N. Barniol

On the breakdown statistics of very thin SiO2 films

In accordance with the idea that the degradation of the SiO2 network and the dielectric breakdown are intimately related, a new model to describe the breakdown statistics of thin SiO2 films is presented. The obtained distribution of failures has been found to provide very good fits of the experimental statistical data that correspond to both constant-current and constant-voltage stress experiments. The fundamental properties of the extreme-value distributions are preserved by the presented model and, what is more important, the two involved statistical parameters have a natural physical interpretation. Finally, the Monte Carlo method has been applied to simulate the degradation of the SiO2 film until breakdown, and this has been demonstrated to be a powerful technique for introducing second-order effects into the study of the breakdown statistics.

Monolithic CMOS MEMS Oscillator Circuit for Sensing in the Attogram Range

This letter presents the design, fabrication, and demonstration of a CMOS/microelectromechanical system (MEMS) electrostatically self-excited resonator based on a submicrometer-scale cantilever with ~1 ag/Hz mass sensitivity. The mechanical resonator is the frequency-determining element of an oscillator circuit monolithically integrated and implemented in a commercial 0.35 mum CMOS process. The oscillator is based on a Pierce topology adapted for the MEMS resonator that presents a mechanical resonance frequency of ~6 MHz, a relative low quality factor of 100, and a large motional resistance of ~25 M. The MEMS oscillator has a frequency stability of ~1.6 Hz resulting in a mass resolution of ~1 ag (1 ag = 10-18 g in air conditions.

Electromechanical model of a resonating nano-cantilever-based sensor for high-resolution and high-sensitivity mass detection

A simple linear electromechanical model for an electrostatically driven resonating cantilever is derived. The model has been developed in order to determine dynamic quantities such as the capacitive current flowing through the cantilever-driver system at the resonance frequency, and it allows us to calculate static magnitudes such as position and voltage of collapse or the voltage versus deflection characteristic. The model is used to demonstrate the theoretical sensitivity on the attogram scale of a mass sensor based on a nanometre-scale cantilever, and to analyse the effect of an extra feedback loop in the control circuit to increase the Q factor.

Ultrasensitive mass sensor fully integrated with complementary metal-oxide-semiconductor circuitry

Nanomechanical resonators have been monolithically integrated on preprocessed complementary metal-oxide-semiconductor (CMOS) chips. Fabricated resonator systems have been designed to have resonance frequencies up to 1.5 MHz. The systems have been characterized in ambient air and vacuum conditions and display ultrasensitive mass detection in air. A mass sensitivity of 4 ag/Hz has been determined in air by placing a single glycerine drop, having a measured weight of 57 fg, at the apex of a cantilever and subsequently measuring a frequency shift of 14.8 kHz. CMOS integration enables electrostatic excitation, capacitive detection, and amplification of the resonance signal directly on the chip.

Integration of RF-MEMS resonators on submicrometric commercial CMOS technologies

Integration of electrostatically driven and capacitively transduced MEMS resonators in commercial CMOS technologies is discussed. A figure of merit to study the performance of different structural layers and different technologies is defined. High frequency (HF) and very high frequency (VHF) resonance MEMS metal resonators are fabricated on a deep submicron 0.18 µm commercial CMOS technology and are characterized using electrical tests without amplification, demonstrating the applicability of the MEMS fabrication process for future technologies. Moreover, the fabricated devices show comparable performance in terms of Q × fres with previously presented MEMS resonators, whereas the small gap allows obtaining a low motional resistance with a single resonator approach.

Integrated CMOS-MEMS with on-chip readout electronics for high-frequency applications

A bridge-shaped first-lateral-mode 60-MHz mechanical resonator, which is monolithically integrated with capacitive CMOS readout electronics, is presented. The resonator is fabricated directly on a commercial CMOS technology using the top metal level as a structural layer. A maskless single-step wet-etching process for mechanical structure release after the standard CMOS integration process is the only postfabrication requirement. Electrical characterization of the electromechanical device demonstrates the feasibility of implementing a CMOS-microelectromechanical system for high-frequency applications using a standard conventional CMOS technology.

Nanometer-scale oxidation of Si(100) surfaces by tapping mode atomic force microscopy

The nanometer‐scale oxidation of Si(100) surfaces in air is performed with an atomic force microscope working in tapping mode. Applying a positive voltage to the sample with respect to the tip, two kinds of modifications are induced on the sample: grown silicon oxide mounds less than 5 nm high and mounds higher than 10 nm (which are assumed to be gold depositions). The threshold voltage necessary to produce the modification is studied as a function of the average tip‐to‐sample distance.

AFM lithography of aluminum for fabrication of nanomechanical systems

Nanolithography by local anodic oxidation of surfaces using atomic force microscopy (AFM) has proven to be more reproducible when using dynamic, non-contact mode. Hereby, the tip/sample interaction forces are reduced dramatically compared to contact mode, and thus tip wear is greatly reduced. Anodic oxidation of Al can be used for fabricating nanomechanical systems, by using the Al oxide as a highly selective dry etching mask. In our experiments, areas as large as 2 micro m x 3 micro m have been oxidized repeatedly without any sign of tip-wear. Furthermore, line widths down to 10nm have been routinely obtained, by optimization of AFM parameters, such as tip/sample distance, voltage and scan speed. Finally, AFM oxidation experiments have been performed on CMOS processed chips, demonstrating the first steps of fabricating fully functional nanomechanical devices.

Nondestructive multiple breakdown events in very thin SiO2 films

Several breakdown events and multilevel current fluctuations have been observed when ultrathin SiO2 films are subjected to constant‐voltage stresses. These breakdown events are sometimes reversible, and consist in a local change of conduction mechanism. This reversibility shows that no catastrophic thermal effects occur, and that the breakdown is only a local switching between two oxide conduction states of very different conductivities.

Design, fabrication, and characterization of a submicroelectromechanical resonator with monolithically integrated CMOS readout circuit

In this paper, we report on the main aspects of the design, fabrication, and performance of a microelectromechanical system constituted by a mechanical submicrometer scale resonator (cantilever) and the readout circuitry used for monitoring its oscillation through the detection of the capacitive current. The CMOS circuitry is monolithically integrated with the mechanical resonator by a technology that allows the combination of standard CMOS processes and novel nanofabrication methods. The integrated system constitutes an example of a submicroelectromechanical system to be used as a cantilever-based mass sensor with both a high sensitivity and a high spatial resolution (on the order of 10/sup -18/ g and 300 nm, respectively). Experimental results on the electrical characterization of the resonance curve of the cantilever through the integrated CMOS readout circuit are shown.