Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1998-07-20
2000-01-18
Sugarman, Scott J.
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359290, 359291, 359295, 359298, G02B 2608
Patent
active
060162171
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention refers to micro swivel actuators and a procedure for the production of the same.
A multitude of micromechanical actuators, which aim at defined deflection of light beams by means of a mirror arrangement, is known in the literature.
An electrostatic deflector unit is described in the DE 42 24 599. The basis is a platelike swiveling element, which was reduced in mass either by realization in a sandwich structure or by recesses between remaining weblike areas. Suspension is provided by two flectional beams fitted in diagonally opposing corners. This element is held in a frame. The DD 298 856 two-dimensional micromechanical moving device contains another solution. The swivel plate is here centrically arranged on a point, which is located on a baseplate and is kept in the initial state parallel to the baseplate with four spring elements. The entire device is again arranged in a frame.
These solutions include individual tilting attachments, which are therefore limited in their use by the determined tilting surface. Furthermore, a relatively large area is being tilted, which results in another limitation in dynamics.
The EP 0 040 302 contains an optical beam deflector unit. A platelike deflector unit made of silicon is here electrostatically tilted with two one-sided torsion springs towards a baseplate. Moreover, this platelike deflector unit is preceded by parallel or non-parallel multiple arrangements, each of which is tightly enclosed by the frame.
The disadvantage here is again the large-surface realization of the tilting attachment. The result is limited dynamics. Solutions without a frame can be found in here tilted around the axis of symmetry.
The disadvantage of these solutions is a large mass and a high mass moment of inertia with regard to the geometrical axis. The preparation of a mirror array is described in the journal Sensors and Actuators, Vol. A 41 complete (1994), pages 324-329, "Lineaddressable torsional micromirrors for light modulator arrays." In order to achieve the base distance between the lower edges of the mirror and the electrodes, a sacrificial layer of silicon dioxide is applied after the production of the electrodes. Windows are etched in this sacrificial layer to mechanically fasten the springs, which enable the excursion of the mirrors on the substrate. The following separation of polysilicon therefore creates a layer which is in part directly connected with the substrate. The mirrors are then formed in those areas of the polysilicon layer that are lined with the sacrificial layer. Afterwards an aluminum layer is applied as reflector. Wet-chemical etching of the sacrificial layer is the last step in the manufacturing process. An overall coverage of mirror arrangement is not achieved.
The described surface technique utilizes a polysilicon layer for the actuators.
A development of Texas Instruments Inc. is presented in the journal Solid State Technology, July 1994, pages 63-68, "Digital micromirror array for projection TV." The array was especially designed for TV applications and consists of a matrix of 768.times.576 individual mirrors. The base distance between the mirrors and the electrodes is here implemented by an organic sacrificial layer, which is spun-on and then leveled to smooth out any unevenness created by underlying structures (electrodes). Mirrors as well as the springs are made of an aluminum alloy. Special posts are designed to support the springs towards the substrate. These posts are created by filling small holes in the sacrificial layer with the mentioned alloy. Following the decollation of the chips, the sacrificial layer is removed by plasma etching.
The described arrangements allow only two conditions for the mirrors (home position or else maximum excursion).
The invention mentioned in the patent claims 1 and 14 takes the problem of creating a micromechanical mirror array, featuring high attainable frequency of resonance and at the same time a large active total surface as a basis. This is to be realized by a procedure
REFERENCES:
patent: 5629790 (1997-05-01), Neukermans et al.
patent: 5673139 (1997-09-01), Johnson
"Digital micromirror array for projection TV" by Michael A. Mignardi, Solid State Technology, Jul. 1994, pp. 63-64.
"Line-Addressable Torsional Micromirros for Light Modulator" by V.P. Jaecklin et al., Sensors and Actuators A. vol. A41, Apr. 1, 1994, No. 1/03, pp. 324-329, XP00450049.
"A silicon Light Modulator" by K. Gustafsson et al. Journal of Physics E. Scientific Instruments, vol. 21, No. 7, Jul. 1998, pp. 680 685, XP000005638.
"Micromechanical Light Deflector Array" by K.E. Petersen, IBM Technical Disclosure Bulletin, vol. 20, No. 1, Jun. 1977, New York, USA, pp. 355-356, XP002015961.
"Color Projection Display System Using Silicon Micromecanics" by A.M. Harstein, IBM Technical Disclosure Bulletin, vol. 22, No. 12, May 1980, New York, USA, pp. 5575-5575, XP002015962.
"Deformable-Mirror Spatial Light Modulators" by L.J. Horbnbeck, Spatial Light Modulators and Applications III, vol. 1150, Aug. 7-8, 1989, San Diego, USA, pp. 86-102, XP000351394.
Dotzel Wolfram
Gessner Thomas
Hahn Ramon
Kaufmann Christian
Lowe Heinz-Ulrich
Burke Margaret
CMS Mikrosystene GmbH Chemnitz
Kasper Horst M.
Sugarman Scott J.
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