Conventionally, dynamic memories, such as dynamic random access memories (“DRAMs”) require a periodic refresh. For DRAMs, this conventionally means a destructive read is done, followed by a write back of the information read. Furthermore, some memory cells in an array of memory cells of a DRAM may need to be refreshed more often than other memory cells. This is generally due to some memory cells being more susceptible to charge leakage at various operating parameters.
To increase yield of DRAMs, as well as to affect overall refresh rate, it has been proposed by others to identify memory cells needing to be refreshed more often than other memory cells. These so-called weaker memory cells could then be refreshed more often than their counterpart stronger memory cells. Additional details regarding this proposed refresh approach may be found in U.S. Pat. No. 5,644,545 B1.
For a new type of memory cell known as a thyristor-based memory cell, no refreshing is used. In other words, there is no destructive read followed by a write back to refresh a memory cell back to its original state. Rather than refreshing, a thyristor-based memory cell is periodically pulsed. This pulsing is done at a frequency such that the thyristor-based memory cell maintains its current state. Additional details regarding periodically pulsing a thyristor-based memory cell may be found in Patent Cooperation Treaty (“PCT”) International Publication WO 02/082504.
Like DRAM cells, some thyristor-based memory cells may be more susceptible to charge leakage at various operating parameters due to defects or statistical variations of process parameters. Accordingly, it would be desirable and useful to provide means to maintain state of such thyristor-based memory cells more susceptible to charge leakage than other such thyristor-based memory cells of the same memory integrated circuit without spending the additional power to pulse all memory cells in an array at a frequency associated with those cells more susceptible to charge leakage, namely a “higher frequency.”