Study on Depletion Mode Operation of Protruding-Tip Field Emitter Triodes
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Study on Depletion Mode Operation of Protruding-Tip Field Emitter Triodes Y-C. Luo, M.Shibata, H.Okada and H.Onnagawa Faculty of Engineering, Toyama University 3190 Gofuku, Toyama 930-8555, JAPAN ABSTRACT Electrical characteristics of Spindt-type Molybdenum (Mo) field emitter triode devices with varied emitter tip-height have been studied based on device modeling and experiment. Potential and electric field distributions with varied the emitter tip-height has been simulated. It is observed that the electric field of the top of the higher emitter tip was strongly affected with the anode-gate distance and the anode voltage compared to conventional field emitter triode device. Experimental results with varied different tip-height were in good agreement with that of calculated results. We present the possibility of "depletion mode" field emitter triode device. INTRODUCTION Application of field emitter triode devices has been developed for flat panel displays, high frequency devices, switching devices and so on. Because operation of the field emitter triode is based on the electron tunneling effect from solid to vacuum, electrical characteristics mainly depend on device structure and its physical dimensions. The fabrication process affects on important device parameters, such as emitter tip radius, radius of gate, half-angle of cone and tip-height. Electrical characteristics are quite sensitive to those geometrical parameters [1,2,3,4]. In this paper, we investigate potential and electric field distributions and also calculate the electron current using Fowler-Nordheim (F-N) equation varied with emitter tip-height. We compare the experimental and calculated results of the electrical characteristics varied with tip-height. MODELS AND SIMULATION METHOD Figure 1 shows a cross sectional view of the field emitter triode model. In this calculation, we need an assumption that all of electrons emitted from the emitter tip are collected by anode. The calculation was carried out for various emitter tips. Parameters of field emitter triode devices, the tip heights (He), half-angle (α) of the cone, tip radius (Re) and number of the tips(Ntip), are listed in Table 1. Gate height (Hg) was 1.0µm and gate thickness (Wg) was 0.2µm. The gate hole radius (Rg) was 0.65 µm. The gate-anode distances (Ha) were 100 and 3µm. The gate voltage (Vg) was 60V. The anode voltage (Va) was 200V. Finite difference method was used for simulating the electrical potential. In this model, we solve the Laplace's equation,
∇ 2V (r , z, ϕ ) = 0.
(1)
The potential has cylindrical symmetry thereby reducing the problem to two dimensions, r and z. 1 ∂ ∂V ∂ 2V = 0. r + r ∂r ∂r ∂z 2
R5.5.1
(2)
anode
Table 1 Parameters of field emitter triode devices. Ha
Device He(μm) α(deg) Re(nm) A 1.6 16.0 42.0 B 1.2 16.0 42.0 C 1.0 14.0 6.0 D 0.7 14.0 6.0
Wg
gate
He
Hg e m itter
Fig.1
Ntip 600 600 7000 7000
The field emitter triode device model.
The following are the boundary conditions of applied voltages, V e , V ( r , z ) = V g , V a .
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