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T. T.-H. Kim
Out
Ref
RWL
BL
SL
Dec.
RD
MTJ
Fig. 15 Conventional sensing scheme
R low
R high
R ref
Frequency
Sensing Current
Fig. 16 Relationship between magnetic memory device resistance distribution and reference
resistance
Jeong et al. proposed a sensing scheme that can generate reference using storage
cells [15]. Since a storage cell itself generate its own reference voltage, it can remove
sensing failures caused by variations in the tunneling oxide thickness. Figure 18
explains the operation of this self-reference generation scheme. In the first stage,
current is applied to a selected MTJ device and converts the resistance to a voltage
value. This voltage is stored in a capacitor. Depending upon the MTJ resistance, the
stored voltage will have two different values. In the second stage, the selected MTJ is
written to have the parallel state. After this, the MTJ resistance is again converted to
voltage by applying current. Here, the current is slightly higher than the current used
in the first stage. The converted voltage is also stored in a capacitor. Note that the
stored voltage in the second stage is higher than that in the first stage if the original
data is “0”. Similarly, the stored voltage in the second stage is lower than that in