The influence of gamma irradiation on charge storage capability of HFO2/DY2O3/AL2O3 based charge trapping memory cell

The impact of annealing temperature and Cs-137 gamma-ray irradiation on Al/ HfO2/Dy2O3/Al2O3/n-Si (100) charge trapping memory (CTM) devices has been examined in this thesis. E-beam evaporation and RF magnetron sputtering procedures were both used to deposit the thin films. The samples were annealed at 300oC, 500oC, 700oC and 900oC in N2 ambient for 40min, while one sample was left as-deposited. The XRD and AFM were used to study the crystalline structure and surface textures of the thin film. It has been observed that the sample annealed at 900oC had only one weak peak (400) of Dy2O3 while other samples turned amorphous. With an increase in annealing temperature, the surface textures have been found to diminish. The lowest RMS value of 2.06nm was found at 900oC. The impact of frequency and annealing temperature on the CTM devices has been investigated through C-V curves. We found that interface state density had a huge impact on the value of capacitance in the accumulation region. It has also been found that the C-V curves decreased with an increase in the annealing temperature between 500oC and 900oC. This might be plausibly due to the formation of dangling bonds and interfacial layers at higher annealing temperatures. The C-V curves have been observed to be shifted to the positive and negative direction, respectively. The memory window (∆Vfb) were analysed and studied through the C-V hysteresis curves for various annealing temperature at -10V to +10V and back. The device annealed at 500oC was found to have a larger ∆Vfb of 0.44V compared to other devices. The ∆Vfb were obtained at different sweeping between ±10V and ±12. The largest memory window of 8.22V was achieved at ±12V for the device annealed at 700oC. This could be related to the good charge storage capability. The effect of radiation on CTM devices has also been studied intensively through C-V curves by using Cs-137 gamma-ray source in different doses of 4Gy to 128Gy. There was a shift both in ΔVmg and ΔVfb evinced from the C-V curves due to the ΔNot and ΔNit charges that were generated by irradiation. Moreover, the memory window was found to increase with an increase in the radiation dose.