ZnO Nanowire Field Emitter Arrays Research Articles

Quantitative Analysis on the Field Strength in the Addressable Gated ZnO Nanowire Field Emitter Arrays: Model and Experiment

Addressable gated field emitter arrays (FEAs) have important applications in vacuum microelectronic devices. To fabricate high-performance device, a comprehensive understanding on the field emission characteristics of gated FEAs is necessary, which requires a quantitative analysis method. In this work, a general model based on Fowler-Nordheim (FN) theory has been established to fulfill this blank. It is found that nonlinear FN plot with positive and negative slopes could occur in gated FEAs, which its turning point is related to the proportion of anode and gate field. This provides a way for obtaining the field strengths applied by the anode and gate structures. Besides, the transconductance of the gated FEAs increases exponentially with the total surface field, which indicates that both the anode and gate field need to be increased for achieving a high transconductance device. As a demonstration, the addressable gated ZnO nanowire FEAs using multimicrosize pattern with radius as small as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5 ~\mu \text{m}$ </tex-math></inline-formula> have been designed and fabricated. The relationship between the transconductance and anode voltage can be well fitted by using the model, which deduces the proportion of anode and gate field in the device to be about 3:1.

Optimizing Performance of Coaxis Planar-Gated ZnO Nanowire Field-Emitter Arrays by Tuning Pixel Density.

Gated ZnO nanowire field emitter arrays (FEAs) have important applications in large-area vacuum microelectronic devices such as flat panel X-ray sources and photodetectors. As the application requires high-pixel-density FEAs, how the pixel density affects the emission performance of the gated ZnO nanowire FEAs needs investigating. In this paper, the performance of coaxis planar -gated ZnO nanowire FEAs was simulated under different pixel sizes while keeping the lateral geometric parameter in proportion. The variations in emission current and gate modulation with pixel size were obtained. Using the obtained device parameters, the coaxis planar-gated ZnO nanowire FEAs were prepared. Field emission measurement results showed that a current density of 3.2 mA/cm2 was achieved from the fabricated ZnO nanowire FEAs when the gate voltage was 140 V. A transconductance of 253 nS was obtained, indicating effective gate control. The improved performance is attributed to optimized gate modulation.

Fully Vacuum-Sealed Diode-Structure Addressable ZnO Nanowire Cold Cathode Flat-Panel X-ray Source: Fabrication and Imaging Application.

A fully vacuum-sealed addressable flat-panel X-ray source based on ZnO nanowire field emitter arrays (FEAs) was fabricated. The device has a diode structure composed of cathode panel and anode panel. ZnO nanowire cold cathodes were prepared on strip electrodes on a cathode panel and Mo thin film strips were prepared on an anode panel acting as the target. Localized X-ray emission was realized by cross-addressing of cathode and anode electrodes. A radiation dose rate of 10.8 μGy/s was recorded at the anode voltage of 32 kV. The X-ray imaging of objects using different addressing scheme was obtained and the imaging results were analyzed. The results demonstrated the feasibility of achieving addressable flat-panel X-ray source using diode-structure for advanced X-ray imaging.

Diagonal 4-in ZnO Nanowire Cold Cathode Flat-Panel X-Ray Source: Preparation and Projection Imaging Properties

Uniform large-area flat-panel X-ray sources have potential applications in projection imaging. Achieving such a source has remained a challenge. A diagonal 4-in cold cathode flat-panel X-ray source device has been fabricated using ZnO nanowire field emitter arrays. A large-area uniform X-ray emission was produced, and projection imaging with a resolution of more than 5.0 lp/mm was realized. Its projection imaging resolution and its dependence on geometric imaging parameter settings were studied along with the imaging performance of the device. Simulations using the fast ray-tracing algorithm were performed, yielding results consistent with those from experiments. Optimal parameter settings for high-resolution projection imaging using the flat-panel X-ray source are presented. This study has significance in the application of this cold cathode flat-panel X-ray source in X-ray imaging.

Fabrication of large-area ZnO nanowire field emitter arrays by thermal oxidation for high-current application

Large-area ZnO nanowire field emitter arrays have important applications in flat-panel displays, light sources, photodetectors and X-ray sources, where it is crucial to realize a high field emission current and current density over a large-area. In this paper, large-area ZnO nanowire arrays with various array spacings were prepared by the thermal oxidation technique from patterned Zn film arrays, and their field emission properties were studied. The results show that the Zn array density is related to the nanowire length and population density. A mechanism is proposed wherein the stress-induced process and mass transport process both play key roles in the growth. Herein, ZnO nanowire arrays in a 4.7 × 4.7 cm2 area exhibited a sufficient quantity of emission sites and diminished field screening effect and a high current of 12.9 mA with a current density of 0.58 mA/cm2. This work provides useful guidance for optimizing ZnO nanowires and enhancing field emission current performance for large-area ZnO nanowire field emission devices.

Coplanar-gate ZnO nanowire field emitter arrays with enhanced gate-control performance using a ring-shaped cathode

Nanowire field emitters have great potential for use as large-area gated field emitter arrays (FEAs). However, the micrometer-scale cathode patterns in gated FEA devices will reduce regulation of the gate voltage and limit the field emission currents of these devices as a result of field-screening effect among the neighboring nanowires. In this article, a ring-shaped ZnO nanowire pad is proposed to overcome this problem. Diode measurements show that the prepared ring-shaped ZnO nanowire pad arrays shows uniform emission with a turn-on field of 5.9 V/µm and a field emission current density of 4.6 mA/cm2 under an applied field of 9 V/µm. The ZnO nanowire pad arrays were integrated into coplanar-gate FEAs and enhanced gate-controlled device characteristics were obtained. The gate-controlled capability was studied via microscopic in-situ measurements of the field emission from the ZnO nanowires in the coplanar-gate FEAs. Based on the results of both simulations and experiments, we attributed the enhanced gate-controlled device capabilities to more efficient emission of electrons from the ZnO nanowires as a result of the increase edge area by designing ring-shaped ZnO nanowire pad. The results are important to the realization of large-area gate-controlled FEAs based on nanowire emitters for use in vacuum electronic devices.

Fabrication of ZnO Nanowire Field-Emitter Arrays With Focusing Capability

ZnO nanowire field-emitter arrays (FEAs) show great application potentials in large-area vacuum microelectronics devices. However, the electron divergence is an issue which should be addressed. In this paper, ZnO nanowire FEAs with co-planar focus electrode were designed. A four-mask fabrication process and lift-off process were adopted to achieve the integration of focus electrode. The device demonstrated line-addressing and focusing capability with a spacing of 5 mm between anode and cathode, and the linewidth of field-emission images was reduced from 2.25 to 1.35 mm when the focus voltage changed from 50 to −50 V. Besides, line-shaped emission patterns were observed during focusing process, which was attributed to the emission pattern from the ZnO nanowire and the asymmetrical focusing electrical field.