A Novel Lateral Field Emission Triode for Microwave Application
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10-8
Torr vacuum chamber
is similar to the anode current measured in atmospheric pressure, which shows that the proposed vacuum sealing process is reliable. The stable current of 300/iA is maintained during 60 h.
I. INTRODUCTION Vacuum microelectronics devices have attracted a considerable interest for high speed and high temperature applications [1][2]. Various field emitter structures have been proposed [3] However, most of those devices require an additional vacuum environments in order to be operated properly and their operating voltage is too high to act as amplifier (VAC --1OOV) [1][2][4] We have reported a novel lateral field emission triode which does not require any additional vacuum sealing process and exhibits superb field emitter triode performance [5] The purpose of this paper is to report a new experimental data of new device, such as variation of tip material, device stability experiment, measurement of the novel device in vacuum chamber in order to verify the proposed vacuum sealing process, and amplifying characteristics at each current level.
25 Mat. Res. Soc. Symp. Proc. Vol. 509 c 1998 Materials Research Society
11.DEVICE FABRICATION A schematic diagram of the fabrication process and key feature of new structure described in our recent paper [5] We summarize the process sequences to help understanding. Lower insulator layer including 5000-A-thick nitride and 500-A-thick oxide was deposited on Si wafer. 1000-Athick amorphous Si was deposited and doped with POCI 3 resulting in N+ poly Si layer. Upper insulator layer including 500-A-thick oxide , 5000-A-thick nitride and 7000-A-thick oxide was deposited. Patterning as shown in Fig. 1 (a)-I was performed and upper insulator layer and N÷ poly Si layer were etched with anisotropic reactive ion etch (RIE) and then the N+ poly-Si layer (poly-Si tip) was over-etched intentionally with SF6 plasma in order to make micro-cavity [Fig I (a)-2]. The oxidation at 10001C for 120 min in dry 02 was performed to sharpen the poly-Si tip, which is used for a cathode, and isolates an anode and a cathode. Cathode tip was sharpened as pencil type during oxidation. The thermal oxide was removed by buffered oxide etchant (BOE) [Fig I (b)-1]. Molybdenum was deposited by electron beam evaporator at base pressure of 10-7 Torr [Fig 1 (c)]. It should be noted that the vacuum of a micro-cavity is identical to the base pressure of evaporator chamber. Plasma enhanced chemical vapor deposition (PECVD) oxide passivation layer was deposited and an electrical interconnection was then fabricated in proper locations by employing mask step. Our previous device shows a stability problem due to poly-Si cathode material. In this work, we have fabricated a new titanium polycide cathode tip array for improving the device stability and performance. We have deposited the 1000-A-thick N+ doped poly-Si, the 500-A-thick titanium layer for titanium polycide tip array instead of N+ doped poly-Si layer for active layer. The two step RTP annealing of 650 1Cfor 20 s and 750 1Cfor 90 s to form ti
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