Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-06-07
2001-03-13
Mai, Huy (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S292000, C359S316000, C359S230000
Reexamination Certificate
active
06201633
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to reflection and projection displays and more particularly to micro-electromechanical shutter assemblies for use in such displays.
Techniques for fabricating micro-electromechanical devices have been set forth in various articles in technical journals. Additionally, patents have issued which address light modulation through the use of micro-electromechanically devised shutters. In particular, U.S. Pat. No. 5,078,479 to Vuilleumier describes a light modulation device with matrix addressing. Each cell of the matrix has two flaps fixed to a substrate by flexible attachments, by proper application of electrical charges, the flaps are activated to twist to a position allowing passage or blockage of light.
A patent to Worley, U.S. Pat. No. 5,552,925 describes a micro-electromechanical shutter array using micro-electromechanical technology and silicon-on-transparent-substrate technology. The array is operated using electro-static forces which allow for the twisting of the shutter which is set forth as a rotor.
A laser beam modulator is described in a paper by Obermeier et al. (Univ. Berlin). A rectangular 2-segment shutter suspended from torsion rods is used to demonstrate the concept of large angle deflection of a torsionally suspended shutter under the influence of an electrostatic force between the plates of a 90°-angle capacitor. The scale of the described shutters are lmm with 450 &mgr;m long torsion rods. The shutters are used in an analog mode, i.e. there's no address electrode, only a bias voltage. The shutters and hinges are shown as being made of polysilicon, Al and Cr/Au.
Obermeier et al. reports lifetimes in the order of 10
5
cycles for the materials they have used (Poly, Al or Cr/Au). For these materials, the springs need to be designed in a way the stress at 90° is below the fatigue limit or elastic stress limit. These materials are likely to require longer, thinner torsion rods than single crystal silicon.
Texas Instruments is known to be working on DMD projection display technology, i.e. using a DC bias voltage to achieve bi-stability and passive matrix addressability with low voltage switching only. Differences between this work and the present invention include the large angle mode, the geometry of the devices, the application to which the devices are applied (direct view vs. projection) and the scale (TI pixels are 17 &mgr;m or so).
Other micro-electromechanical shutter devices are disclosed, for example in U.S. Pat. No. 5,226,099 to Mignardi et al.; U.S. Pat. No. 5,459,602 to Sampsell; U.S. Pat. No. 4,383,255 to Grandjean, et al.; U.S. Pat. No. 4,564,836 to Vuilleumier, et al.; U.S. Pat. No. 4,584,056 to Perret et al.; and U.S. Pat. No. 5,579,149 to Moret et al.
SUMMARY OF THE INVENTION
The present invention is therefore directed to a bistable shutter display device capable of being implemented for both small-screen high-resolution devices such as personal data communicators and large displays such as billboards. In addition, the invention is directed to a micro-electromechanical shutter assembly display which has bi-stability characteristics which allow the use of only a holding voltage to maintain an image, without the requirement of refreshing voltage or charges such as in existing electronic displays. Thus, there is substantially zero power consumption while an image is being displayed. Substantially all power consumption is therefore associated with the switching from one image to another image and not to the displaying of the captured image. The present invention may also be described as a passive matrix display and therefore the requirement of transistors and other devices which add to the cost of constructing a reflection, projection or transreflective display is not required.
In accordance with the present invention, a micro-electromechanical shutter assembly includes a shutter having petal-like shutter segments covering reflective and/or transmittive films. In a black and white display, the films reflect either white or black, and in a color display the films are pixilated color filters. The assembly may be used in reflective, transmissive and transreflective modes to expose the film in a particular shutter assembly, its shutter segments are moved from the horizontal to the vertical position using electrostatic attraction forces to ‘collapse’ the torsionally hinged shutter segments. The shutter assembly can have any number of segments, as long as the resulting shutter assembly shape can be stacked to form a dense 2D array. Square or rectangular 2- or 4-segment or 6-segment hexagon shutter assemblies are shapes which can be used to obtain the desired density.
When configured in the form of sheets the shutter assembly consists of a stack of 3 layers and/or films sandwiched between an insulated backplate, having an incorporated conductive electrode film, and a transparent face plate/film. The first layer is a conductive material formed to have conductive sidewalls. The second layer also is a conductive material which is patterned to form the shutter having shutter segments, and the third layer is an insulator film defining a gap between the shutter and the backplate.
The present invention has as a first object a shutter assembly which can be used with projection and reflection displays, and which is fabricated according to micro-electromechanical technologies.
According to another aspect of the present invention, the shutter assembly is constructed to have bi-stability incorporated within a mechanical configuration whereby when an image is displayed the image may be maintained simply through the use of a bias holding voltage, wherein it becomes unnecessary to refresh the image during such display.
It is another object of the present invention to provide a passive matrix which is compatible with grey scale image formation.
These together with other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims attached to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects obtained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated preferred embodiments of the invention.
REFERENCES:
patent: 4383255 (1983-05-01), Grandjean et al.
patent: 4564836 (1986-01-01), Vuilleumier et al.
patent: 4584056 (1986-04-01), Perret et al.
patent: 5078479 (1992-01-01), Vuilleumier
patent: 5226099 (1993-07-01), Mignardi et al.
patent: 5459602 (1995-10-01), Sampsell
patent: 5552925 (1996-09-01), Worley
patent: 5579149 (1996-11-01), Moret et al.
patent: 6034807 (2000-03-01), Little et al.
E. Obermeier, J. Lin, V. Schlichting, “Design and Fabrication of an Electrostatically Driven Micro-Shutter”, Microsensor Technology, Technical University of Berlin.
Apte Raj B.
Bringans Ross
Connell G. A. Neville
Floyd Philip Don
Fork David
Fay Sharpe Fagan Minnich & McKee LLP
Mai Huy
Xerox Corporation
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