Bipolar Transistor Emitter Segmentation for Base Resistance Reduction
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Solution Overview
Problem
Current bipolar transistors face limitations in achieving higher operating frequencies and switching speeds due to high base resistance and base-collector capacitance, which restrict further miniaturization and frequency performance.
Innovation Solution
The design involves a semiconductor body with a collector region and a base region, where insulating spacers are used to laterally enclose a semiconductor layer, and a two-step emitter deposition process is employed to avoid emitter diffusion into the base region, allowing for reduced base resistance and increased frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bipolar transistor structures are used, then manufacturing is simpler, but base resistance is high and frequency performance is limited
Solution Approach 1:
The emitter is divided into two separate layers: an intrinsic semiconductor layer and a doped semiconductor layer. This segmentation allows the intrinsic layer to form the pn-junction interface with the base while the doped layer provides carriers, reducing base resistance without increasing base-collector capacitance.
Solution Approach 2:
The intrinsic semiconductor layer acts as an intermediary between the base and the doped emitter layer. It forms the pn-junction with the base region while being free of doping-induced diffusion, thereby preventing emitter material from diffusing into the base and reducing base-collector capacitance.
2Length of moving object
If emitter diffusion into base region occurs, then manufacturing is simpler, but base-collector capacitance increases and miniaturization is restricted
Solution Approach 1:
The intrinsic semiconductor layer is deposited first before the doped layer. This preliminary action creates a barrier that prevents subsequent diffusion of dopants into the base region, enabling miniaturization while maintaining manufacturing feasibility through controlled deposition sequences.
Solution Approach 2:
The doping process is extracted from the junction formation step. Instead of doping during junction creation (which causes diffusion), the patent separates these functions: the intrinsic layer forms the junction interface, while doping is applied separately to the upper layer, eliminating harmful diffusion.
3Reliability
If base resistance is reduced through conventional means, then frequency performance improves, but base-collector capacitance increases
Solution Approach 1:
The emitter structure exhibits local quality differentiation: the intrinsic layer at the junction interface provides low capacitance, while the doped layer in the upper region provides high carrier concentration for low base resistance. This spatial differentiation of properties resolves the contradiction between capacitance and resistance.
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 enables a lower base resistance, higher maximum oscillation frequency, and further miniaturization of bipolar transistors by minimizing the spacer width and reducing base-collector-capacitance, thereby enhancing high-frequency performance.
Implementation Method 1
Insulating spacers are arranged on top of the base region. This semiconductor layer is laterally enclosed by the spacers
Implementation Method 2
Elevated temperatures are applied to the semiconductor body, so that dopants diffuse out of the second semiconductor layer into the first semiconductor layer
Data Source
AI summary
A bipolar transistor and a method for fabricating a bipolar transistor are disclosed. In one embodiment the bipolar transistor includes a semiconductor body including a collector region and a base region arranged on top of the collector region, the collector region being doped with dopants of a second doping type and the base region being at least partly doped with dopants of a first doping type and an insulating spacers arranged on top of the base region. The semiconductor body further includes a semiconductor layer including an emitter region arranged on the base region and laterally enclosed by the spacers, the emitter region being doped with dopants of the second doping type forming a pn-junction with the base region, wherein the emitter region is fully located above a horizontal plane through a bottom side of the spacers.