Growth, dielectric properties, and memory device applications of ZrO ₂ thin films

In the advancement of complementary metal-oxide-semiconductor device technology, SiO₂ was used as an outstanding dielectric and has dominated the microelectronics industry for the last few decades. However, with the recent size downscaling, ultrathin SiO₂ is no longer suitable. ZrO₂ has been introduced as a high-k dielectric to replace SiO ₂. This paper reviews recent progress of ZrO₂ thin films as dielectric layers for volatile dynamic random access memory (DRAM) applications and as a gate dielectric for CMOS devices. Materials and electrical properties of ZrO₂ films obtained by different deposition methods are compared. The effects of different top and bottom electrodes, and different doping elements, on ZrO₂ dielectric properties are described. Applications discussed include the use of ZrO₂ in Ge and SiGe nanocrystal-embedded nonvolatile flash memory devices. ZrO₂ films as charge trapping layers in SOZOS (poly-Si/SiO₂/ZrO₂/ SiO₂/Si) and TAZOS (TaN/Al₂O₃/ZrO ₂/SiO₂/Si) based nonvolatile flash memory stacks, and bipolar, unipolar, and nonpolar ZrO₂-based resistive switching memory devices are also briefly discussed. The impact of electrode materials, metal nanocrystals, metal implantation, metal doping, metal layers, and oxide ion conductor buffer layer on resistive switching properties and switching parameters of emerging ZrO₂-based resistive switching memory devices for high speed, low power, nanoscale, nonvolatile memory devices are briefly reviewed. A roadmap of the applications of ZrO₂ thin film in future low power, nanoscale microelectronic device applications is realized from this review.