Analysis and evaluation of HFO2 based resistive RAM devices for new generation non-volatile memories

Tekin, Serdar Burhan
The objective of this thesis is to investigate the most suitable embedded non-volatile memory (eNVM) cell for the 28 nm and below CMOS technology. HfO2 based resistive RAM (RRAM) memories are one of the most important candidates for new generation eNVMs due to their compatibility, reliability, low power consumption and high speed operation. In the scope of this thesis, several HfO2 based memory stacks were built and characterized by optical and electrical characterization methods. Raman and X-Ray diffraction (XRD) measurements were conducted for investigating the structural properties and effects of crystallinity on the oxide material. By these measurements, the difference between crystalline and amorphous HfO2 was observed. Also, the monoclinic and tetragonal phases of multi-crystalline HfO2 were determined. Temperature dependent dielectric permittivity measurements were performed on both samples. Amorphous HfO2 showed a greater temperature dependence compared to crystalline one. After that, 50 nm Ti metal was deposited on both crystalline and amorphous HfO2 coated wafers at different sizes as top electrode by thermal evaporation and 100 nm Al metal was coated on the back side of p-Si by the same way as bottom electrical contact. Therefore, capacitance-voltage (C-V) measurements were performed on these fabricated HfO2 based MOS devices. According to the results, dielectric constant of crystalline HfO2 based device is greater than the amorphous HfO2 based one. Then, 10 nm HfO2 based 1R resistive RAM (RRAM) devices having different metal electrode structures were examined by quasi-static current-voltage (I-V) measurements. Switching mechanisms of each type of memory stack were compared and the most efficient memory types were determined among these structures. According to the experiments, atomic layer deposited TiN and TiWN bottom electrodes are very promising in terms of reliability and power consumption. Finally, a packed crystalline HfO2 based 4K-1T1R RRAM device was electrically characterized by an FPGA based I-V measurement platform. According to the results, the device can be a suitable candidate for implementing security devices such as physical unclonable functions (PUFs) and random number generators (RNGs).
Citation Formats
S. B. Tekin, “Analysis and evaluation of HFO2 based resistive RAM devices for new generation non-volatile memories,” M.S. - Master of Science, Middle East Technical University, 2018.