Nanocomposite-parylene C thin films with high dielectric constant and low losses for future organic electronic devices.

Nanocomposite-parylene C (NCPC) thin films were deposited with a new technique based on the combination of chemical vapor deposition (CVD) for parylene C deposition and RF-magnetron sputtering for silver deposition. This method yields good dispersion of Ag-containing nanoparticles inside the parylene C polymer matrix. Film composition and structure were studied by using several techniques. It was found that the plasma generated by the RF-magnetron reactor modifies the film density as well as the degree of crystallinity and the size of parylene C crystallites. Moreover, silver is incorporated in the parylene matrix as an oxide phase. The average size of the Ag oxide nanoparticles is lower than 20 nm and influences the roughness of the NCPC films. Samples with various contents and sizes of silver-oxide nanoparticles were investigated by broadband dielectric spectroscopy (BDS) in view of their final application. It was found that both the content and the size of the nanoparticles influence the value of the dielectric constant and the frequency-dependence of the permittivity. In particular, ß-relaxation is affected by the addition of nanoparticles as well as the dissipation factor, which is even improved. A dielectric constant of 5 ± 1 with a dissipation factor of less than 0.045 in the range from 0.1 Hz to 1 MHz is obtained for a 2.7 µm thick NCPC with 3.8% Ag content. This study provides guidance for future NCPC materials for insulating gates in organic field-effect transistors (OFETs) and advanced electronic applications.

Capacitance-voltage characteristics of sub-nanometric Al2O3 / TiO2 laminates: dielectric and interface charge densities.

Advanced amorphous sub-nanometric laminates based on TiO2 and Al2O3 were deposited by atomic layer deposition at low temperature. Low densities of 'slow' and 'fast' interface states are achieved with values of 3.96 · 1010 cm-2 and 4.85 · 10-9 eV-1 cm-2, respectively, by using a 40 nm laminate constituted of 0.7 nm TiO2 and 0.8 nm Al2O3. The sub-nanometric laminate shows a low hysteresis width of 20 mV due to the low oxide charge density of about 3.72 · 1011 cm-2. Interestingly, such properties are required for stable and reliable performance of MOS capacitors and transistor operation. Thus, decreasing the individual layer thickness to the sub-nanometric range and combining two dielectric materials with oppositely charged defects may play a major role in the electrical response, highly promising for the application in future micro and nano-electronics applications.

Structural and Dielectric Properties of Subnanometric Laminates of Binary Oxides.

Capacitors with a dielectric material consisting of amorphous laminates of Al2O3 and TiO2 with subnanometer individual layer thicknesses can show strongly enhanced capacitance densities compared to the bulk or laminates with nanometer layer thickness. In this study, the structural and dielectric properties of such subnanometer laminates grown on silicon by state-of-the-art atomic layer deposition are investigated with varying electrode materials. The laminates show a dielectric constant reaching 95 combined with a dielectric loss (tan δ) of about 0.2. The differences of the observed dielectric properties in capacitors with varying electrodes indicate that chemical effects at the interface with the TiN electrode play a major role, while the influence of the local roughness of the individual layers is rather limited.

Dielectric and Conduction Mechanisms of Parylene N at High Temperature: Phase-Transition Effect.

Dielectric and electrical properties correlated with the structure analysis have been studied on 27% semicrystalline parylene-N (-H2C-C6H4-CH2-)n thin films. Transition-phase, AC- and DC-conduction mechanisms, and the MW-interfacial polarization were identified in parylene N at high temperature by experimental and theoretical investigations. The dielectric analysis based on the dc conductivity highlights a temperature of 230 °C as a transition temperature from the α-form to the ß1-form. This structure transition is accompanied by a modification on the DC-conduction mechanisms from ionic to electronic conduction in the α-form and the ß1-form, respectively. The AC conduction mechanism is governed by the small polaron tunneling mechanism (SPTM) with WH,α = 0.23 eV and a tunneling distance of 7.71 Å in the α-form, while it becomes a correlated barrier-hopping (CBH) mechanism with a WM,ß 1 = 0.52 eV in the ß1-form. The imaginary part of the electrical modulus formalism obeys the Kohlrausch-Williams-Watt (KWW) model and shows the presence of the interfacial polarization effect. The theoretical Kohlrausch exponent (ßKWW) confirms the existence of the transition phase on the parylene N in the vicinity of the 230 °C as deduced by the DC- and the AC-conduction parameters. The correlations between the experimental results and the theoretical models are very useful knowledge and tools for diverse parylene N applications at high temperature.

Ionic mobility in DNA films studied by dielectric spectroscopy.

Double-helix DNA molecules can be found under different conformational structures driven by ionic and hydration surroundings. Usually, only the B-form of DNA, which is the only form stable in aqueous solution, can be studied by dielectric measurements. Here, the dielectric responses of DNA molecules in the A- and B-form, oriented co-linearly within fibres assembled in a film have been analyzed. The dielectric dispersion, permittivity and dissipation factor, have been measured as a function of frequency, strength voltage, time, temperature and nature of the counter-ions. Besides a high electrode polarization component, two relaxation peaks have been observed and fitted by two Cole-Cole relaxation terms. In the frequency range that we investigated (0.1 Hz to 5 ·10(6) Hz) the dielectric properties are dominated by the mobility and diffusivity of the counter-ions and their interactions with the DNA molecules, which can therefore be characterized for the A- and B-forms of DNA.

Experimental and theoretical study of AC electrical conduction mechanisms of semicrystalline parylene C thin films.

The electrical conduction mechanisms of semicrystalline thermoplastic parylene C (-H(2)C-C(6)H(3)Cl-CH(2)-)(n) thin films were studied in large temperature and frequency regions. The alternative current (AC) electrical conduction in parylene C is governed by two processes which can be ascribed to a hopping transport mechanism: correlated barrier hopping (CBH) model at low [77-155 K] and high [473-533 K] temperature and the small polaron tunneling mechanism (SPTM) from 193 to 413 K within the framework of the universal law of dielectric response. The conduction mechanism is explained with the help of Elliot's theory, and the Elliot's parameters are determined. From frequency- and temperature-conductivity characteristics, the activation energy is found to be 1.27 eV for direct current (DC) conduction interpreted in terms of ionic conduction mechanism. The power law dependence of AC conductivity is interpreted in terms of electron hopping with a density N(E(F)) (~10(18) eV cm(-3)) over a 0.023-0.03 eV high barrier across a distance of 1.46-1.54 Å.