Sandisk Technologies Inc.

Abuzer Azo Dogan

Changyuan Chen

Biswajit Ray

Nian Niles Yang

Mohan Dunga

Grishma Shah

Philip David Reusswig

Joanna Lai

Chris Yip

Techniques are provided for improving the accuracy of read operations of memory cells, where the threshold voltage of a memory cell can shift depending on when the read operation occurs. In one aspect, read voltages are set and optimized based on a time period since a last sensing operation. A timing device such as an n-bit digital counter may be provided for each block of memory cells to track the time. The counter is set to all 1's when the device is powered on. When a sensing operation occurs, the counter is periodically incremented based on a clock. When a next read operation occurs, the value of the counter is cross-referenced to an optimal set of read voltage shifts. Each block of cells may have its own counter, where the counters are incremented using a local or global clock.

System solution for first read issue using time dependent read voltages

Methods for reducing cross-temperature threshold voltage distribution widening by applying a temperature dependent sensing scheme during read operations are described. In some embodiments, during a read operation, the sensing conditions applied to memory cells within a memory array (e.g., the sensing time and the read voltage applied to the memory cells during the sensing time) may be set and/or adjusted based on a temperature of the memory cells during the read operation, a previous temperature of the memory cells when the memory cells were programmed, and the programmed states of neighboring memory cells. In some cases, the sensing time for sensing a memory cell of a NAND string and the source voltage applied to a source line connected to the NAND string may be set based on the temperature of the memory cells during sensing and the previous temperature of the memory cells when the memory cells were programmed.

Temperature dependent sensing scheme to counteract cross-temperature threshold voltage distribution widening

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San Jose, CA, United States of America

Abuzer Azo Dogan