Xavier Borrisé

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.

Nanolithography on thin layers of PMMA using atomic force microscopy

A new technique for producing nanometre scale patterns on thin layers (<30 nm thick) of PMMA on silicon is described. The method consists of inducing the local modification of the PMMA by applying a positive voltage between the silicon and an atomic force microscope (AFM) tip. At voltages larger than 28 V, it is observed that a hole is directly produced on the PMMA. The silicon surface is simultaneously oxidized even in the case where a hole has not been created. Monitoring of the electrical current through the AFM tip during the application of the voltage allows elucidating the mechanism of the PMMA removal. The process is used to define nanometre scale electrodes by combining the AFM lithography with electron beam lithography, metal deposition and lift-off processes.

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.

V-groove plasmonic waveguides fabricated by nanoimprint lithography

Propagation of channel plasmon-polariton modes in the bottom of a metal V groove has been recently demonstrated. It provides a unique way of manipulating light at nanometer length scale. In this work, we present a method based on nanoimprint lithography that allows parallel fabrication of integrated optical devices composed of metal V grooves. This method represents an improvement with respect to previous works, where the V grooves were fabricated by direct milling of the metal, in terms of robustness and throughput.

Enabling electromechanical transduction in silicon nanowire mechanical resonators fabricated by focused ion beam implantation.

We present the fabrication of silicon nanowire (SiNW) mechanical resonators by a resistless process based on focused ion beam local gallium implantation, selective silicon etching and diffusive boron doping. Suspended, doubly clamped SiNWs fabricated by this process presents a good electrical conductivity which enables the electrical read-out of the SiNW oscillation. During the fabrication process, gallium implantation induces the amorphization of silicon that, together with the incorporation of gallium into the irradiated volume, increases the electrical resistivity to values higher than 3 Ω m, resulting in an unacceptably high resistance for electrical transduction. We show that the conductivity of the SiNWs can be restored by performing a high temperature doping process, which allows us to recover the crystalline structure of the silicon and to achieve a controlled resistivity of the structures. Raman spectroscopy and TEM microscopy are used to characterize the recovery of crystallinity, while electrical measurements show a resistivity of 10(-4) Ω m. This resistivity allows to obtain excellent electromechanical transduction, which is employed to characterize the high frequency mechanical response by electrical methods.

Real time protein recognition in a liquid-gated carbon nanotube field-effect transistor modified with aptamers.

The combination of optimized and passivated Field Effect Transistors (FETs) based on carbon nanotubes (CNTs) together with the appropriate choice and immobilization strategy of aptamer receptors and buffer concentration have allowed the highly sensitive and real time biorecognition of proteins in a liquid-gated configuration. Specifically we have followed the biorecognition process of thrombin by its specific aptamer. The aptamer modified device is sensitive enough to capture a change in the electronic detection mechanism, one operating at low protein concentrations and the other in a higher target concentration range. The high sensitivity of the device is also sustained by the very low detection limits achieved (20 pM) and their high selectivity when other target proteins are used. Moreover, the experimental results have allowed us to quantify the equilibrium constant of the protein-aptamer binding and confirm its high affinity by using the Langmuir equation.

Fabrication of complementary metal-oxide-semiconductor integrated nanomechanical devices by ion beam patterning

The authors present a novel approach to fabricate nanomechanical devices integrated into complementary metal-oxide-semiconductor (CMOS) circuits. It is based on focused ion beam patterning using two different processes: (i) ion-beam-induced deposition of tethraethoxysilane and (ii) direct exposure of silicon or polysilicon surfaces. In both cases, the irradiated areas sustain a reactive-ion etching process, acting as robust masks for defining nanomechanical devices with submicron resolution. These processes are compared, in terms of throughput, with direct milling of silicon and with patterning of thin aluminum layers. Compatibility with prefabricated CMOS circuits is studied and they found that the process is entirely compatible if the proper exposure conditions are used.

Scanning near-field optical microscope for the characterization of optical integrated waveguides

A scanning near-field optical microscope for the characterization of optical integrated devices has been developed. Compatible with a normal optical characterization setup the experimental setup allows a tapered uncoated optical fiber to scan the optical device with constant height by means of a shear force control using a tuning fork, and to obtain the evanescent field emerging from it. In this way, images showing simultaneously the topography with lateral resolution better than 10 nm and vertical resolution of 1 nm, and the optical field distribution have been obtained. Images obtained over rib waveguides show the guided mode intensity distribution, allowing characterization of the propagation of the light in the device for up to 1 mm. Identification of the guided mode propagation has been achieved by comparing the images with computer simulations. Measurement of the experimental decay lengths of the evanescent field obtained by the microscope allows a determination of the effective refractive index of the structure to be made.

Atomic force microscopy local anodic oxidation of thin Si3N4 layers for robust prototyping of nanostructures

Local anodic oxidation by atomic force microscopy (AFM) of thin silicon nitride layers deposited on silicon wafers allows the definition of stamps for nanoimprint lithography. The study of the mechanism and kinetics of the AFM induced oxidation shows that the patterns on silicon nitride can be generated faster and at lower voltages than directly on silicon surfaces. Stamp fabrication is completed by chemical wet etching of the samples after the AFM patterning, resulting in a robust process because of the excellent properties of silicon nitride as a mask for selective wet etching. As a demonstrator, a stamp for nanoimprint lithography is fabricated that will be used for the realization of biosensors based on interdigitated nanoelectrodes.

Atomic force microscope characterization of a resonating nanocantilever

An atomic force microscope (AFM) is used as a nanometer-scale resolution tool for the characterization of the electromechanical behaviour of a resonant cantilever-based mass sensor. The cantilever is actuated electrostatically by applying DC and AC voltages from a driver electrode placed closely parallel to the cantilever. In order to minimize the interaction between AFM probe and the resonating transducer cantilever, the AFM is operated in a dynamic non-contact mode, using oscillation amplitudes corresponding to a low force regime. The dependence of the static cantilever deflection on DC voltage and of the oscillation amplitude on the frequency of the AC voltage is measured by this technique and the results are fitted by a simple non-linear electromechanical model.