N-channel Structure Research Articles

Significant Performance Improvement in n-Channel Organic Field-Effect Transistors with C60 :C70 Co-Crystals Induced by Poly(2-ethyl-2-oxazoline) Nanodots.

Solution-processed organic field-effect transistors (OFETs) have attracted great interest due to their potential as logic devices for bendable and flexible electronics. In relation to n-channel structures, soluble fullerene semiconductors have been widely studied. However, they have not yet met the essential requirements for commercialization, primarily because of low charge carrier mobility, immature large-scale fabrication processes, and insufficient long-term operational stability. Interfacial engineering of the carrier-injecting source/drain (S/D) electrodes has been proposed as an effective approach to improve charge injection, leading also to overall improved device characteristics. Here, it is demonstrated that a non-conjugated neutral dipolar polymer, poly(2-ethyl-2-oxazoline) (PEOz), formed as a nanodot structure on the S/D electrodes, enhances electron mobility in n-channel OFETs using a range of soluble fullerenes. Overall performance is especially notable for (C60 -Ih )[5,6]fullerene (C60 ) and (C70 -D5h(6) )[5,6]fullerene (C70 ) blend films, with an increase from 0.1 to 2.1 cm2 V-1 s-1 . The high relative mobility and eighteen-fold improvement are attributed not only to the anticipated reduction in S/D electrode work function but also to the beneficial effects of PEOz on the formation of a face-centered-cubic C60 :C70 co-crystal structure within the blend films.

Development of the system for vibration diagnosis of bearing assemblies using an analog interface

We have proposed a system for early vibration diagnosis of gas-pumping units, specifically bearing assemblies with improved metrological characteristics. The technique makes it possible to solve the task of early diagnosis of roller bearings under adverse conditions of application. The study has shown that this is achieved through the use of tracking notch filters based on N-channel structures using the iterative-integrating converters. The simulation results of the 4-channel filter under actual input signals of bearing damage have demonstrated its effectiveness. Based on this, we have built the resulting model for the filter’s output signal. Here we show a functional circuit for the root-mean-square values detector with a model of the output signal from the tracking notch filter at actual input signals. To build a model of signal at the input to a root-mean-square values detector, we determined filter responses for each frequency, which is responsible for a certain damage. The time of analysis was selected so that it was equal to a period of the minimum beat frequency, that is, Ta=164 ms (for a bearing of type 222). We investigated effectiveness of the device by simulating a damage to an actual gas turbine engine’s bearing. The procedure for analysis has been proposed and the generalized vibro-diagnostic criterion has been suggested, which takes into consideration the degree of engine’s load. This improves accuracy and reliability of preliminary analysis when diagnosing a roller bearing at the stage of the origin of the damage. Characteristics are given for the electrometric measuring amplifier for work with piezoelectric sensors and the proposed charge measuring amplifier to work with piezoelectric sensors. Under condition for the imbalance of the input link, which is due to the non-identity of parasitic capacitances of the input cable. It is shown that the penetration of a network disturbance to the output of the charge measuring amplifier provides for the signal/noise ratio that is two orders of magnitude better than that for the electrometric measuring amplifier.

High-speed transport in Si/Si1−x−yGexCy heterostructures

The recent progress in the field of modulation-doped Si/SiGe heterostructures is reviewed. Low temperature mobilities in n-channel structures are now close to 1,000,000 cm2/V s, and maximum oscillator frequencies of 120 GHz for n-, and 85 GHz for p-MODFETs were reported for room temperature operation. Progress has also been made toward a production compatible realization of strain-adjusting buffer layers by introducing a high concentration of implanted hydrogen close to the Si/SiGe interface prior to thermally driven relaxation. New simulations in connection with high-quality SiGe bulk crystals shine new light on the important role of alloy scattering in Si1−xGex and Si1−yCy channels. The discovery of a kinetic growth instability on the Si(001) surface may have important consequences for interface roughness scattering.

Analysis of quantum lifetime behaviour in modulation-doped n-channel structures

Shubnikov-de Haas measurements between 0.06 and 1.6 K have been performed on two modulation-doped n-type heterostructures, and analysed to extract the quantum lifetime. Use of the conventional Dingle formula resulted in deviations from the expected theoretical behaviour above . The corresponding quantum lifetime appeared to increase with temperature in the same range. The data were then re-analysed using a modified expression, in which the thermal damping term was neglected. This gave plots with the correct characteristics, and a quantum lifetime which was approximately constant with temperature, as expected for ionized impurity scattering in a degenerate electron gas. A decrease in the quantum lifetime was observed above , and this is attributed to increased small-angle scattering due to acoustic phonons.

The A-MOSFET—A majority carrier accumulation MOSFET

A novel MOSFET device structure is proposed that operates on the principle of majority carrier accumulation in the channel. The basic current equation is obtained for an n-channel structure.

A Limitation of Channel Length in Dynamic Memories

Effects of the channel length on the memory retention characteristics of MOS dynamic RAM (dRAM) cell are studied experimentally by evaluating three different n/sup +/ polysilicon-gate n-channel samples which contain six different channel lengths. A marked decrease of the memory holding time, which results from the subthreshold current, has been observed with decreasing channel length, gate oxide thickness, and substrate doping density in these n-channel samples with n/sup +/ polysilicon gate. In an n-channel structure with p/sup +/ polysilicon gate, the surface potential of the channel increases thus suppressing the surface subthreshold current particularly in a device having a thin oxide layer. A p/sup +/ poly-silicon-gate n-channel dRAM cell having an effective channel length of 0.5 µm has been observed to hold its charge up to 96 s at room temperature for the substrate bias of -4 V, while the n/sup +/ polysilicon-gate n-channel dRAM cell having the same structure exhibits a memory holding time of 6 ms at the same substrate bias voltage. This paper introduces a new dynamic RAM cell, i.e., the p/sup +/ poly-silicon-gate n-channel cell having a buried p+ region along the channel and the storage region. This new device having an effective channel length of 0.2 µm has been demonstrated theoretically to show satisfactory retention characteristics. In this very-short-channel structure, the MOS transistor behaves as a MOSSIT. In addition, it has been demonstrated theoretically that the new dynamic RAM cell has the capability of reducing soft errors due to alpha-particle irradiation.

A limitation of channel length in dynamic memories

Effects of the channel length on the memory retention characteristics of MOS dynamic RAM (dRAM) cell are studied experimentally by evaluating three different n+polysilicon-gate n-channel samples which contain six different channel lengths. A marked decrease of the memory holding time, which results from the subthreshold current, has been observed with decreasing channel length, gate oxide thickness, and substrate doping density in these n-channel samples with n+polysilicon gate. In an n-channel structure with p+polysilicon gate, the surface potential of the channel increases thus suppressing the surface subthreshold current particularly in a device having a thin oxide layer. A p+polysilicon-gate n-channel dRAM cell having an effective channel length of 0.5 µm has been observed to hold its charge up to 96 s at room temperature for the substrate bias of-4 V, while the n+polysilicon-gate n-channel dRAM cell having the same structure exhibits a memory holding time of 6 ms at the same substrate bias voltage. This paper introduces a new dynamic RAM cell, i.e., the p+polysilicon-gate n-channel cell having a buried p+region along the channel and the storage region. This new device having an effective channel length of 0.2 µm has been demonstrated theoretically to show satisfactory retention characteristics. In this very-short-channel structure, the MOS transistor behaves as a MOSSIT. In addition, it has been demonstrated theoretically that the new dynamic RAM cell has the capability of reducing soft errors due to alpha-particle irradiation.