On-Chip Emulation and Measurement of Variable-Length Photocurrents in Sub-50nm ICs

This article presents a circuit design for measuring and emulating radiation-induced photocurrent pulses in dense, highly scaled integrated circuits (ICs) and experimental results from an implementation in a 45-nm partially depleted silicon-on-insulator (PD-SOI) process. This photocurrent measurement circuit (PMC) expands upon other work by introducing new capabilities and measurement procedures, including a method for capturing arbitrarily long pulses and an arbitrary-waveform generator (AWG) that enables flexible built-in self-test (BIST) capabilities as well as emulation of transient radiation events. Experimental PMC measurements of currents generated by flash X-ray irradiation, pulsed-laser irradiation, and AWG emulation show excellent agreement and are corroborated by technology computer-aided design (TCAD) simulations; in particular, AWG recreations of experimental flash X-ray photocurrent responses match the original data with as little as 1.375% mean absolute percentage error (MAPE). Comparisons of different transistor structures also indicate a relatively insignificant photocurrent response in body-tied devices, suggesting that floating body effects are a dominant factor for this process. Holistically, these results demonstrate the efficacy of the PMC.