Reflective Photosensitive Pixel Structure for Thin Retinal Implants
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Solution Overview
Problem
Existing photosensitive pixel structures in implant systems face challenges in maximizing light absorption while maintaining a thin substrate for minimal invasivity and high resolution.
Innovation Solution
A photosensitive pixel structure is designed with a substrate having a reflective layer on its back surface, which increases light absorption without thickening the substrate. The reflective layer can comprise materials like aluminium, titanium, or buried oxide, and is optimized to enhance reflectivity and hermetic sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the thickness of the substrate is increased to increase light absorption, then the charge generation is improved, but the implant size increases and invasivity is reduced
Solution Approach 1:
The patent introduces a reflective layer at the back surface of the substrate to create an optical cavity effect. This adds a dimensional element (the reflective interface) that redirects photons back through the photosensitive layer, effectively increasing the optical path length without increasing the physical thickness of the substrate. The reflective layer creates a feedback mechanism where light that would otherwise be lost is reflected back for additional absorption opportunities.
2Measurement precision
If the size of individual pixels is reduced to increase resolution, then the detection precision is improved, but the light absorption per pixel is reduced
Solution Approach 1:
By incorporating a reflective layer at the substrate back surface, the patent creates an optical feedback path that increases the effective light absorption within each pixel. The reflective layer ensures that photons entering the pixel are more likely to be absorbed by bouncing them back through the photosensitive material, compensating for the reduced pixel size and maintaining adequate charge generation even in smaller pixels.
3Reliability
If the current density is increased to sufficiently stimulate residual cells, then the stimulation effectiveness is improved, but the charge delivery requirements increase
Solution Approach 1:
The reflective layer creates an optical feedback mechanism that increases the probability of photon absorption and electron-hole pair generation. This enhances the charge delivery efficiency by ensuring that more incident photons contribute to the photocurrent, thereby achieving the required current density for effective stimulation with optimized charge delivery.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The enhanced pixel structure achieves higher light absorption and charge generation, leading to improved stimulation of residual retinal cells, while maintaining a thin profile for implantability and increased resolution.
Implementation Method 1
a first material layer is provided at least partially on the back surface of the substrate, wherein that material layer comprises a reflective layer
Implementation Method 2
a fraction of the photons of that light pulse will be absorbed in the substrate and electron-hole pairs are generated by the photoelectrical effect within the substrate
Data Source
AI summary
The present invention refers to a photosensitive pixel structure comprising a substrate with a front surface and a back surface, wherein at least one photosensitive diode is provided on one of the surfaces of the substrate. A first material layer is provided at least partially on the back surface of the substrate, wherein the material layer comprises a reflective layer, in order to increase a reflectivity at the back surface of the substrate. Further, the present invention refers to an array and an implant comprising such a photosensitive pixel structure, as well as to a method to produce the pixel structure.