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This study focuses on optimizing the resonator geometry via the aspect ratio design of a width-extensional mode resonator to improve its quality factor (Q), which is one of the critical performance parameters for resonators in either sensing (Allan deviation) or frequency reference (phase noise) applications. The proposed approach uses finite element analysis to reduce the strain energy at anchor supports by altering the resonator geometric structure, thereby reducing energy loss through anchors. Moreover, process limitations on feature sizes are used as constraints to find aspect ratios that can not only increase the Q but also reduce spurious modes near the targeted frequency. The devices were fabricated using AlN thin film piezoelectric on a substrate (TPoS) process. The simulated energy dissipation trends for specific length-to-width (L / W) ratios closely match the measured changes in the resonator Q values in vacuum. In vacuum, the highest Q -factor achieved by the device is close to 8816, with a motional resistance of a few tens of ohms. Additionally, a board-level oscillator realized using a commercial low-noise amplifier exhibits phase noise performance of −141.21 dBc Hz−1 and −164.25 dBc Hz−1 at 1 kHz and 1 MHz frequency offsets, respectively. The calculated figures of merit for these offsets are 204 and 168, respectively. [ABSTRACT FROM AUTHOR]

With the global market value of sensors on the rise, this paper focuses on the fabrication and testing of a proof-of-concept piezoelectric energy harvester which is able to harvest mechanical energy from the ambient environment and convert it into electrical energy in order to power wireless sensor networks. We focused on obtaining a new device structure based on a comb-type array of piezoelectric MEMS cantilevers (2 × 10) for a resonant frequency in the environmental application domain (a few hundred Hz) and a chip area of only 1 cm2. The configuration of the lead-free piezoelectric cantilever consists of a Si substrate, a pair of Ti-Pt electrodes and a sputtered piezoelectric layer of 12% Sc-doped AlN with a thickness of 1000 nm, a dielectric constant of ~13 and e31,f = 1.3 C/m2. At a resonant frequency of 465.2 Hz and an acceleration of 1 g, the maximum value for the collected power was 2.53 µW for an optimal load resistance of 1 MΩ resulting in a power density of 60.2 nW/mm3 for the unpacked device, without taking into account the vibration volume. By increasing the excitation acceleration to 2 g RMS and using LTC3588-1 for the power circuitry we were able to obtain a stabilized output voltage of 1.8 V. [ABSTRACT FROM AUTHOR]

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Resonating MEMS mass sensors are microdevices with broad applications in fields such as bioscience and biochemistry. Their advantageous surface-to-volume ratio makes their resonant frequency highly sensitive to variations in their mass induced by surface depositions. Recent global challenges, such as water quality monitoring or pandemic containment, have increased the need for low-cost (even disposable), rapidly fabricated microdevices as suitable detectors. Resonant MEMS mass sensors are among the best candidates. This paper introduces a simple and robust fabrication of polymeric piezoelectric resonating MEMS mass sensors. The microfabrication technology replaces the traditional layer-by-layer micromachining techniques with laser micromachining to gain extra simplicity. Membrane-based resonant sensors have been fabricated to test the technology. Their characterization results have proven that the technology is robust with good reproducibility (around 2% batch level variations in the resonant frequency). Initial tests for the MEMS mass sensors' sensitivity have indicated a sensitivity of 340 Hz/ng. The concept could be a starting point for developing low-cost MEMS sensing solutions for pandemic control, health examination, and pollution monitoring. [ABSTRACT FROM AUTHOR]

Resonating MEMS mass sensors are microdevices with broad applications in fields such as bioscience and biochemistry. Their advantageous surface-to-volume ratio makes their resonant frequency highly sensitive to variations in their mass induced by surface depositions. Recent global challenges, such as water quality monitoring or pandemic containment, have increased the need for low-cost (even disposable), rapidly fabricated microdevices as suitable detectors. Resonant MEMS mass sensors are among the best candidates. This paper introduces a simple and robust fabrication of polymeric piezoelectric resonating MEMS mass sensors. The microfabrication technology replaces the traditional layer-by-layer micromachining techniques with laser micromachining to gain extra simplicity. Membrane-based resonant sensors have been fabricated to test the technology. Their characterization results have proven that the technology is robust with good reproducibility (around 2% batch level variations in the resonant frequency). Initial tests for the MEMS mass sensors’ sensitivity have indicated a sensitivity of 340 Hz/ng. The concept could be a starting point for developing low-cost MEMS sensing solutions for pandemic control, health examination, and pollution monitoring.

We characterize the dynamical states of a piezoelectric micrcoelectromechanical system (MEMS) using several numerical quantifiers including the maximum Lyapunov exponent, the Poincaré Surface of Section and a chaos detection method called the Smaller Alignment Index (SALI). The analysis makes use of the MEMS Hamiltonian. We start our study by considering the case of a conservative piezoelectric MEMS model and describe the behavior of some representative phase space orbits of the system. We show that the dynamics of the piezoelectric MEMS becomes considerably more complex as the natural frequency of the system's mechanical part decreases. This refers to the reduction of the stiffness of the piezoelectric transducer. Then, taking into account the effects of damping and time-dependent forces on the piezoelectric MEMS, we derive the corresponding nonautonomous Hamiltonian and investigate its dynamical behavior. We find that the nonconservative system exhibits a rich dynamics, which is strongly influenced by the values of the parameters that govern the piezoelectric MEMS energy gain and loss. Our results provide further evidences of the ability of the SALI to efficiently characterize the chaoticity of dynamical systems. [ABSTRACT FROM AUTHOR]

In the recent decades energy harvesting from ambient vibration by the micro-electromechanical systems (MEMS) has been recognized as a promising solution to boosting lifespan of low-power electronic devices. Apparently, highly efficient MEMS vibration harvesters with lower operational frequencies are advantageous. In this paper we propose a new mechanical structure to aim for energy conversion efficiency enhancement and operational frequency reduction for the piezoelectric MEMS vibration energy harvesters. The proposed structure has a T-shaped geometry with integration of two identical proof masses at the T-segment. Thanks to two degrees-of-freedom, in this structure both bending and torsional mode frequencies can be located close to each other. Its analytic model of frequency response is derived and then validated by finite element modeling (FEM) simulations and prototype measurements. Compared to the conventional straight cantilever configuration, our proposed T-shaped piezoelectric cantilever structure can help distribute mechanical strain in broader areas with higher magnitude and lower resonant frequency. Our analytical, numerical, and experimental studies show that the normalized power density of the proposed T-shaped harvester is 4.8 times higher than that of the conventional one, in addition to 36% resonant frequency reduction. [2019-0146] [ABSTRACT FROM AUTHOR]

Total-ionizing-dose (TID) effects on piezoelectric micromachined ultrasonic transducers (pMUTs) are investigated using 10-keV X-rays under different bias conditions. The corresponding changes in resonant frequency and quality factor are evaluated using impedance analysis methods. Radiation-generated electrons or holes are trapped in the pre-existing defects of piezoelectric materials. Therefore, the sensitivity of pMUTs to X-ray irradiation depends strongly on the device bias during irradiation. The trapped charges change stress and strain in the materials due to the inverse piezoelectric effect, resulting in resonant frequency shifts and quality factor variation. [ABSTRACT FROM PUBLISHER]

Thin films are defined as a two-dimensional material created by condensing, one-by-one, atomic/ lecular/ionic species of matter in contrast to a bulk three-dimensional material. The thin-films have been used for more than a half century for making optical coating, electronic devices, instrument hard coatings, and/or decorative parts. However, e thin-film technology is still being developed on a daily basis since it is a key technology in the twenty-first century for the development of new functional devices. It is also noted that the thin-film technology saves materials and energy consumption. Thin film process is an environment-benign technology. Several deposition processes are used for the thin-film deposition including thermal deposition, chemical vapor deposition, and sputtering deposition. The present author has studied on the sputtering deposition for academic and industrial use for more than 40 years. The sputtering deposition carries exotic/interesting phenomena due to the presence of highly energetic sputtered species. In this paper, the first fundamentals of thin-film materials are described. Then several exotic/interesting phenomena observed in the sputtering deposition are discussed as possible future materials science and technology. The exotic/interesting phenomena include room-temperature growth of diamonds, phase control of high-Curie temperature ( T) oxide superconductors, multilayered structure with enhanced piezoelectricity, and extraordinary high-performance ferroelectric thin-films. [ABSTRACT FROM AUTHOR]

Abstract: The co-integration of piezoelectric actuation and sensing capabilities on microelectromechanical system-based resonators can be a source of electrical cross-talk that, if not properly taken into account, may dramatically affect the interpretation of the device’s output. In this paper, we identify three parasitic electrical effects pertaining to the most commonly used piezoelectric actuation and sensing schemes. To further investigate the impact of such parasitic effects, microcantilevers, bridges and membranes integrating a layer of sol–gel lead zirconate titanate (PZT) were fabricated and electrically characterized. Experimental results on the resonant characteristics were compared with simulations of the studied resonators’ equivalent electrical models. Methods for reducing the design-dependent parasitic electrical effects such as mutual capacitances of less than 10fF, electrical wiring or static capacitance mismatches of less than 20% of the integrated piezoelectric films are discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the design, fabrication, and characterization of an acoustic transducer using a piezoelectric freestanding bulk diaphragm as the sensing element. The diaphragm bearing the spiral electrode operates in d 33 mode, which allows the in-plane deformation of the diaphragm to be converted to the out-of-plane deformation and generates an acoustic wave in the same direction. A finite element code is developed to reorient the material polarization distribution according to the poling field calculated. The first four resonance modes have been simulated and verified by impedance and velocity spectra. The sensitivity and the sound pressure level of the transducer were characterized. The realized sensitivity of 126.21μV/Pa at 1kHz is nearly twenty times of the sensitivity of a sandwich d 31 mode transducer. [Copyright &y& Elsevier]

We are developing a novel MEMS-magnetoresistive hybrid device aimed at ultra low magnetic field detection. The hybrid device combines magnetoresistive (MR) sensors and AlN based piezoelectric MEMS resonators. The MR sensor can achieve highly sensitive magnetic field detection but suffers from high magnetic and electrical 1/f noise, limiting its applicability for dc and low-frequency field detection. We overcome this problem by using two piezoelectric cantilevers with integrated magnetic flux concentrators (MFC) to mechanically modulate the external magnetic fields into the high frequency region where the 1/f noise in the MR device vanishes. In this paper we report our fabrication approach and preliminary characterization of the hybrid device. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents a novel configuration consisting of a micromachined diaphragm and a standing beam for sensing airflow. A piezoelectric Pb(Zr,Ti)O3 (PZT) film is deposited by spin-coating on the diaphragm to actuate and sense the vibration at its resonant frequency. A standing and extruded beam built on the diaphragm responds to the aerodynamic drag force, inducing mechanical strain, increasing the stiffness of the structure, and subsequently shifting the resonant frequency. The finite element method is used to demonstrate the first four mode shapes and predict the frequency shift of the proposed structure when subjected to airflow. The prototype microstructure is fabricated by combining the PZT sol–gel process and silicon micromachining. In particular, a two-step deep silicon etching process is developed to form the diaphragm structure with a standing silicon beam on it. Flip-chip bonding by solder balls is adopted to electrically connect the electrode pads to the circuit board. The characterization of the flip-chip bonded sensor chip exhibits superior piezoelectric and electrical properties. The wind tunnel test shows a 25Hz resonant frequency shift for a wind speed of 10m/s. [Copyright &y& Elsevier]

Abstract: Integration of materials other than silicon and its compounds into micromachined transducers is a rapidly emerging area of MEMS research technology. For example, future innovations and improvements in inertial sensors for navigation, highfrequency crystal oscillators and filters for wireless applications, microactuators for RF applications, chip-scale chemical analysis systems, and countless other applications can be significantly impacted by the successful miniaturization and integration of piezoelectric materials and subsystems onto silicon substrates. Piezoelectric materials are high energy density materials that scale favorably upon miniaturization. In this article, a cursory review of the fabrication technology for piezoelectric MEMS transducers is presented along with a discussion on the challenges and opportunities in the field. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on a membrane-type acoustic transducer fabricated by bonding a piezoelectric ceramic Pb(Zr,Ti)O3 (PZT) plate to a silicon on insulator (SOI) wafer. A special Si backplate with perforated acoustic holes is also bonded to the membrane to broaden the acoustic frequency spectrum. Key techniques in the fabrication include a low-temperature bonding technique using a spin-on polymer, design of electrode interconnect, chemical mechanical polishing (CMP) for thinning down the bulk PZT, and deep reactive ion etching bulk micromachining of silicon. High quality integrated transducers on SOI wafer have been successfully demonstrated and the fabrication and measurement results are presented. [Copyright &y& Elsevier]

Abstract: This paper presents a novel ambient energy scavenging system for powering wireless sensor nodes. It uses a MEMS generator and an ASIC power management circuit. The system is created as a System on a Package with all components fabricated entirely using microfabrication techniques. Its performance is compared with standard approaches using a resistive load or discrete Schottky diodes. The electromechanical transduction is performed using the piezoelectric effect of aluminium nitride thin films. The reported experimental results prove the possibility of exploiting very low amplitude signals delivered by the generator for charging a storage capacitor. It is also shown that a system of 5mm3 can endlessly power a simple wireless sensor node; while a lithium polymer thin film battery of the same volume can do so only for less than 2 months. [Copyright &y& Elsevier]

A novel actuation mechanism that utilizes the inherent piezoelectric properties of Al xGa1-x As compounds is presented for short-wavelength microelectromechanical systems tunable vertical-cavity surface-emitting laser centered at 850 nm. Piezoelectric actuation can provide precise bidirectional displacements and linear tuning characteristics with respect to the applied voltage, does not suffer from travel limitations and catastrophic electrical damage, consumes low power (~1 muW), and has a relatively fast response compared to thermal actuation. In addition, piezoelectric actuation based on AlxGa 1-xAs films offers a large piezoelectric coupling coefficient comparable to those of zinc oxide and quartz, and it can be integrated with high-speed electronic and optoelectronic devices. Single-mode emission with a linear continuous tuning range of 3 nm and low power consumption were experimentally obtained [ABSTRACT FROM PUBLISHER]

This paper successfully demonstrates the potential of weakly coupled piezoelectric MEMS (Micro-Electro-Mechanical Systems) gravimetric sensors for the detection of ultra-fine particulates. As a proof-of-principle, the detection of diesel soot particles of 100 nanometres or less is demonstrated. A practical monitoring context also exists for diesel soot particles originating from combustion engines, as they are of serious health concern. The MEMS sensors employed in this work operate on the principle of vibration mode-localisation employing an amplitude ratio shift output metric for readout. Notably, gains are observed while comparing parametric sensitivities and the input referred stability for amplitude ratio and resonant frequency variations, demonstrating that the amplitude ratio output metric is particularly suitable for long-term measurements. The soot particle mass directly estimated using coupled MEMS resonators can be correlated to the mass, indirectly estimated using the condensation particle counter used as the reference instrument. [ABSTRACT FROM AUTHOR]