Weiguang Zhu

Nanyang Technological University | ntu · School of Electrical and Electronic Engineering

In this work, the influence of annealing temperature on the ferroelectric electron emission behaviors of 1.3-μm-thick sol–gel PbZr0.52Ti0.48O3 (PZT) thin film emitters was investigated. The results revealed that the PZT films were crack-free in perovskite structure with columnar-like grains. Increasing annealing temperature led to the growth of the...

The coupling between dielectric polarization and strain gradient, known as flexoelectricity, becomes significantly large on the micro- and nanoscale. Here, it is shown that giant flexoelectric polarization can reverse remnant ferroelectric polarization in a bent Pb(Zr0.52Ti0.48)O3 (PZT) diaphragm fabricated by micromachining. The polarization induc...

Hybridized sol–gel processing has been adopted to fabricate magnetic CoFe2O4 composite thick films onto Pt/Ti/SiO2/Si substrate by the spin coating technique. The process includes the chemical synthesis of CoFe2O4 sol–gel solution, the modified CoFe2O4 particles via high-energy ball milling, and the synthesis of uniform CoFe2O4 hybrid slurry. Therm...

CoFe2O4–Pb(Zr0.53Ti0.47)O3 (CFO–PZT) multiferroic composite thick films sandwiched by PZT composite films were prepared by sol–gel processing and spin-coating technique. It is shown that although the deeply buried CoFe2O4 spinel ferrite phase could not be detected in X-ray diffraction patterns, the stable magnetic properties of films confirm its ex...

The aging effect of a 0.2 mol % Fe-doped 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 single crystal was investigated. The authors found that aging induced a double ferroelectric hysteresis loop and a giant recoverable electrostrain of 0.8% at an electric field of 1.2 kV/mm in the ⟨001⟩-oriented tetragonal crystal. This result is much higher than the strains ob...

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 a...

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. I...

The X-ray diffraction and transmission electron microscope results show that nanosized-SrTi_1plusmnxO_3-delta material series (27 nm) with perovskite structure can be synthesized using the high-energy ball milling technique. The thick-film screen-printed nanosized-SrTi_1plusmnxO_3-delta-based sensor series wi...

Metallo-organic decomposition derived dielectric thin films of calcium zirconate doped with various concentrations of strontium ((Ca, Sr)ZrO3) were prepared on Pt coated silicon substrate. Mainly in this paper, we present the investigations of their structural developments and present their electric and dielectric properties as well. The structural...

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO2/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600°C, PtTi3+PtTi and PtTi are the reaction products from interfacial...

Nanoscaled (Ba2/3Sr1/3)Ti1 + x O3 powders have been prepared by sol-gel technique. Their phase evolution and densification behaviors have been studied by differential thermal analysis (DTA) and high temperature dilatometer, respectively. It is found the addition of 2 mol%-excess amount of TiO2 lowers the activation energy required for the formation...

Nitrogen doped SrTiO3 (STO) thin films have been fabricated on Si field emitter arrays (FEAs) using reactive RF magnetron sputtering in Ar-N2 mixture ambient for electron emission applications. The nitrogen incorporation in STO films was revealed both in Fourier transform infrared (FTIR) spectroscopy and in Auger electron spectroscopy (AES). Low do...

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 measur...

This paper presents both theoretical and numerical analyses of the piezoelectric and dielectric responses of a highly idealized film-on-substrate system, namely, a polarized ferroelectric film perfectly bonded to an elastic silicon substrate. It shows that both effective dielectric and piezoelectric properties of the films change with the size and...

Ferroelectric microelectromechanical systems (MEMS) has been a growing area of research in past decades, in which ferroelectric films are combined with silicon technology for a variety of applications, such as piezo-electric micromachined ultrasonic transducers (pMUTs), which represent a new approach to ultrasound detection and generation. For ultr...

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 subst...

Nano-sized SrTiO₃-based oxygen sensors were fabricated from synthesized SrTiO₃ and commercial SrTiO₃ using the high-energy ball milling and the thick-film screen-printing techniques. The particle sizes, microstructural properties, oxygen-sensing properties, and humidity effects of the synthesized nano-sized SrTiO<su...

Lead zirconate titanate (PZT) thick films with thickness up to 20 μm with relatively good property have been deposited on silicon wafers using a modified sol–gel slurry process. Submicrosized or nanosized PZT powder was dispersed into regular PZT sol–gel solutions to prepare the composite film. Ultrasonic arrays have been fabricated with 7 μm PZT t...

Composite PZT films with thickness of 3 to 10 μm had been successfully integrated on platinum-coated silicon wafer using a composite process. In this sol–gel based process, submicron-sized PZT powder was uniformly dispersed into a xerogel precursor solution to obtain a suspension/slurry for spin-coating purpose. The properties of the resultant film...

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...

Lead zirconate titanate (PZT) piezoelectric thin films have been prepared by sol-gel method to fabricate microcantilever arrays for nano-actuation with potential applications in the hard disk drives. In order to solve the silicon over-etching problem, which leads to a low production yield in the microcantilever fabrication process, a new fabricatio...

Time evolution of concentration profiles leading to steady-state demixing in oxides under oxygen partial pressure gradient is treated based on a microscopic model by applying the path probability method of irreversible statistical mechanics. The redistribution of vacancies and cations toward the steady-state distribution has essentially been reduce...

Lead titanate and lead zirconate titanate grains were grown in situfrom lead-titanium-boron-silicon and lead-zirconium-titanium-boron-silicon gels prepared via the sol-gel method. The lead zirconate titanate grains were much smaller and more uniform than lead titanate grains grown from gels of similar composition. The crystallization mechanisms of...

This letter reports on a membrane-type piezoelectric micromachined ultrasonic transducer (pMUT). It consists of 3.5 or 7 μm thick composite lead zirconate titanate (PZT) film on a multilayered membrane and works as an ultrasonic transmitter. The ultrasound-radiating performance of the transmitter, in response to a continuous ac driving voltage, has...

This paper presents two-dimensional membrane-type ultrasonic transducer arrays based on thick piezoelectric film and micromachining. The transducer array can be used to generate ultrasound in air or water. Individual array element consists of a thick piezoelectric film and a periphery clamped rectangular membrane. The vibrating membranes, which are...

A hybrid sol–gel process technology has been developed for the fabrication of thick films of lead zirconate titanate (PZT) thick films. In this paper, submicron-sized PZT powder was dispersed into a 2-methoxyethanol (MOE) diluted PZT sol solution uniformly to obtain a suspension/slurry for spin-coating purpose. Thick films on platinized silicon sub...

Ferroelectric Pb(Zr0.3Ti0.7)O3/PbTiO3 multilayer thin films are fabricated by the sol–gel method. The properties of PZT/PT multilayer thin films with different PZT and PT layers stacking structures have been systematically studied. All the films are dense and smooth with single perovskite phase. “Pinched” ferroelectric hysteresis loops are found fo...

BaTiO3 glass-ceramic thin films were deposited on silicon substrates by the sol–gel method. The films exhibited a mixed structure of glass phase and BaTiO3 grains tens of nanometers in diameter, and had a high dielectric constant, low leakage current, and dielectric loss. An interesting self-mending phenomenon for microcracks due to the fluidity of...

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 ar...

A new application using barium strontium titanate (BST) thin films to fabricate the Pd/BST/Pt heterostructure for hydrogen gas detection has been investigated. To further understand the mechanism of this novel hydrogen sensing properties, impedance spectroscopy of the Pd/BST/Pt has been systematically studied and interpreted satisfactorily based on...

This paper investigates dynamic behavior of multilayered piezoelectric diaphragms that are simplified as laminated plates. The validity of the dynamic analysis based on the simplified clamped multilayered plate model has first been studied using ANSYS finite element (FE)-codes. The simplified, clamped, multilayered plate model has been verified to...

Perovskite CaZrO3 gate dielectric thin films were prepared by the sol-gel wet chemical technology, followed by post annealing in O2 ambient at different temperatures from 550 to 700 °C. Based on our best knowledge, it is the first time in the literature to successfully prepare the CaZrO3 thin films using wet chemical deposition methods, including s...

A noble type of oxygen-sensitive and electrical-conductive material, ZrO₂-based with α-Fe₂O₃ thick-film gas sensor, was investigated for low operating temperature. Amorphous-like solid solutions of xα-Fe₂O₃-(1-x)ZrO₂ powders were derived using the high-energy ball milling technique,...

We report in this paper our success in preparation of dielectric SrZrO 3 thin films on Pt/Ti/SiO 2 /Si substrates using wet chemical metallo-organic decomposition (MOD) technique and systematic characterizations in their structural development, optical band gap, and dielectric properties. The results of UV optical reflection spectroscopic measureme...

Dense, crack-free piezoelectric thick film integrated on silicon substrate has been the subject of considerable attention in recent years for potential application in microelectro mechanical systems (MEMS). We have proposed a new spin-coating route for this purpose in which films are made from homogenous slurry of sol-gel precursor and nano-sized p...

Metal–organic decomposition-derived SrZrO3 dielectric thin films were investigated using differential thermal analysis, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared reflectivity spectroscopy and atomic force microscopy to study the mechanism of phase transformation and crystallinity, and were characterized by electric a...

The thermal decomposition process of barium strontium titanate (BST) xerogel precursors has been analyzed using thermogravimetric analysis, Differential thermal analysis and X-ray diffraction. The results indicate that the precursors are amorphous in nature when annealed below 520 °C, and perovskite BST grains crystallize at 620 °C via a solid-stat...

Strontium zirconate (SrZrO3) oxide thin films on Pt/Ti/SiO2/Si substrate were prepared by the metal-organic decomposition wet chemical technology followed by post-annealing at different temperatures in flowing oxygen atmosphere. Strontium acetate Sr(CH3COO)(2) and zirconium (IV) acetylacetonate [CH3COCH=C(O-)CH3](4)Zr were chosen as precursors, sep...

Pyroelectric infrared detectors using sol–gel deposited lead zirconate titanate (PZT) thin films were fabricated. It was found that specific detectivity D* of the detector is a strong function of the modulation frequency of the incident radiation. Noise plays an important role at low frequencies (<20 Hz). When the modulation frequency is low (<10 H...

Dielectric thin films of strontium zirconate doped with 5 mol% calcium were prepared on Pt/Ti/SiO₂/Si substrate by the metallo-organic decomposition (MOD) wet chemical technology followed by annealing at different temperatures in flowing oxygen atmosphere. Those prepared Sr_0.95Ca_0.05ZrO₃ thin films were i...

In order to solve the over etching problem which leads to low production yield in the microcantilever process, a new fabrication process by using DRIE etching of silicon from the front side of the silicon wafer has been developed. Silicon free membrane microcantilever with Lead Zirconate Titanate (PZT) thin films 1 to 2 μm in thickness have been su...

Dispersing fine particles into a sol-gel matrix is a promising process to get a thick 0-3 composite coating layer. In this paper, we have further improved this modified sol-gel process by nanocrystalline composite technique to realize the low temperature annealing. Dense Pb(Zr, Ti)O3 (PZT) thick films of 10 to 50 mum in thickness have been obtained...

A design concept for multilayer piezoelectric microactuator using piezoelectric coefficient d31 was particularly stressed. Accordingly, two kinds of novel piezoelectric multilayer microactuators, called a split-morph and an annular split-morph, have been proposed and discussed for the dual stage actuation systems in high track density hard disk dri...

The effect of silicon substrate thickness on the performance of thin film PZT pyroelectric detectors is theoretically and experimentally investigated. As the silicon substrate thickness increases, the pyroelectric current responsivity drastically decreases. The current responsivity of a pyroelectric thin film detector with no silicon substrate is a...

Crack-free Pb(Zr,Ti)O3 films up to 20 μm thick have been prepared on the Pt/Ti/SiO2/Si substrate using a novel sol–gel route. In this route, surface-modified fine PZT crystalline particles are well dispersed in a sol–gel precursor solution to form uniform slurry. The slurry is then spin-coated onto a substrate, pre-heated and annealed at relatively...

BaTiB glass–ceramic thin films with a substantial number of perovskite barium titanate (BaTiO3) grains were deposited on Pt-coated silicon substrates by sol–gel processing. The prepared films exhibited a mixed structure of glass phase and BaTiO3 grains tens of nanometers in diameter. A self-mending phenomenon for microcracks was observed in the f...

In this paper, we present direct observations of local domain switching in the individual grains of 300nm thick sol–gel PbTiO3 thin films using a piezo-response SPM. It is revealed that almost no domain switching occurs in the c-domain region at 4V, and partially switching takes place at 6V. The switched domain expends the whole grain rapidly by fu...

Pyroelectric (PZT30/70) thin film IR detectors has been fabricated and characterised. The PZT30/70 thin film was deposited onto substrate by the sol-gel process. Four different substrate conditions were studied for their effects on the pyroelectric responses of the IR detectors. The substrate conditions were the combinations of the Si etching and t...

A sol-gel based 0-3 ceramic-ceramic composite processing has been applied to fabricate lead zirconate titanate thick films with a composition near the morphotropic phase boundary, PZT53/47. In order to eliminate the effects of humidity on the stability of the sols, solid PZT precursors are prepared from partially stabilized titanium isopropoxide, l...

A Flip-Chip Transfer (FCT) method is being developed to integrate the ferroelectric thin film with read-out integrated circuit (ROIC), in which, the performance of the ferroelectric thin film is optimized separately with IC integration. Interconnection and mechanical bonding between the ferroelectric thin film and the signal processing circuit will...

Two kinds of novel piezoelectric multilayer microactuators, called a split-morph and an annular split-morph, have been proposed and discussed for the secondary stage microactuators of the dual stage actuation systems for high track density hard disk drives. The novel piezoelectric multilayer micro-actuators possess a useful compromise performance t...

We report results on ferroelectric domain and domain-wall observation in sol–gel PbTiO3 thin films using scanning probe microscopy. By taking the phase and amplitude image of the local domain piezovibration separately, more information is given to interpret the domain contrast owing to the a domain and different crystallographic orientations. Parti...

Micromachining processes have been extensively adapted in developing uncooled infrared imaging array. One of the most important sensing materials in the array is ferroelectric thin film. To integrate the ferroelectric thin film with the signal processing circuitry, an IC compatible process has to be applied. Various methods have been successfully u...

A novel annular rotary piezoelectric microactuator has been proposed for a dual-stage actuation system for future high track density hard disk drives. The microactuator is designed to be mounted on a flexure tongue and drives a slider directly to perform high-frequency track following. The configuration and operation of the microactuator are descri...

Pyroelectric Pb(Zr0.3Ti0.7)O3 thin film IR detectors were successfully fabricated and systematically characterised. The Pb(Zr0.3Ti0.7)O3 thin film was deposited onto Pt/Ti/Si3N4/SiO2/Si substrate by the sol–gel process. Four different substrate processing alternatives were studied for their effects on the pyroelectric responses of the IR detectors....

A novel multilayer split-morph actuator has been designed and fabricated using the thick film screen-printing technology. Deflection characteristics of the split-morph actuator have been investigated by theoretical analysis and experimental measurement. The results indicate that the tip displacement is inversely proportional to the thickness of eac...

An asymmetric behavior of P–E response was observed in Ni/Pb1.1(Zr0.3Ti0.7)O3/Pt multilayer thin films where Ni was used as top electrode. This interesting phenomenon was investigated by comparative analysis of the hysteresis loops and dynamic pyroelectric responses. The PZT thin films were prepared under the same conditions but different Ni and Pt...

A novel multilayer in-plane bending piezoelectric actuator, called a multilayer split-morph, was designed and fabricated by thick-film screen-printing technology for a dual-stage head-positioning actuator system in a hard disk drive. The design, operation and theoretical principles have been described. The electromechanical performance of the fabri...

Polarization correlation was found in the alternatively deposited Pb(Zr, Ti)O3 (PZT 30/70) and La doped Pb(Zr, Ti)O3 (PLZT 17/30/70) multilayered thin films prepared by a modified sol-gel process. HRTEM results revealed that the multilayered thin films had their (111)-pre-ferred orientation and crystalline size of 300 nm. Dielectric constants and l...

Pyroelectric infrared (IR) arrays with 2×8 elements were developed using the PbZr0.3Ti0.7O3 (PZT) thin films and multilayered PbZr0.3Ti0.7O3/PbTiO3 (PZT/PT) thin films. At 1 kHz, dielectric constant of 389 and 558, dielectric loss of 0.012 and 0.011 were obtained for the PZT/PT and PZT thin films. The pyroelectric coefficients for the PZT/PT film a...

A two-stage servo system is needed for high density hard disk drive to achieve the extreme precision track following and the piezoelectric micro-actuator has been identified as a potential candidate. In this paper we report a novel designed trapezoidal bending piezoelectric multilayer PZT actuator fabricated using the screen printing technology. Ex...

In this paper, we report our recent success in preparation and fabrication of Si-based pyroelectric thin film micro-IR sensors using micro-machining technology and systematical characterization results. Ferroelectric PT, PZT, PLZT and multilayered PZT/PT, PZT/PLZT thin films have been prepared on the Pt coated silicon water using a modified sol-gel...

Preferred c-axis orientated Pb1.1(Zr0.3Ti0.7)O3 (PZT30/70) thin films were prepared on the Pt-coated silicon wafer using a sol–gel solid precursor approach. In this modified sol–gel process, the Ti-isopropoxide was chelated with acetylacetone, which makes the sol insensitive to moisture and eliminates the humidity effect on the sol stability. After...

Design and fabrication of a 32 X 32 uncooled IR focal plane array based on Si micromachining technique is presented. Ferroelectric lead zirconate titanate (PZT) thin film was used as the sensing material in the array. The PZT thin film was deposited on the top of Si substrate coated with silicon dioxide, silicon nitrite, titanium and platinum. Sol-...

A self-biased dielectric bolometer has been realized by epitaxially grown lead zirconate titanate Pb1.1(Zr0.3Ti0.7)O3 (PZT 30/70) and lanthanum-doped lead zirconate titanate Pb0.83La0.17(Zr0.3Ti0.7)0.9575O3 (PLZT 17/30/70) multilayered thin films using the sol-gel technique. The high-resolution transmission electron microscopy images and electron d...

To develop a high performance pyroelectric infrared (IR) detector, Pb1.1(Zr0.3Ti0.7)O3/PbTiO3 (PZT/PT) multilayer thin films were deposited onto the top of a Pt/Ti/Si3N4/SiO2 membrane by a modified sol-gel process. For the comparison purpose, Pb1.1(Zr0.3Ti0.7)O3 (PZT) thin films were also prepared with the identical method under same conditions. X-...

A solid precursor was used to prepare ferroelectric lead zirconate titanate (PZT) 30/70 thin films using the sol–gel deposition method. To apply PZT thin films for uncooled pyroelectric IR sensors, a Ni layer was deposited onto the PZT thin films, serving both as a selective absorption layer and as the top electrode. The absorption properties of su...

A new bending mode multimorph actuator was designed and fabricated successfully by a multiple screen printing process. Unlike the conventional bimorph actuator in which the bend occurs in the thickness direction, the bend in the multimorph actuator occurs in the widthwise direction because of synchronistical deformation of each single monolithic la...

A unique piezoelectric multilayer thick film actuator for computer hard disk drives has been designed and fabricated using the screen printing technology. Dielectric and piezoelectric properties of such PZT thick film actuators with grain sizes ranging from 0.8 to 3.0 μm have been investigated. Under an applied electric voltage of 6V. displacement...

Nano-sized PbTiO3 powders have been successfully synthesized using the high energy ball milling technique. The materials used are PbO and TiO2 Anatase and Rutile powders. The powders milled for different hours are characterized using XRD and TEM. Experimental results show that the single perovskite phase of PbTiO3 can be readily formed by the high...

A novel structure for multilayer piezoelectric PZT actuator combining the merits of high displacement/voltage sensitivity, high resonance frequency and low cost is designed. The screen printing technology is adopted to fabricate this newly designed actuator successfully. Such an actuator comprises alternatively a plurality of PZT layers and a plura...

Low-voltage multilayer piezoelectric lead zirconate titanate (PZT) based thick-film displacement actuators were fabricated on Al2O3 ceramic substrate using a multiple screen-printing process. High isostatic pressure was applied on the multilayer green film before firing to increase the material density and the bonding strength between electrode lay...

The sol-gel process is used to prepare BaTiO₃ based Ba-Ti-B ferroelectric glass-ceramics, and ferroelectric thick-film capacitors are then fabricated from such sol-gel derived fine powders using the screen-printing technique. The preparation process for these novel capacitors are described and the structure and dielectric properties of t...

Homogeneous Ba–Ti–B–Si, Ba–Ti–Al–Si and Ba–Ti–B gels have been successfully prepared by the sol–gel process. A novel method is presented for fabricating barium titanate glass-ceramics by sintering the gel powders with small barium titanate crystallites. The structural development, grain size, crystallization process and dielectric properties were s...

Ferroelectric BaTiO3 based Ba-Ti-Al-Si glass-ceramics were successfully fabricated by the chemical sol-gel technique. The structural features: dielectric and ferroelectric properties, such as dielectric constant and loss, leakage current and ferroelectric hysteresis loop, were characterized using X-ray diffraction (XRD), Raman spectroscopy: scannin...

Several ABO3 perovskite ferroelectric crystals, PbTiO3, Pb(Zr, Ti)O3, and BaTiO3 have been in situ grown from amorphous gels with glass elements, and the structural evolution has been systematically investigated using x-ray diffraction (XRD), infrared spectra (IR), differential thermal analysis (DTA), thermogravimetric analysis (TGA), and dielectri...

Pb-Ti-B, Pb-Ti-Si, Pb-Ti-B-Si, and Pb-Ti-Al-Si gels with high Pb and Ti content have been successfully prepared using the sol-gel technique, and lead titanate crystallites have been obtained in these gel-derived glass—ceramic systems through the in-situ growth process. The growth process, structural development and surface morphology of these glass...

In this paper, we report our experimental results of lead zirconate titanate (PZT) thick-films prepared from the sol-gel derived nanocomposites. Transparent Pb-Zr-Ti-B-Si gels were synthesized from various metal organic precursors. PZT grains with the size of one hundred nanometers were homogeneously grown from the gels in the annealing process. Th...

In this thesis, solid solution of mixed zirconium oxide and iron oxide for the application of gas sensing are studied. In this study on semiconductor oxide based gas sensors, the high-energy ball milling technique was used to prepare the nano-sized powders. RG 65/98