Press release

Renesas Electronics Develops New Flash Memory Technology Achieving Larger Capacities, Faster Read Operation, and OTA Support in Automotive Microcontrollers Based on Next-Generation 28nm Process

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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).

Development of noise-reducing technology

By changing the write current applied to each memory cell between
initial operation and later operation when programming the flash memory,
Renesas has reduced the peak current consumption from the external power
supply (Vcc) by 55 percent without reducing the throughput compared to
earlier Renesas devices. This suppresses the adverse influence of supply
voltage noise on the MCU itself during OTA operations when the car is
running. Renesas has also applied the idea of varying the write current
to high-speed write mode, in which the number of simultaneously
programmed cells is increased. As a result, the new device achieves
high-speed programming at 6.5 MB/s in this mode. This makes it possible
to suppress the increased test times associated with the large memory
capacity.

OTA capable of control software switching that is both robust and
high speed

In this test chip, the code storage flash memory is divided into a
storage area for software in use and a storage area for updated
software. This makes it possible to switch the software in less than 1
ms (1/1000 of a second) at ignition off. Furthermore, the software
switching settings are duplicated and new state flags were added to
prevent incorrect operation in the event that the software updates or
switching is unintentionally interrupted. This achieves, at the same
time, the robust operation that allows executable control software to be
selected reliably and a reduction of down time during which the car
cannot be used.

The above technologies make it possible to support the increasing scales
of automotive control software, high-speed real-time control, and
advanced OTA. Moving forward, Renesas is committed to continued
development of embedded flash memory and striving to achieve the higher
capacities, higher speeds, and lower power consumption that will be
required to support new applications.

(Note 1) MONOS: Metal-oxide-nitride-oxide-silicon. A technology that
Renesas has achieved a substantial track record of over 20 years in
EEPROM, secure MCU, and other products. The MONOS technology is used in
the embedded flash memory used in Renesas MCUs.

(Note 2) A Renesas flash memory technology announced at the 2015
International Solid-State Circuits Conference (ISSCC 2015).

About Renesas Electronics Corporation

Renesas Electronics Corporation (TSE:
6723
) delivers trusted embedded design innovation with complete
semiconductor solutions that enable billions of connected, intelligent
devices to enhance the way people work and live. A global
leader in microcontrollers, analog, power, and SoC products, Renesas
provides comprehensive solutions for a broad range of automotive,
industrial, home electronics, office automation, and information
communication technology applications that help shape a limitless
future. Learn more at renesas.com.

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