Renesas has developed an energy-harvesting embedded controller that can eliminate the need to use batteries in IoT devices.
The silicon-on-thin-buried-oxide (SOTB) process technology allows reduction of both active and standby current. The first device built on this process is the R7F0E embedded controller, a 32bit Arm Cortex embedded controller that operates up to 32MHz (64MHz in boost mode) with 20 μA/MHz active current and a mere 150 nA deep standby current.
Shown at the Electronica 2018 trade show in Munich for the first time, the controller has approximately one-tenth that of conventional low-power microcontrollers (MCUs) says Renesas and opens up the opportunity for sourcing energy from light or heat.
The SOTB process technology allows maintenance-free connected IoT sensing devices with endpoint intelligence for applications in industrial, agricultural, business, residential, healthcare, and public infrastructure, as well as health and fitness apparel, wearables, shoes, smart watches, and drones. Renesas has already begun supplying the new embedded controller to beta customers.
In the SOTB process, an oxide film (the BOX layer) is buried under a thin silicon layer on the wafer substrate. With no impurities doped to the thin silicon layer, making it possible to maintain stable operation at low voltages so that the resulting devices can, therefore, deliver high computing performance with power efficiency. At the same time, the potential of the silicon substrate underneath the BOX layer is controlled with a back bias circuit to reduce leakage currents to further suppress standby power consumption.
The R7F0E also includes a configurable Energy Harvest Controller (EHC) function that connects directly to ambient energy sources such as solar, piezoelectric, or vibration, while protecting against harmful inrush current at start-up. The EHC also manages the charging of external power storage devices such as super-capacitors or optional rechargeable batteries.
The R7F0E can sense and capture external analog signals at all times via its internal 14bit Analogue-to-Digital Converter (ADC) as it consumes only 3 uA current. It can retain up to 256 KB of SRAM data content while consuming just 1 nA/KB of SRAM, and can also provide graphics data conversion including scroll, rotation, and colorization by incorporating low-power hardware techniques for driving an external display using Memory-In-Pixel1 LCD technology that consumes virtually no power to retain an image.