For vacuum microelectronic devices to be used in flat panel displays, a low turn-on voltage and stable emission currents are required for the field emitter. Spindt-type metal emitters are commonly employed for field emission displays. However, silicon emitters have been the subject of intense study by many researchers due to the extensive knowledge which exists concerning the process compatibility with integrated circuits. Silicon emitters have certain inherent problems such as relatively poor electrical conductivity, poor thermal conductivity, and easy formation of insulting oxide on the surface. To solve these problems surface modifications such as metal coating, diamond-like carbon film coating, silicide coating, and nitride coating have been performed. Among them, metal-silicide emitters significantly enhanced emission current and stability. But generally, the formation of a metal-silicide structure on silicon emitters requires two steps, such as metal deposition and conversion to silicide by thermal annealing at high temperature. In the case of cobalt silicide, a capping layer on Co metal is required to prevent the formation of oxide during thermal annealing. In this study, we coated a $CoSi_2$ layer in situ on a Si emitter tip at 650℃ from a cobalt metalorganic source by reactive chemical vapor deposition (CVD) to simplify the tip-coating process. CVD commonly offers advantages such as a uniform and conformal deposition over a large area. A $CoSi_2$ layer was grown at a lowered process temperature to 650℃, and epitaxially grown on a Si tip in the partial region. The $CoSi_2$-coated Si emitters showed an enhanced emission due to the increase in the number of emitting sites and decrease of work function from the Fowler-Nordheim plot. The fluctuation of emission currents was reduced by the $CoSi_2$ coating. But the long-term stability was not much improved, which may be due to the agglomeration of $CoSi_2$ near the apex during dc bias stress.
To enhance the long-term stability, TiN having better high temperature stability than $CoSi_2$ was coated on Si tip. The TiN coating greatly reduced the turn-on voltage and improved the long-term stability because TiN has a low work function, high melting point (2950℃) and high thermal conductivity. But TiN did not increase the emission current to a level as high as the $CoSi_2$ coating due to the higher electrical resistivity than that of $CoSi_2$.
The merits of $CoSi_2$ and TiN, high emission current by $CoSi_2$ and low turn-on voltage and long-term stability by TiN can be utilized for field emitter arrays(FEAs) via the introduction of a $CoSi_2$/TiN bilayer coating. The $CoSi_2$ layer was conformally coated on the Si tips and the TiN layer well adhered to the $CoSi_2$ layer. The $CoSi_2$/TiN coated emitters showed a low-turn voltage due to the low work function by TiN a steep current increase caused by $CoSi_2$. The current fluctuation of $CoSi_2$/TiN-coated Si emitter was smaller than that of TiN-coated emitter. The long-term emission stability of $CoSi_2$/TiN coated Si emitter was greatly improved compared to the $CoSi_2$ coated emitter because of the superior high temperature stability of TiN layer.
