Indirect measurements of electrocaloric effect in ferroelectric thin films by positive-up-negative-down method

Abstract

Positive-up-negative-down (PUND) polarization measurement was employed to indirectly estimate the electrocaloric (EC) effect in ferroelectric films. By subtracting the conductive component from the observed charge profile, the polarization values at various electric fields and temperatures were precisely determined. The estimated EC effect for an epitaxial Ba 0.3 Sr 0.7 O 3 thin film fabricated on SrRuO 3 /SrTiO 3 (001) substrate showed the largest temperature change at around the ferroelectric-paraelectric phase transition temperature, which agrees with the theoretical prediction. On the other hand, the EC effect estimated by the conventional hysteresis loop measurement showed different peaking temperature from the theoretical prediction. The deviation became larger with lowering the measurement frequency. The observed results indicate the importance of precise evaluation of polarization for the examined temperature-electric field space.

Experimental study of effect of strain on electrocaloric effect in (001)-epitaxial (Ba,Sr)TiO3 thin films

“…Here, we stress that the PUND measurements eliminate the influence of leakage current; therefore, the true polarization values can be measured. [22][23][24] As shown in this figure, when the electric field is small, the polarization rapidly decreases with increasing temperature toward T Ã 0 . On the other hand, the polarization slowly decreases when the electric field is large.…”

“…To precisely evaluate the pyroelectric coefficient, we measured the electric field dependence of polarization at various temperatures by a positive-up-negative-down (PUND) method, which can eliminate the influence of leakage current. 22) For PUND measurements, inverted voltages of 50 V for the film on STO and 35 V for the film on LSAT, and noninverted voltages of 1-30 V for both films were applied. The duration and interval time of the applied voltages were 25 and 100 µs, respectively.…”

“…The detailed method can be found in Ref. 22. The obtained pyroelectric coefficients were used for the estimation of the electrocaloric effect based on Eq.…”

The ferroelectric orthorhombic phase formation of Hf0.5Zr0.5O2 thin films on (−201) β-Ga2O3 substrate by atomic layer deposition

“…By applying two voltage pulses with the same polarity in sequence, it is possible to eliminate the leakage current component from the apparent remanent polarization. [39][40][41] Based on fundamental experiments on the effect of pulse width and voltage, two clear remanent polarizations can be recognized by subtracting the two leakage components from the polarization differences obtained from the positive and negative biases when pulse width and voltage are 12.5 ms and 6 V, respectively. Figure 3(a) illustrates the PUND results of the PMA-HZO film annealed at 600 °C.…”

“…Positive-up-negative-down (PUND) measurements were carried out using a function generator (WF 1948, NF Co.; Kanagawa, Japan) to accurately evaluate remanent polarization without the effect of leakage current. [39][40][41] Capacitance-voltage (C-V) characteristics for the Pt/HZO/β-Ga 2 O 3 /In MFS structure were measured at 10 kHz using an LCR meter (HP4140B, Hewlett Packard; Palo Alto, Ca). High-speed C-V measurements with a voltage sweeping rate of 0.05-10 Hz were performed using a C-V analyzer (KEITHLEY 590; Tokyo, Japan).…”