Oxidized Cavity Structures for Bulk Silicon RF Linearity
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Solution Overview
Problem
High-cost state-of-the-art trap rich silicon on insulator (SOI) wafers are required for RF devices to achieve high linearity, but they are expensive and devices built on bulk Si substrates suffer from degraded linearity, harmonics, noise, and leakage currents, increasing manufacturing costs.
Innovation Solution
The use of oxidized cavity structures formed in the substrate material under active devices, which reduce harmonics and junction capacitance, and provide full isolation, allowing for the use of bulk silicon wafers instead of expensive SOI wafers, by forming trenches and cavity structures with oxidized sidewalls and filling them with oxide material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expensive SOI wafers are used, then linearity and isolation performance are improved, but manufacturing cost increases significantly
Solution Approach 1:
The substrate is segmented into active regions and isolated regions using oxidized cavity structures and trenches. This segmentation provides vertical isolation between devices on bulk silicon, achieving SOI-like performance without the high cost of full SOI wafers. The oxidation creates distinct electrical zones that segment the conductive path.
Solution Approach 2:
Oxidized regions are created locally at specific positions where isolation is needed, rather than making the entire substrate expensive SOI. The oxidized cavities and trenches provide high resistivity and isolation properties only where required, maintaining low cost for the bulk substrate while achieving local isolation performance.
2Ease of manufacture
If bulk silicon substrates are used, then manufacturing cost is reduced, but linearity, harmonics, noise, and leakage currents are degraded
Solution Approach 1:
Oxidized cavity structures and trenches act as intermediary elements between active devices on bulk silicon. These oxidized regions provide the necessary isolation and electrical properties that bulk silicon alone cannot provide, mediating between the low-cost bulk substrate and the performance requirements of RF devices.
Solution Approach 2:
The electrical parameters of the substrate are changed locally through oxidation. The oxidized regions have fundamentally different electrical properties (high resistivity, low carrier concentration) compared to the bulk silicon, creating the necessary isolation without changing the entire substrate's properties or requiring expensive SOI material.
3Reliability
If oxidized cavity structures are formed in bulk silicon, then isolation performance and linearity are improved, but device complexity increases
Solution Approach 1:
Complex mechanical isolation structures are replaced with oxidized cavity structures formed through chemical oxidation processes. The oxidation naturally creates the isolation regions, replacing what would otherwise require complex multi-layer mechanical isolation structures to achieve the same electrical isolation performance.
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 improves the performance of bulk devices by reducing substrate losses and harmonics, while avoiding the need for costly SOI wafers, thus lowering manufacturing costs and maintaining high linearity.
Implementation Method 1
oxidized cavity structures extending from the oxidized trench structure and formed in the substrate material under active devices
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to oxidized cavity structures within and under semiconductor devices and methods of manufacture. The structure includes: a substrate material; active devices over the substrate material; an oxidized trench structure extending into the substrate and surrounding the active devices; and one or more oxidized cavity structures extending from the oxidized trench structure and formed in the substrate material under the active devices.