Mask ROM cell structure with multi-level data selection by code

U.S. Patent Number: 5736771

Abstract: A multi-level memory cell structure, and a method of fabrication thereby is disclosed. In a mask ROM memory device, the conventional binary data storage cell is replaced with a 16-level data storage cell. The 16-level cell is programmed with a selected one of 16 values by forming a void in a portion of the word line over the memory cell having one of 16 widths corresponding to the preselected code to be stored therein. The portion of the word line associated with the coded memory cell has an effective remaining width corresponding to the preselected code. When the memory cell is enabled by activating its associated word line, due to the variable width of the word line forming the gate of the memory cell, one of 16 discrete currents flow in the 16-level memory cell structure. The current is indicative of the preselected code stored in the cell.

Inventors: Huang; Hon-Shen (Taipei, TW); Wu; Zon-Sheng (Hsin Chu, TW); Chen; Kun-Lu (Hsin Chu, TW)

Assignee: United Microelectronics Corporation (

Application Number: 08/597,980

Issued: 1998-04-07

Expired: 2006-04-07

Classes: 257/390 ; 257/391; 257/E27.102; 365/104; 365/94

Field of search: 257/390,391 365/94,104

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