Investigations On The Application Of Electroless Copper And Its In Situ Derived Micro/Nano Arrays In Electronics

Electroless copper is generally applied as conductive materials in electronics due to its excellent electrical conductivity,strong resistance to electromigration,and low material cost.Electroless copper is usually deposited uniformly on the surface of the substrate in the form of a plating coating.The appropriate substrates include conductors,semiconductors and insulating materials.Benefitting from the ability to metalize the surface of insulating materials,electroless copper has widely applied in printed circuit boards(PCB),flexible circuits boards(FCB)and large-scale integrated circuits(IC)as a key conductive interconnect material to achieve high density electronic packaging.In recent years,it has attracted increasing attention to explore more forward-looking applications for electroless copper in electronics.Most of these investigations are focused on the designing of various electroless deposited copper patterns to construct electronic circuits,in-plane electrodes,and simple in-plane electronic devices.However,most of these electronic materials and devices constructed by electroless copper patterns are based on the simple applications and development for the characteristics of metal copper materials,and thus the corresponding application ranges and functions are very limited.In contrast,copper derivatives are more diversified in applications,which have been widely applied in various fields such as energy storage,thermoelectrics,photoelectrics,and sensors.With the continuous development of consumer electronic products toward miniaturization,multi-function,and high integration,it is becoming more and more important to further explore novel application of electroless copper based on its characteristics and multi-functional copper derivatives.This is greatly significant to the optimization of the fabrication,integration and packaging process of electronic materials and devices.This dissertation will focus on the design and conversion towards electroless copper by various techniques,based on the investigation of current research progress,the development trend,and challenges for the electroless copper and its derivatives.A facile and universal"addition strategy"has been developed to fabricate printed copper circuits,based on the as-prepared high-performance and cost-efficient catalyst for electroless copper deposition.Furthermore,on the basis of the process of electroless deposited coatings and patterns and the multi-functional nanoarrays in situ derived from electroless copper,various in-situ preparation and integration technologies for electroless copper-derived electronic materials and devices have been developed.It provides novel strategy for optimizing the integration and preparation processes of electronic materials and devices,and advances the process of electroless copper materials to diversified applications.The main research work in this dissertation is summarized as follows:1.Currently,high-performance and cost-effective catalyst used in electroless copper deposition is rarely exploited in electronic industry.In order to reduce material cost,promote the production efficiency and reduce environment pollution,a simple ethanol solvothermal method to synthesize a cost-efficient and high-performance Sn/Ag catalyst is proposed in this work.A quartz crystal microbalance is used to quantitatively analyze the catalytic activity of the catalyst for electroless copper deposition reaction,and the influence of metal Sn supporter on the catalytic activity of Ag is further investigated.The result indicates that the metal Sn not only serves as a carrier to prevent Ag particles from agglomerating,it also significantly promotes the catalytic activity of Ag.The catalytic performance of the prepared Sn/Ag nanorods is close to that of commercial Pd black,which meets the requirement of the electroless copper deposition reaction for the catalyst activity.At the same time,the raw materials for preparing the Sn/Ag catalyst are cost effective and easily available,and the preparation process is non-toxic and pollution-free,which meets both economic benefit and environmental protection.2.In view of the tedious process of the conventional lithography technology("subtraction strategy")used to prepare printed electronic circuits,as well as the large amount of raw material consumption and environmental pollution during the etching process,a facile and universal"addition strategy"used for the fabrication of electroless copper conductive patterns is proposed in this work.Based on the catalytic deposition feature of electroless copper,by using epoxy composite catalyst,and combining screen printing technology with electroless copper plating process,high-quality electroless copper conductive patterns are successfully fabricated on a series of rigid and flexible substrates,including rigid commercial PCB epoxy substrate,flexible polyimide film(PI;commercial flexible circuit substrate),transparent polyethylene terephthalate(PET)film,heat-resistant polytetrafluoroethylene(PTFE)film,wearable cotton fabric and paper substrate.The result indicates that the copper patterns prepared by this process exhibit high electrical conductivity comparable to bulk copper,excellent flexibility,and good bonding force with the substrate.In addition,this facile fabrication process is a highly operable and adjustable,which is suitable for the fabrication of electronic circuits and electrode patterns in various electronic devices.Furthermore,this copper patterns fabrication strategy provides technical basis for the further design and construct of various functional in-plane electronic devices in subsequent research.3.In consideration of the shortcomings of the present micro-supercapacitors in electrode processing and the structure design of active electrode materials,and in order to optimize the integration process of micro-supercapacitors in electronics,an in situ integratable micro-supercapacitor is fabricated in this work.Through facile chemical immersion treatments,the designed electroless copper current collector surface can be in situ converted to Cu(OH)₂@FeOOH sub-microtubes with an array structure as the electrode active materials.The research results indicate that this sub-microtubes active materials exhibit large specific surface area(224 m² g^-1)and excellent affinity with electrolyte.In addition,since the active material is in situ derived from the surface of the electroless copper current collector,the active materials can adhere tightly with the current collector.Benefiting from the rational structure design towards the electrode and active materials,the as-constructed micro-supercapacitors achieves high specific capacitance,high energy density and excellent flexibility.In terms of the device manufacturing process,both the electronic circuits and the micro-supercapacitor electrode belong to metal copper patterns,which makes it possible to in situ fabricate and integrate the micro-suprcapacitors into the circuits,thus promoting the process of the application of the micro-suprcapacitors in electronics.4.Considering that thermoelectric films fabricated by conventional methods such as coating,vacuum filtering,and direct printing are undesirable in structure design and thermoelectric performance,a novel thermoelectric film fabrication strategy based on the in-situ conversion of electroless deposited copper coating is proposed in this work,by which a high-performance p-type Cu₂Se thermoelectric film with nanosheets array structure can be fabricated.In terms of thermoelectric performance,the as-prepared Cu₂Se nanosheet array film has wide size ranges with nanoscale thickness,microscale width and atomic scale cation vacancies,which can effectively scatter phonons with wide wavelength ranges,thus exhibits excellent thermoelectric performance(ZT:0.5)and ultra-low thermal conductivity(0.13 W m^-1 K^-1).In terms of the fabrication of flexible film,the thermoelectric film can root in the substrate by in-situ preparation on a porous PI substrate,thereby achieving a thermoelectric film with excellent adhesion and flexibility.In addition,the Cu₂Se thermoelectric films fabricate by the facile in-situ process are cost effective in materials and preparation,which demonstrates a novel approach for the design and application of flexible thermoelectric films.5.Printed thermoelectric devices have unique advantages in scalable manufacturing and device design due to the facile and smart fabrication process,but it is difficult to achieve rational design and processing towards the structure of thermoelectric materials by direct printing strategy.This hinders further optimization of the performance of printed thermoelectric materials and devices.In addition,the difference in the fabrication process of the printed thermoelectric device and printed circuits has caused obstacle to the integrated application of the thermoelectric device in electronics.In view of this,an in situ integratable thermoelectric device fabrication strategy is developed in this work.On the basis of electroless deposited copper pattern,a pCu₂Se-nAg₂Se thermoelectric device can be fabricated through a selenization process and a cation exchange technique,successively.The n-type Ag₂Se film derived from the p-type Cu₂Se film also has a nanosheets array structure,and thus exhibits extremely low thermal conductivity(0.15 W m^-1 K^-1)and excellent thermoelectric properties(ZT:0.7).In addition,the thermoelectric film can root in the substrate by in-situ preparation on the porous PI substrate,thereby realizing the Ag₂Se thermoelectric film and pCu₂Se-nAg₂Se thermoelectric device with excellent adhesion and flexibility.This research demonstrates a feasible approach to in situ fabricate and integrate high-performance thermoelectric devices in copper-based electronic circuit systems,and thus promoting the development and integrated application of thermoelectric devices in electronics.