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Piezoelectric micromachined ultrasonic transducers (PMUTs) have advantages to those of traditional ultrasonic transducers in small form factor, low cost, low power consumption, large bandwidth, and good acoustic impedance matching. A bimorph pinned dual-electrode PMUT is developed for improved vibrational displacement, output sound pressure, and electro-mechanical coupling for several demonstration examples, including 3D space imaging, directional loudspeaker, and non-contact temperature sensing. Analytically, an equivalent circuit model has been built for bimorph, pinned dual-electrode PMUTs and finite element simulation result has shown a 380% boost for the sound pressure per volt per area and increased center displacement at the resonant frequency as compared to those of conventional unimorph PMUTs. Experimentally, prototype devices have been designed, fabricated, and tested with a 58% measured increase in the electromechanical coupling factor and pulse-echo tests have shown a 4-meter traveling distance in air under a 133 kHz driving frequency. As a proof-of-concept, a long-distance (>1.5 meters) ultrasound imaging is demonstrated using a 4×4 array prototype system based on the transmit beamforming scheme in air. A small form factor (6×6 mm2) design and a more than 135o field of view have display the capability of real time 3D object detection with up to 125 fps (frames per second) based on the scheme of ultrasound receive beamforming toward applications such as drone navigation, machine vision and so on. A highly directional air-coupled parametric loudspeaker using a single PMUT chip has been validated based on a parametric array design to generate highly directional audible sound with a half power beam width of less than 5 degrees. The multiple audible frequency sound has been generated by using a single chip with 246 PMUT elements in a footprint of 13 × 13 mm toward low-power and portable directional loudspeakers for private communications. In another example, non-contact surface temperature measurements via a single PMUTs array have been established based on the time-of-flight (ToF) changes. The key advantages of this scheme include the independence of surface material properties, e.g. emissivity; the possible integration with an ultrasonic analog front-end circuitry for both transmitting and receiving. A recorded sensitivity of 143 ns/oC has been achieved in non-contact temperature sensing in various media such as air, liquid, and tissue for broad applications.

This dissertation reports the development of a MEMS PZT-based piezoelectrically driven microlens actuator for potential use in micro-optics applications. The actuator consists of six uniquely arranged piezoelectric beams configured in d31 mode. One end of the beam is fixed to the substrate and the other end connected to a serpentine spring supporting a microlens holding platform. The microlens actuator exhibits large out-of-plane displacement of 145 um at 100kV/cm (22V) with a high resonance frequency of 1.96 kHz when it is free from a microlens loading, and 0.673 kHz with a 330 ug PDMS lens loading. The parameters governing the design and fabrication conditions to obtain an optimum actuation performance are discussed in detail. As part of the microlens actuator development, a series of original studies have been conducted. These include: (i) The study of Ultra-High Vacuum E-beam Evaporated Polysilicon (UHVEEPoly) thin-film for forming Lead Zirconate Titanate (PZT) based piezoelectric MEMS. The film is used as a passive structural layer in a unimorph PZT micro-cantilever actuator to demonstrate its suitability as an alternative platform for forming PZT based devices. In particular, this technique enables a cost-effective process and versatility of forming MEMS structures compared to conventional platforms. (ii) The development of PZT bimorph actuator with polysilicon as the passive structural layer. This novel arrangement has been made possible due to the low stress and low thermal budget properties of the UHVEEPoly film which can be formed without influencing the quality of the piezoelectric layer deposited prior. This configuration has unique suitability for the micro-actuation mechanism presented in this work that enables the possibility of bi-directional actuation and reduction in device footprint area. (iii) A novel approach to enhance the out-of-plane uni-directional actuation without compromising resonance frequency or changing the overall actuator design has been demonstrated. The study exploits the use of the UHVEEPoly and RF-sputtered SiO2 films as the passive structural layer to manipulate the residual moment created from the residual stress in the multi-layered thin-film structure. By residual stress manipulation of the passive layer, an enhancement of more than 36% in the displacement range has been obtained from the microlens actuator; (iv) The proposed microlens actuator has demonstrated the capability to function as an optical focusing mechanism by changing the focus of a laser pointer with actuation; (v) Studies on the development to implement an integration of on-chip piezoresistive sensor with the microlens actuator has been discussed.

A laser micro-machined bulk-piezoelectric PZT-4 (Lead Zirconate Titanate) based lateral bimorph transducer with differential drive and sense capability is demonstrated. Unlike conventional bimorph designs, the approach here does not require adhesive and/or non-piezoelectric layers. The monolithic fabrication makes arrays of bimorphs suitable for micro-systems integration. The in plane bimorph transducer relies predominantly on the d31 coefficient for transduction. A bimorph transducer with length 6.25mm, width 0.45mm and thickness0.5mm is characterized to demonstrate DC actuation and resonance current to displacement sensitivities of 23nm/V and 1.1µA/µm, respectively. Nonlinear effects in the transducer characteristics owing to nonlinear electrical and mechanical properties of PZT-4H is also investigated. The ratio of voltage amplitudes of the first harmonic (2f) to fundamental (f) for drive voltage amplitude V1 is found to be ≈ 1.74×10−5e0.88V1. The sense current noise of transducer is 5nA/√Hz and the sensor tip displacement measurement resolution at resonance is≈0.9nm for small time scales (τ < 10s). A bulk-piezoelectric PZT actuator based ultrasonic motor in which the stator is an array of X-motion PZT bimorphs is demonstrated. X-motion signifies moving diagonally in the XZ plane. The bimorphs have three electrodes that are designed to produce a bimorph tip trajectory consisting of diagonal motion in two orthogonal axes, mimicking’X’, hence the name X-motion planar bimorphs. The X-motion lateral bimorphs apply forces onto the rotor to induce rotation. The PZT bimorphs are fabricated using a laser-micromachining process resulting in monolithically integrated bimorphs to form the stator. Unlike previously reported approaches for ultrasonic motors using piezoelectric bimorphs, the fabrication process used here eliminates the need for manual bonding and selective arrangement of PZT corresponding to different poling orientations. The planar integration of the motor elements helps one to envision many co-located motor elements for multi motor systems. Three combinations of rotors and stators were tested to verify the physical model of the motor, with rotation rates of up to 400−600rpm. One combination of stator and rotor operates with stator resonance of 32.6kHz and can withstand a load of 4.1g for 60Vpeak drive at resonance. One of the stators is used to drive a 3D-printed plastic fan blades that produced maximum air flow rate of 160mm/sec at 60Vpeak drive voltage. A piezoelectric multi-modal mechanical (X,Y,θz) stimuli stage is demonstrated, which is capable of≈ 50ppm precision in-situ calibration of MEMS gyroscopes packaged on the stage. The calibration system is capable of extracting instantaneous scale factor, bias drifts and cross axis sensitivities of MEMS Coriolisforcegyroscopes. The bulk PZT calibration stage is capable of non-resonant sinusoidal angular rates of 0−300deg/s for scale factor and bias measurements and X-Y in-plane acceleration stimulus of 0−90m/s2 to extract the gyroscope in plane acceleration sensitivities at 100Vp,0−250Hz drive voltage, and frequencies. The stage has < 5ppm/V undesirable out-of-plane motion while actuating in-plane for applying desired mechanical stimuli for calibration of the gyroscope. The calibration system consumes ≈ 400mWatts when the gyroscope is in operation at baseband while the gyroscope is calibrated at higher frequencies. To achieve a long term stable calibration stage, an optical metrology system is used to calibrate the motion stage. The optical metrology system can ensure 10ppm stable stage metrology, to enable long term stable gyroscope calibration. The optical system uses an atomically stable laser source and a CMOS imager that can be potentially integrated into the same package as the calibration system, for closed loop control of the calibration stage. A piezoelectric bulk-PZT Z-axis Coriolis force gyroscope is demonstrated, which utilizes spring-mass resonances of the in-plane PZT bimorphs and a PZT proof-mass. The design exploits the large piezoelectric coefficients and high mass density of bulk-PZT to obtain a sensitivity of 1.7µV/deg/s, for10Vpeak drive under mode-mismatched operation and quality factor(Q) of 100−150. The gyroscope is capable of high dynamic range owing to the elimination of micro-gaps that are associated with electrostatic gyroscopes. Nonlinearity in the elasticity properties and piezoelectric coupling in PZT is leveraged for frequency and quadrature tuning, with a DC voltage, applied to control electrodes for a potential closed loop operation. Resonance and quadrature tuning of 10ppm/Vdc and 20deg/sec/Vdc respectively were achieved using nonlinear operation of PZT drive and sense resonators at 10Vpeak drive at a resonance frequency of 108kHz drive. The gyroscope is monolithically integrated within a PZT calibration stage to enable in-situ gyroscope self-calibration. The monolithic device also improved the Q of the gyroscope by a factor of 10 leading to the improvement in sensitivity to 3.4mV/deg/sec at 1Vpeak drive. A 2-axis (X −Y) piezoelectric energy harvester is reported, whose sensitive axis in-plane is rotationally invariant, a result achieved by spiral in-place bimorph, which can be modeled as a cascade of lateral bimorphs. This is different than conventional piezoelectric energy harvesters that are sensitive only along one axis or can realize multi-axis sensitivity through package level assembly of multiple devices at different orientations. Rotational invariance of the sensitive axis is useful when deployed in applications where the device orientation with respect to the vibration is stochastic in nature. At 1g applied acceleration, the vibration energy harvester generates maximum differential voltages of±6.8Vpp across a 1MΩ load, at a resonance frequency of 163.5Hz. The energy harvester has a Q-factor of 129.5 and electromechanical coupling coefficient kt of > 15% for the fundamental lateral mode and a peak normalized output power density of 0.89µWatt/mm3g−2.

The research presented in this dissertation focuses on the development of solid-state materials that have the ability to sense, act, think and communicate. Two broad classes of materials, namely ferroelectrics and wideband gap semiconductors were investigated for this purpose. Ferroelectrics possess coupled electromechanical behavior which makes them sensitive to mechanical strains and fluctuations in ambient temperature. Use of ferroelectrics in antenna structures, especially those subject to mechanical and thermal loads, requires knowledge of the phenomenological relationship between the ferroelectric properties of interest (especially dielectric permittivity) and the external physical variables, viz. electric field(s), mechanical strains and temperature. To this end, a phenomenological model of ferroelectric materials based on the Devonshire thermodynamic theory was developed. This model was then used to obtain a relationship expressing the dependence of the dielectric permittivity on the mechanical strain, applied electric field and ambient temperature. The relationship is shown to compare well with published experimental data and other related models in literature. A model relating ferroelectric loss tangent to the applied electric field and temperature is also discussed. Subsequently, relationships expressing the dependence of antenna operating frequency and radiation efficiency on those external physical quantities are described. These relationships demonstrate the tunability of load-bearing antenna structures that integrate ferroelectrics when they are subjected to mechanical and thermal loads.In order to address the inability of ferroelectrics to integrate microelectronic devices, a feature needed in a material capable of sensing, acting, thinking and communicating, the material Gallium Nitride (GaN) is pursued next. There is an increasing utilization of GaN in the area of microelectronics due to the advantages it offers over other semiconductors. This dissertation demonstrates GaN as a candidate material well suited for novel microelectromechanical systems. The potential of GaN for MEMS is demonstrated via the design, analysis, fabrication, testing and characterization of an optical microswitch device actuated by piezoelectric and electrostrictive means. The piezoelectric and electrostrictive properties of GaN and its differences from common piezoelectrics are discussed before elaborating on the device configuration used to implement the microswitch device. Next, the development of two recent fabrication technologies, Photoelectrochemical etch and Bias-enabled Dark Electrochemical etch, used to realize the 3-dimensional device structure in GaN are described in detail. Finally, an ultra-low-cost, laser-based, non-contact approach to test and characterize the microswitch device is described, followed by the device testing results.

Wind generated electricity using thin, flexible sheets of piezoelectric materials attached to flag like membranes termed bimorphs is presented. Piezoelectric wind generated electricity presents a simple, yet effective means to extract energy from the environment. The harvested energy would most likely be used to power wireless sensor networks and other low power applications where batteries would normally be used. Replacing batteries is inconvenient for the users of wireless sensor networks and consumers of other low power electronics. Recharging batteries with power extracted directly from the ambient eliminates the need for frequent battery replacement. Bimorphs are constructed with piezoelectric materials such as poled Polyvinylidene Fluoride (PVDF) and Lead Zirconate Titanate (PZT). Various thin, flexible polymers such as overhead projector film or ink jet transparency film make up the substrate. Several adhesives are researched to determine which can withstand the high strain levels over long periods of time. Bluff bodies were used to create vortex shedding; to increase the undulation amplitude of the bimorph and overall efficiency of the piezoelectric energy harvesting system. Due to the low source capacitance of piezoelectric materials and the low oscillation frequency of the bimorph, the source impedance is very high. In order to reduce the source impedance of the bimorph (increase output current), an inductor must resonate out some or all of the reactance of the piezoelectric. However, thousands of henries of inductance would be necessary to have a vast impact on piezoelectric source impedance. Hence, a quasi-resonant rectifier switching circuit is employed to reduce the source impedance of the bimorph. An energy harvesting circuit termed ‘Series Synchronized Switch Harvesting on Inductor’ (SSSHI) is implemented in order to maximize AC to DC power flow from a piezoelement bimorph to a storage capacitor. The circuit comprises of a peak-triggering circuit, inductor, switch, and regulated micro-power step-down converter powered directly from the piezoelement.

Piezoelectrics offer high actuation authority and sensing over a wide range of frequencies. A Macro-Fiber Composite is a type of piezoelectric device that offers structural flexibility and high actuation authority. A challenge with piezoelectric actuators is that they require high voltage input; however the low power consumption allows for relatively lightweight electronic components. Another challenge, for piezoelectric actuated aerodynamic surfaces, is found in operating a relatively compliant, thin structure (desirable for piezoceramic actuators) in situations where there are relatively high external (aerodynamic) forces. Establishing an aeroelastic configuration that is stiff enough to prevent flutter and divergence, but compliant enough to allow the range of available motion is the central challenge in developing a piezocomposite airfoil. The research proposed here is to analyze and implement novel electronic circuits and structural concepts that address these two challenges. Here, a detailed theoretical and experimental analysis of the aerodynamic and electromechanical systems that are necessary for a practical implementation of a piezocomposite airfoil is presented. First, the electromechanical response of Macro-Fiber Composite based unimorph and bimorph structures is analyzed. A distributed parameter electromechanical model is presented for interdigitated piezocomposite unimorph actuators. Necessary structural features that result in large electrically induced deformations are identified theoretically and verified experimentally. A novel, lightweight electrical circuitry is proposed and implemented to enable the peak-to-peak actuation of Macro-Fiber Composite bimorph devices with asymmetric voltage range. Next, two novel concepts of supporting the piezoelectric material are proposed to form two types of variable-camber aerodynamic surfaces. The first concept, a simply-supported thin bimorph airfoil, can take advantage of aerodynamic loads to reduce control input moments and increase control effectiveness. The structural boundary conditions of the design are optimized by solving a coupled fluid-structure interaction problem by using a structural finite element method and a panel method based on the potential flow theory for fluids. The second concept is a variable-camber thick airfoil with two cascading bimorphs and a compliant box mechanism. Using the structural and aerodynamic theoretical analysis, both variable-camber airfoil concepts are fabricated and successfully implemented on an experimental ducted-fan vehicle. A custom, fully automated low-speed wind tunnel and a load balance is designed and fabricated for experimental validation. The airfoils are evaluated in the wind tunnel for their two-dimensional lift and drag coefficients at low Reynolds number flow. The effects of piezoelectric hysteresis are identified. In addition to the shape control application, low Reynolds number flow control is examined using the cascading bimorph variable-camber airfoil. Unimorph type actuators are proposed for flow control in two unique concepts. Several electromechanical excitation modes are identified that result in the delay of laminar separation bubble and improvement of lift. Periodic excitation to the flow near the leading edge of the airfoil is used as the flow control method. The effects of amplitude, frequency and spanwise distribution of excitation are determined experimentally using the wind tunnel setup. Finally, the effects of piezoelectric hysteresis nonlinearity are identified for Macro-Fiber Composite bimorphs. The hysteresis is modeled for open-loop response using a phenomenological classical Preisach model. The classical Preisach model is capable of predicting the hysteresis observed in 1) two cantilevered bimorph beams, 2) the simply-supported thin airfoil, and 3) the cascading bimorph thick airfoil.

Thermal infrared detectors based on MEMS bimorph beams have the potential to exceed the performance of current uncooled thermal infrared cameras both in terms of sensitivity and cost. These cameras are part of a rapidly growing industry are used for a vast array of applications such as military and civilian night vision, industrial monitoring, and medical imaging. Many researchers have explored the use of metal-ceramic MEMS bimorphs for this application even though it has long been acknowledged that polymer-ceramic bimorphs would be superior. However, because of the difficulties of designing and fabricating MEMS systems based on polymer-ceramic bimorphs, little progress has been made towards their development. This dissertation describes the initial design, fabrication, and testing of thermo-mechanical infrared sensors based on MEMS polymer-ceramic bimorph beams. Sensors based on bimorphs composed of both the biopolymer chitin on poly-silicon and OCG-825 photoresist on poly-silicon were fabricated and tested. Chitin bimorphs were fabricated using a novel photolithographic chitosan process previously developed for this research.A sensor design based on a residual stress and ambient temperature compensating geometry and which includes novel features such as vertically aligned thermal isolation regions and selective shielding is presented. Simplified sensors were tested using an optical readout method where the deformation of the sensors was observed as variations in the intensity of visible light reflected to a digital camera. In order to obtain quantitative measurements, image analysis was performed. While the feasibility of simply observing the average brightness of the light reflected from a sensor was demonstrated, several image processing algorithms were tested and shown to increase the signal to noise ratio. An IR source approximating a blackbody was combined with a series of filters and lenses to limit transmission of light to the sensor to wavelengths from approximately 1.0 to 3.6 microns.A periodic signal was produced by coupling a mechanical chopper wheel with the IR source. The sensor was able to detect these signals at frequencies of at least 5 Hz. By comparing the sensor signal to a known rate of warming of the IR source and the measured noise level at equilibrium, a noise equivalent temperature difference of as low as 360 mK was measured. In light of this encouraging and clear proof of concept, suggestions for achieving performance gains and developing novel imaging systems based on polymer-ceramic bimorphs through future research efforts are offered.

Active structures flexible enough to be molded in desired shapes and coupled with the ability to be controlled have been pursued for many high precision applications. Membrane-thin but extremely large (>10 m) optical mirrors and reflectors for combined RF-Optical applications are one of the important high precision applications where shape and vibration control of a structure is highly desirable. In this application the precision demands of the optical surface mitigate the combined benefit of the large aperture.Polyvinylidene Fluoride or PVDF is a semi-crystalline piezoelectric polymer with strong orthotropic in-plane properties. This material is suitable for making large reflectors due to its availability in thin sheets and almost linear and nonhysteretic behavior at low to moderate operating voltages. Its low cost and ease of manufacture also make it suitable for shape and vibration control of large reflecting structures.This research focuses on a three-layer laminated actuator with two layers of PVDF film bonded with a layer of epoxy. The electrodes are applied externally on the top PVDF film in a given pattern such that the applied electric field will yield the desired shape of the laminate. The bottom layer of the bimorph is the reflecting surface and acts as the ground. The actuator itself acts as the RF and optical surface and therefore requires no secondary surface. Research has been performed by Sumali et. al. and Massad et. al. for quasi-static deflection of a PVDF bimorph with both simply supported and corner supported boundary conditions under an applied electric field. This methodology produced excellent results under ideal conditions with no disturbances. Due to lack of any kind of feedback, the methodology was an open loop technique lacking the ability to acclimatize under inclement real world conditions.This research takes a step further and removes this demerit by dynamic modeling of a three layer PVDF laminated plate with simply supported boundary conditions and developing a Closed Loop Control Methodology which is capable of rejecting external disturbances. This will not only help in controlling the shape, but also will allow the structure to maintain it under inclement environment. The orthotropic properties of the laminate / actuator are also incorporated into the model, reducing the error due to unmodeled dynamics. Using the developed model and closed loop control methodology, the laminate can be precisely and accurately shaped to function as a satellite antenna, optical reflector or a solar reflector. Typically, these are the type of applications where a shape change is difficult once the system is installed.