Overview and Future Challenge of Ferroelectric Random Access Memory Technologies

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We have developed a low-temperature formation technique for ferroelectrics (${<}500$ °C), which is crucial for the ferroelectric random access memory (FeRAM) to be embedded in a leading-edge complementary metal oxide semiconductor (CMOS). A 53-nm-thick Bi4Ti3O12 film was successfully formed by metalorganic chemical vapor deposition at 450 °C and subsequent annealing at 500 °C. It was found that perovskite grains preferentially orient along the (110) and (111) directions and that the fabricated Bi4Ti3O12 capacitors show a remnant polarization ($2P_{\text{r}}$) of as large as 25.7 μC/cm2. In addition, we have adopted a nondestructive readout operation (NDRO) technique to extend read cycle endurance, in which the switched polarization at reading is automatically rewritten by readout voltage removal. We have demonstrated stable readout characteristics at more than $10^{11}$ cycles for 0.18 μm NDRO FeRAMs.
2007-04-30