Heterojunction Photodiode Layout for Higher CMOS Light Sensitivity

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Solution Overview

Problem

Conventional CMOS image sensors face issues with reduced light sensitivity and increased crosstalk noise due to light being blocked or scattered by interconnection layers, and miniaturization of pixel units is restricted by photodiodes formed in the substrate.

Innovation Solution

A photosensitive device with heterojunction photodiodes formed on the surface of the interconnection layer, using a first and second material layer to create a p-n junction that absorbs light and generates electrical signals, allowing for improved light sensitivity and reduced noise without being limited by substrate constraints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If photodiodes are formed in the substrate, then the device structure is simple, but the photosensitive area is reduced and light sensitivity deteriorates due to interconnection layer interference

Engineering Contradiction:

Improvephotosensitive areaVSAvoiddevice structure

Core Design Contradiction:

Area of stationary objectVSDevice complexity

Solution Approach 1:

The photodiode structure is moved from the substrate plane to the surface of the interconnection layer, transitioning from a two-dimensional in-substrate configuration to a three-dimensional on-surface configuration. This dimensional change allows the photosensitive area to extend beyond the substrate constraints while maintaining electrical connectivity through vertical conductive paths.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The interconnection layer serves as an intermediary platform that supports the photodiode structure. Instead of the substrate directly containing the photodiodes, the interconnection layer acts as a mediator that provides both electrical connectivity and a surface for forming enhanced photosensitive structures with increased light reception area.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Illumination intensity

If lights pass through interconnection layer to reach photodiodes, then the device structure is maintained, but light sensitivity is reduced due to absorption and scattering

Engineering Contradiction:

Improvelight sensitivityVSAvoidlight absorption and scattering

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The photodiode photosensitive region is extracted from the substrate and repositioned on the interconnection layer surface. This extraction removes the photodiodes from the path of incident light, eliminating the problem where light must pass through the interconnection layer to reach the photosensitive area, thereby preventing absorption and scattering losses.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of light passing through the interconnection layer to reach the photodiodes in the substrate, the structure is inverted so that the photodiodes are positioned on top of the interconnection layer, allowing light to reach the photosensitive area directly without penetrating the interconnection layer.

Inventive Principle:

Principle #13The other way round (Inversion)

3Productivity

If photodiodes are formed in the substrate, then the manufacturing process is conventional, but pixel unit miniaturization is restricted

Engineering Contradiction:

Improvepixel unit miniaturizationVSAvoidphotosensitive area

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

By moving the photodiode formation to the surface of the interconnection layer, the design utilizes the third dimension (vertical height) to increase photosensitive area. This allows pixel units to be miniaturized in the planar dimensions while compensating for the reduced area by extending the photosensitive region vertically on the interconnection layer surface.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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

The solution enhances light sensitivity, reduces noise, and increases response speed by forming photodiodes on the surface, allowing for larger photosensitive areas and improved light reception without absorption or scattering by interconnection layers.

Implementation Method 1

the first material layer and the second material layer form a heterojunction photodiode

Methodology Applied

Scientific EffectPhotovoltaic effect: Photovoltaic Effect

Implementation Method 2

lights are incident on the front side of the chip (the front side of the substrate) and will have to pass through the interconnection layer on the substrate to be received by the photodiode (PD) portions formed in the substrate for being converted into electrical signals

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS12094896B2Photosensitive semiconductor device including heterojunction photodiode

Publication Date: 2024.09.17 UNITED MICROELECTRONICS CORP

AI summary

A photosensitive device is disclosed, including an integrated circuit structure, a first pad and a second pad exposed from a surface of the integrated circuit structure, a first material layer disposed on the surface of the integrated circuit structure and covering the first pad, and a second material layer disposed on the first material layer and covering the second pad. The first material layer and the second material layer form a heterojunction photodiode.