Micromachined Ultrasonic Transducer Cavity Thickness Control
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Solution Overview
Problem
Existing micromachined ultrasonic transducer manufacturing techniques face challenges in achieving precise control over cavity thickness and bonding surface roughness, which affect acoustic performance and yield in volume manufacturing of integrated ultrasound transducers.
Innovation Solution
The method involves forming a film stack over a substrate with a metal electrode layer and a chemical mechanical polishing (CMP) stop layer, followed by patterning, planarizing, and measuring the CMP stop layer thickness to determine the membrane support layer thickness, ensuring a desired transducer cavity depth, and using this measurement as a parameter for subsequent device fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional micromachined ultrasonic transducer manufacturing techniques are used, then manufacturing process simplicity is maintained, but cavity thickness control precision and bonding surface roughness deteriorate
Solution Approach 1:
The patent applies preliminary action by performing a preliminary CMP process on the substrate before membrane deposition to pre-establish a planar bonding surface. This preliminary planarization ensures that subsequent membrane bonding occurs on a uniformly flat surface, thereby achieving precise cavity thickness control and reduced bonding surface roughness without requiring complex post-processing steps
Solution Approach 2:
The patent implements feedback control by measuring the actual cavity thickness after formation and using this measurement data to adjust and optimize the CMP process parameters for subsequent production batches. This closed-loop feedback mechanism enables continuous improvement of cavity thickness uniformity and bonding surface quality while maintaining manufacturing process efficiency
2Reliability
If conventional manufacturing techniques are used, then manufacturing speed is maintained, but acoustic performance deteriorates due to poor cavity thickness uniformity
Solution Approach 1:
The patent applies parameter changes by systematically optimizing CMP process parameters including polishing pressure, sliding speed, and polishing pad characteristics to achieve the desired bonding surface roughness and cavity thickness uniformity. By carefully controlling these parameters, the process achieves high acoustic performance while maintaining efficient manufacturing throughput without requiring excessive process steps
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 improved control over cavity thickness variation and bonding surface roughness, enhancing the acoustic performance and manufacturing quality of micromachined ultrasonic transducers, particularly in volume production of integrated on-chip ultrasound devices.
Implementation Method 1
chemical mechanical polishing (CMP) stop layer formed over the metal electrode layer
Data Source
AI summary
A method of forming an ultrasonic transducer device includes forming and patterning a film stack over a substrate, the film stack comprising a metal electrode layer and a chemical mechanical polishing (CMP) stop layer formed over the metal electrode layer; forming an insulation layer over the patterned film stack; planarizing the insulation layer to the CMP stop layer; measuring a remaining thickness of the CMP stop layer; and forming a membrane support layer over the patterned film stack, wherein the membrane support layer is formed at thickness dependent upon the measured remaining thickness of the CMP stop layer, such that a combined thickness of the CMP stop layer and the membrane support layer corresponds to a desired transducer cavity depth.