A Nanoscale Parametric Feedback Oscillator

We describe and demonstrate a new oscillator topology, the parametric feedback oscillator (PFO). The PFO paradigm is applicable to a wide variety of nanoscale devices and opens the possibility of new classes of oscillators employing innovative frequency-determining elements, such as nanoelectromechanical systems (NEMS), facilitating integration with circuitry and system-size reduction. We show that the PFO topology can also improve nanoscale oscillator performance by circumventing detrimental effects that are otherwise imposed by the strong device nonlinearity in this size regime

Piezoelectric Fused Silica Resonators for Timing References.

MEMS resonators have the capability to match or exceed the performance of state-of-the-art quartz timing references at a fraction of the size, power, and cost. To enable this capability, this work investigates the use of fused silica as a substrate for piezoelectrically actuated resonators for applications in timing references. This thesis presents the design and fabrication of a piezoelectrically actuated fused silica resonator. The fabricated resonators show a quality factor (Q) of 19,671 at 4.96 MHz with an insertion loss of 16.9 dB, and is the first reported example of a piezoelectrically actuated fused silica resonator in literature. An in-depth investigation into loss mechanisms in fused silica is performed in order to identify and address the major losses in the device and maximize potential performance. Multiple experimental and analytical investigations are presented, with a new form of loss, known as charge redistribution, presented as a possible dominant loss in these piezoelectric resonators. This loss mechanism is analytically modeled and simulated to have a Q of 25,100, within 20% of the experimentally measured devices. The temperature sensitivity of fused silica is also addressed; as fused silica shows a temperature coefficient of elasticity almost three times higher than that shown in uncompensated silicon. Both active and passive methods of temperature compensation are implemented, including a fused silica ovenized platform and nickel-refilled trenches for temperature compensation. The nickel-refilled trenches are shown to reduce temperature sensitivity in piezoelectrically actuated fused silica resonators from 78 ppm/K to 50 ppm/K, with larger compensation possible but complete compensation infeasible from passive techniques alone. From this, a dual-mode system is proposed for use in ovenized systems where two modes are simultaneously activated in a single device volume. In this system, one mode acts as a stable reference frequency and the second mode acts as a temperature sensor, allowing for extremely accurate ovenization. A silicon-based prototype is developed, showing a +14 ppm/K temperature difference between the two modes, with additional temperature differential possible through the addition of material-based passive compensation.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135878/1/peczalsk_1.pd

3C-Silicon Carbide Microresonators for Timing and Frequency Reference

In the drive to miniaturise and integrate reference oscillator components, microelectromechanical systems (MEMS) resonators are excellent candidates to replace quartz crystals. Silicon is the most utilised resonator structural material due to its associated well-established fabrication processes. However, when operation in harsh environments is required, cubic silicon carbide (3C-SiC) is an excellent candidate for use as a structural material, due to its robustness, chemical inertness and high temperature stability. In order to actuate 3C-SiC resonators, electrostatic, electrothermal and piezoelectric methods have been explored. Both electrothermal and piezoelectric actuation can be accomplished with simpler fabrication and lower driving voltages, down to 0.5 V, compared to electrostatic actuation. The vibration amplitude at resonance can be maximised by optimising the design and location of the electrodes. Electrical read out of the resonator can be performed with electrostatic or piezoelectric transduction. Finally, a great deal of research has focused on tuning the resonant frequency of a 3C-SiC resonator by adjusting the DC bias applied to the electrodes, with a higher (up to 160-times) tuning range for electrothermal tuning compared to piezoelectric tuning. Electrothermal tuning lowers the frequency, while piezoelectric tuning can be used to raise the frequency

Wireless actuation of bulk acoustic modes in micromechanical resonators

We report wireless actuation of a Lamb wave micromechanical resonator from a distance of over 1 m with an efficiency of over 15%. Wireless actuation of conventional micromechanical resonators can have broad impact in a number of applications from wireless communication and implantable biomedical devices to distributed sensor networks.Financial support from FemtoDx is acknowledged. (FemtoDx)http://nano.bu.edu/Papers_files/Wireless-APL-4961247.pdfPublished versio

Thin Film Piezoelectric on Substrate Resonators Electrical Characterization and Oscillator Circuit Design

Electronic systems require at least one reference signal to enable system synchronization. Oscillators and resonators are frequency selective devices that generate a desired reference signal for the systems. MEMS frequency selective devices offer alternative solutions for mechanically vibrating devices. MEMS are suitable for vibration applications by their rugged structure. In the present work, resonant behavior of thin film piezoelectric on substrate resonator (TPoS) is studied. Equivalent electrical circuit model parameters are extracted. It is observed that TPoS resonance characteristics are influenced by design aspects. The effects of perforated and continuous electrode designs on resonant behavior and also the change in resonance characteristics with the substrate thickness are reported. The colpitts oscillator circuit is implemented on a PC Board with a 27 MHz TPoS resonator and a 27 MHz quartz resonator. Jitter results are presented for both device.School of Electrical & Computer Engineerin

Synchronous micromechanically resonant programmable photonic circuits

Programmable photonic integrated circuits (PICs) are emerging as powerful tools for the precise manipulation of light, with applications in quantum information processing, optical range finding, and artificial intelligence. The leading architecture for programmable PICs is the mesh of Mach-Zehnder interferometers (MZIs) embedded with reconfigurable optical phase shifters. Low-power implementations of these PICs involve micromechanical structures driven capacitively or piezoelectrically but are limited in modulation bandwidth by mechanical resonances and high operating voltages. However, circuits designed to operate exclusively at these mechanical resonances would reduce the necessary driving voltage from resonantly enhanced modulation as well as maintaining high actuation speeds. Here we introduce a synchronous, micromechanically resonant design architecture for programmable PICs, which exploits micromechanical eigenmodes for modulation enhancement. This approach combines high-frequency mechanical resonances and optically broadband phase shifters to increase the modulation response on the order of the mechanical quality factor $Q_m$, thereby reducing the PIC's power consumption, voltage-loss product, and footprint. The architecture is useful for broadly applicable circuits such as optical phased arrays, $1$ x $N$, and $N$ x $N$ photonic switches. We report a proof-of-principle programmable 1 x 8 switch with piezoelectric phase shifters at specifically targeted mechanical eigenfrequencies, showing a full switching cycle of all eight channels spaced by approximately 11 ns and operating at >3x average modulation enhancement across all on-chip modulators. By further leveraging micromechanical devices with high $Q_m$, which can exceed 1 million, our design architecture should enable a new class of low-voltage and high-speed programmable PICs.Comment: 18 pages, 5 figures, 5 supplementary figure

A dynamical approach to generate chaos in a micromechanical resonator

Chaotic systems, presenting complex and non-reproducible dynamics, may be found in nature from the interaction between planets to the evolution of the weather, but can also be tailored using current technologies for advanced signal processing. However, the realization of chaotic signal generators remains challenging, due to the involved dynamics of the underlying physics. In this paper, we experimentally and numerically present a disruptive approach to generate a chaotic signal from a micromechanical resonator. This technique overcomes the long-established complexity of controlling the buckling in micro/nano-mechanical structures by modulating either the amplitude or the frequency of the driving force applied to the resonator in the nonlinear regime. The experimental characteristic parameters of the chaotic regime, namely the Poincar\'e sections and Lyapunov exponents, are directly comparable to simulations for different configurations. These results confirm that this dynamical approach is transposable to any kind of micro/nano-mechanical resonators, from accelerometers to microphones. We demonstrate a direct application exploiting the mixing properties of the chaotic regime by transforming an off-the-shelf microdiaphragm into a true random number generator conformed to the National Institute of Standards and Technology specifications. The versatility of this original method opens new paths to combine chaos' unique properties with microstructures' exceptional sensitivity leading to emergent microsystems

Piezoelectric and Magnetoelastic Strain in the Transduction and Frequency Control of Nanomechanical Resonators

Stress and strain play a central role in semiconductors, and are strongly manifested at the nanometer-scale regime. Piezoelectricity and magnetostriction produce internal strains that are anisotropic and addressable via a remote electric or magnetic field. These properties could greatly benefit the nascent field of nanoelectromechanical systems (NEMS), which promises to impact a variety of sensor and actuator applications. The piezoelectric semiconductor GaAs is used as a platform for probing novel implementations of resonant nanomechanical actuation and frequency control. GaAs/AlGaAs heterostructures can be grown epitaxially, are easily amenable to suspended nanostructure fabrication, have a modest piezoelectric coefficient roughly twice that of quartz, and if appropriately doped with manganese, can form dilute magnetic compounds. In ordinary piezoelectric transducers there is a clear distinction between the metal electrodes and piezoelectric insulator. But this distinction is blurred in semiconductors. An integrated piezoelectric actuation mechanism is demonstrated in a series of suspended anisotype GaAs junctions, notably pin diodes. A dc bias was found to alter the resonance amplitude and frequency in such devices. The results are in good agreement with a model of strain based actuation encompassing the diode’s voltage-dependent carrier depletion width and impedance. A bandstructure engineering approach is employed to control the actuation efficiency by appropriately designing the doping level and thickness of the GaAs structure. Actuation and frequency are also sensitively dependent on the device’s crystallographic orientation. This combined tuning behavior represents a novel type of depletion-mediated electromechanical coupling in piezoelectric semiconductor nanostructures. All devices are actuated piezoelectrically, whereas three techniques are demonstrated for sensing: optical interferometry, piezoresistance and piezoelectricity. Finally, a nanoelectromechanical GaMnAs resonator is used to obtain the first measurement of magnetostriction in a dilute magnetic semiconductor. Resonance frequency shifts induced by field-dependent magnetoelastic stress are used to simultaneously map the magnetostriction and magnetic anisotropy constants over a wide range of temperatures. Owing to the central role of carriers in controlling ferromagnetic interactions in this material, the results appear to provide insight into a unique form of magnetoelastic behavior mediated by holes

Gallium Nitride Integrated Microsystems for Radio Frequency Applications.

The focus of this work is design, fabrication, and characterization of novel and advanced electro-acoustic devices and integrated micro/nano systems based on Gallium Nitride (GaN). Looking beyond silicon (Si), compound semiconductors, such as GaN have significantly improved the performance of the existing electronic devices, as well as enabled completely novel micro/nano systems. GaN is of particular interest in the “More than Moore” era because it combines the advantages of a wide-band gap semiconductor with strong piezoelectric properties. Popular in optoelectronics, high-power and high-frequency applications, the added piezoelectric feature, extends the research horizons of GaN to diverse scientific and multi-disciplinary fields. In this work, we have incorporated GaN micro-electro-mechanical systems (MEMS) and acoustic resonators to the GaN baseline process and used high electron mobility transistors (HEMTs) to actuate, sense and amplify the acoustic waves based on depletion, piezoelectric, thermal and piezo-resistive mechanisms and achieved resonance frequencies ranging from 100s of MHz up to 10 GHz with frequency×quality factor (f×Q) values as high as 1013. Such high-performance integrated systems can be utilized in radio frequency (RF) and microwave communication and extreme-environment applications.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135799/1/azadans_1.pd