IGZO Field-Effect Transistor Heat Diffusion Layer Design
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Solution Overview
Problem
Field effect transistors using IGZO oxide semiconductors face heat generation issues during operation, leading to reliability deterioration due to insufficient heat dissipation, particularly on substrates with low thermal conductivity, such as resin substrates, where heat storage causes temperature increases above 100°C or 300°C, affecting TFT characteristics and substrate dimensions.
Innovation Solution
A field effect transistor design incorporating a heat diffusion layer with specific thermal conductivity and film thickness conditions, positioned either as part of or separate from the gate insulating film, to manage heat dissipation effectively, with the heat diffusion layer's thermal conductivity exceeding that of the substrate and satisfying specific conditions to maintain heat generation below critical temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat dissipating layer with higher thermal conductivity than glass substrate is formed, then heat dissipation is improved, but the thermal conductivity relationship between substrate and heat dissipating layer is not clearly defined, making it uncertain whether the function is sufficiently achieved
Solution Approach 1:
The patent establishes specific parameter relationships between substrate thermal conductivity (Nsub) and heat dissipating layer thermal conductivity (Nkaku) through mathematical formulas. These parameter changes define precise conditions under which the heat dissipating layer effectively performs its function, transforming the uncertain qualitative relationship into quantifiable design criteria.
Solution Approach 2:
The patent provides design guidelines that allow selection of appropriate thermal conductivity values based on substrate properties, enabling engineers to choose cost-effective materials and thicknesses that meet minimum performance requirements without over-engineering the heat dissipation system.
2Power
If high voltage is applied during driving, then driving performance is improved, but Joule heat is generated and the temperature of the active layer rises locally, causing deterioration in driving and reliability
Solution Approach 1:
The heat dissipating layer acts as an intermediary thermal management component between the active layer and the substrate. It provides a dedicated thermal conduction pathway that separates the electrical function (performed by the active layer at high voltage) from the thermal management function, allowing high power operation without direct thermal coupling to the substrate.
Solution Approach 2:
The patent divides the thermal management function into separate layers: the active layer generates heat during high-voltage operation, the heat dissipating layer specifically manages heat removal, and the substrate provides mechanical support. This segmentation allows each layer to be optimized for its specific function, enabling high power driving while controlling temperature rise.
3Reliability
If the temperature at the time of heat generation becomes greater than or equal to 100°C, then the minute amount of moisture that exists within the substrate or the active layer, the insulating layer or the electrodes is affected, and the TFT characteristic is changed
Solution Approach 1:
The heat dissipating layer is positioned adjacent to the active layer to preemptively conduct heat away before it can raise the temperature to 100°C or higher. This preliminary thermal management prevents the temperature rise that would otherwise trigger moisture-related degradation mechanisms in the TFT structure.
4Reliability
If the temperature at the time of heat generation becomes greater than or equal to 300°C, then the oxygen that exists within the active layer changes, and the TFT characteristic is changed
Solution Approach 1:
The heat dissipating layer provides continuous thermal conduction path that prevents temperature from reaching 300°C, where oxygen-related changes would occur in the active layer. By maintaining temperature below this critical threshold, the layer preemptively protects against oxygen-induced TFT characteristic changes.
5Adaptability or versatility
If a resin substrate with low thermal conductivity is used for flexible devices, then flexibility is improved, but heat storage is easier and deterioration in driving due to heat generation is more marked
Solution Approach 1:
The patent applies local quality enhancement by inserting a heat dissipating layer with high thermal conductivity specifically at the location where heat is generated (adjacent to the active layer). This localized thermal management solution allows the use of flexible resin substrates with low overall thermal conductivity while preventing heat accumulation at the critical active layer region.
Solution Approach 2:
The patent creates a composite structure combining the flexible resin substrate with a high thermal conductivity heat dissipating layer. This composite approach allows the device to maintain flexibility from the resin substrate while gaining effective heat dissipation capabilities from the integrated heat dissipating layer, solving both requirements simultaneously.
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 solution effectively reduces heat generation temperatures during operation, enhancing the reliability and stability of field effect transistors, particularly on resin substrates, by ensuring the heat diffusion layer's thermal conductivity meets the required conditions to manage heat effectively.
Implementation Method 1
a heat diffusion layer which is the same as or separate from the gate insulating film, and which is different than the gate electrode, the source electrode and the drain electrode
Data Source
AI summary
There is provided a field effect transistor having, on a substrate, at least a gate electrode, a gate insulating film, an active layer mainly containing an oxide semiconductor that contains at least one of In, Ga or Zn, a source electrode, and a drain electrode, the field effect transistor including: a heat diffusion layer, wherein, given that a thermal conductivity of the substrate is Nsub (W/mK), a thermal conductivity of the heat diffusion layer is Nkaku (W/mK), a film thickness of the heat diffusion layer is T (mm), a planar opening ratio of the heat diffusion layer is R (0≦R≦1), and S=T×R, the thermal conductivity Nsub of the substrate satisfies the condition Nsub<1.8, and the thermal conductivity Nkaku of the heat diffusion layer satisfies the conditions Nkaku>3.0×S^(−0.97×e^(−1.2×Nsub)) and Nkaku≧Nsub.