Ferroelectric random access memory (FRAM) is a non-volatile memory. FRAM has significant technical advantages that enable solutions not possible with other memory technology. The underlying molecular structure of an FRAM memory cell is shown in figure 1. When an electric field is applied across the ferroelctric crystal, the central atom moves in the direction of the applied field.
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The polarity of this atom remains when the electric field is removed, preserving the data within the memory without the need for periodic refresh.Understanding the three principle benefits of FRAM enables an electronics engineer to acheive a more efficent and superior design:
* NoDelay Write: FRAM writes so quickly that there is no need to wait for the write to complete. Typical write speed for FRAM is around 55 nanoseconds as compared to the much slower 5 milliseconds write speed for EEPROM.
* Virtually Unlimited Endurance: FRAM can withstand 1E14 (100-trillion) read/write cycles, making it virtually
impossible to wear out.
* Low Power: FRAM requires much less power to perform writes. For example, erasing and writing 64kbits of data in an FRAM consumes 1/60th the power of that used by an EEPROM and 1/400th that used by a serial flash.
Now that we’ve covered the basics, let’s see how we can apply FRAM technology to benefit your product features and time-to-market.
Using FRAM is simple. Serial FRAMs are compatible with serial EEPROMs and parallel FRAMs are compatible with parallel SRAMs. Existing software will work with FRAMs but most engineers chose to re-work the software. There are two significant software modules that may be employed with EEPROM or flash that are not needed for FRAM. Removing this redundant code makes software faster to run, easier to debug, and consumes less code space.
The first of these modules is the function necessary to wait for EEPROM or flash to complete the write operation. There is no point in polling the FRAM to see if the write has completed (the write will have finished before you can check), but this feature is supported in case you don’t want change your EEPROM software.
The second module that is redundant with FRAM is software that performs wear levelling. Wear levelling is a technique often used with flash or EEPROM to distribute memory writes to numerous locations so that the write cycle limit of any location is not exceeded. With FRAM’s virtually unlimited endurance this function is not necessary.