Fraunhofer Institute for Silicon Technology

Fraunhofer Institute for Silicon Technology

TechBlog of the Fraunhofer ISIT

Dr.-Ing. Thomas Knieling, Dr.-Ing. Shanshan Gu-Stoppel, Dr. Wolfgang Reinert, Hans-Joachim Quenzer

MEMS processes for Quantum Computing and Quantum Sensing

TechBlog / September 22, 2021

Since 1994 Fraunhofer ISIT is one of the leading institutes in Europe for applied research in MEMS development and processing. Products like MEMS mirrors, loudspeakers, bio sensors and microfluidics have been manufactured in the ISIT cleanroom fab (2500 m², 8” / 200 mm silicon and crystalline quartz / amorphous glass wafers). Moreover, transistors and batteries for power electronics applications are being developed in our own facilities. Both MEMS and power electronics have been successfully transferred into prototypes and products.

Fraunhofer ISIT provides an extensive process and technology portfolio (fig. 1). Several products and applications have been realized in industrial and public research collaborations.

MEMS Processes and Technologies

© Fraunhofer ISIT
Fig 1: Technologies and application examples: From left to right: Upper line: Interdigital structures with EPI-Poly technology (thickness 80 µm); Optical glass package with inclined optical windows fabricated; x-ray image of MEMS micro mirror in glass package; piezo driven 2D MEMS micro mirror. Lower line: Piezo driven MEMS loudspeakers; Energy harvester beam with magnetic powder MEMS structures, arbitrary shaped 3D powder MEMS structures; 3D vacuum getter integration.

3D Glass forming: Optical vacuum packages for MEMS encapsulation

The ISIT patented 3D glass forming technology enables the production of several optical components like lenses, mirrors, prisms etc. accompanied with hermetic optical packaging and getter integration for getting and maintaining high vacuum (fig. 2).

Moreover, by adding special dielectric coatings it is prepared for UHV applications, for instance for ion trap applications.

© Fraunhofer ISIT
Fig. 2: Fine placement and assembly of 180° mirror with hermetic glass dome cover on Si wafer. Sealing with getter and electrical vias is performed in high vacuum.

Piezo Technology based on PZT, AlN & AlScN

ISIT has long term experience with PZT (e3,1 = -12 1C/m²) sputtering or evaporation. However, ROHS restrictions, material degradation and monopolar characteristics of PZT have led to new developments using sputtered AlN or AlScN with e3,1 = -1C/m² for AlN and -2,4C/m², respectively.

Module Services: Miniaturized Laser Sources

Based on our MEMS wafer processes, we developed a modular glass-/silicon packaging platform for heterogeneous integration of optical components [1]. The glass capping provides a hermetic side looking window in this example. The assembly and wire bond interconnection can be performed on single substrates, panels and on an up to 200 mm wafer.

Silicon provides the required stability of an optical bench. A precision assembly machine configured with in-situ laser soldering and active lens adjust provides the required infrastructure to realize new optical constructions and produce demonstrators, such as a multi-channel laser light source (fig. 3).

© Fraunhofer ISIT
Fig. 3: Process development of a multi-channel laser light source based on optical glass-silicon packaging platform [2].

MEMS Product Application Examples

MEMS Optical Micro Mirrors

Besides our long term proven resonant mirror technology our new piezo actuator design (Fig. 4) and technology extends the application space substantially [4, 5].

Tab. 2 shows the main parameter space where however due to physical restrictions these parameters cannot be combined arbitrarily.

Parameter	Min.	Max.
Frequency / Hz	100 / quasistatic	100000
Optical scan angle (FOV) / °	0,01	40
Aperture / mm	0,2	20

Tab. 2: Main parameters for quasistatic mirrors.

Besides tilting motions with this four electrode/actuator architecture also translational or mixed mirror motions can be performed, all precisely defined in a closed-loop scheme through very accurate optical or piezoelectric position sensing. Simulations have shown that already with this first, non-optimized design large hubs up to 200 µm can be reached (fig. 5).

© Fraunhofer ISIT
Fig. 4: Design of our new quasistatic mirror generation. Left: Rosebud shaped 4 electrode / actuator structures. Right: Au coated 5 mm mirror. The mirror plate will be bonded on the small pin between the electrodes (see left picture center).

Possible Applications can be the compensation of external motion in the optical or atom beam paths in gravimeters based on atom interferometry.

© Fraunhofer ISIT
Fig. 5: Linear translation characteristics of a circular 2 mm quasistatic micro mirror. Mirrors can be coated with metals like Au and Al.

References

[1] V. Stenchly et al., Modular packaging concept for MEMS and MOEMS. DOI.
[2] W. Reinert, A miniaturized RGB-laser light engine. DOI.
[3] S. Gu-Stoppel et al.: A triple-wafer-bonded AlScN driven quasi-static MEMS mirror with high linearity and large tilt angles. DOI.
[4] S. Gu-Stoppel et al.: A designing and manufacturing platform for AlScN based highly linear quasi-static MEMS mirrors with large optical apertures. DOI.

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Thomas Knieling

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Dr.-Ing. Thomas Knieling

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Shanshan Gu-Stoppel

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Hans-Joachim Quenzer

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