Abstract
Scanning micromirrors have been used in a wide range of areas, but many of them do not have position sensing built in, which significantly limits their application space. This paper reports an integrated optoelectronic position sensor (iOE-PS) that can measure the linear displacement and tilting angle of electrothermal MEMS (Micro-electromechanical Systems) scanning mirrors. The iOE-PS integrates a laser diode and its driving circuits, a quadrant photo-detector (QPD) and its readout circuits, and a band-gap reference all on a single chip, and it has been fabricated in a standard 0.5 μm CMOS (Complementary Metal Oxide Semiconductor) process. The footprint of the iOE-PS chip is 5 mm × 5 mm. Each quadrant of the QPD has a photosensitive area of 500 µm × 500 µm and the spacing between adjacent quadrants is 500 μm. The iOE-PS chip is simply packaged underneath of an electrothermally-actuated MEMS mirror. Experimental results show that the iOE-PS has a linear response when the MEMS mirror plate moves vertically between 2.0 mm and 3.0 mm over the iOE-PS chip or scans from −5 to +5°. Such MEMS scanning mirrors integrated with the iOE-PS can greatly reduce the complexity and cost of the MEMS mirrors-enabled modules and systems.
Highlights
Micro-opto-electro-mechanical systems (MOEMS) are microsystems based on micro-optical devices fabricated using micromachining [1,2,3]
It was measured that the frequency of the quadrant photo-detector (QPD) could reach up to 1 MHz, which fully meets the requirement of the micromirror testing, where the typical frequency range is from 1 Hz to 10 kHz
The mirror plate of the MEMS mirror is placed over the integrated optoelectronic position sensor (iOE-PS) chip with the initial distance set at about 2 mm
Summary
Micro-opto-electro-mechanical systems (MOEMS) are microsystems based on micro-optical devices fabricated using micromachining [1,2,3]. Scanning micromirrors have been widely used in biomedical imaging [6], spectroscopy [7], displays [8], optical communication [9], and so on For any of these applications, it is especially necessary to monitor the vertical piston displacement and/or the tip-tilt angle of the mirror plate of the micromirror employed. The most commonly used methods of realizing position sensing of mirror plates include capacitive and piezoresistive sensing [12] These two methods cannot be applied to electrothermal bimorph based micromirrors due to the large displacement and the absence of silicon or polysilicon in the bimorphs/multimorphs. The iOE-PS has been designed and fabricated, and it has been successfully applied to measure the linear displacement and tilting angle of an electrothermally-actuated MEMS scanning mirror.
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