Phototransistor Floating Base Junction Encapsulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Phototransistors face challenges in achieving high sensitivity and low amplification noise while maintaining high speed and gain stability, especially in low light level sensing applications, where existing designs struggle with optimal junction configurations and dielectric encapsulation.
Innovation Solution
A phototransistor design featuring a floating base with p-n junctions between the emitter and base, and base and collector, fully encapsulated by the emitter and collector with a dielectric, such as dry thermal oxide or high-k dielectric, which are in direct physical contact and have minimized capacitance and current density ratios, eliminating type-II hetero-structures and current crowding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the phototransistor uses conventional junction configurations with type-II hetero-structures, then the device can achieve higher current density and faster response, but the sensitivity and noise performance deteriorate
Solution Approach 1:
The patent changes the junction configuration parameters by eliminating type-II hetero-structures and using homojunctions instead. This parameter change in the semiconductor structure achieves lower noise and improved sensitivity while maintaining acceptable response characteristics through optimized doping profiles and junction geometries
2Measurement precision
If the phototransistor uses conventional dielectric encapsulation methods, then the manufacturing process is simpler, but the capacitance of the junctions increases leading to higher noise
Solution Approach 1:
The patent applies thin film dielectric encapsulation layers that directly contact the semiconductor junctions. These thin films provide electrical isolation and protection while minimizing capacitance due to their reduced thickness, thereby lowering noise without requiring complex manufacturing processes
3Measurement precision
If the phototransistor junctions have larger area to improve light collection, then the sensitivity increases, but the capacitance increases leading to slower response and higher noise
Solution Approach 1:
The patent applies local quality by creating non-uniform doping profiles and varying junction geometries in different regions. The emitter and collector regions have optimized local properties that maximize light absorption and carrier collection efficiency while keeping the depletion region areas small to maintain low capacitance
4Stability of the object's composition
If the phototransistor uses floating base configuration, then the gain stability improves, but the manufacturing precision requirements increase
Solution Approach 1:
The patent merges the base region into a floating configuration where the base is not directly connected to external terminals. This combining of the base function into the intrinsic device structure simplifies the external connection requirements and reduces manufacturing precision demands while maintaining gain stability through the floating base operation mode
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 design enhances sensitivity and noise reduction, achieving a photo-response 3-dB bandwidth greater than 10 Hz and transition frequency greater than 100 Hz under low light conditions, with reduced capacitance and current density, improving performance in low light level sensing applications.
Implementation Method 1
the floating base, a p-n junction between the emitter and base (E-B junction) and a p-n junction between the base and the collector (B-C junction) are collectively in direct physical contact only with and completely encapsulated only by the emitter, the collector, and a section of a dielectric
Implementation Method 2
Phototransistors may be integrated into an image sensor, which is a device that converts an optical image into an electronic signal
Data Source
AI summary
Disclosed herein is a phototransistor (PT) comprising an emitter, a collector and a floating base; wherein the floating base, a p-n junction between the emitter and base (E-B junction) and a p-n junction between the base and the collector (B-C junction) are collectively in direct physical contact only with and completely encapsulated only by the emitter, the collector, and a section of a dielectric. Under an operating condition of the PT, a DC current density averaged over the E-B junction or a DC current density averaged over the B-C junction may be at least 100 times of a DC current density averaged over an opto-electronically active region of the PT. A sum of a capacitance of the E-B junction and a capacitance of the B-C junction may be less than 1 fF.