Non-volatile static memory cell

• US 6,556,487 B1
• Filed: 05/31/2001
• Issued: 04/29/2003
• Est. Priority Date: 09/20/2000
• Status: Expired due to Term

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Ratnakumar, Nirmal, Phelan, Cathal G., Murray, Kenelm G. D.
• Primary Examiner(s): Elms, Richard
• Assistant Examiner(s): PHUNG, ANH K
• Application Number:
  US09/871,172
• Time in Patent Office: 698 Days
• Field of Search: 365/189.08, 365/154, 365/156, 365/226, 365/185.01, 365/185.07, 365/185.05
• US Class Current: 365/185.08
• CPC Class Codes: G11C 14/00 Digital stores characterised by arrangements of cells having volatile and non-volatile storage properties for back-up when the power is down

Abstract

A non-volatile SRAM cell including (i) a nonvolatile memory element, (ii) a volatile memory element coupled to the nonvolatile memory element and (iii) a gate circuit coupled to the nonvolatile memory element. The gate circuit is configured to transfer data to and from a first input/output line into the volatile memory element.

Claims

1. A non-volatile SRAM cell, comprising:

a nonvolatile memory element;

a volatile memory element coupled to said nonvolatile memory element;

a gate circuit coupled to said nonvolatile memory element, wherein said gate circuit (i) is configured to transfer data to and from a first input/output line into said volatile memory element and (ii) comprises (a) a first transistor coupled between said first input/output line and said non-volatile memory element and (b) a second transistor coupled between said first input/output line and said volatile memory element.

2. The non-volatile SRAM cell according to claim 1, further comprising a second input/output line coupled to said volatile memory element.

3. The non-volatile SRAM cell according to claim 1, wherein said volatile memory element is coupled to said nonvolatile memory element, and said non-volatile SRAM cell is configured to store data from said volatile memory element in said nonvolatile memory element upon a power fail event.

4. The non-volatile SRAM cell according to claim 1, further comprising a word line coupled to said gate circuit.

5. The non-volatile SRAM cell according to claim 1, wherein said first transistor comprises a first pass transistor, and said second transistor comprises a second pass transistor coupled to a second input/output line, said second input/output line complementary to said first input/output line.

6. The non-volatile SRAM cell according to claim 1, wherein said nonvolatile memory element comprises a floating gate transistor.

7. The non-volatile SRAM cell according to claim 1, wherein said nonvolatile memory element comprises an electrically erasable and programmable nonvolatile transistor.

8. The non-volatile SRAM cell according to claim 1, wherein said volatile memory element comprises a latch.

9. The non-volatile SRAM cell according to claim 8, wherein said first transistor comprises a first pass transistor, and said second transistor comprises a second pass transistor coupled to a second input/output line, said second input/output line complementary to said first input/output line.

10. The non-volatile SRAM cell according to claim 9, wherein said latch is coupled to said nonvolatile memory element and said gate circuit.

11. The non-volatile SRAM cell according to claim 1, wherein said non-volatile SRAM cell forms a cell of a non-volatile SRAM array.

12. The non-volatile SRAM cell according to claim 11, wherein said non-volatile SRAM array comprises a plurality of blocks of the non-volatile SRAM cells, each of said blocks independently comprising N by m cells, wherein n and m are each independently an integer of at least 2.

13. A circuit comprising:

volatile means for storing data;

non-volatile means for storing said data upon a power fail event, coupled to said volatile data storing means; and

means for recalling said data from said non-volatile data storing means into said volatile data storing means when power is reapplied to a device containing the circuit, wherein said recalling means comprises (a) a first transistor coupled between a first input/output line and said non-volatile means and (b) a second transistor coupled between said first input/output line and said volatile means.

14. A method for recalling data previously stored in a volatile memory, comprising the sequential steps of:

storing said data in a non-volatile memory element coupled to said volatile memory upon a power fail event; and

recalling said data from said non-volatile memory element into said volatile memory in response to an application of power to a device containing both the non-volatile memory element and the volatile memory, wherein said non-volatile memory comprises (a) a first transistor coupled between a first input/output line and said non-volatile memory element and (b) a second transistor coupled between said first input/output line and said volatile memory.

15. The method according to claim 14, wherein said recalling step comprises the steps of:

writing a predetermined digital logic value into said volatile memory, and

reading said non-volatile memory element.

16. A circuit comprising:

a memory storage element;

a true bitline and a complement bitline configured to write data to and read data from said memory storage element; and

a floating gate device (i) coupled between said true bitline and said memory storage element and (ii) configured to store data from said memory storage element during a power down condition.

17. The circuit according to claim 16, further comprising:

a second floating gate device (i) coupled between said complement bitline and said memory storage element and (ii) configured to store data from said memory storage element during said power down condition.