Aluminum nitride (AlN) is a promising piezoelectric material suitable for full CMOS compatible MEMS processes. Due
to the transversal inverse piezoelectric effect the use of AlN enables quasistatic deformable mirrors by actively coupling
lateral strain in micro machined membranes. In this work a fast and reliable way for reactive magnetron rf-sputtered aluminum
nitride thin films with piezoelectric properties is shown. The thin AlN films were deposited on amorphous TiAl,
SiO2 and silicon substrates using an industrial PVD cluster system. The morphologies of the deposited polycrystalline
AlN films are characterized by X-ray diffraction measurements and SEM images of the layer surfaces. An enhanced
texture coefficient is used to demonstrate the correlation between the X-ray diffraction pattern and the surface topology.
High values of this enhanced texture coefficient will guarantee piezoelectric properties. Virtual powder X-ray diffraction
experiments are used to determine the relative powder intensities required for texture coefficient evaluation. The transversal
inverse piezoelectric coupling coefficient d31 is measured for tempered and untreated aluminum nitride thin films
with high enhanced texture coefficients by quasistatic deflected wafer cantilevers.
Today, spatial light modulators (SLMs) based on individually addressable micro-mirrors play an important role for use
in DUV lithography and adaptive optics. Especially the mirror planarity and stability are important issues for these
applications. Mono-crystalline silicon as mirror material offers a great possibility to combine the perfect surface with the
good mechanical properties of the crystalline material. Nevertheless, the challenge is the integration of mono-crystalline
silicon in a CMOS process with low temperature budget (below 450°C) and restricted material options. Thus, standard
processes like epitaxial growth or re-crystallization of poly-silicon cannot be used. We will present a CMOS-compatible
approach, using adhesive wafer transfer bonding with Benzocyclobutene (BCB) of a 300nm thin silicon membrane,
located on a SOI-donor wafer. After the bond process, the SOI-donor wafer is grinded and spin etched to remove the
handle silicon and the buried oxide layer, which results in a transfer of the mono-crystalline silicon membrane to the
CMOS wafer. This technology is fully compatible for integration in a CMOS process, in order to fabricate SLMs,
consisting of one million individually addressable mono-crystalline silicon micro-mirrors. The mirrors, presented here,
have a size of 16×16 μm2. Deflection is achieved by applying a voltage between the mirrors and the underlying
electrodes of the CMOS electronics. In this paper, we will present the fabrication process as well as first investigations of
the mirror properties.
We present investigations of a new miniaturized NIR spectrometer
with a size of only 1088 cm3, and a MOEMS-scanninggrating
chip as a main element. It works currently in a spectral range of
1200 to 1900 nm with a resolution of less than 10 nm using only one
single InGaAs diode as a detector. One entire spectral measurement is
done within 6 msec, calculated by a digital signal processor, which is
included in the spectrometer. The MOEMS-scanning-grating chip is resonantly
driven by a pulsed voltage of up to 36 V, has a grating plate 3
3 mm2, and reaches deflection angles of ±8 deg at 25 V. Control and
investigation of the deflection angle, the static deformation, the spectral
efficiency, and the mechanical shock resistance are key parameters to
reach the spectrometer specifications. Results of these measurements
and their influence on the spectrometer are discussed. Special etch control
structures to monitor the fabrication process of the grating structure
in the nanometer range, which can be easily done by microscopic inspection,
are also presented.
"NIR Hyperspectral Imaging" is a universal tool to measure and control chemical properties of objects. The combination
of digital imaging and molecular spectroscopy exhibits a great benefit, especially for in- and on-line analysis. However, a
wide use is impeded at present due to the expensive and complex system approach. One reason is the high cost of two
dimensional InGaAs detector arrays, another one is the special glass that is used in the near infrared NIR.
In this paper a new approach for a NIR Imaging spectrometer is presented. The base of the new Pushbroom
Hyperspectral Imager is a micromechanical scanning device with an integrated diffraction grating. This MOEMS device
is made in a standard SOI fabrication process developed at Fraunhofer IPMS.1 2 3 For the Hyperspectral Imager, a new
all-reflective optical system based on a Schiefspiegler setup has been developed. The simulated optical configuration and
the achieved performance of the system will be presented.
"NIR Hyperspectral Imaging" is a universal tool to measure and control chemical properties of objects. The combination of digital imaging and molecular spectroscopy exhibits a great benefit, especially for in- and on-line analysis. However, a wide use is impeded at present due to the expensive and complex system approach. One reason is the high cost of two dimensional InGaAs detector arrays, another one is the special glass that is used in the near infrared NIR.
In this paper a new approach for a NIR Imaging spectrometer is presented. The base of the new Pushbroom Hyperspectral Imager is a micromechanical scanning device with an integrated diffraction grating. This MOEMS device is made in a standard SOI fabrication process developed at Fraunhofer IPMS. For the Hyperspectral Imager, a new all-reflective optical system based on a Schiefspiegler setup has been developed. The simulated optical configuration and the achieved performance of the system will be presented.
Spectroscopy in the infrared region is today an important application to measure, control and investigate liquids or
gases in industrial, medical or environmental applications. We have developed a small, transportable NIRspectrometer
with a size of only 120 x 80 x 80 mm3, and a MOEMS-scanning-grating chip as main element. The
scanning-grating chip is resonantly driven by a pulsed voltage of only 36V, has a mirror aperture of 3 x 3 mm2 and
reaches maximum deflection angles of +/- 11o. The NIR-micro-spectrometer works currently in a spectral range of
1200 - 1900 nm with a resolution of less than 10 nm using only one single InGaAs-diode as detector. Additionally,
scanning grating chips have been already developed for spectral ranges of 900 - 1800 nm and 1250 - 2500 nm. One
entire spectral measurement is done within 6 milliseconds, calculated by a digital signal processor, which is included
in the spectrometer. Results can be either displayed by special computer software or directly by a graphical user
interface. In this paper, we will focus on the control of the grating fabrication process, which can be done by
microscopy, using new control structures. A time-consuming control with SEM (Scanning electron microscope) is
no longer needed. Furthermore the characterization of the fabrication process and its consequence on the
spectrometer properties will be discussed, as well as the characterization of the scanning grating chip itself
(frequency, movement, static deformation, spectral efficiency...). Characteristic measurement results of an argon
calibration lamp, which shows the performance of the NIR-micro-spectrometer, will be presented as well.
In recent years, Micro Opto Electro Mechanical Systems (MOEMS) have been reached more and more importance in technical applications. This is caused by the increased reliability of micro systems combined with the reduction of costs by high volume production. In this paper, we will present a resonant scanning grating chip with high diffraction efficiency, developed for the NIR region (900 - 2500 nm), which is based on our resonant micro scanning mirror. The grating was additionally applied to the silicon mirror plate by a chemical wet etch process. Therefore, three different fabrication technologies have been developed, showing high efficiencies in the first diffraction order. Compared to investigations with direct structured gratings in the reflective aluminium surface, gratings with up to 714 lines/mm could be fabricated combined with an improved process parameter control. These new resonant driven scanning gratings are still compatible to the scanning mirror fabrication process. They have a large surface of 3x3 mm2 and resonant frequencies of down to 150 Hz, which results in a lower demand on the bandwidth of the electronic read out, when applied to a spectrometer set-up. The maximum mechanically scan angle of the grating mirror plate could be increased to +/- 12° at a driving voltage of 36 V. First measurement results and an improved design of a micro spectrometer, working with only one single InGaAs-Detector in a spectral range of 900 to 2500 nm will be presented and discussed.
Further optimization of the agricultural growth process and quality control of perishable food which can be fruits and vegetables as well as every kind of meat or milk product requires new approaches for the sensitive front end. One possibility is reflectance or fluorescence spectroscopy in a wide wavelength range. By now broad usage is hindered by costs, size and performance of existing systems. MOEMS scanning gratings for spectrometers and translational mirrors for Fourier Transform spectroscopy enable small robust systems working in a range from 200nm to 5μm. Both types use digital signal processors (DSPs) capable to compute the spectra and execute complex evaluation and decision algorithms.
The MOEMS chips are realized by anisotropic etching of a silicon on insulator (SOI) substrate. First the backside silicon and buried oxide is removed by a wet process then the front side structure is realized by dry etching. Depending on the bearing springs a silicon plate up to 3 x 3 mm2 wide and typically 30μm thick can be driven resonantly to rotational or translational movement. Combined with additional optical components and appropriate detectors handheld Czerny-Turner or Fourier Transform spectrometers have been realized and tested.
Results of first measurements of reflection spectroscopy on model substances have been performed with both system types in the NIR range. Measurements on real objects like tomatoes or apples are intended for a wider wavelength range. Future systems may contain displays and light sources as well as data storage cards or additional interfaces.
KEYWORDS: Sensors, Signal processing, Mirrors, Near infrared, Spectroscopy, Digital signal processing, Microopto electromechanical systems, Infrared sensors, Light emitting diodes, LED displays
The examination of spectra in the NIR range is necessary for applications like process control, element analysis or medical systems. Typically integrated NIR spectrometers are based on optical setups with diffraction grating and detector arrays. The main disadvantage is price and availability of NIR array InGaAs-based detectors. The implementation of a scanning grating chip realized in a MOEMS technology which integrates the diffractive element makes it possible to detect spectra with single detectors time resolved. Either simple InGaAs photodiodes or cooled detectors may be used.
The set up is a shrinked Czerny-Turner spectrometer. The light is coupled in by an optical fibre. After focussing the light passes the scanning grating moving at 150-500 Hz in a sinusoidal way. There it is split off in the different wavelength, the monochrome intensity is caught by a second mirror and led to the detector. The detector signal is amplified by a transimpedance stage and converted to digital with 12 bit resolution. The main part of the signal processing is done by a digital signal processor, which is used to unfold the sinusoidal position and calculate the final spectra. The data rate can be up to 3 MHz, then a spectrum is acquired every 2ms by using a 500Hz Mirror. Using the DSP, the spectrometer can operate autarkic without any PC. Then the spectrum is display on a 160 x 80 pixel graphic LCD. A keypad is used to control the functions. For communication a USB port is included, additional interfaces can be realized by a 16-pin expansion port, which is freely programmable, by the system firmware.
KEYWORDS: Spectroscopy, Sensors, Mirrors, Signal processing, Silicon, Digital signal processing, Microopto electromechanical systems, Near infrared, Indium gallium arsenide, Infrared radiation
Optical spectroscopy is a common tool for many applications. Micro systems most often use fixed gratings and array detectors. In the infrared wavelength range above the limit for Si-detectors (1100nm) and Ge-detectors (1700nm) respectively, this is either very expensive or almost impossible. Micro opto electro mechanical systems (MOEMS) offer very promising options. A movable grating can be realized by a silicon chip, using the technology of a well established scanner mirror chips in combination with the realization of a reflective grating either through etching of the aluminium mirror layer or even a more sophisticated technology. The patented resonant drive realizes a mechanical angle of ±7° with CMOS compatible voltages of approximately 20V. This technology leads to the realization of a set up close to a classical Czerny-Turner spectrometer using a single
detector only. The device offers the capability to be scaled down to the size of a cigarette box. The spectrometer presented here was adjusted to 900...2500nm range. The scanning grating chip has either 500, 625 or 714 lines/mm. As detector serves a fast InGaAs photodiode, read out through a 12 Bit AD converter. The sinusoidal
movement is unfolded by a signal processor (TI TMS320F2812) which also computes the spectrum. Acquired data can be shown by a display or transmitted to a host PC. System tests have been performed using infrared LEDs. Wavelengths have been 1300, 1400 or 1550nm for example.
The spectrometer is working accurately. First result of micro shaped grating structures to enhance the sensitivity are presented.
Micro Opto Electro Mechanical Systems (MOEMS) reach more and more importance in technical applications. They are smaller than conventional devices, less expensive when fabricated in higher numbers and offer new options concerning reliability and measuring methods. Resonant movable micro-mirrors produced as single crystalline chips with CMOS-compatible technologies provide a broad field of applications. In this paper, we will present different micro-mirrors, which are developed by the Fraunhofer IPMS in Dresden, Germany. They have different layouts and are thus suitable for several applications. Fabricated 1D-mirrors with mechanical angles of ± 16° can be used for laser deflection in bar-code-scanners, 2D-mirrors with different sizes and frequencies are suitable for imaging, displaying etc. Furthermore processes to apply diffractive structures on the micro-mirror surface were developed, showing an increased efficiency in the first diffraction order. Thus a micro-spectrometer has been built up, working in a wavelength range of 900-2500 nm. Due to the Czerny-Turner set-up, only one fast single InGaAs-photodiode is required.
KEYWORDS: Spectroscopy, Mirrors, Diodes, Near infrared, Digital signal processing, Microopto electromechanical systems, Diffraction gratings, Light emitting diodes, Data processing, Signal processing
In the last few years the importance of Micro Opto Electro Mechanical Systems (MOEMS) increased significantly in technical applications. This is caused by the possibility of combining micro optical elements with micromachining technology that makes it feasible to develop new systems with high volumes and low prices. In this article, we report on the realization of a NIR (near infrared) spectrometer in the range of 900 - 2000 nm using MOEMS technology. It is based on a scanning mirror chip, which mirror plate is structured with a diffractive aluminium layer on top. This offers the possibility to fabricate a spectrometer, which needs only one single InGaAs detector photo diode. In contrast to common CCD arrays, the obtained resolution is only limited by the performance of the spectrometer (entrance slit, exit slit, focus length, diffractive element). The scanning grating chip operates at a frequency of 500 Hz, at an optical scan range of ± 4°. The whole spectrometer has a size of 90 x 60 x 50 mm. For first investigations of the performance, IR LEDs (light emitting diode) with 1300, 1450 and 1550 nm wavelength have been measured.
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