Norman E. Abt

Electrical and reliability properties of PZT thin films for ULSI DRAM applications

The electrical and reliability characteristics of ferroelectric capacitors fabricated using sol-gel derived 50/50 lead-zirconate-titanate (PZT) thin films have been examined for ULSI DRAM (dynamic random access memory) applications. Various electrode materials, film thicknesses (200 nm to 600 nm) and capacitor areas were used. A large stored-energy density (Q/sub c/) of 15 mu C/cm/sup 2/ (at 125 kV/cm) was measured using different methods. The results indicate that PZT thin films exhibit material properties which might satisfy the requirements of ULSI DRAMs.<<ETX>>

Thermal stability of ferroelectric memories

The authors review the latest fatigue and aging data on ferroelectric memory products and discuss thermal characteristics which limit the nonvolatile data retention storage temperature. They evaluate the effects of thermal excursions on the remanent polarization level in polycrystalline films. An excursion to an elevated temperature has been found to cause a reduction in retained polarization. The reduction is a function of the maximum temperature difference. The loss in capacitor polarization imposes constraints on the design of reliable integrated ferroelectric nonvolatile memory devices.<<ETX>>

High frequency fatiguing of ferroelectric capacitors

Abstract Ferroelectric memories which use destructive readout require a rewrite after a read. For such memories every data access adds one cycle of fatigue to the capacitor. High frequency cycling is then required to demonstrate the long term fatigue effects and determine reliability of these memories. To avoid noise and get clean measures of remanent polarization large capacitors are used. Unfortunately, these also present a large capacitive load and attempts to perform high speed cycling are limited by the typically low current drive capabilities of pulse generators. This results in most of the applied voltage being dropped across the output impedance of the driver. In this paper we will describe an exerciser specifically designed to drive multiple ferroelectric capacitors at 6 Mhz. With this system we have measured fatigue characteristics beyond 1013 cycles on 100 × 100 and 20 × 20 μm2 capacitors.