Publications – 2018
Yuhao Zhang, Min Sun, Josh Perozek, Zhihong Liu, Ahmad Zubair, Daniel Piedra, Nadim Chowdhury, Xiang Gao, Kenneth Shepard, and Tomás Palacios. Large Area 1.2 kV GaN Vertical Power FinFETs with a Record Switching Figure-of-Merit. IEEE Electron Device Letters DOI 10.1109/LED.2018.2880306 November 9, 2018
Hyungsik Kim, Gwan-Hyoung Lee, James Hone, and Kenneth L. Shepard. Ambipolar Memristive Phenomenon in Large-Scale, Few-Layered αMoO3 Recrystallized Films. Advanced Material Interfaces 2018 DOI: 10.1002/admi.201801591
C. Shi, T. Costa, J. Elloiain, and K. L. Shepard, “Monolithic integration of micron-scale piezoelectric materials with CMOS for biomedical applications,” IEDM 2018.
Young Duck Kim, Yuanda Gao, Ren-Jye Shiue, Lei Wang , Ozgur Burak Aslan, Myung-Ho Bae, Hyungsik Kim, Dongjea Seo, Heon-Jin Choi, Suk Hyun Kim, Andrei Nemilentsau, Tony Low, Cheng Tan, Dmitri K. Efetov, Takashi Taniguchi, Kenji Watanabe, Kenneth L. Shepard, Tony F. Heinz, Dirk Englund, and James Hone. Ultrafast Graphene Light Emitters. Nano Letters DOI: 10.1021/acs.nanolett.7b04324,Publication Date (Web): January 16, 2018.
Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460% enhancement compared to the gray-body thermal radiation for a broad peak centered at 720 nm. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2000 K under ambient conditions as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes under electrical excitation. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.
Yoonhee Lee, Scott M. Trocchia, Steven B. Warren, Erik F. Young, Sefi Vernick, and Kenneth L. Shepard, “Electrically Controllable Single-Point Covalent Functionalization of Spin-Cast Carbon-Nanotube Field-Effect Transistor Arrays“. ACS Nano Publication Date: September 27, 2018, DOI: 10.1021/acsnano.8b03073.
Single-point-functionalized carbon-nanotube field-effect transistors (CNTFETs) have been used to sense conformational changes and binding events in protein and nucleic acid structures from intrinsic molecular charge. The key to utilizing these devices as single-molecule sensors is the ability to attach a single probe molecule to an individual device. In contrast, with noncovalent attachment approaches such as those based on van der Waals interactions, covalent attachment approaches generally deliver higher stability but have traditionally been more difficult to control, resulting in low yield. Here, we present a single-point-functionalization method for CNTFET arrays based on electrochemical control of a diazonium reaction to create sp3 defects, combined with a scalable spin-casting method for fabricating large arrays of devices on arbitrary substrates. Attachment of probe DNA to the functionalized device enables single-molecule detection of DNA hybridization with complementary target, verifying the single-point functionalization. Overall, this method enables single-point defect generation with 80% yield.
Daniel A. Fleischer, Siddharth Shekar, Shanshan Dai, Ryan M. Field, Jenifer Lary, Jacob K. Rosenstein and Kenneth L. Shepard. CMOS-Integrated Low-Noise Junction Field-Effect Transistors for Bioelectronic Applications. IEEE Electron Device Letters Date of Publication: 06 June 2018, DOI: 10.1109/LED.2018.2844545.
In this work, we present a CMOS-integrated lownoise junction field-effect transistor (JFET) developed in a standard 0.18 μm CMOS process. These JFETs reduce inputreferred flicker noise power by more than a factor of 10 when compared to equally sized n-channel MOS devices by eliminating oxide interfaces in contact with the channel. We show that this improvement in device performance translates into a factor-of-10 reduction in the input-referred noise of integrated CMOS operational amplifiers when JFET devices are used at the input, significant for many applications in bioelectronics.
Andreas J. W. Hartel, Peijie Ong, Indra Schroeder, M. Hunter Giese, Siddharth Shekar, Oliver B. Clarke, Ran Zalk, Andrew R. Marks, Wayne A. Hendrickson and Kenneth L. Shepard. Single-channel recordings of RyR1 at microsecond resolution in CMOS-suspended membranes. PNAS February 20, 2018. 115 (8) E1789-E1798, DOI:10.1073/pnas.1712313115.
Single-channel recordings are widely used to explore functional properties of ion channels. Typically, such recordings are performed at bandwidths of less than 10 kHz because of signal-to-noise considerations, limiting the temporal resolution available for studying fast gating dynamics to greater than 100 µs. Here we present experimental methods that directly integrate suspended lipid bilayers with high-bandwidth, low-noise transimpedance amplifiers based on complementary metal-oxide-semiconductor (CMOS) integrated circuits (IC) technology to achieve bandwidths in excess of 500 kHz and microsecond temporal resolution. We use this CMOS-integrated bilayer system to study the type 1 ryanodine receptor (RyR1), a Ca2+-activated intracellular Ca2+-release channel located on the sarcoplasmic reticulum. We are able to distinguish multiple closed states not evident with lower bandwidth recordings, suggesting the presence of an additional Ca2+ binding site, distinct from the site responsible for activation. An extended beta distribution analysis of our high-bandwidth data can be used to infer closed state flicker events as fast as 35 ns. These events are in the range of single-file ion translocations.