Person:

Kohl, Paul A.

Permanent Link

https://hdl.handle.net/1853/71414

Associated Organization(s)

Organizational Unit

School of Chemical and Biomolecular Engineering

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Now showing 1 - 10 of 19

Transient Polymers for Low-k Dielectrics and Decomposing Electronic Devices

(Georgia Institute of Technology, 2016-09-16) Kohl, Paul A.

Dielectric materials (i.e. insulators) provide critical functions throughout the packaging hierarchy, including on-chip dielectrics, package substrates, and printed wiring boards. Transient polymers, those which vaporize on command, can be used to form ultra low-k dielectrics, such as porous materials or air-cavities. Transient polymers can also be used as coatings or structural materials in electronic packages and devices enabling the disappearance of the device when the collection, recovery or disposal of the device is difficult. In this presentation, the nature of transient polymers will be described including their synthesis, and physical properties. Transient polymers can be decomposed to the liquid or gaseous state when exposed to thermal, chemical or photo-chemical stimulus. The response time and type of stimulus will be described. Finally, several applications for transient polymers in the fabrication of unique devices, structures or packages will be described.
Improved Mechanical Properties of Chemically Amplified, Positive Tone, Polynorbornene Dielectric

(Georgia Institute of Technology, 2014-12) Schwartz, Jared M. ; Sutlief, Alexandra E. ; Kohl, Paul A. ; Mueller, Brennen K.

The mechanical properties of an aqueous developed, chemically amplified, polynorbornene-based permanent dielectric have been investigated. The previously reported hexafluoroisopropanol norbornene and tert-butyl ester norbornene copolymer has been modified via two routes to improve the mechanical properties of the polymer and enable thick-film deposition. First, a third monomer, butyl norbornene (ButylNB) was added to the polymer backbone. The inclusion of 24 mol% ButylNB lowered the elastic modulus from 2.64 to 2.35 GPa and raised the dielectric constant from 2.78 to 3.48. The second approach added a lowmolecular weight, plasticizing additive in the copolymer formulation. Many additives were immiscible with the resin or did not affect the mechanical properties. Trimethyololpropane ethoxylate (TMPEO) was found to be a miscible additive that improved mechanical properties and could participate in crosslinking the final dielectric material. TMPEO interacted with the PAG, lowering its decomposition temperature. An optimal formulation and processing scheme were determined. A formulation with 10 pphr TMPEO was measured to have a dielectric constant of 2.94, an elastic modulus of 1.95 GPa, a sensitivity at 365 nm of 175 mJ/cm2, and a contrast of 4.36.
Positive Tone, Polynorbornene Dielectric Crosslinking

(Georgia Institute of Technology, 2014-05) Schwartz, Jared M. ; Mueller, Brennen K. ; Elce, Edmund ; Pritchard, Zachary D. ; Li, Helen W. ; Grillo, Angelica M. ; Lee, Sang Y. ; Kohl, Paul A.

The processing and properties of a positive-tone, aqueous develop, epoxy crosslinked permanent dielectric based on a polynorbornene (PNB) backbone and bis(diazonaphthoquinone) (DNQ) photosensitive compound were investigated. The developing and cure properties of the films were studied as a function of cure temperature, epoxy crosslinker loading and DNQ loading. Reduced modulus measurements showed that crosslinking of the polymer film occurred via reaction of the polymer with DNQ. The final modulus of the DNQ-crosslinked film was 4.0 GPa. Swelling measurements for a UV exposed film showed material leaching from the film. Residual solvent from swelling measurements was analysed by gel permeation chromatography which showed the indene carboxylic acid form of DNQ leached out of the polymer film. The unexposed film did not exhibit material loss through leaching. When developed, films showed a decline in modulus to 2.6 GPa, likely due to the reaction of DNQ with the aqueous base developer forming nonreactive byproducts that did not contribute to crosslinking. An epoxy crosslinker was added to the formulation which helped crosslink the polymer film by inhibiting uptake of the aqueous base during developing. The epoxy inhibition of the base uptake was confirmed by quartz crystal microbalance, where an increase in epoxy loading led to a decrease in base uptake of the film during developing. 19F-NMR results support the DNQ-PNB crosslinking through esterification. Electrical characterization of the cured PNB films showed a relative dielectric constant of 3.65 for a DNQ and epoxy containing film after curing at 220◦C.
Chemically Amplified, Positive Tone, Polynorbornene Dielectric for Microelectronics Packaging

(Georgia Institute of Technology, 2014-05) Mueller, Brennen K. ; Schwartz, Jared M. ; Sutlief, Alexandra E. ; Bell, William K. ; Hayes, Colin O. ; Elce, Edmund ; Willson, C. Grant ; Kohl, Paul A.

A low permittivity, positive tone, polynorbornene dielectric has been developed that exhibits excellent lithographic and electrical properties. The polymer resin is a random copolymer of a norbornene hexafluoroalcohol (NBHFA) and a norbornene tert-butyl ester (NBTBE). High optical sensitivity and contrast were achieved using a chemically amplified solubility switching mechanism through the acid-catalyzed deprotection of the tert-butyl ester functionality. After developing in aqueous base, the film was thermally cured through a Fischer esterification reaction, resulting in a cross-linked permanent dielectric. The effect of the photoacid generator (PAG) concentration on the lithographic patterning and curing reactions was studied. Higher PAG loading was favorable for both sensitivity and dielectric constant. The sensitivity of a formulation was measured as low as 8.09 mJ/cm2. The molar ratio of the two monomers composing the polymer was varied. A higher NBHFA content was favorable because it resulted in a lower modulus, lower shrinkage, and lower dielectric constant and loss. A formulation with 70 mol% of the NBHFA had a modulus of 2.60 GPa, a 12.2% volume decrease during cure, and a dielectric constant of 2.23. The direction-dependent coefficient of thermal expansion was measured, and it was found that the anisotropy of the PNB films decreased with higher NBTBE content.
Designing of battery systems and study of anode alloy materials for improved lithium battery performance

(Georgia Institute of Technology, 2011-05-25) Kohl, Paul A. ; Kim, Hyea ; Stark, Johanna
Fabrication of avatrel pillars on Fujitsu's quartz wafers

(Georgia Institute of Technology, 2009-06-05) Kohl, Paul A.
High-Performance Chip-to-Chip Communications Using Advanced Materials and Structures

(Georgia Institute of Technology, 2008-09-09) Kohl, Paul A. ; Spencer, Todd ; Osborn, Tyler

The "off-chip" bandwidth is a major bottleneck causing system delays and limited throughput, especially in areas such as processor-to-memory bandwidth and processor-to-network. The ITRS cites off-chip signal bandwidth exceeding 60 GHz within 10 years. Organic substrates (i.e. chip packages or interposers) with flip-chip solder connections are the core of the first and second level of interconnect. Off-chip bandwidth is limited to several GHz due to frequency dependent attenuation, signal reflections, and crosstalk within the polymer dielectric, via structures, and I/O signal path transitions within the chip substrate and mother board. In this work, we have introduced advances in off-chip interconnect using air-isolated, coaxial links on substrates and boards to demonstrate ultra high-speed chip-to-chip and chip-to-network communications. New approaches have been found to fabricating high frequency I/O, air-and isolated coaxial links on the substrate. The materials, processes and electrical characteristics will be presented.
Rapid curing of positive tone photosensitive polybenzoxazole based dielectric resin by variable frequency microwave processing

(Georgia Institute of Technology, 2006-06) Tanikella, Ravindra V. ; Sung, Taehyun ; Bidstrup-Allen, Sue Ann ; Kohl, Paul A.

High performance polymer dielectrics such as polyimides and polybenzoxazoles are used for several applications in the semiconductor industry due to their excellent dielectric and thermomechanical properties. However, these materials require curing at high temperatures for long periods of time in order to achieve the desired properties. High temperature exposure for long periods of time can be detrimental to device characteristics and reliability. In this study, rapid low temperature curing of a positive tone photosensitive polybenzoxazole based dielectric resin by variable frequency microwave (VFM) processing was investigated. The chemical changes occurring in the film during the condensation reaction and the percent conversion achieved as a function of cure condition were monitored by Fourier transform infrared spectroscopy. The effectiveness of rapid VFM curing was studied by characterizing the optical, electrical, and thermomechanical properties of VFM cured films with thermally cured films. The thermal stability of cured films was investigated by thermal gravitational analysis (TGA) and mass spectrometry (MS) studies. The results showed that a higher percent conversion and higher thermal stability can be achieved by using VFM processing than can be obtained using conventional thermal curing at the same cure temperature. However, the complete removal of photopackage related residual products requires slow ramp rates and long cure times.
Polylithic integration of electrical and optical interconnect technologies for gigascale fiber-to-the-chip communication

(Georgia Institute of Technology, 2005-08) Mule’, Anthony V. ; Villalaz, Ricardo A. ; Joseph, Paul Jayachandran ; Naeemi, Azad ; Kohl, Paul A. ; Gaylord, Thomas K. ; Meindl, James D.

Polylithic integration of electrical and optical interconnect technologies is presented as a solution for merging silicon CMOS and compound semiconductor optoelectronics. In contrast to monolithic and hybrid integration technologies, polylithic integration allows for the elimination of optoelectronic and integrated optic device-related processing from silicon CMOS manufacturing. Printed wiring board-level and compound semiconductor chip-level waveguides terminated with volume grating couplers facilitate bidirectional optical communication, where fiber-to-board and board-to-chip optical coupling occurs through a two-grating (or grating-to-grating) coupling path. A 27% increase in the electrical signal I/O projected by and 33% increase in the number of substrate-level electrical signal interconnect layers implied by the International Technology Roadmap for Semiconductors (ITRS) projections for the 32-nm technology generation are required to facilitate 10 Tb/s aggregate bidirectional fiber-to-the-chip communication. Buried air-gap channels provide for the routing of chip or board-level encapsulated air-clad waveguides for minimum crosstalk and maximum interconnect density. Optical signals routed on-board communicate with on-chip volume grating couplers embedded as part of a wafer-level batch package technology exhibiting compatible electrical and optical input/output interconnects. Measurements of grating-to-grating coupling reveal 31% coupling efficiency between two slab, nonoptimized, nonfocusing volume grating couplers.
Next-generation microvia and global wiring technologies for SOP

(Georgia Institute of Technology, 2004-05) Sundaram, Venky ; Tummala, Rao R. ; Liu, Fuhan ; Kohl, Paul A. ; Li, Jun ; Bidstrup-Allen, Sue Ann ; Fukuoka, Yoshitaka

As microsystems continue to move toward higher speed and microminiaturization, the demand for interconnection density both on the IC and the package levels increases tremendously. The 2002 ITRS roadmap update identifies the need for sub-100-µm area array pitch and data rates of 10 Gb/s in the package or board by the year 2010, requiring much finer lines and vias than the current microvias of 50 µm diameter and lines and spaces of 25 µm. After a brief description of the future need for high-density substrates, the historical evolution of microvia technologies worldwide is summarized. With the move toward highly integrated and higher performance system-on-a-package (SOP) technology, the demand for microvia wiring density in the package is increasing dramatically requiring new innovations in fine line, ultralow-loss, and ultrathin-film dielectrics. The low-cost needs of this technology are driving research in high throughput and large area processes in dielectric and conductor deposition. The third section of this paper describes in detail some of the key emerging global microvia research and development in the fabrication of microminiaturized, multifunction SOP packages including rapid curing of low-loss dielectric thin films on organic substrates, environmentally friendly high-speed electroless copper plating, ultrafine lines, and spaces down to 5 µm and low-cost stacked via structures without chemical-mechanical polishing. This paper concludes with a perspective on future directions in dielectrics and conductor materials and processes leading to ultrahigh-density and low-cost microvia technologies for build-up SOP implementation.