Advanced emitters for next generation rf amplifiers

Abstract

Next generation rf amplifiers, in particular the inductive output amplifiers ͑IOAs͒, will require electron sources characterized by high current density, high brightness, low emittance, and the ability to be emission gated. The strong interaction between the beam and the resonant or synchronous electromagnetic field may enable compact, highly efficient, and moderate gain X-band power booster amplifiers. An analysis of amplifier demands on generic emitter candidates is provided. Of the emitter candidates available, two ͑namely, field emitter arrays and wide-band-gap semiconductors͒ are amenable to an analysis predicated on a simple model of field emission from hyperbolas and ellipsoids. The simple model is used to investigate two problems of critical concern: for field emitter arrays ͑FEAs͒, we will investigate the conditions under which important space charge effects exist, and from the model predict optimum FEA performance characteristics for rf IOAs; for wide-band-gap materials, the simple model identifies parameters which limit the maximum electron transport across a metal-semiconductor interface, thereby limiting current flow.

Theory of Field Emission

“…The prolate spheroidal coordinate system is, therefore, ideal for modeling structures which can be approximated by hyperbolic or ellipsoidal surfaces of revolution, and has often been used for field emission problems [15,[105][106][107]. Recently, Forbes and Jensen [108] applied the methodology to emission from ellipsoids retaining the notation of Morse and Feshbach; the treatment here synopsizes that account, but will use the notation of earlier treatments [52,101].…”

“…1/2 is the width of the depletion layer (N D is the doping density) [52]. A novel and interesting theoretical analysis combining the concepts of internal field emission through the Schottky barrier in a diamond thin film with the Nottingham cooling effect has been performed recently by Miskovsky and Cutler [53].…”

CVD Diamond Cold Cathode with High Current Density and Low Threshold Field

“…The display has attracted the most attention, while the microwave devices are most wanted with regard to cathode requirements. In order to apply diamond cold cathodes in these de-vices they must display high emission, a low emission threshold, and good stability [1][2][3].…”

Analysis and simulation of anode heating due to electron field emission

“…This function can be integrated over energy and solid angle to provide the emitted current density (6) where is the azimuthal angle of emission (see Fig. 1).…”

“…Also, field emission arrays are capable of providing power amplification at very high frequencies (up to tens of GHz) and may also be useful as part of plasma-thruster systems for space propulsion. Field emitters also offer advantages in microwave power tube applications (e.g., travelling wave tubes) due to their ability to transmit higher current densities and breakdown voltages than traditional technologies [6]. In addition, field emission arrays show much promise as practical electron sources for flat-panel displays [7], [8].…”