In our Augmented Reality (AR) project, we are investigating the use of a retinal projection display based on the association of pixelated holograms and a dense distribution of waveguides. We study the use of gratings impregnated with liquid crystal to actively extract light from waveguides. We explore two extraction strategies: tuning the refractive index contrast between the grating teeth and grooves to erase the grating diffraction effect and changing the index of the waveguide cladding to tune the evanescence of the guided mode. Firstly, we present and discuss the measurements of the diffraction efficiency of nano-imprint gratings impregnated with liquid crystal and refractive liquid index. Secondly, we discuss the results of integrated switchable extraction grating of the second strategy.

In the field of augmented reality, there is a need for very bright color microdisplays to meet the user specifications. Today, one of the most promising technology to manufacture such displays involves a blue micro-LED technology and quantum dots-based color conversion layers. Despite recent progress, the external power conversion efficiencies (EPCE) of these layers remain under ∼25%, below the needs (>40%) to reach a white luminance of 100,000 cd/m2. In this work, we have synthesized CdSexS1-x nanoplatelet-based conversion layers for red and green conversion, and measured their absorption properties and EPCE performances with respect to layer thickness. On this basis, a model was developed that reliably predicts the layer EPCE while using only few input data, namely the layer absorption coefficients and the photoluminescence quantum yield (PLQY) of color photoresist. It brings a new insight into the conversion process at play at a micro-LED level and provides a simple method for extensive optimization of conversion materials. Finally, this study highlights the outstanding red conversion efficiency of photoresist layers made of core-double shell CdSexS1-x nanoplatelets with 31% EPCE (45% external PLQY) for 8 µm-thick conversion layer.

This paper focuses on the dimensioning of a very bright full color 10 mu m-pitch light-emitting device (LED) microdisplay for avionics application. Starting from the specifications of head-mounted display to be used in an augmented reality optical system, a theoretical approach is proposed that enables predicting the specifications of the main technology building blocks entering into the microdisplay manufacturing process flow. By taking into account various material and technological parameters, kept as realistic as possible, it is possible to assess the feasibility of a very bright LED microdisplay (1 Mcd/m(2) full white) and to point out the main limitations. The theoretical specifications are then compared with the technical results obtained so far in the framework of the H2020 Clean Sky "HILICO" project. It shows that 350 000 cd/m(2) of white emission may be accessible with the present gallium nitride (GaN)-micro-LED technology provided a color conversion solution with stable external quantum efficiency of 30% is available. Beyond such level of luminance, the inherent limitations of driving circuit (4 V, 15 mu A per pixel) commands working with materials enabling higher external quantum efficiency (EQE). In particular, 10-mu m-pitch micro-LEDs with electroluminescence EQE of 15% and color conversion EQE approaching 60% are needed, opening the way to future challenging material and technology research developments.

Demonstrated herein is a fast in-plane switching (IPS) cell with positive dielectric anisotropy liquid crystals using crossed patterned electrodes in three different conditions. The ineffectiveness of one of these three structures due to the ‘Faraday cage’ effect was shown. With another structure, a fast response time was also shown to be impossible to achieve due to several contrast issues. In the third structure, a fast response time was achieved due to a combination of high-driving and crossed patterned electrodes allowing fast turn-off. Two of the three structures was manufactured. With the first one, an experiment confirmed the ‘Faraday cage’ effect. In the second structure, a response time four to eight times faster than the conventional IPS mode was experimentally demonstrated using two different kinds of liquid crystal.

A thin‐film Hard‐Coat (HC) layer was investigated for the collective encapsulation and mechanical protection of top‐emission OLED micro displays on wafer‐scale and as an alternative solution to individual glass‐lid protection. The HC is fabricated by UV‐curing process from a silica‐based hybrid polymer synthetized by sol‐gel process.

We present a technique to measure the temperature dependence of the transverse piezoelectric coefficient e31,f of thin films of lead zirconate titanate (PZT), aluminum nitride, and BaTiO3 deposited on Si wafers. It is based on the collection of electric charges induced by the deflection of a Si cantilever coated with the piezoelectric film. The aim of this work is to assess the role of temperature in the decay of the remnant polarization of these materials, in particular, in optimized gradient-free PZT with composition PbZr0.52Ti0.48O3. It is found that in contrast to theoretical predictions, e31,f decreases with temperature because of the dominance of relaxation effects. The observation of steps in the logarithmic aging decay law is reminiscent of memory effects seen in frustrated spin glasses.

In this paper, we showed the realization and the characterization of a PZT-actuated micro-cantilever. The measurement and the modeling of its resonant frequency allow deducing the cantilever length. Using this value and combining the measurement and the modeling of the cantilever displacement amplitude at a given voltage, we extract PZT d31 piezoelectric coefficient as being 165±25 pm/V; which is among the highest values ever published for PZT thin films. It is worth noting that d31 is homogenous throughout the whole 200mm wafer.

In this study, a self-sensitive piezoelectric cantilever with a new design for sensing is presented. Micro-cantilevers were actuated by a 120nm-thick Lead Zirconate Titanate Oxide (PZT) layer. Detection was done by measuring the resistance of a metallic gauge integrated on the surface of the micro-piezoelectric cantilevers. Some metallic gauges were embedded in a Wheatstone bridge to improve the measured resistance accuracy. Devices with direct resistance measurement were also realized. Gauge resistance responses were compared with an optical measurement by a White Light Interferometer. By biasing the PZT between −5V and 5V, cyclic deflection of the cantilever was detected with both optical and metallic gauge resistance systems. The two measurements fit. This self-sensitive piezoelectric cantilever can be used for fatigue test with packaged devices.

This paper reports RF characterization of a fully packaged RF MEMS piezoelectric switch. The switch demonstrates better than 0.8 dB insertion loss at 2 GHz and 30 dB isolation up to 10 GHz. The presented device combines a piezoelectric actuation and a low electrostatic hold voltage to improve contact force. Actuation voltages of the switch are 5V for both piezoelectric actuation and electrostatic hold. This actuation was sufficient to obtain contact resistance lower than 2 ohms. The switch is packaged by wafer-level packaging technology using gap control, AuSn eutectic bonding and post-process Thru-Silicon Vias.

PbO – MgO – Nb 2 O 5 – TiO 2 (PMNT) pyrochlore thin films were prepared on Pt-coated silicon substrates by radio-frequency magnetron sputtering and postdeposition annealing method. Very interestingly, these pyrochlore-structured PMNT thin films exhibited ultralow dielectric losses, with a typical loss tangent as low as 0.001, and relatively high dielectric constants, typically εr∼170. It was found that the relative permittivity slightly but continuously increased upon cooling without any signature of a structural phase transition, displaying a quantum paraelectriclike behavior; meanwhile, the PMNT pyrochlore thin films did not show any noticeable dielectric dispersion in the real part of permittivity over a wide temperature range (77–400 K). Their dielectric responses could, however, be efficiently tuned by applying a dc electric field. A maximum applied bias field of 1 MV/cm resulted in a ∼20% tunability of the dielectric permittivity, giving rise to a fairly large coefficient of the dielectric nonlinearity, ∼2.5×109 J C−4 m−5. Moreover, the PMNT pyrochlore films exhibited superior electrical insulation properties with a relatively high breakdown field (Ebreakdown∼1.5 MV/cm) and a very low leakage current density of about 8.2×10−7 A/cm2 obtained at an electric field intensity as high as 500 kV/cm.

This paper describes the realisation and characterization of High overtone Bulk Acoustic wave resonators (HBAR) by using (Ba,Sr)TiO3 (BST) as active material. As BST is electrostrictive, it requires a dc voltage to exhibit an electromechanical coupling. Resonances variations versus the dc field are observed and analyzed by using an analytical model based on acoustic propagation. This study proves that BST can exhibit a high electromechanical coupling reaching 8.5% which is higher than Aluminium Nitride, the standard material for acoustic resonators in the GHz frequency range. Moreover, this simple HBAR test vehicle allows extracting the frequency variation experienced by BST. Due to non negligible second order effects as electrostriction, dielectric and stiffness non linearities, these tunable features are highly desirable for tunable filters. A final simulation shows that tunable passband filters could be obtained by using BST based resonators.

This paper describes the realisation and characterization of Bulk Acoustic wave resonators by using (Ba,Sr)TiO3 (BST) as active material. As BST is electrostrictive, it requires a dc voltage to exhibit an electromechanical coupling. Resonances variations versus the dc field are observed and analyzed by using an analytical model based on acoustic propagation. This study proves that BST can exhibit a high electromechanical coupling reaching 8.5% which is higher than Aluminium Nitride, the standard material for acoustic resonators in the GHz frequency range. Moreover, this simple test vehicle allows extracting the frequency variation experienced by BST. Due to non negligible second order effects as electrostriction, dielectric and stiffness non linearities, these tunable features are highly desirable for tunable filters. A final simulation shows that tunable passband filters could be obtained by using BST based resonators.

In this study, a new design for self-sensitive MEMS cantilevers is presented. Cantilevers were actuated with a 120 nm-thick Lead Zirconate Titanate (PZT) layer. Detection was done by using an integrated piezoresistive gauge in top and bottom electrodes. Some piezoresistive gauges were integrated in a Wheatstone bridge to improve the sensitivity. Devices with direct measurement gauge were also realized. Piezoresistive responses were compared with an optical measurement by a light interferometer. By poling the PZT between −5 V and 5 V, the ferroelectric cycle was observed with both optical and piezoresistive detections. The two measurements are fitting. This self-sensitive piezoelectric cantilever can be used for fatigue test with packaged devices. With this new design, piezoresistive gauge can be integrated without cost increase in piezoelectric devices because no technological steps are added for gauges realization.

( 1 − x ) Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 - x PbTiO 3 (PMNT) (with x=0.1) thin films were prepared on Pt-coated silicon substrates by radio-frequency magnetron sputtering and postdeposition annealing method. A well-crystallized pyrochlore phase structure, which started to nucleate and grow at 450–500 °C, was formed in the PMNT thin films. These pyrochlore-structured PMNT thin films show ultralow dielectric losses with a typical loss tangent as low as 0.001, accompanied by a relatively high dielectric constant (εr=176). Such an extremely low dielectric loss, having never been obtained in thin films of perovskite PMNT, is probably ascribed to the specific structural feature of pyrochlore phase, chemically different from its perovskite counterpart, and ascribed to the avoidance of the polar domain-related losses.

This paper reports the piezoelectric properties of sputtered and sol gel PZT thin films investigated in a low thickness range (100-250 nm). Piezoelectric-elastic bimorphs including very thin PZT films were realized and the maximum reachable deflection at 5 V was characterized. The depoling effect experienced by the PZT versus the maximum post process temperature is also discussed which leads to the motivation of developing low thickness range PZT thin films. Elastic-piezoelectric bimorphs were realized and exhibited deflection higher than 5 mum at 5 V. Moreover, these bimorphs showed only a 10% decrease of the deflection after 5 billions cycles.

Three- and four-level matrices of 15 times 70 nm Si Nano-Beams have been integrated with a novel CMOS gate-all-around process (GAA) down to 80 nm gate length. Thanks to this 3D-GAA extension of a Finfet process, a more than 5times higher current density per layout surface is achieved compared to planar transistors with the same gate stack (HfO 2/TiN/Poly-Si). For the first time, several properties of this novel 3D architecture are explored: (i) HfO2/TiN gate stack is integrated, (ii) electrons and holes mobilities are measured on 150 beams matrices (3 levels) and compared to those of planar transistors (hi) a sub-100nm channel width is demonstrated and (iv) specific 3D integration challenges like zipping between nano-beams are discussed

We have studied in reduced pressure chemical vapor deposition the growth kinetics of Si and Si0.8Ge0.2 on bulk Si(001) and on silicon-on-insulator (SOI) (100nm buried oxide/20nm Si over-layer) substrates. For this, we have grown miscellaneous Si/Si0.8Ge0.2 superlattices on both types of substrates that we have studied mainly in secondary ions mass spectrometry but also in X-ray diffraction. Systematic Si and SiGe growth rate decreases (together with a Ge concentration increase) occurred on SOI substrates as the stack thickness increased from zero to more than 100nm. Such phenomena are most likely associated to a decrease of the SOI surface temperature by 12–13°C compared to bulk. For Si, the growth rate on SOI increased back again towards the bulk value as the stack thickness neared two hundred nanometers. This is linked to a SOI surface temperature that went 5°C back up. Such a knowledge will be most useful to form in the near future regular superlattices on SOI substrates that will serve as the active regions of multi-bridge channel field effect transistors. Three periods Si/SiGe superlattices with either 20% or 31% of Ge and varying SiGe layer thickness were also grown on bulk Si(001) to study the critical thickness for plastic relaxation of the compressive strain that builds up in such stacks.