Proving the Business Case for the Internet of Things

Renesas breakthrough could eliminate batteries for IoT devices

Steve Rogerson
November 20, 2018

Renesas unveiled at last week’s Electronica trade show in Munich an energy-harvesting embedded controller that can eliminate the need to use or replace batteries in IoT devices.
Developed based on the Japanese company’s SOTB (silicon-on-thin-buried-oxide) process technology, the controller achieves an extreme reduction in both active and standby current consumption, a combination that was not previously possible to achieve in conventional microcontrollers.
“We spent five to eight years developing this technology,” said senior vice president Michael Hannawald (pictured below). “We have developed a hybrid structure that is a breakthrough in process technology.”

He admitted that it was a complex structure so initially could be more expensive but said this could change when it went into mass production.
The reduced current levels let system manufacturers take a step towards eliminating the need for batteries in some products through harvesting ambient energy sources such as light, vibration and flow. This gives rise to a market of maintenance-free connected IoT sensing devices with endpoint intelligence for applications in industrial, business, residential, agricultural, healthcare and public infrastructure, as well as health and fitness apparel, shoes, wearables, smart watches, and drones. Renesas has already begun supplying the embedded controller to beta customers.
“We see huge markets in areas such as medical and healthcare for wearable devices and smart watches,” said Hannawald. “It could be used for sensors in smart city applications. It can be used for any kind of monitoring such as in industrial control, or it can be for energy management and used in sports and outdoor equipment.”
The first commercial product using SOTB technology, the R7F0E embedded controller, is a 32bit, Arm Cortex-based embedded controller capable of operating up to 64MHz for rapid local processing of sensor data and execution of complex analysis and control functions. Consuming 20μA/MHz active current and 150nA deep standby current, approximately one-tenth that of conventional low-power MCUs, the device is suitable for low-power and energy harvesting applications.
It contains a configurable energy harvest controller (EHC) function that increases robustness and reduces the number of external components. The EHC enables direct connection to many types of ambient energy sources, such as solar, vibration or piezoelectric, while protecting against harmful inrush current at start-up. The EHC also manages the charging of external power storage devices such as supercapacitors or optional rechargeable batteries.
It can sense and capture external analogue signals at all times because the 14bit analogue-to-digital converter (ADC) consumes only 3µA current. The device can retain up to 256kbyte of SRAM data content while consuming 1nA per each kilobyte of SRAM. And it can provide graphics data conversion including rotation, scroll and colourisation by incorporating low-power hardware techniques for driving an external display using memory-in-pixel (MIP) LCD technology that consumes virtually no power to retain an image.
MIP LCDs are display devices that do not require power to retain a displayed image during standby, making them suited to extreme low power applications.
Operating frequency is up to 32MHz, and up to 64MHz in boost mode. Memory is up to 1.5Mbyte flash, 256kbyte SRAM. Current consumption while operating at 3.0V is 20µA/MHz active, 150nA in deep standby with real-time clock source and reset manager, and 400nA in software standby with retention of core logic and 32kbyte SRAM data, real-time clock source and reset manager.
SRAM data retention consumes 1nA per kilobyte of SRAM, optionally up to 256kbyte.
The EHC provides an interface for direct robust connection to energy generating devices, and for charge management of energy storage devices. It has 2D graphics data conversion and a MIP display interface.
For security and encryption, there is a true random number generator, a unique ID for each R7F0E device, and AES encryption acceleration.
The company plans to expand the line of energy harvesting products with varied features and functions to address many extreme low-power applications. It says it is committed to promoting endpoint intelligence with its energy harvesting technology to realise an eco-friendly, smart society in which even higher levels of performance and functionality can be created without power supply or battery replacement issues.
The SOTB process technology realises extreme reduction of both active and standby current, which has typically been a trade-off and is not possible to achieve in conventional MCU process technologies. On the silicon substrate, an oxide film (BOx: buried oxide) is buried under a thin silicon layer on the wafer substrate. No impurities are doped to the thin silicon layer, which makes it possible to maintain stable operation at low voltages. The devices can therefore deliver high computing performance with power efficiency. At the same time, the potential of the silicon substrate below the BOx layer is controlled with a back bias circuit to reduce leakage currents to suppress standby power consumption further.
“With cmos technology, you either get low active current or low leakage current, not both,” said Hannawald. “We have found a way to get both. It uses one tenth the power of conventional technology.”
And he said the next steps planned were adding RF connectivity in 2021 and integrating artificial intelligence in 2023.

Samples of the R7F0E embedded controller are available now for beta customers, and samples are scheduled to be available for general customers from July 2019. Mass production is due to start in October 2019.