Photo Transistor Grating Light Concentration
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Solution Overview
Problem
Photo transistors struggle to function at reduced light levels or with thin layers, as incident light may not generate sufficient charge density to switch the transistor, particularly in CMOS SOI technology.
Innovation Solution
A diffraction pattern or grating is used to concentrate electromagnetic radiation in the light-sensitive area of the photo transistor, enhancing its sensitivity and allowing operation with thin layers by focusing optical energy and forming a conductive channel for charge switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thin layers are used for light absorption in CMOS SOI technology, then device integration density is improved, but the incident light cannot generate sufficient charge density to switch the transistor
Solution Approach 1:
The patent introduces a grating structure that manipulates light in the lateral dimension (x-y plane) to concentrate optical energy vertically into the thin absorption layer. The grating period and geometry are designed to create diffraction orders that focus light at specific depths within the thin layer, enabling sufficient charge generation despite reduced thickness.
Solution Approach 2:
The patent modifies the optical parameters by introducing a periodic grating structure with specific period, depth, and duty cycle parameters. These geometric parameters are optimized to enhance light-matter interaction in the thin layer, creating localized fields that increase charge carrier generation efficiency without requiring thicker layers.
2Area of moving object
If feature size is reduced to increase integration density, then device scaling is improved, but light concentration in the light-sensitive region becomes insufficient
Solution Approach 1:
The grating structure introduces asymmetric geometric features with different widths, depths, or orientations that create directional light concentration. This asymmetric design allows the grating to focus light preferentially into the reduced feature size region, compensating for the smaller area by increasing intensity through controlled diffraction and field enhancement.
3Reliability
If a grating pattern is added to concentrate light, then light sensitivity is improved, but device structure complexity increases
Solution Approach 1:
The grating structure is designed to serve multiple functions: it concentrates light into the thin absorption layer, defines the active region geometry, and can be integrated with existing CMOS fabrication processes. By combining these functions into a single structure, the patent minimizes additional complexity while achieving enhanced light sensitivity.
4Ease of manufacture
If standard transistor structures are used without optimization, then manufacturing ease is maintained, but optical performance is insufficient
Solution Approach 1:
The patent segments the transistor structure by introducing a grating pattern that divides the light incident area into multiple diffraction zones. This segmentation allows standard transistor fabrication processes to be used while the grating segments the optical path to achieve enhanced light concentration, effectively decoupling manufacturing simplicity from optical performance.
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
This solution enables photo transistors to operate effectively at reduced light levels and with decreasing feature sizes, maintaining sensitivity and efficiency without requiring process modifications, supporting the use of sub-wavelength gratings and optimizing charge enrichment in the depletion/inversion layer.
Implementation Method 1
a diffraction pattern or grating is used to concentrate electromagnetic radiation in the light-sensitive area of the photo transistor
Data Source
AI summary
The photo detector (100, 300, 500, 600, 700, 900) comprises a photo transistor (102, 902). The photo transistor has a light sensitive region (112, 910) for controlling the transistor action of the photo transistor. The photo detector further comprises a dielectric layer (118). The dielectric layer is in contact with the photo transistor. The photo detector further comprises a grating pattern (114, 604, 914, 1010) in contact with the dielectric layer. The grating layer and the dielectric layer are adapted for focusing electromagnetic radiation in the light sensitive region.