Patent ID: 6421268
Filing Date: 2002-07-16
Classification: G11C

Abstract:
A method for driving a semiconductor memory including a ferroelectric capacitor for storing a multi-valued data in accordance with displacement of polarization of a ferroelectric film thereof and a reading field effect transistor that is formed on a substrate and has a gate electrode connected to a first electrode corresponding to one of an upper electrode and a lower electrode of said ferroelectric capacitor for detecting the displacement of the polarization of said ferroelectric film, comprising:a first step of writing a multi-valued data in said ferroelectric capacitor by applying a relatively high first writing voltage or a relatively low second writing voltage between said first electrode and a second electrode corresponding to the other of said upper electrode and said lower electrode of said ferroelectric capacitor; a second step of removing a potential difference induced between said first electrode and said second electrode; and a third step of reading the multi-valued data by detecting the displacement of the polarization of said ferroelectric film by applying a reading voltage between said second electrode and said substrate, wherein said reading voltage has the same polarity as said first writing voltage and is set to such magnitude that, in applying said reading voltage, a first potential difference induced between said gate electrode and said substrate when the multi-valued data is written by applying said first writing voltage is smaller than a second potential difference induced between said gate electrode and said substrate when the multi-valued data is written by applying said second writing voltage.