Papers by Keyword: Thermally Stimulated Current

Abstract: In this paper, trap levels around the glass transition temperature (T_g) of polymers have been characterized using Thermally Stimulated Current (TSC) technique. Deconvolution on α-peaks of the T_g for PE (-104 °C), plasticized PVC (-35 °C), PMMA (90 °C) and PET (96 °C) were carried out based on the first-order kinetic theory for non-Debye relaxation. Using temperature, T from TSC experimental data, we have successfully separated the α-peaks of the thermoplastic polymers. It is found that the complex curve of α-peaks can composed of four (4) to eight (8) sub peaks. Dominant sub peaks were identified at T_max = -105 °C, -34 °C, 89 °C and 92 °C for PE, pPVC, PMMA and PET, respectively. These peaks show activation energy, E_a of shallow and deep trap centers ranged from 0.3 eV to 4.6 Ev where they represent the depolarization of localized dipoles and space charges relaxations in the polymers.

Abstract: 3 mol% yttria-stabilized zirconia (YSZ) powders were sintered into pellets. The YSZ ceramics were electrically polarized by applying dc voltage at an elevated temperature. After cooling the samples to room temperature, the polarized YSZ ceramics were heated at a constant heating rate. The formed polarizations were relaxed with increase of the increase temperature. The depolarization current was measured as thermally stimulated depolarization current (TSDC). Each of the TSDC spectra had two peaks located at lower and higher temperatures. The lower and higher peaks are attributed to dipole polarization and space charge polarization, respectively.

Abstract: Effect of surface charges induced by polarization treatment on Low Temperature Degradation (LTD) in 3mol%Y-doped ZrO₂ was studied. Samples were polarized by applying voltage (7kV/cm) at 200°C for various time (1~30min). LTD acceleration test was conducted using polarized samples. LTD was inhibited on negatively charged surface in all the polarized samples, which is independent on polarization time. We carried out thermally stimulated depolarization current (TSDC) analysis for investigate polarization mechanism. Two polarization elements were confirmed: orientation polarization and space charge polarization. A comparison of the result of LTD acceleration test and TSDC analysis indicates that orientation polarization is considered superior element in inhibition of LTD.

Abstract: The lifetime determination model for multilayer ceramic capacitors (MLCCs) is discussed. The accumulation of oxygen vacancies on the cathode/ceramics interface by an electro-migration process is a concept accepted by many researchers. However, the lifetimes and leakage currents measured during a highly accelerated lifetime test (HALT) could not be explained by this concept. To investigate the mechanism, we used a polarity reversal method during the HALT, which provided information on the dominant process for the leakage current. Thermally stimulated current (TSC) measurement provided the relative number of oxygen vacancies both on the cathode/ceramics interfaces and the grain boundaries. Moreover, the microstructure of the MLCC samples was evaluated by both electric property measurements and direct observation. From these results, we concluded that the grain boundaries controlled the leakage current as well as the lifetime.

Abstract: Thermally stimulated current (TSC) measurements on epitaxial and implanted 4H-SiC MOS capacitors are presented. The effect of gamma ray irradiation on the TSC spectra of epitaxial 4H-SiC MOSCAP devices is discussed. On non-irradiated samples, two TSC peaks are observed near 55 K and 80 K. Due to the generated oxide charge during irradiation, the 80 K emission split into two constituent peaks. These have been attributed to hole traps and Al acceptors.

Abstract: Multiple-energy nitrogen ions (energies:1 to 100 keV and a net concentration:2.24 x 1020 cm-3) are implanted into ZnO bulk single crystals grown by the hydrothermal method. Rutherford backscattering-channeling studies show the presence of displaced Zn atoms (Zni) of about 4 % in as-implanted samples. An A-emission band related to the interstitial oxygen (Oi) is observed at 580 nm in 600 oC-annealed samples, and a new emission appears at 515 nm in 800 oC-annealed samples. It is proposed that the new emission band consists of the superposition of the green band (~525 nm) observed in unimplanted ZnO and the residual A-emission band. In 800 oC-annealed samples, a band to acceptor transition at 3.26 eV is also observed in addition to a donor to acceptor pair transition, suggesting that nitrogen acceptor is located at about 180 meV above the valence band. A thermally stimulated current peak, P1 (165 meV), which has been attributed to a native point defect, observed in unimplanted samples almost disappears in nitrogen-implanted samples annealed at 800 oC.

Abstract: A combined isothermal and non-isothermal measurement technique is described for analyzing space charge behavior in dielectric materials. The experimental conditions are chosen so that the dipolar effects are insignificant and the measured current is mainly due to space charge detrapping. For polyamide 11 four peaks have been identified above the poling temperature. As the difference between the peak temperature and the poling temperature increases, the apparent activation energies decrease suggesting that only the faster modes participate to the charging process. The charge associated to the apparent peak and the peak at 96 °C scales linearly with the polarization field. The injected space charge at 35 °C is very stable at 150 °C, an important fact with respect to technological applications of polyamide 11 as an electroactive material.