Sr0. 7Bi2. 3Ta2O9(SBT) films are drawing attention as fatigue-free materials. We prepared an SBT film containing discontinuous crystals in the Bi-layered compound using a misted deposition method. In comparison to films prepared by the spin-on method, leakage current was low and spontaneous polarization is high but saturation performance was low. The low saturation performance seems attributable to the inclusion of discontinuous crystals in the Bi-layered compound, while the low leakage current may be explained by the films smaller, denser particles, which form a film without voids, resulting in higher uniformity. The misted deposition method has advantages of finer grain size and higher uniformity.

The crystallization process of Sr0. 7Bi2. 3Ta2O9 (SBT) ferroelectric thin films with different crystal orientations formed by chemical liquid deposition using an alkoxide precursor was investigated. One film showed strong c-axis orientation (a-type film), while another shows scarcely any c-axis orientation (b-type film). We report that the crystallization process was the same even when crystal orientation differed. Thin films first change from amorphous to fluorite fine grains; the fluorite grains then change to bismuth layer-structure grains. The different orientation of the SBT films is not caused by different crystallization process. Both SBT films with different crystal orientations consist of fine fluorite grains after 650 heat-treatment. Their leakage current density characteristics differ, however. The leakage current density of the a-type film was independent of the electric field, and showed a low value of 10-8 A/cm2. The leakage current density of the b-type film, however, was dependent on the electric field, and increased continuously with the increasing electric field. After 700 heat-treatment, both films consist of large grains with bismuth layer-structure and fine fluorite grains. The matrix of both films contains large grains with bismuth layer-structure that determines the leakage current density characteristics. Since the fluorite grain size after a 700 heat-treatment is the same as that after 650 heat-treatment, nucleation is predominant at the structural phase boundary from amorphous to fluorite. The bismuth layer-structure grains are large and single-crystal grains after both a 700 and 800 heat-treatment. Increased grain size predominates at the structural phase boundary from fluorite to bismuth layer-structure grains. Clearly, ferroelectric SBT films with bismuth layer-structure are crystallized in two steps, each having a different predominant crystal growth mechanism.

We prepared alkoxide solutions to fabricate SrBi2Ta2O9 (SBT) ferroelectric capacitors with IrO2 electrodes. In this process, to minimize excess bismuth, the Sr : Bi : Ta mole ratio was kept at 0. 9 : 2. 1 : 2. 0, i. e. , nearly stoichiometric. Three types of solution - mixed-only (MIX), complexed (COMP), and hydrolyzed (HYD) - were used. The HYD capacitor had low absolute leakage current, 10-7 A/cm2 order, and good saturation properties to 6 V. When voltage was applied to each capacitor at 2 to 6 V, MIX and COMP capacitors showed only partial hysteresis loops due to a high leakage current, reflecting the I-V characteristics. These results are probably due to film density caused by metaloxane network bonding. A fatigue endurance test was conducted using cycling of polarization switching at 6 V using the HYD capacitor with IrO2 electrodes. Slight changes were, however, observed in hysteresis loop configuration, but good hysteresis properties were kept up to 1. 04 1012 cycles. We compared SBT ferroelectric thin films fabricated with Pt electrodes and with IrO2 electrodes. Scarcely any difference due to SBT in the XRD pattern was seen, depending on the substrate material. We found that the use of IrO2 electrodes had the effect of decreasing the crystallization temperature. On Pt and IrO2 electrodes, the two films have surface morphology quite different from that of the rod-like structure wellknown for SBT films prepared using a metal 2-ethylhexanate solution. Their surfaces show a similar morphology with relatively large, closely packed grains. A comparison of the I-V characteristics after reannealing showed that the capacitor with IrO2 electrodes had a higher leakage current than that with Pt electrodes. The leakage current was probably due to the density of the film and interface between the SBT film and electrodes.

Gold on connector contacts is superior in environmental resistance. However, pores existing gold film are source to trigger the corrosion reaction between gold and base metal. For examination of the contacts, it has been popular to apply "Salt Spray Test" and "Sulfur Dioxide Test. " There are some differences of the corrosion products between two tests. Main metal forming the product in Salt Spray is Copper, and main metal in Sulfur Dioxide is Nickel. To investigate the reason, we tried to employ an electro-chemical method. As a result, it was found that there was the difference between the respective galvanic cell combinations generated through pores.

This paper describes a new reduction mechanism of the stress induced leakage current that is induced by step tunneling of electrons through the step tunneling sites. The concept of this mechanism is based on the deactivation of step tunneling sites for thin oxide. It is verified that the deactivation is electrically realized by the injected electrons int the sites. It is because the step tunneling probability of electrons though the deactivated sites is suppressed, since the electron capture cross section of the neutralized deactivation sites becomes extremely low. The deactivation scheme is as follows: (1) The deactivation of tunneling sites can be realized that the tunneling sites trapped holes change to neutralized tunneling sites due to electrons injection. (2) The injected electron can deactivate the activation tunneling sites only under energy level than the energy level of the injected electrons. It is shown that the above reduction phenomenon can be quantifiably with formulation. These results are very important for high reliable thin oxide films and for high performance ULSI.

The use of selective oxidation to fabricate vertical-cavity surface-emitting lasers is described. The nativeoxide impacts the device design in two ways, the first being in the introduction of an intracavity dielectric aperture that laterally confines the mode, and the second in the formation of high contrast dielectric Bragg reflectors to shorten the effective cavity length. To date the more important has been the indexconfinement, with record low threshold currents, threshold voltages, and power conversion efficiencies being reported from several groups. However, future designs will likely also benefit from the reduced diffraction loss for a small mode size that is possible with high contrast native oxide/semiconductor mirrors. We describe some of the most important design issues in obtaining ultralow threshold operation.

Micromachined sensors and actuators applied with electrostatic fields are getting widely developed. At the same time, "electrets," which are dielectrics carrying non-equilibrium permanent space charges or polarization distribution, are in demand because they improve the transducer characteristics. In this paper, we have reported on our successful fabrication of silicon dioxide electrets with extremely superior long-term charge stability by plasma chemical vapor deposition (PCVD). We have also reported on the correlation between the deposition conditions, the long-term charge stability and thermally stimulated current (TSC). Finally, the characterization of the long-term stable electrets will be described and discussed.

We studied the application of precursor solutions that can be fired into oxides to form a protective layer for AC-type Plasma Display Panel (AC-PDP). Our study of alkoxide and metallic soap as MgO precursors revealed that the crystallinity of MgO films depends on the starting substance. Since the electric discharge characteristics of a panel and the lamination effect of the protective layer depend on precursors, it was confirmed that binders having higher crystallinity provide better characteristics. Our study revealed that a compound-oxide film has high crystallinity. The application of a Ba0.6Sr0.4Gd2O4 formation solution to a binder and the application of a Sr0.6Mg0.4Gd2O4 formation solution to a protective layer both are seemed promising We also found that a double-layer film, made by forming a protective layer of fine MgO powder and a Ba0.6Sr0.4Gd2O4 binder, on top of a protective layer made of fine MgO powder and a MgO binder, provides a luminous efficiency 5.3 times higher than that of sputtered MgO film which is one of candidates for the large panel, and the conventional electron beam evaporation is not suitable for the large panel. We further found that a triple-layer protective film made by forming a thin film of Sr0.6Mg0.4Gd2O4 provides low voltages of 1 V in firing voltage (Vf) and 35 V in sustaining voltage (Vs) compared to the double-layer film and provides a luminous efficiency 5.5 times higher than that of sputtered MgO film. A life test revealed the triple-layer film in particular providing a useful life of more than 10,000 hours. From these findings, we concluded that the compound-oxides which is composed of alkaline-earth-metal and rare-earth-element could be applied effectively to a protective layer for AC-PDP.

In order to improve the sensitivity of micromachined sensors applied with electrostatic fields and increase their actuated force of electrostatic micromachined actuators, "electrets," which are dielectrics carrying non equilibrium permanent space charges of polarization distribution, are very important. In this paper, positively corona charged silicon dioxide electrets, which are deposited by Plasma Chemical Vapor Deposition (PCVD) and thermally oxidized, are investigated. Physical studies will be described, in which the charge stability is correlated to Thermally Stimulated Current (TSC) measurements and to Electron Spin Resonance (ESR) analysis. Some intrinsic differences have been observed between materials. The electrets with superior long-term charge stability contain 10,000 times as much E' center (Si3 as the ones with inferior long-term charge stability. Finally, some investigations on the long-term charge storage mechanism of the positively charged silicon dioxide electret will be described.

The data retention characteristics for Flash EEPROM degrade after a large number of write and erase cycles due to the increase of the tunnel oxide leakage current. This paper proposes a new write/erase method which uses a reverse polarity pulse after each erase pulse. By using this method, the leakage current can be suppressed. As a result, the read disturb time after 105cycles write/erase operation is more than 10 times longer in comparison with that of the conventional method. Moreover, using this method, the endurance cycle dependence of the threshold voltage after write and erase operation is also drastically improved.

High-frequency capacitance-voltage (C-V) characteristics of buried-channel MOS capacitors with a structure of subquarter-micron pMOS have been measured and analyzed, emphasizing transient behavior. The C-V characteristics, including transient behavior, of buried-channel MOS capacitors that have a counter-doped p layer at the surface of n substrate are very similar to those of surface-channel MOS capacitors of n substrate if the counter-doped layer is shallow enough to be fully inverted at large positive bias. As gate voltage is decreased, equilibrium capacitance for inversion (accumulation for the counter-doped layer) reaches a minimum value and then slightly increases to saturate, which is peculiar to buried-channel capacitors. The gate voltage for minimum capacitance, which has been used to estimate the threshold voltage, changes dramatically by illumination even in room light. Net doping profiles of n-type dopant can be obtained from pulsed C-V characteristics even for buried-channel capacitors. For MOS capacitors with thinner gate oxide (5 nm), steady-state C-V curve is not an equilibrium one but a deep depletion one at room temperature. This is because holes are drained away by tunneling through the thin gate oxide.

High-performance ULSI devices require ultraclean silicon surfaces, the complete removal of native oxides, and atomic level flatness and stabilization of the cleaned surfaces against molecular contaminants. Dry cleaning techniques are an attractive alternative to conventional wet processing for future ULSI production using cluster chambers or multi-process cham-bers. Organic contaminants, including photoresist polymers, are effectively removed by photo-excited ozone cleaning. We have found photo-excited halogen radicals to be useful for removing trace metals and native oxides from silicon surfaces without damaging on silicon and silicon-dioxide surfaces. We success-fully terminated hydrogen on (100) silicon surfaces by annealing in pure hydrogen ambient. A dry cleaning system with these sequential processes will be useful in constructing fully-integrated mass-production lines of high-performance ULSI devices.

The buried oxide nonintegrities, represented as the equivalent fixed oxide charge and interface trap densities at both the upper and lower interface of buried oxide, are evaluated for low-dose and high-dose SIMOX wafers, and their effects on device characteristics are investigated. The equivalent fixied oxide charge and trap densities at the lower interface, which are measured with buried oxide capacitors, are negligibly small in as-fabricated SIMOX wafers. This result enables us to make an analytical model of the parasitic drain/source-to-substrate capacitance in an SOI MOSFET, in which the effect of the depletion layer under the buried oxide is considered. The influence of thinner buried oxide and process-induced fixed oxide charge on the parasitic capacitance is explored with this model. The equivalent fixed oxide charge and trap densities at the upper interface are evaluated by the threshold voltage measurement in an SOI NMOSFET. The principle of this evaluation as well as the experimental technique are described in detail. The oxide charge and trap densities at the upper interface are higher than those at the lower interface for both SIMOX wafers. With a new model of the subthreshold slope based on a two-dimensional potential analysis the influence of the trap at the upper interface is discussed.

The capacitance and the resistance of the Au/PrBa2Cu3Oy (PBCO)/YBa2Cu3Ox (YBCO) structure were measured at liquid helium temperature. A film of YBCO was deposited by rf magnetron sputtering at 700, and its thickness was 250 nm. A film of PBCO was deposited by rf magnetron sputtering at 690, and its thickness was less than 375 nm. The inverse capacitance and the resistance of the structure increased with PBCO thickness when PBCO thickness was more than 70 nm. However, the inverse capacitance was near zero, and the resistance was much less than that of PBCO itself when PBCO thickness was less than 70 nm. These results show the possibility that the electric property of PBCO within 70 nm from the PBCO/YBCO interface is different from that of PBCO itself, that is, there is a low-resistance region in PBCO near the YBCO/PBCO interface.

In this paper, an electrostatic actuator with electret is proposed. Electrets are the electrical equivalent of magnets. They are dielectric's carrying a non equilibrium permanent space charge or polarization distribution. This distribution can create either an external electric field or internal properties such as piezo or pyroelectricity. In the first case it is possible to make new types of electrostatic actuators by the external electric field. An electrostatic relay with electret is fabricated to demonstrate the possibility of an electrostatic actuator with electret. The size of relay is 5.2 mm11.5 mm. Its amature beam is 50 µm thick, 2.9 mm wide, 6.3 mm long, and acts as a moving electrode. Facing it, the stationary electrode is 20 µm away from the moving electrode. On the stationary electrode, new type of electret made from SiO2 is deposited. We have succeeded in making the armature operate at low applied voltage 20 V. On the same structure without electret, we need more than 120 V to make the same armature operation. We have also succeeded in making the armature latching.

The former experimental results have already shown that it is oxide films formed on contact surface causing the contact resistance to degrade in dc. breaking arcs for Ag and Pd materials. In order to understand the detailed information about it, the experiments are performed to break dc. inductive load at 20 V, 0.5 A and 1.0 A in nitrogen gas with different oxygen concentrations. The contact surface morphology and surface contamination are evaluated by SEM and AES, respectively. The tested results demonstrate that, for Ag contact, the severe oxidation occurs with increasing oxygen concentration, and the critical value of oxygen concentration is found to be about 10% and 5% in 0.5 A and 1.0 A, respectively, above those values the contact resistance degrades due to the oxide films formed on the contact surface, especially on the anode surface. While, for Pd contacts, a remarkable contact resistance degradation is not found even at 1.0 A in oxigen. Evidence shows that the arc duration, in particular the gaseous phase arc duration affects the anode oxidation, which in turn causes the significant fluctuation of contact resistance.

On the surface of contacts which are exposed to the atmosphere, the reaction with gases in the atmosphere produces contaminant films including oxides. The contact reliability is degraded by the contaminant films. Humidity in the atmospheric environment also influences on the surface of contacts. However, influence of humidity on the surface has not been clarified. In the present paper, influence of humidity on the Cu surface and the oxides (CuO + Cu2O) on it were studied with respect to the thickness of the oxide film and contact resistance characteristics both for static and for sliding contacts. The thickness was measured by ellipsometric analysis. Topographic image affected by humidification was also observed by scanning tunneling microscope (STM). In the atmospheric environment, the clean surface of Cu was found to oxidize with fluctuations of the thickness for lapse of exposure time due to the fluctuations of the humidity. It was also found that the thickness of the oxide film decreases immediately after the humidification, and increases under dehumidification. Changes in contact resistance affected by humidity was corresponding to the change in the film thickness. Immediately after humidification contact resistance decreased, and increased with dehumidification both for static and for sliding contacts. For the mechanism of the influence of humidity on the oxide, chemical reduction of hydrogen generated by decomposition of the absorbed water molecule (H2O) was derived. The clean Cu surface was oxidized by oxygen due to absorbed water molecule and atmosphere.

We propose, for the first time, highly reliable flash-type EEPROM cell fabrication using in-situ multiple rapid thermal processing (RTP) technology. In this study, rapid thermal oxynitridation tunnel oxide (RTONO) film formations followed by in-situ arsenic (As)-doped floating-gate polysilicon growth by rapid thermal chemical vapor deposition (RTCVD) technologies are fully utilized. The results show that after 5104 program/erase (P/E) endurance cycles, the conventional cell shows 65% narrowing of the threshold voltage (Vt) window, whereas the RTONO cell indicates narrowing of less than 20%. A large number of nitrogen atoms (1020 atoms/cm3) are confirmed by secondary ion mass spectrometry (SIMS), pile up at the SiO2/Si interface and distribute into bulk SiO2. It is considered that in the RTONO film stable Si-N bonds are formed which minimize electron trap generation as well as the neutral defect density, resulting in lower Vt shifts in P/E stress. In addition, the RTONO film reduces the number of hydrogen atoms because of final N2O oxynitridation. The SIMS data shows that by the in-situ RTCVD process As atoms (91020 atoms/cm3) are incorporated uniformly into 1000--thick film. Moreover, the RTCVD polysilicon film indicates an extremely flat surface. The time-dependent dielectric breakdown (TDDB) characteristics of interpoly oxide-nitride-oxide (ONO) film exhibited no defect-related breakdown and 5 times longer breakdown time as compared to phosphorus-doped polysilicon film. Therefore, the flash-EEPROM cell fabricated has good charge storing capability.

The data retention characteristics of a Flash memory cell with a self-aligned double poly-Si stacked structure have been drastically improved by applying a bi-polarity write and erase technology which uses uniform Fowler-Nordheim tunneling over the whole channel area both during write and erase. It is clarified experimentally that the detrapping of electrons from the gate oxide to the substrate results in an extended retention time. A bi-polarity write and erase technology also guarantees a wide cell threshold voltage window even after 106 write/erase cycles. This technology results in a highly reliable EEPROM with an extended data retention time.

When intermetal oxide film which contains much water deposited on MOSFET, degradation of hot carrier characteristics is enhanced. This mechanism is considered to be as follows. During the annealing process water is desorbed from the intermetal oxide. The desorbed water reaches the MOSFET and eventually hydrogens terminate silicon dangling bonds in the gate oxide. This paper describes a new approach which uses ESR to analyze this mechanism. The ESR measurement of number of the silicon dangling bonds in undoped polysilicon lying under the intermetal oxide shows that water diffuses from intermetal oxide to MOSFET during the annealing process. The water diffusion is blocked by introduction between the polysilicon and the intermetal oxides of P-SiN layer or CVD SiO2 damaged by implantation.