Hans-Joachim Quenzer

Giant magnetoelectric coefficients in (Fe90Co10)78Si12B10-AlN thin film composites

Thin film magnetoelectric (ME) two–two composites consisting of AlN and amorphous (Fe90Co10)78Si12B10 layers were fabricated by magnetron sputtering on Si (100) substrates. Upon magnetic field annealing they show an extremely high ME coefficient of 737 V/cm Oe at mechanical resonance at 753 Hz and 3.1 V/cm Oe out of resonance at 100 Hz. These are the highest reported ME coefficients in thin film composites ever. Furthermore, the induced magnetic anisotropy by field annealing serves the possibility to obtain a sensor element with a pronounced sensitivity in only one dimension, which allows the realization of a three-dimensional vector field sensor.

High-Q MEMS Resonators for Laser Beam Scanning Displays

This paper reports on design, fabrication and characterization of high-Q MEMS resonators to be used in optical applications like laser displays and LIDAR range sensors. Stacked vertical comb drives for electrostatic actuation of single-axis scanners and biaxial MEMS mirrors were realized in a dual layer polysilicon SOI process. High Q-factors up to 145,000 have been achieved applying wafer level vacuum packaging technology including deposition of titanium thin film getters. The effective reduction of gas damping allows the MEMS actuator to achieve large amplitudes at high oscillation frequencies while driving voltage and power consumption can be minimized. Exemplarily shown is a micro scanner that achieves a total optical scan angle of 86 degrees at a resonant frequency of 30.8 kHz, which fulfills the requirements for HD720 resolution. Furthermore, results of a new wafer based glass-forming technology for fabrication of three dimensionally shaped glass lids with tilted optical windows are presented.

Wafer-level vacuum packaged resonant micro-scanning mirrors for compact laser projection displays

Scanning laser projection using resonant actuated MEMS scanning mirrors is expected to overcome the current limitation of small display size of mobile devices like cell phones, digital cameras and PDAs. Recent progress in the development of compact modulated RGB laser sources enables to set up very small laser projection systems that become attractive not only for consumer products but also for automotive applications like head-up and dash-board displays. Within the last years continuous progress was made in increasing MEMS scanner performance. However, only little is reported on how mass-produceability of these devices and stable functionality even under harsh environmental conditions can be guaranteed. Automotive application requires stable MEMS scanner operation over a wide temperature range from -40° to +85°Celsius. Therefore, hermetic packaging of electrostatically actuated MEMS scanning mirrors becomes essential to protect the sensitive device against particle contamination and condensing moisture. This paper reports on design, fabrication and test of a resonant actuated two-dimensional micro scanning mirror that is hermetically sealed on wafer level. With resonant frequencies of 30kHz and 1kHz, an achievable Theta-D-product of 13mm.deg and low dynamic deformation <20nm RMS it targets Lissajous projection with SVGA-resolution. Inevitable reflexes at the vacuum package surface can be seperated from the projection field by permanent inclination of the micromirror.

Resonant biaxial 7-mm MEMS mirror for omnidirectional scanning

Abstract. Low-cost automotive laser scanners for environmental perception are needed to enable the integration of advanced driver assistant systems into all automotive vehicle segments, which is a key to reduce the number of traffic accidents on roads. Within the scope of the European-funded project MiniFaros, partners from five different countries have been cooperating in developing a small-sized low-cost time-of-flight-based range sensor. An omnidirectional 360-deg laser scanning concept has been developed based on the combination of an omnidirectional lens and a biaxial large aperture MEMS mirror. The concept, design, fabrication, and first measurement results of a resonant biaxial 7-mm gimbal-less MEMS mirror that is electrostatically actuated by stacked vertical comb drives is described. Identical resonant frequencies of the two orthogonal axes are necessary to enable the required circle scanning capability. A tripod suspension was chosen, since it minimizes the frequency splitting of the two resonant axes. Low-mirror curvature is achieved by a thickness of the mirror of more than 500 μm. Hermetic wafer-level vacuum packaging of such large mirrors based on multiple wafer bonding has been developed to enable a large mechanical tilt angle of ±6.5  deg in each axis. Due to the large targeted tilt angle of ±15  deg and because of the MEMS mirror actuator having a diameter of 10 mm, a cavity depth of about 1.6 mm has been realized.

A Novel Fabrication Technology for Waferlevel Vacuum Packaged Microscanning Mirrors

This paper presents a novel fabrication technology for wafer level hermetic encapsulated MEMS micro scanning mirrors. This wafer level package enables vacuum operation of the electrostatically driven resonant scanners reducing the required driving voltage and enhancing the mechanical deflection angle even at resonance frequencies of more than 100 kHz. Two nearly independently structured 30 microns thick epipoly silicon layers offer a high design variability due to the possibility to create active silicon structures with two different thicknesses. A buried isolated interconnection layer between the two thick epipoly silicon layers enables the fabrication of lateral feedthroughs which are vital to set up a hermetic package. A structured glass wafer with up to 900 microns deep cavities seals the device wafer at the front side via anodic bonding. An AuSi-eutectic bonded silicon wafer completes the wafer scale vacuum packaging process.

Wafer-level vacuum-packaged two-axis MEMS scanning mirror for pico-projector application

Hermetic wafer level packaging of optical MEMS scanning mirrors is essential for mass-market applications. It is the key to enable reliable low-cost mass producible scanning solutions. Vacuum packaging of resonant MEMS scanning mirrors widens the parameter range specifically with respect to scan angle and scan frequency. It also allows extending the utilizable range of mirror aperture size based on the fact that the energy of the high-Q oscillator can be effectively conserved and accumulated. But there are also some drawbacks associated with vacuum packaging. This paper discusses the different advantageous and disadvantageous aspects of vacuum packaging of MEMS scanning mirrors with respect to laser projection displays. Improved MEMS scanning mirror designs are being presented which focus on overcoming previous limitations. Finally an outlook is presented on the suitability of this technology for very large aperture scanning mirrors to be used in high power laser applications.

New fabrication method of glass packages with inclined optical windows for micromirrors on wafer level

For many applications it is inevitable to protect MEMS devices against environmental impacts like humidity which can affect their performance. Moreover recent publications demonstrates that micro mirrors can achieve very large optical scan angles at moderate driving voltages even exceeding 100 degrees when hermetically sealed under vacuum. While discrete chips may be evacuated and sealed on single die level using small can packages like TO housings, it is obvious that for high volume production a much more economical solution for the realisation of transparent optical packages already on wafer level must be developed. However, since any laser beam crossing a transparent glass surface is partly reflected even when anti-reflective coatings are applied, the construction of a wafer level optical housing suitable for laser projection purpose requires more than the integration of simple plane glass cap. The use of inclined optical windows avoids the occurrence of intense reflections of the incident laser beam in the projected images. This paper describes a unique technology to fabricate glass packages with inclined optical windows for micro mirrors on 8 inch wafers. The new process uses a high temperature glass forming process based on subsequent wafer bonding. A borosilicate glass wafer is bonded together with two structured silicon wafers. By grinding both sides of the wafer stack, a pattern of isolated silicon structures is defined. This preprocessed glass wafer is bonded thereon on a third structured silicon wafer, wherein the silicon islands are inserted into the cavities. By setting a defined pressure level inside the cavities during the final wafer bonding, the silicon glass stack extruded and it is out of plane during a subsequent annealing process at temperatures above the softening point of the glass. Finally the silicon is selectively removed in a wet etching process. This technique allows the fabrication of 8 inch glass wafers with oblique optical surfaces with surface roughness <1 nm and an evenness of < 300 nm.

In-situ large scale deposition of PZT films by RF magnetron sputtering

In the present study, high quality PZT films were deposited by RF magnetron sputtering onto 200mm thermally oxidized silicon substrates at substrate holder temperatures (T<inf>h</inf>) between 550°C – 700°C using PbO-enriched single ceramic PZT targets. The high substrate temperatures used here allowed direct growth of the piezoelectric perovskite phase and rendered an additional post annealing step unnecessary. The PZT layers were grown on (111) oriented Pt bottom electrodes, which were covered by thin TiO<inf>2</inf> seed layers. Over the temperature range investigated here, there was a monotonic reduction in the Pb/(Zr+Ti) atomic ratio with increasing Th; the stoichiometry of the morphotropic phase boundary Pb/(Zr+Ti) ∼ 1 and Zr/(Zr+Ti) ∼ 0.53 was obtained at 700°C. However, the XRD patterns indicated that the films prepared at intermediate T<inf>h</inf> = 600°C exhibited the minimum volume fraction of the spurious pyrochlore phase in addition to tetragonal and rhombohedral piezoelectric PZT structures. All PZT films contained mixed (110), (111) and (200) crystallographic orientations whose relative intensities were significantly influenced by T<inf>h</inf>. The highest piezoelectric coefficients d<inf>33,f</inf> = 120 pm/V and e<inf>31,f</inf> = −12.6 C/m² were obtained for the films deposited at T<inf>h</inf> = 600°C.

PZT-Actuated and -Sensed Resonant Micromirrors with Large Scan Angles Applying Mechanical Leverage Amplification for Biaxial Scanning

This article presents design, fabrication and characterization of lead zirconate titanate (PZT)-actuated micromirrors, which enable extremely large scan angle of up to 106° and high frequency of 45 kHz simultaneously. Besides the high driving torque delivered by PZT actuators, mechanical leverage amplification has been applied for the micromirrors in this work to reach large displacements consuming low power. Additionally, fracture strength and failure behavior of poly-Si, which is the basic material of the micromirrors, have been studied to optimize the designs and prevent the device from breaking due to high mechanical stress. Since comparing to using biaxial micromirror, realization of biaxial scanning using two independent single-axial micromirrors shows considerable advantages, a setup combining two single-axial micromirrors for biaxial scanning and the results will also be presented in this work. Moreover, integrated piezoelectric position sensors are implemented within the micromirrors, based on which closed-loop control has been developed and studied.

Influence of platinum bottom electrode on the piezoelectric performance of hot RF sputtered PZT films

Ferroelectric PZT thin films have been in-situ deposited on 8-inch wafers by a high volume production sputtering tool. The films were grown on oxidized Si substrates covered either with sputtered Ti/TiO<inf>2</inf>/Pt, sputtered Ti/TiO<inf>2</inf>/Pt/TiO<inf>2</inf> or evaporated Ti/Pt bottom electrodes and investigated with respect to their chemical composition, crystallographic and dielectric properties. Moreover the d<inf>33,f</inf> and the e<inf>31,f</inf> coefficients have been examined. At a chuck temperature of 600 °C the intended chemical composition is achieved to nucleate and grow the ferroelectric perovskite phase with a minimum of secondary non-piezoelectric phases. A Zr/(Zr+Ti) ratio of 0.53 has been achieved matching to the morphotropic phase boundary. Notable high e<inf>31,f</inf> and d<inf>33,f</inf> coefficients of 101 pm/V and −13.8 C/m², respectively, have been obtained