SRAM cell with dynamic split ground and split wordline

• US 9,934,843 B2
• Filed: 10/06/2016
• Issued: 04/03/2018
• 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 QUOC
• Application Number:
  US15/287,274
• Publication Number:
  US 20170025169A1
• Time in Patent Office: 544 Days
• Field of Search: 36518905, 365148, 365154, 365156, 36518907, 36518909, 365191, 365208, 365 63
• 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:

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 GNDL and GNDR are kept common.

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 first inverter and the second inverter further comprise PFETs.

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

5. The memory cell of claim 1, wherein:

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.

6. The memory cell of claim 2, wherein the first inverter and the second inverter further comprise PFETs.

7. The memory cell of claim 2, 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.

8. The memory cell of claim 1, 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; and

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.

9. A read operation of a memory cell, comprising enabling a first transistor of an asymmetric memory cell to allow access of a first bitline to a storage cell, while raising or lowering a vertical ground line of two separated ground lines connected to transistors of the storage cell above or below ground, GND.

10. The read operation of claim 9, wherein the two separated ground lines allow for differential signaling.