Impact of lithography variability on analog circuit behavior

Abstract

In this work we present the impact of the variations in lithography on the performance of analog circuits. Matching pairs of devices are critical in the design of many analog circuit blocks. Simple circuits, such as current mirrors and differential pairs, depend on the matching between transistors to provide accurate bias currents and symmetrical ac gains with minimal offsets. Complex analog systems, such as analog-to-digital converters and phase-locked loops, depend on the matching between different active and passive devices, such as transistors and resistors. Variations in lithography encountered during fabrication of analog circuits can lead to matching errors and hence performance and yield losses for the device. The impact of some lithographical errors, such as focus and dose errors, mask errors, and lens aberrations, on some of the key analog building blocks, namely a single transistor, a current mirror and a differential pair is presented. The errors of such cases are also explored for the ring oscillator, demonstrating the extent of performance variation on complex analog circuits.