Three-dimensional micromachined on-chip inductors for high frequency applications

Demands for wireless communication are ever-escalating for consumer and military communication applications. The requirements of portability, more functionality and lower cost have been driving forces toward smaller, more sophisticated and flexible wireless devices with lower power consumption. To meet these requirements, monolithically integrated passive inductors with high Q-factors and high self-resonant frequencies are desirable. Q-factor and self-resonant frequency of an inductor are significantly degraded at high frequencies due to conductor ohmic loss, magnetically induced eddy current in the conductive substrate, and lower self-resonant frequency from capacitance between conductive substrate and conductors. In this dissertation, novel three-dimensional arch-like solenoid and dome-shaped spiral inductors are designed, fabricated, and characterized. MEMS-based fabrication techniques such as copper electroplating through voids in thick SU-8 photoresist molds and EAGLE2100 conformal photoresist molds on sacrificial arch-like or dome-shape SJR5740 photoresist mounds are utilized. An air gap between the inductor and the silicon substrate is used to reduce the degradations of inductor performance. According to the Sonnet electromagnetic simulations, 30 μm air-gap suspension over the substrate is an adequate choice for these inductors. Suspended arch-like solenoid copper inductor has flat bottom conductor connected to arch-like top conductor with an air core in between. This design has only 2 contact points per inductor turn to minimize series resistance. Suspended domeshaped spiral copper inductor is fabricated on a sacrificial photoresist dome with the outer end connected to one probe pad, and the inner end connected to the other probe pad through vias and an air-bridge. The sidewalls of spiral turns in this design overlap less with each other thereby reducing inter-turn capacitances. Fabricated inductors are characterized and modeled at high frequencies from Sparameter measurements. ABCD-parameters, derived from the S-parameters are translated into a simplified physical π-model. The resulting arch-like suspended inductors with 2-5 turns have inductances between 0.62 to 0.79 nH, peak Q-factor values between 15.42 to 17 at peak-Q frequencies between 4.7 GHz to 7.0 GHz, and self-resonant frequencies between 47.6 GHz to 88.6 GHz. The 3-turn dome-shaped spiral inductor has inductance of 3.37 nH, peak Q-factor of 35.9 at 1.65 GHz, and self-resonant frequency at 18.74 GHz

Design and modeling of integrated octagonal shape inductor with substrate silicon in a buck converter

The paper discusses the design and modeling of an integrate octagonal shaped inductor with silicon substrate. A validated equivalent electrical model of the integrated octagonal shaped spiral inductor is developed. The model is used to analyze and evaluate the quality factor and the inductance of the inductor structure proposed under different physical parameters setting. These include the number of turns, spacing between turns and the inner diameter. The simulation results show that an appropriate selection of physic a parameters can achieve an enhanced quality factor and improved inductance. PSIM simulator is used for the implementation of the integrated inductor in a micro buck converter. The simulation results demonstrate that our proposals are very promising approaches for the monolithic integration of DC-DC converters

Modeling, Fabrication, and Characterization of Planar Inductors on YIG Substrates

International audienceThis paper presents the design, fabrication, and characterization of micro planar inductors on a microwave magnetic material (YIG). Planar spiral inductors were designed for monolithic DC-DC converters in System-In-Package with 100 MHz switching frequency (1 W, Vin= 3.6 V, Vout= 1 V). A microwave magnetic substrate (YIG) serves as mechanical support, and also presents a double purpose by increasing inductance value and reducing electromagnetic interferences (EMI). This last point is critical to improve the behavior of a switching mode power supply (SMPS). In order to obtain an optimal design for the inductor, geometrical parameters were studied using Flux2D simulator and an optimized 30 to 40 nH spiral inductor with expected 25 mΩ RDC, 3 mm2 footprint area was designed. Subsequently, samples have been fabricated by electroplating technique, and tested using a vector network analyzer in the 10 MHz to 100 MHz frequency range. Results were then compared to the predicted response of simulated equivalent model

Distributed active transformer - a new power-combining andimpedance-transformation technique

In this paper, we compare the performance of the newly introduced distributed active transformer (DAT) structure to that of conventional on-chip impedance-transformations methods. Their fundamental power-efficiency limitations in the design of high-power fully integrated amplifiers in standard silicon process technologies are analyzed. The DAT is demonstrated to be an efficient impedance-transformation and power-combining method, which combines several low-voltage push-pull amplifiers in series by magnetic coupling. To demonstrate the validity of the new concept, a 2.4-GHz 1.9-W 2-V fully integrated power-amplifier achieving a power-added efficiency of 41% with 50-Ω input and output matching has been fabricated using 0.35-μm CMOS transistor

On the relationship of quality factor and hollow winding structure of coreless printed spiral winding (CPSW) inductor

The principle of using hollow spiral winding is not novel, but the study on this topic is far from complete. In this paper, how hollow the central region of the coreless printed spiral winding (CPSW) inductor should be for a given footprint area in order to achieve the maximal quality factor Q max and to maintain high inductance value is explored. A hollow factor based on the ratio of the inner hollow radius and the outer winding radius τ = R in/R out, is proposed as for optimization and quantifying how hollow a spiral winding is. The relationship between τ and Q max, which depends on the operating frequency and the dimensional parameters of CPSW inductor, is established. For a specific operating frequency, it is discovered that if the conductor width is comparable with the skin depth, or the conductors are placed relatively far away from each others, the hollow design of the CPSW inductor has little improvement on Q but reduces the inductance. If the conductor width is much larger than the skin depth and the conductors are closely placed, the hollow spiral design is recommended. The optimal range of τ with which the Q max can be achieved is found to be around 0.45-0.55. © 2006 IEEE.published_or_final_versio