PURPOSE: To discriminate acceptables or defectives simply with high accuracy by writing data to an EPROM in the quantity of charges less than the quantity of normal writing storage charges, leaving the device at a high temperature for a fixed time as it is and checking contents memorized by line voltage.
CONSTITUTION: Charges are injected to the floating gates of each memory cell of the EPROM not written. The qnantity of charges is set at value smaller than the quantity of normal writing storage charges. The device is left at a high temperature as it is, and the degradation of a memory margin is accelerated. Temperature and leaving time shall be 250°C and twenty-four hrs or longer when memory life is guaranteed for ten years. Contents memorized are read leastly by proper line voltage VCC, and the device is discriminated and removed as GO when they are read normally and as NO GO when they are not read so. Acceptables or defectives can simply be discriminated because the degradation of the memory margin is as shown in C when they are read normally and it is as shown in F1, F2, F3 when writing is insufficient and the holding characteristic of charges is inferior.
MATSUI KIYOSHI
MUSASHI SHINJI
| JPS5244180A | 1977-04-06 |