Defective bit line management in connection with a memory access
Examples herein relate to determining a number of defective bit lines in a memory region prior to applying a program or erase voltages. If a threshold number of bit lines that pass during a program or erase verify operation is used to determine if the program or erase operation passes or fails, the determined number of defective bit lines can be used to adjust the determined number of passes or fails. In some cases, examples described herein can avoid use of extra bit lines and look-up table circuitry to use in place of defective bit lines and save silicon space and cost associated with the use of extra bit-lines. In some examples, a starting magnitude of a program voltage signal can be determined by considering a number of defective bit lines.
1. A memory controller comprising:
an interface to a memory array and
a controller to:
perform a memory access and verify operation in a memory array region, wherein perform a memory access and verify operation comprises:
prior to a memory access signal being applied, determine a number of defective bit lines in the memory array region,
determine a number of memory access fails; and
determine if the memory access operation is defective based on a comparison of the determined number of memory access fails less the determined number of defective bit lines in the memory array region against a threshold number of accepted bit line fails.
2. The memory controller of claim 1 , wherein the memory access and verify operation comprises one or more of: erase and erase verify or program and program verify and wherein the memory access signal comprises a non-zero erase or program voltage signal.
3. The memory controller of claim 1 , wherein the determine a number of defective bit lines in the memory array region comprises determine a number of open bit lines.
4. The memory controller of claim 1 , wherein the determine a number of defective bit lines in the memory array region comprises apply a voltage higher than maximum threshold voltage of cells to word lines of the region and determine bit lines that read as a logical zero.
5. The memory controller of claim 1 , wherein the determine a number of defective bit lines in the memory array region comprises determine a number of shorted bit lines.
6. The memory controller of claim 5 , wherein determine a number of shorted bit lines comprises determine bit lines shorted at least to a neighboring bit line or shorted to select gates.
7. The memory controller of claim 1 , wherein prior to a memory access signal being applied, determine a number of defective bit lines in the memory array region comprises:
identify shorted bit lines and
inhibit shorted bit lines prior to application of a program signal.
8. The memory controller of claim 1 , wherein the memory access signal comprises a program signal and wherein the controller is to determine a starting magnitude of the program signal based on a program voltage magnitude that leads to a passing number of bit lines from a program verify based on a determined number of defective bit lines in the memory array region.
9. The memory controller of claim 1 , comprising a memory array coupled to the interface, the memory array comprising one or more of: a single-level cell (SLC) NAND storage device, a multi-level cell (MLC) NAND storage device, triple-level cells (TLC) NAND storage device, quad-level cells (QLC) storage device, a memory device that uses chalcogenide phase change material, NOR flash memory, single or multi-level phase change memory (PCM), a resistive memory, nanowire memory, ferroelectric transistor random access memory (FeTRAM), magneto resistive random access memory (MRAM) memory that incorporates memristor technology, spin transfer torque MRAM (STT-MRAM), random-access memory (RAM), Dynamic RAM (D-RAM), double data rate synchronous dynamic RAM (DDR SDRAM), static random-access memory (SRAM), thyristor RAM (T-RAM), or zero-capacitor RAM (Z-RAM).
10. The memory controller of claim 1 , wherein the controller is to:
during a read operation of the memory array region, identify read results as weak for soft bit read correction for a read operation that uses bit lines that are open circuit or short circuit.