Investigation of 4H-SiC MOS capacitors annealed in diluted N2O at different temperatures

Thermally grown oxide on 4H-SiC has been post-annealed in diluted N₂O (10% N₂O in N₂) at different temperatures from 900 to 1100 °C. The quality of the nitrided oxide and the SiO₂/4H-SiC interface was investigated by AC conductance and high frequency C-V measurements based on Al/SiO₂/4H-SiC metal-insulator-semiconductor (MOS) structure. It is found that N₂O annealing at 1000 °C produces the lowest interface state density, though the difference is not so significant when compared to the other samples annealed at 900 and 1100 °C. These results can be explained by the high temperature dynamic decomposition process of N₂O. By fitting the AC conductance data, it is found that higher temperature nitridation increases the capture cross-section of the interface traps.     

Traps centers and deep defects contribution in current instabilities for AlGaN/GaN HEMT's on silicon and sapphire substrates

AlGaN/GaN high electron mobility transistors (HEMTs) with Si and Al₂O₃ substrates reveals anomalies on I_ds-V_ds-T and I_gs-V_gs-T characteristics (degradation in drain current, kink effect, barrier height fluctuations, etc.). Stress and random telegraph signal (RTS) measurements prove the presence of trap centers responsible for drain current degradation. An explanation of the trapping mechanism responsible for current instabilities is proposed. Deep defects analysis performed by capacitance transient spectroscopy (C-DLTS), frequency dispersion of the output conductance (G_ds(f)), respectively, on gate/source and drain/source contacts and RTS prove the presence of deep defects localized, respectively, in the gate and in the channel regions. Defects detected by C-DLTS and G_ds(f) are strongly correlated, respectively, to barrier height inhomogeneities and kink anomalies. Gate current analysis confirms the presence of (G-R) centers acting like traps at the interface GaN/AlGaN. Finally, the localization of these traps defects is proposed.     

On the profile of temperature dependent series resistance in Al/Si3N4/p-Si (MIS) Schottky diodes

The temperature dependence of capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of metal-insulator-semiconductor (Al/Si₃N₄/p-Si) Schottky barrier diodes (SBDs) was investigated by considering series resistance effect in the temperature range of 80-300 K. It is found that in the presence of series resistance, the forward bias C-V plots exhibit a peak, and experimentally show that the peak positions with a maximum at 260 K shift toward lower voltages with increasing temperature. The C-V and (G/w-V) characteristics confirm that the interface state density (N_ss) and series resistance (R_s) of the diode are important parameters that strongly influence the electric parameters of MIS structures. The crossing of the G/w-V curves appears as an abnormality compared to the conventional behavior of ideal Schottky diode. It is thought that the presence of series resistance keeps this intersection hidden and unobservable in homogeneous Schottky diodes, but it appears in the case of inhomogeneous Schottky diode. In addition, the high frequency (C_m) and conductance (G_m/w) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real diode capacitance.     

乳清含盐量与电导关系曲线

含盐乳清粉、脱盐乳清粉或乳清溶液，其含盐量都可以用灰化法测定。由于灰化法试样在马福炉内灼烧所需时间长，在脱盐乳清粉的生产过程中及时控制盐分结果就难以做到。这样对于批量生产脱盐乳清粉非常不利。本文开发的电导测定法使用电导仪测出已和含盐量的乳清的电导率，在不同温度下（２０°±１℃；６０±１℃）作出电导率与食盐量的关系曲线，这样在生产脱盐乳清过程中，几分钟即可用电导计法测出明盐乳液的含盐量。     

Prediction of curved oil–water interface in horizontal pipes using modified model with dynamic contact angle

In this study, interface shapes of horizontal oil–water two-phase flow are predicted by using Young-Laplace equation model and minimum energy model. Meanwhile, the interface shapes of horizontal oil–water twophase flow in a 20 mm inner diameter pipe are measured by a novel conductance parallel-wire array probe(CPAP). It is found that, for flow conditions with low water holdup, there is a large deviation between the model-predicted interface shape and the experimentally measured one. Since the variation of pipe wetting characteristics in the process of fluid flow can lead to the changes of the contact angle between the fluid and the pipe wall, the models mentioned above are modified by considering dynamic contact angle. The results indicate that the interface shapes predicted by the modified models present a good consistence with the ones measured by CPAP.     

Analysis of the structure and conductance of Mg2+ acceptor-doped CaBi2Nb2-xMgxO9-3x/2 piezoceramics

In this work, Mg²⁺-doped CaBi₂Nb₂O₉ (CBN-xMg) lead-free piezoceramics were prepared by a common solid-state method to investigate the effects of Mg²⁺ doping content on crystal structure, electrical resistivity, and dielectric and ferroelectric properties. XRD and Raman spectroscopy show that the Mg atoms enter the B-site to form a solid solution of the pure CBN phase. In addition, the XRD refinement results show that Mg²⁺ doping increases the distortion of the NbO₆ octahedron and simultaneously enhances the total contribution of the spontaneous polarization of each position along the a-axis, and that the P_s increases from -28.678 μC/cm² for x = 0 to -31.768 μC/cm² for x = 0.02. However, when x > 0.02, the polarization decreases due to the oxygen vacancy pinning effect. According to SEM analysis, Mg²⁺ doping strengthened the growth rate of CBN ceramic grains on the a-b plane, resulting in a more obvious plate-like structure. The reduced anti-site defects of the CBN ceramic samples strengthened the structure of (Bi₂O₂)²⁺ and improved the resistivity of the samples. The internal dipole moment was also strengthened, resulting in a significant increase in the dielectric constant and a decrease in the dielectric loss. In general, Mg²⁺ doping significantly improved the comprehensive properties of CBN ceramics, with improved values including a d₃₃ of 11.1 pC/N, P_r of 7.22 μC/cm², tanδ (600 °C) of 3.0%, and ρ_dc (600 °C) of 10⁸ Ω?cm.     

Impedance model of electrolyte-insulator-semiconductor structure with porous silicon semiconductor

We present a generic impedance model for the porous silicon|electrolyte structure that is valid for a range of interfacial layers and bias in these structures. The model is validated using three widely different porous structures: short irregular silicon columns and pores, long cylindrical silicon columns and pores; and branched interconnected silicon microchannels and voids in a mesh structure. The model incorporates appropriate RC or constant phase elements for the different parts of the porous structure, namely, the top of the silicon columns (channels)|electrolyte, the column (channel) walls|electrolyte in the pores/channels, and the electrolyte|semiconductor interface at the base of the pores/channels. This physical model underscores the effects of column/channel depletion and accumulation, either due to applied bias or change of surface charge, to the impedance spectra of the device. The model helps to explain why the porosity needs to be optimized for specific applications and helps as a measurement tool for optimization.     

Electrosynthesis and comparative studies on carboxyl-functionalized polythiophene derivatives

Electrochemical synthesis of a novel carboxylic acid functionalized polythiophene – poly(3-thiophene-butyric-acid), PTBA – has been realized. Its morphology, electrochemical, spectral and conducting properties have been compared to those of poly(3-thiophene-acetic-acid), PTAA, which is widely used to immobilise both bioactive molecules and inorganic nanoparticles. According to scanning electron microscopic (SEM) images, the difference in the real and geometric surface area of the modified electrodes is much more expressed in the case of PTBA. Both the symmetry of the cyclic voltammograms and the concurrent, sustained optical changes proved that this polymer possesses an improved and more stable redox activity. According to simultaneously performed in situ ac. impedance and UV–Vis measurements, both films could be uniformly transformed between the insulating and conducting forms, but PTAA exhibited some degradation. The development of the conducting state during the redox switching of both thiophene derivative polymers proved to be primarily connected to the formation of di-cationic species. The electrochemical quartz crystal microbalance (EQCM) results evidenced also differences between the two polymers, which difference can be interpreted by assuming the more expressed effect of the deprotonation-connected (self-) doping process in PTAA. The results confirm that the new conducting polymer, PTBA is much more convenient for being considered as the polymer matrix of practically applicable composites.     

Micellar Properties of Surface Active Ionic Liquid Lauryl Isoquinolinium Bromide and Anionic Polyelectrolyte Poly(Acrylic Acid Sodium Salt) in Aqueous Solution

The complex formation between anionic polyelectrolyte poly(acrylic acid sodium salt) [NaPAA] and surface active ionic liquid (SAIL) lauryl isoquinolinium bromide [C₁₂iQuin][Br] in aqueous media has been investigated by surface tension, isothermal titration calorimetry (ITC), and conductance. The self‐assembled structures have been characterized using dynamic light scattering (DLS) and turbidity measurements. A range of surface parameters have been calculated from tensiometric measurements including critical micelle concentration (CMC), surface excess concentration (Γ_cmc), surface pressure at the interface (Π_cmc), minimum area occupied at air–solvent interface (A_min), adsorption efficiency (pC₂₀), and surface tension at the CMC (γ_cmc). The thermodynamic parameters, i.e., standard enthalpy of micellization , standard free energy of micellization (), and standard entropy of micellization () have also been evaluated. Four different stages of transitions, corresponding to the progressive formation of NaPAA–[C₁₂iQuin][Br] complex (C₁)_, critical aggregation concentration (CAC), critical saturation concentration (C₃) and CMC have been observed owing to strong electrostatic and hydrophobic interactions. The results obtained from DLS and turbidity measurements show that size of the aggregates first decreases and then increases in the presence of polyelectrolyte. The binding isotherms obtained using isothermal titration calorimetry (ITC) show the concentration dependence as well as the highly cooperative nature of interactions corresponding to formation of polyelectrolyte–SAIL complexes.     

Strongly Modulated Conductivity in Ag/PLZT/LSCO Field-Effect Transistor

A possibility of deep (>70%) modulation of La 1.94 Sr 0.06 CuO 4 and La 1.85 Sr 0.15 CuO 4 channel conductance has been shown in all-perovskite field effect transistor with a (Pb 0.95 La 0.05 )(Zr 0.2 Ti 0.8 )O 3 ferroelectric as a gate insulator. Relatively low carrier density (～10 18 m 10 19 cm m 3 ), small thickness, and rather high surface quality of the channel have provided the penetration of the electric field into the major part of the channel and deep conductance modulation, sufficient, in principle, for operation of a nonvolatile memory cell with a nondestructive readout of information.