Application Cases

Experiment Name: Real-Time Monitoring Process of High-Temperature Periodic Polarization

Experiment Purpose: By studying the spontaneous polarization strength, coercive field, and domain growth rate model of MgO:LN crystals under high-temperature conditions, the impact of high temperature on the ferroelectric domain reversal characteristics was explored. Additionally, a real-time monitoring system for the preparation of PPLN crystals using the external electric field polarization method under high-temperature conditions was designed and constructed. Utilizing the transparent properties of indium tin oxide (ITO) electrodes, the real-time state of domain growth was monitored using electro-optic imaging. The nucleation and growth processes of domains under different polarization states were discussed in conjunction with the monitoring results of the real-time monitoring system, supplementing the macroscopic model of ferroelectric domain reversal.

Testing Equipment: High-voltage amplifier, signal generator, oscilloscope, etc.

Experiment Process:

Figure 1: Schematic Diagram of Periodic Polarization Device

The preparation of polarization samples was first conducted, which mainly included processes such as coating, pre-baking, exposure, development, hard baking, etching, and dicing. After photolithography, the wafer had a pre-designed periodic electrode prepared on its +Z surface, and then a uniform electrode was deposited on its -Z surface for the subsequent periodic polarization process. Figure 1 shows the schematic diagram of the periodic polarization device. The signal generator applied the set polarization voltage waveform to the positive and negative Z surfaces of the crystal through the high-voltage amplifier. Meanwhile, using a high-precision oscilloscope, the output voltage of the high-voltage amplifier was detected, and the polarization current through the crystal was monitored via a series resistor.

Experimental Results:

Figure 2: Optical microscope images of PPLN crystals obtained at room temperature and the principle of domain merging: (a) Optical microscope image of the +Z surface of the PPLN crystal; (b) Optical microscope image of the Y surface of the PPLN crystal; (c) Principle of domain merging in MgO:LN crystals polarized by the metal electrode method at room temperature.

Under room temperature polarization, the amount of charge transfer during the polarization time is much greater than the charge transfer required for the crystal to undergo polarization reversal, indicating that there is excessive domain polarization within the crystal. Excessive domain polarization can lead to the phenomenon of domain merging. After the polarization process, the crystal was etched with HF, and the domain structure was observed using an optical microscope. As shown in Figure 2(a)(b), the +Z and Y surfaces of the obtained PPLN have undergone extensive merging, with the reversed domains almost entirely occupying the entire crystal +Z surface. The principle of domain merging in the crystal is illustrated in Figure 2(c). According to the domain reversal kinetics model proposed by experts, the first stage of polarization reversal is the nucleation of reversed domains at the electrode edges, followed by simultaneous lateral and longitudinal growth of the reversed domains. Due to the excessively high polarization voltage, the lateral and expansion growth rates of the domains are accelerated, causing some reversed domains to penetrate to the crystal -Z surface earlier. Studies have found that after MgO:LN crystals undergo polarization reversal, the resistivity of the polarization reversal region will decrease from 610^13 Ω·cm to 710^7 Ω·cm. This significant change in resistivity will make it easier for domains to expand in areas that have already undergone polarization reversal during the polarization process, exacerbating the lateral expansion of the reversed domains in that region, leading to the merging of reversed domains between adjacent electrodes. When the reversed domains grow longitudinally through the crystal, the lateral expansion of the domains has already become severe, resulting in the non-uniform crystal domain structure and severe domain merging shown in Figure 2. Therefore, this non-uniform growth of reversed domains will seriously affect the quality of periodic polarization.

High-Voltage Amplifier Recommendation: ATA-7015

Figure: Specification Parameters of the ATA-7015 High-Voltage Amplifier

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