(Invited) Electron Emission Study of Planar-Type Electron Emission Devices Based on Nanocrystalline Silicon

Abstract

A planar-type electron emission device having a thin film diode structure such as a metal-oxide-semiconductor (MOS) [1] is a promising candidate as a fine electron source for applications of vacuum nanoelectronic devices, including environment-hard electronic devices, flat panel displays and high-sensitive image sensors. This is because the cathode operates at low extraction voltage and produces uniform and highly directional emission, compared with conventional field emitters with needle structure. Furthermore, the cathode is insensitive to the environment. However, the device is limited in emission current by its low efficiency (i.e., the ratio of the emission current to the total tunneling current) of typically less than 0.1 % due to strong scattering of hot electrons while traveling through the conduction band of both the oxide and the gate metal, after tunneling through the potential barrier in the oxide [2]. The reduction of the work function of the gate electrode by adsorption of alkali metals onto the surface [3] and the use of films containing nano- and micro-crystalline structure taking the place of the oxide layer have been proposed to improve the performance on the MOS cathode [4]. Another strategy is to reduce electron scattering within the topmost metal electrode by decreasing the electrode thickness [5-7]. In order to improve the emission efficiency and understand the emission mechanism we have fabricated the planar-type electron emission devices based on oxidized nanocrystalline Si (nc-Si) prepared by a pulsed laser ablation (PLA) technique and investigated their emission properties. The emission area of the device was designed 500 mm in diameter. The emission current and the efficiency are higher for thinner in the gate electrode, indicating tunneling is sensitive to the thickness of the gate. The electron emission efficiency is predicted to reach ~ 10 % if electron scattering on the inside of the topmost metal electrode is perfectly suppressed. In our presentation, we will discuss the detailed electron emission properties of the nc-Si based planar-type electron emission device.