Vertical BJT Double Base Structure for Current Gain
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Solution Overview
Problem
The existing CMOS process for manufacturing vertical NPN BJT devices is limited in achieving optimal current gain due to fixed thickness and width of the base layer, restricting the DC performance of the device.
Innovation Solution
A vertical bipolar junction transistor is designed with first and second collector areas in different epitaxial layers, an emitter area interposed between them, and a double base structure formed over these layers to enhance current flow, allowing for increased current gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single base layer is used in the vertical BJT device, then the manufacturing process is simple, but the current gain cannot be optimized
Solution Approach 1:
The base region is divided into two separate base layers (first base layer and second base layer) with different doping types and concentrations. This segmentation allows each base layer to be independently optimized for specific functions: the first base layer controls electron injection while the second base layer controls hole injection, thereby achieving optimized current gain without significantly complicating the manufacturing process
2Ease of manufacture
If the base layer thickness and width are fixed by the manufacturing process, then the manufacturing is straightforward, but the optimal current gain cannot be achieved
Solution Approach 1:
Different regions of the base structure are assigned different doping types (P-type and N-type) and doping concentrations. The first base layer has P-type doping while the second base layer has N-type doping, creating local quality variations that enable independent optimization of electron and hole transport properties, thereby achieving optimal DC performance while maintaining manufacturing feasibility
3Reliability
If a double base structure is implemented, then the collector current gain is significantly increased, but the device complexity increases
Solution Approach 1:
The double base structure is integrated into the existing vertical BJT architecture by combining the first and second base layers within the same device structure. The emitter connects to both base layers, and the collector collects carriers from both bases, merging multiple functions into a unified structure that achieves high current gain without requiring separate devices
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 double base structure in the vertical BJT device significantly increases the collector current gain compared to similar-sized related BJTs, improving the device's DC performance by allowing collector current to flow both up and down.
Implementation Method 1
A first collector area may be formed by implanting first impurity type ions into the substrate
Implementation Method 2
Second impurity type impurities may be implanted into the first epitaxial layer
Implementation Method 3
A p-well may be formed by implanting the second impurity type impurities into the second epitaxial layer
Data Source
AI summary
A vertical BJT which has a maximal current gain for a photodiode area. According to embodiments, since the BJT can be formed together with the photodiode, and collector current flows up and down based on the double base structure, the magnitude of the current may be increased.