Memory device and refresh method thereof

A memory device, comprising:

• a memory cell array including a plurality of memory cells;
• and
• a refresh control circuit configured to:
• receive a first activation signal and a first activation row address corresponding to the first activation signal from an external device at a first time point, and
• determine a victim row address to be refreshed on a victim row in the memory cell array based on an accumulation value,
• wherein the accumulation value is the number of activation signals received from a time point of receiving a refresh command from the external device to the first time point.

A refresh method of a memory device, the method comprising:

• receiving a first activation signal and a first activation row address corresponding to the first activation signal at a first time point;
• generating a random number when the first activation signal is received;
• generating a reference value based on the number of activation signals received from an immediately previous first target row refresh (TRR) time point to the first time point;
• determining an attack row address based on a magnitude relationship between the random number and the reference value;
• determining a victim row address based on the attack row address;
• and
• performing a refresh operation on a victim row corresponding to the victim row address at a second TRR time point subsequent to the first time point.