Si Substrate Through-Hole Filler for GaN High-Frequency Devices
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Solution Overview
Problem
Conventional semiconductor devices with Si substrates suffer from increased conductor loss and stray capacitance, degrading high-frequency characteristics and thermal management due to low resistivity and heat conductivity, and face challenges in filling defects between GaN-based epitaxial layers and fillers with different lattice constants.
Innovation Solution
A semiconductor device with a Si substrate and an epitaxially grown crystal layer of GaN or AlGaN, featuring a buffer layer of AlxGa1-xN and a filler of the same composition to reduce conductor loss and improve high-frequency characteristics, where a through hole in the Si substrate is filled with AlxGa1-xN filler, facilitating easy deposition and enhancing thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Si substrate with low resistivity is used, then manufacturing cost is reduced, but conductor loss in circuit portion increases and high-frequency characteristics degrade
Solution Approach 1:
The Si substrate is segmented by forming through-holes that remove portions of the substrate below the transistor and circuit portions. This segmentation allows different regions to have different electrical properties: the removed regions eliminate conductive paths that cause loss, while remaining substrate areas maintain mechanical support and low-cost advantages.
Solution Approach 2:
Conductive portions of the Si substrate are extracted by forming through-holes that reach from the back surface to the epitaxial layer. This extraction removes the harmful conductive paths between the substrate back surface and the transistor components, eliminating the source of conductor loss while preserving the low-cost Si substrate material where beneficial.
2Ease of manufacture
If a Si substrate is used, then manufacturing cost is reduced, but stray capacitance between drain electrode and substrate back surface increases, degrading high-frequency characteristics
Solution Approach 1:
The substrate structure is segmented by creating through-holes that disconnect the drain electrode from the substrate back surface in critical regions. This segmentation reduces the effective area for stray capacitance formation while maintaining the low-cost Si substrate elsewhere in the device structure.
Solution Approach 2:
The harmful capacitive coupling paths are extracted by removing Si substrate material through through-holes positioned below the transistor and circuit portions. This extraction eliminates the parasitic capacitance between the drain electrode and substrate back surface, improving high-frequency performance.
3Loss of energy
If a through hole is formed to reach from the back surface of the Si substrate to the epitaxially grown crystal layer and filled with filler, then conductor loss is reduced and high-frequency characteristics are improved, but lattice mismatch between epitaxial layer and filler causes deposition difficulty
Solution Approach 1:
An AlGaN buffer layer serves as an intermediary material between the Si substrate and the GaN epitaxial layer. This buffer layer has a composition ratio (x) that can be optimized to provide lattice matching with the GaN layer (y≠x), acting as a transition layer that eliminates deposition difficulties while enabling the through-hole filler structure to reduce conductor loss.
Solution Approach 2:
The composition ratio parameter x of the AlGaN buffer layer is changed and optimized to achieve lattice matching with the GaN epitaxial layer. By adjusting this compositional parameter, the patent resolves the lattice mismatch problem that would otherwise prevent easy filler deposition in the through-holes.
4Ease of manufacture
If Si substrate is used, then manufacturing cost is reduced, but heat conductivity is lower than SiC, increasing thermal resistance and junction temperature
Solution Approach 1:
Heat-generating regions are extracted by removing Si substrate material through through-holes below the transistor portion. This extraction eliminates the low heat-conductivity Si material from the direct heat path, allowing heat to be dissipated more efficiently through alternative paths while maintaining the cost advantage of using Si substrate in non-critical areas.
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 effectively reduces conductor loss, improves high-frequency characteristics, and enhances thermal management by using a lattice-matched filler, allowing for reliable high-frequency operation and efficient heat dissipation.
Implementation Method 1
a filler formed of AlxGa1-x N having the same composition ratio x as a material of the buffer layer, wherein a through hole is formed in the Si substrate so as to reach from the second major surface to the buffer layer, and the through hole is filled with the filler
Implementation Method 2
The heat conductivity of Si is about 1.5 W/cm·K, lower than that of SiC used as a substrate in a GaN or AlGaN-based semiconductor device. Therefore, heat generated in a transistor in such a semiconductor device cannot easily be released
Data Source
AI summary
A semiconductor device includes: a Si substrate having first and second major surfaces facing in opposite directions; a buffer layer of AlxGa1-xN (0≦x≦1) on the first major surface of the Si substrate; an epitaxially grown crystalline layer of AlyGa1-yN (0≦y≦1, x≠y) on the buffer layer; a transistor on the epitaxially grown crystalline layer; and a filler of AlxGa1-xN and having the same x as the buffer layer. A through hole in the Si substrate extends from the second major surface to the buffer layer, and the through hole is filled with the filler.