We have developed the tactile sensor using the microcantilevers with strain gauge film which can detect normal and shear forces simultaneously. In this work, the tactile sensor and the IC amplifier have been integrated heterogeneously to shorten the wire length by chip-on-chip stacking and reduce the noise in the output voltage. Standard deviation of the noise can be reduced from 27.6 mV to 3.3 mV by heterogeneous integration of the tactile sensor and the IC amplifier using Au wire bonding. By this heterogeneous integration, the device size and wiring numbers can be reduced, and installation of more sensors is allowed on fingertips of the robot. Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC amplifier on the backside of the sensor chip, instead of using Au wires. Although TSV can be fabricated successfully, resistance to sacrificial etching process is problem. As a result, Si3N4 used instead of SiO2 has improved insulation between TSVs.

BiFeO3 (BFO) thin films have been deposited on SrRuO3/SrTiO3 (001) substrate by using ion beam sputtering process. At low oxygen partial pressure of 11 m Pa, rhombohedral and large c/a mixed phase thin film have been obtained in spite of rhombohedral BFO single phase formation at high oxygen partial pressure of 73 mPa. From wide area 2θ-Ψ mappings, diffraction peaks from large c/a phase BFO thin film were obtained with the same extinction rule as those of rhombohedral BFO. Reciprocal space mappings around BFO (003) and BFO (103) spots indicate that lattice parameters of large c/a phase BFO were a = 0.381 nm and c = 0.461 nm (c/a =1.22), respectively. Moreover ferroelectric domain switching could be observed in both of rhombohedral BFO and mixed phase BFO thin films.

In order to apply P(VDF-TeFE) piezoelectric polymer to micro-generator as a membrane, the polymer is deposited on a substrate by spin-coating method. In this process, some changes of properties and quality of the film are caused by a solvent which was used to dissolve the polymer granule. Since a solvent affects the film properties and surface stability, we have carried out the thermal process at a temperature higher than melting point. However, this thermal process due to a temperature higher than Curie point of the polymer causes a falling-off in electrical properties. In this paper, we have studied a method to prevent a falling-off in electric properties of P(VDF-TeFE) film even though the film is annealed at a temperature higher than Curie point.

Ferroelectric Bi1.1Fe0.9Co0.1O3 (BFCO) thin films were prepared on Pt/TiO2/SiO2/Si substrates by chemical solution deposition method using rapid thermal annealing (RTA). The thickness of all BFCO thin films is about 100 nm. Although the BFCO prepared at 545°C has a large value of difference of polarization at zero field, 88 C/cm2, the P-E hysteresis loop of the BFCO thin film prepared at 520°C looks like more saturated and shows 47 C/cm2 of difference of polarization at zero field in the applied electric field of 2 MV/cm. The leakage current of the BFCO film annealed at 520°C, is about 2 × 10-2 A/cm2 at room temperature (RT). Moreover, it is also shown that the saturated possibility of P-E hysteresis loops and in 2 MV/cm their apparent difference of polarization at zero field depend on not only the leakage current but also scanning frequency used to measure BFCO thin films. Accordingly, the P-E hysteresis loops of BFCO thin films prepared from 520°C to 545°C seem to be saturated at high frequency from 10 KHz to 20 KHz when these samples are measured at RT.

We have investigated relationships between leakage current and microstructure or domain structure of BiFeO3 (BFO) thin films, and leakage current mappings of BFO thin films have been performed by current sensitive AFM. 350-nm-thick and 250-nm-thick BFO thin films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) and chemical solution deposition (CSD), respectively. Average grain size of PLD-BFO thin film is about 480 nm, which is the same as the film thickness. From the leakage current mapping at a bias voltage of -16 Vdc, leakage current of the BFO thin film flows through not only grain boundary but also the grain itself. On the other hand, CSD-BFO thin film shows rosette structure and small size grains. From the leakage current mapping at a bias voltage of -10 Vdc, leakage current flows along boundaries of the rosette structures. These results indicate that leakage current of BFO strongly depends on its microstructure.

The tactile sensors for human support robots which can detect both normal stress and shear stress and have human-friendly surface have been proposed. Micro-cantilevers adequately inclined by Cr deflection control layer were fabricated by the surface micromachining on SOI wafer. The cantilevers were covered with the PDMS elastomer for human-friendly surface. When the stress is added to the surface of elastomer, the deformation of cantilevers along with elastomer is detected as piezoresistive layer in the cantilevers. The piezoresistive response of the cantilever is analyzed by FEM calculation. The response of the fabricated tactile sensor to normal stress and shear stress was measured by output from this resistance. The tactile sensor with PDMS elastomer can detect both normal stress and shear stress. On the other hand, it hardly has sensitivity to shear stress of orthogonal direction to the cantilever. It means that the tactile sensor can distinguish the direction of shear stress. The sensitivity of tactile sensor vary widely with cantilever pattern and relation between direction of cantilever and crystallite orientation of Si. It is suggested that the sensitivity of tactile sensor can be improved by using FEM estimation and selective ion implantation.

An Influence of stress of crystal structure of polycrystalline BiFeO3 (BFO) thin film on membrane structure has been investigated. To confirm the stress dependence of the crystal structure, reciprocal space mapping measurement of polycrystalline BFO thin films on Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (625 μm) plate substrate and Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (15 μm) membrane substrate have been performed. These BFO thin films have been prepared by pulsed laser deposition (PLD). The obtained BFO thin films were polycrystalline and mainly oriented to (001) and (110) plane. From reciprocal space mapping measurement, (110) oriented BFO grains on Pt/TiO2/SiO2/Si (15 μm) membrane substrate were expanded perpendicularly to the film plane about 0.15% and compressed in parallel to the film plane about 0.7% comparing to that on Pt/TiO2/SiO2/Si (625 μm) plate substrate. And (001) oriented BFO grains on the Pt/TiO2/SiO2/Si membrane substrate were expanded about 0.20% perpendicularly to the film plane and compressed about 1.3% in parallel to the film plane comparing to that on Pt/TiO2/SiO2/Si (625 μm) plate substrat

Bi-layer-structured mutiferroic Bi5Ti3FeO15 (BTFO15) (m = 4) and natural-superlattice-structured Bi4Ti3O12- Bi5Ti3FeO15 (BIT-BTFO15) (m = 3-4) thin films have been prepared on (001) and (110) oriented SrTiO3 (STO) single crystal substrates by using pulsed laser deposition. X-ray diffraction patterns of these thin films on (00l) STO single crystals shows the obtained thin films were (00l)-oriented layer-perovskite single phase, and BIT-BTFO15 (m = 3-4) natural-superlattice-structure has also obtained. On (110) STO single crystal, layer perovskite (11l) oriented thin films have been also obtained. For characterizing ferroelectric properties, these thin films have been prepared on (001) and (110) oriented La-doped (3.73 wt%) STO single crystal substrates. From ferroelectric D-E hysteresis loops measurements, BTFO15 (m = 4) and BIT-BTFO (m = 3-4) thin films on (110) La-doped STO single crystals shows good ferroelectric hysteresis loops and their double remanent polarizations (2Pr) were 47 μC/cm2 and 44 μC/cm2, respectively. However, these thin films on (001) La-doped STO single crystals do not show ferroelectric characteristics.

We have investigated the effect of Bi-excess surface layers of stoichiometric BiFeO3 thin films prepared by chemical solution deposition. A stoichiometric BiFeO3 thin film with both the Bi-excess top and bottom surface layers shows improved crystallinity with the remanent polarization of 65 μC/cm2 at 80 K, which is larger than BiFeO3 film prepared by the same process using stoichiometric solution. These results are attributed to the reduction of the imperfect crystal at the interface between BiFeO3 film and electrode. Stoichiometric BiFeO3 thin film with Bi-excess top and bottom surface layers also reserves the magnetic property of stoichiometric film. Stoichiometric BiFeO3 thin films with Bi-excess surface layers are an effective way to obtain good multiferroic properties.

A new type of ferroelectric gate field-effect transistor (FET) using ferroelectric-insulator interface conduction has been proposed. Drain current flows along the interface between the ferroelectric and insulator layers and requires no semiconductor. This FET is fabricated by forming of source and drain electrodes on a SiON/Si substrate, dpositing SrBi2Ta2O9(SBT) film, forming topgate electrode, and forming bottom electrode. Drain current versus topgate voltage characteristics show a clockwise hysteresis loop similarly to the conventional metal-ferroelectric-insulator-semiconductor-FET(MFIS-FET). This FET shows that the On/Off ratio of the drain current is 104 to 105 and the Off state current of about 10−9 A.

Multiferroic BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/thick (200 μm) and membrane (15 μm) Si substrate by pulsed laser deposition (PLD) to confirm the influence of stress from substrate. Si membrane was obtained by etching using reactive ion etching (RIE) until thickness is to be 15 μm. The X-ray diffraction peaks of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane substrate slightly shift to lower angles, compared to those on Pt/TiO2/SiO2/Si (200 μm) substrate. Ferroelectric hysteresis loops were also measured at 150 K before and after Si etching by RIE. The BiFeO3 thin film on the Pt/TiO2/SiO2/Si (15 μm) membrane structure shows remanent polarization (Pr) of 95 μC/cm2 for a maximum applied voltage of 18 V, which is larger than Pr = 71 μC/cm2 of BiFeO3 thin film on Pt/TiO2/SiO2/Si (200 μm) substrate at the same measurement conditions. Under magnetic field of 1.1 T, remanent polarization (Pr) of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane structure increased from 95 μC/cm2 to 101 μC/cm2 at 150 K due to stress relaxation of BiFeO3 thin film.

The Cr/Si bilayer cantilevers for an integrated multi-axis tactile sensor were fabricated by Si surface micromachining process. Among the cantilevers with various shapes, the rectangular and semicircular cantilevers can be deflected upward with good controllability. The maximum deflections are compared with those calculated by finite element method. Calculated deflections of Cr/Si cantilever agree considerably with the measured one. So, it is considered that the analysis by finite element method is useful as optimization of layer thickness and size to obtain the Cr/Si bilayer cantilevers with accurate deflection.

Barium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO substrate by combining preparation of initial layer by Pulsed Laser Deposition and main layer by Metal-Organic-Decomposition method. Films with an initial layer of 20, 30 and 40 nm thickness and final thickness of 400, 650 and 800 nm have been obtained. Physical and dielectric properties of the BST thin films have been characterized from the viewpoint of frequency-agile micro and millimeter wave circuit applications. The results reveal that Ba0.6Sr0.4TiO3 thin films have a good crystallinity with characteristic orientation that is affected by the deposition conditions of the initial layer. Interdigital capacitor with a gap of 10 μm has been characterized and the dielectric loss and tunability are as low as 0.002 to 0.004 and 12%, respectively, at frequency of 1 MHz for the applied voltage from -/+40V to +/-40V. At microwave frequencies, classical coplanar waveguide lines formed on BST/(100)MgO were investigated. A differential phase shift of 18 degree was obtained at 20 GHz with insertion loss of about −2 dB at 60 V for Au/Cr interconnection. Finally, a 3-stage LC-ladder-type phase shifter with variable capacitors of BST thin film has been fabricated considering the experimental results obtained for the coplanar waveguide lines and a maximum phase shift of 40 degrees is obtained at 20 GHz at 60 V.

Natural-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 (m =2–3) (BTN–BIT) films have been grown on Pt/TiO2/SiO2/Si substrates at 400 °C to 550 °C by pulsed laser deposition (PLD) using BTN–BIT (1 mol:1 mol) target, and were post-annealed in O2 for 45 minutes at 750 °C. BTN–BIT films prepared above 500 °C have single phase whose c lattice parameter is estimated to 8.300 nm in consideration of periodicity of lattice structures. This lattice constant is very close to the value (8.316 nm) of that of two unit cells of BTN and one unit cell of BIT, that is 2–1 superlattice structure of BTN–BIT. The BTN–BIT film with 2–1 superlattice structure has large remanent polarization (2Pr = 50 μC/cm2) and large coercive field (2Ec= 350 kV/cm). La-doped BTN–BIT thin film has also large remanent polarization (2Pr = 52 μC/cm2) and relatively small coercive field (2Ec= 220 kV/cm). The La-doped BTN–BIT film is fatigue-free on Pt electrodes up to 1010 switching cycles.

Neodymium-modified Bi4Ti3O12(BNdT) thin films have been prepared by pulsed laser deposition (PLD), aiming to realize enhanced ferroelectric properties by a low temperature treatment. When deposited at 500°C, the film shows P-E hysteresis having twice remanent polarization 2Pr of 78.8 μC/cm-2, coercive force Ec of about 250 kV/cm, and leakage current of less than 10-7 A/cm2 from -50 to +50 kV/cm. Good fatigue properties of BNdT films deposited at 5 Hz have been obtained up to 1010 cycles of 500 kHz bipolar square pulses, with less than 25% decrease of +Pr and -Pr.

BiFeO3 thin film has been prepared on Pt/TiO2/SiO2/Si substrate at a temperature as low as 450°C by pulsed-laser deposition. The BiFeO3 thin film is perovskite single-phase, while any nonperovskite phase, such as orthorhombic Bi2Fe4O9, is not included. Dielectric constant of the film is 87, dielectric loss is 0.03, and leakage current density is low. The coexistence of ferroelectricity and ferromagnetism has been confirmed by means of the P-E and M-H hysteresis characteristics. The BiFeO3 thin film shows a well-saturated hysteresis loop with twice the remanent polarization 2Pr = 54 μC/cm2 and coercive field 2Ec = 100 kV/cm for a maximum applied electric field of 100 kV/cm, and also shows a saturated weak ferromagnetic hysteresis loop, as well as a small remanent magnetization with 2Mr = 0.6 emu/cm3 and 2 Hc = 200 Oe for a maximum magnetic field of 10 kOe at room temperature.

Photoelectron spectra by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) have been analyzed to study O2-annealing effects on band diagrams of ferroelectric SrxBiyTa 2O9 (SBT) thin films deposited by pulsed laser deposition (PLD) and metalorganic dcecomposition (MOD) methods. XPS studies on the annealed PLD-SBT film has shown a rapid shift in its Bi 4f core peaks from the oxidized to the metallic ones, as the film suffer Ar+ bombardment. Surface of the annealed film has exhibited lower Fermi level than the as-deposited one in UV-PYS. The result suggests O2-annealing can suppress leakage current through PLD-SBT films. The UV-PYS studies on MOD-SBT have shown almost the intrinsic Fermi levels before and after the additional annealing. The XPS studies have shown that the additional annealing is not effective to improve stabilities of (Bi2O2)2+ layers, once the film is baked and crystallized.

C axis-oriented Bi4Ti3O12–SrBi4Ti4O15 (B IT-SB Ti) intergrowth epitaxial ferroelectric thin films have been grown by pulsed laser deposition (PLD) method on MgO (001) and SrTiO3 (001) substrates. The epitaxial growth of BIT-SBTi intergrowth thin films were confirmed by X-ray diffraction (XRD) θ-2θ scan, pole figure plots and reciprocal space mappings. The c axis lattice constant of the BIT-SBTi intergrowth thin film is very close to that of made up of regular stacking of one-halves of the unit cells of Bi4Ti3O12 (3.296 nm) and SrBi4Ti4O15 (4.189 nm). The annealed BIT-SBTi thin film on Pt/Ti/SiO2/Si substrate shows intergrowth structure, too, and exhibits superior ferroelectricity that the values of 2Pr and 2Ec are 32.0 μC/cm2 and 190 kV/cm, respectively. The annealed BIT-SBTi film shows that the degradation of switching charge after 1×1010 switching cycles was 16.5%. This ferroelectric enhancement is attributed to strain of pseudo-perovskite layers interacting through Bi2O2 layer. The dielectric constant and dielectric loss of the annealed BIT-SBTi film were 433 and 0.037, respectively.

Photoelectron spectra by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) have been analyzed to study O2-annealing effects on band diagrams of ferroelectric SrxBiyTa2O9 (SBT) thin films deposited by pulsed laser deposition (PLD) and metalorganic dcecomposition (MOD) methods. XPS studies on the annealed PLD-SBT film has shown a rapid shift in its Bi 4f core peaks from the oxidized to the metallic ones, as the film suffer Ar+ bombardment. Surface of the annealed film has exhibited lower Fermi level than the as-deposited one in UV-PYS. The result suggests O2-annealing can suppress leakage current through PLD-SBT films. The UV-PYS studies on MOD-SBT have shown almost the intrinsic Fermi levels before and after the additional annealing. The XPS studies have shown that the additional annealing is not effective to improve stabilities of (Bi2O2)2+ layers, once the film is baked and crystallized.

Recently we proposed ferroelectric sodium potassium niobate (Na0.5K0.5NbO3, NKN) thin films to be a candidate for applications in nonvolatile memories and electrically tunable devices [1-5]. In this paper we report on processing and characterization of metal-ferroelectric-insulatorsemiconductor (MFIS) diode structures based on RF-magnetron sputtered NKN films. 0.7 μm thick NKN films have been deposited at 650 °C on the thermally grown 47 nm thick SiO2 layer on Si(001) wafers. Stoichiometric Na0.5K0.5NbO3 ceramic target was sputtered in an O2-Ar atmosphere with a total pressure of 5 mTorr. Grown films were analyzed as deposited as well as after an oxygen annealing at 600 °C for 30 minutes. The NKN films exhibit a strong (001) preferential orientation, which was appreciably improved after the oxygen annealing. A leakage current density of 2.3 nA/cm2 at an electric field of 400 kV/cm, and a memory window of 7.2 V was measured for Au/NKN/SiO2(47nm)/Si(001) diode structures at the programmable voltage of 40 V. I-V measurements were performed in the time domain to distinguish between the relaxation of polarization, “true” leakage current, and the degradation of the resistance in ferroelectric NKN film.