Zhihong Wang

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

About

90
Publications
12,412
Reads
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2,008
Citations
Additional affiliations
June 2009 - present
King Abdullah University of Science and Technology
Position
  • Senior Researcher

Publications

Publications (90)
Article
Full-text available
The fields of photovoltaics, photodetection and light emission have seen tremendous activity in recent years with the advent of hybrid organic-inorganic perovskites. Yet, there have been far fewer reports of perovskite-based field-effect transistors. The lateral and interfacial transport requirements of transistors make them particularly vulnerable...
Article
Full-text available
Persistent photoconductivity (PPC) is an intriguing physical phenomenon, where electric conduction is retained after the termination of electromagnetic radiation, which makes it appealing for applications in a wide range of optoelectronic devices. So far, PPC has been observed in bulk materials and thin-film structures, where the current flows in t...
Article
Surface-enhanced Raman scattering (SERS) is ubiquitous in chemical and biochemical sensing, imaging and identification. Maximizing the SERS enhancement is a continuous effort focused on the design of appropriate SERS substrates. Here we show that a significant improvement in a SERS signal can be achieved with substrates combining localized surface...
Article
Full-text available
Plasmonic metamaterial absorbers (PMAs) have attracted considerable attention for developing various sensing devices. In this work, we design, fabricate and characterize PMAs of different geometrical shapes operating in mid-infrared frequencies, and explore the applications of the PMAs as sensor for thin films. The PMAs, consisting of metal-insulat...
Article
Full-text available
Ferroelectric tunnel junctions (FTJs) have recently attracted considerable interest as a promising candidate for applications in the next-generation non-volatile memory technology. In this work, using an ultrathin (3 nm) ferroelectric Sm0.1Bi0.9FeO3 layer as the tunnelling barrier and a semiconducting Nb-doped SrTiO3 single crystal as the bottom el...
Data
Supplementary Figures 1-16, Supplementary Table 1 and Supplementary References
Article
The paper demonstrates an energy harvester using a freestanding piezoelectric diaphragm combined with a proof mass. The diaphragm bearing double-sided spiral electrodes makes use of the d33 piezoelectric effect to realize energy scavenging. The harvester was fabricated by using a MEMS technique. The energy converting performance of the diaphragm wa...
Article
Full-text available
We describe a hybrid methodology that combines a two dimensional (2D) monolayer of latex particles (with a pitch size down to 1 μm) prepared by horizontal dry deposition, lift-up of a 2D template onto flat surfaces and evaporation lithography to fabricate metal micro- and nano wire-networks.
Article
We report on the switching dynamics of P(VDF-TrEE) copolymer devices and the realization of additional sub-stable ferroelectric states via modulating the coupling between polarizations and space charges. Space-charge-limited current is revealed to be the dominant leakage mechanism in such organic ferroelectric devices, and the electrostatic interac...
Article
Full-text available
Uni-directional liquid spreading on asymmetric silicone-fabricated nanostructured surfaces has recently been reported. In this work, uniformly deflected polydimethylsiloxane (PDMS) micro-pillars covered with silver films were fabricated. Asymmetric liquid wetting and spreading behaviors in a preferential direction were observed on the slanted micro...
Article
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 d33 mode, which allows the in-plane deformation of the diaphragm to be converted to the out-of-plane deformation and generates an...
Article
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...
Conference Paper
This paper presents the characterization of an energy harvester using a piezoelectric diaphragm as the vibration energy conversion microstructure. The diaphragm containing the spiral electrode operates in the d33 mode. The energy harvesting performance of the diaphragm was characterized. The optimal resistance load and the working frequency were ch...
Article
This paper presents the design of a lead zirconate titanate (PZT) diaphragm actuated by double-sided patterned electrodes. Au/Cr electrodes were deposited on bulk PZT wafers by sputtering while patterned by a lift-off process. SU-8 thick film was used to form the structural layer. Double-spiral electrode induced in-plane poling and piezoelectric el...
Conference Paper
This paper reports on the underwater damping characteristics of a micromachined piezoelectric pressure sensor packaged using liquid crystal polymer (LCP) and polydimethylsiloxane (PDMS). In water, its sensitivity is flat about 6 dB (ref. 1 V/Pa) from 20 to 400 Hz while its bandwidth is 1.2 kHz. In air, its sensitivity is about -33 dB (ref. 1 V/Pa)...
Article
In this paper, a piezoelectric diaphragm-based immunoassay chip was developed to simultaneously detect anti-Hepatitis B virus (HBV) and anti-alpha-fetoprotein (AFP). The chip was fabricated by micro-machining technology and consists of eight individual circular sensors with a diameter of 800μm. Hepatitis B surface antigen (HBsAg), Hepatitis C core...
Article
A CoFe2O4/Pb(Zr0.53Ti0.47)O3 (CFO/PZT) multiferroic composite thick film assisted by polyvinylpyrrolidone (PVP) was prepared by a hybrid sol–gel processing and spin coating technique. Scanning electronic microscopy indicated a porous microstructure with a thickness of 6.2 μm. Pure PZT perovskite phase observed from x-ray diffraction suggested that...
Article
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...
Article
In this study, residual stress influences on the vibrational behavior of piezoelectric circular microdiaphragm-based biosensors are investigated theoretically and experimentally. The piezoelectric microdiaphragm was first fabricated by combining sol–gel PZT thin film and MEMS technology. The stress measurements by the wafer curvature method and the...
Article
CoFe2O4/Pb(Zr0.53Ti0.47)O3 (CFO/PZT) multiferroic composite thick films with different CFO mass fractions have been prepared onto Pt/Ti/SiO2/Si substrate by a hybrid sol–gel process and spin coating technique. Polyvinylpyrrolidone (PVP) was employed to be an assistance to the sol–gel solution for enhancing the film thickness and promising a crack-f...
Article
The acoustic boundary element method is applied to solve the Helmholtz boundary integral equation for the sound field problem in the exterior region. Basing on the acoustic boundary element method, the SYSNOISE software is used to numerically calculate the far field sound pressure in the exterior region of piezoelectric micromachined ultrasound tra...
Article
A rapid synthesis process for local growth of the aligned carbon nanotube (CNT) bundle arrays in a quartz tube operated at room temperature is reported. The CNT bundles of 105 microm in length and 130 microm in diameter were thermally and locally synthesized on the wafer areas where the micro-heaters were integrated on the opposite side. The micro-...
Article
In this paper, a high sensitivity carbon nanotubes (CNTs) enhanced piezoelectric diaphragm-based immunosensor array for detecting anti-goat IgGs is reported. Anti-goat IgGs with 6 different concentrations was successfully detected at the same time. The average diameter of CNTs was characterized by AFM, changing from original 58 nm to 82 nm after ab...
Article
Pb(Zr0.53Ti0.47)O3/CoFe2O4 (PZT/CFO) multiferroic thick films were prepared using hybridized sol–gel processing and followed by systematic characterization investigations. PZT sol–gel solution, PZT and CFO nanopowders were used to fabricate the PZT/CFO thick films on Pt/Ti/SiO2/Si substrate. In this process, sol–gel solution was employed as the buf...
Article
This paper reports on a carbon-nanotube (CNT) enhanced piezoelectric membrane for the possible application as a mass sensitive biosensor. CNT possesses a hollow core and large specific surface area that could be used for bio-molecular binding. A larger number of probe molecules on the surfaces of CNT could capture more target molecules and therefor...
Article
A wafer-scale encapsulated DC-contact RF MEMS switch with a stress-reduced corrugated diaphragm is proposed and developed. The design, fabrication and characterization aspects of the MEMS switch are presented in this paper. The introduction of corrugation is proven to be an effective and easier way to reduce the residual stress in the diaphragm as...
Article
We present an ohmic series radio-frequency microelectromechanical system (RF MEMS) switch based on a moveable corrugated diaphragm that activates switch contact. Corrugation technology is introduced in the SiO(2)/Si(3)N(4) diaphragm for reducing the residual stress in the diaphragm. Moreover, a multilayer metallization system containing ruthenium/g...
Article
Pb(Zr0.53Ti0.47)O3/CoFe2O4 (abbreviated as PZT/CFO) multiferroic composite thick films have been prepared on the Pt/Ti/SiO2/Si substrate by using a hybrid sol–gel process. The thick films were finally annealed at 650 °C in air and the ferromagnetic, ferroelectric and dielectric properties of these films were investigated. Both the PZT pervoskite ph...
Conference Paper
This paper reports a novel microfabricated self-polarized piezoelectric biosensor array for simultaneous detection of 3 different types of antigens. This array consists of 8 individual circular sensors with a diameter of 1 mm and self-polarization because of the stress accumulated in the piezoelectric membrane during the fabrication process. HBsAg,...
Article
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-temper...
Conference Paper
The internal rotations (of dimer models), geometries, energies, vibration spectra, dipole moments and molecular polarizabilities of poly (vinylidene fluoride) (PVDF) of alpha- and beta-chain models were studied with the first principle density functional theory (DFT). Electric properties of PVDF affected by chain lengths were examined. The chain le...
Article
This paper reports a micro-machined piezoelectric membrane-based biosensor array for immunoassay. Goat immunoglobulin G (IgG) and HBsAg were immobilized as the probe molecules on the square piezoelectric membranes of the sensors that have dimensions of 3.5 microm x 500 microm x 500 microm. Due to the mass sensitive nature of these sensors, their re...
Conference Paper
Full-text available
This work presents a novel synthesis process for locally growing carbon nanotubes on specific surface area using micro-machined heaters in a room temperature quartz tube. The temperature difference between the heating area (~600 degC) and the bulk silicon substrate (200 degC) is about 400 degC. Therefore, this process is compatible with on-chip mic...
Article
A two-wafer concept is proposed for the fabrication of silicon microphones with emphasis on deep reactive ion etching and wafer bonding techniques. For miniaturized sensor structures with an air gap of 1-2 microns, the viscous damping effect dominates the dissipation mechanism, which can have an adverse influence on the microphone performance, name...
Conference Paper
In this article, we report a novel method of fabrication of carbon-nanotube (CNT) enhanced piezoelectric membrane based biosensor. The piezoelectric membrane was fabricated by micro-machining technique and CNTs were synthesized on the backside of the membrane using thermal chemical vapor deposition. CNT has extraordinary electrochemical property an...
Article
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...
Conference Paper
This paper presents a mass sensitive biosensor utilizing a flexural vibration mode of a micromachined piezoelectric micro-diaphragm. The mass sensitivity of the diaphragm has been investigated with respect to the vibration modes. Theoretical analysis reveals that, for the same multilayer structure, the mass sensitivity is mainly determined by the m...
Conference Paper
In this paper, through-wafer interconnects using carbon nanotube bundles grown by thermal chemical vapor deposition have been reported. The authors have demonstrated a reliable process of synthesizing aligned carbon nanotube bundles through two bonded silicon wafers. The top wafer (100 mum thick) with patterned through-holes allows carbon nanotubes...
Article
Integrating patterned functional piezoelectric layer onto silicon substrate is a key technique challenge in fabrication of piezoelectric Micro Electro Mechanical System (pMEMS) devices. Different device applications have different requirements on the thickness and in-plane geometry of the piezoelectric layers and thus have their own processing diff...
Article
Spatial distributions of piezoelectric displacement response across the top electrode have been used in this paper to measure the piezoelectric coefficient d33 of films based on the converse piezoelectric effect. The technical details and features of a scanning laser Doppler vibrometer have been summarized and discussed for accurately obtaining the...
Article
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...
Article
In this paper dynamic characterization of a MEMS diaphragm is investigated using lens-less time averaged in-line digital holography. The analysis and capability of the numerically reconstructed amplitude and phase information from in-line time averaged holograms as applied to MEMS vibration are presented. Particularly the effect of mean static stat...
Article
With miniaturization, better performance and inexpensive devices can be realized with coveted features such as improved reliability, faster response time, cost effectiveness and mass production capability. For miniaturized mechanical structures, viscous damping dominates the dissipation mechanism, which can have an adverse effect on both the freque...
Article
Through-wafer interconnects by aligned carbon nanotube for three-dimensional stack integrated chip packaging applications have been reported in this letter. Two silicon wafers are bonded together by tetra-ethyl-ortho-silicate. The top wafer (100 μm thick) with patterned through-holes allows carbon nanotubes to grow vertically from the catalyst laye...
Article
A sol-gel based novel technique is used to fabricate Ba0.67Sr0.33TiO3 (BST) thin films with thickness up to several microns. In this technique, surface-modified fine BST particles are dispersed in a sol-gel precursor solution. The pH value of the precursor solution is modified to achieve high zeta potential for the dispersed powder, hence a very st...
Article
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...
Article
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...
Article
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...
Article
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...
Article
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...
Article
In the vicinity of their resonance frequency, piezoelectric resonators are highly sensitive to small perturbations. The present report is focused on the magnetic field as a perturbation source. Magnetocapacitance modulation of more than 5% is achieved at room temperature on both ferroelectric single crystals and quartz disks. Since such piezoelectr...
Article
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...
Article
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...
Article
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...
Article
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...
Article
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...
Article
Ferroelectric MEMS (microelectromechanical systems) has been a growing area of research in past decades, in which ferroelectric films have been utilized for a variety of applications including microsensors and microactuators. For microactuator applications, thicker PZT films are preferred since generative force of the actuator increases with increa...
Article
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...
Article
In the vicinity of their resonance frequency, piezoelectric resonators are highly sensitive to small perturbations. The present report is focussed on the magnetic field as a perturbation source. First, magneto-dielectric modulation of more than 10% is achieved at room temperature on both ferroelectric single crystals and quartz discs. Since such pi...
Article
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...
Article
The effect of WO3 on mullite formation and mullite whisker morphology, in oxide mixtures activated by a high-energy ball milling process, was investigated. Differential thermal analysis (DTA) measurement indicated that WO3 enhanced the mullite phase formation, with mullitization temperature of 951 °C, 921 °C and 835 °C for the samples doped with 5,...
Article
Full-text available
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...
Article
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...
Article
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...
Article
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...
Article
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...
Article
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...
Article
Nanocrystalline KTiOPO4 powders were prepared through a chemical process. This process involved the hydrolysis of KOOCCH3 · 2H2O, Ti(OC4H9)4, and PO(OR)3 to produce a homogeneous solution. A gel was formed by the partial evaporation of this solution. After the gel was decomposed at 450 °C, white amorphous powder remained. On calcinating up to 550 °...
Article
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...
Article
Lead zirconate titanate (PZT) films are promising for acoustic micro-devices applications because of their extremely high electromechanical coupling coefficients and excellent piezoelectric response. Thicker PZT films are crucial for these acoustic applications. A hybrid sol-gel technology has been developed as a new approach to realize simple and...
Article
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...
Article
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...
Article
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...
Article
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...