Ferroelectric memory with multiple-value storage states

• US 5,291,436 A
• Filed: 04/30/1992
• Issued: 03/01/1994
• Est. Priority Date: 07/25/1991
• Status: Expired due to Term

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Kamisawa, Akira
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): KESSELL, MICHAEL
• Application Number:
  US07/876,186
• Time in Patent Office: 670 Days
• Field of Search: 365/145, 365/149, 365/185
• US Class Current: 365/145
• CPC Class Codes: G11C 11/5657 using ferroelectric storage elements

Abstract

A ferroelectric memory using ferroelectric capacitors, in which a plurality of electrodes are juxtaposed on each of the two sides of one ferroelectric substance, and the electric fields between the electrodes are controlled, so that more than two different amounts of charges are provided by the ferroelectric capacitors formed by the electrodes. Thereby, the quantity of storage per ferroelectric cell is increased without increase of the cell area.

Claims

1. A ferroelectric memory comprising:

one electrode relatively large in area provided on a first side of a body of ferroelectric substance;

two electrodes relatively small in area provided on a second side of the same body of ferroelectric substance;

a first circuit for selecting one of said electrodes on said second side of said ferroelectric substance in combination with said electrode on said first side of said ferroelectric substance; and

a second circuit for applying a pulse electric field across said electrodes thus selected and said electrode on said first side of said ferroelectric substance;

whereby three values of polarization inversion states are provided by selectively combining said electrodes on said second side of said ferroelectric substance with said electrode on said first side of said ferroelectric substance.

2. A ferroelectric memory comprising:

at least two electrodes provided on a first side of one ferroelectric substance;

at least two electrodes provided on a second side of said ferroelectric substance;

and circuit components for applying a pulse electric field between one electrode on said first side of said ferroelectric substance and one of the electrodes on said second side of said ferroelectric substance to provide at least three values of polarization inversion states.

3. A ferroelectric memory comprising:

two electrodes provided on a first side of a ferroelectric substance;

two electrodes provided on a second side of said ferroelectric substance;

a first circuit for selecting one electrode from said two electrodes on said first side of said ferroelectric substance and one electrode from said two electrodes on said second side of said ferroelectric substance; and

a second circuit for applying a pulse electric field across the two electrodes thus selected,

wherein four values of polarization inversion states are provided by selection of said electrodes by said first circuit.