Oxide Semiconductor Transistor Multilayer Film Stability

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Solution Overview

Problem

Semiconductor devices with oxide semiconductor layers face challenges in achieving stable electrical characteristics and reliability due to interface state formation and variations in threshold voltage, primarily caused by impurities and oxygen vacancies.

Innovation Solution

A semiconductor device with a multilayer film structure comprising an oxide layer and an oxide semiconductor layer, where the oxide layer has a larger energy gap and contains elements like aluminum, silicon, or gallium in higher proportions, reducing impurities and oxygen vacancies, and is positioned on the back channel side to suppress interface state formation and enhance channel formation in the oxide semiconductor layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an oxide semiconductor layer is used to achieve high field-effect mobility and low leakage current, then transistor performance is improved, but interface state formation and threshold voltage variations occur due to impurities and oxygen vacancies

Engineering Contradiction:

Improveelectrical characteristics stabilityVSAvoidinterface state formation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

An oxide layer is introduced as an intermediary between the gate insulating film and the oxide semiconductor layer. This oxide layer acts as a mediator that prevents direct interaction between the gate insulating film and the oxide semiconductor layer, thereby suppressing interface state formation and improving the stability of electrical characteristics.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs a composite structure consisting of multiple oxide layers with different compositions and properties. The gate insulating film, oxide layer, and oxide semiconductor layer form a composite material system where each layer contributes specific functions, resulting in improved overall device reliability and reduced harmful effects.

Inventive Principle:

Principle #40Composite materials

2Device complexity

If the oxide semiconductor layer is directly contacted with the gate insulating film to simplify structure, then device complexity is reduced, but impurity concentration and oxygen vacancies increase causing threshold voltage variations

Engineering Contradiction:

Improvelayer structureVSAvoidthreshold voltage control

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The oxide layer serves as an intermediary that prevents direct contact between the gate insulating film and the oxide semiconductor layer. This intermediary layer reduces impurity concentration and oxygen vacancies at the interface, enabling better control of threshold voltage without significantly increasing device complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If high-temperature heat treatment or laser light treatment is applied to form polycrystalline silicon layer for high field-effect mobility, then transistor performance is improved, but manufacturing process complexity and cost increase

Engineering Contradiction:

Improvefield-effect mobilityVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the material parameter from silicon-based semiconductors to oxide semiconductors, which inherently provide high field-effect mobility without requiring high-temperature heat treatment or laser light treatment. This parameter change simplifies the manufacturing process while maintaining high transistor performance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The use of oxide semiconductor materials in composite structure with oxide layers enables achievement of high field-effect mobility through material composition rather than complex processing, thereby simplifying manufacturing while improving reliability.

Inventive Principle:

Principle #40Composite materials

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 stabilizes electrical characteristics by reducing impurity concentrations, minimizing interface states, and maintaining low oxygen vacancy generation, thereby improving the reliability and field-effect mobility of the transistor.

Implementation Method 1

The oxide layer contains a common element to the oxide semiconductor layer and has a larger energy gap than the oxide semiconductor layer

Methodology Applied

Scientific EffectEnergy gap:

Implementation Method 2

interface state formation and variations in threshold voltage, primarily caused by impurities and oxygen vacancies

Methodology Applied

Scientific EffectInterface state formation:

Implementation Method 3

minimizing interface states, and maintaining low oxygen vacancy generation

Methodology Applied

Scientific EffectOxygen vacancy:

Data Source

PatentUS9660093B2Transistor with multilayer film including oxide semiconductor layer and oxide layer

Publication Date: 2017.05.23 SEMICON ENERGY LAB CO LTD

AI summary

Stable electrical characteristics of a transistor including an oxide semiconductor layer are achieved. A highly reliable semiconductor device including the transistor is provided. The semiconductor device includes a multilayer film formed of an oxide layer and an oxide semiconductor layer, a gate insulating film in contact with the oxide layer, and a gate electrode overlapping with the multilayer film with the gate insulating film interposed therebetween. The oxide layer contains a common element to the oxide semiconductor layer and has a large energy gap than the oxide semiconductor layer. The composition between the oxide layer and the oxide semiconductor layer gradually changes.