Reza Moazzami

A model for electrical conduction in metal‐ferroelectric‐metal thin‐film capacitors

Time‐zero current‐voltage characteristics and time‐dependent current behavior of metal‐ferroelectric‐metal (Pt‐PZT‐Pt) capacitor structures have been studied. Under constant‐voltage stressing, the current density through the 1500‐A‐thick lead‐zirconate‐titanate (PZT) film exhibits a power‐law dependence on time, with the exponent (∼0.33) independent of temperature and voltage. Electrode material dependence of current density indicates that the conventional model of trap‐limited single‐carrier injection over nonblocking contacts is inadequate to explain the time‐zero current. A change in top electrode material from Pt to In leads to the observation of work‐function‐driven Schottky contacts between the metal and ferroelectric. The current‐voltage characteristics fit a two‐carrier injection metal‐semiconductor‐metal model incorporating blocking contacts, with distinct low‐ and high‐current regimes (PZT is assumed to be p‐type and trap‐free in this model). Temperature‐dependent I‐V measurements indicate a Pt‐...

Materials interactions in the integration of PZT ferroelectric capacitors

Abstract Investigations of materials interactions that complicate the integration of PZT ferroelectric capacitors into CMOS technologies are discussed. These include interactions within the Pt/Ti electrodes structure, the reactions of sol-gel deposited PZT during crystallization with various underlying dielectrics (SiO2, Si3N4, Al2O3, and TiO2), and the impact of other integrated circuit processes on fabricated capacitors.

Impact of Backend Processing on Integrated Ferroelectric Capacitor Characteristics

Integration of a ferroelectric capacitor module in a standard CMOS process subjects the ferroelectric to various ambients during backend processing, some of which can render the ferroelectric essentially non-operational for NVRAM applications. Post-crystallization processing of sol-gel deposited integrated ferroelectric PZT capacitors in the presence of hydrogen-containing, reducing ambients is observed to degrade the nonvolatile polarization. Low-pressure hydrogen anneals at temperatures as low as 200°C substantially degrade the nonvolatile polarization while the DRAM polarization remains roughly constant. Leakage current drops by one order of magnitude and fatigue is accelerated. A ferroelectric capacitor module can be integrated with minimal degradation with careful modifications in the backend processing.

High-permittivity lead-based perovskite dielectrics for DRAM applications

Abstract Suppression of the nonvolatile polarization in lead zirconate titanate films by La doping or by use of films 100 nm or less in thickness provides the highest charge storage densities yet observed. These films also satisfy leakage current density and TDDB requirements for very high density DRAMs, and show good resistance to fatigue.

Integration of ferroelectric capacitor technology with CMOS

Ferroelectric technology has several desirable features for low-power nonvolatile memories including low operating voltages (read and write as low as 1.5 V), high-speed write operation (intrinsic switching times <2 ns), long-term endurance (>10/sup 13/ read/write cycles), and small cell size (potentially near DRAM densities). Realization of practical memories employing ferroelectric technology requires successful integration with CMOS. However, very little has been reported on the process integration issues unique to ferroelectric technology. This paper is the first detailed report of these integration issues. The paper discusses the impact of CMOS backend processing on ferroelectric capacitors as well as the effect of capacitor fabrication on transistor characteristics.<<ETX>>

Ferroelectric PZT Thin Films For Low-voltage Nonvolatile Memory

This study investigates the scaling potential of sol gelderived ferroelectric lead zirconate titanate (PZT) thin films for future nonvolatile memories. Ferroelectric hysteresis loops are exploited to demonstrate nonvolatile memory operation at internal voltages as low as 1.5V with a readwrite endurance cycles. Fenroelectric PZT capacitor technology holds promise as an alternative to conventional floating gate nonvolatile memory technologies for low-voltage low-power nonvolatile memories.