Highly Reliable 0.15 µm/14 F² Cell Ferroelectric Random Access Memory Capacitor Using SrRuO₃ Buffer Layer

Abstract

We investigated a novel technique of modifying the interface between a Pb(ZrxTi1-x)O3 (PZT) thin film and electrodes for high density 64 Mbit ferroelectric random access memory (FRAM) device. Using a SrRuO3 buffer layer, we successfully developed highly reliable 0.15 µm/14 F2 cell FRAM capacitors with 75-nm-thick polycrystalline PZT thin films. The SrRuO3 buffer layer greatly enhanced ferroelectric characteristics due to the decrease in interfacial defect density. In PZT capacitors with a total thickness of 180 nm for whole capacitor stack, a remnant polarization of approximately 42 µC/cm2 was measured with a 1.4 V operation. In addition, an opposite state remnant polarization loss of less than 15% was observed after baking at 150 °C for 100 h. In particular, we found that the SrRuO3 buffer layer also played a key role in inhibiting the diffusion of Pb and O from the PZT thin films.

Preparation of (111)-Oriented SrRuO3/Pt Electrodes for Pb(Zr,Ti)O3-Based Ferroelectric Capacitors: Grain Size and Roughness Impact

“…PZT-based capacitors with thin SrRuO 3 bottom electrodes [Figs. 8(a) and 8(b)] show good electric properties (P r $ 25 mCÁcm 2 and V c $ 0:5 V) comparable with those recently reported by other groups 12,18) A global change in the shape of the hysteresis loop with increasing SrRuO 3 thickness is visible by looking at the opening of the hysteresis loop at high field. Indeed, the hysteresis loops appear more and more opened as the SrRuO 3 thickness increases, which indicates a gradual increase in the leakage currents.…”

“…For these reasons, considerable effort has recently been focused on the integration of an SrRuO 3 bottom electrode for PZT-based ferroelectric capacitors. 8,12,13) In this paper, the impact of the process deposition parameters (temperature and oxygen partial pressure) on grain size, roughness and orientation of (111)-oriented SrRuO 3 films prepared by rf-sputtering is studied systematically by atomic force microscopy and X-ray diffraction (XRD) experiments. A second concern is related to the impact of the thickness of the SrRuO 3 layer on the microstructure and electrical properties of Pb(Zr,Ti)O 3based ferroelectric capacitors.…”

Effect of Film Thickness on Electrical Properties of Chemical Solution Deposition-Derived Pb(ZrxTi1-x)O3/LaNiO3/Si

“…Indeed, no diffusion was observed at PZT/SrRuO 3 interfaces. 24,25) The results of Raman spectra indicate that the stress is compressive. This compressive stress would be derived from the difference in the thermal expansion coefficients between PZT and LNO.…”

Crystal orientation dependency of ferroelectric property in rhombohedral Pb(Zr,Ti)O3 films

“…Tetragonal films also followed the estimated line as we already reported. 6) These data show that 100)-orientation of rhombohedral phase is known to have four equivalent orientation so-called engineering domain configuration. 24,25) This configuration is reported to increase the domain densities and large domain densities decreased the E c because the switching is pointed out to start from the domain boundaries.…”

“…Ferroelectric random access memories (FeRAMs) have been widely investigated due to their nonvolatility with low power consumption. [1][2][3][4][5][6][7][8] Present FeRAMs use tetragonal Pb(Zr x Ti 1¹x )O 3 films with Ti rich composition due to the large remanent polarization (P r ) and the good squareness (P r /P sat ) in polarization electric filed (P-E) relationships, 9) where P sat is the saturation polarization. However, this composition has a fundamental drawback of large switching voltage originated from a large coercive field.…”