| 摘要 |
PURPOSE:To attain accurate memory cell evaluation simply by writing and recording a prescribed measuring item such as measuring data, or the like to a memory cell itself to be evaluated, reading the recorded measuring item after a prescribed time is elapsed and comparing the item with a data measured again. CONSTITUTION:Write is conducted to all unit memory cells and the threshold value of a variable threshold field effect transistor (TR) is decreased to a VTL. The threshold value VTL is measured as to all unit memory cells so as to obtain the maximum threshold value VTLMAX among all measured threshold values. Then said VTLMAX and a measured data T1 are written in the optional address of the memory cell 1. After the data are stored for a prescribed time, the threshold values of (m-1)Xn-set of unit memory cells are measured again, and the maximum threshold voltage VTLMAX', in all the measured threshold and the measuring time T2 are obtained. Then the maximum threshold voltage value VLMAX and the measuring time T1 recorded in the address (m) are read. Further, a time Ts when the threshold voltage is changed to a specified value VTLO is obtained by using the VLMAX', VLMAX', T1 and T2. |
