Heterojunction Bipolar Transistor with Sidewall-Defined Base Strap
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Solution Overview
Problem
Bipolar transistors and heterojunction bipolar transistors face challenges in achieving high transit frequency and maximum oscillation frequency due to parasitic capacitances and resistances, particularly collector-base capacitance and base resistance, which are not effectively reduced by existing technologies.
Innovation Solution
A transistor structure with a sidewall-defined conductive strap for linking the intrinsic base to the extrinsic base, along with a dielectric layer and trench isolation, is introduced to reduce collector-base capacitance and base resistance, and a dielectric spacer is used to minimize base-emitter capacitance, allowing for adjustable geometries to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bipolar transistor structures are used, then device complexity is low, but parasitic capacitances (collector-base capacitance Ccb and base-emitter capacitance Cbe) and base resistance Rb cannot be effectively reduced
Solution Approach 1:
The base region is segmented into intrinsic base and extrinsic base portions, separated by a dielectric layer. This segmentation allows independent optimization of each region's function while reducing parasitic capacitances and base resistance, directly improving transit frequency and maximum oscillation frequency.
Solution Approach 2:
A dielectric layer is introduced between the intrinsic and extrinsic base portions, adding a vertical dimension to the base structure. This dimensional change enables reduced collector-base capacitance and base resistance while maintaining electrical connection through a conductive strap, thereby improving high-frequency performance.
2Object-affected harmful factors
If dielectric layer and trench isolation are introduced to reduce parasitic capacitances, then collector-base capacitance and base resistance are reduced, but device structure becomes more complex
Solution Approach 1:
The harmful dielectric layer between the intrinsic and extrinsic base portions is extracted and removed. This eliminates the complexity associated with maintaining the dielectric layer while preserving its beneficial effect of reducing parasitic capacitances, as the intrinsic and extrinsic bases are now directly adjacent.
Solution Approach 2:
The trench isolation structure, initially introduced to reduce parasitic capacitances, is converted into a beneficial feature by allowing the intrinsic base to extend over it. This creates a natural separation between the intrinsic and extrinsic base regions, reducing parasitic effects while simplifying the overall structure by eliminating the need for additional dielectric layers.
3Object-affected harmful factors
If intrinsic base layer extends over trench isolation regions, then collector-base capacitance is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The crystalline structure parameter of the intrinsic base layer is changed by allowing it to extend over the trench isolation regions. This parameter change enables the intrinsic base to be formed in a more tolerant manner, reducing the need for high manufacturing precision while still achieving reduced collector-base capacitance.
Data Source
AI summary
Disclosed are embodiments of an improved transistor structure (e.g., a bipolar transistor (BT) structure or heterojunction bipolar transistor (HBT) structure) and a method of forming the transistor structure. The structure embodiments can incorporate a dielectric layer sandwiched between an intrinsic base layer and a raised extrinsic base layer to reduce collector-base capacitance Ccb, a sidewall-defined conductive strap for an intrinsic base layer to extrinsic base layer link-up region to reduce base resistance Rb and a dielectric spacer between the extrinsic base layer and an emitter layer to reduce base-emitter Cbe capacitance. The method embodiments allow for self-aligning of the emitter to base regions and further allow the geometries of different features (e.g., the thickness of the dielectric layer, the width of the conductive strap, the width of the dielectric spacer and the width of the emitter layer) to be selectively adjusted in order to optimize transistor performance.