Zhengzheng Wu

Investigation of On-Chip Soft-Ferrite-Integrated Inductors for RF ICs—Part II: Experiments

We report the systematic study and design optimization of CMOS-compatible on-chip ferrite-integrated inductors, including detailed quantitative analysis by simulation and circuit modeling, new ferrite fabrication and characterization, ferrite-integrated-inductor design, measurement, and optimization. A new ferrite nanopowder-mixed-photoresist spin-coating/inkjetting technique is discussed. The design and characterization of ferrite-integrated inductors with various ferrite-filling structures are presented. Measurement shows substantial improvement of up to +160% in inductance (L) and + 220% in quality factor (Q) across the multigigahertz frequency spectrum with a self-resonance frequency (f 0) over 20 GHz for the new ferrite-integrated inductors. This study clearly suggests that the new ferrite-integrated inductor technique is a potential solution to the realization of radio-frequency systems-on-a-chip requiring high-performance compact on-chip inductors. This work is presented in two parts. Part I discusses the design and simulation of ferrite-integrated inductors. This paper is Part II, presenting experimental results for material research and device implementation.

Investigation of On-Chip Soft-Ferrite-Integrated Inductors for RF ICs—Part I: Design and Simulation

We report a systematic investigation and design optimization of CMOS-compatible on-chip ferrite-integrated inductors, including a detailed quantitative analysis by simulation and circuit modeling, new ferrite material fabrication and characterization, and ferrite-integrated-inductor design, characterization, and optimization. A new ferrite nanopowder-mixed-photoresist spin-coating/inkjetting technique is discussed. The design and characterization of ferrite-integrated inductors with various ferrite-filling structures are presented. Measurement shows substantial improvement of up to +160% in inductance (L) and + 220% in quality factor (Q) across the multigigahertz frequency spectrum with a self-resonance frequency (f 0) of over 20 GHz for the new ferrite-integrated inductors. This paper clearly suggests that the new ferrite-integrated-inductor technique is a potentially viable solution to the realization of radio-frequency systems-on-a-chip requiring high-performance compact on-chip inductors. This work is presented in two parts. This paper is Part I, discussing the design and simulation of ferrite-integrated inductors. Part II discusses the experimental work, including material research and device implementation.

Post-CMOS Compatible Micromachining Technique for On-Chip Passive RF Filter Circuits

This paper reports on a post-CMOS compatible micromachining technology for passive RF circuit integration. The micromachining technology combines the formation of high performance microelectromechanical systems solenoid inductors and metal-insulator-metal (MIM) capacitors by using a post CMOS process on standard CMOS substrate. Utilizing this process, novel on-chip 3-D configured RF filters for 5 GHz band are integrated on-chip. Two types of compact filters are designed and fabricated, with the layout size of the bandpass filter as 0.65 times 0.67 mm2 and that of the low-pass filter as 0.77 times 1.25 mm2. From the measurement results, the fifth-order low-pass filter shows less than 1.06 dB insertion loss up to 5 GHz and -1.5 dB cutoff frequency at 5.3 GHz. The bandpass filter is a secondorder coupled-resonator type, with measured 4.3 dB minimum insertion loss and better than 13 dB return loss in the pass band. Both simulation and shock testing results have shown that the filters are almost free of influence from environmental vibration and shock. From the measured results in various temperatures, the bandpass filters were found to show lower loss under low temperatures, while the passband shift is negligible in the various temperatures. Together with the fabricated filters, the developed micromachining technique has demonstrated the potential of onchip integration and miniaturization of passive RF circuits.

Ferrite-integrated on-chip RF solenoid inductor

New on-chip RF solenoid inductors with Ni-Zn-Cu ferrite-filled structure are reported. The concave-suspending solenoids are fabricated by a post-CMOS MEMS process, and then a CMOS compatible low-temperature nano-powder-mixed-photoresist filling technique is used to fill ferrites into the inductor cavities. It shows significant improvements in inductance L and quality factor Q up to +60% and +107%, respectively, to multi-GHz.

An wide-range tunable on-chip radio-frequency LC-tank formed with a post-CMOS-compatible MEMS fabrication technique

An on-chip-micromachined tunable LC-tank, which consists of a metal inter-digitated variable capacitor and a metal solenoid inductor, is developed for wide-range radio-frequency (RF) tuning in multi-GHz band. A low-temperature metal MEMS process is developed to on-chip fabricate the passives. The process can be used for post-CMOS-compatible integration with RF ICs. Both the varactor and the inductor are suspended with a gap from the low-resistivity silicon wafer (i.e. standard CMOS wafer) for effectively depressing RF loss. The fabricated variable capacitor part, the inductor part and the whole tunable LC resonator are sequentially tested, finally resulting in a wide resonance-frequency tuning range of 72% (between about 3.5 and 6.0GHz) under a low tuning voltage range of 0-4V, while the Q-factor ranged within 23 and 8.

(INVITED) High-performance RF passives using post-CMOS MEMS techniques for RF SoC

Real-world realization of RF SoC has been hindered by the lack of high-performance, compact and tunable RF passive devices that are truly CMOS-compatible. This paper presents advances in low-temperature metal MEMS techniques developed to design and fabricate various high-performance RF passives for post-CMOS integration with RF SoC. Constructed with electroplated metal, the RF MEMS passives are suspended above the low-resistivity silicon substrate to depress both ohmic and substrate losses. The MEMS RF passives presented in this paper include concave-suspended high-Q solenoid inductors and transformers, wide-range tunable capacitors and resonant LC-tanks, etc. Key issues such as electrical, mechanical and reliability performance was discussed. Potential applications in RF mobile devices is outlined.

UV-LIGA metal MEMS: A promising tool to serve IC industry

Metal MEMS structures can be formed by metal electroplating with the aid of thick-photoresist molds. The microfabrication features low-temperature process that is post-CMOS compatible and can be used for on-chip integration of high-performance RF parrives for RFICs. On the other hand, The plating process can be combined with silicon micromachining techniques to build operation tools, like probe-cards, for wafer-level IC testing. The presentation addresses the promising techniques and achievements in device prototypes.