Back-Illuminated Imaging Sensor Transistor Layout

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Solution Overview

Problem

Front-illuminated solid-state imaging apparatus with a multi-pixel sharing structure faces challenges in maximizing sensor area due to layout constraints, leading to non-uniform photodiode shapes and pixel-to-pixel sensitivity variations, while back-illuminated types have underutilized potential for optimizing multi-pixel sharing layouts.

Innovation Solution

A back-illuminated solid-state imaging apparatus with a multi-pixel sharing structure where readout circuit transistors are aligned between pixels, reducing the number of readout circuits and minimizing extra space, thereby maximizing sensor area by optimizing the layout of transistors and wiring.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If readout circuit transistors are placed apart due to layout constraints in front-illuminated structure, then transistor placement flexibility is improved, but sensor area is reduced and photodiode shape becomes non-uniform

Engineering Contradiction:

Improvetransistor placement flexibilityVSAvoidsensor area

Core Design Contradiction:

Ease of manufactureVSArea of moving object

Solution Approach 1:

The patent inverts the conventional front-illuminated structure by adopting a back-illuminated structure, where light enters through the opposite surface. This inversion allows readout circuit transistors to be placed on the light-exit side rather than the light-entry side, eliminating layout constraints that previously forced transistors apart and enabling compact, uniform photodiode shapes while maximizing sensor area.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent utilizes the third dimension by stacking the readout circuit transistors vertically below the photodiodes in the back-illuminated structure. This vertical arrangement in the depth dimension allows transistors to be positioned close to photodiodes without interfering with light paths, thereby maximizing sensor area while maintaining placement flexibility.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Area of moving object

If photodiode area is expanded to use extra space, then sensor area utilization is improved, but photodiode shape uniformity deteriorates causing pixel-to-pixel sensitivity variations

Engineering Contradiction:

Improvesensor area utilizationVSAvoidphotodiode shape uniformity

Core Design Contradiction:

Area of moving objectVSManufacturing precision

Solution Approach 1:

By inverting to a back-illuminated structure, the patent eliminates the need to expand photodiode areas into irregular shapes. The inversion allows regular, uniform photodiode shapes to maintain optimal sensor area utilization since readout transistors are positioned on the opposite side, removing the geometric constraints that caused shape non-uniformity.

Inventive Principle:

Principle #13The other way round (Inversion)

3Area of moving object

If multi-pixel sharing structure is implemented in back-illuminated type, then sensor area is maximized, but layout optimization potential remains underutilized

Engineering Contradiction:

Improvesensor areaVSAvoidlayout optimization

Core Design Contradiction:

Area of moving objectVSDevice complexity

Solution Approach 1:

The patent merges multiple pixels' readout functions into shared transistors in the back-illuminated structure. By combining readout circuits for multiple pixels and positioning them compactly on the light-exit side, the patent maximizes sensor area while actually simplifying layout optimization compared to front-illuminated structures.

Inventive Principle:

Principle #5Merging (Combining)

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 allows for increased sensitivity and saturation output while maintaining optical characteristics, reducing pixel size and improving signal processing speed by minimizing wiring resistance and extra space, thus enhancing the overall performance of the imaging apparatus.

Implementation Method 1

a plurality of sensors that are formed on a substrate on a pixel basis and photoelectrically convert the light incident from a first surface side of the substrate

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS7812874B2Solid-state imaging apparatus and camera

Publication Date: 2010.10.12 SONY GROUP CORP

AI summary

A solid-state imaging apparatus includes a plurality of sensors that are formed on a substrate on a pixel basis and photoelectrically convert the light incident from a first surface side of the substrate, and a readout circuit that is formed on a second surface side of the substrate, which is the opposite side to the first surface side, and processes a signal from the plurality of sensors. The readout circuit includes a plurality of transistors and the transistors are disposed in a region between the pixels in an aligned manner.