11.1: Development of vacuum transistor using hafnium nitride field emitter array

We fabricated gated 40,000-tip HfN-FEAs and evaluated HfN-FEA as an active device. The vacuum transistor has triode structure of a gated HfN-FEA and collector electrode. This vacuum transistor has collector current of 1.1 mA, transconductance of 0.27 mS, collector resistance of 2.8 MΩ and voltage amplification factor of 750 when applying emitter voltage of 58 V. This vacuum transistor amplified ac signal, and voltage gain of 29 dB was obtained from a resistance of 100 kΩ as a load. The gain band width product of 1 MHz was obtained from frequency characteristics of voltage gain. Transconductance is greatly improved by increasing the number of tips of FEA when comparing with 2 μS of 1,024 - tip HfN-FEA at applying emitter voltage of 92 V.