Resonating AlN-thin film MEMS mirror with digital control

Konsta Ruotsalainen,Jukka Kyynäräinen,Oili M E Ylivaara,Dmitry Morits

doi:10.1117/1.jom.2.1.011006

Konsta Ruotsalainen, Jukka Kyynäräinen + Show 2 more

Open Access

https://doi.org/10.1117/1.jom.2.1.011006

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Abstract

Piezoelectrically actuated resonant micromirrors were designed to meet the light detection and ranging (LiDAR) system requirements. Key features were a 3-mm mirror aperture, a 40-deg field of view, and a 50-Hz refresh rate. The presented micromirror provides biaxial symmetrical beam steering with ±12.7 deg mechanical tilt angle, resulting in a 50-deg field of view with an adjustable Lissajous XY-scanning pattern for a forward-looking LiDAR system. The mirrors were fabricated using silicon on insulator wafers, and actuation was based on piezoelectric aluminium nitride thin film. The mirrors were vacuum packaged for high-quality factor resonator operation. The device design contained eight separate piezoelectric aluminium nitride elements arranged as differential pairs for each axis, where each actuator was equipped with a sensing element providing a mechanically coupled electrical feedback signal. The piezoelectric elements connected as actuators required only minimal power and were directly compatible with CMOS low-voltage logic, which eases integration to driving digital systems. The sense elements are used to monitor phase, amplitude, and frequency. A digital control system connected to each of these elements provides accurate frequency and phase control of independent orthogonal resonators, permitting control of the X and Y amplitudes and the refresh rate of the Lissajous pattern.

Highlights

Advanced driver-assistance systems and, more generally, autonomous vehicles of any size or type are and will be using light detection and ranging (LiDAR) systems for mapping their surroundings and providing data for decision making
Microelectromechanical system (MEMS)based scanning elements aim to solve the need for miniaturization and cost reduction of LiDAR systems while maintaining high performance in key parameters such as range, angular resolution, and scan rate
Various methods have been applied to miniaturize the optical scanning elements of the LiDAR system, such as the two-mirror systems presented by Wang et al.[1] and Nguyen et al.[2] or the wobbling mirror for circular scanning presented by Pensala et al.[3] and Hoffman et al.[4]

Summary

Introduction

Advanced driver-assistance systems and, more generally, autonomous vehicles of any size or type are and will be using light detection and ranging (LiDAR) systems for mapping their surroundings and providing data for decision making. Various methods have been applied to miniaturize the optical scanning elements of the LiDAR system, such as the two-mirror systems presented by Wang et al.[1] and Nguyen et al.[2] or the wobbling mirror for circular scanning presented by Pensala et al.[3] and Hoffman et al.[4] This work is concentrated on a single-mirror approach for a 2D-scanning pattern suitable for use in forward-looking LiDARs. Different types of 2D-scanning LiDARs have been reported based on PZT-elements[5] and electrothermal,[6,7] electromagnetic,[8] or electrostatic actuators.[9] Actuators fabricated on the aluminium nitride (AlN) thin-film-based process offer comparable performance levels with other state-of-the-art 2D scanning techniques, in which the tilt angle and the mirror size are mainly limited by mechanical considerations. The evolution of devices and processes presented by Pensala et al.[3] is Journal of Optical Microsystems

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