E3S REU Participants and Projects: 2018
Undergraduate Researcher: Alexander Hwang
Major: Electrical Engineering
Home Institution: Rice University
Research Institution: U.C. Berkeley
Research Project: Routing light emission from monolayer-antenna nanoLEDs
Faculty Advisor: Dr. Eli Yablonovitch
Graduate Student Mentor: Kevin Han
Project Abstract: Efficient nanoscale LEDs (nanoLEDs) are attractive for ultrasmall on-chip optical interconnects. Coupling metal nanoantennas to nanoLEDs increases their speed. Emerging monolayer transition metal dichalcogenides are of high interest for use as emitter materials in nanoLEDs, and nanoantennas have been shown to strongly enhance their light emission. However, these studies have focused on optically-injected structures that radiate into free space and practically demonstrating a chip-compatible electrically-injected monolayer-antenna nanoLED that emits unidirectionally into a single-mode waveguide presents several novel design challenges. We discuss design strategies, including computational inverse design, for broad-area, unidirectional enhancement of planar monolayer emitters.
Undergraduate Researcher: Alice Wu
Major: Electrical Engineering
Home Institution: Columbia University
Research Institution: U.C. Berkeley
Research Project: Modeling Effect of Low Index Dielectric on Reflectivity in Thermophotovoltaic & Calorimetry Methods
Faculty Advisor: Dr. Eli Yablanovitch
Graduate Student Mentor: Zunaid Omair
Project Abstract: Thermophotovoltaics convert heat into electricity using photovoltaic cells with a lower bandgap than solar cells to capture infrared radiation. Highly reflective back mirrors can theoretically recycle sub-bandgap energy photons back to the heat source, which decreases the amount of power absorbed by the cell and thus increases the power conversion efficiency. To test the proof of concept, the power absorbed by the photovoltaic cell is measured through calorimetry. Previously, we calculated the power absorption through an indirect method, using the temperature of the source and the reflectivity of the photovoltaic cell. However, power absorption can be more directly calculated using the temperature difference of water in the cooling system before and after heat from the photovoltaic cell is transferred to the water. The project aims to automate data acquisition for the latter method by programming a script. The two calorimetry methods will then be experimentally compared, and we expect them to yield similar results for power absorption.
Undergraduate Researcher: Madison Manley
Major: Electrical Engineering
Home Institution: University of Central Florida
Research Institution: U.C. Berkeley
Research Project: Restricted Boltzmann Machines for Invertible Boolean Logic
Faculty Advisor: Dr. Sayeef Salahuddin
Graduate Student Mentor: Saavan Patel
Project Abstract: Neuromorphic computing comprises of systems that are based on the human brain or artificial neural networks, with the promise of creating a brain inspired ability to learn and adapt. These systems can be used to solve optimization and machine learning problems. We are trying to analyze the accuracy and variation of Boltzmann Machines performing invertible Boolean logic by testing the activation function’s range and how different kinds of noise can affect the system.
Undergraduate Researcher: Jonathan Jeffrey
Major: Electrical Engineering
Home Institution: Georgia Tech
Research Institution: U.C. Berkeley
Research Project: Ab initio calculations of Ca2RuO4
Faculty Advisor: Dr. Sayeef Salahuddin
Graduate Student Mentor: Jason Hsu
Project Abstract: The metal-to-insulator (Mott) transition in calcium ruthenate (Ca2RuO4) has been the focus of recent studies in search of an electric- or magnetic-field-induced transition, with potential applications including efficient resistive memories. In this work, early density functional theory simulations were run within the generalized gradient approximation and local density approximation plus Coulomb interaction to characterize the orbital content of the Ca2RuO4 bands, identifying ruthenium d-orbitals and oxygen p-orbitals as driving behavior at the Fermi level (EF).
Undergraduate Researcher: Kathryn Neilson
Major: Materials Engineering
Home Institution: Iowa State University
Research Institution: U.C. Berkeley
Research Project: Degradation Testing of Implantable Electrodes in vitro
Faculty Advisor: Dr. Vivek Subramanian
Graduate Student Mentor: Jacob Sporrer
Project Abstract: A challenge for the implementation of neural implants to the commercial market is the long and expensive process of in vivo testing of devices and the short lifespan of implanted electrodes. In this work, we describe a representative environment of the brain to simulate in vivo testing of neural implants in order to study the degradation of polyimide and parylene-C coated tungsten wires. We determine, using impedance spectroscopy, a correlation between impedance over accelerated time across all frequencies, but no correlation between impedance and time at 1 kHz.
Undergraduate Researcher: Sahil Dagli
Major: Materials Science
Home Institution: University of Michigan
Research Institution: U.C. Berkeley
Research Project: Reducing adhesion in a nanoelectromechanical (NEM) relay without sacrificing the ON-state conductance
Faculty Advisor: Dr. Junqiao Wu
Graduate Student Mentor: Sara Fathipour
Project Abstract: An alternative to the CMOS transistor must be realized to make electronic devices more energy efficient. Nanoelectromechanical (NEM) relays are a promising alternative to current transistors, as they can provide the ideal characteristics of a switch, including zero OFF-state current, high ON/OFF current ratio, and abrupt switching. NEM relays are hindered in scalability due to their switching hysteresis, caused by contact adhesion. We studied using two-dimensional (2D) materials as an anti-stiction coating to reduce contact adhesion, while maintaining the relay ON-state conductance. 2D materials are an ideal candidate for an anti-stiction coating due to their atomically thin structures, lack of dangling bonds, and high mechanical strength. This study focuses on h-BN, WS 2, and TaS 2. Flakes were mechanically exfoliated from bulk crystals and placed on SiO 2 wafers. Atomic force microscopy (AFM) was used to measure the adhesive force between the AFM tip and the 2D material flakes. TaS 2 was found to have the lowest adhesive force of the three materials. Furthermore, a trend was observed of the adhesive force decreasing with increasing thickness until it saturates at a certain value.
Undergraduate Researcher: Emily Chen
Major: Chemical and Molecular Engineering
Home Institution: Stony Brook University
Research Institution: U.C. Berkeley
Research Project: Poly(ortho-phenylene ethynylene)-based Spin On Carbon Hard Mask
Faculty Advisor: Dr. Felix Fischer
Graduate Student Mentor: Dharati Joshi
Project Abstract: As integrated circuits’ feature size decrease, thin photoresist films can no longer transfer patterns to the desired substrate, necessitating the need for an intermediate hard mask. Poly-(ortho-phenylene ethynylene) (PoPE) are semiconducting π-conjugated polymers that are good polymer candidates for spin on carbon (SOC) hard masks. Linear PoPE films were prepared by spin-coating and were annealed to crosslink polymers to form an insoluble film.
Undergraduate Researcher: Robert Sifuentes
Major: Electrical Engineering
Home Institution: University of Texas at El Paso
Research Institution: U.C. Berkeley
Research Project: Micro-Electro-Mechanical (MEM) Relays for Low Power Electronis Under Extreme Temperatures
Faculty Advisor: Dr. Tsu-Jae King Liu
Graduate Student Mentor: Sergio Almeida
Project Abstract: Micro-Electro-Mechanical system (MEMS) relay switches have been developed as alternatives to modern complementary metal-oxide-semiconductor (CMOS) transistors. This development is required to decrease computer chip power consumption and enable future low-energy, miniaturized computational devices. MEMS relay switches show promise since there is zero leakage current when the devices are in off state [1]. This project aims to further study the temperature effects on MEMS relays. MEMS are tested under a wide range of temperature that goes from 77 K to 400 K and their respective pull-in-voltage and hysteresis voltage are analyzed. It is observed that under low temperatures the pull-in voltage increases, this is attributed to change in the actuation gap due to the difference of thermal coefficient of expansion between the substrate and structural material (Si0.4Ge0.6). Whereas there is not a clear trend on the hysteresis voltage. At high temperatures a small increase in the pull-in is observed. This change is attributed to a change on the Si0.4Ge0.6 stiffness. However, the hysteresis voltage is considerably reduced due to oxidation of the contacts.