Strained Silicon RF Die Structure for Low Distortion Heat Dissipation
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Solution Overview
Problem
Conventional silicon substrates used in RF device fabrication suffer from harmonic distortion and low resistivity, leading to limitations in achieving high linearity and heat dissipation, particularly due to increased heat generation from densely integrated high-speed transistors.
Innovation Solution
A radio frequency (RF) device with a mold device die and multilayer redistribution structure, featuring a strained silicon epitaxial layer with a lattice constant greater than 5.461 at 300K, and a thermal conductivity-enhancing mold compound, along with a wafer-level fabricating and packaging process that includes a multilayer redistribution structure with bump structures for improved thermal and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional silicon substrates are used for RF device fabrication, then manufacturing cost is reduced and manufacturing scalability is improved, but harmonic distortion increases and linearity performance deteriorates
Solution Approach 1:
The patent extracts the active layer from the conventional silicon substrate by using a silicon-germanium sacrificial layer. The active layer is grown on silicon-germanium, then the silicon-germanium is selectively removed, leaving the active layer suspended or supported by isolation structures. This removes the harmful silicon substrate that causes harmonic distortion while maintaining compatibility with standard silicon manufacturing processes.
Solution Approach 2:
The patent introduces silicon-germanium as an intermediary sacrificial layer between the silicon substrate and the active layer. This intermediary layer enables the active layer to be formed with superior electrical properties while allowing the harmful silicon substrate to be completely removed. The silicon-germanium serves as a temporary support during fabrication that is subsequently eliminated, mediating between manufacturing requirements and performance goals.
2Reliability
If high speed and high performance transistors are densely integrated in RF devices, then device performance is improved, but heat generation increases significantly
Solution Approach 1:
The patent extracts heat away from the active layer by removing the silicon substrate and replacing it with a thermal management structure. The active layer is isolated from the heat-generating substrate, and heat is conducted away through dedicated thermal paths including thermal vias and thermal management layers, preventing heat accumulation that would degrade device performance.
Solution Approach 2:
The patent replaces the conventional silicon substrate mechanical support system with a thermal management system. Instead of relying on the silicon substrate to conduct heat away, the invention introduces specialized thermal vias, thermal management layers, and heat dissipation structures that actively manage thermal flow, substituting passive substrate-based thermal management with an engineered thermal conduction system.
3Productivity
If wafer-level fan-out and embedded wafer-level ball grid array technologies are used, then I/O port density is improved without increasing package size, but device complexity increases
Solution Approach 1:
The patent segments the package structure into distinct functional layers including redistribution layers, thermal management layers, and isolation structures. This segmentation allows each layer to perform its specific function independently, enabling high I/O density through systematic redistribution of connections while managing complexity through modular design and clear separation of concerns.
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 enhances RF device performance by reducing harmonic distortion, improving heat dissipation, and maintaining device size, thereby addressing the limitations of conventional silicon substrates.
Implementation Method 1
The active layer is formed from a strained silicon epitaxial layer, in which a lattice constant is greater than 5.461 at a temperature of 300K
Implementation Method 2
a thermal conductivity-enhancing mold compound
Data Source
AI summary
The present disclosure relates to a radio frequency (RF) device that includes a mold device die and a multilayer redistribution structure underneath the mold device die. The mold device die includes a device region with a back-end-of-line (BEOL) portion and a front-end-of-line (FEOL) portion over the BEOL portion, and a first mold compound. The FEOL portion includes an active layer formed from a strained silicon epitaxial layer, in which a lattice constant is greater than 5.461 at a temperature of 300K. The first mold compound resides over the active layer. Herein, silicon crystal does not exist between the first mold compound and the active layer. The multilayer redistribution structure includes a number of bump structures, which are at a bottom of the multilayer redistribution structure and electrically coupled to the FEOL portion of the mold device die.