# Influence of Applied Stress on the Ferroelectricity of Thin Zr-Doped HfO\({}_{2}\) Films
## 3 Results and Discussion  
### Ferroelectricity Characterization  
First, the effect of stress on the ferroelectricity of thin HZO films at a 600 \({}^{\circ}\)C annealing temperature in MFM structures as test devices were investigated. Figure 2 illustrates the P-E hysteresis curves of ferroelectric films under different electric field conditions, where (a) and (b) denote the two cases with and without stress, respectively. The test voltage amplitude gradually increased from 1 V to 3.5 V. As shown in Figure 2, the remnant polarization (P\({}_{\rm r}\)) increased with the voltage amplitude for both conditions. At the same time, the hysteresis loops clearly show observable ferroelectricity in both capacitors. Figure 2c,d show P\({}_{\rm r}\) and E\({}_{\rm c}\) as functions of the test electric field, respectively. The results show that the overall P\({}_{\rm r}\) magnitudes were similar in both conditions, but P\({}_{\rm r}\) in the stressed condition was larger than that in the unstressed condition when the electric field strength was below 3 MV/cm, while an opposite result was obtained when the electric field strength was higher than 3 MV/cm. The E\({}_{\rm c}\) values under the two conditions were also close, but the E\({}_{\rm c}\) with stress was slightly smaller than the E\({}_{\rm c}\) value without stress.  
The 2P\({}_{\rm r}\) values at different annealing temperatures were measured to further investigate the effect of stress on the ferroelectricity of HZO materials as shown in Figure 3a,b. As the annealing temperature increased, the remnant polarization charge of the HZO capacitor was gradually enhanced, and the 2P\({}_{\rm r}\) value increased from about 35 \(\upmu\)C/cm\({}^{2}\) at 450 \({}^{\circ}\)C to about 45 \(\upmu\)C/cm\({}^{2}\) at 650 \({}^{\circ}\)C. The remnant polarization improved by approximately 30%, which is illustrated in Figure 3c. The remnant polarization charges at different annealing temperatures with and without stress were similar and showed a higher ferroelectricity dependence on temperature, indicating that the enhancement of ferroelectricity by stress may not be significant and that the samples have similar ferroelectricity. Figure 3d shows the variation of the coercive electric field with different annealing temperatures. The results show that E\({}_{\rm c}\), with the stress condition was slightly smaller than that without stress, and E\({}_{\rm c}\) varied little with temperature.  
Figure 1: (**a**) The main steps of the fabricated HZO capacitor. (**b**) Structure schematic of the capacitor with stress. (**c**) TEM image of the fabricated HZO capacitor. (**d**) C–V curve of the capacitive structure.  
Figure 3: Comparison of P–E loops (**a**) in the stress free and (**b**) with stress conditions under different annealing temperatures. (**c**,**d**) The extracted remnant polarization and coercive electric field the of two capacitor structures at different annealing temperatures, respectively.  
Figure 2: P–E loops of (**a**) HZO capacitor with stress and a (**b**) HZO capacitor without stress, respectively. Evolution of (**c**) P\({}_{r}\) and (**d**) E\({}_{c}\) of HZO capacitor with and without stress.