Structure and dielectric characteristics of epitaxially strained BaTiO3 thin films

The structure and static dielectric permittivity of BaTiO₃ thin films as a function of epitaxial strain are determined by using first-principle density functional theory calculation based on pseudopotentials and a plane-wave basis. It is found that BaTiO₃ thin films under compressive misfit strain can be grown more easily than those under tensile misfit strain. The static dielectric permittivity of BaTiO₃ thin films under different misfit strain is obtained by calculating optical phonon frequencies and Born effective charges using density functional perturbation theory. The zero-temperature dielectric permittivity of ε ₃₃ increases to the maximal value under compressive misfit strain, while the ε _11/22 reaches to its maximal value under tensile misfit strain. This unsymmetrical dielectric behavior caused by strain is attributed to soft phonons in BaTiO₃ films.     

Fabrication of low resistive CdS thin films

Low resistive and high mobility thin films of CdS have been grown using vacuum evaporation techniques. X-ray diffraction studies show that the films are well oriented with a preferential growth of crystallites in the (002) plane. The value of conductivity observed in these films is in the range 0.088Ω^-1 cm^-1−1.34Ω^-1 cm^-1 at 300 K.     

Structures and resistive properties of sputtered Ti---Zr---Al---N thin films

Mixed nitride films of a Ti---Zr---Al---N system have been prepared by cathodic sputtering from a composite Ti---Zr---Al cathode in a nitriding atmosphere. The structure and electrical conduction of the mixed nitride films are similar to the well-known cermets, metal-dielectric mixtures, with a ternary nitride of Ti---Zr---N as the metallic conductor and Al---N as the dielectric. The resistivity of the mixed nitride films is much higher than that of Ti---N and ranges from 600 to 7800 μω cm with < ± 200 ppm/°C. These sputtered films have a potential in the production of thin film precision resistors in a wide range of resistivity with high electrical stability, and for hybrid circuit elements for microelectronics.     

Effects of the integrity of silicon thin films on the electrical characteristics of thin dielectric ONO film

Capacitors with two kinds of lower electrodes were fabricated and their effects evaluated on the electrical characteristics of oxide–nitride–oxide (ONO) film. One of the electrodes was made of amorphous silicon film chemically deposited using a gas mixture of Si2H6–PH3; the other was made of poly-Si film deposited by SiH4 decomposition and doped by As+ ion implantation. The ONO thin dielectric layer was composed of natural oxide, CVD silicon nitride and thermal oxide formed on the silicon nitride. The capacitance, the leakage current, the dielectric breakdown field and the time-dependent dielectric breakdown (TDDB) were tested to evaluate the electrical properties of the capacitors. The leakage current and the dielectric breakdown voltage showed similar values between the two capacitors, whereas the TDDB under negative bias showed a great difference. This indicates that, with respect to electrical properties, the integrity of the oxide grown on the in situ P-doped amorphous silicon is better than the oxide grown on the As+ ion-implanted poly-Si. What is more, phosphorus in the amorphous silicon did not lead to any problems with junction depth, even after post heat treatment at 950°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

The electrical properties of resistive and dielectric thin films prepared by reactive sputtering from a tantalum-titanium composite target

Resistive thin films of TaTiN and dielectric thin films of TaTiO prepared by reactive co-sputtering in ArN₂ or ArO₂ mixtures from a TaTi composite target were investigated in an effort to extend the data on the electrical properties of films prepared by reactive sputtering from tantalum targets. The composition of the thin films was controlled by changing the ratio of the tantalum area to the titanium area on the composite target surface.For the TaTiN films the resistivity, the temperature coefficient of resistance and the Hall coefficient were investigated as functions of the nitrogen partial pressure and the composition of the films.The dielectric constant, the temperature coefficient of capacitance and tan δ were studied as functions of composition in films of the TaTiO system.The resistivities of TaTiN films sputtered at a nitrogen partial pressure of 4 × 10^?4 Torr varied linearly from 50 to 270 μω cm as the tantalum weight percentage of the films increased from 10 to 90%. The temperature coefficient of resistance for these films decreased, again linearly, from 1000 to ?50 ppm °C^?1 over the same range of tantalum weight percentage.As the titanium weight percentage of the films increased from 10 to 90%, the dielectric constant and tan δ for the TaTiO films varied linearly from 30 to 70 and from 0.008 to 0.025 respectively.It is believed that these resistive and dielectric thin films will be valuable for producing thin film passive elements in hybrid integrated circuits.     

Device for measuring the resistance of thin films

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 54–55, May, 1992.     

Current transport mechanisms in low resistive CdS thin films

The current transport mechanisms in polycrystalline CdS thin films have been studied as a function of temperature over the temperature range 20–230 K. Conductivity data for the high temperature region has been analysed using Seto’s model of thermionic emission. At intermediate temperatures it was found that thermionic emission and tunnelling of carriers through the potential barrier both contribute to the conductivity. Below 100 K Mott’s hopping process appears to be the predominant conduction mechanism. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure-dependent dielectric response of p-terphenyl thin films

The dielectric properties of large-grained and small-grained p-terphenyl layers are reported. The dielectric responses of the two kinds of p-terphenyl polycrystalline structures differed significantly. The dielectric losses of the small-grained layers were found to be of injected carrier origin. The loss peak found in the small-grained films is associated with traps about 0.65 eV deep and interpreted interms of the Dissado-Hill theory.     

Multilayered dielectric/ferroelectric thin films and superlattices

We briefly review the status and new progress on the preparation and characterization of dielectric/ferroelectric multilayered thin films and superlattices and present some of our own research work in this field. It is pointed out that constructing multilayered dielectric/ferroelectric thin films and superlattices is an effective way to improve properties of dielectric/ferroelectric thin films and to probe new physical phenomena. There is no doubt that study on dielectric/ferroelectric multilayered thin films and superlattices will have been a topic of great interest in the forthcoming years, and it is expected that more well-designed dielectric/ferroelectric superlattices will be prepared and some new physical phenomena might emerge.     

Conduction and dielectric polarization in Se thin films

Se films were prepared by thermal evaporation technique in thickness range 150-8500 Å. X-ray diffraction measurements showed that Se films are in the amorphous state. The ac conductivity and dielectric properties of the amorphous Se films have been investigated in the frequency range 100-100 KHz and 100-400 K temperature range. The ac conductivity σ_ac(ω) is found to be proportional to ω^s where s<1. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier (CBH) model. The dc conductivity at the room temperature was also studied in the same thickness range. It was concluded that the same mechanism of carrier motion might be dominant in both ac polarization and dc conduction. This carrier transport mechanism might be electronic.     

Radiofrequency sputter deposition of germanium-selenide thin films for resistive switching

The superionic conducting properties of Ag-doped GeSe thin films make this material a promising candidate for future, resistively switching-based memories allowing for high integration densities and short switching times. This paper reports on the radiofrequency sputter deposition of GeSe thin films and on the properties of the deposited thin films with respect to non-volatile memory applications. As sputter deposition is a widely used deposition method for industrial applications, we focused on the influences of deposition parameters as power and pressure to examine the suitability of sputter deposition for fabricating random access memories using GeSe-based resistive memory cells. Multiple characterization methods were utilized to determine the quality of the deposited thin films. The results of our measurements showed that we obtained smooth, dense and amorphous layers, which reveal good switching properties after doping with Ag, suitable for the use in GeSe-based memories.     

Structural and dielectric properties of parylene-VT4 thin films

58% semi-crystalline thin parylene-VT4 (–H₂C–C₆F₄–CH₂−)_n films, have been investigated by dielectric spectroscopy for temperature and frequency ranges of [−120 to 380 °C] and [0.1–10⁵ Hz] respectively. The study comprises a detailed investigation of the dielectric constant, dielectric loss and AC conductivity of this fluoropolymer. Dielectric behavior of parylene-VT4 is represented by a low dielectric constant with values in the range of 2.05–2.35 while the dielectric losses indicate the presence of two relaxation processes. Maxwell−Wagner−Sillars (MWS) polarization at the amorphous/crystalline interfaces with activation energy of 1.6 eV is due to the oligomer orientation. Electrical conductivity obeys to the well-known Jonscher law. The plateau in the low frequency part of this conductivity is temperature-dependent and follows an Arrhenius behavior with activation energy of 1.17 eV (deep traps) due to the fluorine diffusion. Due to its thermal stability with a high decomposition temperature (around 400 °C under air and 510 °C under nitrogen) and due to its good resistivity at low frequency (10¹⁵–10¹⁷ Ω m⁻¹), parylene-VT4 constitutes a very attractive polymer for microelectronic applications as low k dielectric. Moreover, when parylene-VT4 is subjected to an annealing, the dielectric properties can be still more improved.     

Broadband antireflection properties of thin heterogeneous dielectric films

New exactly solvable flexible models of inhomogeneous thin film with smooth and deep variations of dielectric susceptibility epsilon(z) are presented. Formation of cutoff frequencies of such films (as well as the broadband antireflection), controlled by the profiles epsilon(z), is shown. The crucial role of gradients of epsilon(z) in the optics of strongly inhomogeneous media is emphasized.     

In-situ ellipsometry on sputtered dielectric and magneto-optic thin films

A four-gun magnetron sputtering chamber incorporating in-situ real-time spectroscopic ellipsometric analysis was used to grow magneto-optic memory structures. Data were taken at 44 wavelengths simultaneously from 410 nm to 750 nm, allowing the study of SiC/TbFeCo/SiC depositions on quartz in real time. These data were used to determine the sputter rates, optical constants, and the thicknesses of the films. The SiC data were taken at 1 min time intervals during growth, and the TbFeCo deposition was monitored continuously. Data were taken during the deposition of the entire structure without subjecting the sample to destructive analysis techniques or an oxidizing or reactive atmosphere.