Characteristics of paired Bi(4-x)LaxTi3O12 (BLT) capacitors suitable for 1T2C-type FeRAM

The electrical characteristics of paired Bi(4-x)LaxTi3O12 (BLT) capacitors of the same area but different film thicknesses were investigated for 1T2C-type one-transistor and two-capacitor-type ferroelectric random access memory (FeRAM) application. The paired capacitors were fabricated by a sol–gel method. The thinner capacitor 150 nm in thickness was crystallized at 650°C, 750°C or 850°C for 10 min in O2 ambient, while the thicker capacitor 300 nm in thickness was crystallized at 750°C. It was found that, in the thinner capacitor, the nominal polarization decreased with increase in the crystallization temperature, which is probably due to the decrease in leakage current through the film, and the paired capacitors showed similar polarization vs electric field (P–E) characteristics to the thinner capacitor at 850°C of crystallization temperature. It was also found that the switching time of the thinner capacitor became short with increasing crystallization temperature, and both capacitors were fully switched by a 2-µs-wide pulse at 3 V. Next, the characteristics of data disturbance in writing operations to an array of 1T2C cells were simulated using these capacitors, and it was demonstrated that the data disturbance phenomenon was much improved by applying compensation pulses with opposite polarities.