Optical: systems and elements – Optical modulator – Having particular chemical composition or structure
Reexamination Certificate
1999-02-09
2001-04-24
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Having particular chemical composition or structure
C359S322000, C359S315000, C359S237000
Reexamination Certificate
active
06222667
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to a high-density, high-resolution array of light valves that can be selectively activated by low induced voltages to alter a light beam passing through the array. The present invention also relates to a process for manufacturing such a high density light valve array using semiconductor-type processing equipment and techniques.
2. Background Art
In much the same way that single crystal silicon can be processed to selectively permit or block the passage of electrons (conductivity), an electro-optic material, such as lanthanum modified lead zirconate titanate (PLZT), can be processed to permit or block the passage of a beam of light by application of an electric field, between two electrodes in the material, perpendicular to the direction of the light beam. In both cases, the starting material is a wafer which is cut from a cylindrical boule and then subjected to processing steps that build microstructures on one side of the wafer.
The application of an electric field induces birefringence in a transparent PLZT material. Bi-refringence is a rotation in the plane of polarization within the PLZT material. This phenomenon is referred to as the Kerr effect. The configuration of two oppositely charged electrodes separated by an electro-optic material, such as PLZT, and sandwiched between two polarizers is well known in the art and referred to as a Kerr cell. Once induced, the bi-refringence in the electro-optic material of a Kerr cell can lower, or increase light transmission through the cell. In applications where electrode spacing within the PLZT is very small, selective electronic birefringent addressing can be used to create a small high-resolution display or high quality image, which can be directly viewed, or projected and enlarged.
Reduced electrode spacing within the PLZT material is particularly desirable as it offers benefits of reduced activation voltage, reduced picture cell (pixel) size, and higher image resolution. Higher electrode density also induces the problems of increased manufacturing costs and complexity, and difficulty in connecting the array electrodes to those of other arrays or to controlling electronics, such as printed circuit boards.
Reduced electrode spacing has been achieved in the prior art predominately through the use of mechanical grooving of the PLZT substrate, longitudinal (parallel to light beam) activation of the PLZT, and/or stenciling techniques for placement of the electrodes within the grooves. However, such manufacturing techniques limit the number of light valves, or picture cells (pixels), to numbers on the order of 25 to 100 pixels per linear inch. Pixel dimensions on the order of those disclosed in the prior art also suffer the disadvantages of high activation voltages (100 to 500 VDC), cumbersome requirements for electrical contact designs, and very high lead counts.
The transversely activated electro-optic light valve array in U.S. Pat. No. 5,198,920, co-authored by the inventor of the present invention, discloses means to overcome the switching time, voltage, and addressing shortcomings of the prior art Gobeli et al. '920, discloses a two-dimensional array of Kerr cell pixels defined in an electro-optic material, such as PLZT, between adjacent electrodes deposited onto the substrate. The array may be addressed optically or electronically to generate an electric field in the electro-optic material. Pixel densities as high as 1000 pixels per linear inch are possible using the technology disclosed in Gobeli et al. '920.
The present invention constitutes a significant improvement over this prior aft patent by the use of semiconductor processing technology to further increase pixel density and reduce activation voltage. It further offers the advantage of increased light transmission (brightness) through the PLZT material by a reduction in surface area of the PLZT required for the non-transmissive electrodes.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
The present invention is directed to a light valve array comprising a pattern of very small solid state light valves and a process of manufacture. Each valve consists of two electrodes of one polarity and one electrode of opposite polarity formed using semiconductor processing techniques. Said electrodes are recessed into channels formed in an electro-optic substrate using photolithography, etching, and thin film deposition techniques. The channels have widths of approximately 1.5 to 2.5 microns and the pedestals between the channels have widths of approximately 6 to 8 microns. The electro-optic material can be either LiNbO
3
, BaTiO
3
, or lanthanum modified lead zirconate titanate, but the preferred electro-optic material is non-memory mode lanthanum modified lead zirconate-titanate (PLZT) that responds to an induced electric field through bi-refringence. As the manufacturing process, in accordance with the present invention, is capable of very high pixel densities, the array is preferably activated electronically, with preferably 12 to 15 volts DC, rather than optically, to generate an electric field in the electro-optic material and thus activate the pixels. Light that is passed through the array will either be transmitted through the array or largely blocked depending upon the voltage applied to each Kerr cell.
Further, the preferred means of addressing the large number of pixels is by means of matrix addressing, where each pixel is electronically connected to one row lead and one column lead and is controlled by control circuitry, preferably by means of a microcomputer and appropriate software. In a preferred embodiment of the invention, one set of conductive metallization activation electrodes (“Y” orientation) is deposited in a teeth and backbone comb-shaped configuration into parallel and orthogonal channels etched into the PLZT substrate. The second set of conductive metallization activation electrodes (“X” orientation) are deposited running in X-oriented alternating channels between the teeth of the earlier deposited Y-oriented electrodes. An insulating material is deposited between the Y- and X-oriented electrodes to electrically isolate the two conductive patterns from one another. An applied voltage between a given Y-oriented electrode and a given x-oriented electrode causes a single light valve, or Kerr cell, to be activated, which induces bi-reference in the electro-optic material and affects light transmissivity through the Kerr cell only at that location.
Optionally, transistors can be connected to each pair of electrodes to block voltage to the Kerr cell until a pre-selected voltage is reached and then the cell is activated. Colored filters can also be deposited over the electro-optic material pedestals between each pair of electrodes to enable colored pixels. Also, a conductive flash coating can be deposited near either electrode conductive layer for dissipating residual electric charge.
It is a primary object of the present invention to provide a high density electro-optic light valve array which has reduced operating voltage, enhanced speed of operation, minimum cross-talk between pixels, and high brightness.
It is another primary object of this invention to provide a manufacturing process for a high density electro-optic light valve array using modified silicon semiconductor photolithography, etching, and thin film deposition technology and equipment.
It is another object of the present invention to provide a high density electro-optic light valve array with reduced operating voltages compatible with current commercially available silicon large scale integration technology and display circuitry designed for use with liquid crystal displays.
It is yet another object of the present invention to provide a high density electro-optic light valve array with minimized electrode line widths and maximized light transmission capabilities.
It is yet another object of the present invention to provide a manufacturing process that is capable of producing electr
Advanced Optics Electronics, Inc.
Baker Rod D.
Epps Georgia
Lucas Michael A.
Mays Andrea L.
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