Photodiode Array Adhesion via Intermediary Metallization Layers
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Solution Overview
Problem
The integration of photodiode arrays with TFT arrays in x-ray imaging systems often results in mechanical reliability and integrity issues due to incompatibility between standard TFT array fabrication processes and photodiode array processes, leading to adhesion problems and potential long-term reliability issues with aluminum alloy contacts.
Innovation Solution
The implementation of via structures with additional metallization layers, such as molybdenum-based layers, and silicon nitride layers to enhance adhesion and prevent hydrofluoric acid etching damage, along with strategic placement of vias and metallization layers to improve contact reliability between the diode and TFT arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard TFT array fabrication processes are used, then manufacturing compatibility and ease of manufacture are improved, but adhesion robustness and mechanical reliability deteriorate
Solution Approach 1:
An intermediary adhesion layer comprising titanium (Ti), chromium (Cr), or molybdenum (Mo) is introduced between the photodiode film and the aluminum alloy metal layer. This intermediary layer serves as a mediator that enhances adhesion robustness while maintaining compatibility with standard TFT fabrication processes, resolving the contradiction between ease of manufacture and reliability.
Solution Approach 2:
The metal contact structure is transformed from a single-layer aluminum alloy to a composite multi-layer structure combining aluminum alloy with adhesion-enhancing layers of Ti, Cr, or Mo. This composite material approach maintains the electrical conductivity benefits of aluminum while adding the adhesion properties of transition metals, thereby improving mechanical reliability without sacrificing manufacturability.
2Device complexity
If hydrofluoric acid wet etchant is used to etch oxide and nitride, then via structure formation is simplified, but metal contact integrity deteriorates due to etchant attack
Solution Approach 1:
The adhesion layer acts as a protective intermediary between the hydrofluoric acid etchant and the aluminum alloy metal layer during via formation. This intermediary layer allows the use of simplified HF wet etching processes while preventing direct contact between the etchant and aluminum, thus maintaining metal contact integrity despite process simplification.
Solution Approach 2:
The patent utilizes the selective chemical reactivity properties of different materials with hydrofluoric acid. The adhesion layer materials (Ti, Cr, Mo) exhibit different etching characteristics compared to aluminum, allowing controlled via formation through the adhesion layer while protecting the underlying aluminum from direct HF attack, thereby maintaining integrity during simplified wet etching.
3Ease of manufacture
If aluminum alloy metal layer is used for cost-effectiveness, then manufacturing cost is reduced, but long-term reliability deteriorates due to reactivity with hydrofluoric acid
Solution Approach 1:
A protective adhesion layer of Ti, Cr, or Mo is introduced as an intermediary between the aluminum alloy and the hydrofluoric acid environment. This intermediary preserves the cost advantages of aluminum alloy while shielding it from HF reactivity, thereby maintaining long-term contact reliability without increasing manufacturing cost significantly.
Solution Approach 2:
The patent modifies the chemical composition parameters of the metal contact structure by adding small thicknesses of adhesion layer materials (e.g., 1-10 nm of Ti, Cr, or Mo) to the aluminum alloy layer. This parameter change creates a composite structure that maintains the low cost of aluminum while introducing chemical resistance properties, resolving the contradiction between cost and reliability.
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 the mechanical reliability and adhesion of photodiode films to the TFT array, reduces the risk of etchant attack on metal contacts, and improves long-term reliability by using molybdenum-based metals that are less reactive with hydrofluoric acid, thereby stabilizing the diode-to-metal contacts.
Implementation Method 1
via structures with additional metallization layers, such as molybdenum-based layers, and silicon nitride layers to enhance adhesion
Implementation Method 2
prevent hydrofluoric acid etching damage, along with strategic placement of vias and metallization layers to improve contact reliability
Implementation Method 3
using molybdenum-based metals that are less reactive with hydrofluoric acid
Data Source
AI summary
Briefly, in accordance with one or more embodiments, a detector panel of an imaging system may be produced from a photodiode array integrated with a thin-film transistor array. The thin film transistor array may have one or more vias formed for increasing the adhesion of the photodiode array to the thin-film transistor array. The vias may comprise sidewalls having stepped structures. The thin-film transistor array may comprise a first metallization layer and a second metallization layer. A third metallization layer may be added to the thin film transistor array wherein diodes of the photodiode array may contact the third metallization layer. Diodes of the photodiode array may contact the first metallization layer and/or the second metallization layer via the third metallization layer without directly contacting the first metallization layer or the second metallization layer.