MEMS mirror arrangement for detecting a large angular range

Patent metadata

Field	Value
Publication number	US-11531196-B2
Application number	US-201816634420-A
Country	US
Kind code	B2
Filing date	Jul 25, 2018
Priority date	Jul 28, 2017
Publication date	Dec 20, 2022
Grant date	Dec 20, 2022

Abstract

The invention relates to a MEMS mirror assembly for detecting a large angular range up to 180°, preferably up to 160°, and to a method for producing a MEMS mirror assembly. The mirror assembly comprises a carrier substrate (1), on which a mirror (2) vibrating about at least one axis is mounted, a transparent cover (4), which is connected in a hermetically sealed manner to the carrier substrate (1) and which comprises an ellipsoidal dome (6) having a substantially round base area, and a compensation optical system (8), which is arranged in a predefined beam path for an incident beam outside the dome (6). The middle of the mirror (2) lies in the centre point of the dome, and the compensation optical system (8) collimates the incident beam in such a way that a divergence or convergence of the beam caused by the boundary surfaces of the dome once said beam has exited from the dome (6) is substantially compensated. The MEMS mirror assemblies are produced by joining a cover wafer and a mirror wafer, which each comprise a plurality of hemispherical domes and mirrors mounted on the carrier substrate. The mirror assemblies are then separated from the joined wafers. The domes of the cover wafer are produced by a glass flow process.

First claim

The invention claimed is:

1. A MEMS mirror arrangement for detecting an angular range of up to 180°, comprising:
a carrier substrate on which a mirror which oscillates about at least one axis is suspended,
a transparent cover which is connected to the carrier substrate in a hermetically sealed manner and which comprises a semi-shell dome with an ellipsoidal cross-sectional surface, said dome rising above an essentially circular base surface, wherein the dome is provided with an inner dome shell and an outer dome shell which form boundary surfaces and the ratio of the height F to the diameter D of the inner and/or outer dome shell is between 0.4 and 0.6 and the difference between the ratio of the height Fi to the diameter Di of the inner dome shell and the ratio of the height Fa to the diameter Da of the outer dome shell lies between ±0.002 and
compensation optics which are arranged outside the dome in a predefined beam path for an incident beam bundle,
wherein the middle of the mirror coincides with the middle point of the base surface of the dome with a maximum tolerance of ±20% of the diameter of the base surface of the dome and
wherein the compensation optics collimate the incident beam bundle in a manner such that a divergence or convergence of the beam bundle, caused by the boundary surfaces of the dome, is at least partly compensated after exit from the dome.

2. The MEMS mirror arrangement according to claim 1 , wherein the difference between the ratio of the height Fi to the diameter Di of the inner dome shell and the ratio of the height Fa to the diameter Da of the outer dome shell lies between ±0.001.

3. The MEMS mirror arrangement according to claim 1 , wherein a ratio of the square of a radius R of the dome to a of the wall of the dome is larger than 50, R 2 /d>50.

4. The MEMS mirror arrangement according to claim 1 , wherein a thickness of the wall of the dome is smaller than 10% of the diameter of the base surface of the dome.

5. The MEMS mirror arrangement according to claim 1 , wherein the diameter of the mirror lies between 80% and 5% of the diameter of the base surface of the dome.

6. The MEMS mirror arrangement according to claim 1 , wherein the deviation of the middle points of the base surfaces of the inner and outer dome shell ( 10 ) of the dome in the radial and vertical direction lies in the range of ±10 of the diameter of the base surface of the dome.

7. The MEMS mirror arrangement according to claim 1 , wherein the material of the dome has a thermal coefficient of expansion which is adapted to the thermal coefficient of expansion of the material of the mirror.

8. The MEMS mirror arrangement according to claim 1 , wherein the inner space between the dome and the carrier substrate, said inner space receiving the mirror, is under a vacuum or is filled with a protective gas.

9. The MEMS mirror arrangement according to claim 1 , wherein the focal length of the dome corresponds approximately to and with the opposite sign of the focal width of the compensation optics.

10. The MEMS mirror arrangement according to claim 1 , wherein the focal length of the dome lies between −50 mm and −300 mm.

11. A method for manufacturing a MEMS mirror arrangement according to claim 1 , with the following steps:
a) providing a silicon wafer,
b) structuring the silicon wafer in a manner such that a plurality of deepenings is created,
c) bonding a cover wafer of glass-like material onto the structured silicon wafer, wherein an inert gas is enclosed at a pre-defined pressure in the cavities which are formed by the deepenings and the cover wafer,
d) tempering the composite of the silicon wafer and of the cover wafer in a manner such that a plurality of domes is formed by way of the expansion of the enclosed inert gas,
e) after cooling the composite of the silicon wafer and the cover wafer, partial or complete removal of the silicon wafer,
f) arranging a mirror wafer which comprises a plurality of mirrors which are suspended on the carrier substrate, with respect to the cover wafer in a manner such that the mirror middles each lie in the middle point of the domes,
g) joining and hermetically sealed closing of the cover wafer with the mirror wafer by way of bonding with additively deposited layers or structures,
h) singularising the composite of cover wafer and mirror wafer into individually capped MEMS mirror arrangements.

12. The method according to claim 11 , wherein the tempering is carried out under a vacuum or that during the cooling after the actual tempering procedure in a gas atmosphere the gas pressure within a closed oven is tracked to the temperature change according to the thermal equation of state.

13. The method according to claim 11 , wherein compensation optics are arranged outside the cover which includes a dome, in the beam path of a beam which is incident into the dome, said compensation optics at least partly compensating a divergence or convergence which is caused by the passage of the beam through the outer and inner boundary surfaces of the dome.

14. The method according to claim 11 , wherein the inert gas is enclosed in the cavities at a pressure of 100 mbar to 3 bar on bonding the cover wafer onto the silicon wafer.

15. The method according to claim 11 , wherein the tempering is carried out under a vacuum at 650°-950° C. and is completed after a defined time of 30 min-12 hours and is cooled under a vacuum.

16. The method according to claim 11 , wherein the parameters depth of the deepenings of the structured silicon wafer, pressure of the gas which is enclosed in the cavities, temperature of the tempering and the time of tempering are controlled such that the flow speed of the glass-like material is lower than 0.5 mm per hour during the last 20% of the tempering time.

17. The method according to claim 11 , wherein an anti-reflex coating is deposited onto the inner and/or outer surface of the domes after the tempering and removal of the silicon wafer or of the tool.

18. The method according to claim 11 , wherein a printable sealing material is used as a sealing material on bonding.

19. The method according to claim 11 , wherein the sealing material is deposited on joining zones ( 5 ) between the cover wafer and the mirror wafer, said joining zones lying directly below the walls of the domes for leading away pressure forces on bonding.

20. The method according to claim 11 , wherein the pressure forces are exerted in a pointwise or linear manner on bonding the cover wafer and the mirror wafer.

21. The method according to claim 11 , wherein the cover wafer and the mirror wafer are connected to one another in a sealed manner at their edge regions on bonding and that the bonding is subsequently carried out pneumatically.

22. A method for manufacturing a MEMS mirror arrangement, the method comprising:
a) providing a tool which consists of a material which prevents an adhesion of a hot, glass-like material or is coated with a material which prevents an adhesion of a hot, glass-like material,
b) providing the tool with through-openings before or after the provision,
c) laying the cover wafer of glass-like material onto the tool which is provided with through-openings, wherein a negative pressure is applied at the side which is away from the cover wafer,
d) tempering the composite of the tool and of the cover wafer under atmospheric conditions in a manner such that a plurality of domes is formed by way of the sucking of the cover wafer into the through-openin

Assignees

• Fraunhofer Ges Forschung

Inventors

• Quenzer Hans-Joachim
• Hofmann Ulrich
• Stenchly Vanessa

Classifications

• G02B26/0833 Primary

  the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B) · CPC title

• B81B2201/042

  Micromirrors, not used as optical switches · CPC title

• G02B26/105

  with one or more pivoting mirrors or galvano-mirrors (G02B26/101 takes precedence) · CPC title

• G02B26/10

  Scanning systems · CPC title

• B81C2203/0109

  Bonding an individual cap on the substrate · CPC title