Investigation of Pt/Si/CeO₂/Pt MOS Device Structure by Impedance Spectroscopy

Abstract

Epitaxial growth of dielectric layers on silicon substrates has attracted a great deal of recent interest given their potential applicability in the fabrication of high quality silicon-on-insulator (SOI) structures, high density capacitor devices, and stable buffer layers between silicon and other materials. Cerium dioxide (CeO 2 ) appears to be a particularly attractive candidate, given its high dielectric constant and its compatibility with Si. To date, measurements of the electrical properties of CeO 2 films on Si have been largely limited to room temperature. In this study, thin films of CeO 2 were prepared by in situ pulsed laser deposition (PLD) on n-type (100) silicon substrates, with varied deposition conditions. Capacitance-voltage measurements (C-V) were used to characterize the response of the Pt/Si/CeO 2 /Pt MOS capacitor structure. Impedance measurements were performed from room temperature to 350 °C. This enabled the independent characterization of the electrical signature of the Pt/Si interface which was found to contribute insignificantly above approximately 150 °C. The CeO 2 film conductivity was found to be thermally activated with activation energy of ~0.45 eV, with its magnitude strongly dependent on film microstructure.

Electrical Properties of Nanocrystalline CeO[sub 2] Thin Films Deposited by In Situ Pulsed Laser Deposition

“…Films deposited at the higher oxygen pressure of 1.5 mTorr also showed contributions from ͑311͒ planes and reduced peak intensities suggested a reduced level of order characteristic of highly polycrystalline thin films, i.e., less well oriented ͑samples 2 and 4͒. 20 The mean grain size of the latter samples was estimated to be ϳ11 nm. As reported previously, using SEM and AFM micrographs, 21 no grains greater than ϳ40 to 50 nm in any of the samples were present.…”

“…Contribution from ͑311͒ planes and reduced peak intensities suggest a reduced level of order ͑sample 4͒ when compared to the ͑111͒ oriented films. As it was reported previously 20,21 using FESEM and AFM, both types of films were similar and consisted of grains with a size typically 40-50 nm in diameter, except that the highly oriented film included also bigger crystals up to 100 nm diameter. In the case of nanocrystalline CeO 2 thin film with thickness of 75 nm ͑sample 1͒, the film is considered to consist of parallel sets of grains and grain boundaries reaching through the film.…”

“…This may be compared with the highly oriented, columnar films with mean crystallite size 40-50 nm ͑sample 1͒ that is considered to consist of parallel sets of grains and grain boundaries reaching through the film. 20,21 Similar observations were made for the nanosized CeO 2 bulk ceramics, [24][25][26] nanosized CeO 2 thin film 16 and nanosized BaTiO 3 bulk ceramics 27 in which the electronic conductivity increased and the activation energy decreased dramatically, with decreasing grain size.…”