Thin Film Transistor with Dual-Layer Oxide Semiconductor

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Solution Overview

Problem

Thin film transistors using oxide semiconductors face challenges in controlling threshold voltage due to carrier density increases during the formation of protective films and annealing processes, leading to variations in transistor characteristics and difficulties in maintaining a positive threshold voltage.

Innovation Solution

A thin film transistor design featuring a dual-layer structure with a first oxide semiconductor layer as the channel and a second oxide semiconductor layer of opposite polarity on the source/drain electrodes side, forming a pn junction to suppress carrier accumulation and control threshold voltage without the need for additional annealing or thinning processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If protective films (SiO2 or SiN) are formed by PECVD to suppress oxygen absorption/desorption effects, then transistor characteristic stability is improved, but hydrogen is mixed into the oxide semiconductor layer causing carrier density increase and threshold voltage shift to negative side

Engineering Contradiction:

Improvetransistor characteristic stabilityVSAvoidhydrogen mixing into oxide semiconductor layer

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

A nitrogen-containing oxide semiconductor layer is introduced as an intermediary layer between the oxide semiconductor layer and the protective film. This intermediary layer acts as a barrier to prevent hydrogen from the protective film from mixing into the oxide semiconductor layer, while still allowing the protective film to suppress oxygen absorption/desorption effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The protective film structure is segmented into multiple layers: an outer protective film layer (SiO2 or SiN) for suppressing oxygen effects, and an inner nitrogen-containing oxide semiconductor layer for preventing hydrogen mixing. This segmentation allows each layer to perform its specific function independently.

Inventive Principle:

Principle #1Segmentation

2Manufacturing precision

If annealing process is performed in oxygen atmosphere to recover transistor characteristics after protective film formation, then threshold voltage control is improved, but processing time and complexity increase

Engineering Contradiction:

Improvethreshold voltage controlVSAvoidannealing process time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The nitrogen-containing oxide semiconductor layer is formed in advance during the protective film formation process itself, without requiring separate preliminary treatments. This preliminary action prevents hydrogen mixing from occurring in the first place, eliminating the need for subsequent annealing processes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The harmful annealing process step is extracted and eliminated from the manufacturing process. By preventing hydrogen mixing at the source through the nitrogen-containing layer, the patent removes the need for the time-consuming annealing step that was previously required to correct threshold voltage shifts.

Inventive Principle:

Principle #2Taking out (Extraction)

3Manufacturing precision

If oxide semiconductor layer thickness is reduced to control threshold voltage, then threshold voltage positivity is improved, but film thickness control difficulty and process reproductivity issues increase

Engineering Contradiction:

Improvethreshold voltage positivityVSAvoidfilm thickness control difficulty

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Instead of changing the thickness parameter of the oxide semiconductor layer, the patent changes the compositional parameter by introducing a nitrogen-containing oxide semiconductor layer. This parameter change achieves threshold voltage control without the difficulties associated with extreme thinning of the oxide semiconductor layer.

Inventive Principle:

Principle #35Parameter changes

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 design effectively maintains a positive threshold voltage without requiring lengthy annealing or thinning processes, improving process reproductivity and reducing the influence of hydrogen and oxygen desorption on transistor characteristics.

Implementation Method 1

a second oxide semiconductor layer provided on the pair of source/drain electrodes side of the first oxide semiconductor layer, and having a polarity different from that of the first oxide semiconductor layer

Methodology Applied

Scientific Effectpn junction: Diode

Implementation Method 2

changes in characteristics of the oxide semiconductor caused by absorption/desorption of oxygen are remarkable

Methodology Applied

Scientific EffectOxygen absorption/desorption: Absorption (physical)

Implementation Method 3

hydrogen as a donor is mixed into the oxide semiconductor layer, and desorption of the oxygen occurs

Methodology Applied

Scientific EffectHydrogen doping: Dopants

Data Source

PatentUS8581245B2Thin film transistor, method of manufacturing thin film transistor, display unit, and electronic device

Publication Date: 2013.11.12 MAGNOLIA BLUE CORP

AI summary

There is provided a thin film transistor including: a gate electrode; a pair of source/drain electrodes; a first oxide semiconductor layer provided between the gate electrode, and the pair of source/drain electrodes, and forming a channel; and a second oxide semiconductor layer provided on the pair of source/drain electrodes side of the first oxide semiconductor layer, and having a polarity different from that of the first oxide semiconductor layer.