This paper presents a new analog circuit optimization system for automated sizing of analog integrated circuits. It consists of a genetic algorithm (GA)-based global optimization engine and an artificial neural network (ANN)-based local optimization engine. The key new idea is to use parallel computation to train ANN models for design space neighborhoods thus the local minimum search (LMS) can have a much faster search speed. For the GA-based global optimization, circuit performances are calculated by parallel SPICE simulations. For the LMS, circuit performance data are derived from ANN model predictions instead of SPICE simulations. Since most time for an ANN-based LMS is spent on SPICE calls which can be run in parallel, the LMS process can also exploit the multiple core configuration of a modern computational server in addition to the GA global search. The fully parallelized optimization system is deployed to design a two-stage rail-to-rail operational amplifier and a 5th-order active-RC Chebyshev complex band-pass filter. Experimental results show that the proposed method provides about four times speed enhancement and comparable results compared with traditional approaches employing the same parallel global optimization but sequential SPICE calls during LMS.

Oxide semiconductorsare highly attractive for the new-generation transparent/flexible electronics. In this letter, logic gates (inverter, NAND, and transmission gates) and three-stage ring oscillators based on n-type indiumgallium-zinc-oxide (IGZO) thin-film transistors (TFTs) and p-type tin monoxide (SnO) TFTs are presented. The IGZO TFTs show a mobility of 10.05 cm2/(V · s) and a threshold voltage of 5.00 V. The SnO TFTs exhibit a mobility of 1.19 cm ² /(V·s) and a matched threshold voltage of -5.05 V. At a supply voltage of 10 V, the complementary inverters show an extremely high gain of 112 with a geometric aspect ratio of 5. The dynamic responses of the logic gates based on n-type IGZO and p-type SnO TFTs are also examined. The delay time of the inverter measured from dynamic response is 27.75 μs at a supply voltage of 10 V. The inverter, NAND, and transmission gates all exhibit ideal rail-to-rail output voltage behavior. At a supply voltage of 20 V, the three-stage ring oscillators are able to operate at 32.87 kHz, and the stage delay is 5.07 μs.

The AlGaN/GaN heterostructure FETs with different gate lengths were fabricated. Under different gate biases or for the devices with different gate lengths, the measured parasitic source access resistance values were different. By the analysis of different scattering mechanisms and polarization charge distribution, it is found that the gate bias and gate length can change the polarization Coulomb field scattering, and then affect the parasitic source access resistance. At last, the systematic scattering theories were adopted and the influence of different gate biases and gate lengths on parasitic source access resistance was further confirmed in theory.

Both circular and rectangular Ni Schottky contacts on AlGaN/AlN/GaN heterostructures have been fabricated. Both of the Schottky barrier heights were measured by internal photoemission. The flat-band voltage (V0) for the AlGaN/AlN/GaN heterostructure Schottky contacts was analyzed and obtained from the forward current-voltage (I-V) characteristics. Based on the forward I-V characteristics and with the obtained flat-band voltage, the Schottky barrier heights for the circular and rectangular diodes have been analyzed and calculated by self-consistently solving Schrodinger’s and Poisson’s equations. The evaluated Schottky barrier heights for the prepared circular and rectangular Ni Schottky diodes agree well with the photocurrent measured results.

SnO is the only oxide semiconductor to date that has exhibited ambipolar behavior in thin-film transistors (TFTs). In this work, ambipolar behavior was observed in SnO_x TFTs fabricated at a high sputtering power of 200 W and post-annealed at 150–250 °C in ambient air. X-ray-diffraction patterns showed polycrystallisation of SnO and Sn in the annealed SnO_x films. Scanning-electron-microscopy images revealed that microgrooves appeared after the films were annealed. Clusters subsequently segregated along the microgrooves, and our experiments suggest that they were most likely Sn clusters. Atomic force microscopy images indicate an abrupt increase in film roughness due to the cluster segregations. An important implication of this work is that excess Sn in the film, which has generally been thought to be detrimental to the film quality, may promote the ambipolar conduction when it is segregated from the film to enhance the stoichiometric balance.