Built-in self-test in integrated circuits - ESD event mitigation and detection

Abstract

When enough charges accumulate on two objects, the air dielectric between them breaks down to create a phenomenon known as electrostatic discharge (ESD). ESD is of great concern in the integrated circuit industry because of the damage it can cause to ICs. The problem will only become worse as process components become smaller. The three main types of ESD experienced by an IC are the human body model (HBM), the charged device model (CDM), and the machine model (MM). HBM ESD has the highest voltage while CDM ESD has the highest bandwidth and current of the three ESD types. Integrated circuits generally include ESD protection circuitry connected to their pads. Pads are the connection between the IC and the outside world, making them the required location for circuitry designed to route ESD events away from the IC's internal circuitry. The most basic protection pads use diodes connected from I/O to VDD and I/O to ground. A voltage clamp between VDD and ground is also necessary to protect against CDM and MM event types where the device may not yet have a low impedance supply path connected. The purpose of this research is to investigate the performance of ESD circuits and to develop a method for detecting the occurrence of an ESD event in an integrated circuit by utilizing IC fuses. The combination of IC fuses and detection circuitry designed to sense a broken fuse allows the IC to perform a built-in self-test (BIST) for ESD to identify compromised ICs, preventing manufacturers from shipping damaged circuits. Simulations are used to design an optimized protection circuit to complement the proposed ESD detection circuit. Optimization of an ESD pad circuit increases the turn-on speed of its voltage clamps and decreases the series resistance of its protection diodes. These improvements minimize the stress voltage placed on internal circuitry due to an ESD event. An ESD measurement setup is established and used to verify voltage clamp operation. This research also proposes an ESD detection circuit based on IC fuses, which fail during an ESD event. A variety of IC fuses are tested using the ESD measurement setup as well as a TLP setup in order to determine the time and current needed for them to break. Suitable IC fuses have a resistance less than 5 Ω and consistently break during the first trial.