Lateral Thermal Processing of Thin Films on Low-Temperature Substrates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-temperature substrates are required for thermal processing of semiconductor thin films, which limits the use of low-cost substrates like polyimide and PET due to their low maximum working temperatures, making it difficult to thermally process thin films effectively on these materials.
Innovation Solution
The method involves using pulsed radiation to heat absorbing traces, which are in thermal contact with the thin film, allowing heat to be conducted to the film for thermal processing, even on low-temperature substrates, and employing a heat spreading film to protect the substrate and enhance heat conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high-temperature substrates (fired ceramics or quartz) are used for thermal processing, then the thin film can be processed at required temperatures (e.g., 900-1100°C), but the substrate cost increases significantly
Solution Approach 1:
The substrate system is segmented into two functional parts: a low-cost low-temperature substrate (e.g., PET, polyimide) for mechanical support and a separate high-temperature absorbing trace layer for thermal processing. This segmentation allows each component to perform its optimal function without requiring the entire substrate to withstand high temperatures.
Solution Approach 2:
An absorbing trace layer (intermediary) is introduced between the radiation source and the thin film. This intermediary selectively absorbs pulsed radiation and converts it to localized heat, enabling indirect thermal processing of the thin film without requiring the substrate itself to be heated to processing temperatures.
2Ease of manufacture
If low-temperature substrates (polyimide or PET) are used to reduce cost, then substrate cost decreases, but the maximum processing temperature is limited by substrate thermal stability (450°C or 150°C respectively)
Solution Approach 1:
Instead of continuous heating, pulsed radiation is applied periodically to the absorbing traces. This periodic action allows rapid temperature spikes at the trace locations during the pulse duration, followed by rapid cooling when the pulse ends, enabling high-temperature processing without exceeding the substrate's continuous operating temperature limit.
Solution Approach 2:
The thermal processing is localized to specific regions where absorbing traces are deposited. The heat is concentrated at these trace locations and conducted laterally to the thin film areas requiring processing, while the rest of the substrate remains at safe temperatures. This local quality approach enables high-temperature processing in specific zones without compromising overall substrate integrity.
3Stability of the object's composition
If equilibrium heating (oven processing) is used for thermal processing, then uniform heating is achieved, but the substrate temperature must be uniformly high throughout the process
Solution Approach 1:
The absorbing traces are strategically positioned and patterned to create localized heating zones. By controlling the trace geometry, spacing, and material properties, uniform heat distribution can be achieved in the thin film region of interest through lateral heat conduction, while the substrate itself experiences minimal temperature increase.
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 method enables thermal processing of thin films to higher temperatures than the substrate can withstand, allowing for effective curing of thin films on low-temperature substrates like polyimide and PET, facilitating the fabrication of thin film transistors with reduced parasitic capacitance and improved performance.
Implementation Method 1
Pulsed radiation is utilized to heat the two absorbing traces
Implementation Method 2
the heat from the two absorbing traces is subsequently conducted in the plane of the thin film to the thin film between the two absorbing traces
Data Source
AI summary
A method for thermally processing a minimally absorbing thin film in a selective manner is disclosed. Two closely spaced absorbing traces are patterned in thermal contact with the thin film. A pulsed radiant source is used to heat the two absorbing traces, and the thin film is thermally processed via conduction between the two absorbing traces. This method can be utilized to fabricate a thin film transistor (TFT) in which the thin film is a semiconductor and the absorbers are the source and the drain of the TFT.