Double Layer Photodiode Array for Ambient Light and Proximity Detection

Solution Overview

Problem

Existing ambient light sensors and proximity detectors face challenges in simultaneously achieving enhanced sensitivity to visible wavelengths for ambient light sensing and infrared wavelengths for proximity detection, with prior solutions compromising on infrared sensitivity due to conflicting demands.

Innovation Solution

A double-layered photodiode array with a first set of photodiodes under green filters and a second set under both green and red filters, along with a third photodiode for infrared detection, allows for improved ambient light sensing by reducing common-mode infrared detection and enhanced proximity detection by optimizing junction depth for infrared sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a silicon photodiode is used for ambient light sensing, then it is sensitive to visible light, but it is also overly sensitive to infrared wavelengths outside human vision range

Engineering Contradiction:

Improveambient light sensing accuracyVSAvoidinfrared sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The sensor is divided into two separate photodiode structures: a first photodiode for ambient light sensing and a second photodiode for proximity detection. This segmentation allows each photodiode to be optimized for its specific function, with the first photodiode having reduced infrared sensitivity and the second photodiode having enhanced infrared sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the sensor have different structural properties. The first photodiode has a junction depth optimized for visible light with reduced infrared response, while the second photodiode has a deeper junction depth optimized for infrared detection. This local differentiation resolves the contradiction by giving each region the quality it needs.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the photodiode junction depth is optimized for visible light sensing, then ambient light detection is improved, but infrared sensitivity for proximity detection is reduced

Engineering Contradiction:

Improvevisible light detection accuracyVSAvoidinfrared detection capability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The sensor is divided into two separate photodiode structures: a first photodiode for ambient light sensing and a second photodiode for proximity detection. This segmentation allows each photodiode to be optimized for its specific function, with the first photodiode having reduced infrared sensitivity and the second photodiode having enhanced infrared sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the sensor have different structural properties. The first photodiode has a junction depth optimized for visible light with reduced infrared response, while the second photodiode has a deeper junction depth optimized for infrared detection. This local differentiation resolves the contradiction by giving each region the quality it needs.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If separate ambient light sensor and proximity detector structures are used, then each function can be optimized, but chip area increases

Engineering Contradiction:

Improvedetection accuracyVSAvoidchip area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

Two separate photodiode structures for ambient light sensing and proximity detection are merged into a single integrated sensor array. The first and second photodiodes share common structural elements including the substrate, epitaxial layer, and filter structures, allowing both functions to coexist on the same chip with reduced total area.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The sensor array is designed with multi-functionality, where the first photodiode serves ambient light sensing and the second photodiode serves proximity detection. Both photodiodes can be processed simultaneously through the same manufacturing steps, making the structure universally applicable for both functions without requiring separate dedicated areas.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 enhances the accuracy and reliability of both ambient light and proximity detection, reducing errors and conserving chip area while improving signal-to-noise ratio and reducing sensitivity to process variations.

Implementation Method 1

A double-layered photodiode array for ambient light sensing and infrared sensing

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS8269172B2Double layer photodiodes in ambient light sensors and proximity detectors

Publication Date: 2012.09.18 MAXIM INTEGRATED PROD INC

AI summary

Embodiments of the present invention provide systems, devices and methods for detecting both ambient light and proximity to an object. This detection is performed by a double-layered photodiode array and corresponding circuitry such that ambient light and proximity detection are enabled by a plurality of integrated photodiodes. In various embodiments of the invention, ambient light is sensed using a first set of photodiodes and a second set of photodiodes such that a spectral response is created that is approximately equal to the visible light spectrum. Proximity detection is realized using an integrated photodiode, positioned below the first and second sets of photodiodes, that detects infrared light and generates a response thereto.