ICMCTF1999 Session HP: HP Poster

It can be recognized that the orientation of bottom electrode has a great effect on the growth of PZT ferroelectric films and varies the ferroelectric properties of the film in of MFM(Metal-Ferroelectric-Metal) capacitance structure. In general, Pt has been used as a bottom electrode for the configuration of ferroelectric devices containing PZT, however the orientation Pt-bottom electrode is limitted as (111).

In this study, Pt substrates with preferred orientation of (111) or (100) were specially prepared by sputter deposition technique, PZT thin films were then coated by sol-gel process. In case of the bottom electrode of Pt (100) preferred orientation not reported before, a highly c-axis orientation of PZT films was observed in a tetragonal composition region where capacitive loading can be lower for the real application due to a small amount of lattice mismatch between (001) plane of PZT and Pt (100) bottom electrode. The composition of PZT films was fixed to the ratio of Zr/Ti = 40/60 with excess Pb content of 15 wt % . The influence of bottom electrode orientation on the structured and electrical properties of the films were revealed with XRD and SEM observations and P-E hysterysis curve, leakage current and fatigue measurements.

The specially constructed RF supersonic multi-jet plasma reactor technology was utilised for preparation of magnetic granular films with composition: ferromagnetic material + copper. There are the ferromagnetic granules dispersed in a non-magnetic metal matrix.

The co-sputtering of Fe and Cu nozzles was used to produce Fe-Cu films. Two plasma-jet nozzles (1st Fe stainless nozzle, 2nd copper nozzle) was used for about 50 minutes deposition in the following power regime: 500 W pulse mode for Fe nozzle and 50 W continual mode for Cu nozzle. For both channels the H₂ with Ar as a working gas mixture were used.

X-ray diffraction analysis shows the presence of crystalline Cu and the traces of Fe₂O₃. The composition determined by electron probe microanalysis technique was: 57.5 at.% of Cu , 38.3 at.% of Fe and 3.3 at.% of oxygen. Comparing the results of X-ray and microprobe analysis measurements one may conclude that the films consist of crystalline particles of Cu and traces of Fe₂O₃ which are embedded in Fe-rich amorphous matrix.

In addition the Fe-Ta-O films were prepared by co-sputtering of Fe and Ta nozzles. The distance between the nozzles was varied for two different samples to control stoichiometric ratio both sputtered components. The material prepared with the larger distance between the nozzles shows more sharp resonant peak at the FMR curve. The composition of the both films are: O: 27.1 at.% , Fe: 53.9 at.%, Ta: 19.0 at.% for the film prepared with the larger inter nozzles distance and O: 28.6 at.% , Fe: 62.2 at.%, Ta: 9.2 at.% for another film. X-ray diffraction analysis shows the presence of crystalline Fe, Ta and Fe₂O₃ phases for the both samples.

Such a thin film materials exhibit the effects of high magnetoresistance. Ferromagnetic resonance measurements show a weak and broad resonance peak both in plane and perpendicular orientation of external field. The calculated magnetisation for deposited samples was about 1500 Gs.

Unlike crystalline silicon the barrier formation and the transport mechanism in Schottky diodes of amorphous silicon is not properly understood because of its complex structure of the density of states. Nevertheles, attempts have been made in recent years to fabricate and characterize Schottky devices on a-Si:H films due to its importance as a photo-voltaic material.

In the present investigation we have studied the effect of film thickness on the barrier height and ideality factor of Au/a-Si:H Schottky diodes. Thin films of a-Si:H were grown on Al coated glass substrates by capacitive glow discharge of silane at 280°C, silane flow rate of 90 sccm, chamber pressure of 0.4 mbar and rf power of 12W at 13.56 MHz. Film thickness was varied from 0.32 µm to 2.45 µm by varying the deposition time. Then gold dots were vacuum deposited over the a-Si:H surface for Schottky contacts. The a-Si:H films were characterized for their electrical and optical properties prior to the device fabrication. The I_V characteristics of the diodes were determined at different temperatures and the ideality factor, n, and the barrier height α_bwere estimate.

The ideality factor, n, monotonically decreased with thickness from 2.06 at 0.32 µm to 1.66 at 2.45 µm. The high value of n suggests that the charge transport across the diode is not purely thermionic but also due to diffusion and recombination processes. The decrease in n value at higher film thickness could be due to reduction in recombination via localized states. We have observed a decrease in the density of gap states and the width of the exponential tail in a-Si:H films with increasing thickness from the optical and field-effect studies. This has resulted movement of the Fermi level E_f towards conducting band edge E_c. The reduction in barrier height α_b with thickness from 1.19V at 0.32 µmm to 1.05V at 2.45 µmm observed in the I-V characteristics was attributed to the decrease in E_c-E_f with increasing film thickness. This also gave rise to increase in the reverse saturation current J_o of the Schottky diode.