New Lateral Field Emitter Arrays Inherently Integrated with Thin Film Transistor
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INTRODUCTION In the field emitter arrays, the stability of field emission current is an important issue to practical applications. There are many researches to improve the stability and uniformity of field emission current using the active devices such as Field-Effect Transistors (FETs) and Thin Film Transistor (TFT)[1-3]. However, most of these devices have four terminals. In addition, the fabrication process becomes complicated due to the additional process of the integration of active devices and FEAs and additional area for active devices are required. In this paper, we propose a new three-terminal lateral poly-Si field emitter inherently integrated with Metal-Oxide-Semiconductor (MOS) system, so that anode current is stable, and any additional area is not needed. Moreover, the fabrication process of the device is very simple.
DEVICE STRUCTURE AND FABRICATION Fig. 1 shows the schematic diagram of the new device. The main structure of the new device consists of the n+ poly cathode connected to undoped poly-Si tip and the n+ poly anode. MOS(Metal-Oxide-Semiconductor)-structure is fabricated on the undoped poly-Si tip. The key
9 Mat. Res. Soc. Symp. Proc. Vol. 509 © 1998 Materials Research Society
feature of new field emitter is the undoped tip, which is modulated by the MOS structure. The role of gate electrode is to modulate undoped tip, so the device is controllable by gate electrode. When the gate bias is applied under the anode bias, the device turns on and the anode current is limited by the charges in the inversion layer, so the anode current may be very stable and uniform. In fact, the active layer is poly-crystalline silicon (poly-Si), therefore, the MOS structure becomes Thin Film Transistor(TFT). X
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Fig. 1. Schematic diagram of the new device and its cross section The schematic fabrication sequences of the new emitter is shown in Fig. 2[4]. We use the starting material as the Si substrate which was deposited with 5000 A thick nitride and 500A thick oxide. Subsequently, 1000A thick amorphous Si was deposited. Then the first mask as shown in Fig. 2 (a) was performed using photolithography. The length of the undoped region, that is, the channel length, is 7
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The 1000 A thick amorphous Si was doped with POC13, resulting
in N+ poly-Si layer having undoped region. 3000 A thick oxide was deposited on active layer(N+ poly-Si layer having undoped region). Patterning as shown in Fig. 2 (c) was performed using the second mask. Then, the 3000 A thick oxide, active layer and 500A thick oxide were etched with anisotropic RIE(Reactive Ion Etch) etching and the active layer was over-etched using SF 6 plasma in order to make micro-cavity(Fig 2 (d)). It should be noted t
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