Germanium Photodiode JFET With Doped Silicon Leakage Control

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Solution Overview

Problem

Existing optical image sensors face challenges with high dark current and low optical fill factor due to poor interfaces and surface quality between semiconductor layers, limiting their performance and reliability.

Innovation Solution

The development of germanium-based photosensitive devices with a doped silicon layer between the germanium layer and the silicon substrate, along with a junction field effect transistor (JFET) and pinned photodiode passivation layer, reduces leakage current and improves optical fill factor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional optical image sensors are used, then manufacturing is simpler, but dark current is high and optical fill factor is low

Engineering Contradiction:

Improvedark current performanceVSAvoidsensor structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

An intermediate layer structure is introduced between the germanium photodiode and silicon substrate, consisting of a first doped silicon layer and a second doped silicon layer with different doping types and concentrations. This intermediary structure passivates interface states and reduces dark current leakage without requiring complete redesign of the sensor architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The sensor employs a composite structure combining germanium photodiode layers with multiple doped silicon layers of varying doping characteristics. This composite material approach leverages the complementary properties of germanium (high light sensitivity) and silicon (low dark current) to achieve superior overall performance.

Inventive Principle:

Principle #40Composite materials

2Reliability

If interface quality between semiconductor layers is poor, then manufacturing is easier, but leakage current increases

Engineering Contradiction:

Improveleakage currentVSAvoidinterface quality

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

Different doped silicon layers are positioned at specific locations with different doping types (n-type and p-type) and concentrations tailored to local interface requirements. The first doped silicon layer addresses one interface while the second layer addresses another, providing localized quality enhancement where needed most.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The doping concentration and doping type parameters are varied across different silicon layers to optimize interface passivation. By changing these material parameters locally rather than uniformly, the structure achieves superior leakage current reduction while maintaining manufacturing feasibility.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If optical fill factor is increased, then light sensitivity improves, but device area increases

Engineering Contradiction:

Improveoptical fill factorVSAvoidpixel area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

Thin film doped silicon layers are used to passivate interfaces without adding significant vertical or lateral dimension. These thin film structures enable improved optical fill factor and light sensitivity while maintaining compact pixel dimensions suitable for high-resolution imaging applications.

Inventive Principle:

Principle #30Flexible shells and thin films

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 significantly reduces leakage current, enhances optical fill factor, and improves conversion gain and noise performance, leading to better sensitivity and reliability of the germanium-based sensors.

Implementation Method 1

a doped silicon layer disposed between the germanium layer and the silicon substrate

Methodology Applied

Scientific EffectElectrical conduction control: Conduction (electrical)

Implementation Method 2

a junction field effect transistor (JFET)

Methodology Applied

Scientific EffectField effect: Electric Field

Implementation Method 3

pinned photodiode passivation layer

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11855237B2Germanium-based sensor with junction-gate field effect transistor and method of fabricating thereof

Publication Date: 2023.12.26 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Germanium-based sensors are disclosed herein. An exemplary germanium-based sensor includes a germanium photodiode and a junction field effect transistor (JFET) formed from a germanium layer disposed on and/or in a silicon substrate. A doped silicon layer, which can be formed by in-situ doping epitaxially grown silicon, is disposed between the germanium layer and the silicon substrate. In embodiments where the germanium layer is on the silicon substrate, the doped silicon layer is disposed between the germanium layer and an oxide layer. The JFET has a doped polysilicon gate, and in some embodiments, a gate diffusion region is disposed in the germanium layer under the doped polysilicon gate. In some embodiments, a pinned photodiode passivation layer is disposed in the germanium layer. In some embodiments, a pair of doped regions in the germanium layer is configured as an e-lens of the germanium-based sensor.