Browse Prior Art Database

Volatile Redundancy Fuse Selection and Read Back

IP.com Disclosure Number: IPCOM000037201D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Kalter, HL: AUTHOR [+2]

Abstract

By the addition of registers and comparators to chips having fuse-blow redundancy, identification of blown fuses may be made without opening the chip package and redundant lines enabled by fuse blow may be disabled. Available redundant lines may be selected and used, even at the system level.

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Volatile Redundancy Fuse Selection and Read Back

By the addition of registers and comparators to chips having fuse-blow redundancy, identification of blown fuses may be made without opening the chip package and redundant lines enabled by fuse blow may be disabled. Available redundant lines may be selected and used, even at the system level.

When testing random-access memories (RAMs) having laser fuse blow activated redundancy, the RAM is subjected to test patterns to detect defective cells, rows and columns. Then, redundancy fixes are calculated and implemented by loading registers on the chip. These registers are in series with the fuses and force the redundant address comparator to become active when the test address is equal to the address in the register. Then, the RAM is subjected to test patterns to check for signal margin, pattern sensitivities and data retention with the internal data ORed. Normally, without having the registers, this latter set of tests which takes about 80 percent of the test time may not be ORed with the internal data because fuses have not yet been blown. Thus, test time is reduced.

Once fuses are blown, the register is loaded with the addresses of blown fuses. Thus, visual inspection is no longer required to determine addresses of blown fuses.

Referring to the figure, serial data on line 2, serial shift clock on line 4 and parallel load on line 6 all come into register 8 from test mode circuits 10. Register 8 is clear at power up and...