Micromachining technology for lateral field emission devices

We demonstrate a range of novel applications of micromachining and microelectromechanical systems (MEMS) for achieving efficient and tunable field emission devices (FEDs). Arrays of lateral field emission tips are fabricated with submicron spacing utilizing deep reactive ion etch (DRIE). Current densities above 150 A/cm² are achieved with over 150·10⁶ tips/cm². With sacrificial sidewall spacing, electrodes can be placed at arbitrarily close distances to reduce turn-on voltages. We further utilize MEMS actuators to laterally adjust electrode distances. To improve the integration capability of FEDs, we demonstrate batch bump-transfer of working lateral FEDs onto a quartz target substrate     

Field- and photon-enhanced field emission from thin-film field-emission devices

Thin-film sandwich devices of CdS-SiO-metal have been made. They have current/voltage behaviour characteristics of field emission from semiconductors. With reverse bias, the current is very much smaller. The field-emission current is greatly enhanced by illuminating the device with 2.41 and 2.54eV photons (from an argon-ion laser). Under pulsed laser excitation (pulse duration 1 ?s) the enhanced emission persisted for more than 20ms. These experiments are analogous to some previous work on vacuum field emission. A possible mechanism for the enhanced emission is discussed.     

Noise in space charge limited field emission devices

The noise suppression in space charge limited field emitter cathodes is calculated, and it is shown that the noise can be more strongly space charge suppressed than in thermionic cathodes. The velocity fluctuation noise of the field emitter cathode is also calculated under arbitrary space charge conditions. The results are used to evaluate the noise figure of traveling wave tubes. Low noise figures are possible if the noise suppression of the space charge limited field emitter remains intact at microwave frequencies.     

Deep reactive ion etching for lateral field emission devices

The authors describe the design, fabrication and testing of lateral field emission diodes utilizing the deep reactive ion etch (DRIE). Devices were fabricated on silicon-on-insulator (SOI) wafers of varied thickness, by etching the device silicon in the STS DRIE system in a single mask process. After subsequent oxidation sharpening and oxide removal, diodes were tested on a probing station under vacuum. A typical diode exhibited very high currents on the order of ~100 μA at 60 V, and turn-on voltage between 35 V and 40 V. The high electron current is emitted in such a diode by multiple sharp tips vertically spaced by 450 nm along the etched sidewall due to the pulsed nature of the DRIE process     

分散定向碳纳米管阵列的制备及场发射性能

利用脉冲电化学沉积技术,以NiSO4·6H2O为电镀液在镀Cr硅基片上沉积低密度、直径在150nm左右的Ni催化剂颗粒,在此基础上,采用乙炔、氨气作为气源,采用等离子体增强化学气相沉积(PECVD)技术制备分散定向的碳纳米管阵列。研究了等离子体预处理技术对纳米管制备的影响以及该阵列的场发射性能,证明低密度的碳纳米管阵列阴极能有效地降低场屏蔽效应,进而提高场发射性能,其场发射的开启电场强度约为2.39V/μm。     

High current density operation of oxide cathodes

Oxide-coated cathodes have been used widely in electron tubes due to its high-emission efficiency at low operating temperatures. The maximum limit for dc emission of oxide cathodes has been considered at 0.5 A/cm²due to limitations of sparking or overheating due to Joule effect. We have tested successfully oxide cathodes at operating temperatures of 1000°K at current levels from 1.0 to 4.0 A/cm²with considerable life. Different types of oxide cathodes were tested in planar diodes and triodes. It was found that the operation limitations of an oxide cathode in a triode are far more severe than that in a diode. Diode testing at high current density dc was performed, while triode testing at dc, RF, and pulse conditions were carried out. Experimenting with high current density oxide cathodes in diodes indicated some limitations in the presently used cathode materials only above 4.0 A/cm². In triodes where the limitation was found at present at 2.0 A/cm², several interesting effects occurred. Grid overloading and beaming effects due to the closely spaced grids, produced intrusions on the anode face and poisoning on the cathode. Various grid materials have been tested and results are compared. Triodes in high power RF oscillators have been tested at about 1.0 A/cm²average current density. In this mode of operation, the limiting factor is the grid design and its materials. Evaporation of the grid materials may cause in this mode sudden and catastrophic failure of the tube. Evaporated grid materials deposited on the insulators result in cracking the structure during RF operation. Experiments will be discussed which showed that this effect can be avoided by the proper selection of materials.     

High field emission in germanium point-contact diodes

The effects have been examined of small changes of barrier height on the reverse current of high inverse voltage germanium point-contact diodes. The barrier height was varied by changing the ambient gas. The experimental results are given quantitative interpretation by a field emission theory in the region from about 10 volts to about 150 volts, where other effects become important. Examination of some 50 diodes has shown that diodes which draw low reverse currents behave according to this theory.     

热敷法制备丝状阴极及其在场发射中的应用

采用热敷法将碳纳米管(CNT)浆料直接热敷在Ni丝上制备成丝状阴极,并在圆柱形灯管中采用二极结构测试其场发射性能.扫描电镜(SEM)测试表明,丝状阴极的表面有一层均匀的CNT材料;场发射结果表明,CNT-Ni丝状阴极与传统的场发射阴极相比具有更优良的场发射性能,开启电场为0.15 V/μm,当电压为2280V时发射电流达到4 mA.在腔体中测试其发光亮度,最高值达到了14000 cd/m2.     

基于电流源控制的CNT-FED驱动电路设计

本文为了实现碳纳米管场致发射显示器（CNT-FED）的产品化,采用CNT-FED阴极电流源驱动方法,研究了CNT-FED亮度的均匀性和非线性调节问题。从分立元件驱动电路设计原理出发,采用了高稳定性阴极电流源像素驱动电路,将电流源驱动电路预先制作在硅基底上,再利用室温下生长碳纳米管（CNT）的方法,将CNT发射体和电流源驱动电路集成在同一硅衬底上,最终实现了集成CNT-FED驱动电路的设计。该驱动电路解决了CNT-FED亮度均匀性和非线性调节问题,对场射显示器驱动电路的应用研究和CNT-FED驱动电路的集成化具有参考意义。本文网络版地址：http：//www.eepw.com.cn/article/276357.htm     

Magnetic field and current density imaging using off-line lock-in analysis

In the current paper the application of a custom developed 2-dimenional scanning magnetic field microscope based on tunnel-magnetoresistive sensors and subsequent qualitative and quantitative analysis is described. To improve sensitivity and to enable the detection and evaluation of phase deviations, an off-line lock-in approach was employed by driving the samples under test with an injected current at a fixed signal frequency. Amplitude and phase evaluation was based on simultaneous acquisition of the reference and the measurement signal obtained from the magnetic field sensor. This off-line lock-in approach enables not just the detection but also the estimation of changes in signal phase caused by capacitive, inductive or ohmic coupling of the induced currents. Furthermore assessed magnetic fields were converted into the current density by solving the inverse magnetic problem and post processing of the acquired signals. For verification of the developed set-up the current density distribution was computed from experimentally acquired magnetic fields for a two-wire test structure. In addition quantitative values of the current density were derived for a calibration pattern containing defined structures. Finally, to evaluate the practical relevance a power MOSFET with unknown defect was analysed and an area of unexpectedly increased magnetic field intensity was observed.     

高功率密度系统需要大电流转换器

本文介绍了降压型稳压器设计中需要注意的问题及面临的新挑战,并介绍了LTC7150S和LTC7130两款满足特定需求的降压型变压器.     

High drive current NMOS with Si-SiGe heterostructure low electric field channel

A drive-current enhancement in NMOS with a compressively strained SiGe structure, which had been a difficult challenge for CMOS integration with strained SiGe high-hole-mobility PMOS, was successfully achieved using a Si-SiGe heterostructure low electric field channel of optimum thickness. A 4-nm-thick Si low-field-channel NMOS with a 4-nm-thick Si/sub 0.8/Ge/sub 0.2/ layer improved drive current by 10% with a 20% reduction in gate leakage current compared with Si-control, while suppressing threshold-voltage rolloff characteristic degradation, and demonstrated excellent I/sub on/--I/sub off/ characteristics of I/sub on/ = 1 mA//spl mu/m for I/sub off/ = 100 nA//spl mu/m. These results are the best in ever reported NMOS with a compressively strained SiGe structure and indicate that a Si-SiGe heterostructure low-field-channel NMOS integrated with a compressively strained SiGe channel PMOS is a promising candidate for high-speed CMOS in 65-nm node logic technology.     

High current density and drift velocity in templated conducting polymers

Conducting polymers prepared by a templated vapour phase polymerisation process involving solid phase transition metal complexes are found to produce polymers with charge carriers that exhibit maximum drift velocity in the range of 1 m/s. This super-mobility seems to be related to a high degree of ordering in the materials as evidenced by the X-ray diffraction data. This may result from a templated polymerisation process. The high mobility manifests itself as a capacity to sustain very high current densities (>10000 A/cm²); such high current densities are of importance in thin film conductor applications.     

The EM field of constant current density distributions inparallelepiped regions

The electromagnetic field vectors A¯, H¯, E¯ arising from a constant current density J¯ in an electrically small orthogonal parallelepiped region v are obtained analytically and exactly, up to order (kr)⁴ at any point (x,y,z) a distance τ from the center of v. They are then applied to the solution of an electric field integrodifferential equation (EFIDE) for which the region V has been divided into small parallelpiped cells. These new results are directly applicable to the evaluation of electromagnetic field interaction with natural media     

Fabrication of carbon nanotube arrays for field emission and sensor devices by nanoimprint lithography

This work brings forth the idea of incorporating insulation in the resist used for ultraviolet (UV) curing nanoimprint lithography (NIL). Carbon nanotubes (CNTs) are grown in the space between two insulated resist patterns on the conductive substrate to make CNTs arrays. Two imprinting processes, soft UV curing NIL with DRPPR process and novel NIL without cured residual resist, are presented to achieve the insulation patterns. First the fabricating process is performed using a polydimethylsiloxane (PDMS) stamp. Subsequently, inductively coupled plasma (ICP) is essential to wipe off the residual resist film. To avoid the ICP process, a novel UV curing NIL is presented. Its special hard quartz stamp with chrome shelter can protect the residual resist film out of curing during the UV exposure process, and the uncured resist can be easily removed by ultrasonic vibration in organic solutions. The CNT arrays are prepared on the patterned substrates by the pyrolysis of iron phthalocyanine (FePc). Field emission experiments reveal that the turn-on field of those CNTs arrays is low to 1.3 V/um.     

Theory of transient emission current in MOS devices and the direct determination interface trap parameters

The physics is discussed of the emission of electrons from interface states in metal-insulator-semiconductor (MIS) systems, under isothermal, non-steady-state conditions. Generalized equations are then derived which permit the determination of the non-steady-state, emission current vs time characteristics for MOS systems containing an arbitrary distribution of surface states; the special case of a discrete surface state is also studied. More important, however, by appropriate plotting of the data, it is shown how to directly extract from the experimental data the energy distribution and the capture cross section of the interface traps in the upper-half of the band gap in the case of n-type semiconductors, and in the lower-half of the band gap in the case of p-type semiconductors.     

High current conduction with high mobility by non-radiative charge recombination interfaces in organic semiconductor devices

We report a unique non-radiative p-n-p junction structure to provide high current conduction with high mobility in organic semiconductor devices. The current conduction was improved by increasing p-n junctions made with intrinsic p-type hole transport layer and n-type electron transport layer. The excellent hole mobility of 5.3 × 10^?1 cm²/V s in this p-n-p device configuration is measured by the space charge limited current method with an electric field of 0.3 MV/cm. Enhanced current conduction of 248% at 4.0 V was observed in fluorescent blue organic light-emitting diodes with introduction of non-radiative p-n-p-n-p junction interfaces. Thereupon, the power efficiency at 1000 cd/m² was improved by 22% and the driving voltage also was reduced by 17%, compared to that of no interface device. Such high current conduction with high mobility is attributed to the carrier recombination at p-n-p interfaces through coulombic interaction. This non-radiative p-n-p junction structure suggested in this report can be very useful for many practical organic semiconductor device applications.     

High current density 800-V 4H-SiC gate turn-off thyristors

4H-SiC gate turn-off thyristors (GTOs) were fabricated using the recently developed inductively-coupled plasma (ICP) dry etching technique. DC and ac characterisation have been done to evaluate forward blocking voltage, leakage current, on-state voltage drop and switching performance. GTOs over 800 V dc blocking capability has been demonstrated with a blocking layer thickness of 7 μm. The dc on-state voltage drops of a typical device at 25 and 300°C were 4.5 and 3.6 V, respectively, for a current density of 1000 A/cm². The devices can be reliably turned on and turned off under an anode current density of 5000 A/cm² without observable degradation