SRAM cell with dynamic split ground and split wordline

• US 9,293,192 B1
• Filed: 12/02/2014
• Issued: 03/22/2016
• Est. Priority Date: 12/02/2014
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Wong, Robert C.
• Primary Examiner(s): Le, Thong Q
• Application Number:
  US14/558,238
• Time in Patent Office: 476 Days
• US Class Current: 1/1
• CPC Class Codes: G11C 11/418 Address circuits
• CPC Class Codes: G11C 11/419 Read-write [R-W] circuits
• CPC Class Codes: G11C 8/14 Word line organisation; Word line lay-out

Abstract

An SRAM cell with dynamic split ground (GND) and split wordline (WL) for extreme scaling is disclosed. The memory cell includes a first access transistor enabled by a first wordline to control access to cross coupled inverters by a first bitline. The memory cell further includes a second access transistor enabled by a second wordline to control access to the cross coupled inverters by a second bitline. The memory cell further includes a split ground line comprising a first ground line (GNDL) separated from a second ground line (GNDR). The GNDL is connected to a transistor of a first inverter of the cross coupled inverters and the GNDR is connected to a first transistor of a second inverter of the cross coupled inverters.

Claims

1. A memory cell, comprising:

a first access transistor enabled by a first wordline to control access to cross coupled inverters by a first bitline;

a second access transistor enabled by a second wordline to control access to the cross coupled inverters by a second bitline; and

a split ground line comprising a first ground line (GNDL) separated from a second ground line (GNDR), the GNDL being connected to a transistor of a first inverter of the cross coupled inverters and the GNDR being connected to a first transistor of a second inverter of the cross coupled inverters, and

wherein during read access for the second bitline, the GNDL is raised above common GND and/or GNDR is lowered below GND.

2. The memory cell of claim 1, wherein the GNDR and the GNDL are not strapped together.

3. The memory cell of claim 1, wherein:

the transistor of the first inverter and the transistor of the second inverter are NFETs;

the GNDL is connected directly to the NFET of the first inverter; and

the GNDR is connected directly to the NFET of the second inverter.

4. The memory cell of claim 3, wherein the first inverter and the second inverter further comprise PFETs.

5. The memory cell of claim 3, wherein the GNDL and GNDR are separate vertical ground lines.

6. The memory cell of claim 1, wherein during the read access for the second bitline, the GNDL is raised by about 10% of Vdd above GND and/or GNDR is lowered by about 10% of Vdd below GND.

7. The memory cell of claim 1, wherein during the read access of first bitline on BL, the GNDL is lowered by about 10% of Vdd below common ground GND and/or GNDR is raised about 10% of Vdd above GND.

11. The memory cell of claim 1, wherein GNDL and GNDR are kept common.

12. The memory cell of claim 1, wherein the GNDR and GNDL allow for differential signaling.

8. A memory cell, comprising:

a first access transistor enabled by a first wordline to control access to cross coupled inverters by a first bitline;

a second access transistor enabled by a second wordline to control access to the cross coupled inverters by a second bitline; and

a split ground line comprising a first ground line (GNDL) separated from a second ground line (GNDR), the GNDL being connected to a transistor of a first inverter of the cross coupled inverters and the GNDR being connected to a first transistor of a second inverter of the cross coupled inverters,

wherein during read access of first bitline on BL for, the GNDR is raised by about 10% of Vdd above common ground GND and/or GNDL is lowered by about 10% of Vdd below GND.

9. The memory cell of claim 8, wherein during the read access of the second bitline on BR, the GNDR is lowered by about 10% of Vdd below the common ground GND.

10. The memory cell of claim 8, wherein during the read access of the second bitline on BR, the GNDL is raised by about 10% of Vdd above the common ground GND and/or GNDR is lowered by about 10% of Vdd below GND.

13. A memory cell, comprising:

cross coupled inverters comprising PFETs and NFETs;

a bitline left (BL) which accesses a first inverter of cross coupled inverters by enabling a first access transistor;

a bitline right (BR) which accesses a second inverter of the cross coupled inverters by enabling a second access transistor;

a wordline left (WL) with enables the first access transistor;

a wordline right (WR) which enables the second access transistor; and

a split vertical ground line comprising a first vertical ground line (GNDL) separated from a second vertical ground line (GNDR), the GNDL being connected to the first inverter of the cross coupled inverters and the GNDR being connected to the second inverter of the cross coupled inverters, wherein;

during global reset of memory array to zero state, the GNDL is raised to Vdd to pull down CR and push up CL;

during global set of memory array to one state, the GNDR is raised to Vdd to pull down the CL and push up the CR;

during global set/reset of specific columns of memory array to specific zero state and one state, the GNDL of specific columns are raised to Vdd, and the GNDR of other specific columns are raised to Vdd;

the GNDL is connected directly to an NFET of the first inverter; and

the GNDR is connected directly to an NFET of the second inverter.

14. The memory cell of claim 13, wherein the first inverter and the second inverter further comprise PFETs.

15. The memory cell of claim 13, wherein:

during read access for the first bitline, the GNDR is raised above GND, by about 10% of Vdd and/or GNDL is lowered below GND by about 10% of Vdd; and

during read access for the second bitline, the GNDL is raised above GND, by about 10% of Vdd and/or GNDR is lowered below GND, by about 10% of Vdd.

16. The memory cell of claim 13, wherein GNDL and GNDR are kept common.