Effects of nitrogen doping and working pressure on the crystallization of GeiSb₄Te₇ thin films for PRAM applications

The phase change random access memory (PRAM) has recently been ascending to become the most potential candidate for the next-generation nonvolatile memory. In this paper, we deposited Ge₁Sb₄Te₇ as a phase change material on a glass substrate by DC magnetron sputtering at various working pressures of 5 × 10^-3, 9 × 10^-3 and 13 × 10^-3 Torr and we performed nitrogen doping by flowing nitrogen gas during deposition. To verify the nitrogen doping we analyzed the secondary ion mass spectrometry (SIMS) data and observed the presence of nitrogen-doping contents. We measured the sheet resistance and the thickness reduction. We observed a reduction of the sheet resistance and the thickness of the films that had been annealed, we also observed an increase of the sheet resistance from 4.3 × 10³ Ohm/sq to 2.8 × 10⁵ Ohm/sq with additional nitrogen doping after annealing in the case of the film deposited at 9 × 10^-3 Torr. Through the 3-w thermal conductivity measurements, we observed an increase in the thermal conductivity from 0.37 to 0.49 W/mK and a decrease with nitrogen doping from 0.49 to 0.43 for the films that had been annealed. In X-ray diffraction (XRD) results, FCC and HCP peaks were observed at annealing temperatures of 175 °C and 300 °C and the role of nitrogen doping that disturb the crystallization during a phase change was also observed.