Toyoji Ito

Ferroelectric Nonvolatile Memory Technology and Its Applications

Nonvolatile memory utilizing ferroelectric material is expected to be the ultimate memory due to its theoretical low power operation and fast access. We integrated a ferroelectric thin film using a standard complementary metal-oxide-semiconductor (CMOS) process and evaluated its basic characteristics and reliability including endurance and imprint effect. The film was prepared using a spin-on sol-gel method. A ferroelectric thin film formed using liquid source misted chemical deposition (LSMCD) was found to have almost the same characteristics as those of the film formed by the sol-gel method. No effects of the ferroelectric process on the CMOS transistors were observed. Design of ferroelectric memory cells and applications of the ferroelectric nonvolatile memory have been reviewed.

Embedded ferroelectric memory technology with completely encapsulated hydrogen barrier structure

A 0.18-/spl mu/m system LSI embedded ferroelectric memory (FeRAM) operating at a very low voltage has been developed for the first time. The low-voltage operation has been attained by newly developed stacked ferroelectric capacitors completely encapsulated by hydrogen barriers, which enable us to eliminate hydrogen reduction of the ferroelectric thin film during the back end of the line process including FSG, tungsten CVD (W-CVD), and plasma CVD SiN (p-SiN) passivation. A fabricated 1-Mbit one-transistor one-capacitor SrBi/sub 2/(Ta/sub x/Nb/sub 1-x/)/sub 2/O/sub 9/ (SBTN)-based embedded FeRAM operates at a low voltage of 1.1 V and ensures the endurance cycles up to 10/sup 12/ at 85/spl deg/C and the data retention time up to 1000 h at 125/spl deg/C, which is the most promising for mass production of 0.18-/spl mu/m low-power system LSI-embedded FeRAM and beyond.

A highly reliable ferroelectric memory technology with SrBi/sub 2/Ta/sub 2/O/sub 9/-based material and metal covering cell structure

A multilevel metal process-based highly reliable ferroelectric memory (FeRAM) has been developed. Highly reliable characteristics have been attained by two techniques. One is a newly developed ferroelectric material with mixed superlattice crystal of SrBi/sub 2/(Ta/sub x/,Nb/sub 1-x/)/sub 2/O/sub 9/ and Bi/sub 2/ (Ta/sub x/,Nb/sub 1-x/)O/sub 6/. Which provides an elevated remnant polarization while keeping a low coercive voltage. The other is a metal covering memory cell structure which makes the use of plasma silicon nitride (p-SiN) passivation possible without reduction of the ferroelectric thin film by a hydrogen plasma during p-SiN deposition, which results in no B degradation of the characteristics of cell capacitors. The FeRAM cell capacitors with the above newly developed ferroelectric material and metal covering structure have been fabricated by using a 0.6-/spl mu/ double level metal process. The fabricated cell capacitors show highly reliable characteristics such as the ensured retention of data written at a low voltage of 2.4 V and humidity resistance for 10 y under a high temperature of 70/spl deg/C, which is promising for commercialization of FeRAM and its embedded LSIs.