Green on-chip inductors in three-dimensional integrated circuits

This thesis focuses on the technique for the improvement of quality factor and inductance of the TSV inductors and then on the utilization of TSV inductors in various on-chip applications such as DC-DC converter and resonant clocking. Through-silicon-vias (TSVs) are the enabling technique for three-dimensional integrated circuits (3D ICs). However, their large area significantly reduces the benefits that can be obtained by 3D ICs. On the other hand, a major limiting factor for the implementation of many on-chip circuits such as DC-DC converters and resonant clocking is the large area overhead induced by spiral inductors. Several works have been proposed in the literature to make inductors out of idle TSVs. In this thesis, the technique to improve the quality factor and inductance is proposed and then discusses about two applications utilizing TSV inductors i.e., inductive DC-DC converters and LC resonant clocking. The TSV inductor performs inferior to spiral inductors due to its increases losses. Hence to improve the performance of the TSV inductor, the losses should be reduced. Inductive DC-DC converters become prominent for on-chip voltage conversion because of their high efficiency compared with other types of converters (e.g. linear and capacitive converters). On the other hand, to reduce on-chip power, LC resonant clocking has become an attractive option due to its same amplitude and phases compared to other resonant clocking methods such as standing wave and rotary wave. A major challenge for both applications is associated with the required inductor area. In this thesis, the effectiveness of such TSV inductors in addressing both challenges are demonstrated --Abstract, page iv

Ultrafast Analog Fourier Transform Using 2-D LC Lattice

We describe how a 2-D rectangular lattice of inductors and capacitors can serve as an analog Fourier transform device, generating an approximate discrete Fourier transform (DFT) of an arbitrary input vector of fixed length. The lattice displays diffractive and refractive effects and mimics the combined optical effects of a thin-slit aperture and lens. Diffraction theories in optics are usually derived for 3-D media, whereas our derivations proceed in 2-D. Analytical and numerical results show agreement between lattice output and the true DFT. Potentially, this lattice can be used for an extremely low latency and high throughput analog signal processing device. The lattice can be fabricated on-chip with frequency of operation of more than 10 GHz

Generalized analytical model for RF planar inductors using a segmentation technique

The planar coil inductor has become a very critical circuit component in RF mixed signal application where it can reside either on the package or in the chip. However, there is no clear methodology to accurately analyze the behavior of the inductor over a broad range of frequencies and for obtaining a particular physical layout for a required value of inductance. At present, it has been done by full wave solvers, approximate quasistatic analysis, and lumped element equivalent circuits, each with its own advantages and limitations. This work presents an analytical model based on a segmentation method in conjunction with a Green\u27s function for a power/ground plane model. This method has been used to obtain analytical closed form solution for planar coil inductors of two popular shapes, the rectangular and circular configurations. The model includes a ground plane and the coil configuration such as spacing and line width, and the material characteristic such as conductivity of the metal layer and the dielectric parameters. It is a frequency dependant solution that includes the resonant modes in the cavity formed by the inductor and the ground plane. This method has been applied successfully to rectangular and circular coil inductors of different dimensions where there is excellent agreement with full wave solvers. Inductors on a package and in a chip have been fabricated and experimental results show excellent agreement to predicted values obtained from this analytical work. Also presented in this work is a comparison of popular EM full wave solvers and two quasistatic methods, the advantages and limitations of each have been discussed. Experimental techniques to measure for RF silicon IC Inductors have been developed

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

Master of Science

thesisThe purpose of this thesis was to determine if low-power switching power supplies can be made on-chip using integrated components. Integrated switching supplies are an emerging field that has followed the rise of systems-on-chip devices - especially in the biomedical field. Switching supply theory and implementation were examined systematically to determine the feasibility of such switching supplies. Classical switching power supply theory was presented first, including fundamental principles of operation and essential analysis techniques. Due to the unique constraints placed on integrated power supplies as a result of the small component size, the classical treatment had to be updated and modified. The result was a new methodology for calculating ripple current and voltage, circuit losses, and efficiency of switching supplies in both continuous and discontinuous conduction modes. Integrated and micro-scale switching supply components were then examined. Most importantly, the design of integrated inductors was discussed. Double-layer coils were found to be the best choice for integrated inductors with a small number of coils as they offered four times the inductance and only twice the resistance of similar single-layer coils. Six boards were tested using a variety of loads with manual switching cycle control. The test boards effectively modeled the behavior of integrated supplies and confirmed predictions about power loss and transfer. Using the test results and the equations previously derived, three test cases were simulated. The results were efficiencies of 75.16%, 75.09%, and 75.10% using 2 and 5 turn double spirals, and an external 120 nH coil, respectively. With these results, it should be possible to build integrated switching power supplies that meet or exceed the efficiency of linear supplies