Application of a micromachined translatory actuator to an optical FTIR spectrometer

Abstract

We present a Fourier-transform infrared (FTIR) spectrometer where a micro-opto-electro-mechanical system (MOEMS) replaces the macroscopic mirror drive enabling a miniaturized, robust and low cost system. The MOEMS devices are manufactured in a CMOS compatible process on a silicon on insulator (SOI) substrate. The device consists of a metallized actuator plate with an area of 1.65 mm2 acting as mirror, bearing springs and electrodes for the electrostatic drive. Due to the driving principle based on in-plane electrode combs, 200m translatory displacement can be achieved with comparatively low voltages (<40 V) at an ambient pressure below 500 Pa. The actuator operates at a resonant frequency of 5 kHz. Consequently this yields a maximum spectral resolution of 25 cm-11 and an acquisition time of 200 s per spectrum. Based on a Michelson setup the infrared optical bench of the presented FTIR system is designed to account for the mirror aperture and the desired spectral band width of 2 m to 5m. The integrated signal processing electronics has to cope with a bandwidth of 8 MHz as a result of the mirror motion. A digital signal processor manages system control and data processing. Furthermore, high-level analysis algorithms can be applied without the need of an external PC. The high acquisition rate and integration level of the system makes it appropriate for applications like process control and surveillance of fast reactions. First results of transmission and absorbance measurements are shown

Translatory MEMS actuators for optical path length modulation in miniaturized Fourier-transform infrared spectrometers

“…7͑b͔͒. exceed 90 m due to parasitic oscillation modes ͑e.g., outof-plane rotation mode͒. 13 An extrapolation of the results gives a required driving voltage of over 700 V at ambient pressure, which cannot be supported by the device due to the electromechanical stability of the comb drive.…”

MEMS-based compact FT-spectrometers - a platform for spectroscopic mid-infrared sensors

“…In the first tested layout (type A) of the translational micromechanical mirror, the actual mirror element is suspended on two long bending springs ( Figure 1) [4]. While allowing for high oscillation frequencies, this design showed a number of critical limitations.…”

Precision alignment and assembly of a Fourier transform microspectrometer

“…In contrast with the design in [23,24], we assemble silicon and glass micro parts onto a Silicon-on-Insulator (SOI) die to accomplish scanning, collimation, and interference. A MEMS thermal Chevron actuator [27] is used for moving the scanning mirror.…”

“…Kung L. et al have shown a standing wave transform spectrometer [22] which uses an electrostatically actuated MEMS mirror with onresonance displacement of up to 65 µm, a thin-film photo-detector, and an electrical back plane for actuating the mirror. Fraunhofer Institute for Photonic Microsystems is developing Fourier Transform spectrometers for measurements from near IR to mid IR range [23,24]. The complete devices are around 10 cm×20 cm in size, and use in-plane electrostatic combs which are vacuumpackaged.…”