Simulation of piezoresistivity effect in FETs

AlGaN/GaN and AlGaAs/InGaAs/GaAs HEMT structures are investigated theoretically to calculate the dependence of the 2DEG sheet resistance on strain. The inhomogeneous strain pattern induced by an external force is computed numerically using a continuous media model, assuming that the structures are grown on a thick substrate which remains unstrained. Current transport is simulated by means of a drift-diffusion model taking the spontaneous and piezoelectric polarization into account. The effect of strain onto the band structure is treated in the framework of k · p theory. The structures are simulated for different external pressures in order to study the relative change of resistance. The AlGaN/GaN structure shows an increasing resistance for increasing stress which can be related to the change of the piezoelectric polarization in the device. In the GaAs-based structure the effect depends on substrate termination and is more pronounced for B-face polarity.     

Electrical Signal of Piezoelectric Buzzer by Impact Testing

Abstract

The aim of this paper was to study the electrical signal produced by the commercial piezoelectric buzzer by impact testing. The experiment varied external resistor, sphere weight, incident angle of sphere weight, impact position, the depth of the embedded piezoelectric buzzer in concrete and the impact surface of the embedded piezoelectric buzzer in concrete. As a result, we found that the suitable external resistor is 500?ohm which was related with resonant resistance of piezoelectric buzzer. The electrical signal increased as a result of the increased impact force on piezoelectric buzzer. The impact force will increase as the sphere weight falls at the middle of the piezoelectric buzzer. It is expected to explain electrical signal of piezoelectric buzzer by quantitative evaluation which is the key to understand physical mechanism to embedded piezoelectric materials in the structural health monitoring application.     

DEVELOPMENT OF SELF-SENSITIVE PIEZOELECTRIC CANTILEVER UTILIZING PZT THIN FILM DEPOSITED ON SOI WAFER

ABSTRACT

Piezoelectric micro cantilevers were applied to a resonant type mass sensor, biosensor, vapor sensor and probe for scanning force microscopes. These devices utilize impedance, phase, and charge as output signals. However, the measurement system could be greatly simplified if an output voltage were utilized. Therefore, a self-sensitive piezoelectric cantilever with separated electrode for actuation and sensing was developed. The self-sensitive piezoelectric cantilever was fabricated from a multilayer of Pt/Ti/PZT/Pt/Ti/SiO₂/SOI through MEMS bulk micromachining. The cantilever was oscillated by a sweep sine wave and the output voltage was measured as a function of the input frequency. The resonant frequency determined from the output voltage spectrum agrees well with that measured by a laser Doppler vibrometer.     

MICROMACHINED PIEZOELECTRIC MICROSPEAKERS FABRICATED WITH HIGH QUALITY ALN THIN FILM

ABSTRACT

This paper describes the micromachined piezoelectric microspeakers that can produce the audible signal with 20 V peak-to-peak input voltages. The diaphragm size is 4 × 4 mm² and the thickness of diaphragm is around 1 micron meter except partially etched piezoelectric area. The maximum sound output pressure of the microspeaker is even higher than ever before with a small diaphragm in high frequency range around 10 kHz. This successful result bases upon using high quality AlN thin film. The deposited AlN thin film shows c-axis oriented columnar structure and very fine grains. The highest SPL (Sound Pressure Level) measured from 300 Hz to 12 kHz shows about 100 dB around 10 kHz in case of circular type microspeaker and about 76 dB in case of cross type, respectively.     

Energy harvesting with a cymbal type piezoelectric transducer from low frequency compression

In this paper a piezoelectric energy harvester based on a Cymbal type structure is presented. A piezoelectric disc ?35?mm was confined between two convex steel discs ?35?mm acting as a force amplifier delivering stress to the PZT and protecting the harvester. Optimization was performed and generated voltage and power of the harvester were measured as functions of resistive load and applied force. At 1.19?Hz compression frequency with 24.8?N force a Cymbal type harvester with 250?μm thick steel discs delivered an average power of 0.66?mW. Maximum power densities of 1.37?mW/cm³ and 0.31?mW/cm³ were measured for the piezo element and the whole component, respectively. The measured power levels reported in this article are able to satisfy the demands of some monitoring electronics or extend the battery life of a portable device.     

DESIGN OF A NOVEL PIEZOELECTRIC ACOUSTIC SENSOR USING SURFACE MICROMACHINING

ABSTRACT

A novel structure of piezoelectric acoustic sensors using surface micromachining is proposed and designed. The advantage of surface micromachined acoustic sensors is to reduce the device size while maintaining their good performances compared with bulk micromachined counterparts. The simplified process sequence for the fabrication of acoustic sensors is given and porous silicon is used as a thick sacrificial layer. The PZT-based piezoelectric acoustic sensors exhibit a voltage sensitivity of 61 to 474 μV/Pa, depending on geometry, which ranges from 200 to 500 μm in length of the square membrane.     

Energy harvesting MEMS device based on thin film piezoelectric cantilevers

A thin film lead zirconate titanate Pb(Zr,Ti)O₃ (PZT), energy harvesting MEMS device is developed to enable self-supportive sensors for in-service integrity monitoring of large social and environmental infrastructures at remote locations. It is designed to resonate at specific frequencies of an external vibrational energy source, thereby creating electrical energy via the piezoelectric effect. Our cantilever device has a PZT/SiN_x bimorph structure with a proof mass added to the end. The Pt/Ti top electrode is patterned into an interdigitated shape on top of the sol-gel-spin coated PZT thin film in order to employ the d ₃₃ mode. The base-shaking experiment at the first resonant frequency of the cantilever (170 × 260 μm) generates 1 μW of continuous electrical power to a 5.2 MΩ resistive load at 2.4 V DC. The effect of proof mass, beam shape and damping on the power generating performance are modeled to provide a design guideline for maximum power harvesting from environmentally available low frequency vibrations. A spiral cantilever is designed to achieve compactness, low resonant frequency and minimum damping coefficient, simultaneously.     

MICRO ACOUSTIC DEVICES USING PIEZOELECTRIC FILMS

ABSTRACT

A novel PZT based micro acoustic device with the diaphragms clamped on all four edges has been studied. It can be used both as microphone and microspeaker. Compared with other piezoelectric micro acoustic devices, PZT based device has higher sensitivity for microphone and larger output acoustic pressure for microspeaker. The microfabrication process flow of this device is simple, and the transducer has excellent performance, miniature size and high reliability. The micro acoustic devices could be widely used in various practical audio frequencies and ultrasonic systems.     

High frequency response of Bragg reflector type film bulk acoustic wave resonator

Abstract

We fabricated a Bragg reflector type FBAR using AlN piezoelectric with quarter wavelength thickness, where the Bragg reflector was composed of W-SiO₂ pairs. By numerical simulation considering actual acoustic losses of each layer, we analyzed the frequency response of the resonator and could explain it using an equivalent circuit with parasitic elements. The Effective electromechanical coupling constant (K ² _eff ) and the Quality factor (Q_s ), figures of merit of the resonator, were about 1.1% and 307, respectively.</ab>     

RF-induced heating of interventional devices at 23.66 MHz

Objective

Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.66 MHz) with a focus on the effect of patient size, target organ, and device position on maximum temperature rise.

Materials and methods

To assess RF-induced heating, high-resolution measurements of the electric field, temperature, and transfer function were combined. Realistic device trajectories were derived from vascular models to evaluate the variation of the temperature increase as a function of the device trajectory. At a low-field RF test bench, the effects of patient size and positioning, target organ (liver and heart) and body coil type were measured for six commonly used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle).

Results

Electric field mapping shows that the hotspots are not necessarily localized at the device tip. Of all procedures, the liver catheterizations showed the lowest heating, and a modification of the transmit body coil could further reduce the temperature increase. For common commercial needles no significant heating was measured at the needle tip. Comparable local SAR values were found in the temperature measurements and the TF-based calculations.

Conclusion

At low fields, interventions with shorter insertion lengths such as hepatic catheterizations result in less RF-induced heating than coronary interventions. The maximum temperature increase depends on body coil design.

     

Principle and operation of a new type motor consisting of piezoelectric device and strain wave gearing

The authors have developed a new type of motor consisting of a piezoelectric device and strain wave gearing, and is called a piezoelectric motor. This is a first step in realizing a low-speed, small-size and lightweight motor. The principle of the motor is that the traveling wave is produced by piezoelectric devices and displacement conversion devices without mechanical resonance, and the torque to rotate the motor is generated by a mechanism of strain wave gearing (circular spline and flexspline) without using friction. The motor is operated at variable frequency and its rotational position (angle) is controlled in open-loop because it is basically a synchronous motor. In this paper, the structure and principle of the proposed motor are explained and the driving method and the mechanical characteristics of an experimental motor also are described. The results are as follows:

• 1 The realizability of the proposed piezoelectric motor is verified experimentally. The experimental motor operates at 2920 steps per revolution, and its speed range is 0 to 960 pps [or 0 to 20 (rpms)].
• 2 The torque characteristics are clarified qualitatively.
• 3 The generated torque of the experimental motor is small (less than 0.03 Nm) and therefore the improvement of the torque is an important subject hereafter.
• 4 It is possible to construct the motor with nonmetallic material. This fact is considered to facilitate obtaining a means to lighten the weight of the motor in the future.

     

用于超声电机的新型驱动电源设计

针对超声电机对激励电源频率、幅值、波形的要求,设计了一种新型超声电机压电陶瓷激励电源.该激励电源输入电压为12 V,经过DC-DC降压变换电路调压后输入4路推挽升压电路叠加输出.输出幅值可达600 V,频率在10～100 kHz范围内可调,同时两路电源间可实现任意相位差.在工作频率范围内无须对压电陶瓷进行阻抗匹配即可基...     

MODELING AND SIMULATION OF PIEZOELECTRIC MEMS ENERGY HARVESTING DEVICE

ABSTRACT

Piezoelectric MEMS power generator is used to harvest energy from the ambient vibrations in the environment. This paper proposes a structure design of MEMS power generator for low-frequency applications, which is based on bulk MEMS technology and (110) Si wafer. The structure consists of a silicon cantilever with a piezoelectric layer attached. The cantilever is modeled as an Euler-Bernoulli beam with a lumped mass beneath the tip of the cantilever, and then analytical modeling and simulations are carried out using MATLAB. Simulation results show that a tradeoff between the geometric parameters and the proof mass should be made for a high output power of the device. To increase the output power, the length of piezoelectric layer can be optimized, which is not necessarily equal to that of cantilever. Simulation results point out ways to perform the optimization of MEMS power generator. The analytical modeling and simulations are also helpful for the design of macro-scale power generator.     

Microwave magnetoelectric effects in ferrite—piezoelectric composites and dual electric and magnetic field tunable filters

Magnetoelectric (ME) effects at ferromagnetic resonance (FMR) in ferrite—piezoelectric layered structures have been investigated in lithium zinc ferrite (LZFO)-lead zirconate titanate (PZT) and yttrium iron garnet (YIG)-PZT. When an electric field E is applied to PZT, the piezoelectric deformation is transmitted to the ferrite and results in a shift in FMR. Data on the field shift caused by E are presented and compared with theory. Although the strength of ME coupling is weaker in YIG-PZT than in LZFO-PZT, the E-assisted field shift in YIG-PZT is much higher than the resonance line width and is potentially useful for filter applications. An electric field tunable YIG-PZT microwave band-pass filter based on ME effects at FMR is designed and characterized. The device can be tuned over a wide frequency band with a bias magnetic field and over a narrow band with a voltage applied across PZT. Data on tuning range, insertion loss, and device characteristics are presented.     

MEMS PIEZOELECTRIC ACOUSTIC TRANSDUCER

ABSTRACT

This paper presents the fabrication process and measurement results of microelectro-mechanical (MEMS) piezoelectric acoustic transducers. To increase the output sound pressure, a dome-shaped multi-layer diaphragm is designed and fabricated by adjusting the residual stress in the individual layers. Transducers work in either audio or ultrasonic frequency range if diaphragm is designed in different size. In the frequency range from 100 Hz to 7 kHz, the output sound pressure of audio transducers with 3 mm × 3 mm diaphragm is higher than 0.1 Pa. The maximum output reaches 1.1 Pa at 3.8 kHz. For ultrasonic transducers with 1 mm × 1 mm diaphragm, the maximum output is 1.26 Pa at resonant frequency of 54 kHz. All transducers show acceptable linearity over a wide range of input drive voltage.     

FABRICATION AND ELECTRICAL PROPERTIES OF PZT-PVDF 0–3 TYPE COMPOSITE FILM

ABSTRACT

A film speaker was fabricated with 0–3 type piezoelectric composite. The 0–3 type composite was developed to incorporate the advantages of both ceramic and polymer. The pastes of PZT-PVDF composite were made with various mixing ratio. The paste was printed by conventional screen-printing method on ITO (Indium Tin Oxide) bottom electrode which was deposited on PET (polyethylene terephthalate) polymer film. The prepared composite film was about 80 μm in thickness. After printing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at 120°C for an hour to align the electric dipole in the 0–3 composite film. The piezoelectric charge constant of d₃₃ was increased with increasing the PZT weight percent. The maximum value was 24 pC/N at 70 wt% of PZT. But the piezoelectric voltage constant of g₃₃ had the maximum value about 32 mV · m/N at 65 wt% of PZT. The SPL (Sound Pressure Level) of the speaker fabricated with the 65:35 composite film was tested at various driving voltages of 1 ～ 100V_rms. The SPL was saturated at the driving voltage of 70V_rms and the value was about 68 dB at 1 kHz.     

Enhanced piezoelectric energy harvester performance using magnetic force and thermal energy

One possible approach of improving the performance of energy harvesters is to use energy harvester with an external magnetic force to create a nonlinear coupling system. In this work, we report experimental results of a single piezoelectric cantilever beam (PCB) with tip mass or conventional piezoelectric energy harvester (CPEH), and the effect of applying an external magnetic force. The output voltage and power at optimal resistance was 7.62 V and 0.62 mW, respectively, at the resonance frequency of approximately 11 Hz of a CPEH. Also, the output voltage and average power at optimal resistance was 8.56 V and 0.44 mW, respectively, at resonance frequency of 7 Hz of a PCB with fixed opposing magnet. Furthermore, the output voltage and average power at optimal resistance was 13.31 V and 1.77 mW, respectively, at resonance frequency of 11 Hz of a PCB with opposing magnet attached at a second cantilever. In addition, comparison between the experimental results of all different configurations showed a reasonable enhancement of performance of energy harvester when an external magnetic force added over the main PCB. Finally, the performance of a multisource energy harvester with magnetic, thermal and mechanical sources is also presented in this study. In this case, it is demonstrated that increase in output voltage with temperature gradient under effect of magnetic force; the results of 2^nd and 3^rd model showed 44% and 99% enhancement of its original output voltage value at 1.2 °C and 2.7 °C temperature difference, respectively.     

Application testing of Sr doping effect of PZT ceramics on the piezoelectric transformer gain and efficiency proposed for MEMS actuators driving

Effect of Sr content in lead zirconate titanate PZT ceramic system on performance of piezoelectric transformer application were studied. Our experiments provide consistent evaluation of doping strontium amount on piezoelctric coefficients values and final voltage gain and efficiency of piezoelectric transformer. Extreme values of these parameters are preferred for MEMS device effective driving. Modification of ferroelectric materials with isovalent ions, however with the bigger radii than the original atoms, significantly affects their properties. Particularly the electromechanical coefficients of (Pb_1-xSr_x)(Zr_0,70Ti_0,30)O₃, for mole %??s as x?=?0.05, 0.10 and 0.15 ceramics exhibit marked increase, if the PSZT material stoichiometry is near the ferroelectric/relaxor phase boundary. To determine the piezoelectric coefficients, the resonance-antiresonance method was implemented. The results indicated that addition of Sr²⁺ ions in the amount of 5?mol% in the ceramic structure maximally increased the values of piezoelectric parameter to d₃₁?=?8.2?pC/N and mechanical quality factor Q_m?=?2902. Finally we demonstrated that in spite of the high piezoelectric coefficients for certain material only the practical examination must be applied in order to draw decisive application conclusions due to the complexity of the double energy conversion in such a specific device as the piezoelectric transformer.     

High Quality Silicon-Based AlN Thin Films for MEMS Application

ABSTRACT

Aluminum nitride is an attractive piezoelectric material for MEMS devices such as bulk acoustic wave (BAW) devices. (002)-oriented AlN films were deposited on Si, Al and Pt by reactive sputtering. Optimized AlN (002) peak reaches a full width at half maximum (FWHM) of 5.6°. Auger electron spectroscopy is used to analyze the oxygen contamination of films. To find the suitable electrode material for device application, the growth mechanism of AlN crystallites on different substrates is also discussed. Based on sputtered AlN films, the prototype of AlN thin film bulk acoustic resonator (TFBAR) was fabricated successfully.     

A shoe-equipped piezoelectric transducer system based on PVDF film

Many piezoelectric transducers mounted in shoes have been conducted to harvest energy from walking. However, the energy harvested is influenced by some factors, such as the structure of piezoelectric transducer, piezoelectric material and so forth. Taking into account these factors, a wide-band energy harvester-shoe equipped piezoelectric transducer with cantilever beam structure based on polyvinylidene fluoride (PVDF) piezoelectric film is designed and examined in this paper. The piezoelectric transducer makes little difference in the sensation with the device mounted in the shoes when walking. The harvester can provide a maximum output power of 0.48 mW at the load resistance of 300 kΩ. This study demonstrates that it is feasible to scavenge energy from human motion by piezoelectric harvester to power wearable sensors, such as pedometer, respiration and pulse monitoring system and so on.