Static random access memory (SRAM) tracking cells and methods of forming the same

• US 10,163,496 B2
• Filed: 10/09/2017
• Issued: 12/25/2018
• Est. Priority Date: 01/29/2016
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: Liaw, Jhon Jhy
• Primary Examiner(s): Le, Thong Q
• Application Number:
  US15/728,345
• Publication Number:
  US 20180033481A1
• Time in Patent Office: 442 Days
• Field of Search: 365194, 365156, 365154, 365203, 365191, 365205, 36518518, 36518522, 365196, 365204, 3652101, 365226, 36523006
• CPC Class Codes: G11C 11/419 Read-write [R-W] circuits
• CPC Class Codes: H01L 28/00 Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor testing or measuring during manufacture H01L22/00; integration methods H01L21/70; integrated circuits H01L27/00; two-terminal components with a potential-jump or surface barrier H01L29/00; resistors in general H01C; inductors in general H01F; capacitors in general H01G

Abstract

An embodiment static random access memory (SRAM) array includes a writable SRAM cell disposed in a first row of the SRAM array and an SRAM read current tracking cell in the first row of the SRAM array. The SRAM current tracking cell includes a first read pull-down transistor and a first read pass-gate transistor. The first read pull-down transistor includes a first gate electrically connected to a first positive supply voltage line; a first source/drain electrically connected to a first ground line; and a second source/drain. The first read pass-gate transistor includes a third source/drain electrically connected to the second source/drain and a fourth source/drain electrically connected to a read tracking bit line (BL). The read tracking BL is electrically connected to a read sense amplifier timing control circuit.

Claims

1. A static random access memory (SRAM) array comprising:

a writable SRAM cell in a first row of the SRAM array;

a first SRAM tracking cell in the first row of the SRAM array, the first SRAM tracking cell comprising;

a first pair of cross coupled invertors;

a first transistor comprising;

a first gate electrically connected to an output of the first pair of cross coupled invertors;

a first source/drain; and

a second source/drain; and

a second transistor comprising;

a second gate electrically connected to a first ground line, wherein a voltage applied to the second gate is directly tied to a voltage of the first ground line;

a third source/drain electrically connected to the first source/drain; and

a fourth source/drain electrically connected to a read tracking bit line (BL),

wherein the read tracking BL is electrically connected to a read sense amplifier (SA) timing control circuit.

2. The SRAM array of claim 1 further comprising a first SRAM tracking control cell in the first row of the SRAM array and adjacent the first SRAM tracking cell, wherein the first SRAM tracking control cell electrically connects the second gate to the first ground line, and wherein the first ground line extends through the first SRAM tracking control cell.

3. The SRAM array of claim 2, wherein a gate electrode of the second gate extends continuously from the first SRAM tracking cell into the first SRAM tracking control cell.

4. The SRAM array of claim 1 further comprising a second SRAM tracking cell in a second row of the SRAM array different from the first row and comprising:

a third transistor comprising;

a third gate;

a fifth source/drain electrically connected to a second ground line; and

a sixth source/drain; and

a fourth transistor comprising;

a fourth gate electrically connected to a read current tracking control circuit;

a seventh source/drain connected to the second source/drain; and

an eighth source/drain connected to the read tracking BL.

5. The SRAM array of claim 4 further comprising a second SRAM tracking control cell in the second row of the SRAM array and adjacent the second SRAM tracking cell, wherein the second SRAM tracking control cell electrically connects the fourth gate to the read current tracking control circuit.

6. The SRAM array of claim 4, wherein the third gate is electrically connected to a positive voltage power supply line, and wherein a voltage applied to the third gate is directly tied to a voltage of the positive voltage power supply line.

7. The SRAM array of claim 6, wherein the second SRAM tracking cell comprises a second pair of cross coupled inverters, and wherein the third gate is electrically connected to the positive voltage power supply line through an output of a second pair of cross coupled inverters.

8. The SRAM array of claim 6, wherein the output of the first pair of cross coupled invertors electrically connects the first gate to the positive voltage power supply line, and wherein a voltage applied to the first gate is directly tied to the voltage of the positive voltage power supply line.

9. A static random access memory (SRAM) tracking cell comprising:

a first invertor comprising a first transistor and a second transistor sharing a first gate electrode;

a third transistor sharing the first gate electrode with the first transistor and the second transistor, the third transistor comprising;

a first source/drain electrically connected to a ground line; and

a second source/drain;

a fourth transistor having a second gate electrode, the fourth transistor comprising;

a third source/drain, the second source/drain and the third source/drain being disposed between the first gate electrode and the second gate electrode; and

a fourth source/drain;

a first gate contact electrically connecting the first gate electrode to a power supply line; and

a first source/drain contact electrically connecting the fourth source/drain to a tracking bit line (BL), wherein the tracking BL is electrically connected to a read sense amplifier (SA) timing control circuit.

10. The SRAM tracking cell of claim 9, wherein the first gate electrode is electrical connected to a positive voltage power supply line by a source/drain contact of a second invertor cross coupled to the first invertor.

11. The SRAM tracking cell of claim 9, wherein the first gate electrode is electrically connected to a ground line.

12. The SRAM tracking cell of claim 9, wherein the second gate electrode extends into an SRAM tracking control cell, and wherein the SRAM tracking control cell electrically connects the second gate electrode to a read current tracking control circuit.

13. The SRAM tracking cell of claim 9, wherein the second gate electrode extends into an SRAM tracking control cell, and wherein the SRAM tracking control cell electrically connects the second gate electrode to a ground line extending through the SRAM tracking read pass-gate control cell.

14. The SRAM tracking cell of claim 9 further comprising:

a third gate electrode adjacent the second gate electrode; and

a fourth source/drain region disposed on an opposing side of the third gate electrode as the first gate electrode, wherein the fourth source/drain region is electrically connected to a write tracking BL, and wherein the write tracking BL is electrically connected to a write SA timing control circuit.

15. A method comprising:

applying a positive supply voltage to a tracking bit line (BL), wherein the tracking BL is electrically connected to a read port of a static random access memory (SRAM) tracking cell, the SRAM tracking cell being disposed in a same row of an SRAM array as and having a different layout than a writable SRAM cell;

determining a discharge time of the tracking BL, wherein the discharge time of the tracking BL is an amount of time taken, by the tracking BL, to discharge from the positive supply voltage to ground through the read port; and

adjusting a clock cycle of a read sense amplifier (SA) in accordance with the discharge time of the tracking BL, wherein the read SA is electrically connected to a read bit line (RBL) of the writable SRAM cell.

16. The method of claim 15, the SRAM tracking cell comprises:

a pair of cross coupled inverters;

a first transistor comprising;

a first gate electrically connected to a positive voltage supply line by a first output of the pair of cross coupled inverters;

a first source/drain electrically connected to a first ground line; and

a second source/drain region; and

a second transistor

a second gate;

a third source/drain electrically connected to the second source/drain region; and

a fourth source/drain electrically connected to the tracking BL.

17. The method of claim 16, wherein determining the discharge time comprises:

charging the tracking BL to the positive supply voltage; and

applying the positive supply voltage to the second gate after the tracking BL is charged.

18. The method of claim 16, wherein the SRAM tracking cell further comprises a third transistor electrically connected to a second output of the pair of cross coupled inverters, and wherein a third gate of the third transistor is electrically connected to a second ground line.

19. The method of claim 18, wherein a fifth source/drain of the third transistor is electrically connected to a tracking write bit line (WBL), and wherein the method further comprises:

detecting a discharge time of the tracking WBL, wherein the discharge time of the WBL is a length of time taken, by the tracking WBL, to discharge from a positive supply voltage to ground through the third transistor; and

adjusting a clock cycle of a write SA in accordance with the discharge time of the tracking WBL, wherein the write SA is electrically connected to a WBL of the writable SRAM cell.

20. The method of claim 15, wherein the tracking BL is further electrically connected to a second read port of a second SRAM tracking cell, the second SRAM tracking cell being disposed in a different row of an SRAM array as the writable SRAM cell, and therein the second read port comprises a fourth transistor having a fourth gate electrically connected to a ground line.