SRAM cell with dynamic split ground and split wordline

• US 10,347,327 B2
• Filed: 10/30/2017
• Issued: 07/09/2019
• 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:
  US15/797,788
• Publication Number:
  US 20180068716A1
• Time in Patent Office: 617 Days
• Field of Search: 36518911, 365190, 365203, 365177, 36518908, 36518916, 365194, 365205, 365207, 365102, 365149, 365154, 365156, 365157, 365188
• 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 the 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 left side cell node (CL) across the first access transistor from the BL;

a right side cell node (CR) across the second access transistor from the BR; 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;

the GNDL and the GNDR are separate vertical SRAM GND buses;

the GNDR and GNDL allow for differential signaling, and

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

2. The memory cell of claim 1, further comprising:

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

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

3. The memory cell of claim 1, wherein 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.

4. The memory cell of claim 1, wherein 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.

5. The memory cell of claim 1, wherein the first inverter of the cross coupled inverters comprises a PFET and an NFET and the second inverter of the cross coupled inverters comprises a PFET and an NFET.

6. The memory cell of claim 5, wherein 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.

7. The memory cell of claim 1, wherein each of the first inverter of the cross coupled inverters and the second inverter of the cross coupled inverters comprises two transistors.

8. The memory cell of claim 1, wherein each of the first inverter of the cross coupled inverters and the second inverter of the cross coupled inverters comprises at least two transistors.

9. The memory cell of claim 1, wherein the GNDR and GNDL are kept common to allow for differential signaling.

10. The memory cell of claim 1, wherein voltage of the GNDR and voltage of the GNDL are independently adjustable around a common GND.