The modeling of conventional (deterministic) electronic circuits – ones consisting of transistors, resistors, capacitors, inductors, and other traditional electronic components – is a well established subject. The cycle-to-cycle variability of emerging electronic devices, in particular, certain ReRAM cells, has lead to the concept of stochastic circuits. Unfortunately, even in relatively simple cases, the direct transient analysis of stochastic circuits is computationally demanding and potentially impractical, if possible at all. An important development in this area has been the application of a master equation that is easily implemented in SPICE. In this conference paper, we briefly review the master equation approach and present an improved implementation of this approach in SPICE. Moreover, we find an attractor state in a periodically driven memristive circuit – a stochastic counterpart of deterministic memristor attractors.
We present a dual experimental and computational studies on ruthenium (Ru) induced point defects in wide bandgap semiconductor 4H-silicon carbide (4H-SiC) which is of high interest in alpha, x-ray, and low energy gamma spectroscopy due to Ru’s high weighted metal work function of 4.76 eV which forms a high barrier Schottky contact with low leakage current. We first measured the activation energies and concentrations of deep levels in RF sputtered Ru/n-4H-SiC Schottky diodes annealed at 950°C using deep level transient spectroscopy (DLTS) and identified two deep level defects at Ec – (0.89 ± 0.03) eV and Ec - (1.98 ± 0.03) eV which appear unique to Schottky diodes with Ru. In order to correlate these defects theoretically, we then calculated the formation energies and transition levels of Ru induced point defects in 4H-SiC at charge states [-2, 2] for substitutions and [-2,+4] for interstitials using the projector augmented wave method (PAW) with both PBE and hybrid pseudopotentials on a 3 x 3 x 1 supercell. We found two transition levels which correlate very well with our experimental DLTS results. The transition (-1/0) for Ru substituted into the cubic silicon site at Ev + 2.39 eV and the transition (-1/0) for Ru placed in interstitial site with tetrahedral symmetry to carbon at Ev + 1.23 eV respectively.
We report a similar feature in the response of resistor–memristor and capacitor–memcapacitor circuits with threshold-type memory devices driven by triangular waveform voltage. In both cases, the voltage across the memory device is stabilized during the switching of the memory device state. While in the memristive circuit this feature is observed when the applied voltage changes in one direction, the memcapacitive circuit with a ferroelectric memcapacitor demonstrates the voltage stabilization effect at both sweep directions. The discovered behavior of capacitor–memcapacitor circuit is also demonstrated experimentally. We anticipate that our observation can be used in the design of electronic circuits with emergent memory devices as well as in the identification and characterization of memory effects in threshold-type memory devices.
Some instances of electron field emitters are characterized by frequency-dependent hysteresis in their current–voltage characteristics. We argue that such emitters can be classified as memristive systems and introduce a general framework to describe their response. As a specific example of our approach, we consider field emission from a carbon nanotube array. Our experimental results demonstrate a low-field hysteresis, which is likely caused by an electrostatic alignment of some of the nanotubes in the applied field. We formulate a memristive model of such phenomena, whose results are in agreement with the experimental results.
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