Solid-State Image Sensor Capacitance Switching

Solution Overview

Problem

In solid-state image pickup devices, the dynamic range is limited due to the need to reduce the size of photodiodes and transistors to accommodate a capacitive element for varying capacitance, leading to decreased light sensitivity and image quality under varying illuminance conditions.

Innovation Solution

The implementation of a charge accumulation element that can be selectively connected to a charge-voltage conversion element via a capacitance switch, allowing for adjustment of capacitance to optimize conversion efficiency under different illuminance conditions, thereby improving image quality without reducing the size of other pixel components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a capacitive element is provided between pixels to vary capacitance of the FD region, then dynamic range is increased, but area of photodiode and pixel transistors must be reduced

Engineering Contradiction:

Improvedynamic rangeVSAvoidarea of photodiode

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The charge accumulation element is positioned in the vertical dimension by overlapping with the charge accumulation region of the photodiode, rather than occupying horizontal space between pixels. This allows capacitance variation functionality to be added without reducing the horizontal area of photodiodes or transistors.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The charge accumulation element is nested within the vertical space above the charge accumulation region of the photodiode, utilizing the overlapping area to provide capacitance without requiring additional lateral space. This nesting approach allows the capacitive element to be integrated into the existing pixel structure.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Adaptability or versatility

If area of photodiode is reduced to accommodate capacitive element, then capacitance can be added to FD region, but light receiving sensitivity and saturated signal amount are decreased

Engineering Contradiction:

Improvecapacitance adjustment capabilityVSAvoidlight receiving sensitivity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The charge accumulation element is positioned in the vertical dimension by overlapping with the charge accumulation region of the photodiode, rather than occupying horizontal space between pixels. This allows capacitance variation functionality to be added without reducing the horizontal area of photodiodes or transistors.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Adaptability or versatility

If size of amplifier transistor is reduced to make space for capacitive element, then capacitance can be increased, but random noise is increased and image quality is degraded

Engineering Contradiction:

Improvecapacitance of charge-voltage conversion elementVSAvoidimage quality

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The charge accumulation element is positioned in the vertical dimension by overlapping with the charge accumulation region of the photodiode, rather than occupying horizontal space between pixels. This allows capacitance variation functionality to be added without reducing the horizontal area of photodiodes or transistors.

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

This solution enhances the dynamic range and image quality by allowing for optimal capacitance adjustment, increasing light sensitivity and reducing noise, especially under high-illuminance conditions, without compromising the area of photodiodes and transistors.

Implementation Method 1

a photoelectric conversion element performing photoelectric conversion on incident light and accumulating, in a charge accumulation region, electric charge obtained through the photoelectric conversion

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

a charge-voltage conversion element converting the electric charge into a voltage

Methodology Applied

Scientific EffectCharge-voltage conversion: Capacitance

Data Source

PatentUS10651213B2Solid-state image pickup device and method of driving the same

Publication Date: 2020.05.12 SONY GROUP CORP

AI summary

Imaging sensors, imaging apparatuses, and methods of driving an image sensor are provided. An image sensor can include a semiconductor substrate with a photoelectric conversion element and a charge-conversion element. The sensor can further include a capacitance switch. A charge accumulation element is located adjacent the photoelectric conversion element. At least a portion of the charge accumulation element overlaps a charge accumulation region of the photoelectric conversion element. The charge accumulation element is selectively connected to the charge-voltage conversion element by the capacitance switch.