Volume 88, Issue 10, 15 November 2000
Index of content:
- DEVICE PHYSICS (PACS 85)
88(2000); http://dx.doi.org/10.1063/1.1288783View Description Hide Description
The effects of the grain growth and residual stress of Cuthin films on reflow were investigated. Agglomeration and grain growth of Cufilms occurred during annealing in an oxygen ambient, while they were not observed in inert ambients. In the case of chemical vapor deposited Cufilms, trench patterns of 0.5 μm with an aspect ratio of 2 were completely filled at annealing temperatures higher than 400 °C in oxygen ambient, due to the preferential agglomeration inside the patterns. Upon annealing at 400 °C in an oxygen ambient, the agglomeration terminated within 10 min, while the thickness of Cu oxide increased to 18.3 nm, and normal grain growth, resulting in increased capillary instability of Cufilms, was observed. Because of a larger volume of Cu oxide than Cu, the formation of Cu oxide led to compressive stress in the films. By calculation, it was shown that compressive stress could decrease through grain growth. It is considered that the agglomeration and reflow in an oxygen ambient resulted from the relaxation of compressive stresses via grain growth.
88(2000); http://dx.doi.org/10.1063/1.1319972View Description Hide Description
Gate leakage currents in AlGaN/GaN heterostructurefield-effect transistor(HFET) structures with conventional and polarization-enhanced barriers have been studied. Comparisons of extensive gate leakage currentmeasurements with two-dimensional simulations show that vertical tunneling is the dominant mechanism for gate leakage current in the standard-barrier HFET and that the enhanced-barrier structure suppresses this mechanism in order to achieve a reduced leakage current. An analytical model of vertical tunneling in a reverse-biased HFET gate-drain diode is developed to evaluate the plausibility of this conclusion. The model can be fit to the measured data, but suggests that additional leakage mechanisms such as lateral tunneling from the edge of the gate to the drain or defect-assisted tunneling also contribute to the total leakage current. The vertical tunnelingcurrent mechanism is shown to be more significant to the gate leakage current in III–V nitride HFETs than in HFETsfabricated in other III–V material systems, in which the lateral tunnelingcurrent component generally dominates the gate leakage current.
88(2000); http://dx.doi.org/10.1063/1.1319326View Description Hide Description
The bipolar junction transistor is modeled using the thermodynamic theories. The main reason for using the thermodynamic theories is to ensure that the law of conservation of energy is maintained. Violating such a fundamental law is expected to result in errors in simulating the device performance. Although using some empirical parameters can reduce the severity of such deviations, such a process requires some guessing that cannot be guaranteed to be accurate in all cases. Using the thermodynamic theories, the transistor relationships were derived and the device characteristics were simulated. The results show that the proposed model can predict the device performance without using empirical fitting parameters.
Superconducting multiturn flux transformers for radio frequency superconducting quantum interference devices88(2000); http://dx.doi.org/10.1063/1.1322382View Description Hide Description
This article describes three planar layouts of superconducting multiturn flux transformers integrated with a coplanar resonator for radio frequency (rf) superconducting quantum interference device(SQUID)magnetometers. The best magnetic field noise values of 22 and in the white noise regime were obtained for the layout with two input coils and the layout with the labyrinth resonator, respectively. Excess low-frequency noise (about at 10 Hz) was present. Computer simulation showed that the loss in this trilayer system was dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The rf coupling coefficient between the resonator and the flip-chip-coupled SQUID was also estimated. The values obtained for the layout with two input coils, and for the layout with the labyrinth resonator were considerably higher than the typical value of for the single-layer coplanar resonator. These high coupling coefficients have compensated the somewhat degraded unloaded quality factor of the resonator, thus securing the optimum operation of the rf SQUID.