Random-Oriented (Bi,La)₄Ti₃O₁₂Thin Film Deposited by Pulsed-DC Sputtering Method on Ferroelectric Random Access Memory Device

Abstract

A ferroelectric (Bi,La) 4 Ti 3 O 12 (BLT) thin film fabricated by the pulsed-DC sputtering method was evaluated on a cell structure to check its compatibility to high density ferroelectric random access memory (FeRAM) devices. The BLT composition in the sputtering target was Bi 4.8 La 1.0 Ti 3.0 O 12 . Firstly, a BLT film was deposited on a buried Pt/IrO x /Ir bottom electrode stack with W-plug connected to the transistor in a lower place. Then, the film was finally crystallized at 700℃ for 30 seconds in oxygen ambient. The annealed BLT layer was found to have randomly oriented and small ellipsoidal-shaped grains (long direction: ~100 nm, short direction: ~20 nm). The small and uniform-sized grains with random orientations were considered to be suitable for high density FeRAM devices.

Development of crack free BLT thick films by chemical solution deposition technique

“…From the micrograph, the measured inter-planar spacing is 2.97 Å which corresponds to the (117) , stronger (006) orientation(c-axis) [28], stronger (117) orientation (a-axis) [21]. This result is also comparable to the PLD grown BLT films [4] and BLT films deposited by pulsed DC sputtering [29], although, higher values of remnant polarization are reported for epitaxial films having a-axis orientation. The capacitance vs voltage (C-V) curve…”

“…The dependence of capacitance on voltage is strongly non-linear which confirms the occurrence of ferroelectric domain switching. The dielectric permittivity calculated from C-V curve is around 250 which is in accordance with the permittivity value reported in literature [29].…”