Thermal Behavior of Biaxial Piezoelectric MEMS Scanner

first_page Download PDF settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessAbstract Thermal Behavior of Biaxial Piezoelectric MEMS Scanner † by Laurent MollardLaurent Mollard SciProfiles Scilit Preprints.org Google Scholar *, Christel DieppedaleChristel Dieppedale SciProfiles Scilit Preprints.org Google Scholar , Antoine HamelinAntoine Hamelin SciProfiles Scilit Preprints.org Google Scholar , François GardienFrançois Gardien SciProfiles Scilit Preprints.org Google Scholar , Gwenael Le RhunGwenael Le Rhun SciProfiles Scilit Preprints.org Google Scholar , Jean HueJean Hue SciProfiles Scilit Preprints.org Google Scholar , Laurent FreyLaurent Frey SciProfiles Scilit Preprints.org Google Scholar and Gael CastellanGael Castellan SciProfiles Scilit Preprints.org Google Scholar University Grenoble Alpes, CEA, Leti, F-38000 Grenoble, France * Author to whom correspondence should be addressed. † Presented at the XXXV EUROSENSORS Conference, Lecce, Italy, 10–13 September 2023. Proceedings 2024, 97(1), 223; https://doi.org/10.3390/proceedings2024097223 Published: 14 June 2024 Download keyboard_arrow_down Download PDF Download PDF with Cover Download XML Download Epub Browse Figures Versions Notes Keywords: thermal behavior; 2D MEMS mirror; piezoelectric; Bragg reflector; high optical power management This paper presents the thermal behavior of a non-resonant (quasi-static) biaxial piezoelectric MEMS scanner. Such MEMS mirrors, whose design originates from [1], use either a Bragg coating (multiple (n) dielectric bilayers of amorphous Si and SiO2) or a reflective gold coating. In our case, they are intended for LIDAR (LIght Detection And Ranging) applications, using a 1550 nm pulsed laser with an average power of 2 W. LIDAR is a crucial sensor for autonomous driving as it can provide high-density point clouds with accurate three-dimensional information [2]. For long-range LIDAR (>100 m), the MEMS-LIDAR approach, based on MEMS mirrors, seems to currently be the best solid-state beam-steering option [2].In this way, 2 × 2 mm2 square mirrors were fabricated with Bragg and Gold reflectors. The best result obtained, using a quasi-static mode, is optical angles close to 8°, on both axes, for a driving voltage of 20 V, as reported in Figure 1. The optical angles obtained with 1 × 1 mm2 and 0.5 × 0.5 mm2 square mirrors are also reported using the FoM (Figure of Merit) defined in [2]. Our results reflect the state of the art, with FoM values between 0.6 and 0.7, as shown in Figure 2.This paper presents a series of experimental results concerning the thermal behavior of the Bragg reflector compared to a reflective gold coating. Experimental absorption measurements, performed at 1550 nm with p- and s-type laser polarization, showed, as seen in Figure 3, that the use of the Bragg reflector can lead to up to 24 times lower incident power absorption than the best metallic (Au) reflective coating (s-polarization, four Bragg bilayers (n = 4)). These results pave the way for reducing mirror heating and increasing the tolerable incident laser power. A key parameter of MEMS mirrors is the impact of mirror overheating, in particular the effect of reflector absorption on mirror flatness. To study such an evolution, 400 °C/10 min annealing in air was performed on a full sheet Bragg reflector. It showed a 50% decrease in absorption (p-polarization) after the annealing step, which means better resistance to incident power.Regarding the evolution of mirror flatness with temperature, stress-compensated technology has been developed, which allows a static radius of curvature (SCR) of 250 m at room temperature (25 °C), as shown in Figure 4. Measurements taken at 200 °C showed that the SCR remains close to 300 m, meaning that the mirror remains flat even during overheating.Finally, the evolution of the 2D scan was carried out at mirror temperatures of 30 °C and 150 °C, showing no difference in terms of optical angles and 2D scan figures.These MEMS scanners have been packaged and integrated into a LIDAR system and three-dimensional (3D LIDAR) point cloud images were obtained. Author ContributionsL.M.: project administration, writing—original draft. C.D.: investigation. A.H.: investigation. F.G.: investigation. G.L.R.: validation, investigation. J.H.: validation, investigation. L.F.: validation, investigation. G.C.: investigation. All authors have read and agreed to the published version of the manuscript.FundingThis work was conducted under the framework of the ECSEL VIZTA project funded by the ECSEL Joint Undertaking (JU) under grant agreement no. 826600.Institutional Review Board StatementNot applicable.Informed Consent StatementNot applicable.Data Availability StatementData are contained within the article.AcknowledgmentsPart of this work, performed on the Platform for NanoCharacterisation (PFNC) at CEA, was supported by the "Recherche Technologique de Base" Program funded by the French Ministry for Research and Higher Education. The authors would like to thank Catherine Brunet-Manquat (University Grenoble Alpes, CEA, Leti) for characterizing the micro-mirrors.Conflicts of InterestThe authors declare no conflicts of interest.ReferencesKobayashi, T.; Maeda, R.; Tsaur, J. Fabrication of Optical Micro scanner driven by PZT Actuators. Jpn. J. Appl. Phys. 2005, 44, 7078. [Google Scholar] [CrossRef]Wang, D.; Watkins, C.; Xie, H. MEMS mirrors for LIDAR: A review. Micromachines 2020, 11, 456. [Google Scholar] [CrossRef] [PubMed] Figure 1. Two-dimensional scanning/optical angles—2 × 2 mm2 squared mirror with Bragg reflector (n = 2). Figure 1. Two-dimensional scanning/optical angles—2 × 2 mm2 squared mirror with Bragg reflector (n = 2). Figure 2. FoM values (fe, θe.de) previously reported in [2] (▲) and this work with ◘ Bragg (n = 2) and ◘ gold reflector for 2 × 2 mm2, 1 × 1 mm2, and 0.5 × 0.5 mm2 side-squared mirrors. Figure 2. FoM values (fe, θe.de) previously reported in [2] (▲) and this work with ◘ Bragg (n = 2) and ◘ gold reflector for 2 × 2 mm2, 1 × 1 mm2, and 0.5 × 0.5 mm2 side-squared mirrors. Figure 3. Variation in reflector absorption (%) with p- and s-type polarization at 550 nm incident wavelength; 45° incident laser; Bragg and gold reflector; ambient temperature (○, ◊) and after 400 °C annealing (○, ◊). Figure 3. Variation in reflector absorption (%) with p- and s-type polarization at 550 nm incident wavelength; 45° incident laser; Bragg and gold reflector; ambient temperature (○, ◊) and after 400 °C annealing (○, ◊). Figure 4. Scanner deformation of a Bragg reflector (n = 2) along the Z-axis near ambient temperature (30 °C). Figure 4. Scanner deformation of a Bragg reflector (n = 2) along the Z-axis near ambient temperature (30 °C). Disclaimer/Publisher's Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Share and Cite MDPI and ACS Style Mollard, L.; Dieppedale, C.; Hamelin, A.; Gardien, F.; Le Rhun, G.; Hue, J.; Frey, L.; Castellan, G. Thermal Behavior of Biaxial Piezoelectric MEMS Scanner. Proceedings 2024, 97, 223. https://doi.org/10.3390/proceedings2024097223 AMA Style Mollard L, Dieppedale C, Hamelin A, Gardien F, Le Rhun G, Hue J, Frey L, Castellan G. Thermal Behavior of Biaxial Piezoelectric MEMS Scanner. Proceedings. 2024; 97(1):223. https://doi.org/10.3390/proceedings2024097223 Chicago/Turabian Style Mollard, Laurent, Christel Dieppedale, Antoine Hamelin, François Gardien, Gwenael Le Rhun, Jean Hue, Laurent Frey, and Gael Castellan. 2024. 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