High-Resistance Substrate Diodes for RFIC ESD Isolation
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Solution Overview
Problem
Diodes and diode strings on RFIC chips formed from bulk semiconductor substrates suffer from junction breakdown, poor voltage scaling, and harmonic distortion due to large RF swings, limiting their effectiveness in ESD protection.
Innovation Solution
A semiconductor structure with a bulk substrate featuring a high resistance portion between monocrystalline lower and upper portions, incorporating trench isolation regions and diodes separated from the lower portion by the high resistance layer, which enhances ESD protection by sustaining larger RF voltages, reducing parasitic capacitance, and improving harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diodes are formed on bulk semiconductor substrates for ESD protection, then ESD protection function is provided, but junction breakdown occurs due to large RF swings
Solution Approach 1:
The bulk semiconductor substrate is segmented into multiple portions with different resistance characteristics. A first portion adjacent to the first surface, a second portion adjacent to the second surface, and a third high-resistance portion between them. This segmentation allows the diode to be electrically isolated from the low-resistance first portion, preventing junction breakdown while maintaining ESD protection functionality.
Solution Approach 2:
The high-resistance third portion acts as an intermediary layer between the diode and the low-resistance first portion of the substrate. This intermediary high-resistance portion isolates the diode junction from the bulk substrate, preventing harmful interactions and junction breakdown during large RF swings while still allowing the diode to provide ESD protection.
2Reliability
If diodes are formed on bulk semiconductor substrates, then ESD protection is provided, but poor voltage scaling occurs
Solution Approach 1:
Different portions of the semiconductor substrate are given different resistance qualities tailored to specific functions. The first and second portions have lower resistance for optimal device operation, while the third portion has high resistance for isolation. This local differentiation enables the diode to achieve good voltage scaling characteristics while maintaining robust ESD protection.
3Reliability
If diodes are formed on bulk semiconductor substrates, then ESD protection is provided, but harmonic distortion increases due to large RF swings
Solution Approach 1:
The substrate is segmented into high-resistance and low-resistance portions, creating electrical isolation that prevents the diode from interacting with the bulk substrate during large RF swings. This segmentation eliminates the mechanism that generates harmonic distortion while preserving the ESD protection function.
Solution Approach 2:
The high-resistance third portion serves as an intermediary barrier that prevents RF signals from coupling between the diode and the bulk substrate. This isolation eliminates the source of harmonic distortion generated during large RF swings while allowing the diode to maintain its ESD protection capability.
4Strength
If diodes are separated from the first portion by a high resistance portion, then junction breakdown is prevented, but device complexity increases
Solution Approach 1:
The substrate structure utilizes parameter changes in resistance across different portions rather than adding complex structural elements. By varying the resistance parameter from low in the first and second portions to high in the third portion, the patent achieves junction breakdown prevention through a relatively simple modified substrate structure.
Data Source
AI summary
Disclosed are a structure and method. The structure includes a substrate having monocrystalline lower and upper portions and a high resistance portion (e.g., a trap-rich amorphous portion) between the lower and upper portions. An isolation region extends through the upper portion, is above the high resistance portion, and is positioned laterally adjacent to a device section of the upper portion also above the high resistance portion. One or more devices (e.g., a diode, multiple diodes, a diode string, multiple diode strings, etc.) are on the trench isolation region, on the device section, and/or within the device section. The device(s) are separated from the lower portion by the high resistance portion and, potentially, by the isolation region or the device section. Such device(s) can be employed for electrostatic discharge (ESD) protection on RFIC chips and can sustain a larger RF voltage, provide area savings, reduce parasitic capacitance, improve harmonics, etc.