Erdal Uzunlar

Airgap Interconnects: Modeling, Optimization, and Benchmarking for Backplane, PCB, and Interposer Applications

Frequency and time domain models are developed for backplane (BP), printed circuit board (PCB), and silicon interposer (SI) links using six-port transfer matrices (ABCD matrices) for bumps, vias and connectors, and coupled multiconductor transmission lines for traces. The six-port transfer matrix approach enables easy computation of the transfer function, as well as near-end and far-end crosstalk. The intersymbol interference is accounted for by computing the pulse response for the worst case bit pattern. Furthermore, the models developed here are used to optimize the data-rate and trace width for each of the links, so that the aggregate bandwidth obtained per joule of energy supplied to the link is maximized. The modeling and optimization approach developed here serves as a good platform to compare the air-gap interconnects against BP, PCB, and SI interconnects on lossy dielectrics. It is shown that air-gap interconnects can provide an aggregate bandwidth improvement of 3x-4x for BP links at a comparable energy per bit, and a 5x-9x improvement in aggregate bandwidth of PCB links at the expense of 20% higher energy per bit. For SI links, airgap interconnects are shown to provide a 2x-3x improvement in aggregate bandwidth and a 1x-1.5x improvement in energy per bit.

Design and fabrication of low-loss horizontal and vertical interconnect links using air-clad transmission lines and through silicon vias

In this paper we present the design and fabrication of air-clad planar transmission lines and TSVs that can be used as horizontal and vertical chip-chip interconnects. Performance improvement by using heterogeneous air-clad dielectric is presented for these two types of interconnect structures that establishes the basic motivation for fabricating these structures. The design data is verified by performing simulation using 3D full-wave solver HFSS. We outline the process flow for air-clad transmission lines and TSVs in detail. Several challenges in the fabrication of air-clad structures are also discussed.

Decomposable and Template Polymers: Fundamentals and Applications

Polymers can be used as temporary place holders in the fabrication of embedded air gaps in a variety of electronic devices. Embedded air cavities can provide the lowest dielectric constant and loss for electrical insulation, mechanical compliance in devices where low-force deformations are desirable, and can temporarily protect movable parts during processing. Several families of polymers have been used as sacrificial, templating polymers including polycarbonates, polynorbornenes (PNBs), and polyaldehydes. The families can be distinguished by chemical structure and decomposition temperature. The decomposition temperature ranges from over 400 C to below room temperature in the case of low ceiling temperature polymers. Overcoat materials include silicon dioxide, polyimides, epoxy, and bis-benzocyclobutene (BCB). The methods of air-gap fabrication are discussed. Finally, the use of photoactive compounds in the patterning of the sacrificial polymers is reviewed. [DOI: 10.1115/1.4033000]

Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications

This study aims at investigating a polymer-based air-gap creation method for the packaging of microelectromechanical systems (MEMS), and exploring the chemical composition of the polymer residue on the final package. Polymer-based air-gap formation utilizes thermal decomposition of a sacrificial polymer, poly(propylene carbonate) (PPC), encapsulated within an overcoat polymer. BCB (Cyclotene 4026-46) was used as the overcoat material because decomposition products of sacrificial polymer are able to permeate through it, leaving an embedded air-gap structure around the MEMS device. Sizecompatibility and cleanliness of MEMS devices are important attributes of the polymerbased air-gap MEMS packaging approach. This study provides a framework for size-compatible and clean air-gap formation by selecting the type of PPC, optimizing thermal treatment steps, identifying air-gap formation options, assessing air-gap formation performance, and analyzing the chemical composition of the residue. The air-gap formation processes using photosensitive PPC films had at least twice the residue compared to processes using nonphotosensitive PPC films. The major contribution to the residue in photosensitive PPC films was from the photoacid generator (PAG), which was used to catalyze the thermal decomposition of the PPC. BCB is compatible with PPC, and provides mechanical stability during creation of the air-gaps. The polymer-based air-gaps provide a monolithic, low-cost, integrated circuit compatible MEMS packaging option. [DOI: 10.1115/1.4030952]

Design and fabrication of ultra low-loss, high-performance 3D chip-chip air-clad interconnect pathway

In this study, we are pursuing an ultra low-loss interconnect pathway for 3D chip-chip connectivity, incorporating air-clad planar interconnects, air-clad TSVs, and gradual vertical-horizontal transitions. The motivation is to create an air-gap technology that offers the lowest possible effective k-value and near zero loss tangent minimizing the dielectric loss. The design and modeling of air-gap interconnection is presented. The fabrication challenges in air-clad interconnect lines are discussed. A monolithic inverted air-gap horizontal transmission line structure is proposed as a means for further decreasing the dielectric loss. Extension of air-clad TSV technology for optical transmission is briefly discussed.