共軛材料的設計、合成、性質與在光感式場效應電晶體式記憶體上的應用

Abstract

非揮發性的場效電晶體式記憶體可應用於多階儲存與仿神經元運算單元，而光感式記憶體不僅可以降低功耗、縮短響應時間，還可進一步應用於光感測領域。在材料選用上，以感光聚合物或有機無機複合型鹵素鈣鈦礦材料作為記憶層，可藉由分子設計來調控材料共軛程度、能階、晶體排列等等，以提升電荷儲存密度、光靈敏度、光響應速度、與電荷保留能力，改善記憶體效能。 本論文分為兩個部分，第一部分中我們合成了一系列三芳胺衍生物 TTM、TTP、TTC、DTPm與DTPmC，並經氧化聚合得到聚芳胺，作為光感式有機場效電晶體記憶體的記憶層材料，比較不同共軛能力、極性與共平面性對元件電荷儲存能力的影響。我們測量小分子的光物理、電化學性質，並使用單晶繞射分析分子結構，發現DTPm 與 DTPmC的共軛骨架具有高共平面結構，增強了共軛性質，提高了吸光係數並使單體堆疊更緊密。而TTP則具有比TTC更高的共軛程度。接著經由氧化聚合成功得到三種聚芳胺 PTTC、PTTP和PDTPmC。並且經量測三者皆有適當的能階可穩定正電荷，避免電荷流失。將聚芳胺應用於場效電晶體記憶體的電荷儲存層，發現三者皆具有電場驅動電洞儲存和照光恢復的能力，且電荷儲存密度與側基的共軛能力具有高相關性。PTTC 與 PTTP 的記憶窗口 分別為 13 V 與 44 V，而 PDTPmC 的具有高共平面性與強推拉電子基提高共軛能力，使記憶窗口達到 106 V。高電荷儲存密度使其在 -30 V 電壓驅動下，電流開關比 (on/off ratio) 仍維持在 105，且電壓刺激後的電荷滯留時間 (retention time) 可達 104 秒，耐久性測試中抹寫循環可達 200 次，顯示良好的非揮發性與耐受度。 第二部分，我們設計了帶 D-π-A 型共軛鏈的胺鹽 EATPCNI 與EATPmCNI，試圖應用於二維鈣鈦礦作為胺陽離子，使鈣鈦礦有機層間呈現更緊密的反平行堆疊，提升電荷傳輸能力。二維鈣鈦礦與絕緣體材料混合後可作為浮動閘極式的記憶層應用於光感式電晶體型記憶體。其中EATPmCNI由於嘧啶基團會質子化吸引多碘離子的附著而無法徹底純化，而EATPCNI在應用於光感式場效電晶式記憶體後發現，由共軛鏈的設計使其達到適當的能階，相較一般二維鈣鈦礦使用的有機胺鹽 (e.g. OAI, PEAI)，鈣鈦礦與傳輸層間電洞遷移的能障更小，使記憶體的光響應速度提升且光靈敏度更強。另外，經 GIWAXS、XRD等測量發現，其晶體排列方向混亂無序且結晶大小很小，使記憶體擁有強非揮發性。其電荷保留時間可達 2.4×105 秒、抹寫循環可重複 105 次，證明此分子設計可以使記憶體同時達到非常高的光響應速度、光靈敏度、非揮發性與耐受度。

Photosensitive polymers electrets or organic-inorganic hybrid perovskite materials enables the adjustment of properties such as conjugation, energy levels, and crystal orientation through molecular design, which could fine-tune the performance of photo-responsive transistor memory devices. This study consists of two sections. In the first section, a series of triarylamine derivatives, including TTM, TTC, TTP, DTPm, and DTPmC, were synthesized. These derivatives were then subjected to oxidative polymerization to obtain polyarylamines. We investigated the effects of varying the polyarylamines’ conjugation ability, polarity, and coplanarity on the charge storage capability of the devices. The three polymers, PTTP, PTTC, and PDTPmC, were successfully synthesized. We found that all three PAA-based memory devices had the ability for voltage-driven hysteresis and light recovery and that the charge storage density highly correlates with the π-conjugating characteristic of the pendant groups of PAAs. Our testing revealed that PTTC and PTTP memory devices exhibited memory windows of 13 V and 44 V, respectively, whereas PDTPmC showcased an impressive 106 V. The PDTPmC memory device also exhibited non-volatility and satisfactory endurance, with a retention time of 104 s and maintaining an on/off ratio of 105 even after 200 writing-erasing cycles with the reduced voltage pulses of -30 V. In the second section, we developed the D-π-A-type conjugated ammonium iodides EATPCNI and EATPmCNI, which, when combined with PbI2, forms a two-dimensional perovskite crystal structure. We discovered that the protonation of pyrimidine groups in EATPmCNI results in the adsorption of polyiodides, rendering purification difficult. We mixed (EATPCNI)2PbI4 with the insulating polymer polymethyl methacrylate (PMMA) to create a floating-gate-type memory layer for use in phototransistor memories. The push-pull design of the conjugated chain ensures an appropriate energy level, reducing the energy barrier for hole migration between the perovskite and the charge transporting layer in comparison to other organic ammonium salts (e.g. OAI, PEAI) that are typically used in 2D perovskites. This feature resulted in shorter light response time and stronger photosensitivity. Additionally, the GIWAXS and XRD measurements revealed that the crystal packing is disordered, and the crystal size is very small, which contributes to the device strong non-volatility. The retention time can reach 2.4×105 s, and the endurance testing also revealed that WRER cycles can be conducted up to 105 times, demonstrating that this molecular design enables the memory to achieve simultaneously rapid photo-response, high photosensitivity, robust non-volatility, and exceptional endurance performance.