Electrostatic Discharge Protection and Circuits for Ultrasonic Imager-on-Chip
Electrostatic discharge (ESD) is one of the main reasons that cause integrated circuit (IC) reliability problem. Transient high voltage and current released by ESD in a very short time could produce latent damage or permanent breakdown in ICs, which may affect circuit performance, shorten product life time and increase manufacturing and assembling cost. Various ESD protection structures have been developed to protect ICs against ESD stress. However, with the advancement of IC technology and the increasing applications of mobile electronics, ESD protection design is facing severe challenges.
This dissertation presented two novel ESD protection structures. One is a very-low-triggering-voltage dual-direction silicon-controlled rectifier (VLTdSCR) with adjustable ESD critical parameters and dual-polarity high ESD protection ability, as well as insignificant ESD-induced parasitics. The other one is a new nano crossbar ESD protection device consisting of the SixOyNz composite, as dielectric, and two metal layers, as top and bottom electrodes. This device has insulator between electrodes and hence extremely-low leakage current, ideal for mobile applications where power consumption is a great concern.
Among all the medical imaging technologies, pulse-echo ultrasonic imaging system features low risk, low cost and real time scan, etc. It interprets the reflected ultrasonic waves to build clear inner image of human body or tissues to aid doctor's diagnosis. In recent years, the portability of ultrasonic imaging system is attracting the attention of public, for its promising applications in harsh environments, such as rural villages or battlefields where stable power supply is usually not available.
In this dissertation, the concept of ultrasonic imager-on-chip (UIC), integrating all the function modules in traditional ultrasonic imaging system onto one die, is proposed. It has the advantages of low cost, high power efficiency and great degree of mobility. UIC system architecture, design challenges and reliability issues, especially ESD protection, are discussed, too. A high-voltage pulse generator, as the driver of ultrasonic transducer and usually fabricated in HV process, is designed in a low-voltage (LV) silicon-on-insulator complementary-metal-oxide-semiconductor (SOI CMOS) technology based on an RC-biasing stacked LV device topology, demonstrating the idea of UIC system integration.