3D Image Sensor Floating Diffusion Switching for Compact Pixels

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Solution Overview

Problem

In three-dimensional imaging devices, stacking semiconductor chips with insufficient consideration leads to increased chip size and hindrances in miniaturization due to electrical connections, which is not practical for maintaining current chip size and pixel area density.

Innovation Solution

An imaging device with a three-layer structure comprising a first substrate with photodiodes, a second substrate with pixel circuits, and a third substrate with processing circuits, where a switching unit enables electrical connection between floating diffusions, allowing for adjustable charge-voltage conversion efficiency without increasing substrate area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If three semiconductor substrates are stacked with insufficient consideration of electrical connections, then the chip size increases, but miniaturization of area per pixel is hindered

Engineering Contradiction:

Improvechip sizeVSAvoidarea per pixel density

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The patent transitions from a two-dimensional planar connection structure to a three-dimensional stacked structure. By stacking the first substrate (pixel array), second substrate (pixel circuit), and third substrate (processing circuit) in the vertical dimension, electrical connections are established through the thickness of the chip rather than expanding laterally. This dimensional change allows maintaining small area per pixel while accommodating all necessary circuitry.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent implements a nested structure where multiple functional substrates are stacked and integrated within a compact volume. The first substrate containing pixel arrays is nested with the second substrate containing pixel circuits, which is in turn nested with the third substrate containing processing circuits. This nesting approach consolidates multiple layers of functionality into a compact three-dimensional structure, preventing chip size expansion.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If all semiconductor substrates are bonded with their front surfaces, then electrical connections are established, but chip size increases

Engineering Contradiction:

Improveelectrical connectionVSAvoidchip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent inverts the conventional bonding approach by bonding the back surface of the first substrate to the front surface of the second substrate, rather than bonding front surfaces together. This inversion allows the pixel circuits on the second substrate to be positioned directly beneath the pixel arrays on the first substrate, establishing vertical electrical connections through the substrate thickness without requiring lateral expansion of the chip area.

Inventive Principle:

Principle #13The other way round (Inversion)

3Productivity

If floating diffusion capacitance is increased to improve charge-voltage conversion efficiency, then conversion efficiency improves, but substrate area increases

Engineering Contradiction:

Improvecharge-voltage conversion efficiencyVSAvoidsubstrate area

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The patent changes the capacitance parameter of the floating diffusion by introducing a capacitor structure connected to the floating diffusion node. Instead of increasing the physical area of the floating diffusion region, the patent modifies the electrical capacitance value through the addition of capacitive elements, allowing high charge-voltage conversion efficiency to be achieved without increasing substrate area.

Inventive Principle:

Principle #35Parameter changes

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 efficient switching of charge-voltage conversion levels based on imaging environment without expanding the substrate area, enabling miniaturization and maintaining current chip size.

Implementation Method 1

a pixel including a photodiode and floating diffusion that holds the charge converted by the photodiode

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS12155947B2Imaging device with capacitance switching

Publication Date: 2024.11.26 SONY SEMICON SOLUTIONS CORP

AI summary

An imaging device includes a first substrate, a second substrate, a third substrate, and a switching unit. The first substrate has a pixel including a photodiode and floating diffusion that holds the charge converted by the photodiode. The second substrate has a pixel circuit that reads out a pixel signal based on the charge held in the floating diffusion in the pixel, and is stacked on the first substrate. The third substrate has a processing circuit that detects a pixel signal read out by the pixel circuit, and is stacked on the second substrate. The switching unit is provided to enable electrical connection between the floating diffusion and a floating diffusion of another pixel in the first substrate, and is provided on the second substrate. As a result, by switching the capacitance of the floating diffusion of the pixel using floating diffusion of another pixel, it is possible to switch the charge-voltage conversion efficiency levels.