Growth, dielectric properties, and memory device applications of ZrO2 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 SiO2. 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/ZrO2/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.