Found in many terahertz (THz) and submillimeter-wave systems, GaAs Schottky diodes continue to be one of the most useful THz devices. As a low-parasitic device that operates well into the THz range, Schottky diodes provide useful detection and power generation for a number of practical applications. Mixers and multipliers, working as high as ~3 THz, have already been demonstrated. This paper reviews the current status of diode technology, detailing some of the different ways for fabricating THz chips. An overview regarding the current state of technology and performance for THz frequency multipliers and mixers is presented, along with applications enabled by these diodes.

THz Diode Technology: Status, Prospects, and Applications

Due to the variety of architectures that need be considered while attempting solutions to various problems using neural networks, the implementation of a neural network with programmable topology and programmable weights has been undertaken. A new circuit block, the distributed neuron-synapse, has been used to implement a 1024 synapse reconfigurable network on a VLSI chip. In order to evaluate the performance of the VLSI chip, a complete test setup consisting of hardware for configuring the chip, programming the synaptic weights, presenting analog input vectors to the chip, and recording the outputs of the chip, has been built. Following the performance verification of each circuit block on the chip, various sample problems were solved. In each of the problems the synaptic weights were determined by training the neural network using a gradient-based learning algorithm which is incorporated in the experimental test setup. The results of this work indicate that reconfigurable neural networks built using distributed neuron synapses can be used to solve various problems efficiently. >

A reconfigurable VLSI neural network

This paper presents a concise, although admittedly non-exhaustive, didactic review of some of the main concepts and approaches related to the use of molecularly modified metal nanoparticles in or as chemical sensors. This paper attempts to pull together different views and terminologies used in sensors based on molecularly modified metal nanoparticles, including those established upon electrochemical, optical, surface Plasmon resonance, piezoelectric and electrical transduction approaches. Finally, this paper discusses briefly the main advantages and disadvantages of each of the presented class of sensors.

http://iopscience.iop.org/article/10.1088/0022-3727/40/23/S01/pdf

Chemical sensors based on molecularly modified metallic nanoparticles

A VLSI-compatible approach for vector-matrix multipliers consisting of a two-dimensional array of analog multiplier circuits with the weight matrix values capacitively stored as analog voltages is described. The performances of several MOSFET analog multiplier circuits, including the triode, differential pair, Gilbert, and modified Gilbert multiplier circuits, are evaluated. The weight retention characteristics of the capacitive storage approach are evaluated as a function of temperature with effective weight decay rates of 30 and 0.6 mV/s at room temperature measured for the single- and double-capacitor storage arrangements, respectively. The design approach for a 32*32 programmable vector-matrix multiplier circuit with an analog serial-to-parallel multiplexer for the input vector and an analog parallel-to-serial multiplexer for the output vector is described. An architecture for cascading the 32*32 vector-matrix multiplier circuits to implement multilevel artificial neural networks is described. >

Programmable analog vector-matrix multipliers

This review describes the use of chemically modified pure and alloyed metal nanoparticles for chemiresistive sensing applications. Chemically modified metal nanoparticles consist of a pure or alloyed metallic core with some type of chemical coating. Researchers have studied the electronic properties of 1D, 2D, and 3D assemblies of chemically modified metal nanoparticles, and even single individual nanoparticles. The interaction with the analyte alters the conductivity of the sensitive material, providing a signal to measure the analyte concentration. This review focuses on chemiresistive sensing of a wide variety of gas- and liquid-phase analytes with metal nanoparticles coated with organothiols, ions, polymers, surfactants, and biomolecules. Different strategies used to incorporate chemically modified nanoparticles into chemiresistive sensing devices are reviewed, focusing on the different types of metal and alloy compositions, coatings, methods of assembly, and analytes (vapors, gases, liquids, biological materials), along with other important factors.

Chemiresistive sensing with chemically modified metal and alloy nanoparticles.

Stacking fault (SF) expansion from basal plane dislocations (BPDs) confined in highly doped 4H-SiC buffer layers is observed under high-power ultraviolet illumination (>1000 W/cm2). Once the SFs reach the active drift layers, grown above the buffer layers, they are seen to rapidly expand up to the sample surface where they can cause device degradation. BPD faulting in the buffer appears to have a carrier injection threshold. Carrier density simulations under various injection conditions and carrier lifetimes are used to establish the conditions of BPD faulting within the buffer layer that could prevent SF expansion into the drift layer.

Observation of stacking faults from basal plane dislocations in highly doped 4H-SiC epilayers

Motivated by applications to chemiresistive vapor sensing, the electrical noise properties of large-area gold nanocluster films are investigated experimentally. Measurements show thermal noise to dominate at low voltages and high frequencies, with a 1∕f noise component becoming more important at a higher voltage and a lower frequency. The latter contribution obeys the Hooge formula in its frequency, voltage, and size dependences, and with a Hooge parameter whose relatively large size is attributed to constraints imposed by Coulomb blockade and disorder. Based on these results, a detection limit for nanocluster-based chemiresistors can be projected to approach one part per billion by volume.

Electrical noise in gold nanocluster sensors

Architecture for large microelectronic supervised learning artificial neural networks using a hybrid digital-analog approach

A complementary metal oxide semiconductor (CMOS) device in which a single InxGa1-xSb quantum well serves as both an n-channel and a p-channel in the same device and a method for making the same. The InxGa1-xSb layer is part of a heterostructure that includes a Te-delta doped AlyGa1-ySb layer above the InxGa1-xSb layer on a portion of the structure. The portion of the structure without the Te-delta doped AlyGa1-ySb barrier layer can be fabricated into a p-FET by the use of appropriate source, gate, and drain terminals, and the portion of the structure retaining the Te-delta doped AlyGa1-ySb layer can be fabricated into an n-FET so that the structure forms a CMOS device, wherein the single InxGa1-xSb quantum well serves as the transport channel for both the n-FET portion and the p-FET portion of the heterostructure.

N-and P-Channel Field-Effect Transistors with Single Quantum Well for Complementary Circuits

Antimonide-based p+N junctions have been grown by molecular beam epitaxy and processed into diodes. The diodes have good rectification with ideality factors near 1, and high saturation current densities of 2.5×10−2A∕cm2. S-parameter measurements to 50GHz indicate a 1Ω series resistance and a capacitance of 1.2fF∕μm2 for a 5μm diameter mesa diode. A cutoff frequency of 6.5THz is estimated from the RC product. The high saturation current indicates that this diode will reach forward bias currents at substantially lower voltages than GaAs Schottky diodes. These properties suggest using the diode as a terahertz mixer.

/pdf/antimonide-based-diodes-for-terahertz-mixers-3kpn74cbm6.pdf

Mario Ancona

Papers

Observation of stacking faults from basal plane dislocations in highly doped 4H-SiC epilayers

Electrical noise in gold nanocluster sensors

Architecture for large microelectronic supervised learning artificial neural networks using a hybrid digital-analog approach

N-and P-Channel Field-Effect Transistors with Single Quantum Well for Complementary Circuits

Antimonide-based Diodes for Terahertz Mixers