High Density PMUT Array Architecture via Doped Substrate Vias
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Solution Overview
Problem
The challenge lies in forming high-density arrays of piezoelectric micromachined ultrasound transducers (PMUTs) due to difficulties in integrating vias for voltage distribution, which hinders the production of ultrasound imaging devices capable of producing a wide bandwidth of ultrasound waves for both deep and shallow structures with high-resolution imaging.
Innovation Solution
The design includes a substrate with conductive vias surrounded by isolating structures, an insulating layer with through-holes, and a piezoelectric stack on a membrane that vibrates in response to an alternating voltage, allowing for efficient electrical connection and increased mechanical robustness, enabling the formation of high-density PMUT arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional vias are used to provide voltage to piezoelectric electrodes in PMUTs, then electrical connection is achieved, but the density of the PMUT array is reduced due to the space required for via integration
Solution Approach 1:
The patent merges the substrate and via structure by making the substrate itself conductive through doping, eliminating the need for separate via structures. The conductive substrate directly provides electrical connection to the piezoelectric electrodes, combining the substrate's mechanical support function with the electrical conduction function that would otherwise require separate via components.
Solution Approach 2:
The patent extracts the via structure from the PMUT design by using the doped substrate regions directly as the electrical connection path. Instead of adding separate via components through the substrate, the conductive regions are formed within the substrate plane, removing the vertical via extraction need and simplifying the overall structure.
2Measurement precision
If high-density PMUT arrays are formed, then ultrasound imaging resolution is improved, but manufacturing difficulty increases due to via integration challenges
Solution Approach 1:
The patent replaces the mechanical via formation process with a semiconductor doping process. Instead of physically drilling or etching holes through the substrate to create vias, the electrical conductivity is modified within the substrate material itself through doping, substituting a simpler planar semiconductor manufacturing process for complex mechanical via fabrication.
Solution Approach 2:
The patent changes the electrical parameter of the substrate by introducing dopants to create conductive regions. This parameter change transforms the substrate from electrically insulating to electrically conductive in specific regions, enabling direct electrical connection without structural modifications like via holes.
3Reliability
If PMUTs are used instead of CMUTs, then certain performance advantages are achieved, but array density is reduced due to piezoelectric electrode interconnections
Solution Approach 1:
The patent merges the electrical connection function into the substrate structure itself through doped regions. The conductive substrate regions serve dual purposes: providing mechanical support as part of the substrate and providing electrical connection paths to the piezoelectric electrodes, eliminating the need for separate via structures that would reduce array density.
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 configuration allows for the creation of high-density PMUT arrays that can generate ultrasound waves across a wide frequency range, enhancing the capability of ultrasound imaging devices to produce high-resolution images of both deep and shallow structures.
Implementation Method 1
A PMUT element is formed by a membrane suspended over a cavity carrying a layer of piezoelectric material sandwiched between thin electrode layers. In operation, a voltage is applied across the electrodes, resulting in a lateral strain being induced in the membrane via the piezoelectric effect causing movement of the piezoelectric layer. By applying a suitable AC voltage between the electrodes oscillation of the membrane is induced and an ultrasound wave is generated.
Data Source
AI summary
A PMUT includes a substrate being doped and having a plurality of conductive vias formed therein, each conductive via formed of a portion of the substrate extending completely from a back side of the substrate to a front side of the substrate and being encircled by an isolating structure that electrically isolates that portion of the substrate from other portions of the substrate. An insulating layer stacked on the front side of the substrate and has through-holes therein over the plurality of conductive vias. An interconnection layer is stacked on the insulating layer and is connected to the plurality of conductive vias. A membrane carried is by the interconnection layer and underlying substrate, the membrane being shaped so as to delimit a chamber. A piezoelectric stack formed on the membrane over the chamber and vibrates the membrane in response to application of an alternating voltage to the piezoelectric stack.