Strained Silicon Photo Detector for CMOS Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Implementing high-performance optical detectors on silicon chips is challenging due to lattice constant differences and high doping levels in CMOS processes, leading to limited frequency response and responsivity, and existing solutions like deep trenches or additional semiconductor layers are costly and yield-reducing.
Innovation Solution
A photo detector device utilizing a strained silicon layer with a silicon-nitride or silicon-germanium first layer, integrated within a silicon on insulator (SOI) technology, which enhances electron and hole mobility and allows for longer wavelength light absorption without process modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high doping levels are used in CMOS PN-junctions, then the detector can be manufactured using standard CMOS processes, but the depletion width becomes very narrow (50-100 nm) leading to very high junction capacitances that severely limit the frequency response
Solution Approach 1:
The patent changes the doping parameter from high doping levels to very low doping levels (10^14 to 10^16 atoms/cm³), which increases the depletion width from 50-100 nm to several micrometers. This parameter change reduces junction capacitance and improves frequency response while maintaining CMOS compatibility through the specific doping concentration range.
Solution Approach 2:
The patent transitions from planar junction detectors to deep trench detectors, adding a vertical dimension to the detector structure. The trenches extend 5-20 micrometers into the silicon substrate, creating a three-dimensional detection volume that increases absorption length while maintaining low capacitance through the trench geometry.
2Ease of manufacture
If high doping levels are used in CMOS PN-junctions, then the detector can be manufactured using standard CMOS processes, but the small volume available for photon absorption results in very small responsivity
Solution Approach 1:
The patent uses deep trenches extending 5-20 micrometers into the silicon substrate, creating a vertical detection volume that significantly increases the photon absorption path length. This dimensional change from planar to vertical structure enables high responsivity while maintaining compatibility with standard CMOS manufacturing processes.
Solution Approach 2:
The patent changes the doping concentration parameter to very low levels (10^14 to 10^16 atoms/cm³), which expands the depletion region volume available for photon absorption. This parameter change directly increases the interaction volume between photons and charge carriers, thereby improving responsivity.
3Speed
If deep trenches are used as optical detectors, then depletion width and absorption length are decoupled with depletion forming on sidewalls and absorption perpendicular to wafer surface, but the large capacitance for practical detector area and requirement for process modifications increase cost and decrease yield
Solution Approach 1:
The patent modifies the doping parameter to very low concentrations (10^14 to 10^16 atoms/cm³) that can be achieved through standard CMOS process steps, eliminating the need for special process modifications. This parameter adjustment allows deep trench detectors to be manufactured using existing CMOS technology without compromising yield or increasing cost.
4Manufacturing precision
If additional semiconductor layers are added onto the CMOS layer stack to form a detector, then high performance detectors are feasible, but the process complexity and cost increase significantly
Solution Approach 1:
The patent uses uniformly doped silicon throughout the detector structure, eliminating the need for heterogeneous material layers such as InGaAs or Ge. This homogeneous silicon-based approach maintains compatibility with standard CMOS processes while achieving high detector performance through optimized doping profiles and deep trench geometry.
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 strained silicon photo detector achieves higher charge mobility and responsivity, enabling improved performance for optical communication and compatibility with electronic circuits on the same chip, while maintaining cost-effectiveness and yield.
Implementation Method 1
Photo detectors are devices that convert optical signals into electrical signals
Implementation Method 2
the second layer comprises strained silicon. The second layer further comprises a light absorption region located substantially within the strained silicon
Data Source
AI summary
A photo detector device comprising a first layer comprising a first material, and a second layer arranged adjacent to the first layer, the second layer comprising strained silicon, wherein the second layer further comprises a light absorption region located substantially within the strained silicon, wherein the first or the second layer is arranged on a substrate.