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The vibration amplitude, damping ratio and viscous damping force in capacitive micromachinedultrasonic transducers (CMUTs) with a perforated membrane have been calculated theoretically and compared with the experimental data on its vibration behavior. The electrical bias of the DC and the AC voltages and the operation frequency conditions influence the damping effect because leads to variations in the gap height and the vibration velocity of the membrane. We propose a new estimation method to determine the damping ratio by the decay rate of the vibration amplitudes of the perforated membrane plate are measured using a laser vibrometer at each frequency, and the damping ratios were calculated from those results. The influences of the vibration frequency and the electrostatic force on the damping effect under the various operation conditions have been studied.

Epitaxial BiFeO3(BFO) thin films have been prepared on La-doped (001) SrTiO3substrates (La-STO) by using magnetic-field-assisted pulsed laser deposition. X-ray diffraction patterns of the epitaxial BFO thin films prepared under magnetic fields of 0, 0.1, and 0.4 T show only (00ℓ) diffraction peaks without secondary phases. From the results of reciprocal space mapping for all epitaxial BFO thin films, (003) reflections show splitting spots, and asymmetric spots of (−103) and (103) reflections exhibit a rhombohedral structure. The microstructure of the epitaxial thin films was modified by the strength of magnetic field, and a columnar structure was shown in the film prepared under a high deposition rate for a magnetic field of 0.4 T. The polarization versus electric field hysteresis loops were obtained at room temperature (RT) in all the epitaxial films; in particular, the remanent polarization for the epitaxial film prepared under a magnetic field of 0.1 T was 46 µC/cm2at RT while the current density was reduced in comparison with those of other epitaxial films.

BiFeO3(BFO) thin films with various Bi/Fe ratios have been deposited on SrRuO3/SrTiO3(001) substrates by dual ion beam sputtering. A Bi2O3ceramic disk and an $\alpha$-Fe2O3powder disk were used as targets, and simultaneously sputtered using a dual ion beam. Bi/Fe ratio has been controlled by adjusting the beam current ratio on the Bi2O3- and $\alpha$-Fe2O3-side ion sources. Even a BFO thin film with a Bi/Fe ratio of 0.95 and a smooth surface shows a slightly leaky characteristic. $[\text{Fe$^{2+}$}]/([\text{Fe$^{3+}$}]+[\text{Fe$^{2+}$}])$ ratio has been estimated by Auger electron spectroscopy (AES). From the AES profiles, the $[\text{Fe$^{2+}$}]/([\text{Fe$^{3+}$}]+[\text{Fe$^{2+}$}])$ ratio of the BFO thin film with a Bi/Fe ratio of 0.95 is estimated to be 0.14. It is considered that not only improving surface roughness but also enhancing oxidization is important for reduction in leakage current.

A Tactile sensor system consisting of elements with three microcantilevers embedded in a cylindrical elastomer has been fabricated by micro electromechanical systems (MEMS) technology. These sensor small size ($3 \times 4$ mm2) chips are mounted on a flexible sheet, and thus the fabricated sensor array can be set even on a curved surface. In addition, the spacial distribution of normal and shear forces is obtained when two kinds of objects (an acrylic hemisphere and a brass cylinder) come in contact with the fabricated sensor shifted laterally. The distribution results appropriately reflect the surface shape of the object and give the behavior of the forces vector.

We have fabricated Ge-based p-channel metal--insulator--semiconductor field effect transistor (p-MISFET) devices using a hafnium oxide (HfO2) gate film prepared by photoassisted metal organic chemical vapor deposition (MOCVD). To reduce the interface state of a HfO2/Ge gate stack, we performed a new F2treatment method on a Ge surface. Before the deposition of HfO2insulation thin films on n-type Ge(100), Ge surfaces were treated in fluorine (F2) gas ambient under various conditions. Experimental results show that F is densely distributed at the interface of the HfO2/Ge gate stack with the F2treatment of the HfO2bottom layers. Poorly passivated dangling bonds and oxygen vacancies (V\text{o) near the interface between HfO2and Ge were stabilized by chemically active F. Consequently, the interface state density ($D_{\text{it}}$) of the HfO2/Ge gate stack was reduced and the electrical characteristics of the HfO2/Ge p-MISFETs were improved. Therefore, the new F2treatment method is very useful for fabricating a good HfO2/Ge p-MISFET device.

Deep level transient spectroscopy (DLTS) technique that has some merits such as no assumption of leakage mechanism and characterization of both majority and minority carrier traps is applied for characterization of interface state density to HfO2/Ge gate stack. DLTS and isothermal capacitance transient spectroscopy (ICTS) signals of HfO2/Ge gate stack can be detected, and the results of these measurements show that interface state densities of majority and minority carriers can be reduced by fluorine treatment, and no new traps are created by this treatment. So, fluorine treatment is useful to improve the device performance. Moreover, DLTS and ICTS signals can be simultaneously obtained, and capture cross-section can be estimated by using these results.

Ferroelectric Bi1.1Fe0.9Co0.1O3(BFCO) thin films of 100 nm thickness have been prepared on Pt/TiO2/SiO2/Si substrates by chemical solution deposition (CSD) using iterative rapid thermal annealing (RTA) at 510--560 \mbox{\circC}. A thin film prepared at 520 \mbox{\circC} shows low leakage currents of about $6 \times 10^{-3}$ and $2 \times 10^{-2}$ A/cm2at 80 K and room temperature (RT) at a high electric field of 2 MV/cm, respectively. However, the leakage current is above $10^{-2}$ A/cm2at high applied electric fields from 1 to 2 MV/cm so that $P$--$E$ hysteresis loops of the thin film seem to be unsaturated at RT. As a result, the difference in polarizations at the zero field of the BFCO film prepared at 520 \mbox{\circC} is 150 \mbox{$\mu$}C/cm2at an applied electric field of 3 MV/cm and RT, which is larger than that of 120 \mbox{$\mu$}C/cm2at an applied electric field of 4 MV/cm and 80 K.

In order to apply the P(VDF-TeFE) piezoelectric polymer to the micro-generator based on MEMS technology, we have established a process condition of the film formation. A solvent which is used to cast P(VDF-TeFE) solution is important factor for film formation, and MEK solvent has some problems such as low adhesion for low concentration and drying on a coating process for high concentration. Some problems are suppressed by adding a DMA solvent. However, a DMA solvent affected a molecular structure of the film. A thermal treatment is also an important factor since film stretching cannot be allowed in a spin-coating process. In order to compare the single-solvent solution with the mixed-solvent solution, we have carried out qualitative analysis of the film in formation processes.

The interface traps in HfO2/Ge is reduced by fluorine treatment, and photoreflectance spectroscopy (PRS) which has some merits such as nondestructive and contactless, is applied for characterization of fixed charges distribution to HfO2/Ge gate stack as a new type of measurement method. C-V characteristics show that the sample treated with fluorine before deposition by photo-assisted MOCVD has small hysteresis, and interface states are improved. PRS signal of HfO2/Ge gate stack can be detected, and these measurements show that fixed charges are mainly distributed at interface and reduced by fluorine treatment.

(Ba0.6,Sr0.4)TiO3 thick films have been fabricated on various substrates and their physical and electrical properties were analyzed. The effect of primary powder condition on the quality of the BST fabricated films using aerosol deposition technique has been investigated keeping in mind results shown in the literature for BST films fabricated with classical deposition techniques. Presence of carbonates and TiO2 has been demonstrated by XPS analysis and the leakage current behavior has linked to the presence of TiO2 at the grain boundaries. The films showed good insulating properties, with small leakage densities being on the order of 10-6 A/cm2 for an applied electric field of 150 kV/cm.

The insertion effect of Bi-excess layers on stoichiometric BiFeO3thin films prepared by chemical solution deposition is investigated. A stoichiometric BiFeO3thin film with both the Bi-excess top and bottom surface layers shows improved crystallinity with the remanent polarization of 65 μC/cm2at 80 K, which is larger than for BiFeO3film prepared by the same process using stoichiometric solution. These results are attributed to the reduction of the imperfect crystal at the interface between the BiFeO3film and electrode. By inserting Bi-excess layers, the saturated magnetization of all the films becomes smaller than that of the film using stoichiometric solution. Bi-excess surface layers at the top and bottom interfaces are an effective way to obtain good ferroelectric properties.

Fatigue mechanisms in Pb(Zr,Ti)O 3 thin films prepared by MOCVD and sol-gel are comparatively investigated using a Landau theory-based lattice model with various degradation hypotheses. The correlated analysis of normalized hysteresis parameters offers precise mechanism validation criteria. Fatigue of MOCVD films exhibits transient self-restoring, explained by a crossover from static to dynamical polarization clamping in compact degraded regions.

In this work we have performed a nanoscale characterization of the fresh and fatigued states in Pb(Zr,Ti)O 3 (PZT) films, using piezoelectric displacement hysteresis loops measured simultaneously with the macroscopic polarization hysteresis. A model based on formation of degraded regions in an inhomogeneous ferroelectric lattice has been shown to explain well the fatigue pecularities of PZT films prepared by sol-gel and rf-sputtering, both at nanoscale and macroscale. In light of this model, an original statistical treatment based on a modified cross-correlation technique has been used for quantifying the local-integral relationships. The relevance of local piezoelectric loops for the macroscopic polarization hysteresis has been assessed and the possibility of recovering the latter as a weighted convolution of the former has been shown to depend on the film quality. These results may have implications on the ferroelectric properties scaling towards smaller area cells needed for high-density ferroelectric memories.

A Ba1-xSrxTO3(Bi/Sr=75/25) ferroelectric thin film for detector pixel of uncooled infrared (IR) image sensor was prepared by metalorganic decomposition (MOD) with final annealing at 700 to 800°C. The films electrical characteristics such as temperature dependence of capacitance and insulation are very good from the viewpoints of spatial uniformity and stability against thermal cycling. The MOD film was applied to our proposed dielectric bolometer (DB) mode cf IR detector that has merits in 1) room temperature operation, 2) chopperless, 3) low power dissipation, and 4) high sensitivity. Finally, the DB-mode operation in the detector pixel was confirmed on the integrated device structure, and the resultant voltage sensitivity (Rv) and specific detectivity (D*) were observed to be 0.4 kV/W and 9.8×107 cmHzl/2/W with noise voltage (Vn) of 100 nV, respectively, where the detector size was 200μm2. Excellent output linearity against IR power down to 0.5 mW/cm2 and an IR image from IR source with average power of 6 mW/cm2. were also obtained.

The mechanism of the fatigue in sol-gel derived Pb(Zr,Ti)O3 thin films is investigated using a Landau theory-based lattice model where various degradation hypotheses are implemented. For mechanism validation, a correlated analysis of normalized hysteresis loop parameters is shown to be extremely valuable. The most likely mechanism is the formation of degraded regions gradually spreading across the sample surface, where switching is limited due to a built-in electric field.

BaxSr1-xTiO3 (BST) thin films with perovskite structure have been prepared on /Pt/Ti/SiO2/Si substrate using a combined process of conventional sol-gel process and a hydrothermal treatment. Atomic ratio in the film, Ba/Sr, was controlled by changing the concentration ratio of Ba(OH)2 and Sr(OH)2 of work solution. The BST thin films with polycrystalline structure are obtained on silicon at processing temperature of 140°C. The structure development, stoichiometry, spectroscopic, and dielectric properties of BST thin films have been systematically investigated. X-ray diffraction patterns show that well-developed crystallites with a pure perovskite phase have been formed. The composition of BST thin film derived by sol-gel-hydrothermal treatment depends on the concentration ratio of Ba(OH)2 and Sr(OH)2 of work solution intensively. SEM and AFM results show that the structure of as-treated BST thin film strongly depends on the film thickness.

Retention characteristics of MFIS (metal-ferroelectric-insulator-semiconductor) structures have been investigated theoretically and experimentally. The simulated retention characteristics have indicated that reducing current through the ferroelectric layer is very effective to make the retention time long. In order to reduce the current through the ferroelectric layer, an MFIS with an improved ferroelectric layer and an M-I-FIS (metal-insulator-ferroelectric-insulator-semiconductor) have been investigated theoretically. Both of them have given good retention characteristics. Experimentally, retention characteristics of MFIS have been much improved by annealing, which is considered to suppress the current density in the ferroelectric layer, although those of M-I-FIS have been improved a little.

Barium titanate ceramics having grain sizes between 0.5μm and 20μm were used in a comparative investigation of the ferro-para phase transition, by recording the temperature dependencies of the heat capacity and pyrocharge. The experimental results and the theoretical approach suggest that internal stresses are the main cause of the observed grain size effects

Preferentially (105)-oriented Sr0.7B12.8Ta2O9 thin films on SiO2/n-Si(100) have been prepared by Pulsed Laser Deposition (PLD) at low temperature as low as 350°C, which is the lowest process temperature for growing SrxBiyTa2O9(SBTO) ferroelectric thin films. Insulating properties of the SBTO film have been improved by lowering the process temperature or by increasing Sr/Bi atomic ratio from 0.7/2.8 to 0.7/2.0. After applying the low leakage SBTO films to Metal-Ferroelectric-Insulator-Semiconductor diode structures, it is finally observed that their C-V curves have counterclockwise dielectric hysteresis that indicates the films' ferroelectric hysteresis sufficiently control the Si surface potential. A low temperature process in preparing ferroelectric thin film and Sr-deficient and Bi-excess SBTO thin film by PLD method are very effective and promising for realizing an excellent MFIS FET structure.

Temperature dependencies of the pyrocharge were recorded in view of investigating the ferroelectric-to-paraelectric phase transition in barium titanate ceramics with average grain sizes between 0.5 μm and 20 μm. The transition temperature decreased with decreasing the grain size. The relatively small shift of the Curie temperature detected in these pyrocharge experiments suggests that internal stresses are the main cause of the observed grain size effects.

Highly oriented thin films of La-modified SBN (Sr0.48Ba0.51La0.01Nb2O6:SBLN) have been repeatably prepared on Pt/Ti/SiO2/Si(100) substrate at 600°C and 13 Pa by pulsed laser deposition. The orientation depends on the gas ambient during deposition, such that the ambient N2O gas favors the c-axis orientation while O2 gas favors [311]-orientation. Electrical characterization shows a low leakage current density in these films. Both the films exhibit slim P—E hysteresis loops, while the polarization at the same electric field of the (001)-films is much larger than that of (311)-films. These films also have good fatigue endurance up to 109 switching cycles. Large temperature dependence of P—E hysteresis and dielectric constant have been observed, and show good reproducibility against thermal cycles. In the temperature range from 80°C to 120°C, the average temperature change rate of dielectric constant is about 100 K-1 at 1kHz, suggesting that these SBLN films are adequate for dielectric micro-bolometers.

The grain size and field amplitude dependences of hysteresis loops of barium titanate ceramics have been studied in the framework of Landau theory. The Landau coefficients have been estimated from the hysteresis loops of ceramic samples with different grain sizes and compared with their size dependence predicted by Ishibashi lattice model. The same procedure has been adopted for analyzing the hysteresis loops measured at different electric field amplitudes. A correlation between the size and electric field effects has been proposed by analyzing the values of the Landau coefficients. It is considered that Landau switching occurs in an electric field-dependent confined volume due to the 90° domain walls displacements that are proportional to the applied field. Also another effects were shown to have an important contribution to the electric field dependence of second order Landau coefficient.

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Reflectance and absorption spectra of photo-CVD SiO2films in the vacuum ultraviolet (VUV) light region have been measured. The estimated refractive index, n, and extinction coefficient, k, of the film deposited at 177°C in the 5–25 eV region are close to those of fused quartz. The films deposited at 177 and 280°C extend their absorption tails 0.4 eV more to the low energy region than fused quartz. An absorption peak at about 7.6 eV appears and increases with the deposition-temperature. This peak shows a peculiar deposition-temperature dependence as compared with the absorption peaks in the IR region such as Si-H and Si-OH bondings. The interface state density of MOS diodes made from the films deposited by photo-CVD is extremely low and its minimum value is about 2×1010cm-2eV-1.

A strongly preferential orientation of the (100) or the (110) plane has been obtained in polycrystalline Si films on quartz plates deposited from Si3H8by photo-CVD. The (110) plane is obtained in films deposited below 560°C but it turns to (100) above 575°C. Molecular or atomic species in the gas of the reaction chamber have been measured by mass spectroscopic analysis, and their changes induced by substrate heating and VUV irradiation have been studied. The mechanism of the preferential orientation has been discussed by considering the bonding structure of the crystal plane and decomposed species on the surface.

Bi-layered thin films of PZT(70/30) on BaRuO3 have been prepared on silicon substrate by ArF excimer laser deposition(PLD). BaRuO3 thin film crystallized into perovskite-like structure with (110) orientation and became highly conductive after atmospheric thermal annealing at 700°C for 30 minutes. It was found the subsequent PLD-deposited PZT film can be efficiently transformed to its perovskite structure by rapid thermal processing(RTP) at 700°C for 100sec

Insulating cubic BaTiO3(c-BT) polycrystalline thin films were synthesized on titanium covered silicon substrates using a novel low temperature technique called hydrothermal method. The films were hydrothermally formed by submerging the substrate in a 0.5M Ba(OH)2 aqueous solution sealed inside an autoclave, heating to 160°C with saturated vapor pressure around 0.8MPa and holding for various periods ranging from I to 9 hours. The surface of as-treated samples was dense, smooth pinhole-free with high homogeneity. Scanning electron microscopic (SEM) morphology showed the 6-hour-prepared films were composed of submicrocrystallines with grain size varied from 100 to 300nm in diameter. The films were characterized by X-ray diffraction (XRD), SEM, cross-sectional transmission electron microscopy (XTEM), Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy(RBS) analyses. The experimental results proved that hydrothermal method will become a valuable approach for fabricating perovskite oxide films which is of great significance

A series of technical data for preparing PbTiO3 and La-modified PbTiO3 films by using various deposition methods such as rf sputtering and chemical vapor deposition are described. The resulting thin films show very good ferroelectric, pyroelectric, piezoelectric and electro-optic properties. Infrared sensors using the films show good voltage responsivity, detectivity and fast response, and, in particular, c-axis oriented films have excellent characteristics. The film prepared on Si wafers can be directly combined with active devices such as FET's and bipolar transistors. Sensitivity of the films on Si and MgO substrates has been increased considerably by removing the substrate beneath the sensitive area with chemical etching. Linear and two-dimensional arrays have been developed on some types of the substrates and their basic characteristics have been investigated for improving sensitivity resolution. Infrared imaging has also been tried by using the array sensors.

Infrared absorption in SiO2ultra-thin film has been characterized by the grazing internal reflection (GIR) method, which is a high-sensitivity infrared spectroscopic technique for measuring weak absorption of ultra-thin dielectric film. It is confirmed from theoretical analysis that GIR is very sensitive to measurements of infrared absorption even in nanometer-order-thick SiO2film sandwiched between a metal and semiconductor. The spectral configuration of the Si-O-Si stretching mode in the wavenumber range of 1000 to 1400 cm−1changes drastically by changing the film thickness of 1–100 nm and the incident angle of 20–80°. The experimental spectra agree well with the calculated spectra. The spectral changes are attributed to the fact that optical confinement is subtly changed by the incident angle and the film thickness.

Single-grained ferroelectric Pb(Zr, Ti)O3(PZT) thin films, with thickness varying from 0.1 to 0.7μm, were prepared on Pt-coated silicon substrates by pulsed laser deposition combined with rapid thermal annealing method. The current-voltage characteristics of the Pt/PZT/Pt capacitors, with various thickness of PZT, were measured. Two important turning points in J-V curves, namely flat-band voltage and breakdoiwn voltage according to the totaly minority-carrier injection model, were discussed. The electrical strength of the film was also studied by applying the square test pulses with different pulser duration.

Barium titanate (BaTiO3) thin films with high (111)-orientation were successfully grown on TiO2-covered Si(111) substrate using hydrothermal method, where the TiO2 layer was previously fabricated at room temperature by means of ion-beam-assisted deposition. This processing method provides a simple mild-chemical route for directly producing the analogous crystalline films on different substrates. The BaTiO3 films did not reach the TiO2/Si interface even if the hydrothermal treatment was prolonged to 24 hours. Both Rutherford backscattering and spread-resistance profiling characterizations confirmed the diffusion nature of the formed Ba-TiO3/TiO2/Si system.

The voltage dependence of the high-frequency capacitance of a metal-ferroelectric-insulator-semiconductor (MFIS) structure is analyzed by relating the potential profile to the dielectric hysteresis of the ferroelectric thin film. About one hundredth of the dielectric polarization of ferroelectric ceramic PZT is enough to control the Si surface potential for ferroelectric gate FET memory, and large coercive force is required to obtain enough voltage window. MFIS structures using Bi-layer-structured ferroelectric thin films are also studied from experimental viewpoint. SrBi 2 Ta 2 O 9 and Bi 4 Ti 3 O 12 thin films have been prepared by laser ablation method on both Pt sheet and Si wafers at low temperatures of 400-500°C. SrBi 2 Ta 2 O 9 thin films have a good (105) preferential orientation, and Bi 4 Ti 3 O 12 thin films have (117) and c -axis orientations on these substrates. D-E hystereses are obtained in SrBi 2 Ta 2 O 9 and Bi 4 Ti 3 O 12 thin films prepared on Pt sheet, and are enough to control the Si surface potential. Ferroelectric film-SiO 2 &z.sbnd;Si structures show good C-V hysteresis curves owing to the Si surface potential controlled by the D-E hysteresis.

AbstractFerroelectric SrBi2Ta2O9(SBT) thin films were synthesized on Pt/Ti/SiO2/Si substrates using pulsed laser deposition combined with annealing technique, and structural and electrical properties were investigated. The SBT thin films with fine grain size and well-saturated square hysteresis loop was obtained. The films showed high diffraction peaks of (115) and (008). A dense structure with around 200 nm grain size was observed using the scanning electron microscope (SEM). Good ferroelectric properties were obtained from the films; Pr and ECwere 8.4μC/cm2and 57kV/cm, respectively. No fatigue was observed up to 1010switching cycles. I-V characteristic showed the two peaks at the coercive voltage. It has a 560 pF capacitance and a static dielectric constant of 600 at zero applied voltage from the I-V characteristic. These properties are very attractive for nonvolatile memory application.

AbstractIn this paper, we report the preparation and characteristics of Ca and La doped PbTiO3(PCLT) thin film on Pt/Ti/SiO2/Si substrate by laser ablating a ceramic/metal target. The deposited film is polycrystalline and exhibits good ferroelectric hysteresis loop, low leakage, and good pyroelectric properties. The pyroelectric coefficient of the film is high as 8.81 × 10×8C/cm2K and the effective dielectric constant of the film is about 352. So the figure of merit of the film is high as 0.78 × 10×10Ccm/J, indicating that PCLT is a promising material for pyroelectric application.

Electron emission into vacuum from a thin plate of ferroelectric lead-zirconatetitanate (PZT) ceramic has been observed under the impression of electric field of pulse consisting of a pair of positive and negative voltages. The emission was observed at pressure lower than about 10-1 Torr. The emitted charge increases with increasing the positive and the absolute negative voltages of the pulse and the collector voltage. The minimum absolute value of the negative pulse for electron emission is 30V when the positive voltage is larger than 150V. The maximum peak current density is 70A/cm2. It is considered from the electrode area and thickness dependences of the charge that electrons are emitted not only from the ceramic surface near the electrode edge but also through the thin metal electrode. The emitted charge per one pulse little depends on pulse frequency when it is less than 2kHz, and so the total current density can be enhanced by increasing the frequency. The emission is observed even at temperatures above Curie temperature. It is considered that the emission is induced by abrupt change of dielectric flux as well as the polarization reversal. Cathodoluminescence from phosphors excited by the emitted electrons has been observed.