Dresden, /

Micro assembly of an endoscopical tip
Micro assembly of an endoscopical tip.

June 15 - 18, 2010 in Frankfurt

Booth D50

Fraunhofer IPMS, Dresden carries out customer specific developments in fields of microelectronic and micro systems technology serving as a business partner who supports the transition of innovative ideas into new products. Fraunhofer IPMS develops and fabricates modern MEMS and OLED devices in its own clean room facilities. In addition to R&D services it offers ramp-up within a pilot production. With modern equipment and about 200 scientists and engineers, the range of projects and expertise covers sensor and actuator systems, microscanner, spatial light modulators, lifetronics as well as organic materials and systems.

At the OPTATEC 2010 in Frankfurt Fraunhofer IPMS presents:

1. MEMS Micro Mirror Array Demonstrator

MEMS based light modulators (Spatial Light Modulators, SLMs) are utilised for spatial and temporal modulation of light. They consist of high speed controllable micro mirrors, which can be addressed and deflected independently. This allows the modulation of light intensity and phase on individual pixel scale. The micro mirrors can be arranged in various geometrical configurations. The pixel number can vary from low resolution up to several million mirrors. If high resolution is required, the necessary multiplexing of data is performed by on-chip CMOS electronics. The MEMS of the Fraunhofer IPMS can be adapted for light wavelengths from 193 nm up to 1500 nm according to application specific needs. In contrast to digital micro mirrors typically applied in projection systems the SLMs developed by the Fraunhofer IPMS can display gray values in real-time, i.e. without pulse width modulation. Application fields for SLMs are pattern projection, adaptive optics, Computer To Plate (CTP), PCB manufacturing, waferlevel packaging, mask writing, material processing and marking, copyright protection and holography. The setup demonstrates the functionality of the SLM utilizing a LED illumination. Programmed spatial micro mirror pattern can be observed by naked eye.

2. LDC (Light Deflection Cube) – a 1D scanner module

Based on its competence in developing and fabrication of micro scanner devices Fraunhofer IPMS presents a 1D micro scanner module. Its modular platform approach was developed to bridge the gap between the supply of bare micro scanner dies and the final integration in the customer application. With the drastic enhancement of the short term availability of OEM-capable customized solutions the institute proofs its competence for MOEMS specific packaging, electronics development and system design. The application specific scanner system is based on a modular approach where several prefabricated components are chosen to meet our customers demands.

The complete modular platform LDC consists of:

  • A micro scanner device (selected from available devices or even customized fabricated at Fraunhofer IPMS),
  • Chip carrier with housing and front optics,
  • Scan head with miniaturized optoelectronic position sensor for deflection control,
  • Electronics for driving the micro scanner with a standard communication interface (SPI) and I/O ports and GUI software.

A selected 1D module based on the above-described LDC platform is exhibited at OPTATEC 2010. This LDC module comprises a 1D micro scanner device with 23 kHz resonace frequency mounted on a PCB substrate housed by a glass dome as optical interface, an optical deflection sensor as well as the miniaturized driving electronics. A modular LDC platform for 2D micro scanners is currently under development and will be available, soon.

3. MEMS based Adaptive Optics

Adaptive Optics (AO) is used for the control of the optical wavefront of light, e.g. the compensation of spatially and timely varying wavefront disturbances, which may arise from inhomogeneous or turbulent media within the optical path, in order to facilitate or enhance optical imaging through such media. Originally evolved from astronomy to compensate for atmospheric turbulences, AO techniques can also be used in ophthalmology for aberration correction of the human eye, in optical microscopy for imaging through biological tissue or for any kind of object recognition in machine vision. Furthermore, there are applications in laser beam shaping and in ultra-fast laser pulse modulation as well.

The key component is formed by the actual wavefront controlling device. For that purpose MEMS (Micro Electro Mechanical System) based micro mirror arrays offer several attractive features. The on-chip integration with addressing electronics supports large pixel numbers providing an exceptionally high spatial resolution for an improved reproduction especially of higher order phase aberrations. They also benefit from a step function display capability, fast mechanical response times, low power consumption, broad spectral bandwidth from IR down to DUV and polarization insensitivity. Compared to previous macroscale systems micro mirrors also offer the potential of a substantial cost decrease as well as a significant device miniaturization just facilitating completely new possibilities for a broader commercial exploitation.

The Fraunhofer IPMS has developed a complete MEMS Phase Former Tool Kit. The key component is a high-resolution 240 x 200 piston micro mirror array with 40 µm pixel pitch. The micro mirror stroke can be tuned to >1 µm at 8 bit resolution corresponding to >2 µm phase shift in reflection. Full user programmability and control is established by a comfortable driver software for Windows XP® PCs supporting both a Graphical User Interface as well as an open ActiveX® programming interface for open-loop and closed-loop operation. High-speed data communication is accomplished by an IEEE1394a FireWire interface together with an electronic driving board allowing for maximum data transfer rates of up to 500 Hz. The mirror array itself is capable of operating at maximum frame rates of 5 kHz.

In order to visualize the potential for optical imaging enhancement a complete AO demonstrator system has been set up. It basically consists of a projection system, where extended objects can be imaged through adaptive optics onto a CCD camera. Phasefront errors of different severness can be introduced by rotating phase plates. Employing a Shack-Hartmann sensor for detection and the Fraunhofer IPMS MEMS micro mirror array for correction of the wavefront, the obtainable imaging improvement is visualized by means of the recorded CCD image displayed on a video screen. For a more quantitative performance characterization also MTF measurements can be carried out with the setup.

Addressed business fields are optical system developer and manufacturer in the following areas:

  • Machine Vision (in-situ process control through turbulent media)
  • Optical Microscopy
  • Ophthalmology
  • Astronomy
  • Laser Pulse Shaping
  • Laser Beam Shaping
  • Diffractive Optics (especially optical tweezers)

4. Lamda – Large aperture MEMS scanner module for 3D distance measurement

Traditional laser scanners for 3D distance measurement involve expensive, heavy and large rotating or vibrating mirrors as a means for light deflection of the scanning TOF (time of flight) distance measurement. Typically, the precision of TOF distance measurements is limited by the amount of signal light available at the detector. Hence, a scanning mirror with large aperture is required for LIDAR systems to collect small amounts of light reflected or scattered by the measured target. Its replacement by a micromechanical scanning mirror device is not straightforward, since a large mirror aperture of the receiver optics must by guaranteed in addition to sufficiently large optical scan angles (>40°) and high scan frequency of more then 100 Hz. Contrary, the aperture of a single MEMS scanning mirror is limited to small values of typically 1 … 4 mm diameter due to the dynamic mirror deformation. The Fraunhofer IPMS has developed so far highly miniaturized MEMS scanner devices enabling significant large deflection amplitudes (up to 35°, mechanically) and low power consumption in electrostatic resonant operation, very promising for miniaturized and portable applications. Customized 1D/2D scanner devices are fabricated from single crystalline silicon in a qualified fully CMOS compatible MEMS process suitable for mass fabrication resulting in highly robust and reliable MEMS devices that withstand easily a shock of 2500 g.

The Fraunhofer IPMS presents at OPTATEC 2010 the prototype of a large aperture 1D MEMS scanner module especially designed for laser radar systems. The Lamda module is constructed based on a segmented MEMS scanner device consisting of multiple identical scanning mirror elements realized using the flexible MEMS technology of Fraunhofer IPMS. Therefore, Fraunhofer IPMS has designed a scalable segmented MEMS scanner device composed of identical silicon mirror elements with a comparatively large total scanning aperture of 2.51 x 9.51 mm² and a large optical scan range of ±30°. The 1D MEMS scanner module comprises two separate scanning channels (a) a single scanning mirror of the collimated transmitted beam oscillates parallel to (b) a segmented scanning mirror device of the receiver optics. Light paths of emitting and receiving optics are separated to reduce crosstalk in the final laser radar system. The receiver optics uses a configuration of 2 x 7 identical mirror elements resulting in a total aperture of 334 mm² and a filling factor of 80%. All mirrors are driven electrostatic resonant at 250 Hz by means of separate in-plane comb drives with identical frequency close to the mechanical resonance for oscillation around their long symmetry axes. Thus, the transmitted beam is sent via a separate emitting master mirror of the same mechanical dimensions as one element of the segmented MEMS scanner. Since laser energy is emitted in only one direction, all the receiving mirrors are synchronized to the master scanner by the driving control electronics to point in the same direction. Hence, the effective apertures of the receiving mirrors add up to form a sufficiently large aperture if all receiving mirrors are synchronized in phase to the emitting master mirror in order to maximize the optical signal of the detector system. To realize the mirror synchronization miniaturized position sensors are integrated into the Lamda module for each individual mirror element. Thus, a precise control of the mirror motion is achieved so that all receiving mirror elements can be slaved to the motion of the emission mirror. The Lamda scanner module has a total size of about 52 x 40 x 40 mm³ and provides a synchronous position signal of the actual scan angle required for the final 3D laser radar system. The segmented MEMS scanner satisfies at the same time the demand of a comparatively large optically active area, 2.51 x 9.51 mm² per single mirror element, while keeping the resonance frequency of 250 Hz at a value that matches well to current TOF laser distance measurement systems the with point measurement rates of typical 250 - 1000 kHz. Thus, the optical scan range of ±30 degrees is split into 500 - 2000 intervals. The new concept of using a segmented MEMS scanner of synchronized identical MEMS mirror elements for LIDAR systems permits large reception apertures while preserving the outstanding reliability, high scanning speed, compact size and small system weight that can be expected from MEMS. In comparison to systems with conventional scanner components, the new 1D MEMS scanner module enables 3D LIDAR systems to become significantly smaller and more robust. Higher scan rates can be realized without additional efforts (e.g. air bearings). Hence, the Lamda module is very promising for many applications e.g. in security, machine vision and even for portable outdoor use.

5. Micro assembly of a MEMS based endoscope tip

Fraunhofer IPMS has years of experience in micro scanning mirror and microsystems developments. At the OPTATEC 2010, the institute will publish for the first time ever results from its new competence in micro assembly. A completely mounted microscopical endoscope tip will be shown. The system contains the MEMS device, the miniaturized optics and the optical position detection for the MEMS device. The extremely small microscope tip (8 mm aperture) can be used for imaging in endoscopes as in medical in-vivo cancer diagnosis, but also in the industrie for the monitoring of components, which are difficult to access.

The demonstration systems presents the work of Fraunhofer IPMS in the field of micro assembly of devices on suitable substrates (e.g. silicon, ceramic, glass). Because of the preceding miniaturization of electronical, micro optical and micro mechanical devices and their hybrid combination into a minimum of space the new technological know-how was essential. The extension of the competence will allow a pilot manufacturing of such systems in the future.

Micro mechanical and micro optical components only can operate as a system, if they are very precisely placed and fixed at a defined position. Especially for the assembly of the MEMS and MOEMS developed by Fraunhofer IPMS together with necessary opto electronical components and micro optical devices a high precision is essential.

Respecting the endoscope tip the coupling of light is carried out by fiber optics, which can be choosen for different optical band width (from UV to near infrared). This causes a maximum of flexibility for the selection of light sources and detectors suitable for each particular case of analysis. This is one big advantage over CCD or CMOS based image sensors, which are normally used for endoscopical applications since they have characteristical and rather small optical band widths in visible light. Another advantage is that MEMS based systems eliminate the need for complex optics which are difficult to integrate into miniaturized endoscope tips, especially if high magnification is required.