Cisco predicts that more than 50 Billion devices will be connected to the internet by 2020. It is called “Internet of Things” (IoT). Many wonder how connecting your refrigerator to internet will benefit anyone. But IoT is about much more than automated shopping lists. When you combine sensors, actuators, and networked intelligence the possibilities are endless. It can boost productivity, save resources and even prevent health issues.
Many IoT chips can be made in older, depreciated fabrication plants (0.25um, 180nm, 130nm) that were top-notch 20 years ago. One would argue that foundries have covered every aspect of Electrostatic Discharge (ESD), Electrical Overstress (EOS) and Latch-up in these mature processes long ago. However we learned, by supporting innovative semiconductor startups, that many of the applications in IoT require non-standard on-chip ESD protection clamps.
1) Non-standard signal voltage
Several IoT systems include sensor interfaces with distinctive signal conditions (5V or even 20V), beyond the typical General Purpose I/O (GPIO) interfaces provided by the foundry.
A lot of our customers request 5V tolerant ESD for e.g. battery connection (4.5V-5V battery), legacy interface communication or for USB. We have built 5V tolerant ESD protection clamps in every CMOS from 180nm to 16nm using the standard process. In 28nm, in the 1.8V process, we even went up to 12V based on special request from our customer.
- Sofics’ clipping circuit protects wireless interface circuits against excess voltage
Similarly, small signals (order of a few mV or mA) captured by sensors for motion detection and touch could be lost in the noise or due to leakage from GPIOs.
2) Low leakage requirement
A lot of the IoT applications run on a battery or even harvest energy. Designers move heaven and earth to reduce the leakage of the functional circuits. Foundries on their end provide special low-power process options to reduce both standby and dynamic power. It would be unwise to nullify all that work through the use of leaky ESD clamps.
3) Sub-systems are powered down
To further reduce the leakage only a small part of the system is awake all the time. All the other circuits are turned off unless required. Traditional ESD protection can ruin the efforts when signals applied on the I/O circuits power-up a functional block not required at that time.
4) Wireless interfaces
Every system needs to communicate. Therefore wireless interfaces can be found on all of the IoT systems. This requires on-chip ESD protection with low parasitic capacitance (200fF or lower).
5) System level protection, on the chip
A lot of the innovative systems are meant to be low-cost and mobile and also this relates to ESD. To reduce the size and the Bill of Materials (BOM), system designers remove board level ESD protection blocks from the mini-Printed Circuit Boards (PCB). 20 years ago, such Transient Voltage Suppressors (TVS) devices were added to protect ICs against ESD stress during the actual use of products. Without such TVS protection and due to the shorter PCB traces Integrated Circuits are now stressed with more severe ESD events like IEC 61000-4-2. Moreover, the probability of ESD-stress is much higher in those mobile systems as they are operated in so-called harsh environments.
- IEC 61000-4-2 protection for IoT application
Clearly, IC designers need to think about the ESD protection strategy for their IoT system. It is wise to rely on silicon proven concepts to speed up market introduction.