GaN HEMT Substrate Transfer via High-Resistance Bonding
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Solution Overview
Problem
The challenge in manufacturing high-frequency GaN-based HEMTs is the deterioration of device characteristics due to crystal defects introduced during the substrate transfer process, particularly at the bonding interface, which affects the transistor's performance and reliability.
Innovation Solution
A method involving the formation of a buffer layer on a first substrate, followed by sequential crystal growth of barrier layers, a channel layer, and bonding layers on both substrates, with specific doping and material selection to create high-resistance bonding layers that suppress leak currents and maintain high crystal quality, allowing for substrate transfer with reduced defect introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If substrate transfer is performed to manufacture N-polarity GaN HEMTs, then high-frequency characteristics can be improved, but crystal defects are introduced at the bonding interface which deteriorates device characteristics
Solution Approach 1:
A bonding layer is formed in advance on the GaN layer before substrate transfer. This preliminary action prepares the bonding interface with appropriate material properties that prevent defect formation during the subsequent transfer process, thereby maintaining device characteristics while enabling substrate transfer for N-polarity HEMT fabrication
Solution Approach 2:
A bonding layer is introduced as an intermediary between the GaN layer and the substrate. This intermediate layer mediates the bonding process, reducing direct contact between the GaN layer and substrate that would otherwise cause crystal defects, thus preserving device performance while enabling the necessary substrate transfer
2Length of moving object
If AlGaN barrier layer thickness is reduced to decrease gate-channel distance, then device scaling is achieved, but sheet carrier density decreases and resistance increases
Solution Approach 1:
The Al composition ratio in the AlGaN barrier layer is increased to compensate for the reduced barrier layer thickness. By changing this material parameter, the polarization difference is enhanced, maintaining sheet carrier density and low resistance even when the gate-channel distance is reduced for device scaling
Solution Approach 2:
An AlGaN barrier layer with optimized composite composition is used, where the aluminum gallium nitride material is engineered with specific Al composition ratios to achieve the desired balance between thin barrier thickness (for scaling) and sufficient polarization effect (for maintaining carrier density and low 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 effectively suppresses the deterioration of device characteristics by minimizing crystal defects at the bonding interface, enhancing the reliability and performance of HEMTs with N-polarity GaN, thereby improving high-frequency characteristics.
Implementation Method 1
At least one of the first bonding layer and the second bonding layer is made of the nitride semiconductor doped with C, Fe, Zn, or Mg and increased in resistance or converted into a p type
Implementation Method 2
Since the nitride semiconductor has polarization in a c-axis direction, for example, by forming heterojunction of AlGaN and GaN, it is possible to spontaneously form a sheet carrier having high density of approximately 10^13 cm^-3 according an effect of the polarization
Data Source
AI summary
A first barrier layer, a channel layer, a second barrier layer, and a first bonding layer made of high-resistance AlGaN doped with Fe are formed on a first substrate. Thereafter, the first substrate and the second substrate are pasted in a state where the first bonding layer and a second bonding layer made of high-resistance GaN doped with Fe are opposed to each other.