Method for detecting or preparing intercell defects in more than one array of a memory device

• US 6,167,541 A
• Filed: 03/24/1998
• Issued: 12/26/2000
• Est. Priority Date: 03/24/1998
• Status: Expired due to Term

• Current Assignee: MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management)
• Original Assignee: Micron Technology, Inc.
• Inventors: Damon, Tim G., Siek, David D.
• Primary Examiner(s): De Cady, Albert
• Assistant Examiner(s): LAMARRE, GUY J
• Application Number:
  US09/047,760
• Time in Patent Office: 1,008 Days
• Field of Search: 714/719, 714/718, 714/720, 257/296
• US Class Current: 714/719
• CPC Class Codes: G11C 11/401 forming cells needing refreshing or charge regeneration, i.e. dynamic cells
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/26 Accessing multiple arrays G11C29/24 takes precedence
• CPC Class Codes: G11C 29/50 Marginal testing, e.g. race, voltage or current testing

Abstract

A method of testing a memory device having two arrays of memory cells arranged in rows and columns. Sense amplifiers for respective columns are shared by the arrays, with the sense amplifiers being selectively coupled to the digit lines of respective columns in each array by respective isolation transistors. Cells of the memory array are tested by first writing known data bits to each of the cells. The isolation transistors for the first array are then turned on, and the isolation transistors for the second array are turned off. Predetermined voltages are coupled to the sense amplifiers through the digit lines of the first array by activating a row in the first array. A plurality of rows in the first array are then activated to couple the memory cells in each activated row to respective digit lines. The sense amplifiers are then coupled to respective digit lines in the second array by turning on the isolation transistors for the second array. A plurality of rows in the second array are then activated to couple the memory cells in each activated row to respective digit lines of the second array. The rows in the first and second arrays remain activated for a testing interval of sufficient duration to allow charge to transfer through any inter-cell defects between the cells in the activated rows and cells that are not in an activated row. The cells that are not in an activated row are then read to determine if the data originally written to the cells was altered by charge flowing through inter-cell defects. Inter-cell defects may also be repaired by activating the rows in the first and second arrays in a manner that couples adjacent memory cells to digit lines having different complimentary voltages.

Claims

1. A method of testing first and second memory arrays each having a plurality of memory cells arranged in rows and columns, the memory arrays further including a plurality of sense amplifiers shared by the first and second arrays in which each of the sense amplifiers is selectively coupled to a digit line of a respective column in the first and second arrays, the method comprising:

writing a known data bit to each of a plurality of the memory cells that are to be tested in the first and second arrays;

coupling a memory cell in each of a plurality of columns to a respective sense amplifier through a respective digit line of the first array to set the voltage of the digit lines and the sense amplifier for each of the plurality of columns in the first array;

activating a plurality of rows in the first array to apply the voltage set on each digit line to the memory cells in respective activated rows;

coupling each of the plurality of sense amplifiers to respective digit lines of the second array;

activating a plurality of rows in the second array to apply the voltage set on each digit line to the memory cells in respective activated rows;

leaving the digit lines coupled to the memory cells in the activated rows of the first and second arrays for a period of sufficient duration to transfer charge through any inter-cell defects between the memory cells in the activated rows and at least some of the memory cells that are not in the activated rows; and

reading data from at least some the memory cells that are not in the activated rows.

2. The method of claim 1 wherein the step of activating a plurality of rows in the first and second arrays comprises activating each of the rows in a sequence with only a single row being activated at a time.

3. The method of claim 1 wherein the step of activating a plurality of rows in the first and second arrays comprises sequentially activating groups of the rows.

4. The method of claim 1 wherein the first and second arrays are in respective first and second memory banks.

5. A method of detecting intercell defects in a plurality of memory arrays that share the same sense amplifier, comprising the steps of:

writing data to a first set of cells in the first memory array in a predefined pattern such that adjacent cells in the first set are at different voltage levels;

writing data to a second set of cells in the second memory array in a predefined pattern such that adjacent cells in the second set are at different voltage levels;

coupling the cells in a plurality of columns in a plurality of rows in the first memory array to a sense amplifier for each column so that the sense amplifier maintains the voltage on the memory cells in the first array;

coupling the sense amplifier for each column to digit lines of the second memory array;

coupling the cells in a plurality of columns in a plurality of rows in the second memory array to the sense amplifier for each column so that the sense amplifier for each column maintains the voltage on the memory cells in the second array;

after a selected period of time, decoupling the memory cells from the sense amplifiers; and

reading data from a plurality of memory cells in the first and second array that had not been coupled to a sense amplifier during the selected period of time.

6. The method of claim 5 wherein the step of writing data to a first set of cells in the first memory array comprises:

coupling a cell in each of a plurality of columns to a digit line in the column;

sensing the voltage of the digit line in each column using a plurality of respective sense amplifiers; and

coupling a plurality of cells in each of a plurality of columns to respective digit lines.

7. A method of detecting intercell coupling in a plurality of arrays of memory cells arranged in rows and columns, wherein each array is defined by respective word lines and digit lines, the digit lines including inverting and non-inverting digit lines, comprising the steps of:

prewriting a first selected group of cells in a first of the plurality of arrays to a first voltage level;

establishing the first voltage level on a respective first set of digit lines coupled to the first selected group of cells;

coupling voltages from the first set of digit lines to a second set of digit lines in the second array;

coupling a second selected group of cells in the second array to the second set of digit lines; and

after a testing interval, reading data from a third set of cells adjacent to the cells in the second set of cells.

8. The method of claim 7 wherein the first and second sets of digit lines are complementary digit lines where the first digit line has a true state at a first voltage level and the second digit line has a not true state at the first voltage level.

9. The method of claim 8, further including the step of, before the step of activating selected word lines to couple a second selected group of cells, prewriting the second selected group of cells to the first voltage.

10. The method of claim 8 wherein the step of establishing the first voltage level on a respective first set of digit lines includes the step of sensing cell voltages with sense amplifiers.

11. The method of claim 7 wherein the step of coupling voltages from the first set of digit lines to a second set of digit lines in the second array includes the step of activating isolation transistors coupled between the sense amplifiers and the second array.

12. A method of stressing memory cell nitride layers or repairing inter-cell defects extending between memory cells arranged in rows and columns in first and second memory arrays, the memory arrays further including a plurality of sense amplifiers shared by the first and second arrays in which each of the sense amplifiers are selectively coupled to a pair of complimentary digit lines of a respective column in the first and second arrays, the method comprising:

coupling a memory cell in each of a plurality of columns to a respective sense amplifier through a respective digit lines of one of the first and second arrays to set the voltage of the digit lines for each of the plurality of columns;

coupling each of the plurality of sense amplifiers to respective complimentary pairs of digit lines of the first array while isolating the sense amplifiers from respective pairs of digit lines of the second array;

activating a plurality of rows in the first array to apply the voltage set on a digit line for the respective column to the memory cells in respective activated rows, the rows being activated so that at least some of the memory cells that are adjacent to each other are coupled to respective digit lines that have different complimentary voltages so that a voltage will be developed across any inter-cell defects that are between the adjacent memory cells;

coupling each of the plurality of sense amplifiers to respective complimentary pairs of digit lines of the second array;

activating a plurality of rows in the second array to apply the voltage set on a digit line for the respective column to the memory cells in respective activated rows, the rows being activated so that at least some of the memory cells that are adjacent to each other are coupled to respective digit lines that have different complimentary voltages so that a voltage will be developed across any inter-cell defects that are between the adjacent memory cells; and

leaving the digit lines coupled to the memory cells in the activated rows of the first and second arrays for a period of sufficient duration for current flowing through inter-cell defects to open-circuit the inter-cell defects.

13. The method of claim 12 wherein the step of activating a plurality of rows in the first and second arrays comprises activating each of the rows in a sequence with only a single row being activated at a time.

14. The method of claim 12 wherein the step of activating a plurality of rows in the first and second arrays comprises sequentially activating groups of the rows.

15. The method of claim 12 wherein the first and second arrays are in respective first and second memory banks.

16. A method of establishing voltages on digit lines in first and second memory arrays that share a set of sense amplifiers in which the memory cells are arranged in rows and columns and the sense amplifiers are selectively coupled to a digit line of a respective column in the first and second arrays, the method comprising:

coupling a memory cell in each of a plurality of columns to a respective sense amplifier through a respective digit lines of one of the first and second arrays to set the voltage of the digit lines for each of the plurality of columns;

coupling each of the plurality of sense amplifiers to a respective pair of complimentary digit lines of the first array while isolating the sense amplifiers from respective digit lines of the second array; and

coupling each of the plurality of sense amplifiers to a respective pair of digit lines of the second array.

17. The method of claim 16 wherein the first and second arrays are in respective first and second memory banks.