Matching Properties of Femtofarad and Sub-Femtofarad MOM Capacitors

Hesham Omran, Hamzah Alahmadi, Khaled N. Salama

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

Small metal-oxide-metal (MOM) capacitors are essential to energy-efficient mixed-signal integrated circuit design. However, only few reports discuss their matching properties based on large sets of measured data. In this paper, we report matching properties of femtofarad and sub-femtofarad MOM vertical-field parallel-plate capacitors and lateral-field fringing capacitors. We study the effect of both the finger-length and finger-spacing on the mismatch of lateral-field capacitors. In addition, we compare the matching properties and the area efficiency of vertical-field and lateral-field capacitors. We use direct mismatch measurement technique, and we illustrate its feasibility using experimental measurements and Monte Carlo simulations. The test-chips are fabricated in a 0.18 \mutext{m} CMOS process. A large number of test structures is characterized (4800 test structures), which improves the statistical reliability of the extracted mismatch information. Despite conventional wisdom, extensive measurements show that vertical-field and lateral-field MOM capacitors have the same matching properties when the actual capacitor area is considered. Measurements show that the mismatch depends on the capacitor area but not on the spacing; thus, for a given mismatch specification, the lateral-field MOM capacitor can have arbitrarily small capacitance by increasing the spacing between the capacitor fingers, at the expense of increased chip area.
Original languageEnglish (US)
Pages (from-to)763-772
Number of pages10
JournalIEEE Transactions on Circuits and Systems I: Regular Papers
Volume63
Issue number6
DOIs
StatePublished - Apr 21 2016

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