COLLECTOR-ASSISTED OPERATION OF MICROMACHINED FIELD-EMITTER TRIODES

The field at the tip of a field emitter triode can be expressed by E = betaV(g) + gammaV(c) with V(g) and V(c) the gate and collector voltages, respectively. For small gate diameters and tips below or in the plane of the gate and/or large tip-to-collector distances, gammaV(c) << betaV(g). The device is operated in the gate-induced field emission mode and the corresponding I-V(c) curves are ''pentode''-like. By increasing the gate diameter and/or recessing the gates from the tips, collector-assisted operation can be achieved at reasonable collector voltages. Results will be presented for two devices with gate diameters of 3.6 and 2.0 mum. By obtaining gamma at different emitter-to-collector distances, I-V(c) and transconductance g(m)-V(g) curves have been calculated and compared with experimental results. It will be shown that as a consequence of collector-assisted operation, the transconductance of a device can be increased significantly.