Flash memory cells for high-performance, reliable microcontrollers
Renesas Electronics has successfully developed what is claimed to be the world’s first split-gate metal-oxide nitride oxide silicon flash memory cells employing transistors with fin-shape for use in MCUs with on-chip flash memory having a circuit linewidth of 16nm to 14nm or finer. SG-MONOS technology is reliable for use in automotive applications and the company currently mass produces 40nm MCUs using this technology, and 28nm MCUs are under development. The successful development shows promising scalability of the SG-MONOS technology to 16/14nm process nodes and beyond.
Advances in automotive automation, such as advanced driver assistance systems (ADAS), and the smart society connected via the IoT have created demand for more advanced MCUs fabricated using finer process technology. To address this demand, the company has developed embedded flash memories based on the 16/14nm technology, which succeeds the latest 40/28nm. At the 16/14nm logic process, FinFETs, transistors with a finned structure, are commonly employed to realize improved performance and reduced power consumption to overcome the scaling limit of conventional planar transistors.
However, employing a fin structure for embedded flash memory can become a big challenge depending on the structure of the flash memory. Two types of embedded flash memories have been proposed and implemented: the floating-gate and charge trap. Compared with floating-gate memory, the charge trap flash memory which it has been utilizing in recent years has superior charge retention characteristics and a proven track record in automotive MCUs requiring a high level of reliability. Also, since the memory functional material is formed on the surface of the silicon substrate, they are comparatively easy to be extended into a three-dimensional fin structure. In contrast, floating-gate flash memory cells have a complex structure, and therefore it is difficult to integrate it into a fin structure.