Monocrystalline Base Transistor Structure for Low RF Capacitance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing transistors, such as heterojunction bipolar transistors (HBTs), face challenges in achieving low collector-base capacitance and base resistance while maintaining high frequency handling capabilities, particularly in RF applications.
Innovation Solution
A semiconductor die with a transistor structure that includes an intrinsic base grown in a cavity within a monocrystalline semiconductor material, using a seed layer for the extrinsic base formation, which allows for self-alignment of the collector and emitter regions and reduces surface damage from ion implantation, enabling a monocrystalline path for lower resistance and capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional HBT structures are used, then high frequency handling capability is achieved, but collector-base capacitance and base resistance remain high
Solution Approach 1:
The base region is segmented into intrinsic and extrinsic portions, with the intrinsic base grown in a cavity to be fully depleted and contribute to capacitance reduction, while the extrinsic base provides low-resistance contact paths. This segmentation allows simultaneous optimization of both capacitance and resistance parameters.
Solution Approach 2:
Different regions of the base are given different properties: the intrinsic base region is designed to be fully depleted with high purity for low capacitance, while the extrinsic base region maintains higher doping for low resistance. The collector and emitter are self-aligned to create optimal local electric field distributions for high-frequency operation.
2Manufacturing precision
If ion implantation is used for doping, then doping precision is improved, but surface damage increases
Solution Approach 1:
The harmful ion implantation step is extracted and replaced with in-situ doped epitaxial growth for the intrinsic base. This removes the surface damage problem while maintaining precise doping control through the epitaxial process, which can precisely control dopant incorporation during crystal growth.
Solution Approach 2:
The epitaxial growth process serves as an intermediary method that achieves doping without direct ion implantation. By incorporating dopants during the epitaxial growth of the intrinsic base, the process achieves precise doping profiles without the damaging effects of ion bombardment on the crystal lattice.
3Ease of manufacture
If collector and emitter are not self-aligned, then manufacturing complexity is reduced, but alignment precision deteriorates
Solution Approach 1:
The collector and emitter structures are preliminarily formed with self-alignment during the epitaxial growth process. The intrinsic base is grown in a cavity that is defined by the collector structure, and the emitter is subsequently formed aligned to this cavity. This preliminary structuring ensures precise alignment without requiring complex post-growth alignment steps.
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 approach results in transistors with reduced collector-base capacitance and base resistance, enhancing high-frequency performance and power efficiency in RF applications.
Implementation Method 1
an intrinsic base of monocrystalline semiconductor material grown in an opening of a first semiconductor layer
Implementation Method 2
reduces surface damage from ion implantation
Data Source
AI summary
A semiconductor die includes a transistor with an emitter, base, and collector. The base includes an intrinsic base that is located in monocrystalline semiconductor material grown in an opening of a first semiconductor layer. A second semiconductor layer is located above the first semiconductor layer and includes a monocrystalline portion. In some embodiments, an opening was formed in the second semiconductor layer wherein a portion of the underlying first semiconductor layer was etched to form a cavity in which a monocrystalline intrinsic base was grown.