| 摘要 |
PURPOSE:To judge the information written in a memory cell at high speed as well as to prevent the deterioration in characteristics of the MISFET on which information has been written in by a method wherein the threshold voltage of an MISFET before the writing-in of information is made higher than the threshold voltage of the MISFET to be used for the circuit on the circumference. CONSTITUTION:The threshold voltage of the n-channel MISFET 17, to be used for a circumferential circuit, is set low at 0.55 V or thereabout, for example, in a mask ROM. Also, the threshold voltage of the n-channel MISFET 16 before writing-in of information is set higher than the threshold voltage of the MISFET 17 for the circuit on the circumference at 2V or thereabout, for example, and the threshold voltage for the writing-in of information is set at 4.5V or thereabout, for example, by performing a channel doping. Accordingly, the difference in the drain current of the MISFET 16 before and after writing-in of information can be made larger. As a result, when the source voltage Vcc is 5V or thereabout, the judgement on the information '1' and '0' can be performed easily at high speed even when the read-out of information is performed using the Vcc as the gate voltage VG to be applied to a word line 5. |
