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US6097058A
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Ferroelectric memory device and a method of manufacturing thereof
Assignee: Rohm Co Ltd
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Filing: 1999-01-22
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Granted: 2000-08-01
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Expires: 2019-01-22
Abstract
Abstract A ferroelectric layer having a low dielectric constant which is used for a ferroelectric memory element is provided. Also, the ferroelectric layer having a high melting point used for the ferroelectric memory element is provided. An FET 20 has a stacked structure including a gate oxidation layer 24, a floating gate 26, a ferroelectric layer 28, and a control gate 30 deposited on a channel region CH in that order, the channel region CH being formed in a semiconductor substrate 22 made of silicon. The ferroelectric layer 28 consists of a thin film made of a mixed crystal composed of Sr 2 (Ta 1-x Nb x ) 2 O 7 . The crystal structure of both Sr 2 Nb 2 O 7 and Sr 2 Ta 2 O 7 is pyramid quadratic structure, and their lattice constants are similar to each other. Their relative dielectric constants are low, and their melting points are high. Curie temperature related with their ferroelectricity is, however, too high in Sr 2 Nb 2 O 7 and too low in Sr 2 Ta 2 O 7 . In order to overcome the discrepancies, the ferroelectric layer 28 having desired curie temperature is formed with a mixed crystal made of Sr 2 (Ta 1-x Nbx) 2 O 7 .
Inventors
- 👤 Takashi Nakamura
- 👤 Yoshikazu Fujimori
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 02:50
CPC Classifications
H; H10; H10D; H10D30/00; H10D30/60; H10D30/701; H10D30/68
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
282 words
A ferroelectric memory device including a ferroelectric layer in which information being stored uses its hysteresis characteristics, wherein the ferroelectric layer is composed of a mixed crystal defined by expressions of; (A1 y1 A2 y2 . . . An yn ) 2 (B1 x1 B2 x2 . . . Bm xm ) 2 O 7 , and wherein x1+x2+ . . . +xm=1, and wherein y1+y2+ . . . +yn=1, and wherein each of x1, x2, . . . xm, y1, y2, . . . yn has a value equal to or greater than 0, and equal to or less than 1, and wherein at least two of x1, x2, . . . xm, y1, y2, . . . yn have values greater than 0, and less than 1, and wherein each of A1, A2, . . . , An is an element selected so as to be different from one another from a group consisting of elements belong to IIa group, IIIa group, and lanthanum series, where IIIa group consists of Sc, Y, La, and Ac, and wherein each of B1, B2, . . . , Bn is an element selected so as to be different from one another from a group consisting of Ti, Nb, Ta, Zr, Hf, Y, wherein the ferroelectric memory device includes a first capacitor having the ferroelectric layer, and a second capacitor connected to the first capacitor substantially in series, and wherein information is stored in accordance with a divided voltage applied to the ferroelectric layer of the first capacitor by applying a voltage which corresponds to the information to be stored to both ends of the first capacitor and the second capacitor connected in series.
Claim 2
Dependent Claim
282 words
A ferroelectric memory device including a ferroelectric layer in which information being stored uses its hysteresis characteristics, wherein the ferroelectric layer is composed of a mixed crystal defined by expressions of; (A1 y1 A2 y2 . . . An yn ) 2 (B1 x1 B2 x2 . . . Bm xm ) 2 O 7 , and wherein x1+x2+ . . . +xm=1, and wherein y1+y2+ . . . +yn=1, and wherein each of x1, x2, . . . xm, y1, y2, . . . yn has a value equal to or greater than 0, and equal to or less than 1, and wherein at least two of x1, x2, . . . xm, y1, y2, . . . yn have values greater than 0, and less than 1, and wherein each of A1, A2, . . . , An is an element selected so as to be different from one another from a group consisting of elements belong to IIa group, IIIa group, and lanthanum series, where IIIa group consists of Sc, Y, La, and Ac, and wherein each of B1, B2, . . . , Bn is an element selected so as to be different from one another from a group consisting of Ti, Nb, Ta, Zr, Hf, Y, wherein the ferroelectric memory device includes a first capacitor having the ferroelectric layer, and a second capacitor connected to the first capacitor substantially in series, and wherein information is stored in accordance with a divided voltage applied to the ferroelectric layer of the first capacitor by applying a voltage which corresponds to the information to be stored to both ends of the first capacitor and the second capacitor connected in series.
Claim 3
Dependent Claim
29 words
The ferroelectric memory device in accordance with claim 1, wherein curie temperature Tc of the ferroelectric layer is in a range of about 180° C. to about 600° C.
Claim 4
Dependent Claim
29 words
The ferroelectric memory device in accordance with claim 2, wherein curie temperature Tc of the ferroelectric layer is in a range of about 500° C. to about 600° C.
Claim 5
Dependent Claim
61 words
The ferroelectric memory device in accordance with claim 1, wherein the ferroelectric memory device comprises, a source region, a drain region, a channel region formed between the source region and the drain region, a substantially insulation layer disposed on the channel region, a ferroelectric layer disposed above the substantially insulation layer, and an upper conductive layer disposed on the ferroelectric layer.
Claim 6
Dependent Claim
28 words
The ferroelectric memory device in accordance with claim 4, wherein the ferroelectric memory device has a lower conductive layer between the substantially insulation layer and the ferroelectric layer.
Claim 7
Dependent Claim
42 words
The ferroelectric memory device in accordance with claim 1, wherein the ferroelectric layer is composed of a mixed crystal defined by expressions of; Sr 2 (Ta 1-x Nb x ) 2 O 7 , and wherein the value of x is 0<x<1.
Claim 8
Dependent Claim
24 words
The ferroelectric memory device in accordance with claim 6, wherein the value of x is in a range of about 0.1 to about 0.3.
Claim 9
Dependent Claim
17 words
The ferroelectric memory device in accordance with claim 7, wherein the value of x is about 0.3.
Claim 10
Dependent Claim
29 words
The ferroelectric memory device in accordance with claim 6, wherein curie temperature Tc of the ferroelectric layer is in a range of about 180° C. to about 600° C.
Claim 11
Dependent Claim
29 words
The ferroelectric memory device in accordance with claim 9, wherein curie temperature Tc of the ferroelectric layer is in a range of about 500° C. to about 600° C.
Claim 12
Dependent Claim
61 words
The ferroelectric memory device in accordance with claim 6, wherein the ferroelectric memory device comprises, a source region, a drain region, a channel region formed between the source region and the drain region, a substantially insulation layer disposed on the channel region, a ferroelectric layer disposed above the substantially insulation layer, and an upper conductive layer disposed on the ferroelectric layer.
Claim 13
Dependent Claim
28 words
The ferroelectric memory device in accordance with claim 11, wherein the ferroelectric memory device has a lower conductive layer between the substantially insulation layer and the ferroelectric layer.
References Cited (Backward Citations)
JPH09213899A
Cited
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