Technical Abstracts
In Case You Missed It
Component Technology
“N-Polar GaN-on-Sapphire Deep Recess HEMTs With High W-Band Power Density”

Authors: Brian Romanczyk, Weiyi Li, Matthew Guidry, Nipuram Hatui, Athith Krishna, Christian Wurm, Stacia Keller, and Umesh K. Mishra.

Abstract: This work presents recent progress in the W-band (94GHz) power performance of N-polar GaN deep recess HEMTs grown on sapphire substrates. While SiC has been the substrate of choice to achieve the highest level of performance, sapphire substrates are a lower cost alternative. The authors show that N-polar GaN deep recess HEMTs grown on sapphire match the power performance of a device on SiC up to 14V with 5.1W/mm of output power density. At 16V the device on sapphire starts to suffer from thermal effects but still demonstrated 5.5W/mm with an associated 20.6% power-added efficiency. This work also examines the impact of encapsulating the device in a low dielectric constant film often used for the implementation of an RF wiring environment. Such a device could be critical to efficiently pushing 6G’s terahertz-frequency signals out of the antennas of future smartphones and other connected devices. (IEEE Electron Device Letters, vol. 41, no. 11, November 2020, https://ieeexplore.ieee.org/document/9187650)

IC Packaging Materials
“Sintered Nanocopper Paste for High-Performance 3D Heterogeneous Package Integration”

Author: Yiteng Wang, Atom O. Watanabe, et al.

Abstract: 5G communications have been driving major package innovations to enable low-loss interconnects between ICs and other system components such as antenna arrays. Antenna-in-package with three-dimensional or double-side components is widely pursued as the front-up architecture to realize this vision. The interconnect height and losses are critical parameters in these 3-D package structures. Copper sintering paste is emerging as an ideal candidate to replace solders for both off-chip and on-package interconnects because of the resulting higher electrical conductivity and relatively simple manufacturability with additive processes. This article focuses on computational modeling, optimization of sintering conditions, and electrical conductivity measurements of highly conductive copper paste to verify the proposed model. The model is based on two-particle sintering theory, which describes the neck growth evolution of copper paste at the initial stage of sintering. The neck-growth model shows good consistency with the measured neck size of copper, and hence can be used to provide guidelines for the sintering conditions of copper paste. The electrical conductivity measurements suggest the copper paste sintered at 260°C for 30 min. shows an electrical conductivity of 1.4 x 107 S/m, which is 82% higher than that of solder. In addition, this article investigates the potential of copper paste interconnect technology in high-frequency applications such as in 5G millimeter-wave communications. The transmission lines patterned with the copper paste show good correlation with simulated results in the millimeter-wave frequency band. The high-frequency characterization also indicates the copper paste enables simple circuit patterning, offering equivalent signal losses with plated copper. The detailed analyses suggest the eligibility for multi-applications of copper sintering paste in IC packaging. (Journal of Electronic Materials, Sept. 10, 2020; https://link.springer.com/article/10.1007/s11664-020-08399-x)

Inkjet Printing
“Drop Impact Printing”

Authors: Chandantaru Dey Modak, Arvind Kumar, Abinash Tripathy and Prosenjit Sen.

Abstract: Hydrodynamic collapse of a central air-cavity during the recoil phase of droplet impact on a superhydrophobic sieve leads to satellite-free generation of a single droplet through the sieve. Two modes of cavity formation and droplet ejection are observed and explained. The volume of the generated droplet scales with the pore size. Based on this phenomenon, the authors propose a drop-on-demand printing technique. Despite significant advancements in inkjet technology, enhancement in mass-loading and particle-size have been limited due to clogging of the printhead nozzle. By replacing the nozzle with a sieve, the authors demonstrate printing of nanoparticle suspension with 71% mass-loading. Comparatively large particles of 20µm diameter are dispensed in droplets of ~80µm diameter. Printing is performed for surface tension as low as 32mNm−1 and viscosity as high as 33 mPa∙s. In comparison to existing techniques, this way of printing is widely accessible as it is significantly simple and economical. (Nature Communications, vol. 11, Aug. 28, 2020, www.nature.com/articles/s41467-020-18103-6)

This column provides abstracts from recent industry conferences and company white papers. Our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.