For the further scaling and lower voltage applications of nonvolatile ferroelectric memory, the effect of Kr/O2 sputtering for SrBi2Ta2O9 (SBT) thin film formation was investigated utilizing a SrBi2Ta2O9 target. The 80-nm-thick SBT films were deposited by radio-frequency (RF) magnetron sputtering on Pt/Ti/SiO2/Si(100). Compared with Ar/O2 sputtering, the ferroelectric properties such as larger remnant polarization (Pr) of 3.2 μC/cm2 were observed with decrease of leakage current in case of Kr/O2 sputtering. X-ray diffraction (XRD) patterns indicated that improvement of the crystallinity with suppressing pyrochlore phases and enhancing ferroelectric phases was realized by Kr/O2 sputtering.

We demonstrate a fast shutdown and resumption of a logic circuit applied a nonvolatile latch having SrBi2(Ta,Nb)2O9 (SBT) capacitors without a higher drive voltage than a logic voltage of 1.8 V. By assigning an individual drive circuit of the SBT capacitors to the nonvolatile latch not sharing a drive circuit with multiple nonvolatile latches, the fast shutdown and resumption of a logic circuit were completed in 7.5 ns at a drive voltage of 1.3 V. The fast shutdown and resumption without an addition of a high drive voltage to a logic circuit meets a requirement from power-saving applications of system LSIs fabricated in CMOS technologies at 90-nm and below.

We have integrated a phase change random access memory (PRAM), completely based on 0.24 µm-CMOS technologies using nitrogen doped GeSbTe films. The Ge2Sb2Te5 (GST) thin films are well known to play a critical role in writing current of PRAM. Through device simulation, we found that high-resistive GST is indispensable to minimize the writing current of PRAM. For the first time, we found the resistivity of GST film can be controlled with nitrogen doping. Doping nitrogen to GST film successfully reduced writing current. A 0.24 µm PRAM using N-doped GST films were demonstrated with writing pulse of 0.8 mA-50 ns for RESET and 0.4 mA-100 ns for SET. Also, the cell endurance has been enhanced with grain growth suppression effect of dopant nitrogen. Endurance performance of fully integrated PRAM using N-doped GST shows no fail bit up to 2E9 cycles. Allowing 1% failures, extrapolation to 85 indicates retention time of 2 years. All the results show that PRAM is one of the most promising candidates in the market for the next generation memories.