Dielectric relaxation in piezo-, pyro- and ferroelectric polyamide 11

Ferroelectric polyamide 11 films were prepared by melt-quenching, cold-drawing and electrical poling. Their ferroelectricity was studied by means of dielectric-hysteresis measurements. A remnant polarisation of up to 35 mC/m/sup 2/ and a coercive field of 75 MV/m were obtained. The piezoelectric d/sub 33/ coefficient and the pyroelectric coefficient of the films are reduced by annealing just below the melting region, but remain at about 3 pC/N and 8 /spl mu/C/(m/sup 2/K), respectively, during further heat treatment. Differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarisation (TSD) were applied for investigating the conformational changes induced by melt-quenching, cold-drawing and annealing. The results indicate that the cold-drawn film mainly consists of a rigid amorphous phase which exhibits considerably lower conductivity, no glass transition and consequently no dielectric /spl alpha/ relaxation. Instead, an /spl alpha//sub r/ relaxation is found, which is related to chain motions in regions of the rigid amorphous phase where the amide-group dipoles are not perfectly ordered. Annealing removes imperfectly ordered structures, but does not affect the ferroelectric polarisation. Therefore, it may be concluded that essentially the /spl alpha//sub r/ relaxation causes the thermally nonstable part of the piezo- and pyroelectricity in polyamide 11.     

Er-doped AlGaAs native oxides: photoluminescence characterization and process optimization

We present 300 K photoluminescence (PL) characterization data for wet thermal native oxides of Al/sub 0.58/Ga/sub 0.42/As films grown by metal organic chemical vapor deposition and doped with Er via multiple high-energy ion implants (for 0.0675, 0.135, and 0.27 atomic percent (at.%) peak Er concentrations), and Al/sub 0.5/Ga/sub 0.5/As and Al/sub 0.8/In/sub 0.2/As films doped with Er (0.03-0.26 at.%) during molecular beam epitaxy crystal growth. Broad spectra with a /spl sim/50-nm full-width at half-maximum and a PL peak at 1.534 /spl mu/m are observed, characteristic of Al/sub 2/O/sub 3/:Er films. The dependencies of PL intensity, spectra, and lifetime on annealing temperature (675/spl deg/C-900/spl deg/C), time (2-60 min) and As overpressure (0-0.82 atm) are studied to optimize the annealing process, with As considered as a possible quenching mechanism. Wet and dry-oxidized films are compared to explore the role of hydroxyl (OH) groups identified by Fourier transform infrared (FTIR) spectroscopy. FTIR experiments employing heavy water (D/sub 2/O) suggest that OH groups in wet oxidized AlGaAs come mainly from post-oxidation adsorption of atmospheric moisture. AlGaAs:Er films wet oxidized with 0.1% O/sub 2/ added to the N/sub 2/ carrier gas show a fourfold PL intensity increase, doubled PL lifetime to /spl tau//spl sim/5.0 ms (0.27 at.% implanted sample), and the lowest degree of concentration quenching.     

The stoichiometry of thermal oxidation

At a stoichiometrical relation of silicon and oxygen during the growth of a rapid thermal silicon-oxide layer (RTO) the electrical parameters of the corresponding metal-insulator-semiconductor capacitor show significant behavior. Combining the Henry-Dalton law and the Boyle-Mariotte law with the Deal-Grove model allows an estimation of the fundamental (T, t, C) process, parameters, temperature, time and concentration of the reactive gas for a stoichiometrical processing of ultra thin SiO/sub 2/ films. Electrical measurements show the (T, t, C)-dependency of I-V, time dependent dielectric breakdown (TDDB) and C-V measurements especially of direct tunneling currents j/sub DT/, relative difference of tunneling currents /spl Delta//sub RDT/, charge-to-breakdown Q/sub BD/ and interface state density D/sub it/.     

Electrical insulation characteristics of cold dielectric high temperature superconducting cable

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.     

Flashover voltage of alumina ceramic contaminated by metal vapor in vacuum interrupters

We investigated the influence of metal vapor contamination of ceramic surfaces on flashover voltage (FOV) in vacuum. First, disk shape alumina (Al/sub 2/O/sub 3/) ceramics with surface resistivity (/spl rho/) of 10/sup 2/-10/sup 15/ /spl Omega/ were produced using deposition phenomena of metal vapor emitted from CuCr contacts. The impulse FOV for the ceramics decreased, as /spl rho/ reduced; FOV, the conditioning effect on FOV, and the scattering of FOV decreased when /spl rho/ was below 10/sup 12/ /spl Omega/. Therefore, the criterion value /spl rho/, which maintains excellent flashover performances of ceramic surface, is 10/sup 12/ /spl Omega/. Second, experimental vacuum interrupters (VIs) were produced to measure breakdown voltage before and after forty short-circuit current switchings with 20-40 kA/sub rms/ and were disassembled to measure the /spl rho/ of their inner ceramic surface. In a VI, which has inside diameters at both ends of the main shield much larger than the contact diameter, /spl rho/ was reduced to 10/sup 4/ /spl Omega/, further decreasing breakdown voltage between terminals.     

Intentionally inserted oxygen depleted (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers as a model of DC-electrical degradation

The relative dielectric constant versus voltage (/spl epsiv//sub r/-V) characteristics and the current density versus electric field (J-E) characteristics of (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ films, which have intentionally inserted oxygen depleted layers near the bottom electrodes, were investigated as a model of dc-electrical degradation phenomena. Our investigation demonstrated that the intentionally inserted oxygen depleted layer is the cause of the tunneling conduction.     

Magnetic resonance studies of trapping centers in high-/spl kappa/ dielectric films on silicon

The electrical properties of high dielectric constant materials being considered for replacements of SiO/sub 2/ in metal-oxide semiconductor (MOS) field effect transistors are dominated by point defects. These point defects play important roles in determining the response of these films in almost any imaginable reliability problem. A fundamental understanding of these defects may help to alleviate the problems which they can cause. The best known methods for determining the structure of electrically active defects in MOS materials and devices are conventional electron spin resonance (ESR) and electrically detected magnetic resonance (EDMR). In this paper, we review the limited ESR and EDMR work performed to date on high-/spl kappa/ materials. A discussion of magnetic resonance techniques as well as a brief overview of the extensively studied Si/SiO/sub 2/ system is also included.     

Control of charge on insulating glass in vacuum by plasma processing

In order to control the charging of insulating glass used in HV vacuum equipment, the effect of H/sub 2/ plasma processing on the glass surface was studied. The electron-beam irradiation method was used to verify the effectiveness of the charging control. Borosilicate glass plates were used as test samples. When the glass was exposed to H/sub 2/ plasma produced by ac (60 Hz) voltage application, the surface resistivity of the glass was decreased, varying with H/sub 2/ plasma processing time. By exposure to H/sub 2/ plasma for 20 min, the surface resistivity was reduced from /spl sim/10/sup 17/ to /spl sim/10/sup 12/ /spl Omega/. Due to the reduction of the surface resistivity, charging of the glass can be controlled to a level below that which could cause surface flashover.     

Noise figure of parametric wavelength conversion with quasi-phase-matched LiNbO/sub 3/ waveguide

An analytical model of the noise accumulation in a chain of parametric wavelength converters is proposed. Signal-to-noise electrical power ratio is analytically given as a function of node number k in a chained transparent node system that consists of optical amplifiers, parametric wavelength converters, and several loss elements including optical transmission fiber with parameters of pump light excess noise /spl beta//sub p/, and average photon numbers per unit time of pump light and input signal , and , respectively, and spontaneous emission factor of optical amplifier n/sub sp/. The signal-to-noise degrades inversely proportional to node number k with the coefficient defined by NF/sup (1)/=2n/sub sp/+/spl beta//sub p// when k is lower than /Bo, where B/sub o/ represents optical bandwidth. The noise figure dependence on pump light quality /spl beta//sub p// and average photon number of input light in a single stage configuration are experimentally evaluated using Er-doped fiber amplifiers and quasi-phase-matched lithium niobate waveguide parametric wavelength conversion.     

Comparative study on the spectroscopic properties of Nd:GdVO/sub 4/ and Nd:YVO/sub 4/ with hybrid process

We have proposed a hybrid procedure for determining spectroscopic parameters for uniaxial solid-state laser crystals. Using our procedure, the spectroscopic properties of Nd:GdVO/sub 4/ were evaluated and compared to those of Nd:YVO/sub 4/. As a result, the peaks of absorption and stimulated emission cross sections of Nd:GdVO/sub 4/ in /spl pi/-polarization were determined to be 2.6 and 10.3/spl times/10/sup -19/ cm/sup 2/, respectively, and were smaller than those of Nd:YVO/sub 4/. On the other hand, the fluorescence lifetime of 1 at% Nd:GdVO/sub 4/ was evaluated to be 83.4 /spl mu/s, and was similar to 84.1 /spl mu/s of 1 at% Nd:YVO/sub 4/. Therefore, the product of stimulated emission cross section and fluorescence lifetime (/spl sigma//sub em//spl tau//sub f/ product) of Nd:GdVO/sub 4/ was smaller than that of Nd:YVO/sub 4/ under 1 at% of Nd/sup 3+/ doping concentration. The radiative lifetime of spontaneous emission of Nd:GdVO/sub 4/ was 168 /spl mu/s and was 1.9 times longer than that of Nd:YVO/sub 4/. Because of the low value of radiative quantum efficiency of Nd:GdVO/sub 4/ (50%), careful cavity design is required for creating a well performing solid-state laser with Nd:GdVO/sub 4/, based on the larger /spl sigma//sub em//spl tau//sub f/ product rather than the /spl sigma//sub em//spl tau//sub f/ product of Nd:YAG.     

BTI characteristics and mechanisms of metal gated HfO/sub 2/ films with enhanced interface/bulk process treatments

Significant deviations in BTI characteristics for metal gate HfO/sub 2/ films compared to silicon oxide based films prove that conventional reliability models based on SiO/sub 2/ films can no longer be directly applied to HfO/sub 2/ based MOSFETS. This study shows the use of conventional accelerated reliability testing in the Fowler-Nordheim tunneling regime to extrapolate time to failure at operating voltages (direct tunneling regime) overestimates device lifetimes. Additionally, unlike conventional gate oxides, the slope of /spl Delta/V/sub t/ versus time (or the rate of charge trapping) in HfO/sub 2/ MOSFETS is dependent on stress voltage. The HfO/sub 2/ based metal gated nMOSFETS show poor PBTI characteristics and do not meet the 10 year lifetime criterion for threshold voltage stability. On the other hand, HfO/sub 2/ based pMOSFETS show superior NBTI behavior and meet the 10 year lifetime criterion. These results are contrary to the observations with conventional gate dielectrics. This paper explores the anomalous charge trapping behavior and provides a comprehensive study of the PBTI characteristics and recovery mechanisms in metal gated HfO/sub 2/ films.     

Correlation between dielectric properties and sintering temperatures of polycrystalline CaCu/sub 3/Ti/sub 4/O/sub 12/

Dielectric properties of polycrystalline CaCu/sub 3/Ti/sub 4/O/sub 12/ (CCTO) pellets sintered in the temperature range 1000-1200/spl deg/C were evaluated with impedance spectroscopy at frequency range of 10/sup 2/ to 10/sup 7/ Hz from 90 K to 294 K. A correlation has been established between the pair values of low frequency limit dielectric constant and the total resistivity and the sintering temperature. For example, the sample sintered at 1100/spl deg/C demonstrates higher value of low frequency limit dielectric constant and lower value of total resistivity, while the sample sintered at 1000/spl deg/C demonstrates lower values of low frequency limit dielectric constant and higher value of total resistivity. This correlation has been successfully explained by relating with the difference in grain size and grain volume resistivities of these two polycrystalline CCTO samples. Further, it is suggested that donor doping of oxygen vacancies Vo' and Vo" may be the reason to cause the difference in the grain volume resistivities of these two samples.     

The impact of LOC structures on 670-nm (Al)GaInP high-power lasers

We investigate the potential of large optical cavity (LOC)-laser structures for AlGaInP high-power lasers. For that we study large series of broad area lasers with varying waveguide widths to obtain statistically relevant data. We study in detail I/sub th/, /spl alpha//sub i/, /spl eta//sub i/, and P/sub max/, and analyze above-threshold behavior including temperature stability and leakage current. We got as expected for LOC structures minimal /spl alpha//sub i//spl les/1 cm/sup -1/ resulting in /spl eta//sup d/=1.1 W/A for 64/spl times/2000 /spl mu/m/sup 2/ uncoated devices. We obtain total output powers /spl ges/3.2 W (qCW) and /spl ges/1.5 W (CW) at 20/spl deg/C.     

Recovery of shifted MOS parameters induced by focused ion beam exposure

The effects of focused ion beam (FIB) exposure on MOS transistors within a circuit were examined. It was found that FIB exposure does not cause parameter shifts as long as the gate is connected to the drain of other MOS transistors. However, the threshold voltage (V/sub t/) does shift during isolating the gate using a FIB. Further FIB exposure on MOS transistors with a floating gate is shown to cause larger shifts. Thermal annealing was studied to recover shifted V/sub t/. We demonstrated that a 400/spl deg/C-450/spl deg/C anneal could recover shifted V/sub t/ almost completely. Ninety percent recovery can be reached by annealing at 400/spl deg/C-450/spl deg/C for 1-2 hours, and V/sub t/ shifts can be reduced to about 10 mV.     

Leakage behavior of DC electrically degraded (Ba,Sr)TiO/sub 3/ thin films

The phenomena of dc electrical degradation of (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ thin films was studied. From our experimental and analytical results of current versus voltage (I-V) characteristics, it was shown that the degraded devices exhibited analogous leakage behaviors with the devices which have thin intercalated (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers with intentionally introduced oxygen vacancies between cathodes and thick (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers without intentionally introduced oxygen vacancies. This could be explained by assuming that oxygen vacancies accumulate at the interfaces between the cathodes and the (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ films after fatigue.     

Validity of constant voltage stress based reliability assessment of high-/spl kappa/ devices

Charge trapping in high-/spl kappa/ gate dielectrics affects the result of electrical characterization significantly. DC mobility degradation and device threshold voltage instability and C-V and I-V hysteresis are a few examples. The charging effects in high-/spl kappa/ gate dielectric also affect the validity of conventional reliability test methodologies developed for SiO/sub 2/ devices. In this paper, we review high-/spl kappa/ materials specific phenomena that can affect the validity of constant-voltage-stress-based reliability test methods to address the direction of future reliability study on high-/spl kappa/ devices.     

Power frequency dependence of space charge behavior and partial discharge characteristics in SF/sub 6/ gas

The partial discharge (PD) and breakdown (BD) characteristics in SF/sub 6/ gas under commercial and higher frequency (/spl sim/600 Hz) ac voltage applications were investigated using high-speed electrical and optical measuring techniques with phase gate control method. Experimental results revealed that 400 Hz BD voltage at a certain gas pressure range was higher than that for 60 Hz and PD characteristics especially at the positive PD inception phase were much influenced by the applied power frequency. From these results, we clarified the dependence of space charge behavior on the applied power frequency and discussed the physical mechanism of PD and BD in SF/sub 6/ gas with consideration of the space charge behavior generated by PD in the previous half cycle of ac voltage.     

Thermal-stability improvement of a sulfur-passivated InGaP/InGaAs/GaAs HFET

The temperature-dependent characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor (HFET), using the (NH/sub 4/)/sub 2/S/sub x/ solution to form the InGaP surface passivation, are studied and demonstrated. The sulfur-passivated device shows significantly improved dc and RF performances over a wide temperature range (300-510 K). With a 1/spl times/100-/spl mu/m/sup 2/ gate-dimension HFET by (NH/sub 4/)/sub 2/S/sub x/ treatment, the considerably improved thermal stability over dc performances including lower temperature variation coefficients on the turn-on voltage (-1.23 mV/K), the gate-drain breakdown voltage (-0.05 mV/K), the gate leakage current (1.04 /spl mu/A/mm/spl middot/K), the threshold voltage (-1.139 mV/K), and the drain-saturation-current operating regimes (-3.11/spl times/10/sup -4//K) are obtained as the temperature is increased from 300 to 510 K. In addition, for RF characteristics, the sulfur-passivated device also shows a low degradation rate on drain-saturation-current operating regimes (-3.29/spl times/10/sup -4//K) as the temperature is increased from 300 to 400 K. These advantages provide the promise for high-speed high-frequency high-temperature electronics applications.     

High-saturation current wide-bandwidth photodetectors

This paper describes the design and performance of two wide-bandwidth photodiode structures. The partially depleted absorber photodiode utilizes an absorbing layer consisting of both depleted and undepleted In/sub 0.53/Ga/sub 0.47/As layers. These photodiodes have achieved saturation currents (bandwidths) of >430 mA (300 MHz) and 199 mA (1 GHz) for 100-/spl mu/m-diameter devices and 24 mA (48 GHz) for 100-/spl mu/m/sup 2/ area devices. Charge compensation has also been utilized in a similar, but modified In/sub 0.53/Ga/sub 0.47/As-InP unitraveling-carrier photodiode design to predistort the electric field in the depletion region in order to mitigate space charge effects. For 20-/spl mu/m-diameter photodiodes the large-signal 1-dB compression current and bandwidth were /spl sim/90 mA and 25 GHz, respectively.     

UV laser diode with 350.9-nm-lasing wavelength grown by hetero-epitaxial-lateral overgrowth technology

We have demonstrated a UV-laser diode with a lasing wavelength of 350.9 nm, which has a GaN-AlGaN multiquantum-well (MQW) active layer and was grown on low-dislocation-density Al/sub 0.18/Ga/sub 0.82/N template. The Al/sub 0.18/Ga/sub 0.82/N template was produced by the hetero-epitaxial lateral overgrowth technology on the low-cost sapphire substrate, and has partially low-dislocation density of approximately 2/spl times/10/sup 7/ cm/sup -2/. The lasing operation under pulsed current injection was achieved with the threshold current density of 7.3 kA/cm/sup 2/ and the operating voltage of 10.4 V.