Effect of the sensing capacitance in a 'Sawyer-Tower' set-up on hysteresis loops: Model calculations and SrBi2Ta2O9 experimental results

It is well known that, for a given ferroelectric capacitor, the tilting of the hysteresis loops and the amount of remanent polarization measured in a 'Sawyer Tower' set-up are dependent on the sense capacitance (or load). However, it is less intuitive that a small sense capacitance will cause horizontal loop shifts and that these shifts depend on the state of the ferroelectric capacitor before the measurement. Since typical ferroelectric non-volatile memories operate with small sense-to-bit capacitance ratios, it is important to have models that can predict such effects. Complicated experimentation is necessary to implement the load and initial state effects properly in a load-line model. In contrast, the numerical ferroelectric capacitor model does not require any special experimentation to predict such effects. Experimental results from SrBi2Ta2O9 are compared with both models.