Patent Publication Number: US-2007103759-A1

Title: Applications of light movable liquid crystal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 60/503,083 filed on Sep. 15, 2003 entitled “Applications of Light Movable Liquid Crystal,” which is herein incorporated by reference. 
    
    
     TECHNICAL FIELD  
      The present invention relates to light movable liquid crystal, and more particularly to applications of light movable liquid crystal.  
     BACKGROUND OF THE INVENTION  
      Certain nematic elastomers have optomechanical capabilities. It has been shown that certain nematic elastomers have the property of being able to change their shape by up to 400% in a relatively narrow temperature range. Further, it has been demonstrated that if the nematic order is suppressed, certain elastomers demonstrate mechanical responses in response to optical signal application on the elastomer.  
      As disclosed in the Physical Review Letters by Finkelmann and Nishikawa in their article “A New Opto-Mechanical Effect in Solids,”  Physical Review Letters , Vol. 87, Number 1 (Jul. 2, 2001), which is herein fully incorporated by reference. They demonstrate optomechanical effect on photoisomerizable molecular rods which absorb light when illumination occurs on polarization along the polarization direction. At present, the only disclosure of movement of such materials lateral displacement within a body of fluid.  
      Finkelmann et al. note that the order parameter, back reaction and other related dynamic parameters may determine the rate of photoisomerization depending on the polarization of the rods in the nematic elastomer,  
      Potentially, the discovery may result in a rubber-like liquid crystal which changes shape when placed in a beam of light, the crystal seems to swim away from the point of light impingement. The molecules in the liquid crystal line up in one direction and in the electric field of a laser the rods compress the surface of the material.  
      Finkelmann et al. have shown that when an azo dye is applied to the nematic elastomer the molecules in the nematic elastomer tends to line up in one direction. When a nematic liquid crystal is applied an azo dye, the dye molecules “fold up” when they absorb light.  
      Referring to  FIG. 1 , there is shown a schematic diagram of a nematic liquid crystal with an azo dye applied. A light of wavelength λ is incident on liquid crystal  10  in  FIG. 1 ( a ). Referring to  FIG. 1 ( b ), the dye molecules, in reaction to the incident light applied on liquid crystal  10 , “fold up.” Referring to  FIG. 1 ( c ), the dye molecules enable the liquid crystal  10  to speed up and avoid the light while losing the contraction. The liquid crystal  10  speeds across a direction  15 .  
      The nematic elastomer additionally has the capability of accelerating motion proportional to the intensity of the light.  
      Although the discovery of the light avoiding properties of the particular liquid crystal has been surprising, there remains a need for practical applications of such light or laser movable liquid crystal (“LMLC”).  
      The LMLC is an elastomer liquid crystal that moves in response to an illumination that moves in response to a laser movement or light source. The LMLC is on the order of micrometers. The LMLC may be formed in different shapes, such as rectangular, elliptical or longitudinal.  
     SUMMARY OF THE INVENTION  
      The above-described problems and deficiencies are solved by the present invention. Generally the invention provides:  
      In one aspect, the invention is a switching device actuatable with a light source for transmitting an optical signal therethrough, said switching device comprising: a light movable liquid crystal (“LMLC”) positionable between a first position and a second position, wherein said LMLC is configured for mechanical actuation upon activation with said light source.  
      In another aspect, the invention is a switching device actuatable with a light source for transmitting an optical signal therethrough, said switch device comprising: a light movable liquid crystal (“LMLC”) rotatable between a first position and a second position, wherein said LMLC is configured for mechanical rotation upon activation with said light source at an angular moment.  
      In another aspect, the invention is a semiconductor fabrication mask for fabricating a predetermined pattern on a wafer, said mask comprising: a plurality of LMLC arranged in a predetermined array, wherein each LMLC is positioned between a first position and a second position upon activation with a light source.  
      In another aspect, the invention is a load carrying device comprising: an LMLC configured for carrying a load, wherein said LMLC transports said load upon activation by a light source. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Further features of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following specification with reference to the accompanying drawings, in which:  
       FIG. 1  is a schematic diagram of the operation of a class of nematic elastomer with light avoidance characteristics;  
       FIG. 2  is a schematic diagram of a light movable liquid crystal in accordance with the principles of the present invention;  
       FIG. 3  is a schematic diagram of a LMLC configured as a load carrying device in accordance with the principles of the present invention;  
       FIG. 4  is a schematic diagram of a LMLC configured as a load carrying device in accordance with the principles of the present invention;  
       FIG. 5  is a schematic diagram of a LMLC configured as a load carrying device in accordance with the principles of the present invention;  
       FIG. 6  is a schematic diagram of a LMLC configured for rotatable actuation in accordance with the principles of the present invention;  
       FIG. 7  is a schematic diagram of a LMLC configured as an autonomous device in accordance with the principles of the present invention;  
       FIG. 8  is a schematic diagram of a plurality of LMLC configured as a load carrying device in accordance with the principles of the present invention; and  
       FIG. 9  is a schematic diagram of a LMLC configured as a programmable mask in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE FIGURES  
      To review, referring to  FIG. 2 , a light movable liquid crystal (“LMLC”) is a nematic elastomer which has light avoidance characteristics which enable movement in a viscous fluid to avoid the light. In one embodiment, the LMLC  10  is moved between a first position and a second position (as illustrated by the dotted lines) in a direction  15 .  
      Various optical switches and switching devices may be formed by utilizing the unique properties of the LMLC. Referring to  FIG. 3 , there is shown a LMLC optical switch in accordance with the principles of the invention which takes advantage of the optomechanical switch.  
      Optomechanical switches offer many advantages over electro-optical switches. Typically, optomechanical switches involves physical motion of some optical elements. Electrooptic switches, on the other hand, employ a change of refractive index to perform optical switching. The change of refractive index is typically accomplished by electro-optic or thermo-optic effects.  
      Generally optomechanical switches feature lower insertion loss, and lower crosstalk and higher isolation between the ON and OFF states. The switches of the present invention can also be made bi-directional further realizing savings on valuable chip real estate. Optomechanical switches, unlike electrooptic switches, are also independent of optical wavelengths, polarization and data modulation format. The crosstalk of electro-optic waveguide switches is limited to a range above −30 dB, and can often be in the range of −10 to −15 dB.  
      An optomechanical switch can be implemented either in free space, in fibers or in waveguides. An optomechanical free space switch is disclosed in the invention.  
      The movement from a first position and a second position upon application of light, as shown in  FIG. 2 , can be used to create other types of practical applications, upon application of light. This movement can be used to create a flip-flop for phototransistor devices. Other applications of this movement include reflectors, polarizers, filters, phase shifters, plungers, pistons, oscillators, tuners, choppers or scanners. For example, as a reflectable device, a plurality of LMLCs may be arrayed to form a reflective liquid crystal device, e-paper or switchable window.  
      Another application of the LMLC is as a load-carrying device. Referring to  FIG. 3 , the LMLC  10  is used to pull a load  30 , for example, a strand of molecules (e.g. DNA). Referring to  FIG. 4 , the LMLC  10  may be used to push a load  30 . Referring now to  FIG. 5 , an LMLC  10  may be used as a “raft” to carry a load  30  such as molecules or a nano or micro scale structure. Although not illustrated in the figures, the load may be attached to the underside of the LMLC to allow exposure to the light source. Alternatively, the LMLC may include a cargo area to support a load, leaving the light activated portions of the LMLC exposed.  
      In another embodiment, and referring to  FIG. 6 , a rotational movement of the LMLC may be accomplished by an appropriate incident light source. For example, the light source or laser may direct the beam of light used to initiate movement at an angle to the LMLC.  
      In another embodiment, the range and path of motion may be predetermined by a suitable channel, track, guide wire, or other guidance system. The guidance system may be built of etched substrate on a viscous fluid. Conventional etching techniques can be used.  
      In still further embodiments, any desired path or range of motion may be determined by a suitable light or laser scanning device.  
      In another application an autonomous device may be formed, referring to  FIG. 7 , the autonomous device may include its own light source  70 . The light source may be fashioned conventionally on a substrate. Conventional light sources can include eximer lasers, free electron lasers or dye lasers. Thee light source is electrically coupled to a power source  75 . The power source may be a metal air or electrochemical battery or fuel cell which can provide a mobile autonomous source of power. Accordingly, a self-propelled and a self-powered LMLC may be formed. The self-powered self-controlled LMLC may include, for example, radio frequency antennas (not shown) for accepting control signals, sensors for determining information about characteristics of a subject, loads to carry, or even may be used in a drug release environment. In a still further embodiment, and referring to  FIG. 8 , a plurality of LMLCs may be arranged in parallel to combine strengths to pull a load.  
      Many applications may be derived from the above-described generic applications of LMLC. Various features may also be imparted. For example, for continuous movement, a laser scanning may be used. Further, various beam steering devices, including those invented by Reveo, may be used.  
      In another embodiment, the LMLCs may be arranged to move in circular or elliptical fashion, referring back to  FIG. 6 . Based on the angle of incidence of the laser beam, LMLC will gain angular momentum, causing circular or elliptical motion.  
      One very important application of the LMLCs, which has been sought after for some time, is a programmable mask. A programmable mask may be used in conventional semiconductor wafer processing to etch structures and devices. In this embodiment, as shown in  FIG. 9 , an array of LMLCs may be formed, for example, in the shape of a wafer to be used in a mask in lithography. In  FIG. 9 , wafer mask  93  and  95  are aligned vertically. The second array  95  for the LMLCs positioned in the initial state opposite the first array, is provided. By applying light to selected LMLCs, any desired pattern may be formed.  
      Each LMLC based pixel of the array generally may include an LMLC attached to a suitable mask structure (for e.g., Al), referred to as a “light movable half pixel”. The light movable half pixel may be moved between a first position and a second position. When two arrays of such light movable half pixels are registered appropriately, the mask may be configured for desired complex pattern etching over any conventional wafer. Numerous conventional semiconductor fabrication methods may be used to further customize the fabrication process.  
      While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.