Jiongxin Lu

Synthesis and dielectric properties of novel high-K polymer composites containing in-situ formed silver nanoparticles for embedded capacitor applications

Dielectric properties of in-situ formed silver (Ag) incorporated carbon black (CB)/polymer composites were studied. In-situ formed Ag nanoparticles in the Ag/CB/epoxy composites increased the dielectric constant (K) value and decreased the dissipation factor (Df). The remarkably increased dielectric constant of the nanocomposite is due to the piling of charges at the extended interface of the interfacial polarization-based composites. The reduced dielectric loss might be due to the Coulomb blockade effect of the contained Ag nanoparticles, the well-known quantum effect of metal nanoparticles. The size, size distribution and loading level of metal nanoparticles in the nanocomposite were found to have significant influences on the dielectric properties of the nanocomposite system.

Recent advances in high-k nanocomposite materials for embedded capacitor applications

In this paper, a wide variety of high dielectric constant (k) composite materials which have been developed and evaluated for embedded capacitor application are reviewed. Current research efforts toward achieving high dielectric performance including high-k and low dielectric loss for polymer composites are presented. New insights into the effect of unique properties of the nanoparticle filler, filler modification and the dispersion between filler and polymer matrix on the dielectric properties of the nanocomposites are discussed in details.

Silver/polymer nanocomposite as a high-kpolymer matrix for dielectric composites with improved dielectric performance

A silver (Ag)-polymer nanocomposite has been developed by in-situ formation of metal nanoparticles within the polymer matrix and utilized as a high-dielectric constant (k) polymer matrix to enhance the dielectric properties of high-k composite materials. By using an in-situ photochemical reduction method, uniformly dispersed Ag nanoparticles of size of around 10 nm were generated in polymer matrices. Self-passivated aluminium (Al) particles were incorporated into this Ag-epoxy matrix and the dielectric properties of the as-prepared composite materials were investigated. The composites showed more than 50% increase in k values as compared with an Al/neat epoxy composite with the same filler loading of Al. The dielectric loss tangent of the Al/Ag-epoxy composites was below 0.1, which meets the requirement for embedded decoupling capacitors. These results suggest that the Ag-epoxy high-kpolymer matrix effectively enhances the dielectric constant while maintaining the low dielectric loss of the high-k composites. In addition, detailed dielectric property measurements revealed that the dielectric properties and their frequency dispersion as well as the breakdown behaviors of the Al/Ag-epoxy composites were related to the incorporation and concentration of Ag nanoparticles in the high-kpolymer matrix.

Development of novel silver nanoparticles/polymer composites as high K polymer matrix by in-situ photochemical method

Conductive filler-polymer composite materials have been extensively investigated as conductor-insulator percolative system to achieve high dielectric constant (K). Additionally, the effective dielectric constant of conductive filler/polymer composite can be dramatically enhanced by increasing the dielectric constant of polymer matrix according to scaling theory. However, the high dielectric loss of this type material at high filler loading levels has been a challenging issue, which is originated from the high conductivity and excessive polarized interface induced by the fillers. In this study, an in-situ formed metal nanoparticles/polymer resin compound was developed as a high K polymer matrix by adopting a relatively low concentration of conductive filler to obtain high K retaining low dielectric loss simultaneously. Nano-sized metal particles are preferred because they achieve thinner dielectric films leading to a higher capacitance density. Compared to an ex-situ blending technique by incorporating and dispersing pre-synthesized nanoparticles into polymers, the in-situ synthesis method can offer more advantages such as much more uniform dispersion in polymers and easy size control of nanoparticles. This study explores the in-situ nanoparticle synthesis method by photochemical conduction of a metallic precursor within the polymer matrix. Crystal structure analysis and morphology characterization of the as-prepared nanocomposites by transmission electron microscopy (TEM) demonstrated the success of the in-situ formation of silver (Ag) nanoparticles in various polymer matrices by the photochemical method. Uniform dispersion of nano Ag particles with size of less than 10 nm in polymer matrices was observed. The effects of reducing agent types, concentrations of a metal precursor, epoxy matrix types and additives on the morphology of nanoparticles will be discussed. Based on the results of UV-Vis and FT-IR study, the proposed reaction mechanism of reduction of silver ion to silver will be presented. Aluminum particles were incorporated into the in-situ formed nano Ag/epoxy composite and the dielectric properties of the composite materials were also investigated. The composites showed a more than 50% increase in K values compared with an Al/neat epoxy composite with the same filler loading of Al. Moreover, the dielectric loss was maintained below 0.05. The results suggested that the in-situ formed Ag-polymer nanocomposites via photochemical approach can be employed as a high-K polymer matrix to host various fillers such as conductive metal or high dielectric constant ceramic fillers. The dielectric behavior of the composites materials at various frequency, their morphology, physical properties and their correlations will be discussed

Tailored Dielectric Properties of High-k Polymer Composites via Nanoparticle Surface Modification for Embedded Passives Applications

Novel materials for embedded passive applications are in great and urgent demands, for which high dielectric constant (k), low dielectric loss and process compatibility with the printed circuit boards (PCBs) are the most important prerequisites. Dramatic increase of dielectric constant near the percolation threshold observed by our earlier work in the conductor-insulator percolative system arouses interest of developing these composites as dielectric materials. This material option represents advantageous characteristics over the conventional polymer-ceramic composite. Specifically, the polymer-conductive filler composite demonstrates an ultra-high k with balanced mechanical properties including the adhesion strength. However, the relatively high dielectric loss and narrow processing window have plagued the metal/polymer composites from real applications. In this study, surface modification of nanoparticles with organic molecules was employed to change the surface chemistry of nanoparticles and thus interaction between nanoparticles and polymer matrix. Fully characterization of the surface modified nanoparticle (SMN) by FT-IR, HRTEM, EDS, DSC, TGA et al. methods demonstrated that a thin layer was successfully coated on the surface of the nanoparticles via surface modification of the nanoparticles. The effect of surface modification of nanoparticles on the dielectric and electrical behaviors of SMN/polymer nanocomposites was investigated as well. The surface coating layer on the nanoparticles was demonstrated to be able to decrease the dielectric loss, enhance the dielectric breakdown strength and expand the processing window. This improvement in the performance of the polymer nanocomposites can be attributed to the interparticle electrical barrier layer formed via surface modification of nanoparticles which prevents the metal cores from direct contact. Different surface modification conditions such as surface modification agent type and concentration, solvent media etc., may play complex roles to the degree of surface modification which impact the changes of k and dielectric loss tangent values of SMN/polymer composites dramatically. Therefore, surface modification of nanoparticles is believed to be an effective approach to adjust the electrical features at the nanoparticle surface and the interface between the nanoparticle and the polymer matrix, and thus tailor the corresponding properly of interest of nanocomposites.

High-k Polymer Nanocomposites as Gate Dielectrics for Organic Electronics Applications

Motivated by the recent development in organic electronics such as organic field effect transistors (OFETs), printed electronics,.. etc., these emerging technologies have received increasing attention. In addition to the organic semiconductor, gate dielectrics for organic electronics have been the focus of recent R&D attention as well. For this application, the dielectric materials should ideally be compatible with flexible substrate, solution processible, and exhibit larger capacitance to increase the drain current while operating at low biases. Complementary to conventional high dielectric constant (k) inorganic materials and those readily accessible and solution processible polymer materials, polymer/inorganic hybrid films which could be deposited by spin-coating are well suited to provide a better solution. In this study, a solution processible nanocomposite containing benzocyclobutene (BCB) and barium titanate (BT) nanoparticles was developed. Dielectric and electrical properties of the as-prepared BT nanocomposites were investigated, k values of 50 and capacitance density of 19 nF/cm2 was achieved for a 50 vol.% BT loading. And the dielectric breakdown strength could be maintained 1.65 MV/cm, which is even higher than that of some other polymers themselves. The preliminary result of the electrical output of OFET prototype incorporating high k BT/BCB nanocomposite as gate insulator layer shows that the OFET can be operated at very low voltage. This demonstrates the feasibility of using high k BT/BCB nanocomposite as gate dielectric insulator in the OFET.

Large-area processable high K nanocomposite-based embedded capacitors

In this study, we have developed high dielectric constant (k>50) embedded capacitor dielectrics with a moderate volume fraction of tiller that show good adhesion, good thermal stress reliability and good large area processibility at low processing temperature (<200degC). Material design and processing are critical to obtain a high dielectric constant composite at a moderate filler loading. The material formulations were systematically studied, and by using the combination of a chelating agent, a dispersing agent, and bimodal fillers, dielectric constants above 50 were obtained. However, theses high k formulations had low peel strength and poor thermal stress reliability. It was found that filler pretreatment, which led to the chemical bonding of dispersing agent on filler particle surface, can effectively improve the peel strength and thereby the thermal stress reliability of embedded capacitor components. Meanwhile, to reduce the large moduli of high k composites and thereby reduce the high thermal stress in the embedded capacitor components, the epoxy varnish was modified with a rubberized polymer. The optimized, rubberized nanocomposite formulations had a high dielectric constant above 50 and successfully passed the stringent thermal stress reliability test. A low leakage current (~10-11A/cm2) and a high breakdown voltage (~90 MV/m) were measured in the large area thin film capacitors

The role of self-assembled monolayer (SAM) on Ag nanoparticles for conductive nanocomposite

To improve the electrical property of the isotropic conductive adhesives (ICA), self-assembled monolayer (SAM) compounds were used to help the dispersion of silver nanoparticles in epoxy resin. Silver nanoparticles were first treated by the SAM in order to increase the filler loading of nanoparticles in epoxy resin. The bonding and thermal debonding behavior between silver and SAM was investigated by differential scanning calorimeter (DSC). The amount of SAM coated on Ag nanoparticles was tested by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to study the morphologies of SAM treated Ag nanoparticles before and after the heat treatment. Several kinds of epoxy formulation were prepared by using SAM-treated Ag nanoparticles as conductive fillers and the resistivities were studied.

Recent Advances on Polymers and Polymer Nanocomposites for Advanced Electronic Packaging Applications

The advances of semiconductor technology are mainly due to the advances of polymeric materials. These include the use of polymers as adhesives (both conductive and non-conductive), interlayer dielectrics (low-k, low loss dielectrics), encapsulants (discrete and wafer level packaging), embedded passives (high-k and high-Q materials), superhydrophobic self-cleaning lotus effect surfaces, and etc. In this presentation, we review some of the recent advances of polymeric materials and polymer nanocomposites currently being investigated for these types of applications, such as lead-free electrically conductive adhesives (ECAs) for fine pitch and high current density interconnects, flip chip and wafer level underfills, superhydrophobic self-cleaning lotus effect surfaces, as well as high-k and high-Q nanocomposites for embedded capacitors and inductors

In-situ Photochemical Synthesis of Novel Silver Nanoparticles/Polymer Composites as High K Polymer Matrix for Embedded Passives Applications

In-situ synthesis of Ag nanoparticles was successfully carried out in various epoxy matrix by photochemical method. The effects of reducing agent type, concentration of metal precursor, epoxy matrix type and additives on the morphology of nanoparticles were explored. Transmission electronic microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the microstructure of the in-situ formed Ag nanoparticles within the epoxy matrix, called as Ag-epoxy mixture which can be used as a high-K polymer matrix. The dielectric properties of the Al/Ag-epoxy composites were studied and compared with the Al/epoxy composites