off-State Degradation in Drain-Extended NMOS Transistors: Interface Damage and Correlation to Dielectric Breakdown

Off-state degradation in drain-extended NMOS transistors is studied. Carefully designed experiments and well-calibrated simulations show that hot carriers, which are generated by impact ionization of surface band-to-band tunneling current, are responsible for interface damage during off-state stress. Classical on-state hot carrier degradation has historically been associated with broken equivSi-H bonds at the interface. In contrast, the off-state degradation in drain-extended devices is shown to be due to broken equivSi-O- bonds. The resultant degradation is universal, which enables a long-term extrapolation of device degradation at operating bias conditions based on short-term stress data. Time evolution of degradation due to broken equivSi-O- bonds and the resultant universal behavior is explained by a bond-dispersion model. Finally, we show that, under off-state stress conditions, the interface damage that is measured by charge-pumping technique is correlated with dielectric breakdown time, as both of them are driven by broken equivSi-O- bonds.     

Real-space electron transfer by thermionic emission in GaAsAlxGa1−xAs heterostructures: Analytical model for large layer widths

Calculations are presented for negative differential resistance (NDR) and switching in layered GaAsAl_xGa_1?xAs heterostructures with a high electric field parallel to the interface. The mechanism is based on thermionic emission of hot electrons from the GaAs layers into the Al_xGa_1?xAs layers. An analytical model is obtained in the limit of relatively large layer widths (400 Å or wider). The method of moments is employed to solve the Boltzmann equation, assuming a position-dependent electron temperature and Quasi-Fermi level in the Al_xGa_1?xAs layers, and a position-independent electron temperature and Quasi-Fermi level in the narrower GaAs layer. Thermal conduction of hot electrons from the GaAs layer into the Al_xGa_1?xAs layers is taken into account. The results of the calculations show that the threshold electric field for the onset of NDR and the peak-to-valley ratio can be controlled to a large extent by adjusting the mobility of the Al_xGa_1?xAs layer, the layer dimensions, and the potential barrier (Al mole fraction in the Al_xGa_1?xAs).     

Ion beam studies of events typical of soft errors in semiconductor memories

A fast ion microbeam has been used to study phenomena associated with soft errors in semiconductor memories. A spatially small beam with a fast blanking system is used to study both alpha particle and heavy ion strikes. The heavy ion strikes are typical of the recoil from cosmic-ray-generated neutrons. Charge collection and static RAM error-rate experiments are discussed.     

The hexosamine and sulfate-containing components in the urine of normal children

Report of an infant with aplasia of the proximal part of the fibula on both sides; by our knowledge the second observation in the literature. Furthermore the infant shows an aplasia of the thyroidea, a coarctation of the aorta, an atrial septal defect and an intraperitoneally situated ascending as well as descending colon.     

Co-integration of GaAs MESFET and Si CMOS circuits

Co-integration of GaAs MESFET and Si CMOS circuits is demonstrated using GaAs-on-Si epitaxial growth on prefabricated Si wafers. This is thought to be the first report of circuit-level integration of the two types of devices in a coplanar structure. A 2-μm gate Si CMOS ring oscillator has shown a minimum delay of 570 ps/gate, whereas on the same wafer a 1-μm gate GaAs MESFET buffered-FET-logic (BFL) ring oscillator has a minimum delay of only 70 ps/gate. A composite ring oscillator consisting of Si CMOS invertors and GaAs MESFET invertors connected in a ring has been successfully fabricated     

Device and technology evolution for Si-based RF integrated circuits

The relationships between device feature size and device performance figures of merit (FoMs) are more complex for radio frequency (RF) applications than for digital applications. Using the devices in the key circuit blocks for typical RF transceivers, we review and give trends for the FoMs that characterize active and passive RF devices. These FoMs include transit frequency at unity current gain f/sub T/, maximum frequency of oscillation f/sub MAX/ at unit power gain, noise, breakdown voltage, capacitor density, varactor and inductor quality, and the like. We use the specifications for wireless communications systems to show how different Si-based devices may achieve acceptable FoMs. We focus on Si complementary metal-oxide-semiconductor (CMOS), Si Bipolar CMOS, and Si bipolar devices, including SiGe heterojunction bipolar transistors, RF devices, and integrated circuits (ICs). We analyze trends in the FoMs for Si-based RF devices and ICs and show how these trends relate to the technology nodes of the 2003 International Technology Roadmap for Semiconductors. We also compare FoMs for the best reported performance of research devices and for the performance of devices manufactured in high volumes, typically more than 10 000 devices. Certain commercial equipment, instruments, or materials are identified in this article to specify adequately the experimental or theoretical procedures. Such identification does not imply recommendation by any of the host institutions of the authors, nor does it imply that the equipment or materials are necessarily the best available for the intended purpose.     

Comparison of self-aligned and non-self-aligned GaAs E/D MESFETs

The device characteristics and circuit performance of self-aligned GaAs E/D-MESFETs have been compared. The fabrication process for both devices is discussed. Electrical measurements across a 2-in wafer showed that an average self-aligned 40-μm-wide, 1-μm-long enhancement device has transconductance of 275±17 mS/mm, an intrinsic K -value of 16.3±2.7 mS/V, a series resistance of 0.88±0.1 Ω-mm, and a threshold deviation of 28 mV. Corresponding data for the non-self-aligned devices were 191±19 mS/mm, 10.3±1.4 mS/V, 1.2±0.2 Ω-mm, and 45 mV, respectively. An ECL-compatible 1-kb static RAM and a 4-kb static RAM were fabricated using both self-aligned and non-self-aligned processes for comparison. Using the self-aligned process, the power consumption of the 1-kb SRAM was 230 mW, compared to 530 mW for the non-self-aligned SRAM, while access times remained the same. Typical access times for self-aligned 4-b SRAM devices ranged from a minimum of 2.8 ns to a maximum of 3.8 ns. This 1-ns range is considerably less than that of a typical non-self-aligned device with 2.5 ns of access time scatter     

The effects of anti-asthma drugs on mediator release from cultured human mast cells

BACKGROUND: A method for generating human mast cells in vitro was recently established. Little is known about the pharmacological profiles of allergic mediator release from cultured mast cells. OBJECTIVE: The main objective was to investigate the nature of cultured mast cells from a pharmacological point of view. We examined the effect of anti-asthma drugs on the release of histamine, sulfidoleukotrienes (LTs) and prostaglandin D2 (PGD2) from the cultured mast cells. METHODS: Using the method established by Saito et al. we cultured cord blood mononuclear cells in the presence of 80 ng/mL stem cell factor (SCF), 50 ng/mL interleukin-6 (IL-6) and 300 nmol/L prostaglandin E2 (PGE2), and obtained almost pure (> 99%) mast cells. We sensitized cultured mast cells with immunoglobulin E (IgE)-rich serum, and then treated them with some anti-asthma drugs before challenge with anti-human IgE. Released histamine, LTs and PGD2 were measured by high-performance liquid chromatography, commercial enzyme-linked immunosorbent assay (ELISA) and enzyme immunoassay (EIA) systems, respectively. RESULTS: The cultured mast cells released histamine, LTs and PGD2 following immunological stimulation through IgE. The mast cell stabilizing agents disodium cromoglycate (DSCG, 1 mmol/L) and azelastine (100 micromol/L) significantly inhibited the release of these three mediators. The beta-adrenoceptor agonists isoproterenol, salbutamol, and clenbuterol also inhibited all three mediators' release in a concentration-dependent manner. The non-selective and selective phosphodiesterase (PDE) inhibitors theophylline, rolipram, and cilostazol had no significant effect on mediator release at clinically useful concentrations. BAY x 1005 (a 5-lipoxygenase-activating protein inhibitor) inhibited the LTs release, whereas indomethacin (a cyclo-oxygenase I and II inhibitor) and NS-398 (a cyclo-oxygenase II inhibitor) inhibited PGD2 release. CONCLUSIONS: The present results indicate that cultured mast cells release histamine, LTs and PGD2 following IgE crosslinking. Anti-asthma drugs showed a characteristic suppression of the release of each mediator. The suppressive actions of these drugs are similar to their pharmacological actions on human lung mast cells. These results suggest that cultured mast cells are useful for the analysis of function and pharmacological profiles of lung mast cells.     

Hot-electron degradation of n-channel polysilicon MOSFETs

The stability of the hydrogen passivation in hydrogenated n-channel polysilicon MOSFETs has been studied under thermal stress and hot-electron stress at elevated temperatures. Although the hydrogen passivation is stable at 150°C, channel hot-electron stress at high temperatures appears to create additional grain boundary traps, presumably by breaking the Si-H bonds at the grain boundaries. This mechanism is in addition to the creation of acceptor-type fast interface states that occur in bulk MOSFETs