Optimization on configuration of surface conduction electron-emitters

In this work, a novel nanogap with inclined protrusion cathode in palladium strip fabricated by hydrogen absorption under high-pressure treatment is optimized for the surface conduction electron-emitter. Its field emission is sensitive to the geometry of surface conduction electron-emitters (SCE). For a specified emitter material, the SCE are further investigated by varying the thickness, tilted angle and gap of palladium (Pd). An optimal field emission efficiency with 80° tilted angle, 120 nm gap and 10 nm thickness of Pd is found for certain designed field emission efficiency. We further find that varying the emitter material work function of the emitter material from 5.12 eV to 3.9 eV will further improve the field emission property due to the increase of the emitted current.     

Demonstration of low voltage field emission

The authors describe field emission from a thin-film field emitter array. The process used to fabricate the field emitters is based on the mold technique described by H.F. Gray and R.F. Greene (US patent 4,307,507). Each emitter chip consists of a 10×10 square array of field emitter tips and associated lead bonding pads. There is a 10-μm spacing between emitter tips. The bare chips were packaged by mounting to an alumina substrate, four to eight chips per substrate. The chips were tested in a demountable vacuum system equipped with a movable anode. The testing apparatus makes it possible to accurately measure currents as low as 100 nA at low duty. Fowler-Nordhein-like current-voltage characteristics were measured for most of the chips tested, indicating field emission. Substantial emission currents were observed at less than 20 V. The emitted current was collected almost entirely at the anode: the measured gate current was 1 to 5% of the emitted current     

Ultralow-voltage boron-doped diamond field emitter vacuum diode

A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp² content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters     

Improvement of the field emission characteristics of an oxidized porous polysilicon using annealed Pt/Ti surface emitter electrode

The field emission characteristics of an oxidized porous polysilicon were investigated with different annealing temperatures. Pt/Ti, Ir, and Au/NiCr were used as surface emitter electrodes, and Pt/Ti emitter showed highly efficient and stable electron emission characteristic compared with the conventional Au/NiCr electrode. Thin Ti layer played an important role in promotion of adhesion of Pt to SiO₂ surface and uniform distribution of electric field on the OPPS surface. Additionally, the Ti layer efficiently blocked the diffusion of emitter metal, which resulted in more reliable emission characteristics. Pt/Ti emitter annealed at 350 °C/1 h showed the highest efficiency of 3.36% at V_ps=16 V, which resulted from the improvement of interfacial contact characteristics of thin emitter metal to an oxidized porous polysilicon. Annealing above 400 °C showed that Pt/Ti and Ir emitter electrode were thermally more stable than Au/NiCr emitter.     

Stabilized emission from micro-field emitter for electron microscopy

Micro-fabricated field emitter for the application in miniaturized scanning electron microscope (MSEM) was fabricated on silicon substrate. Field emission studies of the micro-fabricated field emitter were carried out in an ultra high vacuum system. A simple voltage controlled feedback circuit was designed and used to regulate the gate voltage in order to improve the emission current stability of the micro-fabricated field emitter. Preliminary results showed that the emission current fluctuation ((I_max − I_min)/I_ave) was reduced from 80% without feedback current stabilizer to less than 1% with the circuit control.     

Highly uniform and low turn-on voltage Si field emitter arraysfabricated using chemical mechanical polishing

Turn-on voltage of about 30 V is observed in 1-μm gate-aperture Si field emitter arrays fabricated using oxidation sharpening and chemical mechanical polishing. Small emitter tip radius (~10 nm) was achieved from low temperature oxidation sharpening. The gate leakage current is observed to be less than 0.01% of emitter current over the range of measurement. Devices show excellent emission uniformity for different sized arrays. Current saturation was observed at high gate voltages because of low dopant concentration of the substrate. Below the saturation region, the current-voltage characteristics obey the Fowler-Nordheim field emission theory     

Dynamic behavior and instability of field emitter surfaces

The instability of field emission current arises from the atomic changes of the field emitter surface which can be induced by the sputtering of the secondary ions, by surface diffusion of containment atoms, and by the dynamical behavior of the emitter surface itself. There are three major causes of the instability: (1) the ion-bombardment- or ion-sputtering-induced surface changes, (2) contamination and surface diffusion of contaminant-induced emission current fluctuations, and (3) the intrinsic thermal instability of the field emitter surface itself. A few possible means of alleviating these problems are discussed     

楔形发射体的电子场发射理论

本文提出楔形发射体的电子场发射理论并给出计算实例；该理论以单原子发射点假设为基础，用经典电动力学方法计算楔形发射体的隧道势垒，然后用Ｎｕｍｅｒｏｖ方法计算其透射系数，最后用到场发射体伏安特性。     

场发射结构的有限元模拟

采用ANSYS有限元计算程序，对场致发射体进行模拟计算，初步研究了发射体的几何形状尺寸与其发射特性之间的联系。通过对不同几何尺寸发射体的计算结果的分析，认为发射体的尖端曲率半径及栅极的开口直径是影响发射体发射特性最主要的因素。依据合肥国家同步辐射实验室的LIGA深度光刻技术，给出可行的几何形状。     

Effect of diamond-like carbon coating on the emissioncharacteristics of molybdenum field emitter arrays

We have studied the electron emission characteristics of Mo field emitter arrays (FEAs) using a diamond-like carbon (DLC) film deposited by a layer-by-layer technique using plasma enhanced chemical vapor deposition. The turn-on voltage was lowered from 55 to 30 V by a 20 nm thick hydrogen-free DLC coating and maximum emission current was increased from 166 to 831 μA. Also the gate voltage required to get the anode current of 0.1 (μA/emitter) decreases from 77 to 48 V. Furthermore, the emission current from DLC coated Mo FEAs is more stable than that of noncoated Mo FEAs     

Numerical study on performance of pyramidal and conical isotropic etched single emitters

A full three-dimensional model was implemented in order to investigate the electrical characteristics of conical and pyramidal isotropic etched emitters. The analysis was performed using the finite element method (FEM). The simulations of both emitters were modeled using a combination of tetrahedral and hexahedral elements that are capable of creating a mapped and regular mesh in the vacuum region and an irregular mesh near the surfaces of the emitter. The electric field strengths and electric potentials are computed and can be used to estimate the field enhancement factor as well as the current density using the Fowler-Nordheim (FN) theory. The FEM provides results at nodes located at discrete coordinates in space; therefore, the surface of the emitter can be generated through a function interpolating a set of scattered data points. The emission current is calculated through integration of the current density over the emitter tip surface. The influences of the device geometrical structure on its potential distribution, electric field and emission characteristics are discussed.     

Field emission dependence on the tilted angle of palladium nanogaps for surface conduction electron-emitter displays

The emission efficiency of novel surface conduction electron-emitters corresponding to tilted angles (thetas) of a nanogap-typed driving cathode is optimised. Among the parameters of the emitter profile, the apex angle is the most significant because the smaller angles induce a higher electric field. The higher electric field then attracts more particles into vacuum and then increases the emission current. However, the structure of the driving cathode limits the electron trajectory while the angle decreases, and it reflects that the portion of collected current by the anode decreases and results in a drop in emission efficiency. The electric field with larger tilted angles will be weakened, but most of the emitted electrons could be collected by the anode, which increases emission efficiency. This shows there is highest emission efficiency (about 37%) under an optimum angle (thetas) of 60deg owing to a trade-off between emission efficiency and emitter apex.     

锥形与金字塔形场发射尖端电学特性分析

场致电子发射具有高效、响应快等优点,有着广泛的应用前景。锥形和金字塔形尖端是两种常见的场发射尖端结构。主要分析了这两种尖端结构的场发射电学特性,并在此基础上提出了进一步实现结构优化的途径。为此,建立了两种尖端的三维模型,并利用有限元法深入讨论了结构尺寸,包括尖端曲率半径、尖端与阳极间距以及尖端高度对电场分布以及电场强度的影响。结果表明,减小尖端曲率半径、缩短尖端与阳极间距、以及选择适当的锥体高度是优化尖端场致电子发射性能的三个重要途径。在综合考虑电场分布以及电场强度的情况下,可以发现锥形尖端更有利于产生高密度小束径的低能电子束,而金字塔形尖端则更适用于高压力灵敏度的应用需求。     

外加电场和磁场对太赫兹辐射产生的影响

通过对半导体太赫兹发射极在有和没有外加电场和磁场作用下发射光谱的测量。说明了外加电场和磁场对太赫兹电磁辐射的产生具有增强作用。采用反射式发射极在飞秒激光作用下辐射太赫兹脉冲的装置，同时利用电光取样方法探测太赫兹电场，得到了这些发射极的时域发射光谱，并通过快速傅里叶变换(FFT)得到了相应的频域光谱。实验表明，太赫兹时域发射光谱和频谱在外加电场、磁场作用下都有增强，但是所发射的频率成分和带宽都没有改变。借助于经典电磁理论的定性分析，认为太赫兹发射光谱在外加电场、磁场作用下的增强起源于半导体中载流子的加速运动受外加电场和磁场的影响。     

A theoretical study on field emission array for microsensors

The authors present results on the analysis of two generic cone-shaped and wedge-shaped emitter-array diodes. The effects of the variations in device geometrical structure on the potential distribution, electric field, and emission current are discussed. The main geometric design parameters considered are the tip-to-collector distance, the emitter tip radius of curvature, and the intertip spacing. Pressure sensors based on these diode structures with one electrode fabricated on a pressure sensitive thin diaphragm were studied. The analysis shows that a cone-shaped emitter array has a larger emission current per emitter tip, but the wedge-shaped array has better pressure sensitivity     

真空微二极管发射特性的解析解

通过保角变换方法，对具有椭圆锥形发射体的真空微电子二极管进行了研究，求得了二极管区域内电位分布和电场分布的解析表达式，进而得到了电场强度和场致发射电流密度与尖端曲率之间的关系．     

One step hydrothermal synthesis of SnO2-RGO nanocomposite and its field emission studies

Field emission (FE) properties of hydrothermally synthesized, SnO₂-RGO nanocomposite have been investigated at a base pressure of 1×10⁻⁸mbar. The results reveal that the SnO₂-RGO nanocomposite emitter prevails over the pristine RGO emitter. The values of turn-on field, defined at emission current density of 1 μA/cm², are found to be 1.8 and 2.2 V/μm for the SnO₂-RGO and pristine RGO emitters, respectively. Furthermore, the SnO₂-RGO emitter delivers maximum emission current density of ~800 µA/cm² at an applied field of 5 V/μm. The observed values of applied field corresponding to emission current densities of 1 μA/cm² and 10 µA/cm² are superior to those reported for various emitters due to SnO₂ nanostructures and their composites. The emission current at the pre-set value of 1 µA is found to be very stable over a period of 3hrs. The enhanced FE behaviour of SnO₂-RGO nanocomposite emitter has been attributed to synergic effect due to its nanometric dimensions offering high aspect ratio and modulation of electronic properties via formation of heterostructure. The results obtained herein propose the SnO₂-RGO nanocomposite as a prospective candidate for FE based vacuum microelectronic devices.     

双栅极场发射阵列的特性模拟与设计

具有聚焦能力的双栅极场发射阵列(DGFEA)是两类最有发展前途的真空微电子器件(高分辨率场发射显示器和真空微电子微波、毫米波器件)的关键技术。本文简要比较了两种结构的DGFEA的主要性能和优缺点,叙述了双层栅极结构DGFEA的设计与模拟方法.从模拟计算获得的发射特性和聚焦性能可以看到:这种结构的DGFEA能获得几乎平行的场发射电子束,其最大发射电流密度可达到约500A/cm2以上,是发展真空微电子微波、毫米波器件和其它强流电子注器件等较理想的电子源。     

用于场发射显示器的火山口型场发射阴极

介绍一种国内外研究的用于场发射显示器的火山口型场发射阴极,它相对于尖锥型场发射阴极来说，具有制作方法简单，制作成本更低，发射一致性更好，更适合大规模工业化生产。但不足之处是发射电流密度太小和有较大的栅极电流。文章详细介绍了火山口型场发射阴极的制作过程，分析并测试了其发射性能以及转移到玻璃基底上的制作方法。最后还介绍了火山口型场发射阴极的改进型-跑道型场发射阴极。     

Enhancement of electron emission efficiency and stability ofmolybdenum-tip field emitter array by diamond like carbon coating

The effect of diamond like carbon (DLC) films, coated by a layer-by-layer technique using PECVD (plasma enhanced chemical vapor deposition) on the electron emission characteristics of molybdenum (Mo)-tip field emitter array (FEA) is examined. The turn-on voltage was lowered from 80 V for the Mo-tip to 65 V for the DLC-coated Mo-tip FEA while the maximum emission current was increased from 140 μA for the Mo-tip to 320 μA for the DLC-coated Mo-tip FEA composed of 900 emitters. For an anode current of 0.1 (μA/emitter) the gate voltage for the DLC-coated Mo-tip FEA and Mo-tip FEA was about 87 and 107 V, respectively. It was also confirmed that the emission current of a DLC-coated Mo-tip FEA was more stable than that of a Mo-tip FEA