Semiconductor memory and writing method and reading method for the same

摘要

A semiconductor memory includes bit lines, memory cells and a sense amplifier both of which are connected to the bit lines. Each of the memory cells includes a transistor and a capacitor. The capacitor is made of a material having a quantity of residual dielectric polarization in an electroless state in a hysteresis characteristic that is not reduced to less than a threshold value until after a lapse of a time of a refreshing cycle. The refresh cycle includes clock cycles. The sense amplifier detects an output current on the bit lines due to the residual dielectric polarization. The sense amplifier amplifies the output current to refresh the quantity of residual dielectric polarization of the capacitor when the detected level is equal to or larger than the threshold value. The sense amplifier does not amplify the output current when the detected level is less than the threshold value.