Matching properties of femtofarad and sub-femtofarad MOM capacitors
Omran, Hesham; Alahmadi, Hamzah; Salama, Khaled N.;
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 μm 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.
Other data
Title | Matching properties of femtofarad and sub-femtofarad MOM capacitors | Authors | Omran, Hesham ; Alahmadi, Hamzah; Salama, Khaled N. | Keywords | Analog-to-digital converter (ADC) | capacitance-to-digital converter (CDC) | capacitive digital-to-analog converter (CapDAC) | capacitor mismatch | energy-efficient circuits | metal-oxide-metal (MOM) capacitors | mismatch characterization | programmable capacitor array (PCA) | Issue Date | 1-Jun-2016 | Publisher | IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC | Journal | IEEE Transactions on Circuits and Systems I: Regular Papers | ISSN | 15498328 | DOI | 10.1109/TCSI.2016.2537824 | Scopus ID | 2-s2.0-84992294049 | Web of science ID | WOS:000380128200003 |
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