Self-Aligned Bipolar Transistor Base and Emitter Structure
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Solution Overview
Problem
Existing bipolar junction transistor structures and fabrication methods lack improvements for enhanced performance and efficiency.
Innovation Solution
A device structure for a bipolar junction transistor is developed, featuring a trench isolation region, a collector, a base layer with inclined sections, and an emitter positioned on one section of the base layer, along with an extrinsic base layer on another section, where the extrinsic base layer's side surface is inclined away from the emitter, and a method for forming this structure using epitaxial growth and selective doping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional planar base layer structure is used, then the fabrication process is simple, but the emitter-base capacitance is high which limits transistor performance
Solution Approach 1:
The base layer is divided into two distinct sections: an intrinsic base layer and an extrinsic base layer. The extrinsic base layer has a side surface that is inclined relative to the top surface of the base layer, creating a stepped configuration. This segmentation allows the emitter to be positioned such that it overlaps with the intrinsic base layer while the extrinsic base layer provides a larger surface area for electrical contact, thereby reducing emitter-base capacitance while maintaining fabrication feasibility through selective epitaxial growth.
2Reliability
If the base layer surface area is increased to reduce capacitance, then emitter-base capacitance decreases, but the device area increases
Solution Approach 1:
Instead of increasing the base layer area in the planar direction, the invention utilizes the vertical dimension by creating an inclined side surface on the extrinsic base layer. This three-dimensional configuration allows the extrinsic base layer to extend vertically and laterally, providing a larger effective surface area for electrical contact with the emitter without significantly increasing the device footprint. The inclined surface creates additional contact area while maintaining a compact device layout.
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 configuration enhances electrical conductivity and reduces emitter-base capacitance, leading to improved control of collector-emitter current and overall performance of the transistor.
Implementation Method 1
a method for forming this structure using epitaxial growth and selective doping
Data Source
AI summary
Device structures and fabrication methods for a bipolar junction transistor. A trench isolation region surrounds an active region that includes a collector. A base layer includes a first section and a second section that are located over the active region. An emitter is positioned on the first section of the base layer, and an extrinsic base layer is positioned on the second section of the base layer. The extrinsic base layer has a side surface adjacent to the emitter. The side surface of the extrinsic base layer is inclined relative to a top surface of the base layer in a direction away from the emitter.