SuperFlash technology changed the |
endurance for these applications. |
memory block tend to have tail bits which |
industry with its differentiated and |
pose difficulties in reading accuracy. |
Embedded Flash Memory is |
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Scalable |
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Embedded Flash can work at Low
Voltages for IoT applications
IoT applications require low-voltage read / write operation. Even though
Program / Erase operation needs high voltage, it is transparent to the user as the flash macro receives core / IO voltage from the user and uses an internal charge pump to raise the voltage to the required high voltage for Program and Erase operation.
Therefore, embedded flash is ready for low-power IoT applications.
Embedded Flash supports
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Ten years ago, the word on the street was that embedded flash was dead at sub-
90nm nodes because of the perceived difficulty and challenges in scaling the bitcell. That perception has been proven wrong now as embedded flash is already in development at 28nm. The challenge today is to scale embedded flash to FinFet process generations. There are however, foundries such as Samsung and Global
Foundries focusing on FDSOI technology on planar 22nm technology nodes and possibly beyond which may extend the life of embedded flash beyond the 28nm
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nodes. In 2012, embedded flash at pureplay foundries was only available at 90nm.
But, in the last four years, embedded flash availability is reaching 28nm at many leading foundries( Figure 1) and in development for high-end automotive and
IoT solutions. This huge leap in development was primarily driven by automotive applications, which are driving the demand of automotive MCUs on advanced technology nodes.
Automotive, mobile and IoT applications
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EEPROM functionality |
node. |
Traditional EEPROM architecture |
Embedded Flash can not be |
supported Byte-write operation and was |
replaced by OTP for Instruction |
used by applications requiring frequent |
Code Applications |
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data updates. Generally, embedded flash is organized in a group of cells called sectors. A sector needs to fully Erased before new data can be written. However, there are simple design techniques using an SRAM buffer that can be used to mimic
EEPROM functionality at a fraction of the overall embedded flash memory area, and would be transparent to the user.
A frequent misconception is that embedded flash can’ t meet EEPROM endurance. However, an EEPROM can typically meet 1M endurance cycles.
Historically most of the MCU and smartcard applications required less than
100K endurance, though recently more stringent requirements for some applications such as SIM cards have pushed endurance requirements to 500K endurance( typical). In support of this
requirement, the third generation
SuperFlash technology( ESF3) has better endurance characteristics than its predecessor technologies and with plenty of data showing that it can meet 500K
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Some integrated circuits need to be programmed with an on-chip instruction code only once and this programming can be done either during wafer-sort or inpackage during final testing before shipping the integrated circuit to the client or can be done in-field. Although the one- time programming requirement of the non-volatile memory appears to be adequately satisfied with an OTP solution, in practice it has some serious user- experience and reliability issues. First, OTP programming for a large memory block is fraught with intractable low-yield challenges which requires use of multiple redundant bits and associated redundancy management circuitry. This added complexity is a headache for chip designers. Second, a large block of OTP solution in general doesn’ t offer data- retention time that is competitive with that offered by a specialized embedded flash process optimized for long term data reliability. This is because the uncontrolled programming variations on a large OTP |