Multi-SOI Ultrasound Transducer Structure for Crosstalk Isolation
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Solution Overview
Problem
Conventional silicon-on-insulator (SOI) wafer technology faces challenges in achieving precise control of geometries for advanced MEMS devices requiring three-dimensional vertical integration with CMOS circuitry, leading to issues like crosstalk and inefficient acoustic wave transmission in micromachined ultrasound transducers (MUTs).
Innovation Solution
The use of double-SOI technology enables more flexibility in designing and positioning cavities and trenches in the buried oxide and semiconductor layers, allowing for improved acoustic wave transmission and reduced crosstalk through precise alignment tolerances and impedance mismatching via trenches etched at various depths and locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional SOI wafer technology is used, then manufacturing process is simpler, but precise control of geometries for 3D vertical integration is difficult
Solution Approach 1:
The substrate is divided into multiple SOI layers (first SOI layer and second SOI layer) with distinct functions. The first SOI layer provides the base structure and buried oxide, while the second SOI layer enables precise geometry control and 3D integration. This segmentation allows each layer to be optimized independently for its specific function.
Solution Approach 2:
The patent introduces a vertical dimension by stacking multiple SOI layers, transitioning from a single-layer planar structure to a multi-layer three-dimensional structure. This enables precise control of geometries in the vertical direction while maintaining manufacturing precision through the insulating layers that provide alignment references.
2Power
If single-SOI structure is used, then device structure is simpler, but acoustic wave transmission efficiency is reduced
Solution Approach 1:
The substrate is segmented into multiple functional layers including first and second SOI layers with insulating layers between them. This segmentation creates distinct regions for acoustic wave generation, transmission, and containment, improving overall transmission efficiency by directing acoustic energy through optimized pathways.
Solution Approach 2:
The device employs a composite structure combining multiple SOI layers with insulating layers (such as buried oxide layers). This composite material structure leverages the acoustic properties of each layer to enhance wave transmission, using the insulating layers as acoustic barriers or waveguides depending on their positioning and thickness.
3Object-generated harmful factors
If conventional SOI technology is used, then manufacturing process is simpler, but crosstalk between adjacent elements is increased
Solution Approach 1:
The substrate is divided into multiple isolated SOI layers with insulating layers separating them. This segmentation physically isolates adjacent elements and acoustic pathways, preventing crosstalk by creating distinct acoustic domains. The insulating layers act as barriers that block unwanted acoustic coupling between neighboring transducer elements.
Solution Approach 2:
Insulating layers (such as buried oxide layers) are introduced as intermediary structures between the SOI layers and between adjacent transducer elements. These intermediary layers mediate the acoustic interaction by blocking harmful acoustic coupling while allowing intended acoustic transmission pathways to function properly.
4Measurement precision
If double-SOI technology is used, then alignment precision is improved, but manufacturing process complexity increases
Solution Approach 1:
The substrate structure is segmented into multiple SOI layers that can be manufactured and aligned independently. Each layer provides its own reference surfaces and alignment features, enabling precise alignment tolerances to be achieved through sequential assembly rather than requiring perfect alignment across the entire multi-layer structure in a single manufacturing step.
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 enhances the output power of acoustic signals, mitigates crosstalk, and provides better critical dimension control during etching processes, resulting in improved performance of MEMS devices such as pMUTs and cMUTs.
Implementation Method 1
The device also comprises a piezoelectric layer between the membrane and the substrate
Implementation Method 2
Use of double SOI technology may enable designers with more flexibility to size and position cavities (or waveguides) and trenches for etching in the devices' buried oxide (BOX) and semiconductor layers. Thus, a double SOI design may improve acoustic wave transmission (e.g., by increasing wave output power) and reduce crosstalk.
Data Source
AI summary
Disclosed is a multi-silicon on insulator (SOI) micromachined ultrasonic transducer (MUT) device. The device comprises a multi-SOI substrate and a MUT. The MUT is affixed to a surface of the multi-SOI substrate. The multi-SOI substrate has a first SOI layer and at least a second SOI layer disposed above the first SOI layer. The first SOI layer and the second SOI layer each comprise an insulating layer and a semiconducting layer. The first SOI layer further defines a cavity located under a membrane of a MUT and one or more trenches at least partially around a perimeter of the cavity.