Zinc-Oxide Thin Film Transistors for Flexible Substrates
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Solution Overview
Problem
Current thin film transistors (TFTs) face challenges with high processing temperatures and material wastage due to vacuum deposition of amorphous silicon, limiting their use on flexible substrates, and existing organic semiconductors have inferior electronic properties compared to amorphous silicon.
Innovation Solution
A method for preparing zinc-oxide-based semiconductor films using nanoparticles, applied as a seed coating and overcoated with a soluble precursor, followed by annealing at low temperatures, to create n-type or p-type TFTs suitable for flexible substrates with improved mobility and on/off ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vacuum deposition of amorphous silicon is used to make TFTs, then electrical characteristics sufficient for display applications are achieved, but processing temperatures of about 360°C are required which disallow deposition on plastic substrates
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to zinc oxide-based semiconductor, which fundamentally alters the processing temperature requirement from 360°C to below 200°C, enabling deposition on plastic substrates while maintaining functional performance
Solution Approach 2:
The patent replaces the vacuum deposition process with solution-based deposition methods (spin coating, dip coating, inkjet printing), substituting a mechanical/vacuum-based system with a chemical solution-based system that operates at lower temperatures
2Ease of manufacture
If vacuum deposition of amorphous silicon is used, then TFTs are fabricated, but continuous coverage is required leading to time-consuming patterning steps and material waste
Solution Approach 1:
The patent extracts the semiconductor material only where needed by using solution-based deposition methods that allow selective application and patterning, eliminating the continuous coverage requirement of vacuum deposition and reducing material waste
Solution Approach 2:
The solution-based deposition process inherently allows for additive manufacturing where material is deposited only in required patterns, and excess material can be removed or not applied at all, making the process self-sufficient without requiring subsequent subtractive patterning steps
3Temperature
If organic semiconductors are used as alternatives to amorphous silicon, then lower processing temperatures are achieved, but electronic properties are inferior or problematic
Solution Approach 1:
The patent uses zinc oxide-based semiconductor materials that combine the advantages of both organic and inorganic materials: like organic materials, they can be processed at low temperatures from solutions, but like inorganic materials, they provide stable and reliable electronic properties
Solution Approach 2:
The patent employs solution-processed zinc oxide materials that can be applied as thin films and annealed at low temperatures, creating a disposable-like process approach where simple, low-cost materials and processes are used effectively without requiring complex, expensive equipment or high-temperature processing
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
The method enables the production of TFTs with field-effect electron mobility greater than 0.01 cm2/Vs and on/off ratios of at least 104, suitable for flexible substrates and display applications, while maintaining stability in air and reducing material costs.
Implementation Method 1
annealing the porous layer of zinc-oxide-based nanoparticles at a temperature of at least 50° C. to produce a semiconductor film
Implementation Method 2
an overcoat solution comprising a soluble zinc-oxide-precursor compound that converts to zinc oxide upon annealing
Data Source
AI summary
A thin film transistor comprises a zinc-oxide-containing semiconductor material. Such transistors can further comprise spaced apart first and second contact means or electrodes in contact with said material. Further disclosed is a process for fabricating a thin film transistor device, wherein the substrate temperature is no more than 300° C. during fabrication.