STT-Based Non-Volatile Logic-in-Memory Framework - Field-Coupled Nanocomputing: Paradigms, Progress, and Perspectives - page 183

next zone is released. This makes sure that information in the logic propagates
only in one direction, which is from the input(s) to the output(s) and not other
way. The numerical values of t clk is mentioned in Table 2 .

I clk = μ 0 M S eV olH d
G

(7)

To make this STT clocking effective, the MTJs need to have a 45 ⓦ tilt in
the polarization of their fixed layer. The logic states for the tilted MTJs is
shown in Fig. 7 a. Interestingly, this type of tilted polarized fixed layer MTJs are
also widely used in spin torque oscillators [ 14 ]. We will next see how this MTJ
configuration suits computational needs as well. Remember for computation we
are using interaction between free layers of neighboring MTJs. This interaction
becomes most effective with minimum coupling from the fixed layer of MTJs.
Ideally this means that the free and fixed layer in MTJs should have orthogonal
polarizations. On the other hand, the MTJs also need to have good MR for
reading their contents. As we have already seen from Eqs. 4 and 5 ,theMRis
dependent on the relative angle between the magnetizations of free and fixed
layers. The 45 ⓦ polarization therefore provides a good optimal point between
the orthogonal needs of computation and reading from MTJs.

V DD V DD V DD

V DD

Φ 3 Φ 3

M 7 M 5 M 6 M 8

M 9

X Y

E q

Φ 2

Φ 2

M 3 M 4

Comparator

A B

O/P

Φ 1 Φ 1

Φ 1
M 1b

Φ 1
M 2a M 1a M 2b

Logic 0

- -

S a S b S a S b

Logic 1
(a) (b)

Fig. 7. (a) Logic states in MTJs with 45 polarized fixed layer; (b) Variability tolerant
non-destructive differential read circuit.