E3S REU Participants and Projects: 2014
Undergraduate Researcher: Joseph Finley
Major: Electrical Engineering and Computer Sciences
Home Institution: University of California, Berkeley
Research Project: Six-Terminal Carbon Nanotube Relays
Faculty Advisor: Prof. H.-S. Philip Wong
Postdoc Mentor: Dr. Ji Cao
Hosting Organization: Electrical Engineering Department, Stanford University
Project Abstract: Carbon nanotube (CNT) relays are promising NEMS devices due to CNT’s low mass, small dimension, high Young’s modulus, and high current density. Previously, CNT clamped-clamped relays have been fabricated using a bottom-up integration scheme. This process involves resist-assisted assembly, wProject poster single-walled metallic CNTs are self-aligned into electron-beam resist trenches using ac-dielectrophoresis (DEP). These devices have shown excellent ON/OFF current ratios, low off-state current, high yield, and high endurance. Using this same process, we demonstrated a novel six-terminal (6T) CNT relay for low power applications in this work. Project poster
Undergraduate Researcher: Yee Ling Gan
Major: Electrical Engineering and Computer Sciences
Home Institution: Massachusetts Institute of Technology
Research Project: HCG-VCSEL and NEMO Characterization and Design
Faculty Advisor: Prof. Connie Chang-Hasnain
Mentor: Linda Li
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: The use of high-index-contrast subwavelength grating (HCG) to replace 30-50 pairs of top distributed Bragg reflector mirrors of the vertical-cavity surface-emitting laser (VCSEL) is an original design of Professor Chang-Hasnain’s Laboratory. When a mechanical actuator is integrated with the HCG layer, compact nano-electromechanical optoelectronic (NEMO) tunable VCSEL with precise and continuous wavelength tuning and greater tuning speed is obtained experimentally. The main goal of the project is to find a NEMO device with a wider tuning range (>40nm) through simulations, and characterize fabricated HCG-VCSEL and NEMO devices. A NEMO device with tuning range >40nm would be important for bio imaging applications such as Optical CoProject posternce Tomography. Project poster
Undergraduate Researcher: Christopher Gaytan
Major: Electrical Engineering and Computer Sciences
Home Institution: The University of Texas at El Paso
Research Project: Contact Engineering of TMDC Materials: Using Graphene at the TMDC/Metal Interface
Faculty Advisor: Prof. Ali Javey
Postdoc Mentor: Dr. Tania Roy
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Transition metal dichalcogenides (TMDC) materials MoS2 and WSe2 may be implemented for use in CMOS as n-type and p-type semiconductors. Although tProject poster is a challenge in forming a good electrical contact on these materials; traditional metals form a huge Schottky barrier due Fermi level pinning. To mitigate this behavior we use graphene as a lubricant layer between the TMDC material and our metal contacts: palladium and nickel. Ideally this method should decouple the TMDC material and contact resulting in an ohmic contact; unfortunately this is not the case and we still show Fermi level pinning. Project poster
Undergraduate Researcher: Terrell Glenn
Major: Physics
Home Institution: Morehouse College
Research Project: Tunable Magnetic Anisotropy in Perpendicular Exchange-Coupled CoFeB/(Co/Pt) Films
Faculty Advisor: Prof. Sayeef Salahuddin
Graduate Student Mentor: Dr. Long You
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Development of novel magnetic structures suitable for spintronics applications shows that spintronics materials with strong perpendicular magnetic anisotropy (PMA), such as Co/Pd and Co/Pt multilayers, have been introduced to improve the functional performance of both Spintronics and Spin Transfer Torque (STT) devices (e.g. enhanced thermal stability, scalability and lowered switching speeds and switching current of STT-Magnetoresistive Random Access Memory). Moreover, by coupling magnetic layers with PMA and longitudinal magnetic anisotropy (LMA), added benefits such as a variable magnetization tilt angle and tunable damping have been shown. My project involves obtaining strong perpendicular anisotropy from sputtering Co/Pt films, and understanding the dynamics of full magnetization reversal for future STT application. Project poster
Undergraduate Researcher: Justin Laguardia
Major: Electrical Engineering
Home Institution: University of California, Davis
Research Project: Ultrafast Electrical Pulse Generation in Photoconductive Switches
Faculty Advisor: Prof. Jeffrey Bokor
Graduate Student Mentor: Yang Yang
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Ultra-fast photoconductive switches (PCS) can be used to generate very fast electrical pulses. These pulses can be used to further examine the dynamics of magnetic switching. The project goal was to design and experimentally measure a photoconductive switch that exhibits sub picosecond electrical pulses and that can deliver a large current density to a load. Project poster
Undergraduate Researcher: Augustus Lang
Major: Electrical Engineering
Home Institution: University of Southern California
Research Project: Chemically Doped Graphene Contacts for n- and p-type WSe2 Transistors
Faculty Advisor: Prof. Ali Javey
Postdoc Mentor: Dr. Tania Roy
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Chemically doped graphene was used to fabricate n-type and p-type transistors using WSe2 as the channel material. Benzyl Viologen (BV), a strong electron donor, was used as the n-type dopant allowing graphene to contact the WSe2 valence band. BV doping graphene was shown to give n-type behavior in WSe2 that initially showed ambipolar characteristics by increasing (decreasing) electron (hole) current by 1000x and reducing Schottky barrier height. NO2, an electron acceptor, was used as the p-type dopant for graphene. NO2 doping was shown to penetrate the protective oxide on the channel to give degenerate doping of the WSe2. In both cases the dopants are shown to be air stable.
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Undergraduate Researcher: Hannah Masten
Major: Electrical Engineering
Home Institution: Auburn University
Research Project: Back-gated Sub-4 Layer MoTe2 Ultra-thin Body p-MOSFETs
Faculty Advisor: Prof. Ali Javey
Postdoc Mentor: Dr. Mohammad Najmzadeh
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Molybdenum ditelluride (MoTe2) is a heavy carrier concentration 2D layered semiconductor, investigated to achieve high Ion/Ioff ratio as a p-MOSFET with quasi-Ohmic S/D contacts. Back-gated sub-4 layer MoTe2 p-MOSFETs were fabricated and the drain current (Id) – gate voltage (Vg) characteristics were measured at room temperature. Ion/Ioff and the effective mobility values were extracted. Contact studies were performed using Pt/Au and Pd/Au and the impact of annealing were investigated. Project poster
Undergraduate Researcher: Brenda McLellan
Major: Physics and Mathematics
Home Institution: Polytechnic Institute of New York University
Research Project: Rotating Magnetic Microbeads with Electric Fields
Faculty Advisor: Prof. Jeffrey Bokor
Postdoc Mentor: Dr. Mark Nowakowski
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Rotation and transport of micro and nano scale devices has great potential in nanomotor technology. We study the exciting possibility of creating such devices based on the manipulation of magnetic domain walls (DWs) in microrings. We first show rotation of magnetic DWs in Permalloy microrings due to an applied rotating magnetic field. Superparamagnetic (SPM) microbeads are trapped in the magnetostatic potential wells of the DWs and travel along their track with the moving DWs. In consideration of the large cost of energy associated with applying magnetic fields and the non-scalability of vector magnets we particularly study the control of magnetic domain walls and SPM beads with applied electric fields. Our results show the rotation of SPM beads trapped by magnetic DWs in nickel rings attached to a piezoelectric substrate due to an applied voltage.
Undergraduate Researcher: Eric McShane
Major: Chemical Engineering and Physics
Home Institution: Cornell University
Research Project: Determination of Doping Levels in InP Nanopillars Using Photoluminescence Measurements
Faculty Advisor: Prof. Connie Chang-Hasnain
Graduate Student Mentor: Indrasen Bhattacharya
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Indium phosphide nanopillars possess potential to become pivotal materials in the production of energy-efficient optoelectronic devices. These nanopillars have previously been shown to produce optically-pumped lasers and are currently being evaluated as solar cell material. However, rapid and convenient methods for characterizing impurity doping levels are important for device development. Conventional methods of doping level characterization, such as Hall effect and 4-point-probe measurements, are difficult to perform due to the nanoscale electrical contacts required. To improve the characterization procedure, a novel contactless I-V method is proposed, which can be used to determine the doping level through photoluminescence measurements. The contactless I-V doping level was compared to that of 4-point-probe measurements with decent agreement, attesting to the efficacy of the contactless I-V method. Project poster
Undergraduate Researcher: Erick Romo-Mendoza
Major: Electrical and Computer Engineering
Home Institution: The University of Texas at El Paso
Research Project: Reliability of SiC MOSFETs
Faculty Advisor: Prof. Jésus del Alamo
Postdoc Mentor: Dr. Alon Vardy
Hosting Organization: Electrical Engineering and Computer Sciences Department, MIT
Project Abstract: Silicon Carbide (SiC) is an important semiconductor for high power electronics because of its unique properties, such as high electrical breakdown, high thermal conductivity, and high saturated electron drift velocity. Recently, these characteristics have been exploited in fabricating SiC power metal-oxide semiconductor field-effect-transistors (MOSFETs). Understanding the behavior and failure mechanism of these power devices through aging is of particular importance, because of their applications in high power switching circuitry. In order to exploit SiC MOSFET capabilities, it is necessary to understand its aging process. In this work, we studied the SiC power MOSFET in a Transistor Outline (TO) package, able to hold up 1200 V and 20 A. We accelerated the device aging via electrical overstress and monitored its main figures of merit (FOM), namely, the On-resistance (Ron), threshold voltage (Vt), subthreshold swing (S), and Saturation current (Idsat). We developed a measurement system capable of characterizing and stressing the transistor up to 200 V and 100 mA. We considered a variety of stress conditions in order to understand device degradation. Using this system we observed 35% degradation in Vt and 150% in Idsat. The stress causes a negative shift in Vt and consequently Idsat increases. After 1 minute of relaxation (no electrical stress), the original values of these FOMs are fully recovered, as confirmed by several sequential measurement sets. This indicates that the observed degradation is entirely due to carrier trapping somewProject poster in the device. In conclusion, we have developed a measurement system to study the aging process of high power SiC MOSFETs. Using this system, we found stress conditions which accelerate the device aging but do not cause permanent damage. Project poster
Undergraduate Researcher: Michael Statt
Major: Materials Science and Engineering
Home Institution: Cornell University
Research Project: Etch Pit Density Analysis of Ternary III-V Semiconductor Heterostructures
Faculty Advisor: Prof. Eugene Fitzgerald
Graduate Student Mentor: Christopher Heidelberger & Ryan Iutzi
Hosting Organization: Electrical Engineering and Computer Sciences Department, MIT
Project Abstract: Project poster
Undergraduate Researcher: Megan Stephanz
Major: Materials Science Engineering
Home Institution: University of Utah
Research Project: Fabrication of InAs Field Effect Transistors
Faculty Advisor: Prof. Eli Yablonovitch
Graduate Student Mentor: Jared Carter
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: One way to further continue the reduction in energy consumption in computing is to reduce the supply voltage in computing circuits. New lower-voltage transistors are required to reduce the supply voltage to less than 300 mV. The Indium Arsenide Bilayer Tunnel Field Effect Transistor (InAs BT-FET) is one attempt to create a new low voltage transistor. The device will be fabricated by transferring ribbons of epitaxially grown InAs from its native substrate of gallium antimonide to silicon chips. Afterwards, appropriate places to build transistors will be identified and utilized before the BT-FETs will be tested and characterized. Project poster
Undergraduate Researcher: C. Shane Strickland
Major: Physics
Home Institution: Polytechnic Institute of New York University
Research Project: Ferroelectric Switching Dynamics
Faculty Advisor: Prof. Sayeef Salahuddin
Graduate Student Mentors: Asif Khan
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: Negative capacitance effect in ferroelectric capacitors have recently been directly observed in ferroelectric capacitors via time dynamic measurements during polarization switching. However, the effect of switching dynamics, specifically that of a multi-domain switching on the negative capacitance is not yet fully understood. In this work, we study the multi-domain switching dynamics by numerically solving the Landau-Khalatnikov equation. Multi-domain switching is modeled by parallel connected ferroelectric capacitors with varying internal resistances. The results suggest that the negative capacitance time scale becomes much shorter when the switching occurs through multiple domains as opposed to in the single domain fashion. Project poster
Undergraduate Researcher: Jack Wilson
Major: Engineering Physics
Home Institution: Brown University
Research Project: Optical Characterization of WSe2 Monolayers
Faculty Advisor: Prof. Ming C. Wu
Graduate Student Mentor: Michael Eggleston
Hosting Organization: Electrical Engineering and Computer Sciences Department, UC Berkeley
Project Abstract: The realization of feasible optical interconnect technology demands an efficient nanoscale light emitter. Increasing the efficiency of nanoLEDs requires: (1) enhancing radiative recombination rates in semiconductor materials; and (2) lowering non-radiative recombination rates in those materials. Although optical antennas are potential solutions to the first problem, the second also deserves attention. Project poster, we investigate the optical performance of WSe2 at different feature sizes, performing photoluminescence (PL) and lifetime measurements to characterize the non-radiative edge recombination behavior in this 2D semiconductor material. With the results, we model the edge recombination characteristics of WSe2 and use this model to discuss the potential of WSe2 for use as the light emitting material in nanoLEDs. Project poster