CMUT Through-Substrate Via for Die Size Reduction

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Solution Overview

Problem

Conventional capacitive micromachined ultrasonic transducer (CMUT) devices face challenges with increased die size and complex packaging due to the use of bond pads for electrical connections, which complicates the design and performance of 2D CMUT arrays.

Innovation Solution

The implementation of through-substrate vias (TSVs) allows for bottom-side connections to the top plate of CMUT cells, eliminating the need for bond pads and reducing die size, enabling separate addressing of CMUT elements with a single TSV for each element or a common bottom-side electrode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bond pads are used for electrical connection to top plate, then electrical contact is established, but die size increases and packaging becomes complex

Engineering Contradiction:

Improveelectrical contactVSAvoiddie size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent transitions from planar bond pad connections on the top surface to vertical through-substrate via connections that pass through the substrate thickness dimension. This allows electrical contact to be established from the bottom surface, eliminating the need for top-side bond pads and reducing the horizontal die size occupied by interconnect routing.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

Instead of connecting to the top plate from the top surface using bond pads, the invention inverts the connection approach by routing electrical contacts through the substrate from the bottom surface to reach the top plate, thereby eliminating the need for elevated bond pads and complex top-side interconnect routing.

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of manufacture

If bond pads are placed remote from CMUT elements, then wire bonding is facilitated, but interconnect routing lines increase die size

Engineering Contradiction:

Improvewire bondingVSAvoiddie size

Core Design Contradiction:

Ease of manufactureVSArea of stationary object

Solution Approach 1:

The patent eliminates the need for extensive horizontal interconnect routing by transitioning to vertical through-substrate via connections. This dimensional change allows each CMUT element to be connected independently through the substrate thickness, removing the requirement for large-area metal interconnect traces on the top side.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The invention segments the electrical connection approach by providing individual through-substrate via connections for each CMUT element or element group, rather than using shared bond pads and routing lines. This segmentation eliminates the need for extensive metal interconnect traces while maintaining ease of manufacturing.

Inventive Principle:

Principle #1Segmentation

3Reliability

If extensive metal interconnect traces are used, then electrical contact to each element is achieved, but die size increases and performance decreases

Engineering Contradiction:

Improveelectrical contactVSAvoidinterconnect routing

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent resolves the complexity of extensive metal interconnect routing by transitioning to vertical through-substrate via connections. This dimensional change simplifies the interconnect architecture by eliminating the need for complex top-side routing patterns, reducing device complexity while maintaining reliable electrical contact to each element.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Reliability

If bond pads are used for 2D CMUT arrays, then electrical connection is provided, but packaging process becomes complicated

Engineering Contradiction:

Improveelectrical connectionVSAvoidpackaging process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent simplifies the packaging process by inverting the connection approach from top-side bond pads to bottom-side through-substrate via connections. This allows the CMUT array to be packaged with the active top surface facing the load, eliminating the need to accommodate elevated bond pads and complex wire bonding arrangements in the packaging design.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS10335827B2Ultrasonic transducer device with through-substrate via

Publication Date: 2019.07.02 TEXAS INSTRUMENTS INC

AI summary

A Capacitive Micromachined Ultrasonic Transducer (CMUT) device includes at least one CMUT cell including a first substrate having a top side including a patterned dielectric layer thereon including a thick and a thin dielectric region. A membrane layer is bonded on the thick dielectric region and over the thin dielectric region to provide a movable membrane over a micro-electro-mechanical system (MEMS) cavity. A through-substrate via (TSV) includes a dielectric liner which extends from a bottom side of the first substrate to a top surface of the membrane layer. A top side metal layer includes a first portion over the TSV, over the movable membrane, and coupling the TSV to the movable membrane. A patterned metal layer is on the bottom side surface of the first substrate including a first patterned layer portion contacting the bottom side of the first substrate lateral to the TSV.