A synapse is a junction between two biological neurons, and the strength, or weight of the synapse, determines the communication strength between the neurons. Building a neuromorphic (i.e. neuron isomorphic) computing architecture, inspired by a biological network or brain, requires many engineered synapses. Furthermore, recent investigation in neuromorphic photonics, i.e. neuromorphic architectures on photonics platforms, have garnered much interest to enable high-bandwidth, low-latency, low-energy applications of neural networks in machine learning and neuromorphic computing. We propose a graphene-based synapse model as a core element to enable large-scale photonic neural networks based on on-chip multiwavelength techniques. This device consists of an electro-absorption modulator embedded in a microring resonator. We also introduce an encoding protocol that allows for the representation of synaptic weights on our photonic device with 15.7 bits of resolution using current control hardware. Recent work has suggested that graphene-based modulators could operate in excess of 100 GHz. Combined with our work, such a graphene-based synapse could enable applications for ultrafast and online learning.

The grain structure of electrodeposited Cobalt is important to device electrical and reliability performance. This paper describes thermal annealing studies performed on electroplated blanket and pattern Cobalt wafers. A systematic study of Co film properties and effect of various anneal parameters such as temperature, time, hydrogen pressure and thermal cycling was completed. Co film resistivity, purity, grain structure, phase composition and orientation as well as in-feature grain size have been characterized by various analytical methods such as XRD, STEM, SIMS and EBSD. It was observed that electroplated cobalt films with resistivity approaching bulk Cobalt value can be obtained by annealing in the temperature range of 300°C - 350°C which is favorable for hcp Co phase formation.

Copper is a commonly used interconnect metal in microelectronic interconnects due to its exceptional electrical and thermal properties. Particularly in applications of the 2.5 and 3D integration, Cu is utilized in through-silicon-vias (TSVs) and flip chip interconnects between microelectronic chips for providing miniaturization, lower power and higher performance than current 2D packaging approaches. SnAg capped Cu pillars are a common high-density interconnect technology for flip chip bonding. For these interconnects, specific properties of the Cu surface, such as roughness and cleanliness, are an important factor in the process to ensure quality solder bumps. During electroplating, tight processing parameters must be met so that defects are avoided, and high bump uniformity is achieved. An understanding of the interactions at the solder and Cu pillar interface is needed, based on the electroplating parameters, to determine the best method for populating solder on the wafer surface. In this study, surface treatment techniques such as oxygen plasma cleaning were performed on the Cu surfaces and the SnAg plating chemistry for depositing the solder were evaluated through hull cell testing to qualitatively determine the range of current densities to investigate. It was observed that current density while plating played a large role in solder bump deposition morphology. At the higher current densities greater than 60 mA/cm2, bump height non-uniformity and dendritic growth are observed and at lower current densities, less than or equal to 60 mA/cm2, uniform, continuous bump height occurred.

For high switching speed HV Schottky diodes, with very high work function metal and extremely lightly doped epi, the built-in potential may be too high for thermionic emission to occur, when the applied external voltage is quite low (near VF = 0.07V). If the epi is lightly doped p type, the built-in potential (VBuilt-in: potential difference between the metal and silicon Fermi levels) is 1.0V (measured with CV). If the external bias is 0.1V, near the measured VF, it is not enough to overcome the built-in potential for thermionic emission as illustrated. It is likely that in addition to thermionic emission, tunnelling and diffusion currents also contribute to the total HV Schottky diode forward current. TCAD simulation of HV Schottky diodes with N+ guard bands suggests the potential barrier and electric fields at the Schottky junction are relatively high for thermionic emission to occur, when external bias V ≈ VF. In this paper we report HV Schottky diodes fabricated with various metals, metal alloys and epitaxial films. Metal work functions and epi doping profiles are extracted with high frequency Capacitance-Voltage (CV) technique. 150V of breakdown voltage and very low forward voltage (VF = 0.07V) are demonstrated. The measured data indicate very high work function metal or metal alloy is needed to achieve high switching speed and low forward voltage.

In this work, we have investigated the structural and mechanical properties of a new class of soft and superelastic materials, called schwarzynes. These materials are obtained by inserting sp carbon atoms (acetylenic groups) into the schwarzite framework. Using fully atomistic molecular dynamics simulations with the AIREBO force field, our results show that schwarzynes are stable materials up to high temperatures (1000K). Schwarzynes exhibit a very wide elastic regime, some of them up to 70% strain without structural fractures. Our preliminary results show that the elastic properties can be easily engineered by tuning the number of acetylenic groups and the crystallographic directions where they are inserted.

L-Arginine and L-Alanine aminoacids doped ADP crystals were grown from aqueous solution by slow evaporation technique at constant temperature. The crystalline nature of the grown crystals was confirmed using powder X-ray diffraction technique. The vibrational frequencies of the grown crystals were identified using FTIR spectral analysis. Optical absorption study was carried out and a good transparency in the entire visible region was observed with the lower cutoff wavelength of 308 nm and 318 nm for the L-Alanine & L-Arginine doped crystals respectively. The transmission data has been used to evaluate the optical band gap of L-Alanine and L-Arginine doped ADP crystals and is found tobe 5.023 eV. Second harmonic generation (SHG) studies were performed by the classical Kurtz powder technique using a Nd: YAG laser operating at 1064 nm. The SHG efficiency of doped ADP is found to be higher compared to Pure ADP crystals.

Traditionally, CMOS transistors are for low power, high speed, and high packing density applications. CMOS is also commonly used as power regulating devices, and light sensors (CCD or CMOS image sensors). In this paper, we would like to introduce Photonic CMOS as a light emitting device for optical computing, ASIC, power transistors, and ultra large scale integration (ULSI). A Photonic CMOS Field Effect Transistor is fabricated with a low-resistance laser or LED in the drain region, and multiple photon sensors in the channel / well regions. The MOSFET, laser, and photon sensors are fabricated as one integral transistor. With embedded nonlinear optical films, the Photonic CMOSFETs have the capability of detecting and generating focused laser beams of various frequencies to perform optical computing, signal modulation, polarization, and multiplexing for digital / analog processing and communication.

Organic/Polymeric Semiconductor (OSC) based devices have been under extensive study for the past three decades due to their intrinsic potential advantages such as lightweight, mechanical flexibility, biocompatibility, low toxicity, abundant material availability, low cost of processing, etc. A phototransistor incorporates the properties and functions of a transistor and photodetector. In this study, a phototransistor based on a donor/acceptor (D/A) pair (photo-doping) was studied and demonstrated. Unlike in organic photovoltaics (OPV) where 1:1 proportion by mass of the donor:acceptor is utilized to make up the active layer, that ratio appears to be too high for phototransistor applications. According to literature, this 1:1 concentration leads to low overall device performance, lack of I-V curve saturation (kink effect), and bipolar behavior. By altering fabrication techniques and doping concentrations, we were able to demonstrate a donor/acceptor based phototransistor with p-type characteristics with improved performance. In this work, we fabricated a high-performance OFET based on a very small amount of Phenyl-C71-butyric acid methyl ester (PCBM) doped into a Poly(3-hexylthiophene) (P3HT) host. With this work, a greater understanding behind the optimization of D/A based phototransistors is advanced.

We report a simple and feasible technique for the formation of well-distributed nickel nanodot arrays on both oxidized and unoxidized silicon substrate by a conventional annealing process. The shape and distribution of nickel nanodots were maintained by adjusting annealing temperature, time and the SiO2 buffer layer thickness in between nickel film and the silicon substrate. The diffusion of nickel into the silicon is significantly reduced when the nickel film on the oxidized silicon substrate is annealed at high temperature. From this conventional annealing technique, we achieve a maximum nickel nanodots density up to (7.94±1.92) nanodot counts/µm2 on the oxidized silicon substrate with a well-defined spherical shape by adjusting the thickness of nickel film as well as buffer SiO2 layer. In the next experiment, the surface charge distribution on the nickel nanodot arrays were characterized through the Kelvin probe force microscope (KPFM) on tapping mode. It is found that the nickel nanodots can store and release the electric charges under an applied bias voltage.

Photodetectors operating in the ultraviolet (UV) play a pivotal role in applications such as ozone monitoring and biosensing. One key factor to successfully implementing such photodetectors is that they must be solar-blind to avoid detecting ambient visible and infrared light. Unfortunately, UV photodetectors based on silicon and other typical semiconductors are not natively solar-blind, since their band gap energies are in the visible range. Hexagonal boron nitride (h-BN) is an example of a wide band gap semiconductor which shows promise for use as the absorbing medium in a UV photodetector device, since its band gap is wide enough to make it inherently insensitive to light in the visible range and above. Here we report on the fabrication and characterization of a graphene-h-BN-heterostructure photodetector which utilizes a vertical geometry, in principle allowing for highly scalable production. We find that our device shows a finite photoresponse to illumination by a 254 nm light source, but not to a 365 nm source, thus suggesting that our device is solar-blind.