Renesas Electronics Corporation (TSE: 6723), a premier supplier of advanced semiconductor solutions, today announced the development of a new flash memory technology that achieves larger memory capacities, higher readout speeds, and over-the-air (OTA) support for automotive microcontrollers (MCUs) using the next-generation 28nm process. This new technology achieves the industry’s largest capacity of embedded flash memory on an MCU – 24 MB – and reaches 240 MHz random access read speeds, the industry’s fastest for embedded flash memory. The technology also achieves low noise write operations when performing OTA wireless software updates, and high-speed and robust operation for OTA software updates.
Renesas presented these results on June 12 at the 2019 Symposia on VLSI Technology and Circuits in Kyoto, Japan, June 9-14, 2019.
Recently in leading-edge technologies used in car systems, such as autonomous driving and electric drive, there have been increasing demands for larger embedded flash memory capacities in the MCUs due to the increasing scale of the control software. The introduction of OTA technology accelerates the demand for larger capacities to assure adequate storage area for updated programs. Since it is necessary to assure real-time performance given the addition of new functions such as functional safety, faster random access read times from the flash memory are also strongly desired. Furthermore, regarding OTA, three things are now strongly desired. First is low-noise design so that the updated software can be stored reliably even when the car is operating. Second is reduced down time during the software switching. Third is robustness to avoid incorrect operations even if unintentional interruptions occur when updating or switching software.
The newly developed flash memory technology addresses these demands with:
24 MB on-chip flash memory – the industry’s largest in an MCU
Renesas continues to adopt the high-speed, high-reliability SG-MONOS (note 1) technology for the embedded flash memory used in its MCUs. The memory cell size of the 28nm generation developed here is reduced by more than 15 percent, from the earlier 0.053 µm² to smaller than 0.045 µm². While suppressing increases in the chip size, this new technology allows the inclusion of 24 MB of code storage flash memory, the industry’s largest capacity for embedded flash memory. Renesas has also included 1 MB of data storage flash memory in the test chip for parameters and other data.
240 MHz random access read speed – the industry’s highest speeds for MCUs with embedded flash memory
Word line division is an effective method for increasing the speed of random access reads in embedded flash memory. However, this division increases the number of word line drivers and causes reliability degradation due to time-dependent dielectric breakdown (TDDB) of the transistors included in those drivers and word line supply voltage drops due to increased leakage current. Renesas resolved these issues using word line driver stress mitigation and distributed word line supply voltage drivers and has verified 240 MHz high speed random access, the industry’s highest in a test chip, over a wide temperature range (junction temperatures from -40°C to 170°C).
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