Semiconductor nonvolatile memory cell
First Claim
1. In a semiconductor nonvolatile memory cell having a first dielectric film on a semiconductor substrate, a floating gate electrode which lies on the first dielectric film, a second dielectric film which lies on the floating gate electrode and a control gate electrode which lies on the second dielectric film,the improvement comprising said first and second dielectric films being formed such that the relations (a) and (b) hold:
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space="preserve" listing-type="equation">ε
.sub.2 /ε
.sub.1 ≧
13 (a)
space="preserve" listing-type="equation">t.sub.2 /t.sub.1 ≦
ε
.sub.2 /ε
.sub.1 ( b)where ε
1 is the relative permittivity of the first dielectric film, ε
2 is the relative permittivity of the second dielectric film, t1 is the thickness of the first dielectric film and t2 is the thickness of the second dielectric film.
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Abstract
In a floating-gate type nonvolatile memory cell, the second dielectric film between the floating gate and the control gate is made very higher in relative permittivity than the first dielectric film under the floating gate such that the relation ε2 /ε1 ≧13 and the relation t2 /t1 ≧ε2 /ε1 hold, where εand t represent relative permittivity and film thickness, respectively and subscripts 1 and 2 represent the first and second dielectric films, respectively. Strontium titanate, barium strontium titanate or lead zirconate-titanate is suitable as the material of the second dielectric film. In the case of, e.g. barium strontium titanate film, the proportion of Sr to Ba may vary in the direction of the film thickness. The second dielectric film may be made up of two (or more) different dielectric layers. The memory cell is low in writing and erasing voltages and excellent in endurance in terms of write/erase cycles.
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Citations
13 Claims
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1. In a semiconductor nonvolatile memory cell having a first dielectric film on a semiconductor substrate, a floating gate electrode which lies on the first dielectric film, a second dielectric film which lies on the floating gate electrode and a control gate electrode which lies on the second dielectric film,
the improvement comprising said first and second dielectric films being formed such that the relations (a) and (b) hold: -
space="preserve" listing-type="equation">ε
.sub.2 /ε
.sub.1 ≧
13 (a)
space="preserve" listing-type="equation">t.sub.2 /t.sub.1 ≦
ε
.sub.2 /ε
.sub.1 ( b)where ε
1 is the relative permittivity of the first dielectric film, ε
2 is the relative permittivity of the second dielectric film, t1 is the thickness of the first dielectric film and t2 is the thickness of the second dielectric film. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification