Flexible Active Matrix Backplane Transfer via Spalling
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Solution Overview
Problem
Current active matrix devices, such as high-resolution displays and sensors, face limitations due to low carrier mobility in hydrogenated amorphous silicon and high costs, device-to-device variation, and temperature incompatibility of single crystalline silicon with existing substrates, which restricts resolution and flexibility.
Innovation Solution
The method involves fabricating backplane structures on semiconductor-on-insulator wafers with buried insulator layers and flexible handles to spall the backplane structures, allowing for the formation of high-resolution active matrix structures on flexible or rigid substrates, enabling efficient adhesion and fracture toughness for high-resolution applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hydrogenated amorphous silicon (a-Si:H) is used for backplane fabrication, then manufacturing cost is reduced and ease of manufacture is improved, but carrier mobility is too low to provide sufficient drive current at short TFT channel widths
Solution Approach 1:
The patent segments the manufacturing process into two distinct phases: first fabricating high-resolution backplane structures on silicon wafers where high carrier mobility is critical, then transferring these structures to flexible substrates for final device assembly. This segmentation allows each phase to optimize for its specific requirements without compromise.
Solution Approach 2:
The patent introduces silicon-on-insulator wafers as an intermediary substrate that temporarily holds the backplane structures during fabrication. This intermediary enables the use of high-mobility crystalline silicon for the backplane while allowing subsequent transfer to flexible substrates, thus decoupling the conflicting requirements of high mobility and flexibility.
2Reliability
If single crystalline silicon (c-Si) is used for backplane fabrication, then carrier mobility is improved and sufficient drive current is provided, but processing requires high temperatures not compatible with glass substrates
Solution Approach 1:
The patent performs the high-temperature processing of crystalline silicon backplane structures on silicon wafers before transferring them to the final substrate. By completing temperature-sensitive fabrication steps preliminarily on a substrate that can withstand high temperatures, the final flexible substrate is never exposed to incompatible processing conditions.
Solution Approach 2:
Silicon wafers serve as an intermediary platform that temporarily accommodates the backplane structures during high-temperature fabrication. This intermediary substrate handles the thermal processing requirements, while the final flexible substrate only receives the already-fabricated structures at low temperatures.
3Reliability
If LTPS is used for backplane fabrication, then drive current capability is improved, but device-to-device variation of threshold voltage and mobility requires compensation circuitry that limits resolution
Solution Approach 1:
The patent uses photolithographic copying techniques to transfer precise backplane patterns from master silicon wafer templates to the final flexible substrate. This copying process ensures high manufacturing precision and consistency across devices, eliminating the variation problems that would require compensation circuitry.
4Measurement precision
If very high resolution (>1000 ppi) is achieved, then measurement precision is improved, but the combination of high carrier mobility requirement and substrate flexibility creates a technical contradiction
Solution Approach 1:
The patent divides the device into two separate components fabricated on different substrates: the backplane with high-resolution TFT arrays is fabricated on rigid silicon wafers where high carrier mobility is achievable, while the flexible substrate contains only the passive matrix and sensing elements. This segmentation allows each component to optimize for its specific function without compromise.
Solution Approach 2:
The patent uses transfer printing technology as an intermediary process to move the high-resolution backplane structures from silicon wafers to flexible substrates. This intermediary transfer process enables the combination of high-resolution crystalline silicon backplanes with flexible substrates, achieving both high measurement precision and substrate adaptability.
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 enhances efficiency, supports flexible substrates, and enables high-resolution bifacial display/imaging applications, overcoming previous limitations in carrier mobility and substrate compatibility.
Implementation Method 1
spalling the first backplane structure, the metal layer and a residual layer from the support substrate by exerting a force on the metal layer via a flexible handle
Data Source
AI summary
A high resolution active matrix backplane is fabricated using techniques applicable to flexible substrates. A backplane layer including active semiconductor devices is formed on a semiconductor-on-insulator substrate. The backplane layer is spalled from the substrate. A frontplane layer including passive devices such as LCDs, OLEDs, photosensitive materials, or piezo-electric materials is formed over the backplane layer to form an active matrix structure. The active matrix structure may be fabricated to allow bottom emission and provide mechanical flexibility.