Backside Illuminated Photosensor Light Mirror and Guide Structures
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Solution Overview
Problem
Conventional backside illuminated photosensor elements face limitations in sensitivity due to the angle of incidence and reflection of photons, which reduces the opportunity for electron/hole pair generation.
Innovation Solution
Incorporating a backside light mirror with a pupil opening and an underside reflective surface, or a backside light guide with a frustoconical aperture filled with transparent materials, to reflect light back into the active region, enhancing photon interaction and increasing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional backside illuminated photosensor elements are used, then the structure is simple and manufacturing is easier, but sensitivity is reduced due to angle of incidence and reflection limitations
Solution Approach 1:
A light guide layer is introduced as an intermediary component between the back surface and the active region. This light guide layer includes a light pipe structure that mediates the path of incident light, redirecting it multiple times through total internal reflection to increase the probability of photon absorption and electron-hole pair generation in the active region, thereby improving sensitivity without fundamentally changing the photosensor's core structure
Solution Approach 2:
The light pipe structure utilizes three-dimensional spatial arrangement with frustoconical apertures and light guide pathways that extend vertically from the back surface through the substrate. This adds a vertical dimension to light interaction, allowing light to traverse multiple paths and increase interaction length within the active region, thereby enhancing sensitivity
2Reliability
If light is reflected at shallow angles, then reflection efficiency is reduced, but adding light mirror structures increases device complexity
Solution Approach 1:
The light pipe structure employs curved frustoconical aperture walls and angled light guide surfaces instead of flat planar mirrors. These curved and angled surfaces are designed to optimize total internal reflection geometry, ensuring that light rays incident at various angles are effectively redirected into the active region with maximum efficiency, thereby improving sensitivity while maintaining manufacturing feasibility
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 solution significantly enhances the sensitivity of the photosensor elements by increasing the opportunities for photon-induced electron/hole pair generation, improving the overall performance of the imaging array.
Implementation Method 1
a backside light guide with a frustoconical aperture filled with transparent materials, to reflect light back into the active region
Implementation Method 2
including an underside reflective surface configured to reflect light received from the active region back into the active region
Implementation Method 3
increasing the opportunities for electron/hole pair generation
Data Source
AI summary
A photosensor is formed within a semiconductor substrate layer having a front side and a back side. An isolation structure delimits an active region of the semiconductor substrate layer which includes a charge collecting region. The front side of semiconductor substrate layer includes a charge transfer circuit. A reflecting mirror is mounted at the back side of the semiconductor substrate layer. The reflecting mirror includes a pupil opening configured to admit light into the active region at the back side. An underside reflective surface of the reflecting mirror is configured to reflect light received from the active region back into the active region.