Out-of-plane translatory MEMS actuator with extraordinary large stroke for optical path length modulation

Abstract

A translatory MOEMS actuator with extraordinary large stroke -especially developed for fast optical path length modulation in miniaturized FTIR-spectrometers -is presen¬ted. A precise translational out-of-plane oscillation at 500 Hz with large stroke of up to 1.2 mm is realized by means of a new suspension design of the comparative large mirror plate with 19.6 mm² aperture using four pantographs. The MOEMS device is driven electro -statically resonant and is manufactured in a CMOS compatible SOI process. Up to ± 600 µm amplitude (typically 1mm stroke) has been measured in vacuum of 30 Pa and 50 V driving voltage for an optimized pantograph design enabling reduced gas damping and higher driving efficiency.Keywords: Optical SOI-MEMS, translatory micro mirror, optical path length modulation, Fouriertransform infrared spectrometers, optical vacuum packaging 1 Introduction Fourier Transform Infrared (FT-IR) spectroscopy is a widely used method to analyze different materialsorganic and inorganic. Current FT-IR spectrometers are large, usually static, and are operated by qualified personnel. By using translational MOEMS devices for optical path length modulation instead of conventional highly shock sensitive mirror drives a new class of miniaturized, robust, high speed and cost efficient FTIR-systems can be addressed. An early approach of a miniaturized MEMS based FTIR spectrometer has been developed in the past by IPMS and the CTR [1]. It was a combination of classical infrared optics with a translatory 5 kHz MEMS mirror using a folded bending spring mechanism. Due to the limited amplitude of ± 100 µm a spectral resolution of 30 cm -1 was realized allowing dynamic FTIR measurements in the ms-range [2]. To enhance the stroke IPMS introduced a first translational MEMS device with two pantograph mirror suspensions -originally designed for larger stroke of 500 µm. But due to superimposed parasitic torsional modes only ± 140 µm amplitude could be measured [2].In this paper, we now present an optimized MEMS device which overcomes the previous limitations enabling an extraordinary large stroke of 1 mm. The novel translatory MOEMS actuator was specially designed to enable a miniaturized MEMS based FTIR spectrometer with improved system performance of 5 cm -1 spectral resolution ( = 2.5…16 µm), SNR > 1000 and fast operation of 500 scans / sec. Hence, a large mirror aperture of 5 mm, enhanced amplitude of ± 500 µm and a small dynamic deformation of < /4 is required. Due to the significant viscous gas damping in normal ambient the translatory MEMS devices have to operate in vacuum -requiring a long term stable optical vacuum package with broadband IR window. The paper discusses the design, fabrication and experimental characteristics of the novel translatory MEMS actuator including first results of the optical vacuum packaging.To realize a large stroke of the mirror plate a pantograph like suspension was chosen. The new translatory MEMS actuator consists of four symmetric pantograph suspensions in contrast to two pantogr...

Advances in performance and miniaturization of a FT-IR spectrometer system based on a large stroke MOEMS piston mirror

“…The new MOEMS device features a mirror plate of 5 mm in diameter mounted on four symmetric pantograph suspensions where each pantograph consists of six torsional springs and connected by stiff levers. Modal analysis shows an improved mode separation meaning that the first parasitic mode concerning a tilt of the mirror plate can be observed at a frequency of 2238 Hz, which is well separated from the frequency of the mode around 500 Hz [4]. The MOEMS device is electrostatically driven with pulsed driving voltages of 50 V at 50% duty cycle and a pulse frequency twice the mechanical oscillation frequency of about 460 Hz.…”

Wafer-Level Vacuum-Packaged Translatory MEMS Actuator with Large Stroke for NIR-FT Spectrometers

“…In addition to the actuation mechanism, MEMS-based FTS can be subclassified by the principle of optical FTS instrumentation: (i) Michelson interferometer-based FTS, e.g., [ 7 , 12 , 23 , 24 , 25 , 26 , 27 ], or (ii) lamellar grating-based FTS, enabling a simplified interferometer set-up without optical beam splitter [ 6 , 8 , 28 , 29 , 30 , 31 , 32 ]. MEMS technology was also used to simplify the optical system integration of FTS; early approaches using bulk [ 5 , 6 , 33 ] and surface micromachining [ 34 ] were reported.…”

Parametric resonance of a repulsive force MEMS electrostatic mirror

“…Micro-electromechanical systems (MEMS) enabled creating high performance miniaturized optical devices such as spectrometers [1] to measure and detect gases and confocal micro-endoscopes [2][3][4] to obtain high-resolution imaging. Other bio-medical and aerospace applications include optical coherence tomography [5,6], spatial light modulators [7,8], adaptive optic applications [9][10][11], auto-focus camera systems [12,13], telescopes [9,11] and laser-based communications [14]. The main component of these measurement devices is a MEMS mirror used for optical path modulation.…”

“…Researchers have devised methods to extend the travel range of the actuators by using levers [14], pantograph suspensions [10], soft polymers [18] and control-based approaches, including current and charge control [19,20]. The lever-bending approach increases travel range by applying the electrostatic force only to a part of the actuator [21].…”