GaN Transistor Stack With Thermal Dielectric for Vertical Breakdown
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Solution Overview
Problem
Existing GaN-on-Si transistors face challenges in integrating multiple components on a common substrate due to 'current collapse' phenomena, which are exacerbated by the use of thick electrical insulators that reduce substrate potential bias, leading to poor heat resistance and breakdown voltage issues, especially at high voltages.
Innovation Solution
A microelectronic device design featuring a stack with a continuous GaN-based layer and an insulating layer between rear electrodes and active layers, where the insulating layer provides both vertical breakdown voltage and heat conductivity, optimizing thickness to balance bias control and heat discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick electrical insulator is used to replace the silicon substrate to enable independent biasing of multiple components, then the substrate potential bias impact is reduced enabling component insulation, but the 'current collapse' phenomena worsen and heat discharge capability deteriorates
Solution Approach 1:
The device is divided into multiple independent components, each with its own rear electrode and insulating layer, allowing independent biasing while maintaining separate heat dissipation paths to the common substrate
Solution Approach 2:
A thin insulating layer (50-500 nm) is introduced as an intermediary between the GaN buffer layer and the substrate, providing electrical insulation for independent biasing while maintaining thermal conduction through the substrate via heat spreader structures
2Reliability
If a thick insulating layer is used to ensure vertical breakdown voltage, then breakdown voltage is improved, but heat conductivity decreases leading to poor heat dissipation
Solution Approach 1:
The insulating structure has different properties at different locations: a thin insulating layer (50-500 nm) near the active region for electrical insulation with good thermal conduction, and a thicker heat spreader layer (1-10 μm) at the substrate interface for heat dissipation
Solution Approach 2:
The insulating system combines a thin dielectric layer (Al2O3, SiO2, or Si3N4) for electrical breakdown protection with a heat spreader layer for thermal management, creating a composite structure that simultaneously provides both electrical and thermal functions
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 ensures reliable breakdown voltage and efficient heat dissipation, addressing the limitations of previous designs by reducing mechanical stresses and maintaining electrostatic integrity, enabling operation at high voltages without compromising component performance.
Implementation Method 1
an insulating layer extending, in the stack direction, between the first rear electrode and the first active layer, on the one hand, and the second rear electrode and the second active layer, on the other hand
Implementation Method 2
the first dielectric having a heat conductivity λ1 greater than 1 W·m−1·K−1
Data Source
AI summary
A microelectronic device including a first transistor including a first active layer, a second field effect transistor including a second active layer, the second source being electrically connected to the first drain, a first rear electrode and a second rear electrode. The device in addition includes an insulating layer extending, between the first rear electrode and the first active layer, on the one hand, and the second rear electrode and the second active layer, on the other hand. The insulating layer is continuous and has a critical field Ec and a thickness called dielectric thickness e1500 of between 2*e1500,min and 10*e1500,min, with e1500,min=Vtarget/Ec, Vtarget being a target breakdown voltage of the insulating layer, the first dielectric having a heat conductivity λ1 greater than 1 W·m−1·K−1.