Piezoelectric Ultrasonic Transducer Via Formation
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Solution Overview
Problem
Existing methods for forming electrically-conductive connections in piezoelectric micromachined ultrasonic transducers with air-backed cavities face challenges such as insufficient etch stop layers, poor conductivity, and mechanical fatigue, leading to inconsistent connections and altered resonance frequencies.
Innovation Solution
A method involving wafer bonding and oxide growth to form electrically-conductive vias extending from the air-backed cavity through a substrate, using conductive materials to establish direct contact with the first electrode, and engaging a support member to define additional vias for improved conductivity and reduced stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a via is etched through thin dielectric film and electrode to connect conformal metal layer to first electrode, then electrical connection is established, but etching is difficult due to insufficient etch stop layer
Solution Approach 1:
A thick etch stop layer is formed on the substrate surface before depositing the piezoelectric material and electrodes. This preliminary formation of a sufficiently thick etch stop layer enables subsequent via etching to proceed easily through the dielectric film and electrode to reach the conformal metal layer, solving the etching difficulty problem while ensuring reliable electrical connection.
2Reliability
If doped silicon layer is used to provide electrical connection between first electrode and conformal metal layer, then connection is established, but conductivity is poor and nonlinear at low field levels
Solution Approach 1:
The material of the etch stop layer is changed from doped silicon to an insulating material such as silicon oxide or silicon nitride. This parameter change eliminates the conductivity issues and nonlinear behavior at low field levels, while the etch stop layer still provides the necessary function of enabling via etching to reach the conformal metal layer for reliable electrical connection.
3Reliability
If conformal metal layer is deposited about corner or sidewall of via to connect to first electrode, then electrical connection is established, but connection is poor due to rough or incompletely etched surfaces
Solution Approach 1:
The etch stop layer serves as an intermediary surface that provides a smooth, well-defined plane for the conformal metal layer to deposit upon. This intermediary layer ensures consistent and reliable electrical connection between the first electrode and conformal metal layer, eliminating the problems associated with depositing metal on rough or incompletely etched via surfaces.
4Manufacturing precision
If device substrate remains engaged with pMUT device to control resonance frequency, then resonance frequency is controlled, but electrical connection between first electrode and conformal metal layer is difficult to form
Solution Approach 1:
The etch stop layer is formed on the device substrate surface before the pMUT device is assembled. This preliminary formation enables subsequent via etching to easily penetrate through the dielectric film and electrode to reach the conformal metal layer, solving the via formation difficulty while the device substrate remains engaged to control resonance frequency.
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 provides a reliable, efficient electrically-conductive engagement between the first electrode and the conformal metal layer, reducing fatigue and maintaining the transducer's resonance properties, thus enhancing the acoustic signal generation and connectivity.
Implementation Method 1
a piezoelectric material disposed between the first electrode and a second electrode
Data Source
AI summary
Methods are provided for creating a metal or other electrically-conductive member extending from an air-backed cavity of a piezoelectric ultrasonic transducer (pMUT) apparatus defining such an air-backed cavity, through a substrate layer disposed adjacent to the transducer device of the pMUT device, and into electrically-conductive engagement with a first electrode of the pMUT device, such that the electrically-conductive member provides an electrically-conductive engagement between the first electrode and a conformal electrically-conductive layer deposited in the air-backed cavity of the pMUT device. Associated apparatuses are also provided.