Redundant memory array for replacing memory sections of main memory

[0001] Embodiments of the present invention relate generally to semiconductor memory, and more particularly, in one or more of the illustrated embodiments, to semiconductor memory including redundant memory sections for replacement of memory sections of main memory.

[0002] Semiconductor memory typically includes redundant memory that is used to replace memory of a main memory array. Replacement, that is, mapping memory addresses of the memory to be replaced to redundant memory, most often occurs when some of the memory of the main memory array is defective. By replacing the defective memory with functional redundant memory, the memory can be salvaged rather than discarded.

[0003] The main memory array is divided into several sub-parts, for example, into banks of memory, which are further divided into memory sections of the main memory array. In many memory array architectures, a limited amount of redundant memory is provided for each of the memory sections, and can be used only to replace memory in the respective memory section. Unused redundant memory of a memory section cannot be used to replace memory of another memory section that is in need of more redundant memory. Consequently, if the number or arrangement of defective memory of a memory section is such that they cannot be repaired by the limited redundant memory dedicated to that memory section, the entire memory is discarded, or in some instances, downgraded to a memory having less overall capacity. Neither result is as desirable as fully repairing the memory.

[0004] FIG. 1 illustrates a portion of a main memory array 100. The main memory array 100 utilizes an “open-digit line” sense amplifier architecture. Open-digit line sense amplifier architectures, as known, have each digit line (of a pair of digit lines coupled to a respective sense-amplifier) extending into a different memory section of the array. FIG. 1 includes more detailed illustrations of two different groups 110, 120 of memory sections. Each group 110, 120 is shown in FIG. 1 as having a central memory section 132, a first adjacent memory section 134, and a second adjacent memory section 136. Additionally, each group 110, 120 includes a first set of sense-amplifiers 142 disposed between the central and first adjacent memory sections 132, 134 and a second set of sense-amplifiers 144 is disposed between the central and second adjacent memory sections 132, 136. Due to the open-digit line architecture, each sense-amplifier of the first set of sense-amplifiers is coupled to one digit line extending into the central memory section 132 and a second digit line extending into the first adjacent memory sections 134, and each sense-amplifier of the second set of sense-amplifiers is coupled to one digit line extending into the central memory section 132 and a second digit line extending into the second adjacent memory section 136.

[0005] In an open-digit line architecture, some failure modes result in a block of three adjacent memory sections failing. As previously discussed, each of the memory sections typically have limited redundant memory that can be used to repair several failures in the respective section. In order to minimize the extra area needed for the redundant memory, the amount of redundant memory per memory section is much less than would be needed to repair the entire memory section. If the failure requires more redundant memory than is available for the memory section, the memory section is considered un-repairable. In some instances, the inability to repair will result, as previously mentioned, in a block of three adjacent memory sections failing. For example, with reference to FIG. 1, where several of the digit lines of the central memory section 132, in particular, the digit lines coupled to sense-amplifiers of the first set of sense-amplifiers 142 and of the second set of sense-amplifiers 144, have short circuited to one another, the sense amplifiers of both the first and second sets of sense-amplifiers 142, 144 may be rendered inoperable. Consequently, not only is memory of the central memory section 132 defective but memory of the first and second adjacent memory sections may be defective as well, resulting in three adjacent memory sections failing. This type of catastrophic block failure will typically result in the entire memory device being considered inoperable.

[0006] Therefore, there is a need for a redundant memory architecture that can replace memory of entire memory sections and is sensitive to the desire to reduce the additional area used for redundant memory.

[0012] Certain details are set forth below to provide a sufficient understanding of embodiments of the invention. However, it will be clear to one skilled in the art that embodiments of the invention may be practiced without these particular details. Moreover, the particular embodiments of the present invention described herein are provided by way of example and should not be used to limit the scope of the invention to these particular embodiments. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the invention.

[0013] As previously discussed, memory arrays having open digit line sense-amplifier architectures are susceptible to block failures of three adjacent memory sections. Embodiments of the invention include at least one redundant memory array that can be used to replace a memory section of main memory, for example, when the defective memory of a memory section cannot be repaired by the limited redundant memory local to that memory section.

[0014] FIG. 2 illustrates a redundant array of memory 200 according to some embodiments of the invention. The redundant array of memory 200 may be included in a redundant memory architecture according to embodiments of the invention, as will be described in more detail below. The redundant array of memory 200 includes four memory sections 210(0)-210(3). Memory sections 210(0) and 210(1) share a set of sense-amplifiers 220(0) and memory sections 210(2) and 210(3) share a set of sense-amplifiers 220(1). The sense-amplifiers of the sets 220(0), 220(1) have an open-digit line architecture. Column decoder circuits 230(1), 230(2), row decoder circuits 234(1), 234(2), and data sense-amplifiers 240, which can be implemented using circuits and designs known by those ordinarily skilled in the art, are also illustrated in FIG. 2. Operation of the column decoder circuits 230(1), 230(2), row decoder circuits 232(1), 232(2), and data sense-amplifiers 240 is conventional.

[0015] In some embodiments, the digit lines of the sense-amplifiers of the sets 220(0), 220(1) are coupled to the same number of memory cells as digit lines for the memory sections of a main memory array. That is, the digit lines extending through the memory sections 210(0)-210(3) are the same “length” as the digit lines extending through the memory sections of the main memory array.

[0016] In other embodiments, the digit lines extending through the memory sections 210(1)-210(3) of the redundant memory array 200 are coupled to fewer memory cells than the digit lines extending through the memory sections of main memory array. For example, in some of these embodiments, the digit lines of the sense-amplifiers of the sets 220(0), 220(1) are coupled to approximately half as many memory cells as digit lines for the memory sections of the main memory array. That is, the digit lines extending through the memory sections 210(0)-210(3) are approximately half the length of the digit lines extending through the memory sections of the main memory array. In embodiments having digit lines half as long, two redundant memory arrays 200 are used to repair a block failure having three adjacent memory sections (of main memory).

[0017] By having the digit lines of the memory sections 210(0)-210(3) of the redundant memory arrays 200 shorter in length than digit lines of the main memory array, the dimensions of the resulting redundant memory arrays 200 can be reduced in comparison to redundant memory arrays having digit lines the same length as in the main memory array. Such implementations may be desirable, for example, where space on a substrate on which the memory is formed is scarce or there is a desire to reduce the overall size of the memory. Additionally, using digit lines shorter in length than digit lines of memory sections of the main memory array may result in greater data margin for the sense-amplifiers because the shorter digit lines have lower impedance (e.g., capacitance).

[0018] In some embodiments, optional “dummy” digit lines 250 are formed in the memory sections of the redundant memory array. The dummy digit lines 250 are shown in FIG. 2 for only a portion of memory sections 210(0), 210(1). It will be appreciated by those ordinarily skilled in the art that dummy digit lines 250 may be formed for the entire memory section, and may be formed in each of the memory sections 210(0)-210(3). The dummy digit lines 250 are formed to extend into regions between the digit lines coupled to the sense amplifiers 220(0), 220(1). The dummy digit lines 250 provide a shield for noise immunity. In some embodiments, the dummy digit lines 250 may be biased to a voltage, such as one-half of a power supply voltage, to provide further noise immunity.

[0019] FIG. 3 illustrates a portion of memory having a main memory array 302 divided into eight banks of memory 310-317. Each of the banks of memory 310-317 are further divided into memory sections (not shown). The redundant memory arrays 320, 321 include memory sections (not shown) to which memory sections of the main memory array 302 can be mapped for replacement. That is, memory addresses for the memory of a memory section of main memory are mapped to memory of the memory sections of the redundant memory arrays 320, 321. Redundant memory array logic circuits 330, 331 control the mapping of memory sections of main memory to the redundant memory arrays 320, 321. In some embodiments, sense amplifiers (not shown) for the main memory array 302 and the redundant memory array 320, 321 have open-digit line architectures. Each of the digit lines for the main memory array 302 extend into a memory section of the main memory array 302, such as illustrated in FIG. 1, and the digit lines for the redundant memory arrays 320, 321 extend into a memory section of the redundant memory arrays 320, 321.

[0020] The digit lines coupled to the sense-amplifiers for the redundant memory arrays 320, 321 may be coupled to fewer memory cells (i.e., shorter in length) than the digit lines coupled to the sense-amplifiers for the main memory array 302. In some embodiments, the digit lines for the redundant memory arrays 320, 321 are half the length of the digit lines for the main memory array 302. As previously discussed, utilizing redundant memory arrays having shorter digit lines than the memory sections of the main memory array can reduce the dimensions of a memory while still providing repairability for block failures, such as a block failure of three adjacent memory sections of the main memory array. For example, in embodiments having redundant memory array digit lines shorter in length than the digit lines for the main memory array 302, the memory may have a smaller dimension along the y-axis (FIG. 3) than for a memory having redundant memory array digit lines the same length as the digit lines for the main memory array 302.

[0021] In some embodiments of the invention having redundant memory arrays 320, 321 with digit lines half the length of the digit lines of the main array, each of the redundant memory arrays 320, 321 are divided into four memory sections and have two sets of sense-amplifiers, a first set shared by two of the memory sections and a second set shared by the other two memory sections. An example of a redundant memory array having such an arrangement was previously described with reference to FIG. 2. Both redundant memory arrays 320, 321 are used to replace a block failure of three adjacent memory sections of the main memory array. For example, two of the memory sections of the redundant memory arrays 320, 321 are used to fully replace one set of digit lines coupled to a set of sense-amplifiers of the main memory array. With reference to FIG. 1, there are four sets of digit lines coupled to the two sets of sense-amplifiers 142, 144 for a block failure of three adjacent memory sections of the main memory array. In particular, a first set coupled to the set of sense-amplifiers 142 extends into the first adjacent memory section 134, a second set coupled to the set of sense-amplifiers 142 extends into the central memory section 132, a third set coupled to the set of sense-amplifiers 144 extends into the central memory section 132, and a fourth set coupled to the set of sense-amplifiers 144 extends into the second adjacent memory section 136. Thus, a total of eight memory sections of the redundant memory arrays (as previously discussed, two memory sections of a redundant memory are used to fully replace one set of digit lines of the main memory array) are used to repair the four sets of digit lines (three adjacent memory sections) of the main memory array. For example, where both redundant memory arrays 320, 321 have an arrangement of memory sections as that shown in FIG. 2, memory sections 210(0), 210(1) of redundant memory array 320 may be used to replace the first adjacent memory section 134 (FIG. 1), memory sections 210(2), 210(3) of the redundant memory array 320 and memory sections 210(0), 210(1) of the redundant memory array 321 may be used to replace the central memory section 132, and memory sections 210(2), 210(3) of the redundant memory array 321 may be used to replace the second adjacent memory section 136.

[0022] FIG. 4 illustrates a portion of a memory according to some embodiments of the invention. The memory includes a main memory array 410, which is divided into several banks of memory (not shown in FIG. 4). The banks of memory are further divided into memory sections (not shown). The main memory array 410 is coupled to write/read driver circuit 414 that receives read data from the main memory array 410 and provides write data to the main memory array 410. The write/read driver circuits 414 are coupled to write/read data multiplexers 420(0), 420(1) through read and write data busses 416, 418, respectively. The data multiplexers 420(0), 420(1) selectively couple the read or write data busses 416, 418 to data input/output logic 424 in accordance with control signals generated by the command/address circuits 430. The command/address circuits 430 generate internal control signals to execute various memory operations, for example, read and write operations, in response to receiving external commands. In response to external addresses, the command/address circuits 430 generate internal address signals that are provided to, among other things, bank logic 434 to select the memory to be accessed. The bank logic 434 receives a portion of the internal address signals related to a bank address and generates signals for selecting the corresponding bank of memory of the main memory array 410.

[0023] A fuse bank of programmable fuses and fuse decoder circuits 440 is included in the memory for identification of memory address of memory of the main array 410 that are mapped to redundant memory, for example, redundant memory arrays 450(0), 450(1). As previously discussed, the memory typically includes other redundant memory in addition to the redundant memory arrays 450(0), 450(1). However, as also previously discussed, the other redundant memory is typically limited and local to respective memory sections, and is inadequate to replace all the memory of a memory section. As known, memory addresses to be mapped to redundant memory are programmed in the fuses and the fuse decoder circuits interprets the programmed fuses to generate the appropriate internal signals to direct memory access to redundant memory rather than to the main memory array 410. The fuse bank 440 includes programmable fuses that can be programmed to identify memory sections of the main memory array 410 that are mapped to memory sections of the redundant memory arrays 450(0), 450(1). As shown in FIG. 4, the programmable fuses and fuse decoder provide internal signals related to bank addresses to the command/address circuits 430 for identification of bank addresses that are mapped to redundant memory and further provide internal signals identifying memory sections of the main memory array 410 that have been remapped to memory sections of the redundant memory arrays 450(0), 450(1).

[0024] Although the redundant memory arrays 450(0), 450(1) may be used to replace entire sections of the main memory array 410 when entire sections are found to be defective, the redundant memory arrays 450(0), 450(1) may be used more generally to replace an entire section of the main memory array 410 where there is less than the entire section is failing. For example, where local redundant memory for a memory section of the main memory array 410 has been exhausted, but a single bit failure remains to be repaired, a redundant memory section of the redundant memory arrays 450(0), 450(1) can be used to replace that entire memory section of the main memory array 410 to salvage the memory. As a result, although the replaced memory section of the main memory array 410 may have the majority of its memory cells functional, a memory section of the redundant memory arrays 450(0), 450(1) can nevertheless be used to replace that memory section of the main memory array 410 if necessary to salvage the entire memory.

[0025] The internal signals identifying the mapped memory sections of the main memory array 410 are provided to redundant memory array logic 454(0), 454(1). The redundant memory array logic 454(0), 454(1) further receives internal control signals from the command circuits 440 for enabling access to the redundant memory arrays 450(0), 450(1) when the address for a memory location to be accessed matches bank addresses programmed in the programmable fuses 440. Additional internal control signals are provided to the write/read mulitplexers 420(0), 420(1) to control coupling of the data input/output logic 424 to the main memory array (through write and read busses 416, 418) or the respective redundant memory array 450(0), 450(1). In particular, where memory of a replaced memory section identified by programmed programmable elements in the fuse bank 440 is to be accessed, the multiplexers 420(0), 420(1) are controlled to couple the redundant memory section that is replacing the main memory section to the data input/output logic. By coupling the designated redundant memory section to the data input/output logic 424 rather than the replaced main memory section, the redundant memory section is accessed instead.

[0026] FIG. 5 illustrates a portion of a memory 500 in which a redundant memory architecture according to an embodiment of the invention may be implemented. For example, embodiments as shown in FIG. 4 can be integrated with the elements of the memory 500 to provide replacement of memory sections of a main memory array with memory sections of a redundant memory array. The memory 500 includes a main memory array 502 of memory cells, which may be, for example, DRAM memory cells, SRAM memory cells, flash memory cells, or some other types of memory cells. The memory 500 includes a command decoder 506 that receives memory commands through a command bus 508 and generates corresponding control signals within the memory 500 to carry out various memory operations.

[0027] The memory 500 further includes a redundant memory array 532 having memory sections (not shown) and a redundant memory array logic circuit 526. A data multiplexer 540 is coupled to the redundant memory array 532 to provide access thereto when appropriate. In particular, when memory to be accessed corresponds to a memory section of the main memory array 502 has been replaced by a memory section of the redundant memory array 532. A fuse bank 512 includes programmable elements that are programmed to identify the main memory sections that have been replaced by memory sections of the redundant memory array 532.

[0028] Row and column address signals are applied to the memory 500 through an address bus 520 and provided to an address latch 510. The address latch then outputs a separate column address and a separate row address. The row and column addresses are provided by the address latch 510 to a row address decoder 522 and a column address decoder 528, respectively. The column address decoder 528 selects bit lines extending through the array 502 corresponding to respective column addresses. The row address decoder 522 is connected to word line driver 524 that activates respective rows of memory cells in the array 502 corresponding to received row addresses. The selected data line (e.g., a bit line or bit lines) corresponding to a received column address are coupled to a read/write circuitry 530 to provide read data to a data output buffer 534 via an input-output data bus 540. Write data are applied to the memory array 502 through a data input buffer 544 and the memory array read/write circuitry 530. The command decoder 506 responds to memory commands applied to the command bus 508 to perform various operations on the memory array 502. In particular, the command decoder 506 is used to generate internal control signals to read data from and write data to the memory array 502.

[0029] From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.