Reticulated Shallow Etch Mesa Isolation for Infrared Sensors
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Solution Overview
Problem
Existing semiconductor photodiode designs face challenges with surface leakage currents, particularly in infrared sensors, due to band bending and surface states, which degrade performance and increase noise in small-pitch photodiode arrays, where chemical passivation is difficult and gate electrode methods are impractical.
Innovation Solution
The reticulated, shallow etched mesa isolation (RSEMI) structure modifies the mesa sidewall profile by forming a shoulder within the semi-intrinsic layer, increasing the path length for surface electrons and creating a significant electron barrier, thereby blocking majority carriers and reducing surface leakage without the need for chemical passivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep etch isolation is used to isolate pixels, then pixel isolation is improved, but surface leakage current increases due to exposed narrow gap material
Solution Approach 1:
The invention introduces a lateral dimension modification by forming a shoulder structure on the mesa sidewall. This shoulder creates an extended path length in the lateral direction that surface electrons must traverse, effectively increasing the tunneling barrier width without deepening the etch. The shoulder width is designed to be at least 1.5 micrometers, providing sufficient lateral separation to block surface leakage while maintaining shallow etch depth.
Solution Approach 2:
The shoulder structure is formed within the semi-intrinsic layer before final device operation. This preliminary structural modification creates the electron blocking barrier in advance, preventing surface leakage current generation at the source. The shoulder is formed by selective etching or deposition processes that modify the mesa profile prior to device fabrication completion.
2Object-generated harmful factors
If shallow etch isolation is used to reduce surface leakage, then surface leakage current is reduced, but pixel isolation may be insufficient
Solution Approach 1:
The invention compensates for shallow etch depth by introducing lateral separation through the shoulder structure. While the etch depth remains shallow (not reaching the bottom contact), the shoulder creates a lateral barrier that extends the isolation path. This dimensional transformation allows adequate pixel isolation to be achieved through lateral rather than vertical separation.
3Object-generated harmful factors
If chemical passivation is used to reduce surface leakage, then surface leakage current is reduced, but manufacturing complexity increases
Solution Approach 1:
The shoulder structure creates a self-blocking barrier against surface leakage without requiring additional passivation materials or chemical treatment steps. The geometric configuration of the shoulder itself provides the electron blocking function, allowing the structure to serve its own isolation purpose without external assistance from complex chemical passivation processes.
4Object-generated harmful factors
If gate electrode methods are used to reduce surface leakage, then surface leakage current is reduced, but device complexity and cost increase
Solution Approach 1:
The shoulder structure provides intrinsic electron blocking through its geometric configuration and material properties alone, without requiring external gate electrodes or additional control structures. The semi-intrinsic layer combined with the shoulder geometry creates a self-sufficient barrier that eliminates the need for complex gate electrode systems.
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
RSEMI effectively reduces surface leakage currents while maintaining pixel isolation, improving noise characteristics and spatial resolution in infrared sensors, with a greater than 100-fold increase in surface resistivity compared to conventional deep etch isolated structures.
Implementation Method 1
the position of the Fermi level (EF) relative to its intrinsic value (Ei) may be significantly displaced from that in the bulk, resulting in bending of the electronic energy bands
Implementation Method 2
large densities of surface states, arising from unterminated bonds on the surface of the semiconductor
Implementation Method 3
creating a significant electron barrier, thereby blocking majority carriers and reducing surface leakage
Data Source
AI summary
A device including an absorber layer that can be deposited on top of a bottom contact layer. Furthermore, a semi-intrinsic layer with an energy gap wider than that of the absorber layer can be deposited on top of the absorber layer. A top contact layer can be deposited on top of the semi-intrinsic layer. A conduction band and a valence band energy alignment can be positioned between the absorber layer and the top contact layer, and configured to allow photoexcited minority carriers to be collected while the flow of majority carriers from the absorber are blocked. At least one mesa can be formed by processing and removing layered materials to a depth at least near the bottom of the absorber layer. Finally, a shoulder can be formed in the at least one mesa within the semi-intrinsic layer by processing and removing the layered materials.