Y 2 O 3 films deposited by atomic vapor deposition on (100)Si with a 2 or 5 nm thick pregrown thermal SiO2 are investigated as possible charge trapping layers. Analysis of these structures using spectroscopic ellipsometry, photoconductivity, and internal photoemission reveals that Y2O3 has a 5.6 eV wide optical bandgap and a 2.0 eV conduction band offset with silicon. Photo(dis)charging experiments show that the optical energy depth of most of the traps exceeds 1.5 eV with respect to the Y2O3 conduction band, explaining the observed charge retention time of ∼108 s at room temperature, even in the absence of a blocking insulator.

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Metal-insulator-metal capacitors with SrxTiyOz (STO) dielectric films on TiN, Ru, and RuOx bottom electrodes with TiN top electrodes were studied. Metastable perovskite STO films with compositions in the Sr/(Sr+Ti)∼54–64 at. % range were obtained by crystallization at 600 °C in N2 of dielectric stacks grown by atomic layer deposition consisting of Sr-rich STO films [Sr/(Sr+Ti)∼64 at. %] on thin interfacial TiOx layers. The significant decrease in equivalent oxide thickness (EOT) and STO lattice parameter observed with increasing TiOx thickness indicates full intermixing of the TiOx and STO layers during the crystallization anneal, which results in the formation of an STO layer with higher Ti content and higher dielectric constant. The Sr-rich STO on TiOx stacks crystallize with small grain size, favorable for low leakage (JG). A significant improvement in JG for e-injection from the bottom electrode is obtained when using RuOx, as compared to TiN or Ru. A milder JG improvement with RuOx bottom electrode is also seen for e-injection from the top TiN electrode, indicating that higher quality perovskite STO films are formed on RuOx, or equivalently, that their trap density is lower. We propose oxygen scavenging from the STO by TiN or Ru electrodes, eliminated or reversed when using RuOx, as an explanation for the improvement. Using an optimized RuOx/TiOx/STO/TiN stack we obtained leakage of 10−7 A/cm2 (at 0.8 V) and 0.4 nm EOT.

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Effective electron tunneling mass mtunnel is extracted from trap-assisted leakage in Sr-rich strontium titanate and rutile titanium oxide films in metal–insulator–metal (MIM) capacitors and compared with theoretical values obtained from first principles calculations of the imaginary band structure. Optimum orientations of films and stoichiometry impacting mtunnel are also discussed. Because future vertical DRAM integration schemes also stipulate maximum thickness of the MIM capacitor, mtunnel is shown to be a critical parameter influencing intrinsic leakage and potentially limiting further scaling.