Monolithic mass sensor fabricated using a conventional technology with attogram resolution in air conditions

Abstract

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...

The influence of the parasitic current on the nonlinear electrical response of capacitively sensed cantilever resonators

“…The remaining resonator shown in Figure 2(a) is of a combination of different layers of metals and was fabricated using the MET4 metal layer of the complementary metal-oxide-semiconductor (CMOS) technology AMS 0:35 lm. 16 …”

Nanomechanical test structure for optimal alignment in stencil-based lithography

“…The mass sensitivity of this device has been calibrated by depositing a 2 nm thick silver layer, indicating an areal mass sensitivity of 3.4·10 -11 g.cm -2 .Hz -1 . The resonator is electrostatically self-excited so that it sets the oscillation frequency of the entire oscillator circuit [13]. The frequency stability level (measured in terms of Allan deviation), combined with the device mass sensitivity, leads to a mass resolution of dM = 450 pg.cm -2 , corresponding to a thickness resolution of 0.43 pm for Ag deposition.…”

Parallel optical read-out of micromechanical pillars applied to prostate specific membrane antigen detection

“…In the last decade, applications in different fields were demonstrated (Arlett et al 2011;Bargatin et al 2012;Pang et al 2012;Tamayo et al 2013): single atom sensitivity was reached in vacuum condition (Yang et al 2006), applications in air and liquid were proposed, with a detection limit reduced to attogram (10 -18 g) (Verd et al 2007) and to nanogram (10 -9 g) (Braun et al 2009) respectively.…”