A. Deineka

Hardness, intrinsic stress, and structure of the a-C and a-C:H films prepared by magnetron sputtering

Abstract The 1.5-μm thick carbon films prepared by magnetron sputtering of a carbon target in Ar, Ar +CH 4 and Ar+O 2 gas mixtures show that the higher their intrinsic stress, the higher their microhardness and the lower their resistivity. The a-C films obtained without ion bombardment (unbiased; the mean free path of sputtered C atoms larger or equal to the cathode–anode distance) show microhardness up to 25 GPa. The biased a-C films (i.e. with ion bombardment) achieve the highest microhardness (up to 50 GPa) and the lowest resistivity (0.01 Ω cm). An increase in Ar pressure, or the optional addition of O 2 , results in a decrease in the microhardness and intrinsic stress and an increase in the film resistivity. In comparison to a-C films, by adding CH 4 to Ar up to certain limit, the microhardness and intrinsic stress of these a-C:H films increase and subsequently decrease steeply. It was specified by analysis of the electron diffraction patterns of thin films (30–60 nm) deposited under the same conditions that the radius of the first co-ordination sphere of C atoms for all the films is in a good agreement with the value for graphite. The prime interplanar distance for biased a-C films is considerably lower than that for unbiased ones and for graphite. Our data indicate the sp 2 -bonded carbon structure of the deposited hard carbon films, in which the prime interplanar distance is reduced due to intrinsic stress. Thus, it is more suitable to explain the hardness origin as a consequence of the film nanostructure rather than the presence of sp 3 bonds .

Ion-beam induced chemical and structural modification in polymers

In order to increase the sensitivity to moisture uptake of polyimide (PI) and polyethersulfone films applied in bimorphic humidity sensors 50, 130 and 180 keV boron ions with irradiation doses between 1013 and 1016 B+/cm2 were implanted. A complex investigation of the following features has been carried out: chemical changes in the surface regions by attenuated total reflection–FTIR spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS); optical properties by spectroscopic ellipsometry; hardness and elastic modulus by depth-sensing low-load indentation technique; conductivity of modified polymer films. It could be shown, that the partial destruction of chemical bonding under ion bombardment leads to the creation of new amorphous and graphite-like structures, which increase the surface film conductivity by several orders of magnitude, and enhances the sensitivity of these polymer films to moisture uptake. The ion-beam irradiation destroys the anisotropic features of the refractive index of PI layers leading to its isotropization. Radiation-induced changes in the layer structure result in an increase of the hardness and elastic modulus of the modified layers up to ten and six times, respectively. The hardness and refractive index depth profiles were determined. The detectable effective modification depth estimated from the depth profiles is 250–300 nm at an ion energy of 50 keV and 400–450 nm at an ion energy of 180 keV.

Characterization of RF-sputtered self-polarized PZT thin films for IR sensor arrays

Abstract In this work, a complex investigation of film composition, microstructure and physical properties of RF-sputtered self-polarized PZT thin films for IR sensor arrays was carried out. Hydrostatic stresses in Si substrates near edges of Pt/PZT microstructures were predicted theoretically by finite element calculations and measured by spatially resolved Raman spectroscopy. High hydrostatic stresses were obtained in patterned sensor pixels by Raman piezo-spectroscopy. The laser-intensity-modulation method was applied for the investigation of the self-polarization profile, whereas the depth profile of the refractive index was determined by means of spectroscopic ellipsometry. Polarization and refractive index profiles as well as interface stresses affect IR-radiation sensor performance. Thickness and area dependences of IR-radiation detector detectivity and noise equivalent temperature difference were calculated. The applications of self-polarized IR sensor arrays in presence detection and IR imaging are demonstrated.

Influence of Surface and Interface on PZT Film Optical Properties

We present our results of spectroellipsometric investigation of PbZr0.235Ti0.765O3 (PZT) films deposited onto Si/SiO2/adhesion-layer/(111)Pt substrate by rf sputtering. By means of spectroscopic ellipsometry the depth profile of refraction index was obtained. It exhibits a strong dependence of optical properties of the PZT film on the distance to its interfaces. The depth of these disturbed layers reaches the value of 200 to 250 nm that is much more than can be expected on the base of usual considerations. The refractive index of the middle undisturbed part of the PZT film approaches the value for PZT bulk.

Optical Properties of Self-Polarized PZT Ferroelectric Films

In this work, the refractive index profile and the optical gap E 02 of PZT thin films was determined for the first time at elevated temperatures up to 500°C. Measurements were performed with J. A Woollam spectral ellipsometer working in rotate analyzer mode. To obtain the temperature dependence of optical constants, a specially constructed heating device was applied.

Optical refraction index and polarization profile of ferroelectric thin films

Abstract Analytical calculations of polarization and optical refraction index in ferroelectric thin films are performed in the framework of thermodynamic theory. The solution of Euler-Lagrange equation with different extrapolation lengths δ1 and δ2 on different surfaces enables to obtain the thickness dependence of inhomogeneous polarization. The maximal polarization decreases with the decrease of film thickness. The dimensionless critical thickness l 1c of thickness induced ferroelectric phase transition was expressed via extrapolation lengths and was shown to decrease from l 1c= π (δ1 = δ2 = 0) to l c = 0 (δ1, δ2 → ∞). The thickness dependence of the optical refraction index was found to be proportional to squared polarization. Refraction index and pyroelectric coefficient profiles were measured respectively by ellipsometry and LIMM methods in PbZr0,235Ti0,765O3 (PZT) thin films deposited onto Si/SiO2/ adhesion layer/(111) Pt substrate by RF sputtering. The comparison of the theory with observed refraction index profiles in PZT films with 1780, 1000 and 470 nm as well as pyroelectric coefficient in the film 1000 nm had shown that the theory describes the main features of observed profiles and their thickness dependence.

Oxidation of graphite-like carbon films with different microhardness and density

Abstract Evolution of microhardness, internal stress and thickness of three types of carbon (a-C) films (#1–3) with predominantly sp 2 bonds with different microhardness ( H =60, 24 and 20 GPa) and density after annealing in air for 1 h at temperatures of 100, 200, 300, 350 and 400 °C was investigated. The stable behavior of these quantities up to 400 °C demonstrated only superhard films from set #1. The films from set #2 ( H =24 GPa) showed the noticeable decrease in these values after annealing at 350 °C. The largest decrease of all the measured values after annealing at 350 °C showed the films from set #3. The films from series #2 and 3 fully vaporized after annealing at 400 °C. A considerable decrease has been observed not only in film thickness, but also in the density of films from set #3 after annealing at temperatures more than 300 °C, that indicates a modification of the film structure. Significant penetration of oxygen into film body without a loss of film thickness was observed in the range of 250–300 °C only for film #3. It was registered by the increase of resistivity, D band intensity in Raman spectra and sharp increase of the IR transmittance. Absorption bands at approximately 1750 and 1610 cm −1 which correspond to the vibrations of CO and CC appear in these IR spectra and simultaneously the G band in Raman spectra shifted to 1605 cm −1 . The film obtained has a graphite-like structure and its composition corresponds approximately to formula CO 0.15 CO 0.18 . This structure is very unstable and very quickly vaporized starting from 350 °C.

Polarization profile of RF-sputtered self-polarized PZT thin films

Abstract In this work, the laser-intensity-modulation method (LIMM) is applied for investigation of self-polarized sputtered Pb(Ti1−xZrx)O3 thin films. By means of spectroscopic ellipsometry the depth profile of refractive index was obtained. C-V measurements on samples of various thickness were performed to determine the interface capacitance and the space charge density. The work function of Pb(Ti1−xZrx)O3 surfaces was estimated by a modified Anderson method in an electron beam setup using graphite as a reference. The experimental results are discussed in terms of space charge formation and oxygen vacancy drift in the interface layer during thin film deposition. The influence of dipoles formed by intrinsic point defects on self-polarization is considered.

Nondestructive investigations of the depth profile of PZT ferroelectric films

Abstract Investigations of PbZr0.235Ti 0.765O3 (PZT) films of perovskite (pe) and pyrochlore(py) structure deposited onto Si/SiO2/ adhesion layer/(111) Pt substrate by RF sputtering were performed with J. A. Woollam spectral ellipsometer. Experimental data were compared with theoretical predictions.

Degradation and stress evolution in a-C, a-C:H and Ti-C:H films

Abstract Presented in this contribution are some observations of the stress evolution and degradations of diamond-like a-C, a-C:H and Ti-C:H (10–20 at.% of Ti) films deposited by magnetron sputtering of the C or Ti target in the Ar or Ar+CH 4 gas mixture. The compressive stresses increased during several days for all the Ti-C:H films regardless of their structure (amorphous or a-C:H with TiC nanocrystalline inclusions) and composition (10–20 at.% of Ti). This phenomenon was not observed for a-C and was slightly displayed for a-C:H films having high hydrogen content. The growth of stress was accompanied by a decrease of optical constants, n and k . Simultaneously, Raman spectra and composition of Ti-C:H films remained unchanged. The degradation in ambient air during several hours or days takes place mostly for the films prepared by reactive sputtering in the Ar+CH 4 gas mixture, while a-C films, sputtered from the C target in argon, demonstrated stable behavior despite their high compressive stress level.