Ferroelectric capacitor with an asymmetric double-layer PLZT structure for FRAM

Abstract

We developed a lanthanum-doped Pb(Zr0.4,Ti0.6)O3 (PLZT)-based ferroelectric capacitor for low-voltage operation of ferroelectric memory for use in edge devices in the internet of things. The structure, consisting of PLZT stacked layers 30 and 90 nm thick, showed drastically improved performance in three main measures: low leakage current, high saturation polarization, and low saturation voltage. Secondary ion mass spectroscopy indicated that atomic interdiffusion between PLZT and IrOx in the top electrode (TE) was suppressed by the 30 nm thick PLZT, which plays the role of a diffusion barrier, producing a low leakage current and high saturation polarization. The higher oxygen atomic density of the PLZT near the TE interface lowers the oxygen vacancy, which should also suppress the leakage current and the P–V hysteresis shift (imprint). The large grain size and high crystalline quality of PLZT near the TE interface in the PLZT structure provide a high saturation polarization with low leakage current.

An improvement of low temperature characteristics of an La-doped Pb(Zr,Ti)O3 capacitor

“…In this experiment, we prepared two types of FC. One is called FC1, as a control specimen, fabricated by our previous method, 21) and the other is called FC2, fabricated by the newly developed method. After Pt and PLZT1 were sequentially deposited at RT on a SiO 2 -coated 200 mm diameter Si wafer, the specimens were annealed by rapid thermal annealing (RTA) at 600 °C in an Ar-based 2.0% O 2 atmosphere for 90 s (RTA 1).…”

“…We have reported that our developed ferroelectric capacitor (FC) consisting of two PLZT stacked layers revealed excellent electric properties of a low leakage current, high saturation polarization, and low saturation voltage. 21) However, polarization properties at lower temperatures up to −45 °C were found to be insufficient for low-voltage operation. Therefore, we sought to improve the polarization properties of PLZT-based FCs at low temperature.…”

“…Therefore, we sought to improve the polarization properties of PLZT-based FCs at low temperature. Since the control of the interface between the top electrode (TE) and PLZT was found to be crucial for obtaining polarization properties in our experiment, 21,22) we tried to employ a hightemperature sputter-deposited IrO x (1 < x < 2) or (HT-IrO x ) instead of our previously used RT deposited IrO x (RT-IrO x ). Furthermore, we tried to make both the PLZT and IrO x thinner, aiming at a precise patterning of the FC, because the FC was generally patterned by physically assisted plasma etching using an argon-containing etchant.…”