Development and Characterization of a Piezoelectrically Actuated MEMS Digital Loudspeaker

International audienceThe MEMS digital loudspeaker consists of a set of acoustic transducers, called speaklets, arranged in a matrix and which operate in a binary manner by emitting short pulses of sound pressure. Using the principle of additivity of pressures in the air, it is possible to reconstruct an audible sound. MEMS technology is particularly well suited to produce the large number of speaklets needed for sound reconstruction quality while maintaining a reasonable size. This paper presents for the first time the modeling, realization and characterizations of a piezoelectric digital loudspeaker based on MEMS technology. Static, dynamic and acoustic measurements are performed and match closely with theoretical results

Biaxial piezoelectric MEMS mirrors with low absorption coating for 1550 nm long-range LIDAR

This paper presents the fabrication and characterization of a biaxial MEMS (MicroElectroMechanical System) scanner based on PZT (Lead Zirconate Titanate) which incorporates a low-absorption dielectric multilayer coating, i.e., a Bragg reflector. These 2 mm square MEMS mirrors, developed on 8-inch silicon wafers using VLSI (Very Large Scale Integration) technology are intended for long-range (>100 m) LIDAR (LIght Detection And Ranging) applications using a 2 W (average power) pulsed laser at 1550 nm. For this laser power, the use of a standard metal reflector leads to damaging overheating. To solve this problem, we have developed and optimised a physical sputtering (PVD) Bragg reflector deposition process compatible with our sol-gel piezoelectric motor. Experimental absorption measurements, performed at 1550 nm and show up to 24 times lower incident power absorption than the best metallic reflective coating (Au). Furthermore, we validated that the characteristics of the PZT, as well as the performance of the Bragg mirrors in terms of optical scanning angles, were identical to those of the Au reflector. These results open up the possibility of increasing the laser power beyond 2W for LIDAR applications or other applications requiring high optical power. Finally, a packaged 2D scanner was integrated into a LIDAR system and three-dimensional point cloud images were obtained, demonstrating the scanning stability and operability of these 2D MEMS mirrors.This research was funded by ECSEL Joint Undertaking (JU) grant number No. 826600 (project VIZTA).Peer ReviewedPostprint (published version

New challenges for piezoelectric MEMS

International audienceLead zirconate titanate, Pb(Zr,Ti)O$_3$ (PZT), has been the most studied piezoelectric thin film for MEMS actuators the last two decades due to its high transverse piezoelectric coefficient d31. The PZT technology is now available in several MEMS foundries and PZT thin film actuators are already integrated in commercialized devices like inkjet printheads, micro-speakers and autofocus camera. Emerging applications such as micro-mirror for LIDAR, haptics for human-machine interface, micro-pumps, as well as PMUT for fingerprint, medical probe or gesture recognition are also based on thin film PZT actuators. The potential of use of PiezoMEMS is thus expanding, but it may require to functionalize non silicon substrate (Glass, Flex, Metal,…), large surface (smart windows), curved surface (haptics). In some cases also, transparency is requested.One of the constraints that limit the use of PZT in microsystems is its high crystallization temperature, usually from 500°C to 700°C depending on deposition method/process. It is thus very complicated to integrate PZT on Si for Above IC applications (Temp <450 °C), glass substrate (optical applications, haptics) or flexible (low cost applications, large format) as require for some applications. Low temperature deposition processes and film transfer techniques are the main ways to bypass the thermal budget issue. At Leti, we developed a technological process that allows transferring films stack from silicon substrate to any other substrate. It was used for transferring high quality sol-gel deposited PZT films from silicon growth substrate to either Si, glass or polymer. The transferred PZT film keeps its high (100) texturation obtained during deposition, which is required for optimal piezoelectric properties. PZT based devices subsequently fabricated as test vehicles show excellent ferroelectric and piezoelectric properties. In this presentation, we will show the potential of this process for realizing non standard piezoMEMS devices such as capacitors on glass or transparent PZT membranes

Electrical response of Pt/Ru/PbZr 0.52 Ti 0.48 O 3 /Pt capacitor as function of lead precursor excess

International audienceWe investigated the influence of the surface microstructure and chemistry of sol-gel grownPbZr0.52Ti0.48O3 (PZT) on the electrical performance of PZT-based metal-insulator-metal (MIM)capacitors as a function of Pb precursor excess. Using surface-sensitive, quantitative X-ray photo-electron spectroscopy and scanning electron microscopy, we confirm the presence of ZrOx surfacephase. Low Pb excess gives rise to a discontinuous layer of ZrOx on a (100) textured PZT film witha wide band gap reducing the capacitance of PZT-based MIMs whereas the breakdown field isenhanced. At high Pb excess, the nanostructures disappear while the PZT grain size increasesand the film texture becomes (111). Concomitantly, the capacitance density is enhanced by 8.7%,and both the loss tangent and breakdown field are reduced by 20 and 25%, respectively. The role ofthe low permittivity, dielectric interface layer on capacitance and breakdown is discussed

Unexpected band-bending of donor-doped PbZr0.52_{0.52} Ti0.48_{0.48} O3_3 films

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DART-SSPFM multi-imaging of ferroelectric and electrostatic properties of KNN thin film at nanoscale

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PbOx phase separation in PbZr0.52Ti0.48O3 based capacitors made using sol-gel films with high Pb precursor excess

International audienceWe present a study of the impact of Pb excess content on electrical performance of lead zirconate titanate (PbZr0.52Ti0.48O3, PZT) thin-film capacitors. High Pb excess eliminates the ZrOx interface layer between the PZT and the electrode but also reduces the breakdown field, while the linear dielectric character of the capacitor response increases with Pb excess. The chemical sensitivity of hard x-ray photoelectron spectroscopy with in situ bias provides direct evidence of a polar but the non-ferroelectric PbOx phase in the bulk of the sol-gel film. The phase has a distinct core level signature and is consistent with the dielectric response at low field, which becomes more ferroelectric at higher field, as well as the lower remanent polarization and breakdown field

Cartographies DFRT-SSPFM des propriétés ferroélectriques et électrostatiques d'un film mince de KNN

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Structural Insights of Electrical Aging in PZT Thin Films as Revealed by In Situ Biasing X-ray Diffraction

International audienceElectrical aging in lead zirconate titanate (PbZrxTi1−xO3) thin films has been intensively studied from a macroscopic perspective. However, structural origins and consequences of such degradation are less documented. In this study, we have used synchrotron radiation to evaluate the behavior of ferroelectric domains by X-ray diffraction (XRD). The sample was loaded with an AC triangular bias waveform between ±10 V with a number of cycle varying from one up to 108. At each step of the aging procedure, XRD spectra had been collected in situ during the application of an electric field on a capacitor. The fine analysis of the (200) pseudo-cubic peak structure allows to separate the evolution of the volume of a/c tetragonal and rhombohedral domains along the electrical biasing. Throughout the aging, both intrinsic and extrinsic responses of tetra and rhombohedral domains are altered, the behavior depending on the observed phase. This methodology opens up new perspectives in the comprehension of the aging effect in ferroelectric thin film