MEMS Resonator Isolation Joint for Cost and Stability
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Solution Overview
Problem
Existing MEMS resonators face challenges in achieving stable resonant vibration and high manufacturing costs due to the need for expensive silicon on insulator (SOI) substrates and the difficulty in removing impurities from the surface of the MEMS structure during bonding processes.
Innovation Solution
The use of an isolation joint made of silicon oxide between the MEMS structure and the substrate, along with a cap layer formed through epitaxial growth at high temperatures, allows for electrical insulation and reduces manufacturing costs by eliminating the need for SOI substrates and effectively removing impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon on insulator (SOI) substrates are used to provide electrical insulation between the electrode and substrate, then electrical insulation is achieved, but manufacturing cost increases
Solution Approach 1:
The patent extracts the electrical insulation function from the expensive SOI substrate structure and implements it separately using a silicon oxide layer formed by thermal oxidation. This isolates the insulation requirement from the substrate, allowing use of cheaper bulk silicon substrates while maintaining the necessary electrical insulation between the electrode and substrate.
Solution Approach 2:
The patent introduces a silicon oxide layer as an intermediary element between the electrode and substrate to provide electrical insulation. This intermediary layer, formed through thermal oxidation of the substrate surface, replaces the need for SOI substrates and achieves the same insulation function at lower cost.
2Ease of manufacture
If glass frit bonding is used to bond the substrate to the SOI substrate at relatively low temperature (450°C), then bonding is achieved, but impurities remain on the MEMS structure surface
Solution Approach 1:
The patent changes the temperature parameter from the low temperature (450°C) glass frit bonding process to a high temperature (900-1100°C) thermal oxidation process. This parameter change enables effective removal of impurities from the MEMS structure surface through the thermal oxidation process, achieving surface purification that was not possible with lower temperature bonding.
Solution Approach 2:
The patent converts the potentially harmful high temperature thermal oxidation process into a beneficial purification step. While high temperature might seem detrimental to already-formed structures, it is used here to oxidize and remove surface impurities, transforming a potentially damaging process into a cleaning and purification mechanism that improves device reliability.
3Reliability
If high temperature processing is used to remove impurities from the MEMS structure surface, then surface purity improves, but existing low temperature bonding processes become incompatible
Solution Approach 1:
The patent performs the high temperature thermal oxidation process as a preliminary step before the final bonding process. By removing impurities through thermal oxidation first, and then proceeding with bonding at the appropriate temperature for the chosen bonding method, the process sequence is optimized to achieve both surface purity and process compatibility.
Solution Approach 2:
The patent changes the bonding temperature parameter to match the high temperature thermal oxidation process. Instead of using low temperature glass frit bonding (450°C), the patent employs high temperature bonding methods (such as direct silicon-silicon bonding at 900-1100°C) that are compatible with the preceding thermal oxidation step, ensuring both impurity removal and successful bonding.
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 enables stable resonant vibration at a lower cost by providing electrical insulation with the isolation joint and removing impurities during cap layer formation, resulting in a reliable MEMS resonator suitable for applications like oscillation circuits, filters, and sensors.
Implementation Method 1
an isolation joint having an insulation property disposed to electrically insulate the first end from the second end
Implementation Method 2
a cap layer which is formed over the substrate and seals the MEMS structure therein
Data Source
AI summary
Provided is a MEMS resonator which is inexpensive in manufacturing cost and can secure long-term stability of vibration. A MEMS resonator includes: a substrate; a cavity provided in the substrate; a MEMS structure held within the cavity, the MEMS structure including: an anchor having a first end and a second end, the first end being connected to the substrate; a vibrator connected to the second end of the anchor and held in a hollow; and an electrode disposed around the vibrator, the vibrator and the electrode forming a capacitive vibrator; and a cap layer which is formed over the substrate and seals the MEMS structure therein, in which the anchor includes an isolation joint having an insulation property disposed to electrically insulate the first end from the second end.