Phase change memory devices and read methods using elapsed time-based read voltages

A variable resistance memory device comprising:

• a memory cell connected to a bit line;
• and
• a clamp circuit configured to provide either a first read voltage or a second read voltage to the bit line according to an elapsed time from a write operation of the memory cell,
• wherein the memory cell comprises a variable resistance substance having a resistance value variable according a write current provided to the bit line;
• and a select element configured to switch in response to a selection signal provided via a word line.

A read method of a variable resistance memory device comprising:

• determining an elapsed time from a program time of a memory cell to a point of time when a read operation is conducted;
• and
• sensing data of the memory cell by variably providing a clamp voltage to clamp a bit line of the memory cell according to the elapsed time,
• wherein the determining comprises detecting whether an input command is a write command or a read command;
• and
• wherein the bit line is clamped to a first read voltage when the write command is detected and to a second read voltage higher than the first read voltage when the read command is detected.