Malik Pinki, Sengupta Dipanjan, Kumar Ajay, Saini Dalip, Mandal Dipankar
Quantum Materials and Devices Unit, Institute of Nano Science and Technology, Knowledge City, Sector-81, Mohali 140306, India.
Langmuir. 2023 Aug 1;39(30):10511-10520. doi: 10.1021/acs.langmuir.3c00959. Epub 2023 Jul 17.
Organic nonvolatile memory with low power consumption is a critical research demand for next-generation memory applications. Ferroelectric switching characteristics of poly(vinylidene fluoride) (PVDF) thin films modified with a trace amount of hydrated Cu salt (CuCl·2HO) are explored in the present study. Herein, a Cu salt-mediated PVDF (Cu/PVDF) thin film with preferential edge-on β-crystallites is fabricated through the orientation-controlled spin coating (OCSC) technique. This work proposes a convenient and effective approach to produce edge-on-oriented electroactive PVDF thin films with a high degree of polar β-phase, so as to realize the favorable switching under low operating voltages. Herein, chemically modified PVDF is anticipated to form a complex intermediate, which attains its stability by undergoing favorable hydrogen bonding that reorients the C-C structure of PVDF to obtain the β-conformation. Such information is verified by X-ray photoelectron spectroscopy (XPS). Grazing incidence Fourier transform infrared (GI-FTIR) spectroscopy revealed that the Cu salt incorporated into the PVDF matrix favored the formation of the electroactive β-phase with edge-on crystallite lamellae. Consequently, the Cu/PVDF thin film demonstrates a good contrast between electric field-assisted written and erased data bits in the piezoresponse force microscopy (PFM) phase image. Furthermore, to obtain the ferroelectric memory window, a metal-ferroelectric-insulator-semiconductor (MFIS) diode with Cu/PVDF as a ferroelectric layer has been fabricated. The capacitance-voltage (-) characteristic of the MFIS diode exhibits a memory window of 12 V with a long-term retention behavior (∼longer than 7 days). In a nutshell, we tried to represent a clear understanding of the interfacial interactions of the Cu salt with PVDF, which favor the edge-on formation that results in the promising low-voltage ferroelectric switching and excellent retention response, where any additional electrical poling and/or external stretching is completely possible to be ruled out, thus offering a new prospect for the evolution of devices with long-lasting nonvolatile memories.
低功耗有机非易失性存储器是下一代存储器应用的关键研究需求。本研究探索了用微量水合铜盐（CuCl·2H₂O）改性的聚偏二氟乙烯（PVDF）薄膜的铁电开关特性。在此，通过取向控制旋涂（OCSC）技术制备了具有优先边向β-微晶的铜盐介导的PVDF（Cu/PVDF）薄膜。这项工作提出了一种方便有效的方法来制备具有高度极化β相的边向取向电活性PVDF薄膜，从而在低工作电压下实现良好的开关性能。在此，化学改性的PVDF预计会形成一种复合中间体，该中间体通过形成有利的氢键来实现其稳定性，这种氢键会使PVDF的C-C结构重新取向以获得β-构象。此类信息通过X射线光电子能谱（XPS）得到验证。掠入射傅里叶变换红外（GI-FTIR）光谱表明，掺入PVDF基体中的铜盐有利于形成具有边向微晶片层的电活性β相。因此，Cu/PVDF薄膜在压电响应力显微镜（PFM）相位图像中显示出电场辅助写入和擦除数据位之间的良好对比度。此外，为了获得铁电存储窗口，制备了以Cu/PVDF作为铁电层的金属-铁电体-绝缘体-半导体（MFIS）二极管。MFIS二极管的电容-电压（C-V）特性表现出12 V的存储窗口以及长期保持行为（约超过7天）。简而言之，我们试图清晰地理解铜盐与PVDF的界面相互作用，这种相互作用有利于边向形成，从而产生有前景的低电压铁电开关和优异的保持响应，在此完全可以排除任何额外的电极化和/或外部拉伸，从而为具有持久非易失性存储器的器件发展提供了新的前景。
