Characterization Of Photocurrent and TID-Induced Leakage Current Using On-Chip Measurement Techniques

Abstract

Device-level radiation-induced photocurrent measurements, for characterization purposes and use in radiation hardening by design (RHBD) techniques, have historically been performed through off-chip measurements of parallel-amplified photocurrent collection nodes. These amplification arrays often connected over a hundred thousand transistors and occupy enough on-chip space to require an entire test chip dedicated to the array. Though costly, this technique was effective, producing off-chip photocurrent with clear transient characteristics. However, the magnitude of photocurrent generated in modern technology nodes has greatly decreased due to technology scaling, especially in silicon-on-insulator (SOI) topologies. Resulting from this decreased collection volume, the signal-to-noise (SNR) ratio of off-chip sub-50nm SOI photocurrent measurements has been insufficient. With no alternative method to measure on-chip photocurrent in these sub-50nm technologies, the reliability of device operation in photocurrent environments cannot be guaranteed through RHBD techniques, since RHBD heavily relies on known characteristics of the radiation response for a specific technology node. In response to these challenges, this work presents a circuit designed for on-chip photocurrent measurement, which is named the Vanderbilt Photocurrent Measurement Circuit (PMC). The PMC circumvents off-chip SNR challenges with measurement and quantification of the photocurrent transients taking place entirely on-chip using several mixed-signal design techniques. The PMC design is technology-agnostic and space-efficient, designed to act as a permanent solution for photocurrent measurement. In addition, the PMC is capable of measuring transistor leakage and total-ionizing-dose (TID) induced leakage. At the time of writing, the PMC has been implemented in GlobalFoundries 22FDX, a 22nm fully-depleted SOI (FD-SOI) topology. The full design of the PMC is presented, including simulations in 22FDX as well as instructions for porting the technology-agnostic design into other technologies. Additionally, the capability of the PMC to measure TID-induced leakage is shown through preliminary tests results which exposed the technology characterization vehicle (TCV) housing the PMC to 10keV x-rays up to 100kRad(SiO2).