Low Temperature Poly-Silicon TFT Ohmic Contact via ALD
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Solution Overview
Problem
Low temperature poly-silicon thin film transistors (LTPS TFTs) manufactured on flexible substrates using existing ion implantation and high temperature activation processes exhibit poor device performance due to the inability to achieve high temperature activation below the flexible substrate's temperature limit, resulting in numerous defects and suboptimal electrical characteristics.
Innovation Solution
The method involves forming an ohmic contact layer using atomic layer deposition (ALD) with conductive ionic layers and monocrystalline or poly-silicon layers on the active layer, allowing for the formation of good ohmic contacts between the source and drain electrodes and the active layer without the need for high temperature activation, thereby improving device performance on flexible substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ion implantation and high temperature activation processes are used to manufacture LTPS TFTs, then good ohmic contacts and electrical characteristics are achieved, but the manufacturing temperature exceeds the flexible substrate temperature limit of 400°C
Solution Approach 1:
The patent changes the temperature parameter from high temperature (600°C or more) to low temperature (below 400°C) processing. This is achieved by replacing the conventional ion implantation and high temperature activation process with a low temperature deposition process that forms ohmic contact layers without requiring high temperature activation, thus resolving the contradiction between achieving good electrical characteristics and staying within the flexible substrate temperature limit.
Solution Approach 2:
The patent substitutes the mechanical/thermal process (ion implantation followed by high temperature thermal activation) with a deposition-based process (forming conductive ionic layers and monocrystalline silicon layers through deposition). This replacement eliminates the need for high temperature activation while still achieving good ohmic contacts, resolving the temperature contradiction.
2Reliability
If high temperature activation is performed to eliminate doping defects, then device performance is improved, but the flexible substrate cannot withstand the temperature
Solution Approach 1:
The patent converts the limitation of low temperature processing (which would normally prevent proper activation and leave defects) into a benefit by using a deposition process that inherently forms high quality, defect-free ohmic contact layers without requiring activation. The deposition process itself creates the desired crystalline structure and electrical properties without thermal damage, turning the temperature constraint into an advantage for flexible substrate compatibility.
3Reliability
If conventional non-flexible substrate manufacturing methods are used, then good TFT characteristics are obtained, but the method is not suitable for flexible substrate manufacturing
Solution Approach 1:
The patent creates a universal manufacturing process that can be applied to both flexible and non-flexible substrates. The low temperature deposition process that forms ohmic contact layers is substrate-agnostic, meaning it works equally well on flexible substrates (below 400°C) and non-flexible substrates. This multi-functional approach resolves the contradiction by making the process adaptable to different substrate types while maintaining good device characteristics.
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 approach enables the formation of LTPS TFTs with enhanced performance by accurately creating ohmic contacts at lower temperatures, reducing defects and improving electron mobility, making the process compatible with flexible substrate manufacturing while maintaining low processing temperatures.
Implementation Method 1
forming an ohmic contact layer on the active layer through an atomic layer deposition process
Implementation Method 2
The ohmic contact layer includes a plurality of conductive ionic layers and a plurality of monocrystalline silicon layers/poly-silicon layers
Data Source
AI summary
A low temperature poly-silicon thin film transistor and a manufacturing method thereof are disclosed. The method includes forming an active layer on a base substrate, forming an ohmic contact layer on the active layer through an atomic layer deposition process, and forming a source electrode and a drain electrode on the ohmic contact layer. The ohmic contact layer includes a plurality of conductive ionic layers and a plurality of monocrystalline silicon layers/poly-silicon layers. The source electrode and the drain electrode are in contact with the active layer through the ohmic contact layer.