Junji Itoh

Fabrication Of Lateral Triode With Comb-shaped Field-emitter Arrays

Ultrafast and radiation resistant device is one of the most promising application targets of vacuum microelectronics. For this purpose, we fabricated a new 1 teral triode with the combshaped field emitter array (FEA)lv27 and measured its triode characteristics. 3, The cross sectional diagram of the present triode is illustrated in Fig.1. The triode consists of the comb-shaped FEA made of 0.25-am-thick (t e in the figure) W film, an anode of 0.5-am-thick Nb/W (t a) film and a gate of 0.5-am-thick Nb film. The gate is formed by a self-aligned technique on a groove being located between the emitter and the anode. The emitter has an array of 150 rectangular tips with 3-am-wide (w) edges and 9Ltm pitch (p); p/w=3 is an optimum ratio for the comb-shaped FEA.2) Figure 2 shows a SEM micrograph of the triode fabricated. The emitter-to-anode distance D and the emitter-to-gate spacing g were D=5~tm and g=0.5am, respectively. In the measurement of the characteristics, resistors RE (=110 kn), R ~ ( = 1 0 0 kn) and R ~(=100 kn) were connected in series to the emitter, the gate and the anode, respectively. All measurements were made at pressures less than 10-6Pa. Figure 3 shows an example of triode characteristics. As shown, the anode current IA increases with the anode voltage. The transconductance estimated roughly from this result is about 0.8~s at V G=11ov and vA=15ov. to the emission current, IA/IE, is very small and is about 25% at vA=15ov as shown in Fig.4; 75% of the emitter current enters the gate electrode. This poor current fraction is undesirable for triode operation and is caused by the asymmetric gate configuration. We believe, however, the fraction can be effectively increased by reducing further the emitter-to-anode spacing D down to l-2ctm. For further improvement of the performance, the emitter current and the anode-current fraction should be increased by reducing the device dimensions, especially the emitter-to-anode spacThe fraction of the anode current