隨著大數據時代的來臨，傳統計算機的馮紐曼架構（von Neumann architecture）因處理器與記憶體分離而面臨的傳輸瓶頸日益凸顯。類神經運算（Neuromorphic Computing）作為一種用於模擬人腦突觸可塑性（Synaptic Plasticity）的新型運算架構，因其運算與儲存並行性與低功耗特性，被視為解決此瓶頸的關鍵技術。本研究聚焦於二維Ruddlesden-Popper相有機-無機雜化鈣鈦礦（PEA₂PbI₍₄₋ₓ₎Brₓ），利用其層狀結構帶來的低能耗與優異的環境穩定性，開發高效能之人工突觸元件。本研究的核心貢獻在於系統性地探討了鹵素比例（I/Br ratio）對阻態切換（Resistive Switching, RS）機制的決定性影響。實驗發現，隨著溴（Br）含量的增加，元件的電性行為呈現從「電感性（Inductive）氧化還原切換」向「電容性（Capacitive）極化」的連續轉變。富含碘（Iodide-rich）的元件展現了典型的雙極性切換行為，其開關比（ON/OFF ratio）高達10⁴，並成功模擬了脈衝相依可塑性（SNDP,SVDP,SDDP,SFDP）。相對地，富含溴（Bromide-rich）的元件則表現出顯著的順時針電容迴圈，顯示極強的離子屏蔽效應。基於上述實驗結果，本研究提出了一套「離子動力學通用模型」（Universal Ion-Kinetics Model）。該模型結合了Kröger-Vink缺陷化學理論與離子遷移機制，闡明了在低電壓區由離子位移主導的介電極化，與高電壓區由碘空缺VI•成核主導的導電通道生長之間的競爭關係。此外，透過改變掃描速率（Scan-rate dependent）實驗，本研究進一步證實了導電通道的形成受限於動力學時間尺度（Kinetic time-scale）。此發現為解決混合鹵素鈣鈦礦在人工突觸元件應用中的問題提供了重要的證據。

Mixed ionic-electronic conduction in metal halide perovskites has attracted considerable attention for neuromorphic computing because ion migration enables analog conductance modulation similar to biological synapses. In this study, two-dimensional Ruddlesden–Popper (RP) mixed-halide perovskites, PEA₂Pb(I₄₋ₓBrₓ) (x = 0–4), were employed as the active layer to fabricate Au/PEA₂Pb(I₄₋ₓBrₓ)/FTO artificial synaptic devices. The influence of halide composition on crystal structure, electrical characteristics, and synaptic plasticity was systematically investigated.
Electrical measurements demonstrated that the iodide-rich device exhibited stable bipolar resistive switching with an ON/OFF ratio of approximately 10⁴ and a read current of 10⁻⁷ A. In contrast, increasing the Br content gradually suppressed resistive switching and transformed the hysteresis from inductive to capacitive behavior. Furthermore, scan-rate-dependent measurements indicated that slower voltage sweeping promoted conductance modulation, whereas fast voltage sweeping mainly resulted in capacitive polarization due to insufficient ionic migration.
The fabricated devices successfully emulated various synaptic functions, including spike-number-dependent plasticity (SNDP), spike-voltage-dependent plasticity (SVDP), spike-duration-dependent plasticity (SDDP), and spike-frequency-dependent plasticity (SFDP). The PEA₂PbI₄ device exhibited the largest synaptic weight modulation, while Br-rich devices showed lower energy consumption but reduced conductance variation.
Based on the experimental observations and previous reports on ion migration and halide redox chemistry, a Universal Ion-Kinetics Model is proposed. Under low electric fields, the device behavior is dominated by ionic polarization. At higher electric fields, selective iodide oxidation generates iodine vacancies that gradually accumulate to form vacancy-mediated conductive pathways. The resulting defect-assisted hopping transport continuously modulates device conductance, accounting for both resistive switching and analog synaptic behavior. This work demonstrates that halide composition engineering provides an effective strategy for regulating ionic kinetics and optimizing two-dimensional perovskite neuromorphic devices.

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