Electronic device

1. An electronic device comprising a semiconductor memory unit,

wherein the semiconductor memory unit comprises:

a storage cell comprising a variable resistance element;

a first selecting element coupled to one end of the storage cell and having a threshold voltage set to a first voltage;

a second selecting element coupled to the other end of the storage cell and having a threshold voltage set to a second voltage higher than the first voltage,

one or more additional storage cells, each comprising a variable resistance element;

one or more additional first selecting elements corresponding to the one or more additional storage cells, respectively, each additional first selecting element coupled to a first end of the corresponding additional storage cell and having a threshold voltage set to the first voltage; and

one or more additional second selecting elements corresponding to the one or more additional storage cells, respectively, each additional second selecting element coupled to a second end of a corresponding additional storage cell and having a threshold voltage set to the second voltage.

2. The electronic device of claim 1 , comprising a word line to supply a control voltage, wherein the storage cell further comprises a selecting element coupled to one end of the variable resistance element and coupled to the word line to receive the control voltage so that the variable resistance element is turned on or off in response to the control voltage of the word line.

3. The electronic device of claim 1 , wherein the electronic device passes a read current from the first selecting element to the second selecting element during a read operation.

4. The electronic device of claim 1 , wherein the variable resistance element has a first state with a first resistance value or a second state with a second resistance value higher than the first resistance value.

5. The electronic device of claim 4 , wherein the variable resistance element is switched to the first state when a first switching current is passed from the other end to the one end, and switched to the second state when a second switching current higher than the first switching current is passed from the one end to the other end.

6. The electronic device of claim 1 , wherein the first selecting element and the second selecting element are turned on or off in response to a select signal.

7. The electronic device of claim 1 , wherein the first selecting element and the second selecting element are fabricated to have the threshold voltages of the first voltage and the second voltage, respectively.

8. The electronic device of claim 1 , wherein a distance between gates of two adjacent the second selecting element is larger than a distance between gates of two adjacent the first selecting element.

9. The electronic device of claim 7 , wherein an active region of the second selecting element has a higher doping concentration than an active region of the first selecting element.

10. The electronic device of claim 7 , wherein a gate of the second selecting element has a larger width than a gate of the first selecting element.

11. The electronic device of claim 7 , wherein a distance between a gate and a contact coupled to an active region of the second selecting element is larger than a distance between a gate and a contact coupled to an active region of the first selecting element.

12. The electronic device of claim 1 , wherein the first selecting element receives a back bias voltage such that the threshold voltage becomes the first voltage, and the second selecting element receives a back bias voltage such that the threshold voltage becomes the second voltage.

13. An electronic device comprising a semiconductor memory unit,

wherein the semiconductor memory unit comprises:

a first global line;

a second global line;

one or more cell arrays each including a plurality of storage cells, each storage cell having a variable resistance element, a first local line coupled to one ends of the storage cells, and a second local line coupled to the other ends of the storage cells;

one or more first selecting elements coupled between the first global line and the first local line of the corresponding cell array and having a threshold voltage set to a first voltage; and

one or more second selecting elements coupled between the second global line and the second local line of a corresponding cell arrays and having a threshold voltage set to a second voltage higher than the first voltage.

14. The electronic device of claim 13 , wherein the storage cell further comprises:

a selecting element coupled to one end of the variable resistance element and a corresponding word line, and turned on or off in response to a voltage of the corresponding word line.

15. The electronic device of claim 14 , wherein the electronic device passes a current from the first global line to the second global line through a selected storage cell during a read operation.

16. The electronic device of claim 13 , wherein the variable resistance element has a first state with a first resistance value or a second state with a second resistance value higher than the first resistance value.

17. The electronic device of claim 16 , wherein the variable resistance element is switched to the first state when a first switching current is passed from the other end to the one end, and switched to the second state when a second switching current larger than the first switching current is passed from the one end to the other end.

18. The electronic device of claim 13 , wherein the first selecting element and the second selecting element are turned on or off in response to a corresponding select signal.

19. The electronic device of claim 13 , wherein the first selecting element and the second selecting element are fabricated to have the threshold voltages of the first voltage and the second voltage, respectively.

20. The electronic device of claim 13 , wherein the first selecting element receives a back bias voltage such that the threshold voltage becomes the first voltage level, and the second selecting element receives a back bias voltage such that the threshold voltage becomes the second voltage level.