Gallium Nitride MEMS

Principal Investigator: Marc FAUCHER

Participating Researchers: Didier Theron, Steve Arscott, Lionel Buchaillot

Collaborations: Yvon Cordier, Fabric Semond, CNRS-CRHEA. B. Dulmet, J. Imbaud FEMTO ST.

The group has pioneered the GaN MEMS field since 2008. We still improve the R-HEMT concept that was proposed in 2009 in GaN MEMS, applying it recently to a first inertial sensor. We are working on ultrathin epilayers (Fig. 2), and more recently NEMS transducers, both to increase the force sensitivity and make III-N based sensors compatible with specific harsh environments.

Figure 2: GaN MEMS/NEMS
a) GaN doubly clamped beam microresonator made on 700 nm epilayers, preparing the NEMS needs for harsh environments compatible  force  sensors.
(b) piezoresistive transducer using the 2-DEG as strain sensor. (c) assessment of the Young modulus evidencing a high value, a challenge given the very low epilayers thickness. (d) resonator electrical response validating the first prototype of GaN resonator on ultrathin layers. Coll. CRHEA Valbonne. Supported by PIA labex GANEX. [J. Micromech. Microeng. 26 (2016) 105015]

Probes  for AFM microscopy based on MEMS with integrated transducers

Principal Investigator: Marc FAUCHER

Participating Researchers: Didier Theron

Collaborations: Past: Bernard Legrand (LAAS)

Present: Benjamin Walter (Vmicro SAS), J.F Lampin, S. Barbieri (IEMN THz Photonics)

is a continuing topic. Over the period of the report we have matured MEMS ring-probe resonators for high frequency Atomic Force Microscopy. This technology has been pushed above TRL4, disseminated in small volumes to other partners and transferred to Vmicro company. Successful demonstration activities (Fig 3) position this probe as the highest frequency operated AFM in real conditions.

Figure 3: Ring-Probes for high-frequency AFM
(a) ring-probe developed at TRL>4 by NAM6 group, featuring a 12 MHz resonant tip engineered using bulk vibration mode.
(b) integrated silicon tip batch fabricated with a 10nm apex.
(c) using an RF reflectometer technique based on a 4GHz carrier, we demonstrated an AFM head able to reach a 0.65 fm/Hz1/2 amplitude noise floor. the thermal peak is recorded and the minimum detectable force is 280 fN/Hz1/2 .
(d) first image of two-phase block copolymers obtained using the Ring-probe. Coll CRPP Bordeaux. [Ultramicroscopy 175 (2017) 46–57]

As a joint work with Vmicro, the Vprobe technology was released in 2017. This silicon vertical probe (Fig. 4) is based on a totally different design strategy. It intends to unlock the AFM instrumentation in vacuum, were the performances in any modes (FM, AM, electrical, optical) are limited by the quartz approach.

Figure 4: Vertical Probe technology for AFM in vacuum;
(a) image of the Vprobe technology jointly developped by NAM6 and Vmicro SAS, for UHV applications beyond the limits of current sensors. Vprobes combine the highest tip lengh, low impedance transducers, and high f/k ratios
(b) – the original in plane resistive nanotransducers provide a wide range of actuation with moderate input signal power level. (c) first imaging demonstration on SiC vicinal surface, scale bar 4.5 µm). Coll. Vmicro SAS.  [APPLIED PHYSICS LETTERS 110, 243101 (2017)]

Probes for multimodal measurements

PI: steve arscott

NAM6 is also working on or RF measurements. We address demands made to us by near-field NSOM/Raman community that lacks of a reliable dedicated probe. For example we are nw developing  a cantilever technology with integration of metal nano-cones to control and enhance the Raman effect.  To provide a solution to growing demands in high frequency, on wafer probing of RF-CMOS technologies (Keysight, STmicroelectronics) a miniaturized microfabricated ground-signal-ground (GSG) have been developed in NAM6 during the period of the report (supported by PIA equipex excelsior). Figure 5a shows an example of such probes destined for on-chip microwave measurements in a dedicated scanning electron microscopy/microwave measurement setup (not shown here). The probes tips are much smaller than commercial tips—by a factor of >100—enabling direct on-chip testing of isolated devices and objects—see Figure 5b. Measurements indicate a drastic reduction in parasitic capacitance compared to commercial probes—see Figure 5c.

Figure 5: Microfabricated MEMS-based ground-signal-ground (GSG) probes for on-chip microwave measurements. (a) upper–chips based on silicon-on-insulator wafers comprising a metallized micro-cantilever,;lower—image zoom of the tip of the probes – incorporating gold contacts (~2×2µm) and coplanar lines. (b) MEMS probe alongside a commercial µwave probe. (c) evidence of reduced paracitic capacitance when using MEMS probes.

Advanced Instrumentation integrating RF, MEMS and near field

PI: Didier Théron

Collaborations: Groupe ANODE (G. Dambrine, K. Haddadi), Groupe NCM (N. Clément, F. Alibart, D. Vuillaume).

in parallel to our sensors and technological topics, we pursue activities related to instrumentation ’beyond the current limits’. We develop RF techniques based on interferometry to increase measurement sensitivity and resolution at high impedance (MΩ range) and, as an application, provide the readout of capacitive MEMS with high signal to noise ratio, which has been applied to ring-probe resonators. We also apply these techniques to Scanning Microwave Microscopy at 2-18 GHz (and higher in the future), which makes us able to measure RF properties of nanoscale surfaces and devices. This has been applied for instance to 17 GHz  measurements of sets of molecules grafted on Au nanodots: see Figure 6.

Figure 6: Instrumentation for microwave nanoscale measurements
(a) setup coupling a VNA, a home-made microwave interferometer, an AFM and a resiscope.
(b) 2D |S11| histogram (normalized to 1) versus tip bias (V) generated from images of 100 molecular rectifier junctions. The rectifying behavior is clearly observed. (the voltage step is 50 mV and meas. frequency is 17 GHz).
(c) Conductance estimated from both d.c. measurement (dI/dV) —red curve—, and S11 parameters —blue curve—. The error bar in log scale is considered to be the same as the full width at half maximum in current histograms.

NEMS for microwave optomechanics

PI: Xin Zhou

collaborations: Eddy Collin, CNRS Neel, Grenoble, France

Microwave optomechanics (w-optomechanics), in which mechanical motion can be manipulated and detected through microwave photons, is a highly interdisciplinary research topic. It is at inter section of mesoscopic condensed matter physics, microwave engineering, circuits quantum electrodynamics and nanotechnology.  Here, we focus on develop novel 2D and 3D mw-optomechanical platform for wiede range of the temperature, from room temperature to ultra-low temperature. Based on this platform, we explore several functional devices for both fundamental research and applications, such as quantum limited non-destructive phonon detectors, single phonon-phonon coupling platform and w-optomechanical signal processing for classical analog of quantum computation.

Figure a: Multiplexing readout for microwave optomechanical circuits. Each microwave resonator capacitively couples with nanomechanical resonators with structure of Si3N4 suspended beam.

Figure b: 3D microwave optomechanical design. The chip contains a hybrid structure: antennas and mechanical oscillators to form a wireless optomechanical scheme.