PMUT Deep-Trench Isolation for Acoustic Crosstalk Reduction
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Solution Overview
Problem
The process of creating deep trenches to reduce acoustic crosstalk in ultrasonic transducers with a three-dimensional architecture composed of PMUT and CMOS is challenging due to the complexity of forming deep trenches through piezoelectric materials and their upper and bottom metals, which are difficult to etch and pattern, especially for thinner materials.
Innovation Solution
A deep-trench isolation method is employed, where deep trenches are formed around PMUT units on a CMOS unit by pre-designing or post-designing processes based on the size and area of the PMUT units and cavities, involving etching, deposition, and chemical mechanical polishing to create a Si/damping material/air interface, reducing acoustic crosstalk effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deep trenches are etched through piezoelectric materials and metal layers to reduce acoustic crosstalk, then acoustic isolation is improved, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The patent divides the deep trench formation process into multiple stages: first forming shallow trenches through the piezoelectric material and metal layers, then forming deeper trenches through the silicon mechanical layer separately. This segmentation allows each trench type to be optimized for its specific depth and function, reducing overall process complexity while achieving the required acoustic isolation.
Solution Approach 2:
The patent performs preliminary actions by first forming the shallow trenches and depositing damping material before forming the deeper trenches. This preliminary structure provides initial acoustic isolation and a foundation for subsequent processing, making the overall complex task more manageable and reducing final process difficulty.
2Object-affected harmful factors
If deep trenches are formed to isolate adjacent PMUT units, then acoustic isolation is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the trench formation into two distinct processes: shallow trenches with controlled depth through the piezoelectric material and metal layers, and deeper trenches through the silicon mechanical layer. Each segment has its own optimization for depth control and positioning, reducing the precision burden on any single process while achieving the required overall isolation.
Solution Approach 2:
The patent introduces damping material as an intermediary substance filled in the trenches to enhance acoustic isolation. This intermediary layer provides additional acoustic damping and isolation效果, allowing the trench geometry to be optimized for manufacturing precision rather than solely for acoustic performance.
3Length of moving object
If the piezoelectric material layer thickness is reduced for miniaturization, then device size is reduced, but deep trench formation becomes more difficult
Solution Approach 1:
The patent segments the trench formation process to first create shallow trenches through the thin piezoelectric material and metal layers, then separately form deeper trenches through the silicon mechanical layer. This segmentation makes trench formation easier in thin-material architectures by avoiding the need to etch through all layers simultaneously with a single process.
Solution Approach 2:
The patent performs preliminary trench formation through the thin piezoelectric material and metal layers before forming the deeper trenches. This preliminary action establishes the upper portion of the isolation structure first, making the subsequent deeper trench formation more manageable and less difficult despite the reduced material thickness.
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 method simplifies the deep-trench process for thinner materials, effectively reducing acoustic crosstalk by forming a Si/damping material/air interface that significantly attenuates mechanical wave propagation, achieving good isolation results.
Implementation Method 1
The deep trench is filled with damping material, and a damping layer is formed on the bottom and side walls of the deep trench through deposition. The Si/damping material/air interface significantly attenuates mechanical wave propagation.
Data Source
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AI summary
The present disclosure relates to the field of interference blocking. Disclosed are a deep-trench isolation method for reducing acoustic crosstalk of an ultrasonic transducer, and an ultrasonic transducer. The ultrasonic transducer comprises a CMOS unit, wherein at least one PMUT unit is arranged on the CMOS unit, all the PMUT units share a PMUT substrate, and each PMUT unit is provided with a cavity. The deep-trench isolation method comprises the steps of when the size and area of a PMUT unit are both less than corresponding preset values thereof and the area of a cavity is greater than a preset value thereof, first etching a deep trench from a mechanical layer towards a PMUT substrate and around the cavity, and then depositing a piezoelectric laminated layer on the mechanical layer within the area, which is isolated by the deep trench, otherwise, first depositing the piezoelectric laminated layer on the mechanical layer, then etching a contact hole from the surface of the piezoelectric laminated layer towards the surface of the mechanical layer and around the cavity, and etching, towards the PMUT substrate, at least one deep trench from the surface of the mechanical layer in the contact hole. In the present disclosure, a deep trench is provided between PMUT units to hinder transverse propagation of ultrasonic waves, such that acoustic crosstalk of an ultrasonic transducer can be effectively reduced.