Patent ID: 6195287
Filing Date: 2001-02-27
Classification: G11C

Abstract:
A data programming method for a nonvolatile semiconductor storage device comprising:a number of field effect transistors each having a control gate, a drain and a source with an electrically data-programmable and erasable floating gate, arranged matrix-wise in rows and columns forming an array;a plurality of row lines, each being connected to the control gates of the field effect transistors in one row; anda plurality of column lines, each being connected to the drains of the field effect transistors in one column and also connected to the sources of the field effect transistors in the adjacent column so that each is shared by the two adjacent columns, forming a virtual ground type array, wherein three or more classes of data can be electrically written into each field effect transistor by differentiating the threshold level of the charge amount accumulated on the floating gate, the method comprising:the first writing step for setting the charge amount on the floating gate of each field effect transistor to be programmed with target data by a first programming voltage at a first threshold level other than the threshold level of target data by setting a reference voltage for verification to a first reference voltage; andthe second writing step for setting the charge amount on the floating gate of the field effect transistor by the first programming voltage at the threshold level of target data by setting the reference voltage for verification to a second reference voltage, after the first writing step.