Method for programming phase-change memory and method for reading date from the same

Abstract

When a phase-change element that can transition between a reset state (amorphous state) and a set state (crystalline state) is to be caused to transition to the reset state, a first pulse having a first voltage is applied to the phase-change element. The first voltage is higher than the threshold voltage in the reset state, and can cause current to flow that corresponds to an amount of generated heat required for placing the element in the reset state. When the phase-change element is to be caused to transition to the set state, a second pulse having a second voltage and the same time width as the first pulse is applied to the phase-change element. The second voltage that is higher than the threshold voltage but lower than the first voltage, and can cause only a current to flow that does not attain the necessary amount of generated heat.

1 . A method of a phase-change memory having a phase-change element that transitions between a reset state corresponding to an amorphous state and a set state corresponding to a crystalline state, said method comprising:
 taking, as a first threshold voltage, a threshold voltage for causing said phase-change element when in said reset state to start threshold switching, and, as a second threshold voltage, a threshold voltage for causing said phase-change element when in said set state to start threshold switching; and   applying to said phase-change element a read voltage that is a voltage between said first threshold voltage and said second threshold voltage and detecting whether current has flowed due to threshold switching in said phase-change element or not to read information that has been programmed in said phase-change element.   
     
     
         2 . A method of a phase-change memory having a phase-change element that transitions between a reset state corresponding to an amorphous state and a set state corresponding to a crystalline state, said method comprising:
 when said phase-change element is to be caused to transition to said reset state, applying to said phase-change element a first pulse of a first current such that said phase-change element is placed in a state in which threshold switching is brought about at a first threshold voltage after application of said first pulse;   when said phase-change element is to be caused to transition to said set state, applying to said phase-change element a second pulse of a second current such that said phase-change element is placed in a state in which threshold switching is brought about at a second threshold voltage that is lower than said first threshold voltage after the application of said second pulse, wherein said second current is smaller than said first current, and the time width of said first pulse is equal to the time width of said second pulse; and   applying to said phase-change element a read voltage that is a voltage between said first threshold voltage and said second threshold voltage and detecting whether current has flowed due to threshold switching in said phase-change element or not to read information that has been programmed in said phase-change element.   
     
     
         3 . The method according to  claim 1 , further comprising:
 applying said read voltage to said phase-change element by way of a bit line that is connected to a sense-amplifier and that is precharged to said read voltage;   amplifying, by means of said sense-amplifier, the voltage change of said bit line when said read voltage is applied; and   determining the information based on an output of said sense-amplifier.   
     
     
         4 . The method according to  claim 2 , further comprising:
 applying said read voltage to said phase-change element by way of a bit line that is connected to a sense-amplifier and that is precharged to said read voltage;   amplifying, by means of said sense-amplifier, the voltage change of said bit line when said read voltage is applied; and   determining the information based on an output of said sense-amplifier.   
     
     
         5 . A method of a semiconductor device including a phase-change element that transitions between a first state and a second state, the first state of the resistance-change element having a first threshold voltage, the second state of the resistance-change element having a second threshold voltage that is different from the first threshold voltage, the method comprising:
 applying said phase-change element with a read voltage that is between said first threshold voltage and said second threshold voltage.   
     
     
         6 . The method according to  claim 1 , further comprising detecting a current through the phase-change element when the phase-change element is applied with the read voltage to determine a state of the resistance-change element.