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Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional 0.35 m complementary metal-oxide-semiconductor ͑CMOS͒ process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of 6 ϫ 10 −11 g/cm 2 Hz equivalent to 0.9 ag/ Hz for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of 2.4ϫ 10 −17 g in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2753120͔ Cantilever-based sensors are very attractive transducers for physical, chemical, and biological sensors based on micro-/nanoelectromechanical systems 1-11 ͑NEMSs͒ due to its simplicity, wide range of sensing domains, and extremely high sensitivity when cantilever is scaled down into submicrometer scale dimensions. [6][7][8][9][10] One approach is the use of these cantilevers in dynamic mode for mass sensing applications where the mass is measured as a change of the resonance frequency. Monolithic integration of the cantileverbased transducer with readout electronics provides interesting advantages in terms of size, portability, and cost 10,11 in front of the use of optical readout techniques commonly used. [2][3][4][5][6][7][8][9] In previous works, 10 a post-complementary metal-oxidesemiconductor ͑CMOS͒ fabrication process based on a combination of electron beam lithography and direct write laser lithography has been used in order to define and release the cantilever of fully integrated mass sensors. In this letter, the mechanical structures are defined directly during the standard CMOS process used to fabricate the overall sensor ͑cantilever-based transducer plus readout circuitry ͓Fig. 1͑a͔͒, without the need of any additional lithographic process. 12 The reported results corresponding to calibration, real time mass measurements, and resolution analysis indicate the benefits in terms of resolution and operation stability of a fully integrated mass sensor operating in air conditions, which has been fabricated using a conventional CMOS technology.Cantilever structures 10 m long ͑l͒, 600 nm wide ͑w͒, and 750 nm thick ͑t͒ ͓Fig. 1͑b͔͒ have been fabricated by using the top metal layer of a commercial 0.35 m CMOS technology. 12,13 We use a three-electrode configuration constituted by the cantilever that is biased at a dc voltage ͑V dc ͒ and two electrodes for electrostatic excitation ͑V ac ͒ and capacitive readout purposes ͑V sense ͒, respectively. The cantilever displacement is detected with a full-custom designed readout CMOS circuit with a high-sensitivity and low-noise front-end stage. 14 The electrical scheme used presents an input capacitance as low as 11 fF and an input refereed noise of 21 nV/ Hz...

This letter presents the design, fabrication, and demonstration of a CMOS-MEMS filter based on two high-Q submicrometer-scale clamped-clamped beam resonators with resonance frequency around 22 MHz. The MEMS resonators are fabricated with a 0.35-μm CMOS process and monolithically integrated with an on-chip differential amplifier. The CMOS-MEMS resonator shows high-quality factors of 227 in air conditions and 4400 in a vacuum for a bias voltage of 5 V. In air conditions, the CMOS-MEMS parallel filter presents a programmable bandwidth from 100 to 200 kHz with a < 1-dB ripple. In a vacuum, the filter presents a stop-band attenuation of 37 dB and a shape factor as low as 2.5 for a CMOS-compatible bias voltage of 5 V, demonstrating competitive performance compared with the state of the art of not fully integrated MEMS filters. Index Terms-Bandpass filter, CMOS-MEMS, micromechanical filter, system-on-chip.

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