Publications

Nordquist, Christopher N.; Skogen, Erik J.; Fortuna, S.A.; Hollowell, Andrew E.; Hemmady, Caroline S.; Saugen, J.M.; Forbes, T.; Wood, Michael G.; Jordan, Matthew J.; McClain, Jaime L.; Lepkowski, Stefan M.; Alford, Charles A.; Peake, Gregory M.; Pomerene, Andrew P.; Long, Christopher M.; Serkland, Darwin K.; Dean, Kenneth A.

Abstract not provided.

ECS Transactions

Nordquist, C.D.; Skogen, Erik J.; Fortuna, S.A.; Hollowell, Andrew E.; Hemmady, C.S.; Saugen, J.M.; Forbes, T.; Wood, M.G.; Jordan, Matthew J.; McClain, Jaime L.; Lepkowski, Stefan M.; Alford, Charles A.; Peake, Gregory M.; Pomerene, Andrew P.; Long, C.M.; Serkland, Darwin K.; Dean, Kenneth A.

Heterogeneous Integration (HI) may enable optoelectronic transceivers for short-range and long-range radio frequency (RF) photonic interconnect using wavelength-division multiplexing (WDM) to aggregate signals, provide galvanic isolation, and reduce crosstalk and interference. Integration of silicon Complementary Metal-Oxide-Semiconductor (CMOS) electronics with InGaAsP compound semiconductor photonics provides the potential for high-performance microsystems that combine complex electronic functions with optoelectronic capabilities from rich bandgap engineering opportunities, and intimate integration allows short interconnects for lower power and latency. The dominant pure-play foundry model plus the differences in materials and processes between these technologies dictate separate fabrication of the devices followed by integration of individual die, presenting unique challenges in die preparation, metallization, and bumping, especially as interconnect densities increase. In this paper, we describe progress towards realizing an S-band WDM RF photonic link combining 180 nm silicon CMOS electronics with InGaAsP integrated optoelectronics, using HI processes and approaches that scale into microwave and millimeter-wave frequencies.

Journal of Electronic Materials

Klein, Brianna A.; Baca, A.G.; Lepkowski, Stefan M.; Nordquist, Christopher N.; Wendt, J.R.; Allerman, A.A.; Armstrong, Andrew A.; Douglas, Erica A.; Abate, Vincent M.; Kaplar, Robert K.

Gate length dependent (80 nm–5000 mm) radio frequency measurements to extract saturation velocity are reported for Al0.85Ga0.15N/Al0.7Ga0.3N high electron mobility transistors fabricated into radio frequency devices using electron beam lithography. Direct current characterization revealed the threshold voltage shifting positively with increasing gate length, with devices changing from depletion mode to enhancement mode when the gate length was greater than or equal to 450 nm. Transconductance varied from 10 mS/mm to 25 mS/mm, with the 450 nm device having the highest values. Maximum drain current density was 268 mA/mm at 10 V gate bias. Scattering-parameter characterization revealed a maximum unity gain bandwidth (fT) of 28 GHz, achieved by the 80 nm gate length device. A saturation velocity value of 3.8 × 106 cm/s, or 35% of the maximum saturation velocity reported for GaN, was extracted from the fT measurements.

Kaplar, Robert K.; Baca, A.G.; Klein, Brianna A.; Wendt, J.R.; Lepkowski, Stefan M.; Nordquist, Christopher N.; Armstrong, Andrew A.; Allerman, A.A.; Douglas, Erica A.; Reza, Shahed R.; Flicker, Jack D.

Abstract not provided.

Kaplar, Robert K.; Baca, A.G.; Klein, Brianna A.; Wendt, J.R.; Lepkowski, Stefan M.; Nordquist, Christopher N.; Armstrong, Andrew A.; Allerman, A.A.; Douglas, Erica A.; Reza, Shahed R.; Flicker, Jack D.

Abstract not provided.

IEEE Electron Device Letters

Baca, A.G.; Klein, Brianna A.; Wendt, J.R.; Lepkowski, Stefan M.; Nordquist, Christopher N.; Armstrong, Andrew A.; Allerman, A.A.; Douglas, Erica A.; Kaplar, Robert K.

Al-rich AlGaN-channel high electron mobility transistors with 80-nm long gates and 85% (70%) Al in the barrier (channel) were evaluated for RF performance. The dc characteristics include a maximum current of 160 mA/mm with a transconductance of 24 mS/mm, limited by source and drain contacts, and an on/off current ratio of 109. fT of 28.4 GHz and fMAX of 18.5 GHz were determined from small-signal S-parameter measurements. Output power density of 0.38 W/mm was realized at 3 GHz in a power sweep using on-wafer load pull techniques.

IEEE Magnetics Letters

Monson, Todd M.; Zheng, Baolong; Delany, Robert E.; Pearce, Charles J.; Langlois, Eric L.; Lepkowski, Stefan M.; Stevens, Tyler E.; Zhou, Yizhang; Atcitty, Stanley; Lavernia, Enrique J.

Novel multilayered FeSiCrB-Fe x N (x = 2-4) metallic glass composites were fabricated using spark plasma sintering of FeSiCrB amorphous ribbons (Metglas 2605SA3 alloy) and Fe x N (x = 2-4) powder. Crystalline Fe x N can serve as a high magnetic moment, high electrical resistance binder, and lamination material in the consolidation of amorphous and nanocrystalline ribbons, mitigating eddy currents while boosting magnetic performance and stacking factor in both wound and stacked soft magnetic cores. Stacking factors of nearly 100% can be achieved in an amorphous ribbon/iron nitride composite. FeSiCrB-Fe x N multilayered metallic glass composites prepared by spark plasma sintering have the potential to serve as a next-generation soft magnetic material in power electronics and electrical machines.

Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS)

Siddiqui, Aleem M.; Nordquist, Christopher N.; Grine, Alejandro J.; Lepkowski, Stefan M.; Henry, M.D.; Eichenfield, Matthew S.; Griffin, Benjamin G.

Biasing a MEMS switch close to static-pull in reduces the modulation amplitude necessary to achieve resonant pull-in, but results in a highly nonlinear system. In this work, we present a new methodology that captures the essential dynamics and provides a prescription for achieving the optimal drive waveform which reduces the amplitude requirements of the modulation source. These findings are validated both experimentally and through numerical modeling.

Siddiqui, Aleem M.; Nordquist, Christopher N.; Grine, Alejandro J.; Lepkowski, Stefan M.; Henry, Michael D.; Eichenfield, Matthew S.; Griffin, Benjamin G.

Abstract not provided.

Henry, Michael D.; Young, Travis R.; Wolfley, Steven L.; Sierra Suarez, Jonatan A.; Lepkowski, Stefan M.; Lewis, Rupert; Wolak, Matthaeus W.; Missert, Nancy A.

Abstract not provided.

Blain, Matthew G.; Haltli, Raymond A.; Hogle, Craig W.; Hollowell, Andrew E.; Nordquist, Christopher N.; Lepkowski, Stefan M.; Lobser, Daniel L.; Yale, Christopher G.; Maunz, Peter L.

Abstract not provided.

Maunz, Peter L.; Haltli, Raymond A.; Hollowell, Andrew E.; Lepkowski, Stefan M.; Lobser, Daniel L.; Nordquist, Christopher N.; Rembetski, John F.; Revelle, Melissa R.; Yale, Christopher G.; Blain, Matthew G.

Abstract not provided.

IEEE MTT-S International Microwave Symposium Digest

Nordquist, Christopher N.; Henry, M.D.; Nguyen, Janet H.; Clews, Peggy; Lepkowski, Stefan M.; Grine, Alejandro J.; Dyck, Christopher D.; Olsson, Roy H.

Inductive coupling and matching networks are used to increase the bandwidth of filters realized with aluminum nitride contour-mode resonators. Filter bandwidth has been doubled using a wirebonded combination of a wafer-level-packaged resonator chip and a high-Q integrated inductor chip. The three-pole filters have a center frequency near 500 MHz, an area of 9 mm × 9 mm, insertion loss of < 5 dB for a bandwidth of 0.4%, and a resonator unloaded Q of 1600.

Nordquist, Christopher N.; Henry, Michael D.; Nguyen, Janet N.; Clews, Peggy J.; Lepkowski, Stefan M.; Grine, Alejandro J.; Dyck, Christopher D.; Olsson, Roy H.

Abstract not provided.

Lepkowski, Stefan M.

The work here presents a review of beam forming architectures. As an example, the author presents an 8x8 Butler Matrix passive beam forming network including the schematic, design/modeling, operation, and simulated results. The limiting factor in traditional beam formers has been the large size dictated by transmission line based couplers. By replacing these couplers with transformer-based couplers, the matrix size is reduced substantially allowing for on chip compact integration. In the example presented, the core area, including the antenna crossover, measures 0.82mm×0.39mm (0.48% the size of a branch line coupler at the same frequency). The simulated beam forming achieves a peak PNR of 17.1 dB and 15dB from 57 to 63GHz. At the 60GHz center frequency the average insertion loss is simulated to be 3.26dB. The 8x8 Butler Matrix feeds into an 8-element antenna array to show the array patterns with single beam and adjacent beam isolation.