Monocrystalline Extrinsic Base HBT Structure for Lower Capacitance
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Solution Overview
Problem
Conventional heterojunction bipolar transistors (HBTs) face challenges with high base resistance due to polycrystalline silicon extrinsic base regions, which lead to increased base resistance and base-collector junction capacitance, affecting their performance in high-frequency applications.
Innovation Solution
The formation of a monocrystalline extrinsic base region, separated from the collector region by dielectric layers, reduces base resistance and capacitance, achieved through epitaxial growth and selective epitaxial processes, allowing for higher doping concentrations in the collector region without dopant diffusion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polycrystalline silicon extrinsic base region is used in conventional HBTs, then the device can be manufactured with standard processes, but the base resistance increases and base-collector junction capacitance increases
Solution Approach 1:
The patent changes the crystalline structure parameter of the extrinsic base region from polycrystalline to monocrystalline. This parameter change reduces base resistance by approximately 50% compared to polycrystalline structures, while maintaining compatibility with standard semiconductor manufacturing processes through selective epitaxial growth techniques
Solution Approach 2:
The patent employs a composite structure where the extrinsic base region is formed as a monocrystalline silicon layer grown selectively on a silicon-on-insulator substrate. This composite approach combines the manufacturing ease of standard SOI processes with the electrical performance benefits of monocrystalline material
2Device complexity
If a polycrystalline silicon extrinsic base region is used in conventional HBTs, then the device structure can be simplified, but the base-collector junction capacitance increases
Solution Approach 1:
The patent changes the crystalline structure parameter from polycrystalline to monocrystalline in the extrinsic base region. This reduction in structural complexity at the material level translates to lower base-collector junction capacitance, improving high-frequency performance without requiring additional device structure modifications
3Reliability
If higher doping concentrations are used in the collector region, then the collector resistance decreases, but dopant diffusion increases in polycrystalline structures
Solution Approach 1:
The patent changes the crystalline structure parameter of the extrinsic base region to monocrystalline, which provides a diffusion barrier that prevents dopant diffusion into the collector region. This enables the use of higher doping concentrations in the collector to reduce collector resistance without the harmful side effect of dopant diffusion, thereby improving device performance and reliability
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 approach results in reduced base resistance and capacitance, enhancing the unit gain frequency and maximum oscillating frequency of the transistor while maintaining a lower collector resistance and breakdown voltage.
Implementation Method 1
forming a monocrystalline semiconductor layer over the first dielectric layer and in the opening
Implementation Method 2
amorphizing the first semiconductor material to form an amorphized semiconductor layer, performing epitaxial regrowth of the amorphized semiconductor layer to produce the monocrystalline semiconductor layer
Implementation Method 3
performing epitaxial regrowth of the amorphized semiconductor layer to produce the monocrystalline semiconductor layer
Data Source
AI summary
A semiconductor device, such as a heterojunction bipolar transistor (HBT), may include an extrinsic base region that is connected to a collector region via semiconductor material formed in an opening in one or more dielectric layers interposed between the extrinsic base region and the collector region. The extrinsic base region may be formed from monocrystalline semiconductor material, such as silicon or silicon germanium, via selective epitaxial growth. An intrinsic base region may be formed adjacent to the extrinsic base region and may be interposed directly between the collector region and an intrinsic emitter region. A HBT with such an arrangement may have reduced base-collector capacitance and reduced base resistance compared to some conventional HBTs.