Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1998-11-18
2001-01-30
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000, C359S221200, C359S224200, C359S281000, C438S052000, C257S415000
Reexamination Certificate
active
06181460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a micro-electromechanical system and, more particularly, to an electromagnetic force controlled micromirror array system.
2. Discussion of the Related Art
A reflective, spatial light modulator composed of an array of rotatable aluminum mirrors has shown promise as an alternative to LCD technology for high-definition projection television systems. This modulator, commonly referred to as a digital micromirror device (DMD), is an advanced micro-electromechanical system (MEMS). Generally, surface micromachining technology provides the primary means of fabrication for an array of micromirror devices which are built over conventional static random access memory (SRAM) address circuitry.
More particularly, DMD technology involves depositing an x-y grid array of aluminum micromirrors on one silicon wafer, such that each micromirror represents one pixel of the projection screen resolution. Each micromirror is electronically controlled to allow the mirror to tilt either up or down via a congruent, electronically addressed, x-y grid array of SRAM cells. A micromirror is suspended by metal posts above an individual SRAM cell and a metal hinge is used for connecting each micromirror to its corresponding metal post.
The micromirrors rotate due to electrostatic forces created between the aluminum micromirror and a corresponding metal electrode being formed on the wafer and connected to the SRAM cells. For example, when a SRAM cell receives a “1” voltage, its corresponding micromirror will deflect or twist around the hinge, thereby tilting the mirror closed and changing the direction of reflected light. This same mirror will remain closed until the same SRAM cell receives a “0” voltage which in turn twists the mirror in the opposite direction around the hinge, thus reflecting light in the opposite direction. Light reflected from the micromirror array is projected onto a field projection screen system which differentiates light tilted in one direction as compared to light tilted in the other direction, thereby producing a high resolution digital image.
Although DMD technology has recently achieved digital resolutions of 2048×1152 micromirrors, this technology continues to exhibit some disadvantages. For instance, the response time needed for an electrostatic charge to develop between the micromirror and the electrode of the SRAM cell decreases performance for actuating an electrostatic micromirror. In addition, the friction between the metal micromirror and the electrode may cause the micromirror to “stick” closed when the voltage is no longer applied, thereby causing an electronically addressed pixel to fail to open. Moreover, the DC voltage required to develop the electrostatic force for micromirror tilting also makes existing micromirror systems unsuitable for high frequency optical projection switching applications.
Therefore, it is desirable to provide a micromirror device for use in digital image processing applications. An optical component is deposited on a rotatably actuated platform positioned over a recess formed in a semiconductor wafer. The micromirror device structure exposes the rotatable platform to a substantially uniform magnetic field that improves control of the optical component over a wider deflection angle. Additionally, these micromirror devices are manufactured using standard semiconductor fabrication techniques.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a micromirror device including a rotatable optical component is provided for use in a digital image processing application. The micromirror device includes a semiconductor wafer, having a recess formed therein, and a platform with the optical component deposited thereon that is movably coupled to the side surface of the recess. A first magnetic field source is disposed around the periphery of the optical component on the platform and a second magnetic field source is disposed proximate to this first magnetic field source, such that these magnetic field sources are selectively activatable to generate an electromagnetic field for rotating the platform. More specifically, the second magnetic field source is disposed on the angular side surfaces of the recess or adjacent to the recess on a top surface of the wafer.
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Anderson Eric R.
Jones William L.
Rezek Edward A.
Tran Dean
Ben Loha
TRW Inc.
Yatsko Michael S.
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