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Modulated laser interferometer with picometer resolution for piezoelectric characterization
Review of Scientific Instruments
Abstract
A modified double-beam interferometric measurement system is established and tested for displacement measurement of ferroelectric lead zirconate titanate bulk samples. To overcome the optical path-length drift or laser intensity instability, a modulation technique is introduced, and desired resolution (down to several picometers) and reliability are achieved without the complicated close loop servo system. This modified interferometer provides us a powerful yet easily accessible tool for piezoelectric thin/thick film characterization.
... Optical Interferometry is mainly used in fine precision equipment, especially in cases which require both large range and fine resolution displacement measurement [37][38][39][40][41][42]. The basic form for this method of sensing relies on splitting coherent light into two beams, arranging the beam paths such that one path length is dependent on the displacement of interest and recombining the beams to generate an interference pattern [37,[42][43][44]. This pattern will vary with the displacement measurement, and can be measured to infer the change in the path length. ...
... Optical Heterodyne Interferometers are extremely sensitive to environmental conditions such as temperature and pressure, both of which change the optical properties of the medium through which the beam travels [37,42,44]. The range of measurement of an optical heterodyne interferometer is effectively decoupled from its resolution because the relative phase measurement cyclically shifts only through 0 to 2π as the displacement value changes. ...
As mechanical devices move towards the nanoscale, smaller and more sensitive force and displacement sensors need to be developed. Currently, many biological, materials science, and nanomanufacturing applications could benefit from multi-axis micro- and nanoscale sensors with fine force and displacement resolutions. Unfortunately, such systems do not yet exist due to the limitations of traditional sensing techniques and fabrication procedures. Carbon nanotube-based (CNT) piezoresistive transducers offer the potential to overcome many of these limitations. Previous research has shown the potential for the use of CNTs in high resolution micro- and nanoscale sensing devices due to the high gauge factor and inherent size of CNTs. However, a better understanding of CNT-based piezoresistive sensors is needed in order to be able to design and engineer CNT-based sensor systems to take advantage of this potential. The purpose of this thesis is to take CNT-based strain sensors from the single element test structures that have been fabricated and turn them into precision sensor systems that can be used in micro- and nanoscale force and displacement transducers. In order to achieve this purpose and engineer high resolution CNT-based sensor systems, the design and manufacturing methods used to create CNT-based piezoresistive sensors were investigated. At the system level, a noise model was developed in order to be able to optimize the design of the sensor system. At the element level, a link was established between the structure of the CNT and its gauge factor using a theoretical model developed from quantum mechanics. This model was confirmed experimentally using CNT-based piezoresistive sensors integrated into a microfabricated test structure. At the device level, noise mitigation techniques including annealing and the use of a protective ceramic coating were investigated in order to reduce the noise in the sensor. From these investigations, best practices for the design and manufacturing of CNT-based piezoresistive sensors were established. Using these best practices, it is possible to increase the performance of CNT-based piezoresistive sensor systems by more than three orders of magnitude. These best practices were implemented in the design and fabrication of a multi-axis force sensor used to measure the adhesion force of an array of cells to the different material's surfaces for the development of biomedical implants. This force sensor is capable of measuring forces in the z-axis as well as torques in the [theta]x and [theta]y axis. The range and resolution of the force sensor were determined to be 84 [mu]N and 5.6 nN, respectively. This corresponds to a dynamic range of 83 dB, which closely matches the dynamic range predicted by the system noise model used to design the sensor. The accuracy of the force sensor is better than 1% over the device's full range.
... Therefore, a further modification regarding the position of the focusing lenses has been made to keep the interferometer as compact and, consequently, as sensitive as possible. To overcome the optical path-length drift and laser intensity instability, the interferometer was equipped with the modulation technique after Chao et al. 28 In order to increase the sensitivity of the system and thus characterize piezoelectric thin films, the lock-in technique was used. The interferometer was tested and verified using a LiNbO 3 single crystal of the orientation (0001). ...
Defect engineering is an effective tool to manipulate material properties and produce completely new ones that are symmetry-forbiddenin a defect-free crystal. For example, single crystals of SrTiO3form, as a long-term reaction to external static electric fields, a strainednear-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. It was previouslyshown that this near-surface phase exhibits pyroelectric and piezoelectric properties, which are symmetry-forbidden in centrosymmetricbulk SrTiO3. In the present paper, different approaches have been used to better understand the nature of this reaction.In situXRDmeasurements were carried out to investigate the dynamics of the lattice distortion during the formation and relaxation of this phase.Interferometry measurements were carried out to determine the piezoelectric thickness change of the samples and to indirectly investi-gate the polar property of the unit cell before, during, and after electroformation. We observe the instantaneous formation of a polarstrontium titanate unit cell at room temperature, explainable by electrostriction, and the expected additional contribution after a long-term field application.
... While there are numerous examples of precision laser interferometry in the literature [4,5,6,7,8], these instruments are somewhat complex in their design and are therefore not optimally suited for a teaching environment. Below we describe a laser interferometer designed to demonstrate precision physical measurement techniques in a compact apparatus with a relatively simple optical layout. ...
We describe a laser interferometer experiment for the undergraduate teaching
laboratory that achieves picometer sensitivity in a hands-on table-top
instrument. In addition to providing an introduction to interferometer physics
and optical hardware, the experiment also focuses on precision measurement
techniques including servo control, signal modulation, phase-sensitive
detection, and different types of signal averaging. After students assemble,
align, and characterize the interferometer, they then use it to measure
nanoscale motions of a simple harmonic oscillator system, as a substantive
example of how laser interferometry can be used as an effective tool in
experimental science.
... Other nanometric-resolution techniques used a photorefractive GaP crystal [4], a magnetoresistive sensor [5], a fibre-optic interferometer [6] , a multiplereflection interferometer [7] and a magnetic spring [8]. Also, it is possible to measure picometric oscillations by means of optical interferometry [9]. Another possible tool to measure a linear displacement is the linear variable differential transducer (LVDT), which has been applied in many research fields. ...
A method to determine very low amplitudes of harmonic vibrations was developed. The basic idea is to mount a large magnet onto the vibrating surface and measure the induced voltage on a small, fixed coil. The uniform magnetic field through the coil's area allows the use of a simple calculation to determine the vibration amplitude without any fitting factor. Our measurements were successfully compared with other methods. The range of measured amplitudes varies from picometres to millimetres, with an uncertainty of less than 10%.
Hydroxyapatite (HAp) qualities such as biocompatibility and piezoelectricity make it an excellent material for biomedical applications. Here, HAp thin film samples were fabricated onto silica substrates to study their piezoelectric behavior with optical interference. Thin solid films were deposited using previously synthesized HAp powder, sol-gel, and spin-coating techniques. The samples were characterized by scanning electron microscopy, energy dispersive X-ray, Raman, and UV-Vis spectroscopies. The statical piezoelectric effect of the samples was studied by using a finite element method and computational software. Additionally, an experimental Bode analysis allows computing the internal electrical components of the films using high-frequency AC voltage. The electrical behavior is related to the equivalent circuit of a piezoelectric crystal, which indicates the range of frequencies where the electromechanical effect is maximum. A Sagnac interferometer was used to characterize the strain in the HAp as a function of the electrical input frequency. The displacement of the interferometric fringe pattern allows us to estimate the change in the thickness of the sample and compute the piezoelectric constant. The synthesis of HAp thin films with piezoelectric properties provides an effective way to produce sensors and actuators for technological applications.
Piezoelectricity is the coupling between the mechanical and electric property of materials, which manifests itself by the generation of electric charge upon a pressure or conversely the produce of strain under an electric field.
Laser interferometers are very useful tools for non-contact measurement of nano-level small vibrations. Two categories of interferometers have been used for this purpose. One is heterodyne interferometers which measures the velocity of the vibration and then converts the velocity data into displacements. The other is homodyne interferometers with fixed λ/4 path difference, where a small path length change is proportional to the interfered laser intensity. Both of the two methods have their limitations in accuracy, in bandwidth, or in some other aspects. In this chapter, a quasi-static method is proposed to modify the conventional homodyne interferometers for measurement of nano and sub-nano level vibrations. Based on the method, a Mach-Zehnder type quasi-homodyne vibrometer with picometer resolution is developed. Compared with conventional homodyne or heterodyne interferometers, the quasihomodyne system possesses simpler configuration, higher bandwidth potential and higher immunity to external disturbances.
The various laser interferometer systems are used for the measurement of piezoelectric and electro-optics coefficients of piezoelectric materials. Both Michelson single beam and Mach-Zender double beam homodyne systems are working at dynamic modes. The alternating voltage (frequency in range 1 Hz-100 kHz) is applied on the samples. The amplitude of samples displacement is determined by lock-in amplifier technique. It enables to measure very small amplitudes of the order of 10-12 m. The new unique system is used for measurement of coefficients in wide temperature range. The cryogenic cooling system, based on closed circuit of helium gas, is used for low temperature measurements and evacuated temperature chamber for the measurements above room temperature. The fundamental interferometer measurement problems as a temperature instability and mechanical vibration of cryostat are sold. The all parts of interferometer are placed inside the cryostat. The relative motion of interferometer's parts is almost suppressed by this way. To locate a double beam Mach-Zehnder interferometer to small temperature chamber was problematic because it consists of many optical elements. The new type of double beam interferometer with minimum of elements was constructed and located inside cryostat. The similar interferometric methods are used for electro-optical coefficients measurements too.
Traditional MEMS sensing systems do not scale down well to the nanoscale due to resolution and fabrication limitations. Therefore, new sensing systems need to be developed in order to meet the range and resolution requirements of nanoscale mechanical systems. Several nanoscale mechanical sensing systems have emerged that take advantage of nanoscale phenomena to improve the quality of nanoscale sensors. In this paper, we will discuss some of the fundamental limitations in scaling mechanical sensors down to the nanoscale and some of the emerging technologies for nanoscale sensing.
The laser interferometer technique with noise level up to 10-12 m is described. It is based on a precise interference fringe measuring servo-system with wide range displacement linearity. The r.m.s. deviation of displacement-to-voltage transform factor is below 1% in the range of plusmn105 periods of the interference pattern shifts. The dynamic range of available displacement amplitude is near of 210 dB. The system characteristics have been accurately tested and investigated. The examples of precise interferometer applications to geophysics and technological measurements are shown.
A scanning homodyne interferometer is developed based on the combination of a modulated Mach-Zehnder interferometer and a high-precision two-dimensional translation stage. Due to its ultrahigh out-of-plane resolution (down to pico meters) and wide bandwidth potential, the scanning interferometer is well suited for characterization of piezoelectric thin films as well as for vibration measurement of microelectromechanical systems devices such as micromachined ultrasonic transducers. (c) 2005 American Institute of Physics.
This paper reports on the design, fabrication, and characterization of diaphragm-type piezoelectric micromachined ultrasonic
transducer (pMUT) and arrays. A combination of piezoelectric composite thick film techniques and silicon micromachining has
been proven to be a promising approach for a batch production of pMUTs, especially pMUT transmitter arrays for ultrasound
radiation. In this paper, some important issues related to the pMUT element design and micromachining processes are addressed.
Thanks to the well-developed processing technology, pMUTs and arrays operating at different resonance frequencies by dimension
variation have been successfully fabricated with a high yield for possible mass manufacturing. The characterization of piezoelectric
composite thick film will be briefly reported. The performance of the prototype devices has been characterized in terms of
vibration modes, dependency of the resonance frequency on bias voltage, nonlinearity, electromechanical coupling efficiency,
equivalent circuit, output sound pressure level and directivity of a two-dimensional pMUT array.
Developing a well accepted method for piezoelectric characterization of piezoelectric thin/thick films is an essential issue in the research of piezoelectric micro-electromechanical systems. This article presents a scanning interferometric technique for piezoelectric characterization of lead zirconate titanate (PZT) thin/thick film on silicon substrate. This technique is established using a newly developed scanning Mach-Zehnder interferometer with ultra-high resolution. The apparent longitudinal piezoelectric coefficients of both sol–gel derived PZT thin films and hybrid PZT thick films are measured using the scanning technique. The roles of several film processing factors on the piezoelectric properties of the resultant films are also discussed.
Piezoelectric thick films (up to 10 μm thick) and piezoelectric micromachined ultrasonic transducer (pMUT) have been successfully demonstrated at low temperatures of 650 °C using a composite thick film processing route. Submicron-sized PZT powder was dispersed into sol–gel solution to form homogeneous slurry for spin-coating on silicon substrate. Issues associated with recipe of the slurry, deposition process and sintering of films have been summarized with a view to optimizing the properties of the films and pMUTs. Typical microstructure, ferroelectric and piezoelectric properties of the composite films are given. Thermal stability of bottom electrode, a key issue about device fabrication, has also been investigated. The ultrasound-radiating performance of the pMUT element in response to a continuous alternating current driving voltage has been reported. The generated sound pressure level is 116.8 dB at 76.3 kHz at a measuring distance of 12 mm. The pMUT is suitable for application of airborne object recognition.
A scanning-modulated interferometer has been designed to measure the effective d33 coefficient of piezoelectric film by monitoring the modality of surface vibration of an active electrode area together with its passive surroundings in response to the applied ac voltage. By introducing a slow modulation to an ordinary interferometer, accurate measurement of the maximum intensity change corresponding to the small vibration at the most sensitive quarter-wavelength point can be achieved by measuring the envelope amplitude of the modulated vibration signal. The environment disturbance can only affect the position at which the envelope peak occurs but cannot change its amplitude value. Therefore, very reliable measurement results can be achieved. The modulation technique enables the simultaneous measurement of the vibration signal Vout and the reference signal Vp–p, thus a real time calibration can be realized. Since the small displacement is proportional to the ratio of Vout and Vp–p, the testing result is neither susceptible to the roughness or reflectance change of the sample surface, nor to the instability of the laser intensity. Taking this advantage, it is possible to realize automatic scanning of the sample surface for measuring the vibration modality, while maintaining the measurement accuracy. The d33 value of piezoelectric thick films made by composite coating processing was characterized by using this scanning-modulated interferometer. Typically, films with thicknesses ranging from 3 to 7 μm have effective d33 value of more than 100 pm/V.
A pneumatic pressure rig was designed to measure the effective d33 coefficient of thin film piezoelectrics by applying a known stress and monitoring the induced charge. It was found that the stress state imposed included components both perpendicular and parallel to the film plane. The later were due to friction and could largely be relieved through sliding of the O-rings to their equilibrium positions for a given pressure. The induced charge stabilized as equilibrium was reached and most of it was produced by the normal component of the stress. By minimizing the surface friction and compensating for the remnant in-plane stress, very good agreement was obtained among the d33 values measured by the Berlincourt method, double-beam interferometry and this method for a bulk lead zirconate titanate (PZT) sample. The d33 value of PZT thin films made by sol-gel processing was also measured. The as deposited films usually showed very weak piezoelectricity with d33 values ranging from 0 to 10 pC/N, indicating little pre-existing alignment of the domains. With increasing poling field, the d33 value also increased and saturated at poling fields exceeding three times the coercive field. Typically, films with thicknesses around 1 mum had d33 values of 100 pC/N. Good agreement between double-beam interferometry and this technique was also obtained for thin films. The small difference between the two measurements is attributed to the effect of mechanical boundary conditions on the effective d33 coefficient.
An atomic force microscope (AFM) is used to measure the magnitude of the effective longitudinal piezoelectric constant (d33) of thin films. Measurements are performed with a conducting diamond AFM tip in contact with a top electrode. The interaction between the tip and electric field present is a potentially large source of error that is eliminated through the use of this configuration and the conducting diamond tips. Measurements yielded reasonable piezoelectric constants of X-cut single-crystal quartz, thin film ZnO, and nonpiezoelectric SiO2 thin films. © 1998 American Institute of Physics.
In this paper we analyse the main characteristics of some micro-devices which have been developed recently for biomedical applications. Among the many biomedical micro-systems proposed in the literature or already on the market, we have selected a few which, in our opinion, represent particularly well the technical problems to be solved, the research topics to be addressed and the opportunities offered by micro-system technology (MST) in the biomedical field. For this review we have identified four important areas of application of micro-systems in medicine and biology: (1) diagnostics; (2) drug delivery; (3) neural prosthetics and tissue engineering; and (4) minimally invasive surgery. We conclude that MST has the potential to play a major role in the development of new medical instrumentation and to have a considerable industrial impact in this field.
Soft materials are finding applications in areas ranging from microfluidic device technology to nanofabrication. We review recent work in these areas, discuss the motivation for device fabrication with soft materials, and describe applications of soft materials. In particular, we discuss active microfluidic devices for cell sorting and biochemical assays, replication-molded optics with subdiffraction limit features, and nanometer-scale resonators and wires formed from single-molecule DNA templates as examples of how the special properties of soft materials address outstanding problems in device fabrication.
Interferometric measurements of electric field‐induced displacements in piezoelectric thin films using single‐beam and double‐beam optical detection schemes are reported. It is shown that vibrational response measured with a single‐beam interferometer includes a large contribution of the bending motion of substrate. Therefore, it is difficult to apply single‐beam technique for piezoelectric measurements in thin films. To suppress the bending effect a high‐resolution double‐beam interferometer is proposed. The sensitivity of the interferometer is significantly improved in comparison with previously reported system. The interferometer is shown to resolve small displacements without using a lock‐in technique. An example of the interferometric capabilities is demonstrated with experimental results on electric field, frequency, and time dependences of piezoelectric response for quartz and Pb(Zr,Ti)O 3 thin film. © 1996 American Institute of Physics.
In this paper, we report the development of a simple but precise piezoelectric spectrometer using a Michelson–Morley interferometer. The measurement system has been developed to study the frequency and temperature dependence of the complex piezoelectric and electrostriction coefficients of ferroelectric materials. The spectral data are collected by computer and has significantly wider frequency range and lower noise than other such systems. Results are reported for a quartz sample, a La‐modified lead zirconate titanate ferroelectric, and a lead zirconate titanate sol‐gel derived ferroelectric thin film. © 1995 American Institute of Physics.
A double beam laser interferometer is built up to study high‐frequency piezoelectric and electrostrictive strains. The system is capable of resolving a displacement of 10-2 Å using lock‐in detection and measuring the strain all the way to the piezoelectric resonance frequencies using a digital oscilloscope for detection. The interference of sample bending to the detected signal is effectively avoided.
An accelerometer fabricated by a combination of screen printing and
silicon micromachining is reported. This is the first device of its kind
fabricated in this manner. Details of the finite element model (FEM) of the
sensor and its method of fabrication are described. Initial results indicate a
sensitivity of 16 pC g-1, which compares very favourably with
a sensitivity of 0.15 pC g-1 reported for thin-film devices.
Experimental results show a good level of agreement with the FEM results.
Analysis of the results highlight the need to further improve the mechanical
properties and consistency of the thick-film PZT layer.