Ultra-Sensitive Capacitive Detection Based on SGMOSFET Compatible With Front-End CMOS Process
ABSTRACT Capacitive measurement of very small displacement of nano-electro-mechanical systems (NEMS) presents some issues that are discussed in this article. It is shown that performance is fairly improved when integrating on a same die the NEMS and CMOS electronics. As an initial step toward full integration, an in-plane suspended gate MOSFET (SGMOSFET) compatible with a front-end CMOS has been developed. The device model, its fabrication, and its experimental measurement are presented. Performance obtained with this device is experimentally compared to the one obtained with a stand-alone NEMS readout circuit, which is used as a reference detection system. The 130 nm CMOS ASIC uses a bridge measurement technique and a high sensitive first stage to minimize the influence of any parasitic capacitances.
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ABSTRACT: Measurements of the gauge factor of suspended, top-down silicon nanowires are presented. The nanowires are fabricated with a CMOS compatible process and with doping concentrations ranging from 2 × 10(20) down to 5 × 10(17) cm(-3). The extracted gauge factors are compared with results on identical non-suspended nanowires and with state-of-the-art results. An increase of the gauge factor after suspension is demonstrated. For the low doped nanowires a value of 235 is measured. Particular attention was paid throughout the experiments to distinguishing real resistance change due to strain modulation from resistance fluctuations due to charge trapping. Furthermore, a numerical model correlating surface charge density with the gauge factor is presented. Comparison of the simulations with experimental measurements shows the validity of this approach. These results contribute to a deeper understanding of the piezoresistive effect in Si nanowires.Nanotechnology 09/2011; 22(39):395701. DOI:10.1088/0957-4484/22/39/395701 · 3.67 Impact Factor
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ABSTRACT: In the field of resonant NEMS design, it is a common misconception that large-amplitude motion, and thus large signal-to-noise ratio, can only be achieved at the risk of oscillator instability. In the present paper, we show that very simple closed-loop control schemes can be used to achieve stable largeamplitude motion of a resonant structure, even when jump resonance (caused by electrostatic softening or Duffing hardening) is present in its frequency response. We focus on the case of a resonant accelerometer sensing cell, consisting in a nonlinear clamped-clamped beam with electrostatic actuation and detection, maintained in an oscillation state with pulses of electrostatic force that are delivered whenever the detected signal (the position of the beam) crosses zero. We show that the proposed feedback scheme ensures the stability of the motion of the beam much beyond the critical Duffing amplitude and that, if the parameters of the beam are correctly chosen, one can achieve almost full-gap travel range without incurring electrostatic pull-in. These results are illustrated and validated with transient simulations of the nonlinear closed-loop system.Journal of Applied Physics 02/2010; 107(1). DOI:10.1063/1.3277022 · 2.19 Impact Factor
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ABSTRACT: In this paper, we present preliminary results in the field of resonant Nano- Electro-Mechanical Systems (NEMS), where the gas/bio detection is performed by the frequency shift due to mass loading of the adsorbed analyte. The sensitivity of the resonant NEMS chemical sensors based on SOI-CMOSFET technology platform and a given sensor geometry is theoretically proven to be equal to 1 Hz/zeptogram in mass loading for the case of a novel detector circuit based on MOSFET transistor. The minimum frequency shift of 1 ppm is designed for the case of an readout consisting of a MEMS/NEMS based oscillator. Piezoresistive detection circuits performed in SOI- CMOSFET technology are also investigated due to their attractiveness for integrated resonant NEMS sensors. Surface functionalization for NO2 detection with CNT moieties is described, in accordance with the HSAB theory. Also, localized functionalization with NH2 self-assembled monolayer followed by biotin attachment or Au nanoparticles decoration is experimentally proven within SOI-CMOS technology. Novel reliability challenges due to Wan Der Waals and Casimir forces acting in the nanometer gaps between different parts are identified. Finally, the noise limitations for the minimum detectable mass in resonant NEMS are shown. The adsorption-desorption noise on the functionalized surface appears to be the most important, and this may be in agreement with the kinetic theory of gases giving us a first indication of the number collisions per second per our sensing surface, in the range of 2·10^9.