R. Gaddi

Bio: R. Gaddi is an academic researcher from University of Bologna. The author has contributed to research in topics: Wafer & Capacitive sensing. The author has an hindex of 13, co-authored 40 publications receiving 508 citations.

High power time domain measurement system with active harmonic load-pull for high efficiency base station amplifier design

Abstract: A measurement system combining vector corrected waveform measurements with active harmonic load-pull extends, for the first time, real-time experimental waveform engineering up to the 30 W power level. This novel harmonic load-pull approach is demonstrated on a 4 W LDMOS device. A 20% increase in maximum output power to 4.7 W without degrading gain and efficiency was realized.

Symmetric toggle switch—a new type of rf MEMS switch for telecommunication applications: Design and fabrication

Abstract: In this paper, we present a new type of rf MEMS switch with low actuation voltage and high isolation, for high rf power and reliability applications in telecommunication. ‘Symmetric toggle switch’ (STS) is based on push–pull mechanism and utilizes torsion springs and levers, placed symmetrically and transverse to CPW line. The switches designed for 8–14 GHz applications have analytically calculated and FEM simulated actuation voltages in the range of 8–10 V. The simulated insertion loss and isolation for the devices are 0.25 and 35 dB, respectively, at 10 GHz. The fabrication process and preliminary experimental results are also presented.

Experimental Validation of Mixed Electromechanical and Electromagnetic Modeling of RF-MEMS Devices Within a Standard IC Simulation Environment

Abstract: The validity and applicability of a high-level simulation approach of radio-frequency microelectromechanical-system (RF-MEMS) devices, based on a library of analytical compact models of elementary MEMS components, are investigated through an extensive comparison between simulation results and measurements of some representative devices (variable capacitors and series ohmic switches). The in-house developed simulation tool is implemented in a standard IC simulation environment supporting behavioral description capabilities. The devices are built in a silicon substrate technology with suspended gold membranes. We analyze the mechanical, electrical, and RF response of the devices. The RF behavior is modeled by extracting a lumped element network from measured S-parameters (scattering-parameters) to account for parasitic effects and by wrapping this network around the intrinsic MEMS device simulated with the compact models. We show that an accuracy within 5% is obtained in all considered physical domains and conditions, provided that some effective parameters (including the residual air gap in the actuated state and the RF parasitic elements) are properly extracted from measurements and accounted for in the simulations. The main factors limiting the model's predictive capability are due to process nonidealities, such as plate bending due to residual stress gradient, oxide charging, surface roughness, and suspended membrane thickness variations, rather than for instance in-plane geometric process variations.

RF–MEMS wafer-level packaging using through-wafer interconnect

Abstract: In this paper, development of a wafer-level packaging (WLP) process suitable for RF–MEMS applications is presented. The packaging concept is based on a high-resistivity silicon capping substrate that is wafer-level bonded to an RF–MEMS device wafer providing MEMS device protection and vertical electrical signal interconnect. The capping substrate contains Cu-plated through-wafer electrical vias and optional through-substrate cavities allowing for hybrid integration. The RF–MEMS device wafer and the capping substrate are bonded using either solder reflow or an electrically conductive adhesive. After solder bump formation and singulation, this packaging solution results in surface-mount technology compatible components. Moreover, the presented WLP solution allows hybrid integration of additional IC dies that are flip-chip bonded within the capping substrate cavities.

Interdigitated Low-Loss Ohmic RF-MEMS Switches

Abstract: An interdigitated design for MEMS RF-switches is applied to both a shunt and a series ohmic contact configuration. Interdigitated Al-Ti-TiN RF-signal paths and poly actuation electrodes are arranged underneath an electrodeposited gold plate, suspended by four thinner gold beam springs. Ohmic contact occurs at pullin between the gold plate and the RF-signal elecrodes only. Measurements show insertion loss better than 0.8 dB and isolation better than 20 dB up to 13 GHz. Extracted lumped element equivalent circuits show intrinsic contact resistances of 1.6 Ω in the shunt and 4.5 Ω in the series switch. The interdigitated topology of RFsignal and actuation electrodes results in uniform contact pressure distribution and consistently low contact resistance.

A Methodology for Realizing High Efficiency Class-J in a Linear and Broadband PA

Abstract: The design and implementation of a class-J mode RF power amplifier is described. The experimental results indicate the class-J mode's potential in achieving high efficiency across extensive bandwidth, while maintaining predistortable levels of linearity. A commercially available 10 W GaN (gallium nitride) high electron mobility transistor device was used in this investigation, together with a combination of high power waveform measurements, active harmonic load-pull and theoretical analysis of the class-J mode. Targeting a working bandwidth of 1.5-2.5 GHz an initial power amplifier (PA) design was based on basic class-J theory and computer-aided design simulation. This realized a 50% bandwidth with measured drain efficiency of 60%-70%. A second PA design iteration has realized near-rated output power of 39 dBm and improved efficiency beyond the original 2.5 GHz target, hence extending efficient PA operation across a bandwidth of 1.4-2.6 GHz, centered at 2 GHz. This second iteration made extensive use of active harmonic load-pull and waveform measurements, and incorporated a novel design methodology for achieving predistortable linearity. The class-J amplifier has been found to be more realizable than conventional class-AB modes, with a better compromise between power and efficiency tradeoffs over a substantial RF bandwidth.

Integrating MEMS and ICs

Abstract: The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control phys ...

Integrating MEMS and ICs

Abstract: The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control physical, optical or chemical quantities, ICs typically provide functionalities related to the signals of these transducers, such as analog-to-digital conversion, amplification, filtering and information processing as well as communication between the MEMS transducer and the outside world. Thus, the vast majority of commercial MEMS products, such as accelerometers, gyroscopes and micro-mirror arrays, are integrated and packaged together with ICs. There are a variety of possible methods of integrating and packaging MEMS and IC components, and the technology of choice strongly depends on the device, the field of application and the commercial requirements. In this review paper, traditional as well as innovative and emerging approaches to MEMS and IC integration are reviewed. These include approaches based on the hybrid integration of multiple chips (multi-chip solutions) as well as system-on-chip solutions based on wafer-level monolithic integration and heterogeneous integration techniques. These are important technological building blocks for the More-Than-Moore paradigm described in the International Technology Roadmap for Semiconductors. In this paper, the various approaches are categorized in a coherent manner, their merits are discussed, and suitable application areas and implementations are critically investigated. The implications of the different MEMS and IC integration approaches for packaging, testing and final system costs are reviewed.

MEMS Reliability Review

Abstract: Microelectromechanical systems (MEMS) represents a technology that integrates miniaturized mechanical and electromechanical components (i.e., sensors and actuators) that are made using microfabrication techniques. MEMS devices have become an essential component in a wide range of applications, ranging from medical and military to consumer electronics. As MEMS technology is implemented in a growing range of areas, the reliability of MEMS devices is a concern. Understanding the failure mechanisms is a prerequisite for quantifying and improving the reliability of MEMS devices. This paper reviews the common failure mechanisms in MEMS, including mechanical fracture, fatigue, creep, stiction, wear, electrical short and open, contamination, their effects on devices' performance, inspection techniques, and approaches to mitigate those failures through structure optimization and material selection.

Crystal oscillator emulator

Abstract: An integrated circuit comprises a microelectromechanical (MEMS) resonator circuit that generates a reference frequency. A temperature sensor senses a temperature of the integrated circuit. Memory stores calibration parameters and selects at least one of the calibration parameters as a function of the sensed temperature. A phase locked loop module receives the reference signal, comprises a feedback loop having a feedback loop parameter and selectively adjusts the feedback loop parameter based on the at least one of the calibration parameters.