Abstract:
A liquid crystal light valve and manufacturing method thereof is disclosed in which a light-reflecting layer and a light-intercepting layer are constituted by a single metal layer of aluminum with black matrices in a pattern for separating pixels and formed by anodization.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a liquid crystal light valve (LCLV) used for a large-screen image projection apparatus and optical data processing apparatus and manufacturing method thereof, and more particularly to an LCLV with an improved layer structure having a reflecting layer. 
     Using the electro-optical characteristic of liquid crystal whose dynamic characteristic changes according to the presence or absence or the amount of incident writing light, an LCLV modulates projection light with the liquid crystal and is used to provide amplification light and to form an image and in the changing of its wavelength of the applied light. Such an LCLV is used for light reflection and transmission projection systems and optical data processors. Recently, the study of its application to household equipment has been proceeding. 
     FIG. 1 illustrates a conventional LCLV. In FIG. 1, transparent electrodes 3 and 3a to which a driving voltage is applied adhere to the inner surface of two parallel transparent substrates 2 and 2a. Liquid crystal LQ between transparent substrates 2 and 2a  keep a certain distance between spacers 8 and 8a is in contact with orientation layers 7 and 7a. A sandwich layer composed of a photoconductor 4, a light interceptor 5 and a reflecting layer 6 is placed between electrode 3 of transparent substrate 2 which is on the side of incident writing light 9a, and the opposing orientation layer 7. In FIG. 1, reference numeral 1 denotes a filter while 9b denotes projection light. 
     In operation of the LCLV, a control voltage for dynamically controlling the liquid crystal which double-refracts projection light 9b forming an actual image must be switched by photoconductor 4 activated by writing light 9a having an image signal. Therefore, an LCLV should be designed so that when no writing light is incident, the impedance of a photoconductor is far greater than that of liquid crystal and when writing light is incident, the impedance of the photoconductor is far less than that of liquid crystal. However, the elements of the layer structure are physically joined, meaning that a deviation of the junction characteristic (for example, electrical contact resistance, that is, impedance) actually exists at each junction portion. Particularly, the junction characteristic of the elements of the layer structure is disadvantageous if each layer is thick. Since reflecting layer 6 is a multilayer consisting of dielectrics having high or low refractive indexes, it greatly affects the deterioration of the overall junction characteristic. Such a reflecting layer is usually stacked with more than ten layers of material made of SiO 2  and TiO 2  or MgF 2  and ZnS and has a high reflectance of about 95%. However, since the wavelength region in which complete reflection takes place is only plus or minus tens of nanometers from a specific reference wavelength according to the difference in reflectances of the two materials, complete reflection throughout the whole visible light spectrum can not be expected. To solve such a problem, the reflecting layer should be a stack of dielectrics having various reference wavelengths, eventually increasing the overall thickness of the layer. The increased thickness of layer results in raising the stress on the reflecting layer so that the junction characteristic of an adjacent layer, for example, the photoconductor or light intercepting layer, becomes poor, which in turn lowers product reliability and increases production costs. 
     As an improvement to the problem, an LCLV having an additional junction layer was disclosed in U.S. Pat. No. 4,799,773 which usually uses SiO 2  or CdTe as the junction layer. However, such an LCLV has a thicker photoconductor (over 30μm or so) for an impedance matching, which results in increase in production cost and reduction in productivity. In addition, since the reflecting portion of the reflecting layer is narrow, a filter (as an additional improvement) is required to be adhered to a light source. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an LCLV which is inexpensive and easy to manufacture. 
     It is another object of the present invention to provide a most favorable method for manufacturing the LCLV. 
     To accomplish the objects, the liquid crystal light valve comprises a photoconductor the impedance of which is changed by writing light having an image signal, a double-refracting layer having liquid crystal which double-refracts incident projection light by a predetermined potential, a light-intercepting/reflecting layer interposed between the double-refracting layer and photoconductor, and electrodes for providing a driving voltage to the double-refracting layer, wherein the light-intercepting/reflecting layer is made of an aluminum thin layer and is oxidized in a pattern to form nonconductive black matrices and unoxidized conductive reflecting portions. 
     To accomplish the objects of the present invention, there is further provided a manufacturing method of a liquid crystal light valve comprising a photoconductor the impedance of which is changed by writing light having an image signal, a double-refracting layer having liquid crystal which double-refracts incident projection light by a predetermined potential, a lightintercepting/reflecting layer interposed between the double-refracting layer and photoconductor, and electrodes for providing a driving voltage to the double-refracting layer, 
     wherein a process for forming the lightintercepting/reflecting layer comprises the sequential steps of stacking an aluminum thin layer on the photoconductor placed on one of the electrodes, forming a pattern screen having a shape corresponding to a pixel pattern on the aluminum thin layer, oxidizing portions unprotected by the pattern screen on the aluminum thin layer to form blackened pixel-separating matrices, eliminating the pattern screen from the aluminum thin layer, and abrading the blackened pixel-separating matrices that are projected from the surface of the aluminum thin layer during the oxidizing step, to create a uniform surface. 
     In the LCLV of the present invention, conventional light-intercepting and reflecting layers are formed by a single layer which is constructed so that its aluminum thin layer reflects projection light and its black matrices provided in a pattern on the aluminum thin layer absorb and intercept unnecessary light. 
     In the manufacturing method of the present invention, it is desirable that the aluminum thin layer be formed by a sputtering method with which excellent adhesion can be obtained and formation of the pattern screen on the surface of the aluminum thin layer be carried out by conventional photolithography. It is further desirable that, during the step of forming the black matrices, which blackens the exposed portions of the aluminum thin layer between the pattern screen, an anode oxidization method be used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and other advantages of the present invention will become more apparent by describing in detail a preferred embodiment of the present invention with reference to the attached drawings in which: 
     FIG. 1 shows a schematic cross-sectional view of a conventional LCLV; 
     FIG. 2 shows a schematic cross-sectional view of an LCLV of the present invention; 
     FIG. 3 shows an extracted front view of the reflecting layer of the LCLV according to the present invention shown in FIG. 2; and 
     FIGS. 4A through 4E illustrate the process of manufacturing the LCLV according to the manufacturing method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, transparent electrodes 30 and 30a to which an AC driving voltage is applied are adhere on the inner surface of two parallel transparent substrates 20 and 20a. Liquid crystal LQ between transparent substrates 20 and 20a keep a certain distance with spacers 80 and 80a is in contact with orientation layers 70 and 70a. A sandwich layer composed of a photoconductor 40 and a light-intercepting/reflecting layer 60 for intercepting and reflecting projection light 90b is placed between electrode 30 of transparent substrate 20 located on the incident writing light side, and the opposing orientation layer 70. Here, the photoconductor is made of i-type amorphous silicon. 
     As the main feature of the present invention, light-intercepting/reflecting layer 60 is formed by processing aluminum via a sputtering or vacuum deposition method. As is shown in FIG. 3, light-intercepting/reflecting layer 60 comprises a conductive reflecting portion 61 and a nonconductive black matrix 62 which provide pixel separator means for enabling the absorption and interception of light. In the embodiment of the present invention, black matrix 62 is in the form of a honeycomb, but may be modified to a simple lattice structure, a complex combination of the two, or some other form. In FIG. 2, reference numeral 10 denotes a filter. 
     The LCLV of the present invention operates in the same way as a conventional LCLV. That is, when writing light 90a having an image signal is incident, the impedance of photoconductor 40 is changed according to the projected light of an image signal by a local luminance difference. This enables double refraction of the projection light by liquid crystal LQ while oriented in a certain direction and the projection light is re-reflected. The re-reflected projection light 90b reaches the screen to form an image. 
     Here, as the main feature of the present invention, light-intercepting/reflecting layer 60 reflects most of writing light 90a, with some being absorbed, thus changing the impedance of photoconductor 40. Since each reflecting portion 61 is conductive, it transmits the change of the impedance of photoconductor 40 to orientation layer 70. By encircling each reflecting portion 61 and being placed between photoconductor 40 and orientation layer 70, black matrix 62 always keeps its impedance so as to electrically isolate photoconductor 40 from orientation layer 70, and absorbs and disperse external light incident thereto. Black matrix 62 functions as a pixel separator. The double-refraction of projection light 90b by liquid crystal LQ occurs due to the change of impedance of photoconductor 40. The impedance change of liquid crystal LQ becomes distinctive due to conductive reflecting portion 61 and the nonconductive black matrix 62, so that a high-sharpness picture can be realized. 
     The LCLV of the present invention is characterized in its light-intercepting/reflecting layer wherein conventional light-intercepting layer and reflection layer are integrated into one. Further, the present invention is characterized in that a conventional bonding layer compensating for the junction between layers is eliminated. Features of the LCLV of this invention are as follows: 
     1) Since a dielectric of common inorganic material is not used as the reflecting layer material, the device is advantageous in the matching of the overall impedance and the reflecting layer&#39;s thickness is greatly reduced as compared with a conventional one; 
     2) In its manufacturing process, contrary to the conventional reflecting layer requiring a process of forming multiple thin layers, since only a process of forming a single metal layer (and the post-processing thereof) is required, productivity is improved due to manufacturing process reduction; 
     3) Since the reflecting portion is metal, it has a higher reflectance than the conventional one throughout the entire visible light spectrum to be suitable for color LCLVs; 
     4) The overall thickness of the layer structure is reduced so that the junction characteristic between surfaces of the interlayers is excellent and the concentration of its stress is relieved, to enhance the product&#39;s reliability; 
     5) Since neither a compensating filter nor specific conditions on the light source are required, the overall cost of the system is reduced; 
     From here on, a manufacturing method for the LCLV of the present invention will be described which in general follows the conventional manufacturing process. After the subsequent formation of an electrode and photoconductor on one substrate, the light-intercepting/reflecting layer, which is the main feature of the LCLV of the present invention, is formed. 
     First, in forming the light-intercepting/reflecting layer, as shown in FIG. 4A, an aluminum thin layer Al is formed on photoconductor 40 by vacuum deposition or a sputtering method. 
     Then, as shown in FIG. 4B, a photosensitive resin layer is formed on aluminum thin layer A1 and is etched by photolithography to form a pattern screen PS having a form corresponding to a pixel pattern which is, for example, in the form of a honeycomb, a lattice structure, a complex combination of the two, or some other form. 
     Subsequently, as shown in FIG. 4C, those portions of aluminum layer A1 which are unprotected by pattern screen PS, are oxidized to form a pixel-separating black matrix 62. Here, an anode oxidization method is desirably used under the conditions prescribed in the following &lt;TABLE&gt;. 
     
         &lt;TABLE&gt;______________________________________electrolyte     oxalic acid     2.5composition (%) sulfuric acid   0.2           dissolved aluminum                           0.2voltage         50-70 Vcurrent         2A/dmtemperature     8-12° C.cathode         graphite______________________________________ 
    
     Since, in this method, the object of oxidization (the aluminum layer) is the anode, its power is applied through an electrode connected to the photoconductor. Here, to improve electrical conductivity, external light is radiated onto the photoconductor to lower its impedance. By doing so, the anode current stays steady and high to enable uniform and fast oxidization of the anode. 
     Due to such oxidization of the anode, as shown in FIG. 4D, the oxidized portions thereof become relatively thick. To prevent this, after pattern screen PS is eliminated by a corrosive, the oxidized portions are abraded to form one plane flush with the unblackened portions, as shown in FIG. 4E. 
     Through the above process, light-intercepting/reflecting layer 60 as the main feature of the present invention, is formed on photoconductor 40, and subsequent conventional process steps complete the LCLV of the present invention. 
     The manufacturing method of the present invention is most suitable in forming a light-intercepting/reflecting layer, especially an excellent black matrix. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.