0.19 dB (from 0.55 to 0.36 dB) were achieved at 5.2 and 8 GHz, respectively, for an SMIS transformer with an overall dimension of 170times240 mum2 after the backside ICP etching. The GAmax of 0.85 and 0.92 are both state-of-the-art results among all reported on-chip transformers. Furthermore, the reasons why the SMIS transformer exhibits better performances than the traditional bifilar and the traditional stacked transformer are explained. These results show that the micromachined SMIS transformers are very promising for RF integrated circuit applications

In this paper, we demonstrate a comprehensive analysis of the temperature effect (from −25°C to 175°C) on the quality-factors (Q1 and Q2), magnetic-coupling factor (KIm), resistive-coupling factor (KRe), maximum available power gain (GA max), and minimum noise figure (NFmin) performances of RF bifilar and stacked transformers for RFIC applications. Excellent GA max of 0.713 and 0.806 (that is, NFmin of 1.469 and 0.937 dB) were achieved at 5 and 7 GHz, respectively, at room temperature, for a 1:1 stacked transformer mainly due to its high KIm and KRe. In addition, for the 1:1 bifilar transformer at room temperature, though its KIm and KRe are low, good GA max of 0.636 and 0.631 (that is, NFmin of 1.965 and 2.0 dB) were still achieved at 5 and 7 GHz, respectively, mainly due to its high Q1 and Q2. The present analysis is helpful for RF engineers to design temperature-insensitive ultra-low-voltage high-performance transformer-feedback low-noise-amplifiers (LNAs) and voltage-controlled-oscillators (VCOs), and other radio-frequency integrated circuits (RF-ICs) which include transformers. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1460–1466, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21732

In this paper, we propose a single-turn multiple-layer interlaced stacked transformer structure with nearly perfect magnetic-coupling factor (k IM ∼ 1) using standard mixed-signal/RF CMOS (or BiCMOS) technology. A single-turn six-layer interlaced stacked transformer was implemented to demonstrate the proposed structure. Temperature dependence (from -25 °C to 175°C) of the quality-factor (Q-factor), k Im , resistive-coupling factor (k Re ), maximum available power gain (G Amax ), and minimum noise figure (NF min ) performances of the transformer are reported. State-of-the-art G Amax of 0.762 and 0.904 (i.e. NF min of 1.181 dB and 0.437 dB) have been achieved at 5.2 GHz and 8 GHz, respectively, at room temperature, mainly due to the perfect magnetic-coupling factor and the high resistive-coupling factor. The present analysis is helpful for RF engineers to design ultra-low-voltage high-performance transformer-feedback LNAs and VCOs, and other RF-ICs which include transformers.