Piezoelectric MEMS mirrors for the next generation of small form factor AR glasses

The adoption of MEMS mirrors has been rapidly growing in recent years, involving different types of applications. One of the most challenging applications for Laser Beam Scanning (LBS) displays are Augmented Reality (AR) glasses, since they require high resolution images, small volume occupation and low power consumption. To comply with these requirements, MEMS scanners are moving to piezoelectric actuation, a technology that enables high actuation forces and high efficiency in a small die area. In this work, two compact MEMS mirrors with piezoelectric actuation are presented: a 27.5kHz resonant mirror (MMR40100) with 1.1mm diameter and 56deg FOV and a quasi-static mirror (MML40100) working at 60Hz with 2.45x1.44mm2 reflective area and 32deg FOV. The working voltage is <40V for both mirrors, keeping the power consumption low (<20mW). To enable the mirror control, diffused piezoresistive sensors in Wheatstone bridge configuration are integrated in both mirrors. In this paper it will be described the working principle of the MEMS designs, the manufacturing process, the FEM simulations and the experimental findings obtained on fabricated samples. Once coupled together, the two mirrors enable a 720p display module with 65deg diagonal FOV and a volume occupation of the entire display module of <0.7cc making this solution one of the most promising for the next-generation AR glasses.