In recent months, some major semiconductor companies and IC foundries have announced that they have scaled down transistor sizes in ICs to as little as 14 nanometers, setting the stage for the next step in reducing size and cost of Internet of Things system-on-chip designs.
Not so fast, said Tom Starnes, semiconductor industry analyst at Objective Analysis. He points out that most of these announcements have more to do with standard microprocessor architectures and are unrelated to the requirements of Internet of Things (IoT} devices.
"These are mainly digital systems and while scaling to such geometries there is not easy, it is child's play next to what is necessary in microcontroller-based IoT devices,” he said.
MCU-based SoCs are a mix of not only digital components but also large amounts of analog functionality, wireless RF circuitry, flash and static RAM -- none of which scale as easily or predictably as digital transistors.
"We will eventually have a viable market for MCU-based SoCs for the IoT which will be able to make use of process node scaling to 14nm to 20nm or smaller, but not right now," Starnes said.
Sandeep Kumar, senior vice president of worldwide operations at Silicon Labs agreed. End node IoT SoCs have a different set of requirements and challenges relative to all-digital SoCs, he said in an interview with EE Times.
"Wireless connectivity, an integrated MPU, low power operation, low-leakage SRAM, and nonvolatile memory (NVM) IP make the process technology choice critical," Kumar added. "These IoT SoCs do not chase Moore’s law in the same manner that predominantly digital SoCs do.”
MCU SoCs in wireless Internet of Things endpoints combine a variety of functions beyond the MPU in the core, including nonvolatile memory, and circuitry for sensors, analog/mixed signal, narrow and wide band RF, and peripheral functions for antenna, battery, and power management.
Kumar speaks with considerable experience, as Silicon Labs targets designs in low power, low data rate wireless connectivity applications in such markets as consumer wearables, home automation, smart metering, smart lighting, health and fitness, factory automation, transportation, logistics and agriculture. To support such designs, Silicon Labs is now manufacturing its 32-bit ARM-based wireless SoCs in 90nm, and Kumar said the company does not see any urgency in pushing its process nodes any further in the near term.
"Complex, energy-efficient RF design for wireless connectivity, as well as analog functions used for sensing or connecting to a low-voltage current sensor, are as critical as the IoT SoC’s digital performance,” said Kumar. “These SoCs are not going into desktop PCs, mobile PCs, tablets or even handsets where power consumption is less critical compared to an IoT end node.
“IoT SoCs are used in wireless applications that often run on coin cell batteries with a five to 10 year lifetime," he continued. "The availability of low-leakage SRAM and high-endurance NVM IP in the technology node chosen makes it difficult to follow the smallest geometries tracking Moore’s law when designing these SoC products."