Process for the production of a substrate for an electrically controlled device and display screen produced from such a substrate

Abstract

The invention relates to a process for the production of a substrate for an electrically controlled device such as a display screen, said substrate integrating non-linear elements and control elements of the elementary display points. The invention relates to the production of a substrate, in its active part, has non-linear elements associated with each image element and produced from amorphous silicon and, in its peripheral part, polycrystalline silicon controlled elements. Initially the substrate has amorphous silicon layers, the peripheral crystallization being obtained by annealing in a temperature gradient furnace.

What is claimed is: 
     
       1. A process for producing a silicon substrate useful for the incorporation therein of transistors and diodes comprising the steps of positioning an amorphous silicon substrate in a furnace which has a non-uniform temperature distribution such that edge regions of the substrate are in a zone at a temperature high enough to convert the amorphous silicon to the polycrystalline form while the interior regions of the substrate are in a zone at a temperature insufficiently high to crystallize the amorphous silicon, and removing the substrate from the furnace after desired edge regions of the substrate have been crystallized. 
     
     
       2. The process of claim 1 followed by the forming of thin-film transistors in the polycrystalline edge regions of the substrate and of nonlinear diodes in the amorphous interior region. 
     
     
       3. The process of claim 1 in which the amorphous silicon substrate comprises in succession a relatively lightly doped first layer, a relatively heavily draped second layer, and a relatively lightly doped third layer, each formed by the thermal decomposition of silane. 
     
     
       4. The process of claim 3 in which the amorphouse silicon substrate had earlier been exposed to a hydrogen plasma for post-hydrogenation of the amorphous silicon formed by the thermal decomposition of silane. 
     
     
       5. A process for making a matrix access display screen having image elements at intersections of row and column access electrodes including forming a substrate in accordance with claim 1, forming in the amorphous regions a plurality of oppositedly poled diode pairs and in the polycrystalline regions a plurality of thin filrm transistors, incorporating the transistors into circuitry with the row and column electrodes of the display screen and incorporating the diode pairs in series with electrooptical image elements of the display screen. .Iadd. 
     
     
       6.  A display screen of the matrix access type incorporating an electro-optical material layer inserted between a transparent layer and a silicon substrate comprising: first active elements in a region of the silicon substrate consisting of amorphous silicon, said first active elements being in series with the image elements of the display screen, and   second active elements in a region of the silicon substrate that were initially amorphous but were transformed by annealing to polycrystalline silicon, said second active elements being used to address the matrix access display screen. .Iaddend. .Iadd.7. The display screen of claim 6 in which the region of the silicon substrate transformed to polycrystalline silicon is situated in the periphery of the substrate. .Iaddend. .Iadd.8. The display screen of claim 7 in which the first active elements consist of oppositely pole diodes pairs and the second active elements consist of thin film transistors. .Iaddend.