Electron spin resonance (ESR) measurements on (100)Si/SiOx/ZrO2 and (100)Si/Al2O3/ZrO2 stacks with nm-thick dielectric layers reveal, upon postdeposition oxidation (PDO) in the range of 650-800 degreesC, the appearance of various SiO2-characteristic defects, including E-' and EX centers and a 95-G doublet. These defects generally grow during PDO treatment, attesting to significant modification of the SiOx interlayer, and/or additional SiOx interlayer growth. The ESR results on E-' indicate that the SiOx interlayer formed in (100)Si/SiOx/ZrO2 is drastically inferior to standard thermal (100)Si/SiO2, exhibiting over one order of magnitude more O-deficiency centers. The (100)Si/Al2O3 system appears more robust in terms of SiOx interlayer growth, and has better interlayer properties. (C) 2004 American Institute of Physics.