## 4 Discussion and Conclusions  
In this study, a vertical high-density SiNW photodetector was fabricated and integrated into a switched capacitor stimulator circuit for retinal prosthesis applications. SiNW arrays with a diameter of 300 nm were fabricated in multiple layers using a simplified and modified DRIE process. This fabrication process enabled the creation of high-density SiNW configurations with finite dimensions. The electrical and optical characteristics of the SiNW photodetector were measured to assess its feasibility for retinal prosthesis applications. The linear I-V characteristics confirmed the formation of an ohmic contact between the Ti/Al electrodes and the silicon device layer. The optical properties demonstrated that higher current amplitudes can be generated under the same illumination conditions as the vertical density of the SiNW layers increased, owing to the increased light absorption and enhanced photoelectric response. The SiNW photodetector developed in this study achieves superior photoresponsivity and sensitivity in a smaller area due to its vertically stacked structure. This makes it advantageous for miniaturized applications such as retinal implants. The lower dark current of 56 nA, compared to 100-178 nA in previous studies [35], provides higher sensitivity under the same photocurrent conditions. The fabricated device operated effectively under various lighting conditions and was particularly sensitive to low light intensity. Moreover, it exhibited excellent photoresponsivity, exceeding 10\({}^{5}\) A/W across the wavelength range of 400-800 nm. The SiNW photodetectors were integrated with a switched capacitor stimulator circuit, demonstrating that the stimulation current increased proportionally with the light intensity and SiNW density. The stimulus currents were effectively controlled by adjusting the charging time and load resistance. The in vitro experiments, which were measured electrically, evoked neural responses from retinal cells, indicating that more neural spikes were evoked as the light intensity and SiNW density increased. Notably, these findings demonstrate that high photosensitivity was ensured even at low light intensities, with its benefits becoming especially evident under typical indoor conditions. This study provides guidelines for the integration of SiNW photodetector systems, serving as a test bench that can contribute to the advancement of direct implantable integrated retinal prosthesis systems. The integration of vertical high-density vertically stacked SiNW photodetectors with a switched capacitor stimulator circuit presents considerable potential in high-resolution retinal prosthesis applications. [PERSON] supervised the study; [PERSON] and [PERSON] designed and fabricated the device; [PERSON] and [PERSON] conducted the experiments; [PERSON], [PERSON] and [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript. This research was supported by the MSIT (Ministry of Science and ICT), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2024-RS-2024-00438239), supervised by the IITP (Institute for Information and Communications Technology Planning and Evaluation). Not applicable. * [PERSON] et al. (2022) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Age-Related Macular Degeneration: Epidemiology, Genetics, Pathophysiology, Diagnosis, and Targeted Therapy. _Genes Dis._**2022**, \(9\), 62-79. [CrossRef]
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