Logic non-volatile memory cell with improved data retention ability

• US 7,968,926 B2
• Filed: 01/30/2008
• Issued: 06/28/2011
• Est. Priority Date: 12/19/2007
• Status: Expired due to Fees

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: Hsu, Te-Hsun, Huang, Cheng Hsiang, Huang, Chin-Yi
• Primary Examiner(s): Sandvik; Benjamin P
• Assistant Examiner(s): KUO, WENSING W
• Application Number:
  US12/022,943
• Publication Number:
  US 20090159946A1
• Time in Patent Office: 1,245 Days
• Field of Search: 257/300, 257/306, 257/315, 257/E27.102, 257/E27.103
• US Class Current: 257/300
• CPC Class Codes: G11C 16/0441 comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates
• CPC Class Codes: G11C 2216/10 Floating gate memory cells with a single polysilicon layer
• CPC Class Codes: H10B 41/30 characterised by the memory core region
• CPC Class Codes: H10B 41/60 the control gate being a doped region, e.g. single-poly memory cell
• CPC Class Codes: H10B 69/00 Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices

Abstract

A memory cell includes a semiconductor substrate; and a first, a second, and a third transistor. The first transistor includes a first dielectric over the semiconductor substrate; and a first floating gate over the first dielectric. The second transistor is electrically coupled to the first transistor and includes a second dielectric over the semiconductor substrate; and a second floating gate over the second dielectric. The first and the second floating gates are electrically disconnected. The memory cell further includes a first capacitor; a second capacitor electrically coupled to the first capacitor; a third capacitor; a fourth capacitor electrically coupled to the third capacitor, wherein each of the first, the second, the third and the fourth capacitors includes the semiconductor substrate as one of the capacitor plates. The third transistor is a selector of the memory cell and is electrically coupled to the first and the second transistors.

Claims

1. A non-volatile memory cell comprising:

a semiconductor substrate;

a first transistor comprising;

a first dielectric over the semiconductor substrate; and

a first floating gate over the first dielectric;

a second transistor electrically coupled to the first transistor, the second transistor comprising;

a second dielectric over the semiconductor substrate; and

a second floating gate over the second dielectric, wherein the first and the second floating gates are electrically disconnected;

a first capacitor;

a second capacitor electrically coupled to the first capacitor;

a third capacitor;

a fourth capacitor electrically coupled to the third capacitor, wherein each of the first, the second, the third, and the fourth capacitors comprises the semiconductor substrate as one of capacitor plates;

a third transistor as a selector of the non-volatile memory cell, wherein the third transistor is electrically coupled to the first and the second transistors, and wherein sources of the first and the second transistors are connected to each other when the selector is turned on and when the selector is turned off, and drains of the first and the second transistors are connected to each other when the selector is turned on and when the selector is turned off; and

a bit line electrically connected to a first source/drain region of the third transistor, wherein a second source/drain region of the third transistor is electrically connected to a second source/drain region of each of the first and the second transistors.

2. The non-volatile memory cell of claim 1, wherein the first and the second transistors share a common active region as one of the source/drain regions.

3. The non-volatile memory cell of claim 1, wherein the first and the second capacitors are electrically coupled to the first floating gate.

4. The non-volatile memory cell of claim 3, wherein the third and the fourth capacitors are electrically coupled to the second floating gate.

5. The non-volatile memory cell of claim 3, wherein the first and the second capacitors each comprises the first floating gate as one of capacitor plates.

6. The non-volatile memory cell of claim 3 further comprising:

a source line connected to a first source/drain region of each of the first and the second transistors; and

a word line connected to a gate electrode of the transistor.

17. The non-volatile memory cell of claim 1, wherein the drains of the first and the second transistors are directly connected.

7. A non-volatile memory cell comprising:

a semiconductor substrate;

a first transistor comprising;

a first dielectric over the semiconductor substrate; and

a first floating gate over the first dielectric;

a second transistor electrically coupled to the first transistor, the second transistor comprising;

a second dielectric over the semiconductor substrate; and

a second floating gate over the second dielectric, wherein the first and the second floating gates are electrically disconnected, and wherein source regions of the first and the second transistors are interconnected, and drain regions of the first and the second transistors are interconnected;

a first capacitor comprising the first floating gate as one of capacitor plates;

a second capacitor comprising the first floating gate as one of capacitor plates;

a third capacitor comprising the second floating gate as one of capacitor plates;

a fourth capacitor comprising the second floating gate as one of capacitor plates;

a third transistor comprising a first source/drain region connected to one of the interconnected source regions and the interconnected drain regions of the first and the second transistors;

a third floating gate over and electrically disconnected from the first and the second floating gates;

a fifth capacitor comprising the third floating gate as one of capacitor plates; and

a sixth capacitor comprising the third floating gate as one of capacitor plates.

8. The non-volatile memory cell of claim 7, wherein the first capacitor has a smaller capacitance than the second capacitor, and the third capacitor has a smaller capacitance than the fourth capacitor.

9. The non-volatile memory cell of claim 8, wherein:

the first capacitor comprises a first capacitor plate, wherein the first capacitor plate comprises a first active region, and a second active region interconnected to the first active region; and

the second capacitor comprises a second capacitor plate, wherein the second capacitor plate comprises the second active region, and a third active region interconnected to the second active region, and wherein the second active region has an opposite conductivity type than the first and the third active regions.

10. The non-volatile memory cell of claim 9, wherein:

the third capacitor comprises a third capacitor plate, wherein the third capacitor plate comprises a fourth active region, and a fifth active region interconnected to the fourth active region; and

the fourth capacitor comprises a fourth capacitor plate, wherein the fourth capacitor plate comprises the fifth active region, and a sixth active region interconnected to the fifth active region, and wherein the fifth active region has an opposite conductivity type than the fourth and the sixth active regions.

11. The non-volatile memory cell of claim 7 further comprising:

a source line connected to the interconnected source regions of the first and the second transistors;

a word line connected to a gate electrode of the third transistor; and

a bit line connected to a second source/drain region of the third transistor.

18. The non-volatile memory cell of claim 7, wherein the third transistor is physically located between the first and the second transistors.

19. The non-volatile memory cell of claim 7, wherein the third transistor is physically located on a same side of the first and the second transistors, and wherein the third transistor is electrically connected to an active region commonly shared by the first and the second transistors.

12. A non-volatile memory cell comprising:

a semiconductor substrate;

a first dielectric over the semiconductor substrate;

a first floating gate over the first dielectric;

a second dielectric over the semiconductor substrate;

a second floating gate over the second dielectric and electrically disconnected from the first floating gate;

a first, a second, and a third implanted region in the semiconductor substrate and adjacent the first floating gate, wherein the first, the second, and the third implanted regions are isolated by insulation regions in the semiconductor substrate;

a fourth, a fifth, and a sixth implanted region in the semiconductor substrate and adjacent the first and the second floating gates, wherein the fourth, the fifth, and the sixth implanted regions are isolated by the insulation regions;

a seventh, a eighth, and a ninth implanted region in the semiconductor substrate and adjacent the second floating gate, wherein the seventh, the eighth, and the ninth implanted regions are isolated by the insulation regions;

a third gate dielectric over the semiconductor substrate;

a word line over the third gate dielectric;

a tenth implanted region in the semiconductor substrate and adjacent the word line; and

an eleventh implanted region in the semiconductor substrate and adjacent the word line, wherein the eleventh implanted region is electrically connected to the fifth implanted region.

13. The non-volatile memory cell of claim 12 further comprising:

a bit line connected to the tenth implanted region; and

a source line connected to the second and the eighth implanted regions.

14. The non-volatile memory cell of claim 12, wherein the fourth and the sixth implanted regions are of p-type, and wherein the first, the second, the third, the fifth, the seventh, the eighth, and the ninth implanted regions are of n-type.

15. The non-volatile memory cell of claim 12, wherein the first, the fourth, and the seventh implanted regions are interconnected, the second and the eighth implanted regions are interconnected, and the third, the sixth, and the ninth implanted regions are interconnected.

16. The non-volatile memory cell of claim 15, wherein the first, the fourth, and the seventh implanted regions are connected to a program node, and wherein the third, the sixth, and the ninth implanted regions are connected to an erase node.