Integrated Piezoelectric AlN Thin Film with SU-8/PDMS Supporting Layer for Flexible Sensor Array

This research focuses on the development of a flexible tactile sensor array consisting of aluminum nitride (AlN) based on micro-electro-mechanical system (MEMS) technology. A total of 2304 tactile sensors were integrated into a small area of 2.5 × 2.5 cm2. Five hundred nm thick AlN film with strong c-axis texture was sputtered on Cr/Au/Cr (50/50/5 nm) layers as the sacrificial layer coated on a Si wafer. To achieve device flexibility, polydimethylsiloxane (PDMS) polymer and SU-8 photoresist layer were used as the supporting layers after etching away a release layer. Twenty-five mM (3-mercaptopropyl) trimethoxysilane (MPTMS) improves the adhesion between metal and polymers due to formation of a self-assembled monolayer (SAM) on the surface of the top electrode. The flexible tactile sensor has 8 × 8 channels and each channel has 36 sensor elements with nine SU-8 bump blocks. The tactile sensor array was demonstrated to be flexible by bending 90 degrees. The tactile sensor array was demonstrated to show clear spatial resolution through detecting the distinct electrical response of each channel under local mechanical stimulus. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.1

The Design and Optimization of a Compressive-Type Vector Sensor Utilizing a PMN-28PT Piezoelectric Single-Crystal

Underwater sensors that detect the distance and direction of acoustic sources are critical for surveillance monitoring and target detection in the water. Here, we propose an axial vector sensor that utilizes a small (~1 cm3) compressive-type piezoelectric accelerometer using piezoelectric single crystals. Initially, finite element analysis (FEA) was used to optimize the structure that comprised piezoelectric Pb(Mb1/3Nb2/3)O3-28%PbTiO3 single crystals on a tungsten seismic mass. The receiving voltage sensitivity (RVS) was enhanced through geometric optimization of the thickness and sensing area of the piezoelectric material and the seismic mass. The estimated maximum RVS of the optimized vector sensor was −212 dB. FEA simulations and practical measurements were used to verify the directivity of the vector sensor design, which exhibited a dipole pattern. The dipole beam pattern was used to obtain cardioid patterns using the simulated and measured results for comparison. The results clearly showed the feasibility of using the proposed piezoelectric single-crystal accelerometer for a compressive-type vector sensor. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.1

Development of a high-density piezoelectric micromachined ultrasonic transducer array based on patterned aluminum nitride thin film

This study presents the fabrication and characterization of a piezoelectric micromachined ultrasonic transducer (pMUT; radius: 40 μm) using a patterned aluminum nitride (AlN) thin film as the active piezoelectric material. A 20 x 20 array of pMUTs using a 1 μm thick AlN thin film was designed and fabricated on a 2 x 2 mm2 footprint for a high fill factor. Based on the electrical impedance and phase of the pMUT array, the electromechanical coefficient was ~1.7% at the average resonant frequency of 2.82 MHz in air. Dynamic displacement of the pMUT surface was characterized by scanning laser Doppler vibrometry. The pressure output while immersed in water was 19.79 kPa when calculated based on the peak displacement at the resonant frequency. The proposed AlN pMUT array has potential applications in biomedical sensing for healthcare, medical imaging, and biometrics. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.1

Effect of piezoelectric layer thickness and poling conditions on the performance of cantilever piezoelectric energy harvesters on Ni foils

Lead zirconate titanate (PZT) films grown on flexible Ni foils were utilized to explore the effects of thickness and poling conditions on the performance of mechanical energy harvesters. In the case of Mn doped 1 μm thick (001) oriented sol-gel PZT (52/48) films on Ni foil, the dielectric constant and |e31,f| are 390 at 10 kHz and 11.3 C/m2, respectively, after hot poling. This film has a large figure of merit ([Formula presented]), of around 0.4 C2/m4, for piezoelectric energy harvesting. Unimorph cantilever beams were easily fabricated from PZT films on Ni foil using simple mechanical cutting. The maximum power increases from 12 to 60 μW as the thickness of Nb doped PZT film increases from 1 to 3 μm at resonance frequency (∼70 Hz) at 0.5 G. The optimum poling condition (150 °C, at 3 times the coercive for 15 min) enhanced the voltage and power output of the cantilever harvester prepared using (1 μm) PZT films on Ni foil. It was found that the power performance of harvesters strongly depends on the thickness of the film with resonant harvesters of the same footprint area (0.385 cm2) using PZT films on Ni foils. © 2018 Elsevier B.V.1

Fabrication of surface-micromachined circular piezoelectric micromachined ultrasonic transducers with various etching holes using XeF2 and simulation of their vibrational characteristics

Piezoelectric micromachined ultrasonic transducers (pMUTs) are of great interest for numerous applications, including fingerprint imaging, precise acoustic sensing, and ultrasonic medical imaging, due to their properties of high design freedom and low power consumption when miniaturized for a transducer array. However, micromachined transducers tend to have relatively low acoustic intensity compared with conventional ceramic-based transducers. Therefore, it is preferable and recommended to achieve high acoustic intensity and enhanced displacement of the pMUTs. This paper presents circular pMUTs with various clamped membranes and explores the displacement and mode shape of membranes at resonance frequencies that are critical for enhanced acoustic intensity. Each circular clamped membrane had four etched holes at the edge of the membrane to control the boundary condition, which affected the resonance frequencies and membrane displacement by controlling the effective stiffness. The displacement and effective area as a function of etching hole size were simulated using COMSOL software and verified experimentally. The maximum displacement of a membrane 60 µm in diameter exhibited a 25% improvement when the etching hole angle was 20° compared with the fully clamped membrane. The effective area for acoustic intensity increased from 54.2% to 61.7% at 60° when the mode shape changed from circular to square. The experimental and simulation results were in reasonable agreement, and the results helped clarify how the geometric design of the suspended membrane of the pMUT affects its vibrational characteristics. © 2023 Elsevier B.V.FALS

A 28.7V Modular Supply Multiplying Pulser With 75.4% Power Reduction Relative to CV2f

This paper presents a high voltage modular supply multiplying pulser in a 0.18-μm BCD CMOS process. Two prototypes of the pulser were implemented for target loads of 55pF and 1nF, and generated up to 1MHz and 28.7V pulse from 1.2 and 5V supplies. Proposed modular based stepwise pulse generation achieved a peak power reduction of 75.4% relative to CV2f and a peak power efficiency of 82.3%. The proposed pulser was used for driving piezoelectric micromachined ultrasound transducer (pMUT) and achieved a relative efficiency improvement of 113.7% against conventional two-level square wave pulsing.1

Spontaneous Bleeding from a Short Gastric Artery after Vomiting Successfully Treated without Surgery

Spontaneous bleeding from a short gastric artery in the absence of pre-disposing trauma is reported very rarely. To the best of our knowledge, the published literature includes only 14 cases. Young men comprise almost all of the patients, and were induced by vomiting or gagging. The patients usually required emergent surgery. Our patient, a 32-year-old man, was diagnosed with spontaneous hemoperitoneum due to short gastric artery tearing after a few instances of vomiting. We managed him conservatively including fluid, vitamin K and antifibrinolytic agent without surgery. (Korean J Gastroenterol 2016;68:152-155

The Design and Optimization of a Compressive-Type Vector Sensor Utilizing a PMN-28PT Piezoelectric Single-Crystal

Underwater sensors that detect the distance and direction of acoustic sources are critical for surveillance monitoring and target detection in the water. Here, we propose an axial vector sensor that utilizes a small (~1 cm3) compressive-type piezoelectric accelerometer using piezoelectric single crystals. Initially, finite element analysis (FEA) was used to optimize the structure that comprised piezoelectric Pb(Mb1/3Nb2/3)O3-28%PbTiO3 single crystals on a tungsten seismic mass. The receiving voltage sensitivity (RVS) was enhanced through geometric optimization of the thickness and sensing area of the piezoelectric material and the seismic mass. The estimated maximum RVS of the optimized vector sensor was −212 dB. FEA simulations and practical measurements were used to verify the directivity of the vector sensor design, which exhibited a dipole pattern. The dipole beam pattern was used to obtain cardioid patterns using the simulated and measured results for comparison. The results clearly showed the feasibility of using the proposed piezoelectric single-crystal accelerometer for a compressive-type vector sensor

A piezoelectric micro-electro-mechanical system vector sensor with a mushroom-shaped proof mass for a dipole beam pattern

Vector hydrophones based on a micro-electro-mechanical system (MEMS) hold great promise for underwater communications, due to their potential for miniaturization and mass production. Piezoelectric materials have recently been utilized in the fabrication of MEMS-based vector hydrophones, as less power is typically required for their operation. Here, we propose a millimeter-scale piezoelectric MEMS vector sensor with a suspended cross-shaped beam and a mushroom-shaped proof mass configuration. This design was inspired by the bio-transducer of the lateral line of fish. Sensor fabrication involved piezoelectric Pb(Zr0.52Ti0.48)O3 thin-film deposition by radio-frequency magnetron sputtering onto the beam structure, followed by a multi-etching process and assembly using a three-axis microassembly technique. The fabricated MEMS vector sensor showed a resonance frequency above the working frequency range, which was suitable for naval applications. The directivity of the proposed sensor was determined by dipole patterns in the x and y directions, with a maximum relative sensitivity difference of −42 dB at 1 kHz. Finite element analysis results for the resonance frequency and directivity were in good agreement with the experimental results, suggesting that the proposed vector sensor could be used in underwater communications as a vector hydrophone. © 2021 Elsevier B.V.1