On the parallel programming of flash memory cells

Abstract

Parallel programming is an important tool used in flash memories to achieve high write speed. In parallel programming, a common programm voltage is applied to many cells for simultaneous charge injection. This property significantly simplifies the complexity of the memory hardware, and is a constraint that limits the storage capacity of flash memories. Another important property is that cells have different hardness for charge injection. It makes the charge injected into cells differ even when the same program voltage is applied to them. In this paper, we study the parallel programming of flash memory cells, focusing on the above two properties. We present algorithms for parallel programming when there is information on the cells' hardness for charge injection, but there is no feedback information on cell levels during programming. We then proceed to the programming model with feedback information on cell levels, and study how well the information on the cells' hardness for charge injection can be obtained. The results can be useful for understanding the storage capacity of flash memories with parallel programming.