Circuit simulation

Deeds is a simulation environment for e-learning in digital electronics. The simulators cover combinational and sequential logic networks, finite state-machine design, and microcomputer interfacing and programming. They are integrated together, and therefore allow the design and test of embedded digital systems. The environment guides students' activities by delivering learning materials through specialized browsers. An extensive collection of learning materials is available. This paper includes an example of activity on a problem assignment.

Integrated circuits for analog and telecom applications require metal insulator metal (MIM) capacitors with not only a high capacitance value (typically 5 nF/mm 2 ), but also a low series resistance R s . The optimization of this latter parameter is investigated in this paper, by means of a simple analytical model, taking into account both the impact of material parameters and device architectures, suggesting possible strategies for R s minimization. Such a model is also suitable for MIM circuit simulation, and can be also extended to other devices, such as to the gate series resistance modeling of RF MOSFET. Results are in good agreement with numerical simulations and HF measurements, performed on state of the art planar MIM devices. Moreover, discussion on via placement to access the top electrode has been held, in order to optimize the series resistance of the capacitor.

This paper presents the following recent investigations of transparent amorphous-oxide semiconductors (TAOS) from materials to devices and circuits. 1) Composition of metals in TAOS are widely explored with the aim of seeking semiconductors suitable for the channel layers of thin-film transistors (TFTs) composing backplanes for flat-panel displays. It is found in combinatorial approaches to the materials exploration that indium-based ternary TAOS (In--O) and their TFTs show the properties and the performance as good as those of the most popular material of amorphous In-Ga-Zn-O ( -IGZO) when = Zn or Ge. 2) Defects and impurities in TAOS are investigated by theoretical approaches. The first-principle calculation of the electron states reveals that charge-neutral oxygen vacancy or interstitial forms the density of states around mid-gap level and does not generate carriers directly, while hydrogen impurity raises the Fermi level beyond the conduction-band minimum and acts as a donor in TAOS. 3) Device structures of TAOS-TFTs are also investigated extensively for better performance and stability. It is found in channel-etch type TFTs with bottom-gate inverse-stagger structures that the TFT characteristics and stability are significantly improved by chemically removing the back-channel layer in a wet-etching process. Coplanar homojunction (CH) structure is proposed as a novel device structure where conductive -IGZO regions work as the source and drain electrodes to the channel region of semiconductor -IGZO. The CH TFTs show excellent characteristics and stability, with low series resistance without any difficulty in making good electrical contact between metals and TAOS. 4) Circuits using TAOS-TFTs are demonstrated. A ring oscillator composed of fifteen-stage inverters with a buffer circuit operates as designed by circuit simulation with a TFT model for hydrogenated amorphous Si TFTs. Pixel circuits composed of three TFTs and one transparent capacitor successfully drive organic light-emission diode cells without a planarization layer on a 2-in diagonal panel having 176 144 3 pixels. Index Terms-Oxide semiconductor, thin film transistor (TFT), first-principle calculation.

The simulation of large digital and mixed-signal integrated circuits is one of the challenges of the electronics design automation industry. In this work, a fast linear solver, KLU, is implemented into NGSPICE circuit simulator and its performances have been verified on standard netlists.

Industry-standard TCAD software packages are widely used by semiconductor companies to optimise processes and devices in integrated circuits fabrication. After process and device simulation one can go ahead with circuit simulation using Spice. This paper focuses on the matching of these program packages in the area of parameter and characteristics extraction. We compared the transfer characteristics of n-type MOSFET, biased in the linear region, obtained from Synopsys package including TSUPREM4 and MEDICI with transfer characteristics from PSpice package.