Lateral HBT Structure With Thermal Exit Paths for Self-Heating
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Solution Overview
Problem
Lateral bipolar junction transistors (BJTs) integrated into advanced silicon-on-insulator (SOI) technology platforms face issues with self-heating and poor performance, including low cut-off frequency (fT)/maximum oscillation frequency (fmax) and beta cut-off frequency.
Innovation Solution
A semiconductor structure with a lateral heterojunction bipolar transistor (HBT) is developed, featuring a silicon germanium intrinsic base region and epitaxially grown collector and emitter regions that extend through an insulator layer to a substrate, forming thermal exit paths and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If lateral BJTs are formed in SOI technology platforms, then integration with CMOS devices is achieved, but self-heating and poor performance occur
Solution Approach 1:
The patent transitions from conventional vertical BJT architecture to a lateral BJT configuration, changing the spatial dimension of current flow. This dimensional change enables integration with CMOS planar structures while maintaining bipolar transistor functionality, though it initially introduces self-heating issues that are subsequently addressed through thermal management structures
Solution Approach 2:
The collector and emitter are segmented into multiple regions with different semiconductor materials (e.g., SiGe collector/emitter regions with Si base region). This segmentation allows optimization of each region's properties - the SiGe regions provide better carrier injection and collection, while the Si base provides good thermal conductivity to reduce self-heating
2Area of stationary object
If lateral BJT structure is used, then area consumption is reduced, but cut-off frequency and beta cut-off frequency decrease
Solution Approach 1:
Different regions of the lateral BJT are assigned different material compositions and doping profiles optimized for their specific functions. The base region uses intrinsic or lightly-doped Si for high mobility, while collector and emitter regions use SiGe with graded composition to enhance carrier injection efficiency. This local optimization maintains high frequency performance despite the lateral configuration's area advantages
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 solution minimizes self-heating and enhances performance by increasing fT/fmax and beta cut-off frequency through the use of a silicon germanium intrinsic base region and epitaxial growth of collector and emitter regions.
Implementation Method 1
The connection(s) of the collector and/or the emitter to the substrate effectively form thermal exit path(s) into the substrate and, thus, minimize self-heating
Implementation Method 2
a lateral heterojunction bipolar transistor (HBT) ... which can include an intrinsic silicon germanium base region for improved performance
Implementation Method 3
a first region, which is epitaxially grown within a trench that extends through the semiconductor layer and the insulator layer to the substrate; and a second region, which is epitaxially grown on the first region
Data Source
AI summary
Disclosed is a semiconductor structure including a lateral heterojunction bipolar transistor (HBT). The structure includes a substrate (e.g., a silicon substrate), an insulator layer on the substrate, and a semiconductor layer (e.g., a silicon germanium layer) on the insulator layer. The structure includes a lateral HBT with three terminals including a collector, an emitter, and a base, which is positioned laterally between the collector and the emitter and which can include a silicon germanium intrinsic base region for improved performance. Additionally, the collector and/or the emitter includes: a first region, which is epitaxially grown within a trench that extends through the semiconductor layer and the insulator layer to the substrate; and a second region, which is epitaxially grown on the first region. The connection(s) of the collector and/or the emitter to the substrate effectively form thermal exit path(s) and minimize self-heating. Also disclosed is a method for forming the structure.