Ferroelectric capacitor renewal method

US5525528A · kind A · utility

Assignee

• RAMTRON INTERNATIONAL CORPORATION · US

Inventors

• Stanley C. Perino · Fort Collins, US
• Sanjay Mitra · Colorado Springs, US

Key dates

• Filing date: Feb 23, 1994
• Grant date: Jun 11, 1996
• Expiry date: Feb 23, 2014

Classification

• Technology area (CPC H): Electricity
• CPC primary: H10B53/30

Abstract

Ferroelectric capacitors in an integrated memory are renewed to improve retention performance. The renewal method is performed on a wafer containing ferroelectric memory die. In one method, a rejuvenation anneal is performed after all electrical tests, including those at elevated temperatures, have been accomplished, but before the failed die have been inked. The rejuvenation anneal is performed at or above the Curie temperature of the ferroelectric material. In the preferred embodiment, the ferroelectric material is PZT, and the rejuvenation anneal is a thermal treatment at 400.degree. Centigrade in a nitrogen flow of roughly ten liters per minute for about an hour. In another method, separate electrical cycling and depoling operations are performed to provide the equivalent benefits of the single rejuvenation anneal. The electrical cycling operation is accomplished by writing about one hundred cycles at five volts alternating logic states into each ferroelectric capacitor into the array. The electrical cycling operation restores the symmetry and location of the hysteresis loop. The ferroelectric capacitor is then returned to the virgin state by a depoling operation. The electrica…