News
Recent Paper Editor’s Pick JVST B
Congrats to Hyung Wan Do on his recent paper being chosen as an editor’s pick in JVST B.
Editor’s Pick
Congrats to Adam and Sarah for Fellowship
Congrats to Adam McCaughan and Sarah Goodman both received NSF iQuise Training Fellowships for the coming year. Adam is continuing this fellowship, and Sarah is a new receipient.
Superconducting Devices
We design and fabricate superconducting nanowire single photon detectors (SNSPDs). SNSPDs are appropriate for many applications because they have low jitter, a fast reset time and good sensitivity to infrared light. Thus, we are working on several research projects to improve device performance. For example, we are trying to increase the active area and the detection efficiency, and we are pushing the limits of electron-beam lithography to pattern more sensitive detectors reliably. We are also interested in understanding their operation, including their thermal behavior and the origin of jitter. With better understanding, we’ll be able to design higher performance detectors for quantum communication and other applications.
Superconducting Nanowire Avalanche Photon detectors (SNAPs)
Superconducting Nanowire Avalanche Photon detectors (SNAPs) combine multiple Superconducting Nanowire Single Photon Detectors (SNSPDs) into one device. By arranging two to four SNSPDs in parallel, a device can be created that is more sensitive to incoming photons. The increased sensitivity of a SNAP device allows narrowing the wire width and thereby enabling the detection of higher wavelength photons. We have demonstrated saturated detection efficiency into the mid-IR range.
“Single-Photon Detectors Based on Ultranarrow Superconducting Nanowires,” Francesco Marsili, Faraz Najafi, Eric Dauler, Francesco Bellei, Xiaolung Hu, Maria Csete, Richard J. Molnar, and Karl K. Berggren, Nano Letters 11(5) 2048 (2011).
Integration of optical systems with SNSPDs
We developed a fiber-coupled superconducting nanowire single-photon detector system in a close-cycle cryocooler and achieved 24% and 22% system detection efficiencies at wavelengths of 1550 and 1315 nm, respectively. The maximum dark count rate was ~ 1000 counts/s. The system included a 9mm circular detector with an integrated microcavity to enhance the optical absorption. Nanopositioners were used to achieve ~ 80 % coupling efficiency between the optical fiber and the detector.
“Fiber-coupled nanowire photon counter at 1550 nm with 24% system detection efficiency,” Xiaolong Hu, Tian Zhong, James E. White, Eric A. Dauler, Faraz Najafi, Charles H. Herder, Franco N. C. Wong, and Karl K. Berggren, Optics Letters 34, pp. 3607-3609 (2009)
Quantum Optics
In addition to integrating optical cavities to superconducting nanowire single-photon detectors (SNSPDs), we proposed a design for SNSPDs integrated with a silicon nitride waveguide and an inverse-taper coupler for fiber coupling. According to finite-element simulations, the absorptance of the NBN nanowire can reach 76% at a wavelength of 1550 nm [1].
We also recently demonstrated detection of 1.3-µm polarization-entangled photons over 200-m fiber-optic cables. The high efficiency and low dark counts of the SNSPD allowed a coincidence rate per unit power that was improved by a factor of 150 over previous measurements using gated InGaAs detectors [2].
- “Efficiently Coupling Light to Superconducting Nanowire Single-Photon Detectors,” Xiaolong Hu, Charles W. Holzwarth, Daniele Masciarelli, Eric A. Dauler, and Karl K. Berggren, IEEE Transactions on Applied Superconductivity 19, pp. 336-340 (2009).
- “High-quality fiber-optic polarization entanglement distribution at 1.3µm telecom wavelength,” Tian Zhong, Xiaolong Hu, Franco N. C. Wong, Karl K. Berggren, Tony D. Roberts, and Philip Battle, Optics Letters 35, pp. 1392-1394 (2010).
Transmission Line Integrated Superconducting Ion Traps
In collaboration with Isaac Chuang we have developed superconducting surface electrode ion traps with integrated transmission lines. We initially plan to use these transmission line integrated ion traps to perform microwave spectroscopy on trapped polar molecular ions. We have also used superconducting microwave cavities in place of the transmission lines and shown that superconducting resonators can be integrated into surface electrode ion traps.
“Superconducting microfabricated ion traps,” Shannon X. Wang, Yufei Ge, Jaroslaw Labaziewicz, Eric Dauler, Karl K. Berggren and Isaac L. Chuang, Applied Physics Letters 97 244102 (2010).
Congrats to Kristen Sunter for her PhD Defense
Nanofabrication
Nanofabrication, and nanolithography in particular, are the cornerstone of the modern microelectronics industry, and are integral to the future of nanotechnology as a whole. We are investigating fundamental challenges associated with continued scaling of electronic and nano-photonic device components. We are investigating the resolution limits of charged-particle lithography, including electron-beam and ion-beam lithography. The group also actively investigates the use of nanostructure arrays fabricated by nanolithography, as templates for: self-assembly of block copolymers, placement control of biomolecules or quantum dots, and as sources for the production of coherent electron pulses.
Continued scaling of devices toward molecular dimensions continues to unearth fascinating physical phenomena, which are of fundamental scientific interest as well as being critical to the development of future applications.
Charged Particle Lithography
For several years now, the group has worked on novel nanofabrication technologies to push the boundaries of the electronics industry well into the nanotechnology regime (sub-100 nm)[42, 48, 66], and charge particle lithography (CPL) is a big part of this effort. The work done has ranged from improving the resolution limits of resists for CPL (HSQ and PMMA) [80, 87] to the development and characterization of new lithography systems (Helium and Neon Ion Beam Lithography). Important and exhaustive studies have been developed to understand the fundamental limits of CPL (acceleration voltage[85], beam spot size, charged particle used[67, 88], resist[80, 87], etc.). This group is now working on improved ways to implement the knowledge obtained to increase the resolution[89], yield, quality of nanofabrication, and the use of this nanofabrication to different areas of electronic research.
Templated Self-Assembly
The group has focussed considerably on the use of high-resolution nanofabrication for the direction of many different self assembly systems. The templated-self assembly of block copolymer thin films has been an area of significant investigation and interest over the past few years. Work has focussed on the PS-b-PDMS polymer of many different morphologies and templating mechanisms. The group has achieved complex and long-range control as reported in many different papers[53, 70, 71]. The templating of other self-assembly systems is of interest and future research.
42. “Enhancing etch resistance of hydrogen silsesquioxane via postdevelop electron curing,” Joel K. W. Yang, Vikas Anant, and Karl K. Berggren, Journal of Vacuum Science and Technology B 24, 3157 (2006)
48. “Using high-contrast salty development of hydrogen silsesquioxane for sub-10-nm half-pitch lithography,” Joel K. W. Yang and Karl K. Berggren, Journal of Vacuum Science and Technology B25, 2025 (2007)
53. “Graphoepitaxy of Self-Assembled Block Copolymers on Two-Dimensional Periodic Patterned Templates,” Ion Bita, Joel K. W. Yang, Yeon Sik Jung, Caroline A. Ross, Edwin L. Thomas, and Karl K. Berggren, Science 321, 939 (2008).
58. “Si-Containing Block Copolymers for Self-Assembled Nanolithography (invited),” C.A. Ross, Y.S. Jung, V.P.Chuang, F. Ilievski, J.K.W. Yang, I. Bita, E.L. Thomas, H.I. Smith, K.K. Berggren, J.G.Vansco, and J.Y. Cheng, Journal of Vacuum Science and Technology B 26, pp.2489-2494 (2008)
66. “Understanding of Hydrogen Silsesquioxane Electron Resist for Sub-5-nm-Half-Pitch Lithography,” Joel K.W. Yang, Bryan Cord, Karl K. Berggren, Joseph Klingfus, Sung-Wook Nam, Ki-Bum Kim, and Michael J. Rooks, Journal of Vacuum Science and Technology B 27, pp. 2622-2627 (2009).
67. “Scanning-helium-ion-beam lithography with hydrogen silsesquioxane resist,” D. Winston, B. M. Cord, B. Ming, D. C. Bell, W. F. DiNatale, L. A. Stern, A. E. Vladar, M. T. Postek, M. K. Mondol, J. K. W. Yang, and K. K. Berggren, Journal of Vacuum Science and Technology B 27, pp. 2702-2706
(2009).
70. “A Path to Ultranarrow Patterns Using Self-Assembled Lithography,” Yeon Sik Jung, J. B. Chang, Eric Verploegen, Karl K. Berggren and C. A. Ross, Nano Letters 10, pp. 1000-1005 (2010)
71. “Complex self-assembled patterns using sparse commensurate templates with locally varying motifs,” Joel K. W. Yang, Yeon Sik Jung, Jae-Byum Chang, R. A. Mickiewicz, A. Alexander-Katz, C. A. Ross and Karl K. Berggren, Nature Nanotechnology 5, pp. 256-260 (2010).
80. “Sub-10-nm Half-Pitch Electron-Beam Lithography by Using PMMA as a Negative Resist,” Huigao Duan, Donald Winston, Joel K. W. Yang, Bryan M. Cord, Vitor R. Manfrinato, and Karl K. Berggren, Journal of Vacuum Science and Technology B 28 C6C58-C6C62 (2010).
85. “Sub-5 keV Electron-Beam Lithography in Hydrogen Silsesquioxane Resist,” Vitor R. Manfrinato, Lin Lee Cheong, Huigao Duan, Donald Winston, Henry I. Smith, Karl K. Berggren, Journal of Microelectronic Engineering To be published (2011).
87. “Electrochemical development of hydrogen silsesquioxane by applying an electrical potential,” Sebastian Strobel, Katherine J Harry, Huigao Duan, Joel K W Yang, Vitor R Manfrinato and Karl K Berggren, Nanotechnology 22 375301(2011).
88. “Neon Ion Beam Lithography (NIBL),” Donald Winston , Vitor R Manfrinato , Samuel M Nicaise, Lin Lee Cheong , Huigao Duan , David Ferranti , Jeff Marshman , Shawn McVey , Lewis A Stern, John A Notte , and Karl Berggren, Nano Letters Available Online(2011).
89. “Controlled Collapse of High-Aspect-Ratio Nanostructures,” Huigao Duan, Joel K. W. Yang, and Karl K. Berggren, Small, 7, No. 18, 2661-2668 (2011).