Single-Ended-to-Differential and Differential-to-Differential Channel-Select Filters Based on Piezoelectric AlN Contour-Mode MEMS Resonators

This paper reports on the first demonstration of single-ended-to-differential and differential-to-differential (S2D and D2D) channel-select filters based on single-layer (SL) and dual-layer-stacked (DLS) AlN contour-mode MEMS resonators. The key filter performances in terms of insertion loss (as low as 1.4 dB), operating frequency (250-1280 MHz), and out-of-band rejection (up to 60 dB) constitute a significant advancement over all other state-of-the-art RF MEMS technologies. The fabrication process, namely stacking of two piezoelectric AlN layers (600 nm each) and three Pt electrode layers (100 nm each), is fully compatible with the previously demonstrated AlN RF MEMS switch process (also post-CMOS compatible), which makes it possible to implement multi-frequency switchable filter banks on a single chip. The S2D configuration is also able to combine the balun, filter, and impedance transformer functions in a single MEMS structure and only takes on a very small form factor (60×200 μm). These unique features will potentially revolutionize the field of RF and microwave IC design by enabling MEMS-IC co-design and the development of unconventional and low-power RF architectures

The Resonant Body Transistor

With quality factors (Q) often exceeding 10,000, vibrating micromechanical resonators have emerged as leading candidates for on-chip versions of high-Q resonators used in wireless communications systems, sensor networks, and clocking sources in microprocessors. However, extending the frequency of MEMS resonators generally entails scaling of resonator dimensions leading to increased motional impedance. In this dissertation, I introduce a new transduction mechanism using dielectric materials to improve performance and increase frequency of silicon-based RF acoustic resonators. Traditionally, electrostatically transduced mechanical resonators have used air-gap capacitors for driving and sensing vibrations in the structure. To increase transduction efficiency, facilitate fabrication, and enable GHz frequencies of operation, it is desirable to replace air-gap transducers with dielectric films. In my doctoral work, I designed, fabricated, and demonstrated dielectrically transduced silicon bulk-mode resonators up to 6.2 GHz, marking the highest acoustic frequency measured in silicon to date. The concept of internal dielectric transduction is introduced, in which dielectric transducers are incorporated directly into the resonator body. With dielectric films positioned at points of maximum strain in the resonator, this transduction improves in efficiency with increasing frequency, enabling resonator scaling to previously unattainable frequencies. Using internal dielectric transduction, longitudinal-mode resonators exhibited the highest frequency-quality factor (f.Q) product in silicon to date at 5.1 x 10 exp(13) s exp(-1) . These resonators were measured by capacitively driving and sensing acoustic vibrations in the device. However, capacitive detection often requires 3-port scalar mixer measurement, complicating monolithic integration of the resonators with CMOS circuits. The internal dielectric bulk-mode resonators can be utilized in a 2-port configuration with capacitive drive and piezoresistive detection, in which carrier mobility is dynamically modulated by elastic waves in the resonator. Piezoresistive sensing of silicon-based dielectrically transduced resonators was demonstrated with 1.6% frequency tuning and control of piezoresistive transconductance gm by varying the current flowing through the device. Resonant frequency, determined by lithographically defined dimensions, was demonstrated over a wide frequency range. These degrees of freedom enable acoustic resonators spanning a large range of frequencies on a single chip, despite design restrictions of the CMOS process. As we scale to deep sub-micron (DSM) technology, transistor cut-off frequencies increase, enabling the design of CMOS circuits for RF and mm-wave applications greater than 60 GHz. However, DSM transistors have limited gain and integrated passives demonstrate low Q, resulting in poor efficiency. A successful transition into DSM CMOS requires enhanced-gain and high-Q components operating at microwave frequencies. In this work, a merged NEMS-CMOS device is introduced that can function as a building block to enhance the performance of RF circuits. The device, termed the Resonant Body Transistor (RBT), consists of a field effect transistor embedded in the body of a high-frequency NEMS resonator implementing internal dielectric transduction. The results of this work indicate improved resonator performance with increased frequency, providing a means of scaling MEMS resonators to previously unattainable frequencies in silicon. With the transduction methods developed in this work, a hybrid NEMSCMOS RBT enables low-power, narrow-bandwidth low noise amplifier design for transceivers and low phase-noise oscillator arrays for clock generation and temperature sensing in microprocessors

One and Two Port Piezoelectric Higher Order Contour-Mode MEMS Resonators for Mechanical Signal Processing

This paper reports on the design, fabrication and testing of novel one and two port piezoelectric higher order contour-mode MEMS resonators that can be employed in RF wireless communications as frequency reference elements or arranged in arrays to form banks of multi-frequency filters. The paper offers a comparison of one and two port resonant devices exhibiting frequencies approximately ranging from 200 to 800 MHz, quality factor of few thousands (1000–2500) and motional resistances ranging from 25 to 1000 Ω. Fundamental advantages and limitations of each solution are discussed. The reported experimental results focus on the response of a higher order one port resonator under different environmental conditions and a new class of two port contour resonators for narrow band filtering applications. Furthermore, an overview of novel frequency synthesis schemes that can be enabled by these contour-mode resonators is briefly presented

Two-Port Stacked Piezoelectric Aluminum Nitride Contour-Mode Resonant MEMS

This paper reports on design, fabrication and experimental testing of a new class of two-port stacked piezoelectric aluminum nitride contour-mode micromechanical resonators that can be used for RF filtering and timing applications. This novel design consists of two layers of thin film AlN stacked on top of each other and excited in contour mode shapes using the d31 piezoelectric coefficient. Main feature of this design is the ability to reduce capacitive parasitic feedthrough between input and output signals while maintaining strong electromechanical coupling. For example, these piezoelectric contour-mode resonators show a quality factor of 1,700 in air and a motional resistances as low as 175 Ω at a frequency of 82.8 MHz. The input to output capacitance has been limited to values below 80 fF, therefore simplifying signal detection even at high frequencies

Bandpass electromechanical sigma-delta modulator

Ph.DDOCTOR OF PHILOSOPH

Nonlinear vibration of micromechanical resonators

Ph.DDOCTOR OF PHILOSOPH

Performance Parameters of Micromechanical Resonators

Ph.DDOCTOR OF PHILOSOPH

Silicon-Integrated Two-Dimensional Phononic Band Gap Quasi-Crystal Architecture

The development and fabrication of silicon-based phononic band gap crystals has been gaining interest since phononic band gap crystals have implications in fundamental science and display the potential for application in engineering by providing a relatively new platform for the realization of sensors and signal processing elements. The seminal study of phononic band gap phenomenon for classical elastic wave localization in structures with periodicity in two- or three-physical dimensions occurred in the early 1990’s. Micro-integration of silicon devices that leverage this phenomenon followed from the mid-2000’s until the present. The reported micro-integration relies on exotic piezoelectric transduction, phononic band gap crystals that are etched into semi-infinite or finite-thickness slabs which support surface or slab waves, phononic band gap crystals of numerous lattice constants in dimension and phononic band gap crystal truncation by homogeneous mediums or piezoelectric transducers. The thesis reports, to the best of the author's knowledge, for the first time, the theory, design methodology and experiment of an electrostatically actuated silicon-plate phononic band gap quasi-crystal architecture, which may serve as a platform for the development of a new generation of silicon-integrated sensors, signal processing elements and improved mechanical systems. Electrostatic actuation mitigates the utilization of piezoelectric transducers and provides action at a distance type forces so that the phononic band gap quasi-crystal edges may be free standing for potentially reduced anchor and substrate mode loss and improved energy confinement compared with traditional surface and slab wave phononic band gap crystals. The proposed phononic band gap quasi-crystal architecture is physically scaled for fabrication as MEMS in a silicon-on-insulator process. Reasonable experimental verification of the model of the electrostatically actuated phononic band gap quasi-crystal architecture is obtained through extensive dynamic harmonic analysis and mode shape topography measurements utilizing optical non-destructive laser-Doppler velocimetry. We have utilized our devices to obtain fundamental information regarding novel transduction mechanisms and behavioral characteristics of the phononic band gap quasi-crystal architecture. Applicability of the phononic band gap quasi-crystal architecture to physical temperature sensors is demonstrated experimentally. Vibration stabilized resonators are demonstrated numerically

Dielectrically transduced single-ended to differential MEMS filter

Single-ended to differential micromechanical filters with large stop band rejection are ideal replacements for conventional SAW and FBAR filters [1,2] in sensor network transceivers and GSM and W-CDMA cell phones, which depend on differential signal paths. A differential output from the front-end filter eliminates the need for an off-chip balun in front-end radio design and increases filter linearity (Fig. 17.6.1). This paper reports on the design and performance of a single-ended input to differential output resonant electromechanical filter at 425MHz center frequency with 1MHz bandwidth (BW), 8dB insertion loss (IL), <5dB pass-band ripple,-50dB stop-band rejection, and-48dB common mode suppression (CMS), for a footprint of about 150×150µm 2. Fully differential mechanical filters can be operated in singleended to differential mode by providing only one of two input signal