TiO2 Based Conductive-Bridge-Random-Access-Memory

Abstract

NAND flash is currently facing physical limitations for 10nm technology because as NAND flash cells have been getting smaller, cell to cell interference significantly increase. To overcome these challenge, new memories have been developed. Conductive Bridge Random Access Memory (CBRAM) is a one of the most promising new memories due to its simple structure, low power consumption, high scaling potential, large on/off margin and high speed. It has been reported that resistivity switching of CBRAM is induced by filament formation and rupture due to metal cation movement in the solid electrolyte. In the previous our research work, we studied CuO based CBRAM using CuTe top electrode. But CuO is not a fab-friendly material. In this work, instead of CuO based material, TiO2 are used for solid electrolyte because TiO2 is fab-friendly material and it has a good compatibility with a conventional CMOS process. TiO2 exist in three phases in atmospheric pressure, i.e. anatase, rutile and brookite, which phase of TiO2 presents different physical properties. In this work, we compared switching characteristics of amorphous with anatase phases TiO2 CBRAM. XRD confirmed amorphous-anatase phase transition at annealing temperature of 400 oC, as shown in Fig.1. Based on the crystallinity of TiO2 thin film, two different samples were prepared, amorphous (W/O annealing) and anatase phase TiO2 CBRAM (400 oC annealing). The CBRAM was fabricated on plug type TiN bottom electrode patterned wafer. The size of the bottom electrode was 34nm to 1921nm. TiO2 layer was deposited by RF magnetron sputter. And CuTe electrode was deposited by DC magnetron sputter. The structure of the device was shown in Fig.2 (a). On/Off ratio of TiO2 based CBRAM with amorphous phase was greater than that with anatase phase TiO2 CBRAM because HRS (High Resistive State) of the amorphous phase TiO2 CBRAM was lower than that of anatase phase TiO2 CBRAM. The amorphous and anatase phase TiO2 based CBRAMs demonstrated the endurance cycles of 105 and 2X106 respectively. We will report the memory characteristic of two phases TiO2based CBRAMs and explained why they showed the different memory characteristic. * This work was financially supported by the Industrial Strategic Technology Development Program (10039191, The Next Generation MLC PRAM, 3D ReRAM, Device, Materials and Micro Fabrication Technology Development) funded by the Ministry of Trade, Industry and Energy (MOTIE), Republic of Korea and the Brain Korea 21 Plus, Republic of Korea. Figure 1