隨著人工智慧 (AI) 和數據驅動應用的迅速發展，對高速、高密度及高能效記憶體技術的需求日益迫切。然而，傳統馮·諾依曼 (von Neumann) 運算架構在處理器與記憶體之間存在物理分離，導致頻繁的資料搬移、延遲及功耗上升，嚴重限制系統效能。為了克服這些挑戰，記憶體內運算 (In-Memory Computing, IMC) 被視為具潛力的解決方案，可直接於記憶體陣列中進行資料處理，進而降低延遲與能耗。
儘管中央處理器 (CPU)、圖形處理器 (GPU) 及張量處理器(TPU) 在高效能運算中扮演重要角色，隨著摩爾定律接近極限，其可擴展性逐漸受限。此外，電子資料傳輸本質上仰賴電荷載子的移動，易產生電阻性損耗及熱耗散。相較之下，光子運算以光子作為資訊載體，具備高速、寬頻與遠距傳輸的可靠性，能在低熱效應下實現高效率資料傳輸。
本研究以矽光平台為基礎，開發多種高折射率微縮電阻式記憶體 (ReRAM) 光學整合元件，實現光非揮發性及多階調變功能，稱為「光記憶體」，亦可視為光憶阻器(Optical memristor)。整體設計共包含五種光記憶體結構，分別編碼為Optical Memory 1至Optical Memory 5。其中，Optical Memory 1至3整合於矽光波導，並以Optical Memory 3為重點，透過類crossbar結構將三顆微縮Ag/Al2O3/TiOx/ITO記憶體整合至光波導路徑，模擬多級存取行為。依據ReRAM導電燈絲的建立數，定義不同邏輯狀態L0 (初始)至L3。實驗顯示，在電源關閉條件下，相較於初始狀態，消光比隨導電燈絲數目增加而顯著提升，分別達6.34dB (76.7%)、11.73dB (93.2%) 及13.24dB (95.2%)，且共振頻譜呈現明顯波長位移。
由於Optical Memory 1至3並無波長循址能力，光頻譜的觀察主要依賴特定頻譜特徵辨識。為了實現多波長位址與平行資料傳輸，研究進一步將矽光被動元件設計為環形共振器，並採用多模干涉(MMI)結構的自成像原理，取代傳統以耦合間隙(gap)實現的直接耦合方式，以展寬頻寬並提升製程容忍度。
所製作之50 µm、100 µm及串聯雙環結構，因MMI強耦合效應，皆展現較大的自由光譜範圍(FSR，9.91-16.86nm)，有助於提升記憶體讀取分辨性與通道間隔，並具備較寬的半高全寬(FWHM)，有利於提升資料吞吐量與操作穩定性。
接著，進一步將Ag/Al2O3/BFO/ITO EFS結構微縮記憶體嵌入環形共振器進行光調變，其中Optical Memory 4採用單環100 µm結構，具備0.91nm的FWHM，為所有設計中頻寬表現最優，有助於在資料運行時支援高速訊號傳遞並保持低失真，因而選定作為被動元件整合平台。實驗顯示，相較初始狀態，透過銀離子燈絲調變可達8.81dB(86.8%)之消光比調製深度。另外，Optical Memory 5則採用串聯雙環結構整合ReRAM，實現多階可循址的非揮發性光記憶調變。相較最初狀態，L1及L2分別呈現4.72nm與5.49nm之波長偏移，並達6.44dB(77.3%)及8.73dB(86.6%)的消光比變化，其多階可波長循址的非揮發性光記憶特性與高效調變性能，為記憶資料處理提供了支持資料並行與高通量操作的潛力。

With the rapid development of artificial intelligence(AI) and data-driven applications, the demand for high-speed, high-density, and energy-efficient memory technologies has become increasingly urgent. However, the traditional von Neumann computing architecture features a physical separation between processors and memory, resulting in frequent data transfers, increased latency, and rising power consumption, which severely limit overall system performance. To address these challenges, in-memory computing (IMC) has been regarded as a promising solution, enabling data processing directly within memory arrays to reduce latency and energy consumption.
Although central processing units (CPUs), graphics processing units (GPUs), and tensor processing units (TPUs) play vital roles in high-performance computing, their scalability has gradually become constrained as Moore’s Law approaches its limit. Additionally, electronic data transmission inherently relies on the movement of charge carriers, which inevitably leads to resistive losses and thermal dissipation. In contrast, photonic computing employs photons as information carriers, offering high speed, broad bandwidth, and reliable long-distance transmission, thereby enabling high-efficiency data transfer with minimal thermal effects. This study utilizes a silicon photonic platform to develop various high-refractive-index miniaturized resistive memory(ReRAM)optical integration devices, realizing non-volatile and multi-level modulation capabilities referred to as “optical memory,” which can also be considered optical memristors. The overall design includes five optical memory structures, designated as Optical Memory 1 through Optical Memory 5. Among them, Optical Memory 1 to 3 are integrated on silicon waveguides, with Optical Memory 3 as the focus, employing a crossbar-like configuration to integrate three miniaturized Ag/Al2O3/TiOx/ITO memory cells along the waveguide path to emulate multi-level storage behavior. Different logic states, L0 (initial) through L3, were defined based on the number of conductive filaments formed in the ReRAM. Experimental results showed that under power-off conditions, compared to the initial state, the extinction ratio significantly increased with the number of conductive filaments, reaching 6.34 dB (76.7%), 11.73dB (93.2%), and 13.24dB (95.2%), respectively, accompanied by pronounced spectral wavelength shifts.
Since Optical Memory 1 to 3 lack wavelength addressing capability, their optical spectra were primarily identified through characteristic spectral features. To achieve multi-wavelength addressing and parallel data transmission, this work further designed the silicon photonic passive elements as ring resonators and adopted a multimode interference (MMI) structure based on self-imaging principles to replace the conventional direct coupling gap, thereby broadening the operational bandwidth and enhancing fabrication tolerance.
The fabricated 50 µm, 100 µm, and cascaded dual-ring structures exhibited larger free spectral ranges (FSRs) of 9.91-16.86nm due to the strong coupling effect of the MMI, which contributes to improved readout resolution, channel spacing, and wider full-width at half-maximum (FWHM), facilitating higher data throughput and operational stability.
Subsequently, miniaturized Ag/Al2O3/BFO/ITO EFS memory devices were embedded within the ring resonators for optical modulation. Among them, Optical Memory 4 utilized a single 100 µm ring structure with an FWHM of 0.91nm, achieving the best bandwidth performance among all designs, thereby supporting high-speed signal transmission with low distortion during data operation, and was thus selected as the integration platform for passive devices. Experimental results demonstrated an extinction ratio modulation depth of 8.81dB (86.8%) relative to the initial state by modulating silver ion filaments. In addition, Optical Memory 5 employed a cascaded dual-ring structure integrated with ReRAM to realize multi-level, wavelength-addressable, non-volatile optical memory modulation. Compared to the initial state, L1 and L2 exhibited wavelength shifts of 4.72nm and 5.49nm, respectively, and extinction ratio changes of 6.44dB (77.3%) and 8.73dB (86.6%). These multi-level, wavelength-addressable non-volatile optical memory characteristics and efficient modulation performance provide promising potential for supporting parallel data processing and high-throughput operations.

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