THE OBTAINABLE ACCURACY OF ANALOG METAL OXIDE SEMICONDUCTOR INTEGRATED CIRCUIT ELEMENTS (MOS)

The metal-oxide-semiconductor (MOS) technologies employed in the large-scale integrated (LSI) fabrication of digital circuits are being evaluated to determine their applicability to analog circuits. Unlike digital integrated circuits, the performance of analog MOS integrated circuits depends heavily upon the element matching accuracy. The key elements are usually the capacitors, but in some applications the matching accuracy of MOS transistors as current sources is also critical. Therefore, the matching properties of MOS capacitors and transistors have been investigated in this dissertation.;A new statistical model was proposed to analyze the random errors which are due to the local and global variations of the linear dimensions and parameters of the circuit elements. These random variations were modelled as random processes, with zero mean and stationary characteristics. This is more relevant to the realistic properties of MOS capacitor and transistor matching.;In addition to theoretical predictions, experimental work as well as the Monte Carlo simulation had been performed for both devices to confirm the theoretical results. A large number of experimental test chips with "on-chip" measurement capability had been fabricated for both devices using 3.5 (mu)m silicon-gate NMOS technology at Xerox Microelectronics Center, El Segundo, California. The experimental results indicate that a 9-bit capacitor matching accuracy and an 8-bit transistor current matching accuracy can be easily achieved. The results are in good agreement with the theoretical predictions.;The elements of MOS integrated circuits are inherently subject to errors from two sources. One is systematic error, which affects adjacent elements with identical geometries similarly. The other is random error, which differs from element to element, and therefore cannot be corrected by improved matching techniques. It hence represents the ultimate limitation on the achieveable accuracy.