arXiv subjects

M. Faucher

Publications and source records attributed to M. Faucher.

6 recordsLinked to original sources

arXiv2026

Circuit-Level Design, Modeling, and On-Wafer Characterization of a Coplanar THz Optoelectronic Mixer

We report the design, modeling, and on-wafer characterization of a photoconductive heterodyne mixer implemented as a true terahertz monolithic integrated circuit (TMIC). Unlike previous photoconductive heterodyne demonstrations, the proposed circuit is characterized using RF integrated circuit metrics including input return loss, RF/IF isolation, broadband impedance matching, and conversion loss. The mixer combines a microcavity photoconductor with a broadband coplanar matching network incorporating a Ti shunt resistor, an RF DC-blocking MIM capacitor, and an RF/IF decoupling capacitor. A circuit-level model including both the photoconductor and the distributed CPW accesses is developed and validated. The passive circuit is experimentally characterized up to 500 GHz using on-wafer VNA measurements and accurately reproduced by simulation. Under illumination, the model predicts an input reflection coefficient below -10 dB up to 215 GHz and better than -6.5 dB up to 500 GHz. Measured and simulated conversion losses agree within +/-1 dB over the entire 1-500 GHz range. Conversion loss varies from 22.5-25.5 dB below 320 GHz and 26-34 dB up to 500 GHz. The proposed TMIC demonstrates broadband operation and provides a validated circuit design methodology for future integrated THz photonic mixers.

physics.app-ph↗

arXiv2022

SOI-based micro-mechanical terahertz detector operating at room-temperature

We present a micro-mechanical terahertz (THz) detector fabricated on a silicon on insulator (SOI) substrate and operating at room-temperature. The device is based on a U-shaped cantilever of micrometric size, on top of which two aluminum half-wave dipole antennas are deposited. This produces an absorption extending over the $\sim 2-3.5$THz frequency range. Due to the different thermal expansion coefficients of silicon and aluminum, the absorbed radiation induces a deformation of the cantilever, which is read out optically using a $1.5\mu$m laser diode. By illuminating the detector with an amplitude modulated, 2.5 THz quantum cascade laser, we obtain, at room-temperature and atmospheric pressure, a responsivity of $\sim 1.5 \times 10^{8}$pm/W for the fundamental mechanical bending mode of the cantilever. This yields an noise-equivalent-power of 20 nW/Hz$^{1/2}$ at 2.5THz. Finally, the low mechanical quality factor of the mode grants a broad frequency response of approximately 150kHz bandwidth, with a response time of $\sim 2.5\mu$s.

physics.optics↗

arXiv2007

Electrostatic Actuators Operating in Liquid Environment : Suppression of Pull-in Instability and Dynamic Response

This paper presents results about fabrication and operation of electrostatic actuators in liquids with various permittivities. In the static mode, we provide experimental and theoretical demonstration that the pull-in effect can be shifted beyond one third of the initial gap and even be eliminated when electrostatic actuators are operated in liquids. This should benefit to applications in microfluidics requiring either binary state actuation (e.g. pumps, valves) or continuous displacements over the whole gap (e.g. microtweezers). In dynamic mode, actuators like micro-cantilevers present a great interest for Atomic Force Microscopy (AFM) in liquids. As this application requires a good understanding of the cantilever resonance frequency and Q-factor, an analytical modeling in liquid environment has been established. The theoretically derived curves are validated by experimental results using a nitride encapsulated cantilever with integrated electrostatic actuation. Electrode potential screening and undesirable electrochemistry in dielectric liquids are counteracted using AC-voltages. Both experimental and theoretical results should prove useful in micro-cantilever design for AFM in liquids.

cs.OH↗

arXiv2001

Niobium and niobium nitride SQUIDs based on anodized nanobridges made with an Atomic Force Microscope

We present a fabrication method of superconducting quantum interference devices (SQUIDs) based on direct write lithography with an Atomic Force Microscope (AFM). This technique involves maskless local anodization of Nb or NbN ultrathin films using the voltage biased tip of the AFM. The SQUIDs are of weak-link type, for which two geometries have been tested: Dayem and variable thickness nanobridges. The magnetic field dependence of the maximum supercurrent Ic(flux) in resulting SQUIDs is thoroughly measured for different weak link geometries and for both tested materials. It is found that the modulation shape and depth of Ic(flux) curves are greatly dependent on the weak link size. We analyze the results taking into account the kinetic inductance of nanobridges and using the Likharev-Yakobson model. Finally we show that the present resolution reached by this technique (20nm) enables us to fabricate Nb weak-links which behavior approaches those of ideal Josephson junctions.

cond-mat.mes-hall↗

arXiv2001

Josephson junctions and superconducting quantum interference devices made by local oxidation of niobium ultrathin films

We present a method for fabricating Josephson junctions and superconducting quantum interference devices (SQUIDs) which is based on the local anodization of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained either by partial or total oxidation of the niobium layer. Two types of weak link geometries are fabricated : lateral constriction (Dayem bridges) and variable thickness bridges. SQUIDs based on both geometries show a modulation of the maximum Josephson current with a magnetic flux periodic with respect to the superconducting flux quantum h/2e. They persist up to 4K. The modulation shape and depth for SQUIDs based on variable thickness bridges indicate that the weak link size becomes comparable to the superconducting film coherence length which is of the order of 10nm.

cond-mat.mes-hall↗

arXiv2000

Magnetic and Thermodynamic Properties of the Collective Paramagnet-Spin Liquid Pyrochlore Tb2Ti2O7

In a recent letter [Phys. Rev. Lett. {\bf 82}, 1012 (1999)] it was found that the Tb$^{3+}$ magnetic moments in the Tb$_2$Ti$_2$O$_7$ pyrochlore lattice of corner-sharing tetrahedra remain in a {\it collective paramagnetic} state down to 70mK. In this paper we present results from d.c. magnetic susceptibility, specific heat data, inelastic neutron scattering measurements, and crystal field calculations that strongly suggest that (1) the Tb$^{3+}$ ions in Tb$_2$Ti$_2$O$_7$ possess a moment of approximatively 5$μ_{\rm B}$, and (2) the ground state $g-$tensor is extremely anisotropic below a temperature of $O(10^0)$K, with Ising-like Tb$^{3+}$ magnetic moments confined to point along a local cubic $<111>$ diagonal (e.g. towards the middle of the tetrahedron). Such a very large easy-axis Ising like anisotropy along a $<111>$ direction dramatically reduces the frustration otherwise present in a Heisenberg pyrochlore antiferromagnet. The results presented herein underpin the conceptual difficulty in understanding the microscopic mechanism(s) responsible for Tb$_2$Ti$_2$O$_7$ failing to develop long-range order at a temperature of the order of the paramagnetic Curie-Weiss temperature $θ_{\rm CW} \approx -10^1$K. We suggest that dipolar interactions and extra perturbative exchange coupling(s)beyond nearest-neighbors may be responsible for the lack of ordering of Tb$_2$Ti$_2$O$_7$.

cond-mat.dis-nn↗