Analysis of the field emitter triode (FET) as a pressure sensor

Field emitter triodes (FETs) have usually the current produced and controlled by the gate voltage V_g. However, if the emitter is allowed to protrude through the gate opening, the emission current can be controlled by the anode voltage V_a and the emitter-anode distance d. In this collector-assisted mode of operation the triode can be used as a pressure sensor allowing the anode to be mobile. The FET model used in this paper has parallel cathode, gate and anode planes, the gate having near the emitter a “volcano” shape. The emitter is conical with spherical tip. The emitter protrudes through the gate circular opening. The Laplace equation is solved numerically and the emission current is obtained through integration of the current density-electric field J(E) Fowler-Nordheim relationship over the emitter area. The constant voltage mode of operation was studied and the sensitivity of the FET pressure sensor as a function of the model parameters was derived. Under similar conditions referring to the gate, better sensor sensitivity is obtained for those situations which assure higher emission current I. Higher I is obtained for higher V_a and emitter height h and also for smaller d, emitter opening angle φ and work function Φ