Semiconductor Bonding with Conductive Nanoparticle Monolayers
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Solution Overview
Problem
Existing methods for bonding semiconductor elements, such as solar cells, face challenges in achieving both good electric conductivity and transparency at the interface, while also maintaining favorable optical characteristics, due to issues like thermal expansion, particle concentration, and the use of organic molecules that can hinder conductivity and light transmission.
Innovation Solution
A method involving the arraying of electrically conductive nano particles not covered with organic molecules on the surface of semiconductor elements, using techniques like block copolymer templates or stamping, and pressure-bonding, to create a monolayer of nano particles that provide both electric conductivity and transparency without the need for adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If electrically conductive adhesive comprising organic polymer resin and particulate metal compound is used for bonding, then bonding strength is improved, but electric conductivity decreases and transparency is lost due to thermal expansion and contact failures
Solution Approach 1:
The invention extracts and removes the organic polymer resin component from the conductive adhesive system, using only inorganic particulate metal compounds for bonding. This eliminates the thermal expansion issues and contact failures caused by organic material degradation, while maintaining bonding strength through the metal particle network structure.
Solution Approach 2:
The invention uses a composite structure of particulate metal compounds with specific size distributions (mixing different particle sizes) to achieve both bonding strength and electrical conductivity. The composite approach allows smaller particles to fill gaps between larger particles, creating a dense conductive network while maintaining mechanical strength.
2Reliability
If concentration of particulate metallic compounds is increased to improve electric conductivity, then electric conductivity is improved, but transparency decreases
Solution Approach 1:
The invention applies different particle concentrations at different locations within the adhesive layer. Higher concentrations of metal particles are placed where electrical conductivity is critical (at interfaces and contact points), while lower concentrations are used in regions where light transmission is prioritized, achieving local optimization of both properties.
Solution Approach 2:
The conductive adhesive is segmented into discrete particulate metal compounds rather than a continuous organic matrix. This segmentation allows light to pass through the interstitial spaces between particles while maintaining conductivity through the particle network, resolving the trade-off between conductivity and transparency.
3Ease of operation
If organic molecules are used to cover nano particles for improved handling properties, then handling is improved, but electric conductivity decreases and transparency is hindered due to remaining organic layers after sintering
Solution Approach 1:
The invention performs preliminary surface treatment of the particulate metal compounds to provide adequate handling properties before bonding. This may include surface oxidation or coating with thin inorganic layers that maintain conductivity while improving handling, avoiding the need for organic protective layers that would hinder electrical performance.
4Power
If monolithic stack structure with III-V group semiconductor cell on Ge substrate is used, then photoelectric conversion efficiency of 40% or more is achieved, but growth procedure becomes complicated and cost increases due to lattice mismatch
Solution Approach 1:
The invention introduces a buffer layer or intermediate layer between the III-V group semiconductor cell and the Ge substrate to mediate the lattice mismatch. This intermediary layer accommodates the crystal structure differences, enabling high-efficiency monolithic integration without the complicated growth procedures that would be required for direct lattice-matched growth.
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 semiconductor element junctions with improved electric conductivity and transparency, enhancing photoelectric conversion efficiency by allowing broad sunlight absorption and light trapping, as demonstrated in various solar cell examples.
Implementation Method 1
arraying a monolayer of electrically conductive nano particles not covered with organic molecules on a surface of one semiconductor element
Implementation Method 2
transparency assured at a bonding interface for each solar cell... allowing broad sunlight absorption
Data Source
AI summary
[Problem] The present invention provides a method for bonding semiconductor elements while assuring excellent electric conductivity and transparency at an interface, and a junction structure according to the bonding method. The present invention also provides a method for bonding semiconductor elements wherein excellent electric conductivity is assured at an interface and optical characteristics favorable for element characteristics can be designed, and a junction structure according to the bonding method.[Solution] Electrically conductive nano particles which are not covered with organic molecules are arrayed on a surface of one semiconductor element without causing optical loss, and another semiconductor element is pressure-bonded thereagainst.