# Optimization of Bifurcated Switching by Enhanced Synthetic Antiferromagnetic Layer
## 2 Results and Discussion  
### 2.1 p-MTJ Performance in a Blanket Wafer  
A standard perpendicular magnetic anisotropy (PMA) MTJ stack structure (bottom electrode/seed layer/synthetic antiferromagnetic (SAF) layer/RL/MgO/FL/capping layer/top electrode, as shown in Figure 1) for high performance was fabricated on a Si/SiO\({}_{2}\) substrate by DC/RF magnetron sputtering. The stack structure is not disclosed in more detail due to the constraints of proprietary information.  
In order to make a preliminary observation of magnetization switching, the magnetic properties of the p-MTJ stack in a blanket wafer, such as the amplitude of the Kerr signal and the coercivity, were mapped by magneto-optical Kerr effect (MOKE) measurement. As shown in Figure 1b,c, about 50 sampling points were distributed on a 12-inch wafer to verify the uniformity within the wafer. In the case of a major hysteresis loop, the magnetic moment of different magnetic layers was switched when the applied magnetic field was swept from +15,000 Oe to \(-\)15,000 Oe, returning to +15,000 Oe. The magnetization direction of the bottom pinning p-MTJ layer was switched when the applied magnetic field was about 10,000 Oe, which is defined as _Hex_ (similarly to our previous work [29]). In order to evaluate the stability of the RL, the _Hf_ was defined here as the flip-flop field of the reference layer (RL) and SAF, which was about 5700 Oe in our original stack. The _Hf_ was large enough to avoid the reference layer switching in the write operation that leads to the back-hopping phenomenon in the WER curves. When it came to the minor loop,the magnetic moment of the free layer was switched when the applied magnetic field was swept from \(+600\) Oe to \(-600\) Oe, returning to \(+600\) Oe. The sharp switching in the minor loop in the perpendicular-direction magnetic field indicated the good PMA of the free layer. Ferromagnetic resonance (FMR) studies were also conducted from 25 GHz to 45 GHz at room temperature. Figure 1e shows the dependence of the resonant field H on the frequency f. As can be seen, the \(H\) of the film increases linearly with frequency. Also, the effective perpendicular anisotropy fields \(H_{K}\) can be obtained by applying the following resonance conditions: [30; 31].  
\[f=\frac{\gamma}{2\pi}\bigg{(}\mu_{0}H+\frac{2K_{i}}{M_{S}}-\mu_{0}M_{S}\bigg{)} \tag{1}\]  
\[H_{K}=\frac{2K_{i}}{\mu_{0}M_{S}}-M_{S} \tag{2}\]  
where the parameter \(\mu_{0}\) represents the permeability in free space, \(\gamma\) is the gyromagnetic ratio, \(M_{S}\) is the saturation magnetization, and \(K_{i}\) is the interface anisotropy energy. From the \(x\) intercept, we obtain \(H_{K}=5020\) Oe. The absorption linewidth (full width at half maximum, FWHM, \(\Delta H\)) at a fixed frequency is given by Equation (3). The linewidth in these cases is proportional to the frequency with a slot determined by \(\alpha\). That is,  
\[\Delta H=\Delta H_{0}+\frac{4\pi\alpha}{\mu_{0}\gamma}f \tag{3}\]  
where \(\Delta H_{0}\) refers to the inhomogeneous contribution to the linewidth. The inhomogeneous contribution may cause bifurcated switching or a balloon effect. From FMR results, we obtain \(\alpha=0.00475\) and \(\Delta H_{0}=226\) Oe.