Ferroelectric thin film, method of manufacturing the same, ferroelectric memory device and ferroelectric piezoelectric device

Abstract

A ferroelectric thin film formed of a highly oriented polycrystal in which 180° domains and 90° domains arrange at a constant angle to an applied electric field direction in a thin film plane and reversely rotate in a predetermined electric field.

Description

[0001] Japanese Patent Application No. 2002-379418, filed on Dec. 27, 2002, is hereby incorporated by reference in its entirety. BACKGROUND OF THE INVENTION [0002] In recent years, research and development of a thin film such as PZT or SBT, and a ferroelectric capacitor and a ferroelectric memory device using such a thin film have been extensively conducted. The structure of the ferroelectric memory device is roughly divided into 1T, 1T1C, 2T2C, and simple matrix. Since the 1T ferroelectric memory device has retention time (data retention time) as short as one month due to occurrence of an internal electric field in the capacitor because of its structure, it is considered to be impossible to secure a 10-year guarantee generally required for semiconductors. The 1T1C and 2T2C ferroelectric memory devices have almost the same configuration as that of a DRAM, and include a select transistor. Therefore, the DRAM manufacturing technology can be utilized. Moreover, since the 1T1C and 2T2C ...

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Problems solved by technology

Since the 1T ferroelectric memory device has retention time (data retention time) as short as one month due to occurrence of an internal electric field in the capacitor because of its structure, it is considered to be impossible to secure a 10-year guarantee generally required for semiconductors.

However, PZT in the tetragonal region has not been put into commercial use as a ferroelectric memory device since reliability cannot be secured.

Moreover, Pb has the smallest bond energy with oxygen (38.8 kcal / mol), and tends to cause Pb deficiency to occur in the PZT crystal.

These defects result in space charge polarization, and cause imprint characteristics to deteriorate.

Moreover, O deficiency occurs from the charge neutrality principle, whereby Schottky defects occur due to the ionic crystal structure.

This causes leakage current characteristics to deteriorate, whereby reliability cannot be secured.

Therefore, in the case of using PZT as the ferroelectric material, it is impossible to utilize the Zr-rich composition used for a small capacity memory.

However, if the hysteresis shape becomes further narrowed, deterioration of imprint characteristics will come to the surface.

This causes the above-described problems to occur.

Therefore, it is impossible to increase the integration of the ferroelectric memory unless the problems of Ti-rich PZT are solved.

However, this technology does not describe the hysteresis loop of the ferroelectric capacitor necessary for the operation in detail.

Specifically, it becomes difficult to use the ferroelectric capacitor at a low voltage.

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