Fabrication and investigation of three-dimensional ferroelectric capacitors for the application of FeRAM

Abstract

Ferroelectric capacitors made by lead zirconate titanate (PZT) thin films and iridium electrodes are fabricated on three-dimensional structures and their properties are investigated. The iridium films are grown by Plasma Enhanced MOCVD at 300°C, while the PZT films are deposited by thermal MOCVD at different process temperatures between 450°C and 550°C. The step coverage and composition uniformity of the PZT films on trench holes and lines are investigated. Phase separation of PZT films has been observed on both 3D and planar structures. No clear dependences of the crystallization and composition of PZT on 3D structure topography have been found. STEM EDX line scans show a uniform Zr/(Zr+Ti) concentration ratio along the 3D profile but the variation of the Pb/(Zr+Ti) concentration ratio is large because of the phase separation. 3D ferroelectric capacitors show good ferroelectric properties but have much higher leakage currents than 2D ferroelectric capacitors. Nevertheless, during cycling tests the degradation of the remnant polarization between 2D and 3D capacitors is similar after 109 switching cycles. In addition, the sidewalls and bottoms of the 3D structures seem to have comparable remnant polarizations with the horizontal top surfaces.

A computational study of hafnia-based ferroelectric memories: from ab initio via physical modeling to circuit models of ferroelectric device

“…The generation rate is given by = 1/τ in Eq. (11). Within this picture, the polarization of the grain is considered reversed when a certain critical number n of generated nuclei merge together into a single domain occupying the entire grain.…”

“…This is adding new integration challenges for the complex materials not only of the ferroelectric itself but also the required metal-oxide electrodes. For this challenge no solution can be provided yet [10,11]. Therefore, the development of such perovskite based memories were successful but at the same time seem to have hit a wall at about the 100 nm groundrules [12].…”

“…(11), represents a source of flexibility and of new opportunities for a future memory design. Field and time dependence of ferroelectric switching in ultra-scaled FeFETs.…”

Nonvolatile Random Access Memory and Energy Storage Based on Antiferroelectric Like Hysteresis in ZrO2

“…Furthermore, the high fields needed to reach the high ESD values when using perovskite‐based supercapacitors draw direct concerns on reliability and stability of such devices. ZrO 2 ‐based dielectrics are, in contrast to perovskites, fully established within a 3D integration process which would yield much higher ESDs (see Figure a) which is owed to the much higher breakdown field strength. In state‐of‐the‐art DRAM process, an Al 2 O 3 interlayer is utilized between the two ZrO 2 layers for reduction of the leakage current and thus increase the reliability …”

Four-State Anti-Ferroelectric Random Access Memory

“…fabrication of 3D ferroelectric capacitor structures [9]. In this paper an alternative solution is proposed: the use of antiferroelectric capacitors for non-volatile 4-state antiferroelectric random access memory, termed here AFRAM.…”