Monocrystalline Extrinsic Base Structure for Lower HBT Capacitance
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Solution Overview
Problem
Conventional heterojunction bipolar transistors (HBTs) face challenges due to higher resistivity in polycrystalline silicon extrinsic base regions, leading to increased base resistance and base-collector junction capacitance, which can be mitigated by using a monocrystalline extrinsic base region.
Innovation Solution
The formation of a monocrystalline extrinsic base region, separated from the collector region by dielectric layers, reduces resistivity and capacitive coupling, allowing for higher doping concentrations in the collector region to enhance unit gain frequency and breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polycrystalline silicon extrinsic base region is used, then the manufacturing process is simpler, but the base resistance increases and device performance deteriorates
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 one order of magnitude while maintaining manufacturing feasibility through modified fabrication processes including selective epitaxial growth and laser annealing.
2Reliability
If a monocrystalline extrinsic base region is used, then base resistance decreases and device performance improves, but the manufacturing process becomes more complex
Solution Approach 1:
The patent segments the base region into two distinct parts: an intrinsic base region and a monocrystalline extrinsic base region. The intrinsic base maintains the original polycrystalline structure for simplicity, while the extrinsic base is converted to monocrystalline through selective processing. This segmentation allows the device to benefit from low resistance without requiring complete structural transformation.
Solution Approach 2:
The patent introduces an intermediate layer of monocrystalline silicon between the polycrystalline intrinsic base and the metal contact. This intermediate monocrystalline layer acts as a mediator that provides low-resistance electrical contact while allowing the bulk of the base to remain structurally simple.
3Speed
If doping concentration in the collector region is increased, then unit gain frequency and breakdown voltage increase, but base-collector junction capacitance increases
Solution Approach 1:
The patent applies local quality by creating a monocrystalline extrinsic base region with specific electrical properties adjacent to the collector, while the intrinsic base maintains different properties. This local differentiation allows high doping concentrations in the collector for improved frequency and breakdown characteristics without the full negative capacitive effect, as the monocrystalline-extrinsic/base interface optimizes the junction properties.
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, lower base-collector capacitance, and increased maximum oscillating frequency, improving the overall performance of the HBT.
Implementation Method 1
performing epitaxial regrowth of the amorphized semiconductor layer to produce the monocrystalline semiconductor layer
Implementation Method 2
separated from the collector region by dielectric layers, reduces resistivity and capacitive coupling
Implementation Method 3
amorphizing the first semiconductor material to form an amorphized semiconductor layer
Data Source
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AI summary
A semiconductor device, such as a heterojunction bipolar transistor (HBT), may include an extrinsic base region (114) that is connected to a collector region (104) via semiconductor material formed in an opening (111) in one or more dielectric layers (110, 120) interposed between the extrinsic base region and the collector region. The extrinsic base region is formed from monocrystalline semiconductor material, such as silicon or silicon germanium, via selective epitaxial growth. An intrinsic base region (122) may be formed adjacent to the extrinsic base region and may be interposed directly between the collector region (104) and an intrinsic emitter region (124). An isolation region (105) is present in the collector, splitting the collector in a region connected to the extrinsic base and a region connected to the intrinsic base. An HBT with such an arrangement may have reduced base-collector capacitance and reduced base resistance compared to some conventional HBTs.