Revathy Padmanabhan

Bio: Revathy Padmanabhan is an academic researcher from Technion – Israel Institute of Technology. The author has contributed to research in topics: Capacitance & Capacitor. The author has an hindex of 6, co-authored 22 publications receiving 97 citations. Previous affiliations of Revathy Padmanabhan include Indian Institutes of Technology & Indian Institute of Science.

High-Performance Metal–Insulator–Metal Capacitors Using Europium Oxide as Dielectric

Abstract: We report the first demonstration of metal-insulator-metal (MIM) capacitors with Eu2O3 dielectric for analog and DRAM applications. The influence of different anneal conditions on the electrical characteristics of the fabricated MIM capacitors is studied. FG anneal results in high capacitance density (7 fF/μm2), whereas oxygen anneal results in low quadratic voltage coefficient of capacitance (VCC) (194 ppm/V2 at 100 kHz), and argon anneal results in low leakage current density (3.2 ×10-8 A/cm2 at -1 V). We correlate these electrical results with the surface chemical states of the films through X-ray photoelectron spectroscopy measurements. In particular, FG anneal and argon anneal result in sub-oxides, which modulate the electrical properties.

Simplified parameter extraction method for single and back-to-back Schottky diodes fabricated on silicon-on-insulator substrates

Abstract: We describe a technique to extract room temperature parameters of Schottky diodes based on single or double-terminal configurations whose barrier height is bias dependent. This method allows us to extract the zero bias barrier height without specific knowledge of interface states or the existence of insulator layers at the metal-semiconductor boundaries. This technique enables us to establish the type of thermionic emission mechanism, limited by a bias dependent image force potential and/or diffusion, taking into account interfacial states or layers. This technique makes use of experimental current-voltage (I-V) characteristics measured at both bias polarities and different intensities of illumination and the corresponding voltage-dependent differential slope-voltage characteristics α=dln(I)/dln(V). This method is verified experimentally on a conventional p-Silicon based Schottky diode and on metal-semiconductor and metal-insulator-semiconductor diodes fabricated on n-silicon-on-insulator substrates. Pd/A...

Dynamical Properties of Optically Sensitive Metal-Insulator-Semiconductor Nonvolatile Memories Based on Pt Nanoparticles

Abstract: We describe the optical properties of nonvolatile memory cells based on metal–insulator–semiconductor structures with embedded Pt nanoparticles, fabricated by atomic layer deposition. We show the effect of illumination on the static as well as dynamic properties of two devices, which differ by their respective thicknesses of the tunneling layer. The device with the thicker tunneling layer exhibits a faster response under illumination and significantly better retention properties, while the device with the thinner tunneling layer is faster under dark conditions.

Optically sensitive devices based on Pt nano particles fabricated by atomic layer deposition and embedded in a dielectric stack

Abstract: We report a series of metal insulator semiconductor devices with embedded Pt nano particles (NPs) fabricated using a low temperature atomic layer deposition process. Optically sensitive nonvolatile memory cells as well as optical sensors: (i) varactors, whose capacitance-voltage characteristics, nonlinearity, and peak capacitance are strongly dependent on illumination intensity; (ii) highly linear photo detectors whose responsivity is enhanced due to the Pt NPs. Both single devices and back to back pairs of diodes were used. The different configurations enable a variety of functionalities with many potential applications in biomedical sensing, environmental surveying, simple imagers for consumer electronics and military uses. The simplicity and planar configuration of the proposed devices makes them suitable for standard CMOS fabrication technology.

Performance and Reliability of TiO 2 /ZrO 2 /TiO 2 (TZT) and AlO-Doped TZT MIM Capacitors

Abstract: Metal–insulator–metal capacitors for dynamic random access memory applications have been realized using TiO2/ZrO2/TiO2 (TZT) and AlO-doped TZT [TiO2/ZrO2/AlO/ZrO2/TiO2 (TZAZT) and TiO2/ZrO2/AlO/ZrO2/AlO/ZrO2/TiO2 (TZAZAZT)] dielectric stacks. High-capacitance densities of 46.6 fF/ $\mu \text{m}^{2}$ (for TZT stacks), 46.2 fF/ $\mu \text{m}^{2}$ (for TZAZT stacks), and 46.8 fF/ $\mu \text{m}^{2}$ (for TZAZAZT stacks) have been achieved. Low leakage current densities of about $4.9\times 10^{-8}$ , $5.5\times 10^{-9}$ , and $9.7\times 10^{-9}$ A/cm2 (at −1 V) have been obtained for TZT, TZAZT, and TZAZAZT stacks, respectively. We analyze the leakage current mechanisms at different electric field regimes, and compute the trap levels. The effects of constant voltage stress on the device characteristics were studied, and excellent device reliability was demonstrated. The electrical characteristics of the devices were correlated with the structural analysis through X-ray diffraction measurements and the surface chemical states analysis through X-ray photoelectron spectroscopy measurements. The doped-dielectric stacks (AlO-doped TZT: TZAZT and TZAZAZT) help to reduce leakage current density and improve reliability, without substantial reduction in capacitance density, compared with their undoped counterparts (TZT).

Photon Enhanced Thermionic Emission for Solar Concentrator Systems

Abstract: Solar-energy conversion usually takes one of two forms: the 'quantum' approach, which uses the large per-photon energy of solar radiation to excite electrons, as in photovoltaic cells, or the 'thermal' approach, which uses concentrated sunlight as a thermal-energy source to indirectly produce electricity using a heat engine. Here we present a new concept for solar electricity generation, photon-enhanced thermionic emission, which combines quantum and thermal mechanisms into a single physical process. The device is based on thermionic emission of photoexcited electrons from a semiconductor cathode at high temperature. Temperature-dependent photoemission-yield measurements from GaN show strong evidence for photon-enhanced thermionic emission, and calculated efficiencies for idealized devices can exceed the theoretical limits of single-junction photovoltaic cells. The proposed solar converter would operate at temperatures exceeding 200 degrees C, enabling its waste heat to be used to power a secondary thermal engine, boosting theoretical combined conversion efficiencies above 50%.

Future of dynamic random-access memory as main memory

Abstract: Dynamic random-access memory (DRAM) is the main memory in most current computers. The excellent scalability of DRAM has significantly contributed to the development of modern computers. However, DRAM technology now faces critical challenges associated with further scaling toward the ∼10-nm technology node. This scaling will likely end soon because of the inherent limitations of charge-based memory. Much effort has been dedicated to delaying this. Novel cell architectures have been designed to reduce the cell area, and new materials and process technologies have been extensively investigated, especially for dielectrics and electrodes related to charge storage. In this article, the current issues, recent progress in and the future of DRAM materials, and fabrication technologies are discussed.

Engineering Hexagonal Array of Nanoholes for High Sensitivity Biosensor and Application for Human Blood Group Detection

Abstract: In this study, the design of refractive index sensor with high sensitivity would be provided. This consists of a metal substrate with two metal-insulator-metal waveguide and an array of hexagonal nanoholes. Using the refractive index model obtained for different blood groups A, B, and O, we show that the structure can be used as a sensor to determine a human blood group. We used the array of nanoholes due to the unique optical properties, which leads to nanoscale confinement, high sensitivity to surface, and low propagation losses. Based on the results, resonance wavelength has a linear relationship with the refractive index of a material that is placed inside the nanohole; this feature makes it easy to identify the material. Considering a tradeoff between the transmitted power, structure size, and sensitivity, finite-difference time-domain simulations show that the sensitivity can be as large as 3172 nm per refractive index unit. In general, our plasmonic sensor can promote the sensitivity through the phenomenon of plasmon exciting on the surface of the nanoholes and would have useful applications in the medical field such as determining blood group, hemoglobin, and deoxyribonucleic acid (DNA) quantification.

Ultrathin ferroic HfO2–ZrO2 superlattice gate stack for advanced transistors

Abstract: With the scaling of lateral dimensions in advanced transistors, an increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the operating voltage1. This led to a fundamental change in the gate stack in 2008, the incorporation of high-dielectric-constant HfO2 (ref. 2), which remains the material of choice to date. Here we report HfO2-ZrO2 superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors, and scaled down to approximately 20 ångströms, the same gate oxide thickness required for high-performance transistors. The overall equivalent oxide thickness in metal-oxide-semiconductor capacitors is equivalent to an effective SiO2 thickness of approximately 6.5 ångströms. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO2-based high-dielectric-constant gate stacks without scavenging the interfacial SiO2, which has adverse effects on the electron transport and gate leakage current3. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. This work demonstrates that ultrathin ferroic HfO2-ZrO2 multilayers, stabilized with competing ferroelectric-antiferroelectric order in the two-nanometre-thickness regime, provide a path towards advanced gate oxide stacks in electronic devices beyond conventional HfO2-based high-dielectric-constant materials.