Nitride Semiconductor Bipolar Transistor Eave Structure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing GaN-based heterojunction bipolar transistors (HBTs) face challenges in achieving low base resistance and high-frequency characteristics due to high activation energy of p-type dopants and limitations in reducing the distance between the emitter and base electrode, which increases manufacturing costs and hinders downsizing of radio communication systems.
Innovation Solution
A nitride semiconductor-based bipolar transistor configuration with an emitter or collector electrode forming a 'eave' to shorten the distance between the emitter and base electrode, using InAlGaN for low resistance ohmic contacts, and employing self-aligned processes with InGaNAs and InGaNP layers to lower base resistance and parasitic capacitance, along with a heterojunction structure and benzocyclobutene film to enhance high-frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the emitter and base electrode is reduced to lower base resistance, then high-frequency characteristics are improved, but manufacturing precision requirements increase and costs rise
Solution Approach 1:
The base electrode pattern is formed using the emitter electrode pattern itself as a mask through self-aligned etching. This self-service approach eliminates the need for separate photolithography alignment, automatically achieving the required precision without additional manufacturing complexity or cost.
Solution Approach 2:
The emitter electrode pattern is formed first, and then this pre-formed pattern is used to define the base electrode position through self-aligned etching. This preliminary action ensures that the critical distance is controlled by the already-formed emitter structure rather than by subsequent alignment operations.
2Reliability
If Mg doping concentration in the base layer is increased to lower base resistance, then electrical conductivity improves, but activation energy remains high at 160 meV
Solution Approach 1:
The base layer composition is changed from pure GaN to InGaN alloy, which fundamentally alters the doping parameters. This composition change reduces the activation energy of Mg dopant from 160 meV in GaN to a lower value in InGaN, enabling higher carrier concentration and lower base resistance at the same doping level.
Solution Approach 2:
The base layer uses InGaN composite material instead of pure GaN. This composite structure combines the benefits of lower activation energy for p-type doping while maintaining the wide bandgap characteristics necessary for high-frequency operation, achieving both low resistance and high-frequency performance.
3Ease of manufacture
If conventional two-photolithography process is used to form base electrode, then manufacturing process is standard, but the distance cannot be reduced below alignment accuracy limit
Solution Approach 1:
The base electrode pattern is formed using the emitter electrode pattern itself as a mask through self-aligned etching. This self-service approach eliminates the need for separate photolithography alignment, automatically achieving the required precision without additional manufacturing complexity or cost.
Solution Approach 2:
The patent extracts and eliminates one of the two photolithography steps from the conventional process by using the already-formed emitter electrode as the masking pattern for base electrode formation. This removes the alignment step entirely, allowing distance reduction without proportionally increasing process complexity.
Data Source
AI summary
In a nitride semiconductor based bipolar transistor, a contact layer formed so as to contact an emitter layer is composed of n-type InAlGaN quaternary mixed crystals, the emitter layer and the contact layer are selectively removed so that the barrier height with the emitter formed thereon is small, and the ohmic electrode contact resistance can be lowered on the InAlGaN quaternary mixed crystals, for example, so that a WSi emitter electrode becomes an eave. A base electrode is formed by a self-aligned process using the emitter electrode as a mask. By such a configuration, the distance between the emitter and the edge of the base electrode is sufficiently shortened, and the base resistance can be lowered. As a result, a bipolar transistor having favorable high-frequency characteristics can be realized.